The Polaris is 792.6 tons of propellant and 396.3 tons of everything else. How big is this, exactly?
When comparing the spacecraft to other vehicles, just use the "everything else" value, ignore the propellant mass. This is because few earthly vehicles have total masses dominated by fuel mass as much as rockets are. How does 396.3 tons stack up?
Rick Robinson notes that is pretty small compared to "wet-navy" vessels. It's under the size of a coastal corvette. But compared to aircraft, it's huge. A Boeing 747 is only 180 tons empty. If you want to get an idea of other sizes, go check out Jeff Russell's huge Starship Dimensions website and Florian Käferböck's impressive Rockets and Space Ships Size Comparison.
|0||Human Being||1.77 meters/5.8 feet|
|1||Giraffe||6 meters/20 feet|
|2||City Bus||12 meters/40 feet long|
|3||Small Orion Drive ship||21 meters/70 feet|
|4||Millennium Falcon||35 meters/115 feet||Star Wars|
|5||Polaris||43 meters/140 feet||Tom Corbett, Space Cadet|
|6||Moonship||44 meters/144 feet||Chesley Bonestell,|
Conquest of Space
|7||Luna||46 meters/150 feet||Destination Moon|
|8||Arc De Triomphe||50 meters/164 feet|
|9||Orion Drive Mars|
|50 meters/165 feet|
|10||United Planets Star|
|51 meters/170 feet wide||Forbidden Planet|
|11||Nautilus||51 meters/170 feet long|
|12||Space Shuttle stack||56 meters/180 feet|
|13||Absyrtis||60 meters/197 feet||G. Harry Stine,|
|14||Boeing747||71 meters/231 feet|
|16||Ferry Rocket||81 meters/265 feet||Collier's Magazine,|
22 March, 1952
|17||Statue of Liberty||93 meters/300 feet|
|18||DE-51 Destroyer Buckley||93 meters/306 feet|
|19||Saturn V||111 meters/363 feet|
|20||DY-100 Botany Bay||92 meters/302 feet||Star Trek|
|21||California Redwood||112 meters/367 feet|
|15||RS-10||128 meters/420 feet||Andre Norton Star Born|
|22||Discovery||140 meters/459 feet||2001, A Space Odyssey|
|23||Romulan Bird of Prey||131 meters/430 feet||Star Trek|
|24||Great Pyramid of Cheops||139 meters/455 feet|
|25||Oscar class submarine||155 meters/509 feet|
|26||Galactic Cruiser Leif Ericson||168 meters/551 feet||Leif Ericson Model|
|27||Washington Monument||169 meters/555 feet|
|28||Klingon D7 battlecruiser||228 meters/750 feet||Star Trek|
|245 meters/804 feet|
|30||BB-62 Battleship New Jersey||270 meters/887 feet|
|31||NCC 1701 Starship Enterprise||289 meters/950 feet||Star Trek|
|32||Eiffel Tower||300 meters/984 feet|
|33||CVN-65 Carrier Enterprise||342 meters/1,123 feet|
|34||Empire State Building||443 meters/1,454 feet|
|35||Al Rafik||102 meters/335 feet||Attack Vector: Tactical|
|36||Tachi/Rocinante||46 meters/151 feet||The Expanse|
|37||10 Story Building||30 meters/98 feet|
|38||International Space Station||109 meters/358 feet|
|39||X-Wing Fighter||13 meters/41 feet||Star Wars|
|40||Eagle Transporter||31 meters/100 feet||Space 1999|
|41||Shuttle Orbiter||37 meters/122 feet|
|42||Type S Scout||39 meters/128 feet||Traveller RPG|
|43||Serenity||58 meters/190 feet||Firefly|
|44||DDG-90 Destroyer Chafee||155 meters/510 feet|
|45||ISV Venture Star||1,646 meters/5,400 feet||Avatar|
|46||CVN-68 Aircraft Carrier Nimitz||333 meters/1,092 feet|
|47||Imperial Star Destroyer||1,600 meters/5,249 feet||Star Wars|
|48||Scoutship Vega||20 meters/66 feet||Leif Ericson Model|
|49||Michael Battleship||132 meters/433 feet||Footfall|
|50||Orion Battleship||78 meters/256 feet|
|51||ANNIC NOVA||78 meters/256 feet||Traveller RPG|
|52||Valley Forge||1,600 meters/5,249 feet||Silent Running|
|53||Klingon K't'inga class|
|349.54 meters/1,147 feet||Star Trek|
Note: according to the blueprints the Michael Battleship (49) is 408 feet tall. However, this would make the Shuttle Orbiters mounted on the battleship too small. I scaled the blueprint so the Orbiters were at their official length, which made the Michael 433 feet tall.
Credits for the computer meshes used in the images below:
- 10 Story Building: KG
- ANNIC NOVA: Winchell Chung (me)
- Al Rafik: Charles Oines
- Boeing 747: Jay
- CVN-68 Aircraft Carrier Nimitz: Toby
- DDG-90 Destroyer Chafee
- Eagle Transporter: James Murphy
- Galactic Cruiser Leif Ericson: Winchell Chung (me)
- Giraffe: BMS
- Human: ?
- ISV Venture Star: krabz
- Imperial Star Destroyer: Blenderwars
- International Space Station: ?
- Klingon K't'inga Battle Cruiser: ?
- Michael Battleship: Winchell Chung (me)
- Millennium Falcon: Blenderwars
- NCC 1701 Starship Enterprise: William P. "Tallguy" Thomas
- Ogre Mark V: Winchell Chung (me)
- Orion Battleship: Winchell Chung (me)
- Polaris: Winchell Chung (me)
- Saturn V: Tesler
- School Bus: tamias6
- Scoutship Vega: Winchell Chung (me)
- Serenity: JayThurman (Cyberia23)
- Space Shuttle Orbiter: NASA
- Space Shuttle Stack: ?
- Statue of Liberty: Damo
- Tachi/Rocinante: Chris Kuhn
- Type S Scout: Winchell Chung (me)
- Valley Forge: ?
- X-Wing Fighter: Blenderwars
If you just want something really quick and dirty:
Estimate somehow the volume (m3) of your spacecraft. Calculate the mass by multiplying the volume by the average density (kg/m3) of a spacecraft.
- There are equations to calculate the volume of simple geometric objects such as cubes, spheres, cylinders, and cones. Approximate the spacecraft as an assemblage of such objects, calculate the volumes, then add them all up. Example: here.
- Create a scale model inside a 3D modeling package, and use the included tools to calculate the internal volume. Example: On my mesh model of the Galactic Cruiser Leif Ericson, the AreaVol script informs me the ship has an internal volumeof 68,784.87 cubic meters.
- See if somebody else has already calculated the volume. Example: According to ST-v-SW.Net the internal volume of the TOS Starship Enterprise is 211,248 cubic meters.
- Use the known volume of a comparable existing object. Example: a Russian Oscar submarine has a volume of 15,400 cubic meters. It is a good size for a spaceship.
- If the spacecraft is approximately a sphere or approximately a cylinder, just use the ship's average radius and height to calculate an approximate volume using the sphere or cylinder volume formulae. Close enough for government work.
- Make it up out of your imagination.
Of course there is some differences of opinion on the exact value of the average density of a spacecraft.
One easy figure I've seen in various SF role playing games is a density of 0.1 to 0.2 metric tons per cubic meter (100 to 200 kilograms). That corresponds to average pressure compartments being cubes 10 meters on a side, with pressure bulkheads averaging 17 to 33 kg/m2.
Ken Burnside did some research when he designed his game Attack Vector: Tactical. He found that jet airliners have an average density of about 0.28 metric tons per cubic meter, fighter aircraft 0.35 tons/m3, wet navy warships from 0.5 to 0.6 tons/m3, WWII battleships 0.7 tons/m3 (it don't take much excess mass to send them straight to Davy Jones locker), and submarines 0.9 tons/m3. For the combat spacecraft in AV:T, Ken chose a density of 0.25 tons/m3.
|Attack Vector: Tactical||0.25 ton/m3|
|Jet Airliners||0.28 ton/m3|
|Fighter Aircraft||0.35 ton/m3|
|Wet Navy Warships||0.5 to 0.6 ton/m3|
|WWII Battleships||0.7 ton/m3|
A student of the game Orbiter (who goes by the handle T. Neo) used the 3D models in the game to figure the volume of various space constructions. Dividing by their known masses yielded the densities.
|Space Shuttle External Tank||0.011 ton/m3*|
|Long Duration Exposure Facility||0.049 ton/m3|
|Leonardo Multi-Purpose Logistics Modules||0.058 ton/m3|
|Hubble Space Telescope||0.061 ton/m3|
|International Space Station||0.074 ton/m3|
|Space Shuttle Orbiter||0.088 ton/m3|
|Space Station Mir||0.175 ton/m3|
|Space Shuttle Solid Rocket Booster||0.206 ton/m3*|
* Large portion of volume is dedicated to propellant
Fans of the Traveller role playing game have to do a bit of work. Starships in Traveller are rated in terms of "displacement tons" or "dtons". This is a measure of volume, not mass. 1 dton is 14 cubic meters, which is approximately the volume taken up by one metric ton of liquid hydrogen (actually closer to 14.12 m3). Liquid hydrogen is starship fusion fuel.
So if you assume a Traveller starship has an average density of 0.2 tonnes/m3, then given dtons the starship mass in metric tons is:
starshipMass = dtons * 14 * 0.2
starshipMass = mass of starship (metric tons)
dtons = displacement of starship (displacement tons or dtons)
0.2 = average density of starships (tonnes/m3)
Example: a Broadsword class mercenary cruiser has a volume of 800 dtons (or 1200 depending on where you read it). This means its mass is 800 * 14 * 0.2 = 2,230 metric tons.
Traveller deck plans are confusing as well. If they are ruled off in a square grid, chances are the squares are 1.5 meters on a side. The space between the floor and the ceiling of a deck is assumed to be 3 meters. Bottom line is that on a Traveller deck plan 1 dton is represented by two grid squares.
The second quick and dirty method:
Estimate the mass (kg) of each major component. Divide the mass of each major component by its density (kg/m3) to find the volume of each major component. Total the masses to get the spacecraft mass, total the volume to get the spacecraft volume.
Often you have the total mass, and the propellant mass. The dry mass is the total mass less the propellant.
If you have the mass ratio, you can figure your dry mass by totaling up the various components, then use the mass ratio to calculate the propellant mass and total mass.
remember that average NASA spacecraft dry mass (i.e., sans propellant) divides up to include:
|Thermal (heat radiators)||3.4%|
|Guidance, Navigation, and Control||8.0%|
Keep in mind that this is for NASA style spacecraft. The percentages for, say, the Starship Enterprise will be totally different and anybody's guess.
Now all you need are some figures on the average density of these various items and you can calculate quick and dirty ship volumes. I'm looking into it but it's hard.
The following is a method to calculate the spacecraft's structural mass. It is derived from a document at Christopher Thrash's web site. He bases his analysis on data from the book all the pros in astronautics use, Space Mission Analysis and Design. There is some additional information here.
Lucky you, Eric Rozier has implemented the algorithm below as an on-line calculator.
Assumptions: as a first approximation, the spacecraft is modeled as a free standing column resting upon the engines. The column is "thin-walled", that is, the column radius divided by the hull thickness is less than 0.1. The column is only supported by its walls (monocoque construction). The column has its mass uniformly distributed along its length. The ratio of column's length to its diameter is 3.2 : 1.0. The hull is assumed to be capable of withstanding forces equal to its mass times gs of acceleration on any axis: axial, lateral, or bending.
This means that the following formula only work for a cigar-shaped rocket, not a spherical one.
Decide upon the volume, or total displacement of the hull in cubic meters (m3). This will boil down to volume for reaction mass plus volume for the crew and cargo. Calculate the volume for your reaction mass by
Vpt = Mpt / Dpt
- Mpt = mass of propellant (kg)
- Dpt = density of propellant (kg/m3) = 71 for liquid hydrogen, 423 for methane, 682 for ammonia, and 1000 for water
- Vpt = volume of propellant (m3)
If you don't know the mass of the propellant, it can be calculated from the dry mass and the mass ratio:
Mpt = (R * Me) - Me
- R = mass ratio (dimensionless number)
- Mpt = mass of propellant (kg)
- Me = mass of rocket with empty propellant tanks (kg)
Add the volume of the reaction mass to the desired living space volume to get the spacecraft's volume. Later you can figure the approximate spacecraft dimensions by using the formula for the volume of a cylinder ( v = π r 2h ), keeping in mind that it should be about 3.2 times as high as it is wide (although you can get away with larger values).
Now comes the fun part. This is going to be what they call an "iterative process". This means you do the calculations, take the results and do the calculations again on the results.
Remember that the mass of the propellant tanks will be approximately equal to full propellant mass times 0.15. The tank mass will be included in the structural mass, if the ship designer is not totally incompetent.
The shortcut is to stop at step seven, reduce M~st by Mst, and everything will add up.
Figuring the hull volume of an existing design is a bit more tricky.
By way of example, a Russian Oscar-II submarine is an oval cylinder about 18 meters wide by 9 meters tall by 154 meters long. It has an internal volume of about 15,400 cubic meters. It has a density of about 0.9 metric tons per cubic meter, so it has a mass of about 15,400 x 0.9 = 13,900 metric tons.
There are equations for calculating the internal volume of various geometric shapes. What you have to do is approximate your spacecraft design using only these shapes. A sphere is easy. A classic cigar shape is sort of a cylinder with a cone on each end. You'll find a crude example of that here.
If your spacecraft is a complicated shape like the Starship Enterprise, you have a real problem.
If you have a physical model of your spacecraft, you can try estimating its displacement by caulking it water-tight, immersing it in a container of water, and measuring the water it displaces. Alternatively, fill a box with sand, dump the sand into measuring cups to measure the volume of sand, put the model in the box and fill it with sand, dump the sand out into measuring cups, and finally subtract the two volumes to discover the volume of the model.
Alternatively, you can proceed like graphic artist Myn.pheos, creating your mesh in the amazing free program Blender and using the 3D Printing Toolbox to calculate the volumes. Myn.pheos also has some techniques to find the center of gravity of various components, and to discover optimal placement of heat radiators.
The following tips are specific to the Blender software, but an artist skilled with another 3D computer modeling program could adapt the tips to their software. Myn.pheos is a native of Slovakia, and English is his second language. Myn.pheos:
I must say that I am very impressed with Myn.pheos' technique. I am reasonably skilled with Blender, but it never occurred to me that it could be used to find centers of gravity and optimal heat radiator placement. Myn.pheos is a genius.
He decided to make a Gaseous-core Open-cycle nuclear thermal rocket mod for KSP. He is using Blender 3D as his modeling program.
He wanted to add some heat radiators (because GCR need lots of them), when he became aware of the dangers of neutron embrittlement, neutron activation, and radiation scattering. It seems that William Black was working on a similar project.
Meanwhile William Black was already hard at work on a GCR. He is also using Blender 3D.
When William Black read Ron Fischer's brilliant suggestion, he quote "found this to be a compelling proposition, an opportunity to test out the validity of my design" unquote.
Physicist Luke Campbell had some additional suggestions:
Something like Myn.pheos technique for placing heat radiators was used to solve the mystery of the Pioneer Anomaly. The trajectory of space probes in general and the Pioneer probes in particular should follow precisely Newton's Laws of Motion. Once you've accounted for all the extra factors, of course. So scientists were quite upset when the probes started to gradually diverge from their calculated trajectory. There are all sorts of proposed explanations, ranging from observational errors to new laws of physics.
Dr. Frederico Francisco (Instituto Superior Técnico, Lisbon) and colleagues believe they have the answer. Others have tried and found wanting the hypothesis that heat radiated from the probes could be the culprit. But Dr. Francisco et al submit that this is because the radiation mathematical models are too simplistic. Using the 3D CGI rendering technique known as "Phong shading", they have shown this will account for the Pioneer Anomaly. Phong shading takes into account not just the heat radiated, but the heat that hits parts of the probe's structure and is reflected from it.
As you can see, this is very similar to the technique used by Myn.pheos.
Figuring the surface area of a spacecraft is about the same level of difficulty as figuring the internal volume. The same techniques apply: approximate the spacecraft as a series of easy to calculate shapes, or use a CGI package that can calculate it for you.
Usually it isn't worth the bother unless you are trying to figure the mass of the armor required for a warship. Or you worry if there is enough space on the hull to place all the stuff you want to put.
The British Interplanetary Society (BIS) in general, and Sir Arthur C. Clarke in particular figured that there were three main types of spacecraft needed for the exploration of space: Space Ferry, Orbit-to-Orbit, and Airless Lander. Each is optimized for their own particular area of use.
However, space warships are an entirely different kettle of fish.
The space ferry concept is what evolved into the NASA space shuttle. Its function is to boost payload into orbit, though you can think of it as an "atmospheric lander." Refer to the section on Surface To Orbit.
These are sometimes called "interface vehicles" because their function is to transport payload through the interface boundary between Terra's atmosphere and airless space.
The idea was to re-use as much of the rocket as possible, which is why the upper section has wings and the lower stages had parachutes. In Robert Heinlein's Space Cadet, the rocket is launched from a rocket sled going up the side of Pike's Peak. Nuclear powered rockets could boost more massive payloads, but a space elevator could boost so much more cheaply and efficiently.
Hop Davis estimates that space ferries launching from Terra will require a delta-V budget of around 10 kilometers per second (with orbital propellant depot) and require a thick atmosphere for aerobraking. It will require a bit more if there is no orbital depot, but not much more because coming down it uses aerobraking instead of propellant. The delta-V budget means they will probably have to be multi-stage if they are chemical rockets (good luck getting permission to use nuclear rockets). They will require a propulsion system with a thrust-to-weight ratio above 1.0.
Orbit-to-orbit spacecraft never land on any planet, moon, or asteroid.
Therefore they are free to use efficient propulsion systems with a thrust-to-weight ratio below 1.0, such as ion drives or VASIMR. They require no landing gear or parachutes. If there ain't no landing gear, it is an orbit-to-orbit. No streamlining is required either. They require no ablative heat shields unless they are designed to perform aerobraking to burn off delta-V without requiring propellant (like the Leonov in the movie 2010 The Year We Make Contact).
Hop Davis estimates that a orbit-to-orbit spacecraft will require a delta-V budget of only 3 to 4 kilometers per second, if orbital propellant depot are available. Otherwise it will be twice that, with along with a dramatic reduction in payload capacity. 4 km/s is well within the capabilities of a chemical rocket, but any higher and you will probably need staging or a propulsion system with more exhaust velocity.
The old image of orbit-to-orbit ships look like dumb-bells, the front ball is the cargo and habitat module, the rear is the propellant and radioactive atomic drive. The stick in between is a way to substitute distance for lead radiation shielding.
These are designed for landing on bodies that have no atmosphere, but you probably could get away with using them on Mars. They evolved into NASA's Apollo Lunar Module. So they will require some sort of landing gear. But no streamlining. They will require a propulsion system with a thrust-to-weight ratio near 1.0, depending on the surface gravity of the bodies they are designed to land on. This probably means chemical propulsion, maybe a solid-core NTR. Hop Davis estimates that airless lander spacecraft will require a delta-V budget of around 5 kilometers per second if orbital and surface propellant depots are available. Otherwise it will be twice that, with along with a dramatic reduction in payload capacity.
So the smart way to design is to use an orbit-to-orbit spacecraft to travel between planets, and at a planetary destination use locally based surface-to-orbit services: either a space ferry, airless lander or surface-to-orbit installation at a spaceport.
But what if there are no locally available surface-to-orbit services? If NASA dispatches a Mars mission, there ain't no Martian space shuttles to ferry the crew down to the surface.
Making the entire spacecraft land-able is often a bad idea. For one, optimizing a spacecraft for both orbit-to-orbit and surface-to-orbit operations will probably result in an inefficient ship with the disadvantages of both and the advantages of neither. If you are designing with a weak propulsion system, it might not even be possible. And even if your propulsion system is up to the task, often it is better to park your ticket home in orbit where it is safe while other means are used to send crew into a possibly dangerous situation.
The standard solution is for the main spacecraft to carry small auxiliary spacecraft as landers, either aerodynamic space ferries or airless landers. The popular term from Star Trek is "Shuttlecraft".
A large space ferry shuttlescraft on modestly sized orbit-to-orbit spacecraft can make the ship look like an arrow.
Many aerospace engineers have pointed out that all of these spacecraft can be far more cheap and efficient if there were orbital depots of propellant and/or fuel established in various strategic locations where space travel is desired. This will necessitate some sort of tanker-type spacecraft to keep the depots supplied. They will be a species of orbit-to-orbit spacecraft optimized to carry huge amounts of propellant, and hopefully be unmanned drones or robot controlled. They can use an efficient propulsion system with thrust-to-weight ration below 1.0, ion or VASIMR. Like standard orbit-to-orbit, probably a delta-V budget of 4 km/sec, unless they are in a real hurry.
There will also be a species of airless lander optimized to carry propellant to planetary based depots, this is called a "lighter". As all landers the propulsion thrust to weight ratio will have to be near 1.0, probably chemical propulsion. As standard airless lander, probably a delta-V budget of 5 km/sec. The lighter will probably be designed to land a single modular tank from the cluster carried by the tanker.
This is far more speculative, since as far as we know there have not been any space warships created yet. Refer to Warship Design, Space War: Intro, Space War: Detection, Warship Weapons Intro, , Warship Weapons Exotic, Space War: Defenses, Space War: Tactics, and Planetary Attack .
Fundamentally they are weapons platforms, so by definition they will be carrying various weapons systems. They may or may not have armor or other defenses, they may or may not have human crews. They probably will have an over sized delta-V capacity, and a large thrust capacity so they can jink around and complicate the enemy's targeting solution (i.e., dodge around so you are harder to hit). Lasers will require large amounts of power, and huge heat radiators and heat sinks to cope with waste energy. They will probably be carrying little or nothing that cannot be used to attack the enemy.
Reduced to fundamentals, there are two basic shapes for your atomic rocket: the cylinder (cigar shape) and the sphere. Both have advantages and disadvantages. Of course matters are different in the totally unscientific world of media science fiction.
Any Freudian symbolism is the responsibility of the reader.
Flying saucers are not atomic rockets and are therefore beyond the scope of this website. If you want the absolute best information (including blueprints) of the most famous flying saucers from movies and TV, run, do not walk, and get a copy of The Saucer Fleet by Jack Hagerty and Jon Rogers. For rocket-like spacecraft, the last word is Spaceship Handbook by the same authors. Both books are solid gold.
The cylinder is more aerodynamic (for take-off and landing on planets with atmospheres), and allows the use of a smaller anti-radiation shadow shield (because from the point of view of the reactor the body of the ship subtends a smaller angle). It also lends itself well to the tumbling pigeon concept since it does not have to spin as fast as a sphere of the same volume in order to generate the same centrifugal gravity.
Drawbacks include a larger surface area, and a larger "moment of inertia" for yaw and pitch maneuvers (but a lower moment of inertia for roll maneuvers). This means it takes forever to point the ship's nose in different directions as compared to a sphere, which means poor maneuverability (See short story "Hide and Seek" by Sir Arthur C. Clarke for details). Larger gyros or stronger attitude jets will be needed. A faster roll rate is actually not of much use, unless you are trying to get a weapon turret to bear on an enemy ship (See the wargame Attack Vector: Tactical for details).
Cylinder shapes are also better if your ship has a so-called "spinal mount" weapon, that is, where instead of mounting a weapon on your ship you instead build the ship around the weapon. Such weapons are typically long and skinny, which fits the profile of a cigar more than a sphere.
Spheres have the largest enclosed volume for the smallest surface area of any shape, which is a major advantage where every gram of structural mass is a penalty. They also have a smaller moment of inertia for yaw and pitch maneuvers. Drawbacks are the opposite of the cylinder: they are only slightly more aerodynamic than a brick, they don't shadow shield well, and they are lousy tumbling pigeons.
Spheres also require more internal support structure than cylinder to handle the same acceleration load, particularly if you're going to be putting decks inside of it that rely on the structural framework of the spheroidal hull for rigidity. Cylinders under acceleration support themselves in the same manner as a skyscraper building, spheres need extra bracing to keep the equator from sagging. Of course this only becomes a problem if the acceleration is greater than a tenth of a gee, neither spheres nor cylinders have any problem coping with milligee acceleration.
On the other tentacle, if the shape has to be pressurized, like a fuel tank or a crew compartment, non-spherical shapes require more bracing mass and are more expensive to construct than spherical shapes.
Ken Burnside noted that another drawback of a sphere is that your internal volume is going to have a lot of "wasted dead spaces" near the hull. Odd shaped volumes that are what happens when you have an interior wall sectioning off part of the curved surface of the sphere. Anybody who has tried to lay out a floor plan inside a Buckminster Fuller geodetic dome house knows the problem.
Yet another thing to keep in mind is that using current manufacturing techniques, constructing a cylindrical hull costs about 70% of the cost of constructing a spherical hull with the same volume.
Why? Because it is more difficult to manufactured girders and plates that are bent compared to straight ones. A cylinder is constructed using straight stringers. The frames are circular, but all the frames have the same radius and radius of curvature. A sphere on the other hand uses curved stringers and circular frames all of different sizes (well, there are actually two frames of each given radius, but you understand the point I'm trying to make).
On most modern wet-navy warships, the hull plates are mostly straight, with a few bent in one dimension, and only a couple bent spherically in two dimensions. Bending is expensive. Eliminating the bending cost will require one and perhaps two breakthroughs in manufacturing technology.
Many early designs were cylindrical but also carrying a winged landing craft. This gave the spacecraft the appearance of an arrow or a spear. Granted, the landing craft was usually for the return trip to land the astronauts on Terra, but there were a couple intended for landing on Mars, and even one for landing on a hypothetical planet with an atmosphere around another star.
Other ship geometries are possible. In Sir Arthur C. Clarke's Islands in the Sky there is an Terra-Mars passenger liner shaped like a doughnut (torus). The power plant and propulsion system is in the hole, and the ship spins for centrifugal gravity.
And there is also the open-frame design, where components are attached wherever is convenient and braced by girders. The von Braun Moonship from the Collier's article is an example.
Remember that in a spacecraft under acceleration, "down" is in the direction the exhaust is shooting (i.e., under acceleration the ship will seem like it is landed, sitting on its tail fins with the nose pointed straight up). The spacecraft living quarters will be arranged stacked like floors in a skyscraper. The floors will be at ninety degrees to the exhaust direction. Spacecraft arranged this way are called Tail-sitters. Most spacecraft are tail-sitters.
Usually spacecraft will NOT have their floors parallel to the exhaust direction, i.e., sideways like an aircraft or boat. This is the idiotic "Confusing-a-spaceship-with-an-passenger-airliner" school of ridiculous spacecraft design, found in science fiction with moronically bad science such as Star Trek, Star Wars, Battlestar Galactica and practically all the rest. Get it through your head: Rocket Are Not Boats people! The only way this will work is with some sort of hand-waving paragravity. And even then why would anybody use such a stupid layout? If the paragravity fails, the rear wall abruptly becomes the floor, the floor becomes the wall, everybody falls to the new floor and breaks their ankles, and all the control panels are out of reach on the freaking ceiling. Now what, Flash Gordon?
There are only two situations where it makes sense to use the passenger-airliner arrangement:
- For spacecraft that actually do act like aircraft at some point, e.g., the Space Shuttle.
- For cargo spacecraft that do not want to use a crane to move cargo up and down over tens of meters. Instead they become belly-landers.
Things get confusing if you have a spacecraft equipped with a centrifuge for artificial gravity. Under thrust with centrifuge deactivated, "down" is in the direction of thrust. With no thrust and centrifuge spinning, "down" is in the direction away from the spin axis. Under thrust with centrifuge spinning, "down" will be in a weird corner direction that is the vector sum of the two accelerations. There are ways of dealing with this.
The producers of the TV series The Expanse understand this. In the first episode, a rescue party approaches the silent derelict ship the Scopuli.
But what's this? The ship's name plate looks upside down! Did the special effects artists make a mistake?
WRONG, you trekkie! Ships do not move through space on their bellies like an airplane. The producers of The Expanse got it exactly right. Ships move vertically like a sky-scraper. If we view it that way:
...suddenly we see that the name plate is perfectly correct.
The Expanse gets a big platinum star from me for that bit of accuracy. With the exception of the 2001 movies I don't recall anybody getting that correct (well, also maybe SyFy's Ascension, but that almost doesn't count). And that is only the start of things they got right. I love this show.
There was an interesting hybrid in Larry Niven's World of Ptavvs. The "honeymoon special" was laid out sideways like an aircraft. The spacecraft resembled a huge arrow. It sat on the takeoff field like any aircraft while the passengers boarded. It would taxi down the runway and take off with JATO units, the "tail feathers" acting as wings. Once aloft, the scramjets kicked in, boosting the ship into Terra orbit. In space, the main fusion propulsion system was in the belly, not the tail. The ship flew through space sideways, which kept the direction of "down" still pointed at the floor. The wings also contained the heat radiators.
The scientifically accurate layout of Niven's honeymoon special was commendably used in the otherwise forgettable movie Lifeforce (forgettable unless you are fond of nude space vampires). The British spacecraft HMS Churchill has its NERVA engine also located in the ship's belly instead of the tail.
This makes sense since the Churchill is a belly lander, as are all NASA derived space shuttles. Under NERVA thrust the direction of "down" matches the interior arrangement of the shuttle's habitat module. The fact that the ship appears to be moving through space sideways is of no concern.
For what it is worth , the game GURPS Traveller: Starships defines the following terms:
- Drive Axis: a line that originates in the center of thrust in the engines. Sometimes called the Thrust Axis. One end points in the direction the exhaust goes, the other end points in the direction the ship moves (Newton's "equal and opposite reaction"). Remember that "down" is in the same direction the exhaust goes. The drive axis should pass through the ship's center of gravity, otherwise under thrust the ship falls off its tail and spins wildly.
- Tail Lander: a spacecraft whose decks are perpendicular to the drive axis. Almost all the ships described in this website are tail landers. SpaceX's Falcon line of boosters are tail landers.
- Belly Lander: a spacecraft whose decks are parallel to the drive axis. The Space Shuttle is a belly lander.
- Fore: in the direction of the drive axis towards the ship's nose. This is the direction of "up".
- Aft: in the direction of the drive axis towards the ship's tail. This is the direction of "down".
- Port: a line perpendicular to the drive axis passing through the spacecraft's main airlock. Ship's "left."
- Starboard: a line perpendicular to the drive axis 180° from Port. Ship's "right."
- Dorsal: a line perpendicular to the drive axis 90° from Port, counterclockwise when looking aft. Ship's "top" or "back."
- Ventral: a line perpendicular to the drive axis 90° from Port, clockwise when looking aft. Ship's "bottom" or "belly."
- Outboard: away from the drive axis.
- Inboard: towards the drive axis.
The problem with the definition of port is that in a nuclear powered spacecraft, the logical place for the main airlock (and the ship docking point) is the ship's nose. Which makes "port" the same as "fore", thus ruining the nomenclature system. The idea is to have the directions at ninety degrees to each other, not coinciding. Some other distinguishing spacecraft feature will have to be used, but there doesn't seem to be any good candidates.
And what gets my goat is the terms "Dorsal" and "Ventral". They only apply to belly-landers. Applying those terms to a tail-lander is just propagating that accurséd "Confusing-a-spaceship-with-an-airbus" fallacy. Unfortunately there does not seem to be an alternate term for dorsal and ventral. Come to think of it, "Port" and "Starboard" are also airbus like.
Of course there will be a few spacecraft that actually are belly-landers, mostly cargo and aerospace shuttles. That is: spacecraft designed to have the cargo access hatch as near to the ground as possible, or spacecraft that can also operate as aircraft. Most spacecraft will be either tail-landers, or orbit-to-orbit ships that never land (but still have a tail-lander's internal layout).
On NASA spacecraft, they arbitrarily pick a direction for port. The spacecraft's X axis is the Drive axis, with +X in the direction the spacecraft accelerates and -X is the direction the exhaust goes. The astronauts lie on their backs, with eyes facing +X (up) and backs facing -X (down). Y axis passes through astronaut's left and right shoulders. +Y is right (starboard) and -Y is left (port). The Z axis passes through the astronaut's head and feet. +Z is in the feet direction (ventral, pfui!) and -Z is in the head direction (dorsal, ditto). This is important for the pilot to know when they are using rotation and translation controls.
If the ship has some sort of centrifugal gravity where spin gravity does not match thrust gravity, there will be some sort of jargon for "thrust gravity downward direction" and "spin gravity downward direction." The wet navy won't help you with this one, make it up yourself. If the centrifuge's spin axis happens to be the same as the drive axis, up is "inboard" and down is "outboard". Inside a centrifuge the directions "spinward" and "trailing" (anti-spinward) will be used, refering to the direction of centrifuge spin.
You serve "in" a ship, not "on" one. "Abaft" means "behind", "forward" means "in front of." It is a "deck", not a "floor".
Pressure-tight walls are "bulkheads", pressure-tight doors are "pressure-tight doors." Non-pressure tight doors are just doors and non-pressure tight walls are just walls. Generally non-pressure type items are pretty flimsy. Doors in the decks (floor and ceiling) are "hatches.".
It's not a "restroom" it's a "head", it's not a "kitchen" it's a "galley." It's not the "dining room", it's the "mess deck" (unless it's for officers, then it's the "wardroom"). The "mess" refers to the crewmen currently eating on the mess deck. It's not a "bunk" its a "rack", it's not a "ceiling" it's an "overhead." It's not a "hallway" it's a "companionway" or "passageway", it's not the "stairs", it's a "ladder." And the "brow" is any walkway or catwalk leading to the main airlock.
These are all from the naval tradition, the air force jargon is totally different.
In the US Navy, each compartment had a "bullseye" or Navy Ship Compartment Number. It is sort of a three-dimensional address of each space or compartment. While this is useful to keep new recruits from getting lost, the more important use is for damage control. Reporting a damaged location to, from, or between damage control parties must be rapid and unambiguous.
The compartment number is often stenciled on the walls and/or the doors.
Every door, hatch and manhole aboard the LST is labeled. This metal sign provides certain information and learning to read these labels help one navigate through the vessel. These labels were helpful in reporting emergencies because they utilized a standard method for giving describing any location aboard the ship. Each label will have a combination of numbers and a name for the compartment.
The first number indicates the deck number. The second number indicates that the opening is abaft of a particular frame and the last number indicates the number of the opening from the inboard out (port even numbers, starboard odd). A letter after the numbers indicates the use of the compartment.
A-Supply and Storage L-Living Quarters C-Control M-Ammunition E-Machinery T-Trunks and Passage F-Fuel V-Voids
So in this example from a hatch aboard the LST:
AUX ENG ROOM
So in English, 2-28-2 ESC TRUNK, would mean that the opening before you was an escape trunk, starting on the second deck, just aft of the twenty-eighth frame and is the first opening inboard out on the port side. The second line, 4-28-2-T tells you the trunk continues all the way to the fourth deck, just aft of the twenty-eighth and here it is still the first opening from the inboard out. This trunk gives access to: ELEC STORES 3-28-2-A or a store room for electrical parts on the third deck, which is aft of the twenty-eighth frame and is the first opening from the inboard out; and AUX ENG ROOM 4-28-O-E or the auxiliary engine room on the fourth deck aft of the twenty-eighth frame and the space is a machinery space.
(ed note: A different system will be needed for spacecraft, since they do not really have a port or starboard and the frames are parallel to the decks instead of perpendicular to them.)
Compartments are numbered for identification to facilitate location. The identification number assigned locates each compartment specifically, and generally indicates the function and use of the compartment. Compartment numbers consist of four parts, separated by hyphens, for example 6-150-0-E, in the following sequence:
Deck Number: The main deck is the basis for this numbering scheme and is numbered 1. The first deck below the main deck is numbered 2, and so on. The first horizontal division above the main deck is numbered 01, and the numbers continue consecutively for subsequent upper division boundaries. Compartments are numbered by the lowest deck within the space.
- Deck Number
- Frame Number
- Position in relation to centerline of ship
- Compartment use
Frame number: The forward perpendicular is the basis for this numbering scheme and is numbered "0" (zero). "Frames" are consecutively numbered, based on frame spacing, until the aft perpendicular is reached. Forward of the forward perpendicular, frames are "lettered" starting from the perpendicular to the bull nose (A, B, C, etc.) while frames aft of the after perpendicular are "double lettered" to the transom (AA, BB, CC, etc.). Compartments are numbered by the frame number of the foremost bulkhead of the compartment. If this bulkhead is located between "frames," the number of the foremost "frame" within the compartment is used. Fractional numbers are not used except where frame spacing exceeds four feet.
Frame spacing examples:
CG/DD/DDG/FFG 12IN Cutters 1FT LPD 2FT CVN/LSD 4FT LHD/LHA 7FT
Position in relation to centerline: The ship's centerline is the basis for this numbering scheme. Compartments located so that the centerline of the ship passes through them are assigned the number 0. Compartments located completely to starboard of the centerline are given odd numbers, and those to port of centerline are given even numbers. The first compartment outboard of the centerline to starboard is 1, the second is 3 and so forth. Similarly, the first compartment outboard the centerline to port is 2, the second is 4 and so forth. There may be cases in which the centerline of the ship would pass through more than one compartment, all of which may have the same forward bulkhead number. Whenever this occurs, that compartment having the portion of the forward bulkhead through which the centerline of the ship passes is assigned the number 0 and the other carry numbers 01, 02, 03 etc.
Compartment Use: A capital letter is used to identify the assigned primary use of the compartment. Only one capital letter is assigned, except that on dry and liquid cargo ships a double letter identification is used to designate compartments assigned to carry cargo. Examples of compartment use are storage areas, various tanks, and living quarters.
Some examples from NSTM 079 volume 2:
A Storage area C Ship and Fire Control operating spaces normally crewed E Machinery spaces which are normally crewed F Fuel or Fuel Oil tanks J JP-5 tank L Living quarters M Ammunition (stowage and handling) Q Areas not otherwise covered T Vertical access trunk V Void
Example of Compartment Numbering
Given Compartment "6 - 150 - 0 - E," we can determine that it is located:
a) five decks below the Main Deck,
b) foremost bulkhead is at frame 150,
c) centered upon the centerline of the ship, and
d) is used as an engineering space.
In the science-fictional GURPS Traveller: Starships, they use the following system. Odd numbers are port, even numbers are starboard. Numbering is consecutive in order from inboard to outboard, fore to aft, dorsal to ventral.
On a naval vessel, "doors" lead from one side of a deck to another side of the same deck; hatches go between decks. In other words, doors are in the walls, hatches are in the floor and ceiling. Doors in non-pressure tight walls are "doors", doors in pressure-tight bulkheads are "pressure-tight door." On a spacecraft with no artificial gravity the distinction between openings in the walls and openings in the decks is sort of academic. Of course all the mechanical details are identical.
A small circular or oval access hatch is called a "scuttle." An escape hatch is usually a quick-acting scuttle (see below), because crew members trying to escape are generally in a hurry.
An opening into an uncrewed space for purposes of inspection and maintenance are called "manholes." This is generally into the interior of tanks and crawl spaces between equipment.
Pressure tight doors have "dogs", which are individual fasteners that clamp the door to maintain the seal with the door coaming. Ordinary doors do not have dogs, and cannot be "dogged down". On wet-navy ships, water-tight doors have eight dogging latches around the edges.
Some pressure tight doors have a clever arrangement where a single handle can close all the dogs simultaneously (a "quick acting" door). Otherwise the dogs have to be turned individually. Naturally the clever doors require more scheduled maintenance than the standard kind.
A pressure-tight door is a damage control barrier, while an ordinary door is an access control barrier.
Fancy pressure-tight doors will have some sort of indicator telling you if there is pressure or vacuum on the other side. The fanciest will have manometers, more bargain-basement models will just have a valve attached to a whistle. Turn the knob, and if it screeches there ain't no air over there.
On wet navy vessels, doors and hatches leading into compartments containing flammables, weapons, high explosives, or petroleum engine fuel are forged out of bronze instead of iron. The latter can strike sparks when closing the hatch or turning the handwheel, with unfortunate results. Bronze is non-sparking. You might see something similar in a spacecraft hab module insanely designed to use pure oxygen as a breathing mix.
On a high-tech spacecraft, there might be an automatic mechanism which will shut pressure-tight doors and hatches if it detects a hull breach or other unexpected drop in air pressure. There is a safety question of just how much the door will insist upon closing if an unfortunate crew member has a body part trapped. If the pressure drop is gradual enough or the well being of the crew is important enough, the door will be programmed to allow the crew member to open the door a bit and free themselves. Otherwise the blasted door will do it darnedest to amputate the unlucky crew member's limb. Also note that such automatic doors will contain complicated components and thus require lots of regular maintenance.
Submarine Pressure-Tight Doors
Submarine watertight bulkhead door are entertaining, though they are probably far too wasteful of mass to use on a real spacecraft. But they are instructive. And they are so retro. The technical term is "quick-acting water-tight doors", as opposed to the doors with "dogs."
These are damage control barriers for use when the hab module's hull is breached. As such it is uncertain which side of the door will suddenly contain vacuum. However, in an airlock (or other situation where you are pretty sure you know which side will always have pressure), as a safety measure you want the door to open such that the air pressure will be constantly pushing the door safely shut instead of trying to blow the door open and kill everybody. And to prevent morons from opening a door leading to vacuum, since they cannot possibly tug open something being held shut by 14.7 pound per square inch. If you have a low-IQ individual on your ship who can pull with over 19 metric tons of force, you have a bigger problem than inadequate safety on your pressure-tight doors.
As a rule of thumb you'll want your hab module doors set so that they close in the outboard direction and open inboard. Presumably the drop in air pressure will be from a catastrophic hole in the hull, not the center of the spacecraft. So at a door connecting two compartments, the compartment closer to the hull is more likely to be in vacuum during a disaster. This will not always be true, but that's the way to bet. Thus the air pressure will be helpfully holding the door shut.
On wet-navy surface ships they mount doors such that the gears and mechanism of the quick-acting-door are on the dry side so they are not exposed to corrosive seawater. This means the machinery faces the inboard side, because presumably the water will be coming from a breach in the hull on the outboard side. Whether this is a concern on a spacecraft depends upon how much wear and tear the machinery suffers under vacuum.
Keep in mind that submarine doors have to contain an order of magnitude more pressure than a spacecraft door ever will. That's why they look like bank vault doors. A spacecraft pressure door will only need to cope with one atmosphere of pressure or so, while a submarine at 200 meters depth needs to be able to handle 20 atmospheres. Former Navy Jennifer Linsky is of the opinion that a spacecraft would probably use pressure doors similar to the quick-acting-door pictured above as opposed to these massive submarine doors.
I have yet to locate any description about how submarine bulkhead doors operate, so I had to look at lots of images and use my raw powers of deduction. Besides, the quickest way to find the answer to something on the internet is to post an inaccurate explanation. Experts will come boiling out of the woodwork eager to tell you just how wrong you are.
I got nowhere fast with analyzing the images until I realize there were two types of doors that looked similar. Since I do not know the proper terminology, I'm dubbing them "Innie" and "Outie", much like navels.
- When the door is opened, the side of the door revealed is concave (full of gears and machinery). When door is shut you see a smooth convex surface.
- The strike plates are bulges in the door frame
- Actuators are attached to part of latch farthest from door body
- The latches rotate towards the door body to engage the strike plate
- When the door is opened, the side of the door revealed is convex (with no gears exposed). When door is shut you see a concave surface full of gears.
- The strike plates are curved arching knobs
- Actuators are attached to part of latch nearest to door body
- The latches rotate away from the door body to engage the strike plate
How Quick-Acting Water-Tight Doors Work
- Red: Handwheel and Worm. The handwheel can look like a wheel, a cross bar, or a wheel with a bar extending from the center.
- Yellow: Worm gears and levers
- Green: Actuators
- Blue: Latches
The mechanism of Innie and Outie doors work pretty much the same, with the exception that the latches rotate in opposite directions.
The wheel or crossbar (red) in the center of the door is spun. This rotates the worm of a worm drive (not shown).
The worm engages the four worm gears (yellow) attached to four levers, moving the levers into extended position (far ends of the levers move further away from center).
The ends of the levers push four oddly-shaped actuators (green) away from the center of the door body and closer to the door body edge.
The actuators push on the edge of pivoted latches (blue). The latches rotate on their pivots to engage the strike plates. Innie latches rotate in the opposite direction from Outie latches. To do so, the Innie door has the actuators attached to the latches on the part of the latch furthest from the door body, while Outie actuators are attached to part of latch closest to door body.
An airlock is a way for an astronaut (presumably dressed in a spacesuit) to exit the pressurized habitat module without all the atmosphere blowing out into the limitless vacuum of space.
Basically it is a chamber with two airtight hatches, which do not open simultaneously. One hatch opens into the hab module, one opens into space, and the pressure inside the chamber can be switched from ship pressure down to vacuum. Before opening either hatch, the pressure inside the chamber is equalized with the environment beyond. This is called "cycling" an airlock.
As a mundane analogy, imagine a spaceship is a house, a space suit is winter coat, vacuum is the bitter cold of winter, air is the warmth inside the house, and the airlock is an entryway (the "warmth-lock"). To leave the house, you walk into the entryway, close the door behind you so the heat does not escape, put on your winter coat hanging in the coat closet, open the front door into the cold of winter, leave the house, and close the front door behind you. Just like an airlock.
When cycling down to vacuum all the air in the lock is stored in tanks, of course. Just venting it to space is a criminal waste of limited breathing mix. This would not be done unless it was an emergency or if it was an incredibly primitive airlock. Even with a reasonably designed airlock there is going to be some small unavoidable breathing mix loss with each cycle.
Very small or very cut-rate spaceships might not have an airlock. They take up lots of room and are expensive. They might be optional on a one-man Belter asteroid mining ship. Of course this means the pilot will have to put the toothpaste and any other pressure sensitive supplies into a pressurized locker before they vent the entire hab module and open the hatch. An example is the Lunar Module from NASA's Apollo program.
A stripped-down variant on the airlock is the "suitport". Instead of a chamber, the backpack of a space suit attaches to the ship's hull. An astronaut enters the suit by crawling through the backpack, seals the inner door, then detaches from the hull. It requires much less mass and volume than a full airlock. On the other hand, they are difficult to design if the atmospheric pressure inside the ship/spacestation is not the same as inside the suit. Soft suits commonly have lower pressure than the habitat.
"Spacing" is a nasty form of execution, where the victim is forced into the airlock while not wearing a spacesuit. The airlock is then cycled, hurling the victim into airless space where they suffocate. Sometimes this is made as a threat, e.g., "Follow orders or I'll throw you out the airlock stark naked!"
Some writers have the nasty idea of opening the airlock while it is still pressurized so as to blow the victim into space. This avoids the necessity for a space suited person to enter the lock and kick the body out. However standard air pressure is not enough to blow the victim into space. You need about ten atmospheres for that. Also the victim will probably be frantically hanging onto anything they can grab inside the airlock in any event. Using air pressure to remove the excecuted is probably a waste of good breathing mix.
There are two main styles of "iris" doors: Leaf Iris and Petal Iris.
Leaf Iris Doors
In the role playing game Traveller, airlock doors are often in the form of a iris. This is probably due to the authors of Traveller taking the advice of Robert Heinlein. He noted that science fiction writers can evoke a futuristic vibe by throwing out a weird detail as if it was commonplace, e.g., The door dilated. This phrase has evolved to science fiction fan jargon meaning "cool, but inefficient", but I digress.
Anyway, in the artwork for Traveller game supplements, iris doors are generally depicted as something like a titanic camera diaphragm iris. Sort of like the iris shield on the Stargate, but without the sharp pointy bits.
An iris actually will not work on an airlock, since those always have a small hole in the center where the air will leak out. However, NASA is looking into a rugged iris design that is air-tight.
Besides the lack of a hermetic seal, the individual leafs have to be very thin or they cannot interleave. Which makes for a flimsy door, not a good idea for a hatch which is the only thing standing between you and a horrible suffocating death from the airless vacuum of space.
The Traveller drawings and deck plans also ignore the fact that there has to be space around the edge of the door for the leaves to retract into. The entire door diameter is about 1.55 the size of the door opening. If a standard Traveller iris door had an opening 1.5 meters in diameter, the entire door mechanism would be 2.33 meters in diameter.
Petal Iris Doors
Another design that would work is a four, five, or six petal door; like the one on the roof of the Millennium Falcon which Lando Calrissian exited to rescue Luke Skywalker from the underside of Bespin, in the movie The Empire Strikes Back. Like the NASA design they are actually air-tight.
The petals can be of any arbitrary thickness, allowing an overwhelming safety margin protecting you from death by space asphyxiation. The thickness also allows the use of locking cylindrical bolts like in bank vault doors, providing additional protection from door breaches by air pressure or space pirates.
Unfortunately such doors need even more space around the edge for the petals to retract into. For a six-petal rotating design the door diameter is 1.83 times the size of the door opening.
A docking port is specialized pressure hatch on a spacecraft that can mate to another docking port on another spacecraft or space station. It creates a pressurized connection so that crew can walk from one spacecraft into the other without having to put on space suits. It also makes a strong mechanical connection, because if the connection between the two ships fails when the hatches are open the results will be most unfortunate.
An airlock is not required as part of a docking port, but it is insanely dangerous to leave it out of the design. Having said that, as far as I am aware there are no real-world spacecraft with airlocks due to the mass and volume of an airlock (with the exception of NASA's space shuttle).
Spacestations components can be connected in a semi-permanent fashion by docking ports.
A docking mechanism is used when one spacecraft actively maneuvers under its own propulsion to connect to another spacecraft.
A berthing mechanism is used when space station modules or spacecraft are attached to one another by using a robotic arm — instead of their own propulsion — for the final few meters of the rendezvous and attachment process. Berthing typically involves connection to a space station.
Currently there exist no mechanisms that can perform both docking and berthing. NASA is developing the NASA Docking System which will do both, but the design has not been finalized yet.
It is also a very bad idea to have no international standards for docking ports. If the Russian ports cannot dock with Chinese ports, this will drastically reduce the number of rescue options if an emergency happens. There is work being done on a Universal Space Interface Standard, but nothing hs been completed yet.
Early docking ports were even more stupid. They were non-androgynous systems, with a male part and a female part. Sort of like the two ends of an electrical extension cord, one with prongs the other with a receptacle. Which means if the rescue spacecraft and the stricken spacecraft both had male ports, they were out of luck. Or at least the stricken ship is.
If spacecraft commonly have nuclear propulsion systems and/or nuclear power systems, ship design will more or less force ships to dock bow-to-bow (nose-to-nose). Here's why. Radiations shields by their very nature are massive, and thus cut into the payload capacity. So instead of coating the entire reactor, ships will use "shadow shield" as the smallest possible shield. In the left diagram below, the white area is safe, and the blue area is filled with the deadly radioactive shine from the reactor.
Now say that a lunar shuttle vehicle arrives, and wants to dock. It does not want to wander into the blue radiation zone, or its crew will be irradiated. The crew of the nuclear ferry vehicle does not want the lunar shuttle in the radiation zone either, because the shuttle's metal structure could scatter (reflect) radiation from the ferry's reactor into the ferry's crew.
If you examine the situation, the only safe way seems to be bow-to-bow. Even more so if two nuclear spacecraft want to dock. You may remember this is how the Apollo command and service module docked to the lunar module.
This does throw a monkey wrench into Traveller's definition of "Port", but that's just too bad.
In the space environment, it is possible for parts of a spacecraft to charge up (like shuffling your feet on the carpet on a dry winter's day) which can result in an electrostatic discharge (like when you've shuffled, then touch the door knob).
This can cause a spark to jump between spacecraft components or between two docking spacecraft, resulting in damage. In addition if an astronaut on EVA touches the wrong spacecraft or space station component they could get zapped with a severe electrical shock.
When NASA was developing the windows for the Apollo spacecraft, there were some failures. After that, they decreeded the following: A spacecraft window is structurally defined as any piece of glass that is thermally or mechanically stressed and will endanger the crew or mission success if it breaks.
Huge windows on a spacecraft are not a good idea for many of the same reasons as they are not used on a submarine.
- Window frames create a structural weakness in the hull.
- If they break they let all the air out of the compartment, killing everybody. At the least you need airtight shutters.
- They let in deadly space radiation.
- If the spacecraft performs aerobraking or aerocapture the windows have to be protected from the blowtorch heat. This was a headache when NASA designed the Apollo Command Module. Windows melting or shattering could ruin your whole day.
- With a few exceptions, there isn't anything to see. Outside of the exceptions the only things to see are
- Endless black space dusted with stars
- The eye-melting fury of the Sun
- The planet you are orbiting, for the small fraction of the total space mission time that you are close enough to see the planet.
"But…but…but…!" you protest, "what about watching the dazzling spectacle of a space battle?" RocketCat does a face-palm at your naïveté. Star Trek, Star Wars, Battlestar Galactica, et al to the contrary, space battles will NOT be fought at spitting distance. Directed energy weapons will force ranges such that the enemy ships will only be visible through a telescope.
Watching a space battle through a port hole, you will either:
- See nothing because the enemy ships are too far away to see without a telescope
- See nothing because a reflected laser beam or nuclear explosion has permanently robbed you of your eyesight
Instead of windows, spacecraft will have lots of external sensors and video monitors inside for the crew to watch. Much like watching a football game: you will get a far superior view of the game if you stay home and watch it on TV.
As points of reference, the side windows on the Apollo Command Module (CM) are 33 centimeters square. The CM docking windows were 20×33 cm. The Apollo Lunar Module landing windows were 64×71 cm triangles, with the top edge further from the hull so the pilot can look down at the landing legs. The windows on the Space Shuttle airlock hatches were 10 cm in diameter.
The Cupola on the International Space Station has the largest windows used in space to date, the top window is an 80 cm disc. Yes, it has very thick shutters (made of Kevlar and Nextel). It is used to conduct experiments, dockings and observations of Terra. It also helps with the use of the amazing Canadarm2 remote manipulator.
Places where windows might be worth the drawbacks are"
- Emergency navigational astrodomes
- Docking (rendezvous) windows
- Airlock doors
- Landing windows
- Cockpit windows for shuttles that fly like aircraft when they land
Trusting the astronaut's lives to something made out of glass is nerve wracking, since glass is notoriously brittle. The strength of glass is measured by the modulus of rupture (MOR). A safety factor of 3.0 was used.
The Apollo command module has five double-pane windows, as shown in the diagram.
All five windows are double-panes of aluminosilicate glass. The space between the panes is evacuated and fill to 7.0 psia with dry inert nitrogen gas.
Every attempt is made to prevent stress on the windows. The mounting process was designed to preclude installation stress. The frames were design to avoid loads on the window. This was done by injecting a silicone elastomer around the edge of each pane and curing it in place. This potted the windows in their frame and provided an air-tight seal.
The only load was the pressure of the nitrogen, since there wasn't anything that could be done about that.
The aluminosilicate glass thermally tempered to 25,000 psi MOR for hatch and side windows and 23,200 psi MOR for the rendezvous windows. A safety factor of 3.0 was used. Each pane of a double-pane has the same thickness. Hatch 0.23 inch, side 0.25 inch, and rendezvous 0.20 inch. All panes are coated on both sides with a high-efficiency antirefection (HEA) coating.
The double-pane windows are covered with a 0.7 inch thick fused amorphous silica pane as a heat shield. When the command module does its flaming re-entry, the windows have to be protected or the results will be most unfortunate. They will be exposed to thermal loading for about 15 minutes.
The heat shield panes are insulated around the edge by a 0.02-inch-thick fiberglas layerr using a silicone elastomer bonding agent. The 0.080-inch-thick steel frame and retainer were designed so that the flat glazing would fit on the conical hull. It had a 0.05 inch gap on all edges between the insulation and frame so the shell could contract when it hit the cold Pacific ocean without shattering the glass. The pane had an outboard coating of magnesium fluoride, and an inboard blue-red coating.
Docking or rendezvous windows are generally aimed parallel to the axis of the docking port. Since the NASA Apollo CS module and the Russian Soyuz have the docking port on their nose, their docking windows are aimed straight ahead.
There may be a "docking control station" with special windows, either for guiding small craft to docking ports or for bringing the ship itself up to dock to another ship or a station. You could use video screens, but a viewport is simpler, and less likely to go to "snow" at the worst possible moment. The docking control station might be out on a boom or otherwise elevated to give a better field of view.
The Russian Soyuz does not use either a video screen nor a window. It uses a periscope which rear-projects onto a frosted glass screen. This is an admirable low-tech solution. There is no electronic screen which could malfunction, but neither is there a large vulnerable glass window letting in radiation.
With the advent of virtual reality there is a semi-plausible solution to the spacecraft window problem: use virtual windows instead. Mount some huge computer monitors on the walls and have them display what would be seen through an actual physical window in that location.
Or even more cyberspacelike: wear some virtual reality goggles, and have the computer paint a fake window wherever you want in your field of vision. With this you can change the location of the windows at your whim. All the immediacy and instinctual utility of a physical window, but with none of the vulnerability.
Except of course if the virtual reality computer is stopped or destroyed, suddenly you are trapped in a metal box you cannot see out of. You might want a couple of emergency physical windows you can unshutter for just such an situation.
In all the crew's "blastoff stations", they will have acceleration couches. As most space fans know, the human body can tolerate more gravities of acceleration when lying horizontal than when sitting upright in a chair. Crew members who will have to operate controls while under multi-gravity acceleration will have fancy chairs which hold their bodies horizontal, vital controls at their fingertips, and critical dials, telltales, repeaters, and read-outs mounted above them in easy view. The rest of the crew will be lucky to get glorified cots or hammocks (They will probably be stuck with using whatever it is that they sleep in. Tough if they are using a "hot bunk" system.). In the movie DESTINATION: MOON, the pilot had the important controls located on a sort of lap-board for easy access. For real high gravity acceleration, the crew will have to use couches that are high-tech waterbeds.
And remember that Rockets Are Not Hotels. They are going to be cramped. Though keep in mind that in free-fall the entire three-dimensional living area can be used so it won't be as cramped as the floor space might lead you to believe.
The corridors will have cables, pipes and ducting either exposed or behind easily removable panels. This is to facilitate repairs. The panel brackets can double as hand-holds. The main function of panels is to protect the cables from clumsy crew members flying in free-fall. Of course all the cables and pipes will be color-coded. If the designers are smart they will double-key them as well.
The corridors will become instantly dark if the power goes off (since port-holes let all the radiation in the ship won't have any). Navy veteran Jennifer Linsky says that US Naval ships have so-called "battle lanterns." They are located in all corridors and most compartments. Each contains a rechargable 12 vold battery hooked to the ship's power grid, constantly charging. If the power grid goes dead, the lamps switch to battery power and turn on. They have red lenses to preserve the night vision of the damage control teams.
This also means that all those color-coded pipes and cables will also have stenciled labels or other double-keying, since red lighting renders color coding worthless.
In James Blish's SPOCK MUST DIE, shuttlecraft have "glow-pups", which are tubes filled with (imaginary) "ethon" gas excited by a built-in radioactive source. They will glow with no power for millions of years.
As with so many other things, high tech items predicted by Star Trek have come to pass. The modern version is called a "Gaseous Tritium Light Source", and is used in submarines. A tube of borosilicate glass is internally coated with a phosphor. It is filled with a trace amount of radioactive Tritium gas and sealed. It will glow for about 10 to 20 years, and is not particularly radioactive. Even if the tube breaks, the gas is too rarefied to be a health hazard. They sell these things in England as glow-in-the-dark keychain fobs.
Glow-pups will be in strategic places for lighting, and will also be placed to indicate hatches and sharp corners of equipment. Anywhere to help getting around in the dark.
Rick Robinson notes that the corridors will probably not be cramped like those on a submarine. The main reason subs are so claustrophobic is because the entire sub has to have, on the average, exactly the density of water. Spacecraft don't have to. (spacecraft designers do have to worry about how much air it takes to pressurize the lifesystem, and the mass of the bulkheads enclosing the interior space.)
While not cramped, the interior will probably be similar to the inside of a conventional Naval vessel. That is, it will be full of sharp corners and hard girders to bark your shins or to give you a concussion. The rule in the U.S. Navy is "one hand for the ship, one hand for you." In other words, always keep a hand free, and when moving through the corridors, you put you hand on the thing sticking out into the passageway as you reach it.
The duty stations of the crew members will probably be cramped. In NASA speak the "work envelope" will be small.
Ladderways may be offset between decks. You don't want to have a five story fall awaiting somebody who slips off the ladder. Especially if the spacecraft is pulling three gees. If they are offset, the farthest one can fall is one deck's worth. However, Rick Robinson has an interesting alternate solution. He notes that moving equipment and supplies through a ship is always a problem, and will be exacerbated by offsetting the ladderways. His solution is to have the ladderway openings in a straight line, but while the spacecraft is under thrust, the ladders will be inclined to become stairs. The stairs will prevent fall-through. When the spacecraft enters free-fall, the stairs are rotated to a vertical position, becoming a ladder again and allowing the ladderway to become a fast route for moving equipment. The stair/ladders can be secured in either position by cotter pins. Don't forget to attach the pins to the ladders with wires to prevent them from floating away while the ladders are rotated. And obviously places where the ladderway penetrates a pressure bulkhead will have large hatches.
has some important observations:
In the movie Forbidden Planet, there is a small crane mounted over a deck hatch to facilitate moving equipment between decks. It is shown in the scene where the invisible monster enters through the hatch into the bunkroom full of sleeping enlisted men. It is the long metal arm that the invisible monster bumps out of the way.
If you want to ignore this entire website and just make a tired old standard TV or Movie spaceship utterly without scientific accuracy, Mythcreants has you covered. But don't let RocketCat catch you or he will give you an atomic wedgie.
But if you actually want such a thing, what are you doing in this website in the first place?
An example are the Spline ships from Stephen Baxter's Xeelee series. The Spline are an alien species who wanted job security. So they genetically engineered their bodies to become exceptionally good spacecraft. Then they rent themselves out to other species as the best spacecraft in known space. The Spline figures there will always be a market for good spacecraft, so it matters little if their current client species go extinct or something. Rhys Taylor has some great Spline artwork here.