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.
|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||27 meters/90 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||49 meters/160 feet|
|9||Orion Drive Mars Exploration Vehicle||50 meters/165 feet|
|10||United Planets Star Cruiser C-57D||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, Contraband Rocket|
|14||Boeing747||72 meters/232 feet|
|15||RS-10||73 meters/240 feet||Andre Norton Star Born|
|16||Ferry Rocket||84 meters/280 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||102 meters/335 feet|
|20||DY-100 Botany Bay||111 meters/365 feet||Star Trek|
|21||California Redwood||112 meters/367 feet|
|22||Discovery||113 meters/370 feet||2001, A Space Odyssey|
|23||Romulan Bird of Prey||131 meters/430 feet||Star Trek|
|24||Great Pyramid of Cheops||140 meters/500 feet|
|25||Oscar class submarine||154 meters/500 feet|
|26||Galactic Cruiser Leif Ericson||169 meters/554 feet|
|27||Washington Monument||170 meters/560 feet|
|28||Klingon D7 battlecruiser||228 meters/750 feet||Star Trek|
|29||LZ-129 Passenger airship Hindenburg||245 meters/800 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||324 meters/1060 feet|
|33||CVN-65 Carrier Enterprise||336 meters/1101 feet|
|34||Empire State Building||444 meters/1500 feet|
|35||Al Rafik||102 meters/335 feet||Attack Vector: Tactical|
The following 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.
If you just want something really quick and dirty, decide upon the hull volume of your spacecraft, and multiply it by the average density of a spacecraft. 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. 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.
Figuring the hull volume 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 Quantities Bill script 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.
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.
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. Each is optimized for their own particular area of use. More recently, orbital propellant depots and their related tanker ships also seem like a good piece of infrastructure. There are some sample realistic designs here.
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. 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 orbit-to-orbit spacecraft will require a delta-V budget of from 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. 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.
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.
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.
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.
Any Freudian symbolism is the responsibility of the reader.
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, not sideways like an aircraft. (The latter arrangement is the "Confusing-a-spaceship-with-an-airbus" school of spacecraft design, found mostly in bad SF TV shows and in old "Space Ghost" cartoons). For a compromise solution, one can mount things on gimbals. Note that it is allowed to use an airbus arrangement for a spacecraft that actually does act like an aircraft at some point, e.g., the Space Shuttle.
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 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.
GURPS Traveller: Starships defines the following terms:
- Drive Axis: a line from the center of thrust in the engines passing through the ship's center of gravity. One end points in the direction the exhaust goes, the other end points in the direction the ship moves. Remember that "down" is in the same direction the exhaust goes.
- Tail Lander: a spacecraft whose decks are perpendicular to the drive axis. All the ships described in this website are tail landers.
- Belly Lander: a spacecraft whose decks are parallel to the drive axis. Space Ghost's ship 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", which is worthless. The idea is to have the directions at ninety degrees to each other, not coinciding.
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 accursed "Confusing-a-spaceship-with-an-airbus" fallacy. Unfortunately there does not seem to be an alternate term for dorsal and ventral.
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" will be used.
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 "hatches." Non-pressure tight doors are just doors. Generally they are pretty flimsy (in some traditions "hatches" are openings in the deck while "doors" are openings in the bulkheads).
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.
A hatch is a pressure tight door. Which will prevent you from dying from asphyxiation if the adjacent compartment is hulled by a meteor.
Hatches have "dogs", which are individual fasteners that put pressure on the hatch to maintain the seal with the hatch coaming. Doors do not have dogs, and cannot be "dogged down". This is why doors are not pressure tight but hatches are.
Some hatches have a clever arrangement where a single handle can close all the dogs simultaneously (a "quick acting" hatch). Otherwise the dogs have to be turned individually. Naturally the clever hatches require more scheduled maintenance than the standard kind.
A hatch is a damage control barrier, while a door is an access control barrier.
Fancy hatches will have some sort of indicator telling you if there is pressure or vacuum on the other side of the hatch. 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.
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 spacecraft, 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.
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!"
In the role playing game Traveller, airlock doors are often in the form of an 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 camera iris. That actually will not work, since those always have a small hole in the center where the air will leak out. The petals also have to be thin so they can interleave. However, NASA is looking into a rugged iris design that is air-tight.
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.
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 above, 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 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.
There may be a "docking control station" with all-around viewports, 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 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.
The corridors will become instantly dark if the power goes off (since port-holes are often more trouble than they are worth). 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.
The interior walls will be flimsy with flimsy doors (for "flimsy" read "low mass"). All except for the pressure bulkheads dividing the lifesystem into compartments. These will be solid, airtight, and contain emergency hatches that will automatically slam shut into their gaskets if they detects a pressure drop (or if that much automation is too much of a maintenance nightmare, there will be a regulation requiring the hatches to be sealed at all times, only opened long enough to allow passage). The hatches will be substantial, but not as massive as those on a submarine. Sub hatches have to handle several atmospheres worth of pressure, while spacecraft hatches just has to manage one.
The hatches will probably have a numeric label stenciled on (note that the link describes a 1941-era ship). This helps when reporting emergencies, as it provides a standard way to describe a location on the spacecraft. On a World War II LST ship, it was in the form of three numbers separated by hyphens. The first number is the deck, the second is the frame it is abaft, and the last indicates the number of the opening from the inboard out (port even numbers, starboard odd). 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. In 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.
The hatches will have a pressure gauge indicating whether there is any air on the other side. Just in case of meteors...
The section of the spacecraft that the crew lives and works in is called the Habitat Module (Larry Niven calls it a "Lifesystem"). It is pressurized with a breathable atmosphere, and protects the crew from extremes of temperature and from radiation. Unlike spacecraft in TV and movies, most of a spacecraft is not pressurized. The vast majority of the ship is composed of the propellant tanks, rocket engine, and power plant. The habitat module is sort of tucked into some convenient corner.
Because every cubic meter of habitat module has to be pressurized and protected from the space environment, interior volume will be at a premium. Due to mass constraints, spacecraft designers will have no choice but to minimize the volume. Which will of course make them very cramped.
The TransHab concept was a NASA project to create an inflatable space station, which is not quite as insane as one would think. The walls include layers of Kevlar, and are probably harder to puncture than the metal walls of the International Space Station. The private company Bigelow Aerospace has purchased the rights to TransHab patents, and is in the process of developing a commercial space station. Bigelow already has launched two prototypes into orbit and they are working just fine.
In the Mars Reference Mission, they had a bimodal nuclear thermal rocket on a Mars mission. The rocket could deliver the mission to Mars, come back to approach Earth but with dry propellant tanks. So the rocket would go sailing past Earth into the abyss while the crew bailed out to be rescued. Bye-bye rocket.
However, if you replaced the relatively massive hard-shell habitat module with a lightweight inflatable TransHab module, the increase in delta-V was enough so that the rocket would have enough extra delta-V to be able to brake into Earth orbit and be re-used.
There is an online calculator for TransHab modules here.
Troy Campbell pointed me at a fascinating NASA report about spacecraft design (warning, 2 MB PDF file). The report shows how much easier it is to design a habitat module if it for a one gravity environment instead of free fall (surprise, surprise). It has the spacecraft separate into two parts connected by tethers, spinning for artificial gravity.
Some of the details of this design cannot be used with, say, a warship. You do not want to used an inflatable habitat module on a ship going into battle. But the lists of required equipment are very useful for your ship designs, as are their masses, volumes, and power requirements.
For its habitat module, the report take a TransHab inflatable habitat module, and modifies it for one gravity. TransHab modules are low mass since the walls are made of woven Kevlar instead of metal. For the report design, interior suspension cables are added to support the decks (since the basic TransHab is designed for free fall), and an anti-radiation storm cellar added to the core. The other main reason for using a TransHab is because the proposed launch vehicles used to boost the module into orbit had severe payload size limits. The TransHab could fit into the limits while collapsed, then inflated to full size when in space. For your design, you probably will not have such payload size limits, so you will not need to use an inflatable habitat.
To cool off the module, a small heat radiator is wrapped around the exterior. This radiator can only collect and reject 15 kilowatts of heat, since it is only for life support. The propulsion system and power system will require a much larger radiator (read the report for more details).
The report gave a sample set of deck plans. The first floor is the lowest, at the 1.03g level. For some odd reason the first floor deck plan is rotated 45 degrees counterclockwise with respect to the other two deck plans, as you can see if you try to match up the ladder and pass throughs on the three plans.
Note how all the crew beds are inside the storm cellar.
The module is designed to house a crew of six for eighteen months. According to the report, the bare minimum internal volume for a crew of six is 101 cubic meters (about 17 m3 per crewperson). This design has more than that. The TransHab has 350 cubic meters of internal volume, and of that 193 is habitable (about 32 m3 per crewperson). Please note that this is the total habitable volume, the crew's personal volume is much smaller (basically their bunk and their desk).
The module has an exterior surface area of 233 m2. Just the cylindrical exterior surface has an area of 153 m2.
Again remember that this is for a crew of six and an endurance of eighteen months. The values for mass and volume of all the components will have to be scaled up or down with the size of the crew and the amount of endurance.
|System||Mass (kg)||Stowed Vol. (m3)|
|Power Management and Distribution||625||1.05|
|Displays & Controls||14||0.01|
|Environmental Control & Life Support||5030||31.50|
|Temperature and Humidity Control||113||6.32|
|Fire Detection and Suppression||13||0.05|
|Water Recovery and Management||2199||6.02|
|Thermal Control System||576||2.43|
|Internal Thermal Control System||135||0.34|
|External Thermal Control System||167||0.13|
|Galley and Food System||8063||31.35|
|Waste Collection System||327||8.83|
|Recreational Equipment and Personal Stowage||150||3.00|
|Operational Supplies and Restraints||120||0.01|
|Vehicle Support for EVA||291||0.40|
|EVA Translation Aids||123||3.36|
|Structure and Mechanism||12941||84.51|
|Human Research Facility||289||2.50|
|Crew Health Care Systems||759||3.67|
From the report (which goes into this in much greater detail):
|Mass (kg)||Stowed Vol. (m3)||Quantity|
|Fiber Li-Ion Battery||0.17||335||1|
|Battery Charge/Discharge Unit||0.09||50||3|
|Main Bus Cable||0.84||7.5||3|
|Secondary Power Distribution|
|Wiring Harness Secondary|
|Power Management and Distribution|
|Galaxy Inverter Boxes||0.04||28||3|
|Custom Built 400 Hz, 115 Vac|
|Unitron PS-95-448-1 400 Hz|
to 60 Hz Frequency Converter
|Vikor AC/DC Rectifiers||0.0007||2||9|
The primary power system for the spacecraft is a pair of nuclear reactors on the other end of the boom. Since they are external to the habitat module, their mass and volume are not included here.
The secondary power system is internal to the module. It consists of three main subsystems:
- Secondary Power
- Power Management and Distribution
These three subsystems can be further broken down to the component level as shown in the table to the right.
The assumption was made that the power entering the habitat would be 115 Vac, delivered at 400 Hz. A final assumption that was made was that the habitat would nominally use 15 kW of power. The final subsystem that needed to be sized for this habitat was the secondary power source. Upon analyzing the architecture and the type of primary power sources, a decision was made to supply 24 hours of emergency power to the habitat that will accommodate 50% of the nominal load (180 kW-h).
Includes a communication system; a guidance, navigation and control system; a crew interface system; and an integrated vehicle management system. It has a peak power consumption of 864 watts. It provides for the command, control, communications, and computation required for the carrying out the mission including insertion into transit orbits. This involves provisions for crew displays; data, voice, and video communications home base, other orbital assets, and EVA crewmembers; an integrated health management system for onboard and ground monitoring of all systems; and a full flight system capability for Guidance, Navigation, and Control. The flight system must also integrate requirements for data communication and computational support for remote commanding of the spacecraft during any uncrewed phase as well as ground commanding during crewed phases. The crew interface must be integrated with data communications and computational support for remote commanding of visiting vehicles.
The Air Management Subsystem is characterized by a 4-Bed Molecular Sieve (217.7 kg, 0.6 m3, 733.9 W), a Sabatier CO2 Reduction Unit (26 kg, 0.01 m3, 227.4 W), an Oxygen Generation Subsystem (501 kg, 2.36 m3, 4,003 W), and high-pressure storage tanks for O2 (20.4 kg, 0.78 m3, 6 W) and N2 (94.4 kg, 3.6 m3, 6 W). The Water Management Subsystem uses a Vapor Phase Catalytic Ammonia Removal system (1,119 kg, 5.5 m3, 6,090.7 W) and potable water storage tanks (145.9 kg, 0.54 m3, 5 W). The Waste Management Subsystem uses a Warm Air Dryer (527.2 kg, 11.2 m3, 2,043.7 W).
|Fluid mass (kg)||Dry mass (kg)||Volume (m3)||Power (kw)|
The TCS system concept makes use of flexible lightweight body mounted radiators, which are attached to the outer surface. The TCS system has been sized to collect and reject 15.0 kW of heat. Mass, power, and volume are listed below. ITCS refers to coldplates, heat exchangers, and plumbing located inside Transhab, while ETCS refers to similar equipment mounted on the outside. Radiators are listed separately.
A propylene glycol/water coolant is circulated inside the module to collect heat from heat exchangers and coldplates and this heat is rejected to space through the body mounted radiators mounted on the outer shell of the module. Radiator size was determined for the warmest case (0.5 A.U. orbit). The results indicate a required area of 78 m2. This represents 51% of the available area of the cylindrical portion of the shell.
Two other sizing exercises were also conducted for the module. The first determined the radiator area needed to reject twice the average load of 15 kW. Assuming the warmest environment temperature at 0.5 A.U., the analysis indicated approximately 157 m2 was required. This is just slightly over the total cylindrical area of the shell of 153 m2, therefore rejecting just under 30 kw on average is the maximum amount of heat rejection possible without adding something like a heat pump to raise the radiator temperature.
Another sizing exercise determined the heat rejection given the following scenario: The module is in Mars orbit and the crew has left the module for the Martian surface leaving the AG module uninhabited. If the heat loads are reduced and the TCS fluid is allowed to approach its freezing temperature of -50°C, the question becomes how much heat can be rejected. The analysis indicated that the radiators could still reject up to 11 kW of heat with the TCS fluid just above its freezing temperature. This is in part due to the much colder environment at the low Mars orbit assumed. At the 0.5 A.U. orbit location heat rejection would be approximately zero because the radiator and sink temperature would be identical for this scenario.
Propylene glycol was selected for the working fluid. The relevant options are water or 60% propylene glycol with 40% water or some other working fluid. While water is non-toxic and has greatest thermal capacity per mass of working fluid, it also freezes at 273.2 K and thus may not allow sufficient radiator availability for some mission phases. 60% propylene glycol with 40% water is also non-toxic but, compared to water, it is a less desirable thermal working fluid. However, 60% propylene glycol with 40% water freezes at roughly 223 K, a significant advantage over water. Thus, tentatively the working fluid for the thermal control fluid loops is 60% propylene glycol with 40% water. As above, complete resolution of this issue also requires in-depth thermal environment modeling focusing on radiant rejection from the habitat.
This provide crew accommodations systems and layout to make an 18-month mission habitable for six crewmembers. Functions covered include the following: crew support (meal preparation, eating, meal clean-up, full-body cleansing, hand/face cleansing, personal hygiene, human waste disposal, training, sleep, private recreation and leisure, small-group recreation and leisure, dressing/undressing, clothing maintenance), and operations (facilities for meetings and teleconferences, planning and scheduling, general housekeeping). It is also responsible for configuring work and personal stations such that traffic congestion are minimized. Work efficiency, space use, crew comfort, and convenience should be maximized.
The EVA system is designed to be used for three planned, two person EVA days per mission. The airlock will transfer two crewmembers per cycle. If full crew transfer is required in LEO, this system assumes all three EVAs are used to transfer crew out of the habitat. EVA days are sized to be 8 hrs, and are accomplished with a personal life support system (PLSS) that is sized for eight hours. The system includes a single flexible airlock with umbilical support and PLSS recharge system; no gas reclamation is planned due to the minimal number of EVAs (3). Two EVA tools boxes are provided. Translation aids are provided to aid crew transportation about the vehicle. EVA system spares are also provided.
Included in the airlock arrangement is a single flexible airlock that allows two persons to egress the AGH at one time. A staging area by the inside airlock door is included in the concept. This area provides volume to store all space suits as well as space suit spares and expendables. Provisions for donning, suit expendables recharge, and checkout are included as well. An unpressurized area by the outside airlock doors is included in the concept. It provides a place for EVA tool storage and allows handling of large objects.
EVA tools provided consist of two toolboxes containing mechanical, electrical, and storage/tie downs. The tools are stowed in the unpressurized area just outside the airlock. EVA system spares as needed to support the six suits and airlock suit recharge provisions are stowed in the AGH in the EVA staging area and remain stored there until needed.
|Unpressurized End cone||650|
|Pressurized End cone||800|
|Internal fixed structure||2,120|
|Internal deployable structure||1,870|
|Crew Quarters Radiation Insulation||1,500|
The structure and shell are to provide a safe habitat for the crew and the necessary space to store supplies and equipment to sustain them for the duration of the entire mission. The inflatable module design was chosen because it is the best means to effectively increase the habitable volume of a spacecraft while keeping the diameter of the core within acceptable payload size limits set by current launch vehicles. The airlock system is to provide the crew with the capability to perform extravehicular activities. It is to be located atop the habitat module, so as to allow the fully suited EVA astronauts to take advantage of a slightly lower gravitational pull.
The medical operation capabilities onboard the artificial gravity habitat during transit will provide medical contingencies to promote successful mission completion, crew health, safety, and optimal crew performance.
The potential medical contingencies that are to be addressed include those currently required for International Space Station and additional procedures unique to a continuously rotating spacecraft. Following the convention for classification of medical contingencies onboard ISS, the artificial gravy habitat will enable the practice of emergency medicine, environmental medicine, countermeasures or preventive medicine, rehabilitation, and dentistry. Emergency medical procedures will provide for Advanced Cardiac Life Support (ACLS), Basic Cardiac Life Support (BCLS), and trauma. Additionally, emergency medical contingencies may include shock, behavioral, compromised airway or breathing, drug overdose, and smoke inhalation. Environmental medicine will enable treatment for exposure to toxic and hazardous materials. Countermeasures/Preventive Medicine and Rehabilitation will enable countermeasures to prevent neurovestibular dysfunction resulting from the Coriolis effect induced by the rate of rotation of the spacecraft. Coriolis effects induced by rotation of the spacecraft develop within the neurovestibular system and impacts motor performance, behavior, and motion sickness. Exposure to partial gravity, 0.38G, may greatly impact musculoskeletal and cardiopulmonary systems. Dentistry onboard the artificial gravity habitat will enable basic cleaning, crown replacement and treatment of exposed pulp.
And we can't forget lifeboats. There are some nifty lifeboat and one man re-entry vehicles detailed here. There is a good description of them in the eponomously named novel Lifeboat (AKA Dark Inferno) by James White. His lifeboats are inflatable spheres. They are launched perpendicular to the stricken nuclear propulsion ship with three persons per sphere. After the ship has moved out of radiation range the life boats burn a pre-measured solid fuel thruster to move back to the central point to await the arrival of the rescue vessel.
Christopher Weuve says that a merchant ship's primary piece of damage control equipment is a lifeboat.
Please note there are two different types of rescue craft here that are being lumped together. "Lifeboats" are long duration devices that generally are not re-entry capable. "Re-entry capsules" are short duration devices that allows an astronaut to bail out of a spacecraft in orbit around a planet and safely land on the surface. In other words, the lifeboat is more like a wet-navy lifeboat, while the re-entry capsule is more like a parachute on an aircraft. Also note that all of the re-entry capsules shown here rely heavily upon aerobraking, they would not work on an airless planet or moon.
Under the heading of "some people have too much free time", there are a few science fiction writers who talk about bored people using reentry capsules as a sport, much like sky-diver do today. Adrenaline junkies will always be with us.
However, Jim Cambias raises an important point: