Saturday, October 31, 2009

Spaceship Design 102: Life Support

Growing Algae
Human life support is complicated, bulky, and it smells bad. If we only sent robots we would not have to mess with it. But if we go in person we have to deal with it. First, go to the life support page at Atomic Rockets.

To begin with we will need a cabin. Here there is a big difference between short missions, up to a day or two, and longer ones. Short term passengers can sit in airliner style seats, crew at their work stations, and the galley needn't be much more than a refrigerator and microwave oven. But as missions get longer you need bunk space for off duty crew, and at some point cabins or bunkrooms and a real galley.

From a comparison of railroad sleeping cars versus coaches, sleeping accommodations take up about 10 cubic meters per person, 2-4 times as much room as airliner style seating. Add a galley and dining compartment, storage space, and some this and that brings the minimum requirement to around 15 cubic meters per person, give or take.

(The ISS is much roomier, Wikipedia claiming a 'living volume' of 358 cubic meters for a crew of six, or nearly 60 m3 per person. But I don't know how living volume is defined, for example whether it includes working spaces. Total pressurized volume of the ISS is reported as about 1000 m3.)


Man does not live by bread alone, but along with water and oxygen it is a start. Human beings need about 5 kg/day in food, water, and oxygen, food accounting for about half the total. Unless you have regenerative life support you will need to carry it all with you. This does have the advantage of simplicity - we know how to do it, which is not the case for regenerative life support. For missions up to a few months the mass penalty is not excessive; 200 days' provisions and supplies come to about a ton per person, requiring about 3 cubic meters of storage space.

With storerooms, equipment bays, and assorted plumbing, our hab compartment for deep space transports may thus have a volume around 20 cubic meters per person. This in turn equates to about a ton or two per person for the basic hab pressure vessel, plus another ton or two of fittings and equipment, and for a 6 month mission a ton of consumables. So, altogether, each person (passenger or crew) carried by a transport class ship accounts for 3-5 tons of payload capacity.

In the rocketpunk era the standard way to reduce this was to carry passengers in Cold Sleep. But at our current level of knowledge this is magitech. We haven't a clue how to drastically slow down human metabolism, or even produce mere hibernation, let alone how to do it safely.


Another rocketpunk era classic was regenerative life support, those famous hydroponics tanks somewhere aft/below decks. Details were sometimes vivid, occasionally charming (fresh flowers in the wardroom of PRS Aes Triplex), rarely quantitative.

There is a rule of thumb that it takes 10 kg of food source biomass to support 1 kg of whatever is eating it: thus, for a purely vegetarian diet, about 0.75 tons of plant biomass per person. Biochemistry conveniently sees to it that the plants we eat also replenish our oxygen.

On this basis the break even point for regenerative life support is about 150 days. A 1953 (!) source cited at Atomic Rockets says 145 days. But this ignores the penalty mass of the hydroponics tanks. (Or aeroponics, whateva.) Greenhouse hydroponics on Earth seems to achieve yields of about 30-35 kg per square meter. One source mentions a 4 month growing season, suggesting that with year round operation we might do three times better, approaching 100 kg/m2.

Since we eat about a ton of food per year, this corresponds to about 10 square meters of growing surface per person. With access and working space perhaps 20 cubic meters per person - comparable, that is, to our estimate for living space, and probably with a comparable mass, about 3-5 tons per person, including a ton or so of biomass.

The structure and equipment mass needed to grow food shifts the tradeoff point: For missions less than about 2 years, the mass of stores plus storeroom capacity is less than the mass of a regenerative system. Most transport class ships - which for this purpose includes most military craft - are used for shorter missions that that, so they will dispense with the extra bulk and mass of full regenerative life support. They might have a garden deck, more for human factors than for its modest life support contribution.

There's also the little detail that we don't yet know how to do regenerative life support. This is one type of space research that can be done on Earth, and as space research goes it does not require a lot of expensive hardware. The Biosphere 2 fiasco doesn't prove a lot in and of itself, given the possible flake factor, but building a human supporting ecohab cannot be easy, or someone would have done it by now.

But we won't really need regenerative life support until we are establishing long term stations or bases. And my guess is that we'll learn the techniques gradually, in the process of reducing dependence on costly supplies from Earth. Regenerative life support is, on some level, a sophisticated form of gardening, and gardening has always called for patience.


Two other life support considerations: Radiation, and heat.

Without shielding, the cosmic radiation dose in deep space is about 400-900 millisieverts per year, where 1 Sievert = 100 old fashioned rems. The current career limit is 4 Sieverts for astronauts, 2 Sieverts and change for nuclear industry workers. Thus for long term habitation we will need enough shielding to diminish the penetrating radiation by about tenfold. This requires about 100 grams per square centimeter - a ton per square meter. And this shielding has to be applied all around, because cosmic rays can come at you from any direction.

This is not a problem for big permanent habs, but it is far too massive for transport class ships. This is one more reason to favor fast orbits for human travel. A ship's habitat might provide enough shielding to cut radiation by half, so that a 3 month tranfer mission provides about the same radiation exposure as a year living aboard a shielded hab.

And don't forget plain old heat management. An object at room temperature radiates about 400 Watts per square meter, which you will have to replace - but at 1 AU you are also exposed to a solar flux of 1400 W/m2 on surfaces directly facing the Sun. Managing heat, both from onboard power and solar flux, to keep the hab in the human comfort zone will be a constant task.


In fact, all of life support will be a constant task. In rocketpunk days maintaining the life support system was treated as an afterthought to the cool space stuff like astrogation and engineering. This is unlikely to be the case.

This being All Hallows' Eve, I'll just leave you with this thought for your contemplation: Cascading life support malfunction.


Related post: Spaceship Design 101.

56 comments:

Nyrath said...

Occasionally when researching food for spaceflight, I stumble over references to something called "Nutraloaf".

Apparently this is something prisons serve to problem prisoners. It theoretically contains all the necessary nutrients to sustain life, but in some states it is considered cruel and unusual punishment.

Nyrath said...

RE: cascading life support failure

I get the distinct impression that many early SF authors did not truly understand that in space you cannot open the window to get some fresh air. The many novels where the heroes routinely light up cigarettes spring to mind.

The reality is much more akin to life on a submarine. The atmosphere system is the only thing keeping the crew from a hideous death, you jolly well better treat it with respect.

Peste said...

[W]e don't yet know how to do regenerative life support

First step on that thousand-mile journey: in 2009, that's this year, they started recycling urine at the ISS. Don't hold your breath.

francisdrake said...

I estimate the daily consumption being split up like this:
1 kg oxygen (the actual value is a little lower, approximately at 0.7 kg/day)
3.5 kg water (2 kg to drink, 1 kg for personal hygiene, 0.5 kg to make up meals)
0.5 kg dry meals

By recycling the water (urine, washing water, and freeze drying feces) the daily supply rate can be reduced considerably, to about 1.5 kg/day.

Provided enough energy you could try to run something like oxygenic photosynthesis inside illuminated water tanks filled with plankton. But I am not sure if the weight of all this apparatus would outweigh the oxygen carried in tanks.

Citizen Joe said...

If we don't solve the radiation problem, there is no point doing the recycled system. If people can't take more than a couple months radiation, that limits the mission schedule to the point where simply packing supplies is less mass intensive.

That solution may involve repairing the damage done by radiation faster than the radiation hurts. So, maybe retro-viral or nanite curing agents that fix radiation damage. These cures could be administered through the food system. Of course, that is still magitech, although there is a lot of research in cancer cures.

Another possibility is a tiered exposure system where some places are heavily shielded while other locations are less shielded. People then gear up appropriately, using skin suits or full environment suits in the higher radiation zones.

Anita said...

Using francisdrake's water calculation, I come up with minimum 36,000 pounds of water based on five crew members, 900 day round trip. Sorry about the pounds and gallons, but we old Yanks can't think meteric.

That's a container of 600 cubic feet.

(I could be laughably wrong here. If I were a math expert, I'd be in another line of work.)

Re cascading life support failure

Live through a tornado, hurricane or ice storm (she holds up paw), it's like being hanged in the morning; it does focus your attention on essentials, water and food and heat. At least you can still breathe. Yeah, unlike a sub, a space ship can't surface for a breath of the good stuff.

Rick said...

Nyrath - From the description you gave, Spirulina sounds like it falls in the same category as Nutriloaf. Do we really want to go into space badly enough to eat that stuff?

A flip side to those rocketpunk era cigarettes is how rarely (in my recollection) things like onboard fire figured in the classic space emergencies.

The good news in your submarine analogy is that nuclear sub operations show that it can be done, with a good measure of safety. Admittedly a sub with a serious life support emergency can reach fresh air by surfacing.


Peste - Drink up! :-)


francisdrake - Those are similar to the figures at Atomic Rockets. The question, as you say, is the mass of water saved by recycling versus the mass of recycling gear.


Citizen Joe - Even with magitech, fixing radiation damage after the fact is still subjecting the human organism to a beating.

Radiation shielding is much easier for big hab installation that aren't intended to change orbit a lot. Sheer size benefits from the square-cube relation of surface to volume, plus you can surround the main habitation areas with storage areas, water tanks, equipment rooms, etc.

So I see big, shielded, regenerative habs for long term occupancy, and lightly built, non-regenerative, fast-orbit ships for travel between them.

Anonymous said...

This sounds as though future spacecraft will have life support systems rated in crew endurance...a spacecraft that only needs to support its crew for a few days could get by with only air and water tanks, CO2 scrubbers, and a locker full of food bars; a spacecraft that needs to support its crew for several week or a few months would need a more elaberate system that includes bioreactors, plankton/alge tanks, waste seperators/reducers, as well as bulk food storage. Space stations and long-term mission ships (those needing crew endurance of more than a year), would need all of that as well as food vats and/or aeroponic stacks, as well as regular gardens for psychological effects. This means that the percentage of life support increases as the mission endurance increases: from 4 m3 to 20 m3 to 40-50 m3 as the crew endurace requirements increase.

As far as radiation protection goes; there isn't one type of shielding (except huge amounts of mass)that will protect people from all types of radiation; future manned spacecraft will need several types of radiation protection; some are easy (we have them now), some of them are more difficult, and some we are still working on. A future manned spacecraft will probably need both active and passive radiation protection; layers of different materials in the hull, magnetic fields, and radiation medicines for the crew, for example. I'm sure that over the next century we'll learn the right mix of what is needed for deep space travel.

Heat management seems to be a matter of engineering and design; making sure that the radiator fins are placed correctly, that they're of the correct type, and that you have the right number/square footage for the ship type.

It may be that future life support system designers for spacecraft might sit in the same training classes as those that design submarine life support systems.

Ferrell

Rick said...

Anita - Just don't mix 'em up with metric in one calculation, like NASA did with that one Mars probe.

It comes to about 16 (metric) tons and 16 cubic meters.

Space is so unrelentingly hostile that most disasters will be internal. Unlike your examples, or even the cruel sea, space never even pretends to be benign.

What the old writers didn't realize is that you don't need meteor strikes to make for big trouble. A good old fashioned galley fire could ruin your whole day out there.

Anita said...

If I screwed the calculations, I'm in good company. Ever see the movie The Dish about the Parks Radio 'scope that brought us the TV pictures of Apollo 11? NASA handed off to the Aussies dish coordinates for the Northern Hemisphere.

Yeah, all it would take is a power generator to go cranky and a generator's default is cranky.

"Space is disease and danger, wrapped in darkness and silence."

Admiral Leonard McCoy, MD

"90% boredom, 10% terror."

Every entity that ever left the ground for more than 5 seconds at a time.

And my personal favorite: The astronaut who pointed out he was zipping around space in a tin can built by the lowest bidder.

Anita said...

One other thought: Mama Nature is neither hostile nor beneign. She's indifferent.

"Don't take it personal."

Anonymous said...

When thinking about life support-perhaps crew shifts would be broken up into nav, engineering, and life support watches.

Ferrell

Citizen Joe said...

That sounds more like our modular scenario. You've got your mission commander, which watches over external threats. Then you have the engineer watching the drive bus. And Ship's Steward watching over the habitat.

Rick said...

Anita - Indifference sums it up nicely. 'Ground Control to Major Tom ...'


Ferrell & Citizen Joe - It could easily work out either way, or even both at once, depending on circumstances.

One thing to note is that 'space station' is in a way a very misleading term. It is not stationary the way terrestrial things are. A station is a spacecraft, traveling on orbit like other spacecraft. It has to be navigated and maneuvered by stationkeeping burns. So it has to keep pretty much the same operating watches a ship does.

If anything, a station has to keep a more active piloting watch, because of arriving/departing traffic as well as local traffic. Often robotic, but requiring human scheduling and supervision.

Mike said...

Does anyone have information on O2 production/energy input for different plants? After watching this I wonder what plants give the best bang for your buck...

Anonymous said...

Personally, I'm surprised that nobody has mentioned the little viral problem the Atomic Rocket's Tweeter page has mentioned some days ago. Here and Here. And considering that recycling EVERYTHING possible to reduce mass is a big enough staple in design, especially in the life support department regardless of duration, general health and sanitation if not sterilization might also be a big enough concern for future space travelers that would probably make airline-borne illnesses seem more like a bother then an actual threat.

Anyway, getting away from that little ramble, there is also this little comment from Ferrel: "future manned spacecraft will need several types of radiation protection"

Like the magical shielding that is a staple of nearly every science fiction media, people tend to group the radiation protection problem into a singular solution instead of multiple solutions since it suffers from the "Out of sight, out of mind" syndrome until the aforementioned Cascading life support malfunction and similar problems as demanded by the plot. With multiple, one is not completely screwed over if one is not malfunctioning. Granted, there would probably be a high popularity with passive radiation systems and radiation damage corrective medicines. Something tells me that they'll be a bit more simpler and not as energy intensive as the more active versions.

And then there is Citizen Joe's suggestion of a "tiered" radiation protection levels which might save up in the mass department more. Such as non-essential work areas or even low priority systems could have little if any radiation shielding and work could be either done by robots or crews performing EVA while utilizing suits that have something of a more personal radiation-resistant protection for only a limited amount of time for whatever reason (i.e. the waldo is not working and someone may need to sacrifice themselves in order to get it working so that the rest of the crew may survive). Granted, I have no idea how much of a mass budget savings this would have in comparison to overall radiation protection on anything similar to a submarine space-wise.

- Sabersonic
Gmail Address

Anonymous said...

Sorry, ran out of space in the last one. Anyway, as I was saying:

As for overall life support, well one could separate the numerous systems between recyclable and consumable. Recyclable being resources that could be reused again and again with proper filtering and purification with a good example being air and water. Consumables are finite resources with the best example being food, which itself can be sub-divided into preserved and fresh. That is consumables that could be preserved and stored for an extended period of time while fresh are consumables whose self life is severely limited who benefit the highest from on board regenerative gardens and such. We already have (argumentatively) experience and experimentation with recyclable resources for space-born and orbital missions, and we have been utilizing preserved consumables for millenia and many of those have a reduced mass compared to the raw product. However, Fresh Consumables are currently a problem whose solution isn't as efficient as some would like for space travel. One could foresee near future travelers and settlers migrating to their new homes or crews on missions surviving on nothing more than jerky and MREs for the entire duration if not the majority of it. Stations and other similar colonial settlements might have an edge on transport spacecraft and similar if only because they may have the extra room to have that hydro/aeroponic garden to have a more replenishable fresh consumable supply than spacecraft if only because they are designed with extended or permanent life support of those within the can than those who are just sitting in the spacecraft until they reach the next spaceport. Even Orbital Stations would have a better quality of life than space transports since stations don't have to worry too much about mass limitations: They don't have an engine drive whose performance would be altered by a few extra kilograms in the payload decks.

And speaking of space stations, there is this idea that suddenly popped into my mind: Some time ago I mentioned the Cycler Stations, I can't remember the exact blog entry though. Anyway, the idea is that what if a transport, even a high speed Torch Drive type, did not need to carry or even be equipped with regenerative supplies? Rather it only needs enough supplies to get to the nearest Cycler Station that is en-route to the colony/settlement destination. Granted, this heavily depends upon enough resources and will to have such slow orbiting vessels as opposed to higher acceleration-capable designs. However this does give the advantage that not all of the on board supplies have to be enough for the trip to say Earth to Mars. It could even prove to be the basis of an interplanetary economy where (assuming) the Cycler Station's own regenerative life support is stable and reliable enough to not only support the on board crew and passengers/residents, but also have a little left to export to passing transport craft that the transport craft itself would trade via luxury goods.

- Sabersonic
Gmail Address

Citizen Joe said...

I think there will always be a need for those emergency reserves which are isolated from the regenerative system and used to rebalance the system. A bioproduction system is going to be balanced off a set amount input and output. Add an extra person to that load and it could go way out of balance fast. If you go with the cycler model (and I've used it for scifi setting), then the cyclers could be enormous space plantations that harvest just before outbound rendezvous. The food/air/fresh water gets offloaded and the waste water/raw material/CO2 gets loaded up for the next growing season. Mass could then be balanced out with incoming space products like deuterium or helium-3 fusion fuel. One fo the big tricks is to use some sort of elastic collision process to transfer inbound momentum to the outgoing vessel without the sudden accelerations. Probably some sort of repulsive magnetic fields

Jim Baerg said...

Sabersonic: Those articles you noted about infectious disease being a greater problem in zero gee, indicates one more reason to go for rotational 'gravity' for any space habitat that people stay in for more than a few weeks.

This is one more thing to check for at lunar & martian gravity levels. For all these things that we know go wrong biologically at zero gee, is 1.6 m/s^2 or 4 m/s^2 enough to keep people healthy?

BTW there is a curious tendency for surface gravity of solar system objects to cluster near values that differ by a ratio of about 2.5 see:
http://www.gdnordley.com/_files/QSG.rtf

so studying biological effects of Mars gravity also covers Mercury & lunar gravity covers most of the large moons in the outer solar system.

Citizen Joe: What are you thinking of in terms of a 'radiation protection suit' that could possibly do any good?

IINM it takes at least several cm of dense material to significantly attenuate cosmic or gamma rays. If some sort of electro-magnetic shield is being used that would shield the whole spacecraft & fade out over a distance scale of kilometers.

So if you are going outside the raiation shielding mass of the habitat section, I think the only thing to do is carry a dosimeter so you know how much you have to limit your time.

Citizen Joe said...

The full exposure suit would probably look more like a miniature submarine. Partial exposure suits would probably be more like the current space suits, possibly even the hardshell stuff. The minimal exposure suits, would probably be skin suits with some sort of reflective material. The crew would probably operate the ship from protected areas while wearing these suits. Passengers would be restricted to the storm cellars, without suits, for the duration of the trip.

Citizen Joe said...

I'm gonna go back to my idea that you just grab a big ol' ice asteroid, melt a socket into it and jam your drive and habitat into that. Use the ice as propellant but also as shielding and even heat sinks.

I know I know... what about the crappy Isp? Well, assuming that an infrastructure gets put into place, ice from the outer system or even from the asteroid belt can be lobbed into the appropriate flight paths so that the ice ships can simply leap frog from asteroid to asteroid. Isp is critical when you only get one fill up, but if there are gas stations along the way, it becomes less of a concern.

It seems to me that the infrastructure would involve placing these refueling asteroids into specific orbits well ahead of time. Then space ships would plot their courses around intercepting them. Of course, missing a rendezvous leaves you out of gas out in the boondocks and those 'space hicks' could have you squealing like a pig for remass.

Nevertheless, the huge mass of ice around your ship would go a long ways towards radiation shielding.

Rick said...

Mike - I imagine there is a whole literature on that. But at a guess, any biosystem that can feed us will also provide enough O2 to 'burn' the food biomass it produces, just by how the equations balance.


I remember some previous discussion of cycler stations, but I also don't know which post. Cyclers might work well especially if we are doing a lot of work in the asteroid belt. A cycler will pass through a different section of the Belt each time around on about a 3 year orbit.

I held back from discussing the infectious disease issue because it is part of a larger question of space health. Spin gravity and radiation shielding may solve the problem, or there may be other factors.

In the worst case, living in a can for years, with limited sensory variety, might have the psychological and health effects of imprisonment. We may only ever be sojourners in space, not residents.

Or a sufficiently large and varied hab may negate any sense of confinement, and provide an environment in which humans can flourish. We will not know until we test it.

Outside of radiation belts, natural space radiation is more a chronic issue than an acute one. You wouldn't have to take a dosimeter for an EVA; just log the time. But if you have nuke reactors they are hot even when shut down.

As an aside, I think there is a lot to be said for EVA pods a la 2001, because you can use them with the standard onboard breathing air instead of having to transition to a special spacesuit mix.

I would consider jacketing big spacehabs not with ice but a jacket of liquid water that can serve as heat ballast against short term hab temperature excursions due to changing power consumption, etc.

Jim Baerg said...

"As an aside, I think there is a lot to be said for EVA pods a la 2001, because you can use them with the standard onboard breathing air instead of having to transition to a special spacesuit mix."

I think there is a lot to be said for keeping the standard onboard breathing air low enough in nitrogen (or other inert gasses) so prebreathing pure O2 isn't needed before an EVA.

I suspect that living in 20 kPa O2 & 20 kPa N2 would allow one to work in a spacesuit with 20 kPa pure O2 with no pre-breathing required to prevent bends.

Citizen Joe said...

I've made the suggestion that using Helium as the buffer gas in microgees would be better since it doesn't form bubbles like nitrogen. It is not a good idea in spin habs because it is so light that the gasses would stratify giving you a dead zone up high and an explosive pure oxygen bath down low.

Jim Baerg said...

Joe:
According to the Wikipedia article on Decompresions Sickness

you can get the bends with helium, but the decompression time is shorter.

Also why do you expect helium to separate from oxygen like oil & water? I'm pretty sure they mix more like alcohol & water.

Ie: if helium is added at the top of a room already full of oxygen it will tend to stay as a separate layer with only slow mixing, but if O2 & He are thoroughly mixed, they will not separate.

Citizen Joe said...

In no gravity, Helium should stay mixed. But in a spin hab, the centripetal force will cause the heavier oxygen to move outwards while the lighter helium doesn't go as far out. For the same reason that helium floats, it will separate out.

It may be feasible that 'on-call' EVA personnel may keep duty station in a Heliox microgravity area where they can work normally. This would minimize the time needed to acclimate to reduced pressures in a space suit.

Additionally, the pods instead of suits can be fully pressurized (I think someone already mentioned that). There's also the idea of a mechanical counter pressure suit with just the helmet being at atmospheric pressure.

Rick said...

Any motion probably keeps gases well mixed. I won't swear to it, but that is sure the impression I get.

And as Citizen Joe alluded to, the big complication with EVA is that you need a low pressure mix, O2 rich, in a space suit or you'll be like the Michelin man, unable to move.

Anonymous said...

"the big complication with EVA is that you need a low pressure mix, O2 rich, in a space suit or you'll be like the Michelin man, unable to move." -Rick

That is true for the conventional space suits such as the EMU that many of us are familiar with, but that isn't the only choice of space suit design, with the more well known alternative being the Mechanical Counter Pressure (MCP) Suit that really doesn't require a low pressure, high O2 mix, or as far as I know. Granted, they're just as hard, if not more so, than the conventional space suit but might be considered speedier than Harduit alternatives.

- Sabersonic
Gmail Address

Jean Remy said...

The problem with normal suits is the ballooning. The problem with skinsuits is they will be a pain to put on. You'll need to dab your negative spaces (underarms etc) with some putty to avoid the skin to balloon out in the interstitial space.

Hardsuits are actually a good compromise between 2001 pods and normal suits or skinsuits. I'm thinking of suits like deep undersea workers use, perhaps coupled with exoskeletons. There are already a lot of exoskeleton suits being tested and prototyped. They would be smaller than the pods, and more natural for human operators to use. They would be easier to shield against radiation than a suit, and able to go in places a bigger pod might not get to. You wouldn't put it on like an american suit, as much as enter it.

The Russian and European suit designs generally have the backpack build like a hinged door, and you slide into it from the back. You can even store the suits "outside" with the backpack fitted to an airlock. Because it is a hardsuit, you can use the same mix (whether O2-N or O2-He) as the station/ship.

Rick said...

The Russians use hardsuits? I just realized that I don't know the first thing about Russian EVA practice. I'm familiar with Soyuz images, but I don't recall ever seeing an image of a cosmonaut doing a spacewalk.

Going in another direction, I think there will be a place for what I call space taxis: small, simple pressurized 'short range' transfer vehicles for a few passengers.

Anonymous said...

"Going in another direction, I think there will be a place for what I call space taxis: small, simple pressurized 'short range' transfer vehicles for a few passengers." - Rick

Which probably would lead to the age old Sci-Fi story of the stranded Lifepod which is effectively the Life Boat IN SPACE!.

And from Jean Remy's apparent favoring of Hardsuits, I admit I was kind of surprised. I was thinking of a powered Hardsuit that utilized an exoskeleton-like frame to help with the movements since traditional hardsuit designs are rather difficult to move using human strength alone. I had figured that there would be strong arguments against such an idea. And to be honest, even though it is as scientifically correct as any Star Trek or Space Ghost episode, the Mech nut within me can't help but wonder and hope if such powered hardsuits would lead to some interesting combat machine designs.

Anyway, getting back to the original blog post topic, one could potentially predict that like Propulsion Drives, Reaction Mass and Fuel storage, and on board Power Generation, reducing the overall mass of the various life support systems to increase overall payload allowance is going to be extremely difficult to perform in the near or even mid-future. Especially considering how delicate its possible primary cargo (i.e. crew and passengers) are when traveling in between planets and orbit trajectories, let alone interstellar.

- Sabersonic
Gmail Address

Citizen Joe said...

Once you get into hard suits, is there a good reason to actually have your arm inside the suit's apparent arm? Wouldn't it be easier and more functional to have a robotic arm controlled by a waldo attached to your own arm? Then you just need sort of a spherical pod with life support and not have to worry about sealing joints.

Jean Remy said...

Sorry for the misunderstanding: no, Russians use standard suits, but rather than American suits which have to be assembled on the astronaut, they get into theirs by going in through the backpack. It's still a low pressure soft suit. It was merely arguing their way of getting the suit on would apply to a hardsuit.

Jean Remy said...

As far as sphere and waldos: that's essentially what Rick was talking about when he said a 2001-type pod. They were spherical. And had Waldo arms... so yeah.

My argument for the hardsuit over the pod is it would be smaller than a pod, since it is form fitting to the astronaut rather than a big sphere, two, that ergonomically it would feel more natural to the user, since there is not interface to speak of: you'd move more naturally, and though constrained, less so that in a pod.

http://www.osti.gov/bridge/servlets
/purl/459340-C0yAX0/webviewable/459340.pdf

This document illustrates some of the issues with remote manipulators, the first one being that it takes a lot of room to set up waldo systems. In case of a hardsuit there is no separation between the controller, the controls, and the manipulators. As I stated, it is a lot more compact. Since it is also fitted to form, it is probably more natural for a human operator. In a pod, he will have to worry about piloting the craft *and* using the waldo controls. Or you need a pilot and mechanic, which causes the pod's size to increase even further. In the suit, the astronauts movements can control both piloting and manipulation in a more natural manner.

Citizen Joe said...

There is an assumption that you will need some sort of mechanical assistance with the hard suit limbs. If you stick your arm inside, that mechanical assistance has to be exterior. That makes the arm much more bulky. If you don't put the arm in there, then you can fill the arm with the mechanical stuff and have utility beyond that of the human arm (like a spinning wrist.

Barring the full waldo, a glove, with tactile pickups, could transmit the hand's intents to a robotic hand, which may have a built in camera for close up inspections.

I think that the complaints about waldos and robotics are the same complaints that the Air Force has about unmanned recon vehicles. It is taking jobs away from officers and putting it in the hands of enlisted men with minimal training. With a little more progress in feedback, VR simulation and some robotics, the whole issue of tele-operations can be solved.

Jean Remy said...

Follow this argument to its logical conclusion and you wouldn't need a suit or a pod at all, just remotely-operated robots. However I think that, like an air force made entirely of drone, a space workforce made entirely of robots is likewise unlikely, maybe even unfeasible, for many reasons.

1/ Communication delay: as indicated in the paper linked previously (sorry for broken link, just copy-paste URL it should work) there is a latency between command input and remote manipulator execution. The further removed the operator is from the robot, the more the latency is pronounced, and the greater the errors.

2/ Feedback: It is one thing to try and use a torque wrench and feel resistance in your arm as something locks up, and other to have a control pane beep a warning at you. A remote operator has to do things almost solely by sight, when the human mind is very much conditioned to react to physical rather than optical stimuli (space sickness is a conflict between vision and inner ear, for example. That's not even mentioning what a fixed camera would miss when our constantly roving eyes are naturally drawn to motion and unexpected sights. That cracked bolt flying away? a camera focused on a task will miss it, an astronaut will see it through peripheral vision and clue in right away to a problem.

While perhaps the US Air Force is too reticent to use drones, let's not get into an opposite mindset of excessive automation. Even robotic factories employ human workers to monitor the process, intervene in emergencies, and do the delicate work that requires a human touch and difficult to program. There's probably a good compromise, and I think that the hardsuit fits into that compromise a lot more nicely than a pod, which indeed could be completely replaced by a robot since it removes a lot of the reason you'd want a human on-site by isolating him in a cabin. At this point, does it matter the control cabin for the arm is in the pod or back on station?

Citizen Joe said...

I refute your torque wrench with the notion that you can't use it in zero gees anyway. The tools used in space grab on to the part and then twist and you don't get the sensation of a locked up part anyway.

Peripheral vision and feedback from whatever you're doing is important though. I would recommend a picture in picture arrangement and a screen significantly larger than the visor on your helmet. Cameras can be tuned to IR or UV spectrums with visible light overlays so you can see a lot better through the camera. There are touch/pressure sensitive robotic arms being tested now. They also have a voting system control scheme in autopilots whereby if the pilot does something stupid, the autopilot can outvote him. Applied to grabbing stuff, the arm would stop at a predetermined pressure and ask "You are about to crush object. Continue?"

Waldos may not even be necessary in the future. Project NATAL uses cameras to recognize actions by the user and then translate them into game commands. A room, a little over 2 meters in diameter could house a harness for an operator plus projectors and a feedback suit (like the rumble packs in game controllers). The robotic avatar could then pipe back data to give the operator full surround sensations.

Rick said...

I don't know enough about teleoperator technology to have an informed opinion on waldo versus direct manipulation.

But even with cumbersome space suits, I have to say that EVA has worked out pretty well in terms of our capabilities. Even more than the ISS, the Hubble repairs are indicative, because it was never intended for on-orbit servicing.

It need not be an either/or. (Unless hard suits turn out to offer the best of both worlds.) Pods for convenient egress without complications like prebreathing a special mix, soft suits when real hands-on manipulation is called for.

And yes, hardsuit tech does lead somewhat inevitably to speculation about power armor!

emdx said...

I am impressed. This is the first space page I see who mentions passenger rail accommodations.

People always overlook railroads for technological solutions; yet they have solved many important technological problems a century ago (distributed operations, communication protocols, ressource-sharing management). After all, 100 years ago, railroading was the high-technology of the day... And they had pretty acute problems to solve; like packing the maximum horsepower possible into a machine that could pass through a hole 10 feet wide by 15 feet high at speeds as high as 100 mph... (I am as interested by space as I am by railroads).

Regarding accommodations, for example, it is hard to beat the efficiency of a slumbercoach room. In single-passenger configuration, it packs a bed, a seat, a table, a toilet and a sink in less than 3m³ (yes, it's cramped); for a double passenger, make that 5m³ (but still cramped, and if one passenger wants to use the bathroom, the other has to go out in the corridor). Then you have duplex roomettes, where a single passenger has all the amenities in about 6m³, and so on, all the way to the double bedroom en-suite with two private bathrooms in about 20m³. All those were in widespread use 50 years ago.

One can also look at small sailboat configuration for examples of cramming accommodation in wierd spaces, but large ship accommodations can be deceiving. (I was actually very disappointed the last time I had a cabin on a tramp cargo; the space was very inefficiently used. In 50% more space than a double bedroom, there was no sofa/chairs at all; only two berths and a toilet that would have had a shower were it on a train).

Rick said...

Welcome to the comment boards! I first thought of the railroading analogy with respect to modular spacecraft - how cool to use the term 'consist' for the assemblage of a mission.

People may not consider rail sleeping accommodations as an example because the cultural association is not 'compact' but 'luxurious.' If you're thinking of utilitarian accommodations, as for a space crew, Pullman cars are not what comes to mind!

But in fact sleeping car accommodations are a good deal more compact than even the junior enlisted accommodations aboard a late 1960s vintage Newport News class LST, certainly more compact than JO accommodations.

Though one consideration is that you don't spend more than 2-3 days aboard a transcontinental train, compared to months at sea / in space. Also, a roomette feels a LOT less cramped because of the window!

f said...

For fixed interplanetary routes, once the traffic allows for it, it could be convenient configuring a "orbital convoy". What I means is, if we build a big habitat, with plenty of shielding, cargo-space, ample permanent life-support etc. etc, and we put it in an orbital permanent route between 2 or more destinations, you still have to expend plenty of delta-v for loading passenger and cargo, but you've only to expend a little for all the infrastructure.

Rick said...

Welcome to the comments threads! I believe that what you are suggesting is much like the cycler stations mentioned upthread.

There is no particular saving for rugged cargo, but potentially a big saving for passengers. They can make the short transfer hops in airliner type seating, minus all the bulky and heavy cabins and fittings, not to mention life support and shielding.

emdx said...

Thanks for the welcomes.

Regarding "trains in space", I recall the Apollo spacecraft, while being en route to the moon, being described as the "space train" on french-canadian TV... And why not? After all, the SM+CM+LEM ascent stage+LEM descent stage combination was coupled and uncoupled all the time during the mission... :)

Concerning accommodations, do we need huge staterooms? In zero-G, we can sleep "standing up" (recall the Skylab "bedrooms"), so one can effectively sleep in a closet; I suppose that 3 m³ will suffice for everyone and have room for luggage too. Compared to this, a duplex roomette is sumptuous accommodation...

But initially, I am sure the exitement will be so much that people won't mind spending a long time in an aircraft seat/couch with a good entertainment system screen (the "roomette window"), especially if zero-G will make it easy to go about the cramped quarters. Curtains could provide for privacy, and a white-noise generator close to the ears will easily muff-out ambient noise and help to sleep.

* * *

Regarding helium/oxygen mixes, helium is used in deep-sea diving because, unlike nitrogen, it does not induce narcosis (I SCUBA dive, too). With air, you can become impaired as "shallow" as 120 feet down. Whereas adding helium to your air (which becomes "trimix") can boost your unimpaired depth to about 250-300 feet. Helium alone can allow to go to about 500-600 ft, and with hydrogen (yup, breathing 95% H² and 95% O²), depth below 1000 feet have been attained. But in those cases, decompression times is measured in days if not weeks.

Gases won't stratify. Brownian motion will make sure that the lighter gas will diffuse and remain so. We always make fun of newbies who shake their tanks when they add oxygen to make "nitrox"...

emdx said...

Pure oxygen spacecraft atmospheres are not a solution. Recall the Apollo 1 fire. Pre-breathing O² to scrub one's nitrogen will remain for a long time.

As of putting-on skintight spacesuit, it's not really a problem; we put wetsuits on all the time, and have developped plenty of methods to do so, like using talcum powder or shampoo (as a joke, for a while, I was using K-Y jelly after I stumbled upon a big stash of it); but there is nothing that precludes having zippers or belts that can be closed/adjusted to help easing-into the suit.

* * *

The reasons why not using helium in a breathable spaceship atmosphere are many:

* Helium seeps out through anything. After a while, helium atoms sneak between metal atoms; so does hydrogen. Worse, hydrogen will alter the crystalline matrix of metals, weakening them. You don't want your pressure hull to dissolve, no? (and this is why the much-touted "hydrogen economy" will never take-off, given the enormous problems of transporting and storing hydrogen. In reality, it's just a big racket to keep the oil companies' stakes in everyone's transportation by having them buy hydrogen from gas stations rather than plug their electric cars at home - but I disgress).

* Helium is a tremenduous heat-sink. Astro-nuts breathing helium will get cold very quick, and they'll need to wear special insulating suits made of non-breathable foam in order to not freeze to death. Wearing a wetsuit - which does not breathe at all - on land gets uncomfortable very quick - no matter how big is the fetish value. Helium breathing atmospheres are a big problem for deep-sea divers; they lose so much heat trough their lungs that they have to use open-circuit hot-water heated wetsuits that are fed a continuous stream of hot water piped-in from the surface; if the stream stop, they have minutes to get back to their diving bell before freezing. The US Navy has experimented with portable plutonium heaters, but the sailors are understandably a little bit weary of strapping those to themselves...

* If someone suggests using hydrogen instead of helium, well, there goes your proverbial cigarette break...

* And lastly, helium (and hydrogen) are much less dense than nitrogen, hence the "donald duck" voice effect that, so far, no one has been able to solve. Cue the "ducks in space" jokes.

Jean Remy said...

emdx let me add my welcome.

Absolutely priceless data. The only time I ever put on SCUBA gear was in the micro-g simulation tank at Hunstville's Space Academy. All this information is absolutely fascinating, especially the fact that hydrogen weakens metals over time.

On the subject of sleeping arrangements I don't think a closet is going to be very satisfactory. It would feel too "closed in" for one, and secondly it is not enough private space for an extended trip. There's a fine line between space economy and keeping the crew sane and not homicidal. However since the "bed" is just a sleeping bag starpped to the wall when needed and stashed away when not, and because in micro-g any space becomes a lot larger (a lot more volume is usable once gravity is not an issue) the cabins don't need to be all that much larger. The walls won't be bulkheads and the doors won't be hatches, I'm thinking thin curtain-like plastic sheets. As far as sound insulation there have bee some pretty good experiments with sound cancellation technology: emit a sound wave that is the exact opposite and they cancel out.

Jean Remy said...

I hope I put all my ducks in a three-dimensional grid.

Rick said...

Thanks for the breathing mix information!

On sleeping accommodations, I am thinking in terms of missions lasting weeks or months. I would greatly prefer ample viewports, even if there's not much to see during transfer missions, but I don't know whether viewports in a spin habitat are psychologically helpful.

Jean Remy said...

Windows in the deck might by too unnatural and windows facing along the spin axis might cause dizziness. I would have an observation blister in the non-rotational section, however. Another possibility would be false windows. The cabins could have PC's with a flat screen display, screensaver could be a feed from an axis-mounted camera.

emdx said...

Jean: (I always wanted to dive in a zero-G tank - in a spacesuit)...

Just curious: before you put that tank on, what instructions did they gave you? Because there are extremely important precautions one must take before breathing compressed air under water (very unobvious precautions, I might add)...

Jean Remy said...

Well it wasn't in a spacesuit, sadly, just a standard wetsuit and tank/rebreather apparatus. Also the dive tank was fairly shallow (say deep enough for an Olympic diving competition) so there was no decompression issues.

However we did go in slow, with pressure equalizing pauses every four or five rungs. I actually had to climb back up a little at one point because of pressure in my ears that wouldn't clear. Went up four rungs, cleared it, and did the rest of the descent fine.

That's all the specifics I really remember. It was...

... Oh crap 18 years ago... thanks for making me feel old!

Anyways I do remember a pretty long lecture on precautions, and there always an instructor hovering at my shoulders. Once in there we had to perform a few simple "repair" tasks on a mock-up satellite. It was pretty fun, and over too soon.

emdx said...

I was wondering about if they told you to never hold your breath. Because if you hold your breath and ascend, the air in your lungs will expand and blow them up. And this can happen from as deep as three (3) feet…

This is the reason why you cannot get SCUBA gear unless you are suitably certified.

Rick said...

I've read about 'don't hold your breath' with respect to escaping from crippled subs, but it stands to reason it would apply to SCUBA as well.

Jean Remy said...

Now that you mention it, yes. This was stressed. "Breathe normally" was repeated a lot.

Harker said...

Hmm.... Aside from people being squemish about it this would be a good time to consider genetically modifying some plants. Particularly trying to get a higher rate of CO2 to O2 so that you could bring less biomass for the same result.

Rick said...

Welcome to the comment threads!

Raising the rate of CO2 - O2 conversion would certainly reduce the biomass needed. How doable that is, is way above my bio pay grade. (Though since you have a biochem background, you likely know a lot more about this than I do!)

If the biomass is also supposed to feed the crew, that introduces another complication ... one that is even more above my bio pay grade.

Jim Baerg said...

My understanding is that the low concentration of CO2 in the atmosphere is a major factor in keeping the efficiency of photosynthesis low. Also that CO2 concentrations can be several times the level in the atmosphere before there is any problem for human physiology. So maybe keeping CO2 in the hab at about 2000 ppm rather than 400 ppm & optimizing the GM plants for that would be best.