A space suit is a protective garment that prevents an astronaut from dying horribly when they step into airless space. SF author Ken MacLeod said that the specification of a human being is "a space suit for a fish."
Current NASA suits look like baggy inflated coveralls with a large back pack and a spherical fishbowl over the head. Often in old illustrations there are accordion bellows at the joints. The accuracy of space suits in science fiction was very much hit or miss.
NASA astronaut always put on a transdermal dimenhydrinate anti-nausea patch when suiting up in a space suit, in case of drop sickness. The chances of that are slight, but suffocating inside a helmet full of vomit is a nasty way to die.
Most space suits are Full Pressure suits: they offer full pressure protection of the body in space for extended periods. Partial Pressure suits only pressurize certain parts of the body for a limited time. They are only used as a precaution, worn inside the habitat module during times when there is danger of it springing a leak (such as during lift-off).
Full Pressure suits can be either Low Pressure (pure oxygen at 32.4 kPa) or High Pressure (breathing mix at 101.3 kPa, normal Terran atmospheric pressure).
All NASA spacecraft and space station habitat modules are High Pressure. At least the ones designed after the Apollo 1 tragedy claimed the lives of three astronauts. Ever since NASA has avoided using pure oxygen atmosphere wherever possible, which means using high pressure.
The problem is if you go from a high-pressure environment (like a habitat module) into a low-pressure environment (like a low-pressure space suit) you run the risk of the bends. To avoid this the astronaut must do pre-breathing for a couple of hours. If you go from a high pressure habitat module into a high-pressure space suit the bends does not happen. This is why high pressure spacesuits are called "zero-prebreathe" suits.
I suppose some space-faring nation could use low pressure pure oxygen habitat modules to avoid pre-breathing with low pressure suits, but that would be insanely dangerous. It would be the outer-space equivalent of those stubborn elderly hospital patients who insist on smoking cigarettes while wearing oxygen tanks.
NASA tolerates low pressure pure oxygen pressurization in their soft space suits because they have no choice. There is not a lot of research, but NASA seems to think that if an astronaut in such a suit got punctured by a micro-meteor and it caught fire, the main hazard is a fire enlarging the diameter of the breach, not an astronaut-shaped ball of flame.
Soft suits have flexible exteriors. This means they cannot be pressurized to the same level as the inside of the habitat module or the space suited person will be forced into a posture like a star-fish and be unable to bend any joints. Lower pressure means the suit uses pure oxygen unlike the habitat module. And pure oxygen means the astronaut has to do hours pre-breathing before wearing the suit or they will be stricken by The Bends.
Soft suits also take forever to put on, they fight your every movement (making EVA work very fatiguing), and if you tear the suit skin you will die horribly in about 90 seconds. When I say "fight your every movement" I mean "raise the energy expenditure to do a task by about 400%".
Currently most of NASA's space suits are soft suits.
Hard-shell suits have rigid exteriors. The advantage is they can be fully pressurized so no pre-breathing is required. They are also much more tear and puncture resistant than soft suits.
The drawback of hard-shell suits is that they make the "forever to put on" and "fight your every movement" problems much worse.
As far as I know there are no hard-shell suits in active use, they are all experimental.
Semi-rigid or Hybrid suits are a cross between soft and hard-shell. For instance, NASA's EMU has a hard-shell upper torso and soft fabric limbs. Current NASA semi-rigid suits are low pressure, but they are working on a high-pressure model.
Skintight suits are a radical concept that is so crazy it just might work. They make the astronaut's skin into the spacesuit, using high-tech spandex to supply pressure instead of using atmosphere. They can be quickly put on, fight your every movement only to the point of a +20% increase in energy, and if the suit is torn the astronaut only gets a bruise instead of certain death. The suits are also much inexpensive than a soft or hard-shell suit. The major draw-back is they require low pressure breathing mix (or the wearer cannot exhale), so astronauts have to pre-breath or face the Bends.
"Planetary suits" are used when there is an atmosphere, but it isn't breathable. They have a slightly different design from space suits.
To recap: Partial Pressure suits only pressurize certain parts of the body for a limited time. They are only used as a precaution, worn inside the habitat module during times when there is danger of it springing a leak, such as during lift-off or if an enemy spacecraft is shooting at you. Partial pressure suits are a trade-off: they only protect you for a short time but in exchange they do not encumber you anywhere near as much as a full pressure suit.
The NASA version is the Launch Entry Suit aka "pumpkin suit." It has ten minutes worth of life support internal to the suit, and can be hooked up to the vehicles life support system for longer duration.
The image above from First Men to the Moon is a partial pressure suit based on an old school Air Force high-altitude suit. If the pressure drops, the pressure regulating tubes along the suit's seams inflate to put the suit under tension. The wearer will then put on the oxygen mask attached to the small tank strapped to their leg.
The crew of a combat spacecraft in battle probably will not wear a soft, hard-shell, or semi-rigid suit during battle. This is for the same reasons that the crew of a military submarine do not wear SCUBA gear in battle even though they too are in a craft surrounded by countless miles of unbreathable stuff while being shot at. It gets in the way.
But they might wear a partial-pressure suit or a skintight suit.
Or a skintight partial-pressure hybrid suit. This might be so unencumbered that it could be used as everday wear. Then if the habitat module loses pressure all you'd need is an oxygen mask and earplugs to survive for a few hours. Wear it with overalls because such a suit will make you almost as naked as wearing nothing but body paint.
To recap, Soft Suits:
- Must have lower pressure than the habitat module or the wearer turns into a starfish and cannot bend their limbs. This means the wearer needs an hour of pre-breathing or they will suffer the Bends.
- In case of emergency, when there is no time for pre-breathing, NASA helpfully directs the astronauts to gulp aspirin, so they can work in spite of the agonizing pain
- The breathing mix will be close to pure oxygen, with a higher fire risk.
- Suit encumbrance increases the energy cost to do various tasks by +400%, with a corresponding increase in wearer fatigue.
- If the soft skin of the suit is torn or punctured, the wearer will die in about 90 seconds.
- They take forever to put on
For a list of the parameters for a NASA spec space suit, go here.
The only thing that allows an astronaut to bend their limbs at all is the magic of constant volume joints. These are why most pictures of space suits look like the Michelin Man (i.e., like a stack of donuts).
In The Millennial Project Savage suggests that the helmet will have an outer layer of five millimeters of high density lead crystal. Inside will be two layers of dense borosilicate glass sandwiched between two layers of Lexan. The middle layer of Lexan will add strength and prevent shattering, the inner will act as a reserve helmet. The outer surface will be gold anodized to block glare, ultraviolet, and infra-red. There may be a nested set of telescoping curved armor plates that can be deployed for further protection.
NASA helmets are not quite so grandiose.
NASA helmets are spherical domes, which hits the sweet spot between low mass, pressure compensation, and field of view. All current NASA suits have the astronaut's head is held facing forwards, you have to turn your entire body in order to look sideways. Astronauts call this "alligator head".
The helmet has to be comfortable to wear, and help in controlling the humidity inside the helmet (so it doesn't fog up). Another important part is the radio communication unit, since the lack of air in space prevents the sound of your voice from reaching anybody. The old tagline to the first ALIEN movie was "In Space No One Can Hear You Scream". Well, no one can hear Floyd asking somebody to pass him a socket wrench either. NASA suits use "Snoopy caps" to hold the communciation earphones and microphones (in NASA-speak this is called the Communications Carrier Assembly (CCA)).
Other items might include windshield wipers (inside for condensation, outside for dust), a build-in set of binoculars, headlights for shadowed areas, a mirrored sun-visor to prevent sunlight from burning out your retinas, a water drink dispenser, and maybe a gadget that can supply various medications (pain relievers, anti-nausea, stimulants).
Some SF novels have a space helmets equipped with a tiny airlock near the mouth, called a "chow-lock." It is used to allow the astronaut to eat and drink without venting the helmet's air to the vacuum of space. I am uncertain how practical this concept is, or how idiot proof it can be made. It would be a bad thing if trying to get a bite of a candy bar accidentally killed you.
As previously mentioned, NASA astronaut always put on a transdermal dimenhydrinate anti-nausea patch when suiting up in a space suit, in case of drop sickness. The chances of that are slight, but suffocating inside a helmet full of vomit is a nasty way to die.
In NASA-speak, the backpack is called the Personal (or Primary or Portable) Life Support System (PLSS). At a minimum, it provides breathing mix, removes carbon dioxide, and regulates the suit's pressure.
Additionally it may remove humidity, odors, and contaminants from the breathing mix; cools the astronaut's body with oxygen or a liquid cooling garment; provides radio communication; displays and/or does telemetry of suit parameters; displays and/or does telementry of astronaut's health; and/or provides propulsion for EVA.
NASA's current design for PLSS is not foolproof, as astronaut Luca Parmitano discovered on July 16, 2013 when he almost died as his helmet filled up with water. The drum holes in the PLSS water separator got clogged, and the PLSS designers had a mistaken understanding of how water acts in microgravity (the designers thought it was impossible for the water to back up into the helmet).
As is usually the case, the reason astronaut Parmitano is alive today is because he did not panic. He had to move to the airlock and re-enter from memory, since he could not see with 1.5 liters of water covering his eyes.
The gloves are especially a problem. Back in the 1950's it was unclear if space suit gloves were even possible. You need to make the various protective layers thin enough to be able to fit between adjacent fingers. And with miniature constant volume cuffs at each finger joint. Some suit designers took a tip from deep sea diving suits and postulated mechanical pincers instead of gloves.
But as we know NASA did manage to design actual space suit gloves. However, they do not work very well. Almost every single NASA astronaut who has performed EVA has complaints about the difficulty of doing any fine work while wearing those gloves.
Many SF novels have magnetized space boots to allow the rocketeers to adhere to the hull, but magnets do not work very well on hulls composed of titanium, aluminum, or magnesium. If one does have a ferromagnetic hull, it might be best to have magnets just in the boot toes but not the heels, to facilitate walking. These might be used inside the spacecraft's lifesystem, if you think those velcro footies used by the stewardess in 2001 A Space Odyssey are just too unmanly for words.
To recap, Hard-Shell Suits:
- Can have the same pressure as the habitat module without the wearer turning into a starfish. The Bends are avoided.
- The breathing mix will be the same or very close to that of the habitat module. No additional fire risk.
- Suit encumbrance increases the energy cost to do various tasks by many times that of a soft suit, with a incredible increase in wearer fatigue.
- The hard shell of the suit is very puncture resistant.
- They take longer to put on than a soft suit.
Hard-shell suits try to fix the tearing problem at the expense of making the first two problems much worse. True, hard suits do solve the depressurization problem, but at such a cost.
The AX-5 hard suit was developed by Hubert Vykukal at NASA Ames Research center in the 1960's. It was based on deep sea diving suit technology created by Phil Nuytten of Nuytco Research. The rotating joints are angled with respect to a limb, with two halves each comprising a thick wedge section and a thin section. When a limb is bent, the joint rotate so that the thin sections come together, allowing the suit limb to bend in a correspoinding fashion. For more details, refer to The Rocket Company.
Semi-rigid Suits are sort of a cross between soft suits and hard-shell suits, typically with the chest or torso hard and the limbs soft.
The ideal design is to have a hard-shell torso allowing the suit to be high-pressure with zero-prebreathing required, coupled with separately pressurized soft limbs to avoid the encumbrance penalty suffered by full hard-shell suits.
Which is why NASA's EMU puzzles me, it is a semi-rigid suit that appears to have the disadvantages of both with the advantages of neither. No doubt there were other considerations that I am unaware of.
The company ILC Dover made the Mark III suit as a technology demonstrator in 1992. It actually was a zero prebreathe suit. It is pressurized to 57 kPa, which is close enough to the 101.3 kPa used in NASA habitat modules so that the bends is not an issue. The Mark III had the shell covering the entire torso, not just the chest like the EMU. There is a hard upper torso, a hard lower torso. There are bearings at shoulder, upper arm, hip, waist, and ankles. There are soft fabric joints at elbow, knee, and ankle. I do not know why there are both types of joints at the ankles.
One of its main drawbacks was that the suit could not separate at the waist like other NASA suits, you had to enter the suit from the backpack. As with all hard-shell and semi-rigid suits, it is heavier than a soft suit (59 kilograms).
NASA decided against further development of the Mark III, for whatever reasons.
An innovative alternative approach is the Mechanical Counter Pressure (MCP) Suit. Instead of trying to hold your body intact with air pressure, it holds it in with spandex. It sounds crazy but it just might be crazy enough to work.
To recap, Skintight Suits:
- Must have lower pressure than the habitat module or the wearer cannot empty their lungs. This means the wearer needs an hour of pre-breathing or they will suffer the Bends. Higher pressure also increases the risk of catastrophic failure of the helmet, i.e., shooting off like a champagne cork and killing the wearer.
- In case of emergency, when there is no time for pre-breathing, NASA helpfully directs the astronauts to gulp aspirin, so they can work in spite of the agonizing pain
- The breathing mix will be close to pure oxygen, with a higher fire risk.
- Suit encumbrance only increases the energy cost to do various tasks by +20%, compared to the +400% of soft suits and the astronomical increase of hard-shell suits.
- Suit punctures result in bruises on the wearer's skin, instead of certain death.
- Skintight suits are the most inexpensive of all the space suits, about $60,000 US in 2005 dollars.
- It tends to grab male wearers uncomfortably in the crotch.
A skin-tight suit of high tech cloth exerts pressure over the rocketeer's body to provide pressure. A bubble helmet with oxygen supply allows one to breathe. Open pores in the suit actually allow the body to be cooled by perspiration. Tears will cause bruising to the skin, but are not as lethal as they are on a conventional suit. The suit can be quickly put on. They do not interfere as much with movement (+20% energy expenditure, compared with +400% for a NASA suit). And you can store them by folding them up and putting them inside the bubble helmet. The back pack is still bulky, though.
They do need some care in design, though. Any concave areas on the body that the suit does not hug will bulge out under internal body pressure until it fills the void (i.e., your armpits will become armhills). Putty or fluid filled bladders will be needed to prevent this. Care must be taken around those nether regions, the small of the back, and in certain locations of the female chest. Male wearers will need a rather sophisticated cup to cover the genitals. Even with the cup, the suit will tend to grab male wearers uncomfortably in the crotch.
And upon entering vacuum, one will have an instant attack of dire flatulence. Don't be polite, let it out right away or you may damage your intestines.
There may be a length of tubing added along the seams of the arms, legs, and torso. The suit will be relaxed for easy dressing, then the tubing will be pressurized to put tension on the fabric (This was used in the g-suits worn by early jet pilots). The tubing will automatically pressurize when the helmet is put on and pressured up.
This used to be a standard feature of partial-pressure suits.
A more advanced design uses a strip of "shape metal alloy'. An applied voltage can toggle the metal strip between expanded and contracted.
Unlike other types of space suits, the helmets for skintight suits require something called a "neck dam." This goes around the neck, and tries to keep an air-tight seal. Otherwise the helmet shoots off like a champagne cork and all the air in the helmet will spray out.
I'm sure the neck dam will be the part of the suit that will cause designers the most headaches. I personally would be in favor of straps that go from the neck dam and loop around ones arm around the armpits, but I'm no expert.
In The Millennial Project Savage suggests that light tungsten armor plates be worn over the suit to give some anti-radiation protection (this would only be needed in high radiation areas, like the Van Allen belts).
A minimal version of the skintight suit can be developed for everyday wear inside a spacecraft, i.e., a Partial-pressure Skintight suit. In cases of emergency air pressure loss, all you'd need is an oxygen mask and earplugs to survive for hours (This was used in Jerry Pournelle's "Tinker". The suit was worn like long johns under a coverall. The coverall is due to the fact that the suit is about as modest as wearing a coat of paint.).
Amusingly, the skintight suit made an appearance in a 1995 novel and anime television series called Rocket Girls. Maybe not so surprisingly, Japanese media in general is noted for its high standards of scientific accuracy. In this case the anime series had JAXA (the Japanese Aerospace eXploration Agency) and real-life Japanese astronaut Naoko Yamazaki as technical advisors.
The fictitious Solomon Space Association is developing the low-mass suits since their anemic one-lung LS-5 rocket can barely lift itself off the launch pad, let alone any payload. In a further desperate attempt to save on mass, they are reduce to using 16 year old girls as astronauts (which is a predictable development for a Japanese anime). They only weigh 38 kilograms, instead of the sixty-odd kilograms of the adult male astronauts. They take up less room in the control cabin as well.
And in Clarke's "The Haunted Spacesuit" aka "Who's There?" they chant "FORB" for Fuel, Oxygen, Radio, Batteries.
While wearing a space suit in vacuum, the iron-clad rule is The Buddy System. There are many mishaps that are trivial if you have a companion but fatal if you don't. Imagine that your suit springs a slow leak on your back just where you can't reach it with a repair patch. Oops.
In cases of emergency, two space suited people can "cross-connect" their oxygen supplies. This is generally done when one of them runs out of breathable gas, the other shares their oxygen until they get to shelter.
Once people are suited up, it does become hard to tell who is who. In Destination Moon, there were four spacemen, and each had a uniquely colored suit. Kind of like colored tooth-brushes. But this won't work if you have more than a few spacemen, er, spacepeople. The person's name stenciled in large letter across the front and back is a possibility.
In Piers Anthony's The Kirlian Quest, he notes that this problem has occurred before: knights in armor are similarly anonymous. The solution is coat of arms and heraldry. When a proposed heraldic "device" (coat of arms) is submitted to the college of heralds, it is compared with all existing devices. The new device must have at least one major and one minor point of visual difference from those already registered. Otherwise it would be too easy to confuse the two devices in the heat of battle. Mistaking a foe for a friend could be fatal.
In Larry Niven's Protector, the Belters of the asteroid belt spend most of their lives inside their space suit. They have a tendency to paint their suits in extravagant colors. One of the characters had Salvador Dali's Madonna of Port Lligat on the front of their suit. In an interesting psychological quirk, Belters also tend to be nudists when in a pressurized environment.
For strict safely, static lines or safety lines are mandatory. The spacecraft should have plenty of small steel rings bolted at regular intervals over the hull for spacemen to attach their safety lines to. Without a static line, a spaceman who manages to get both magnetic boots separated from the hull will suddenly find themself on a slow impromptu tour of the solar system. If their widows are real lucky the bodies might actually be recovered for burial.
Another useful item is a "line throwing gun". This allows one to shoot a safety line from one spacecraft to another. The line will have to be made of special materials, since most terrestrial ropes and cables will turn glass-like and shatter in vacuum.
Things get real nasty if the ship is a tumbling pigeon or otherwise rotates to provide artificial gravity. The poor EVA spacemen have to swing from hand-hold to hand-hold like trapezes artists. From their viewpoint, the spacecraft is overhead and below is a long fall to infinity. For details read Heinlein's short story "Ordeal in Space".
Astronauts also have to watch what they say. There is no air in space, so unless you are touching helmets together, you cannot talk with others without a radio. But while speaking on Terra means your voice becomes fainter with distance, over a radio it will be loud and clear out to the limit of the radio's range. This means cursing under your breath or muttering behind somebody's back will not work. There might be several channels to allow a bit of privacy, or if several conversations are going on at once.
Some SF novels suggest that for privacy, two space suited people might turn off their raidos, and touch helmets. The theory is that the sound of the conversation will be conducted through the contact between helmets. However, others maintain that the area of contact will be so small (since the helmets are basically spherical) that no audible sound will manage to pass. In Poul Anderson's TAU ZERO, he says that instead astronauts will learn how to read lips.
They may also need a "beeper". This is a low powered radar used to locate small objects nearby (like that zero-recoil wrench you let go of "just for a minute"). You wave it around until is starts beeping (heard over your suit radio). As you approach the object the beep rate increases.
As one adds more gadgets and attachments to a space suit, it gradually morphs into a tiny spaceship. It starts with spring-loaded broomsticks and picks up speed with the addition of tiny attitude jets and maneuvering rockets. As a parallel development, a rocket engine with a skeletal frame to hold astronauts is the first "space taxi". When a space suit is massive enough that one climbs into it instead of putting it on like clothing, equipped with mechanical arms and waldoes, you suddenly have a space pod. Then if the pod grows to the size of a baby spaceship, but with massive over-sized engines, you finally have a space tug.
It will also be useful to supplement one's supply of space suits with emergency life support balls. These are basically bare essential spherical suits with no arms, legs, or heads for use by people who are injured or untrained in suit operations. When a passenger liner has a problem, the crew members will stuff the passengers into these balls, zip them up, and tow them to safety. In this case, one would be wise to use balls that cannot be opened from the inside. Passengers can do remarkably silly things at the worst possible moment. And even a person highly skilled in space suits can be a problem if they are unconscious and suffering from a broken arm. It will be much quicker to slip them into a ball instead of trying to suit them up.
A broomstick is a spring loaded gizmo used by astronauts to launch themselves from place to place, and to bring themselves to a stop upon arrival.
While engaging in extra-vehicular activity, our space-suited rocketeers may use a "broomstick", or some kind of small jets (a Manned Maneuvering Unit or MMU). NASA has also developed a nitrogen-gas propelled unit that fits on the backpack, called the Simplified Aid for Extravehicular Activity Rescue (SAFER). The SAFER can help an astronaut return to the shuttle or station in the event that they gets separated from the spacecraft. SAFER has a deltaV capacity of 3 m/s.
Many early designs of spacesuits for use in free fall were lacking legs. This simplifies the design. This gradually becomes a hard suit which allows an astronaut to work in a pressurized environment and so avoid the bends.
A space taxi is a short ranged orbit to orbit vehicle used to carry astronauts and small amounts of cargo. At its simplest, it is a frame that astronauts attach themselves to, with a rocket engine at one end. More complicated taxis have an enclosed hull which may or may not be pressurized. Do keep in mind that the direction of "down" will appear to be in the same direction the rocket exhaust shoots.
|Orion Space Taxi|
|Specific Impulse||450 s|
|Exhaust Velocity||4,500 m/s|
|Wet Mass||1,584 kg|
|Dry Mass||759 kg|
|Payload||136 kg (2 people)|
|Diameter||1 m wide|
|General Dynamics 2-Man Space Taxi|
|Specific Impulse||450 s|
|Exhaust Velocity||4,500 m/s|
|Wet Mass||361 kg|
|Dry Mass||155 kg|
|Propellant Mass||206 kg|
In this document about Orion drive spacecraft, they mention a space taxi. It carries two crew members, has a hardware mass of 623 kilograms, and a propellant mass of 825 kilograms. As near as I can measure from the diagram, it can be approximated as a cylinder with a height of two meters and a radius of 0.5 meters, with a hemisphere of radius 0.5 meters on each end.
This gives it an internal volume of 2 m3. Assuming it has chemical propulsion, the propellant would take up about 0.8 cubic meters, and the two crew would take up 0.14 cubic meters. Carrying two crew, it would have a mass ratio of about 2, and thus a deltaV of about 3,120 m/s.
In Volume 10: "Space Age in Fiscal Year 2001". Proceedings of the Fourth AAS Goddard Memorial Symposium, 15-16 March 1966, Washinton DC Krafft Ehricke has a diagram featuring what appears to be the same space taxi.
General Dynamics had designs for one and two-man space taxis that again appear to be the same ones. The two man version was described to have a dry mass of 155 kg and 206 kg of propellant (probably space storage hpergolic propellants). This would give it a mass ratio of 2.3 and thus a deltaVof about 3,750 m/s. For more details refer to US Spacecraft Projects #01 by Scott Lowther.
This is an emergency lunar escape vehicle concept, in case an Apollo Lunar Module crashed upon landing. It was designed to be assembled from various parts canibalized from the wreck. Note that in the two-man version, the pilot gets an acceleration chair, but the poor second astronaut is slung under the chair by straps. You can read more about this here, here, and here.
A space pod is a small pressurized vehicle with one or more waldoes or mechanical arms. They are often used for space construction and maintenance. In the movie 2001 A Space Odyssey, they were referred to as "EVA pods." In Wernher von Braun and Disney's Man In Space series, they were called "bottle suits." They are also known as "closed-cabin cherry picker", "manned autonomous work system", and the ever popular "man-in-a-can." One of their main advantages over a soft space suit is that they solve the depressurization problem.
A space tug is a tiny spacecraft with over-sized engines and some means of grappling another spacecraft. If the tug pushes its cargo,it will have a massive push plate on its bow, with a core of structural members to transmit the thrust of its engines to the push plate. If the tug pulls its cargo, it will have cables and winches on its stern, and the engines will be vectored to fire backwards at an angle so it does not torch the ship it is dragging. The engines will suffer a reduction thrust penality proportional to the cosine of the engine angle.
Note that if nuclear propulsion spacecraft are involved, the tugs and the spacecraft will generally be designed to dock bow to bow. Otherwise you will be exposing the other ship to the radiation from your engine.
Space tug concept by Frank Tinsley. Tug has grapples and grippers on its stern. The four square plates around its waist are ion drive units (The crewman's hatch is unfortunately placed right in the line of fire of one of the ion drives).
The petals near the bow are heat radiators. Sadly the radiators are spaced too closely. In reality one would want two radiators at 180° or at the most four radiators at 90°. The arrangement shown would have the heat from one radiator impinging on its neighbors.
And at the tip of the pointed prow would be the tiny nuclear reactor. It would be nice to include a small shadow shield to protect the crew from nuclear radiation.
Details are sparse on this design. Click on blueprints for larger image. Blueprint is written in Italian but it has been translated for the website by Alberto Bursi. The engines are around the waist, on swivels. The designers also appear to have a flippant attitude towards maintaining a sense of up and down. If the pilot turns his head he will see his copilot's feet.
The diagram is from here. Annoyingly it included lots of facts and figures about the tug, then said and here is a diagram of a totally unrelated Boeing concept that we will not give you any data for. I do like the slanted windows, allowing the crew to view the docking port.
This design was faintly seen in an article The Resources of the Solar System by Dr. R. C. Parkinson (Spaceflight, 17, p.124 (1975)). It was off in the corner of a small diagram. I had an old photocopy of the article in my files since the late 1970's. I supplied them to William Black and he made stunning images of Dr. Parkinson's lighter and tanker. These images attracted the attention of a former colleague of Dr. Parkinson, a certain Dr. James Garry. He kindly introduced us to Dr. Parkinson and provided contact information. Dr. Parkinson generously supplied us with never before published diagrams and commentary.
In a private correspondence, Dr. Parkinson told William Black and I: “As a matter of interest, the "Space Tug" & Lunar Lander were based on some earlier design work done in Europe when it looked as if a cryogenic Space Tug might be the European contribution to the Space Shuttle program (those were the days!).”
In his visualization, William Black added additional engineering details. He put more struts to support the reaction-control jets and liquid oxygen tanks. Dr. Parkinson's notes indicated that the manned capsule had its own propulsion, so William added a single gimbaled low-thrust engine. He also added: a high-gain antenna for communications and a radar dish; forward-facing view ports for visual orientation during docking maneuvers; four forward-facing and four aft-facing cameras to aid in docking procedures.