Reasons against Mars Direct

RobertDyck · 2003-12-18 01:42:10

Politics will change anything designed to something less functional. We must work against this trend and educate people so they also fight it.

Rather than fighting, let's try to work co-operatively. The politicians control funding to the space agencies, and right now they are the only ones with funding to start space exploration or settlement. Let's get them to work with us, not fight against them. Yes, we need effective equipment, and we need to make effective use of what we have. Politicians do tend to get distracted, and their term in office is limited. However, they are also trying to get the "biggest bang for the buck". We have to convince them it is in the long-term interests of the economy and/or society they serve so they don't opt for a single-purpose flashy photo-op. We also have to convince all political parties so the project doesn't get cancelled after the next election. Nixon cancelled Apollo to direct funds to the Vietnam War; we don't want that to happen again. We need to convince them that space colonization is a cash cow they can milk to fund their next pet project. Anyone who has read my posts on this board knows I think it is; the question is who will reap the profits. For now, let's not bite the hand that feeds us.

GCNRevenger · 2003-12-18 14:26:12

I disagree that the technology plays no role compared to politics in keeping a manned Mars mission from becoming Apollo-II. If it will cost a given amount and risk death a certain amount for one technology and a different amount for another technology, then it is a factor. There is a threshold, however hard it is to detect, when the difficulty of going to stay is too much of a sacrifice to pay.

A few 18 month missions is very much a flags & footprints if there is no provision for perminance afterward. Mars Direct and its immediate decendants could support a limited colony role with many expendable SDV/TMI/Lander shots if given unlimited funding and an unlimited supply of expendable astronaut-martyrs, but the question is can it comfortably achieve this threshold? No. Even with launch from high Earth orbit, it is still not enough and over the space of twenty years development costs begin to become quite small compared to operational costs, especially for throw-away hardware.

The #1 technology that determines if we are above or below the threshold is and will continue to be propulsion; the less trouble it takes to get from A to B, the easier it is to reach this threshold. Chemical/Aerobrake, NTR/Aerobrake, and the low-thrust SEP/NEP/(Aerobrake?) are unable to go to and from Mars fast enough with enough mass margin for manned travel of any scale. Can they get people there? Yes. Can they do it easily and safely enough for a colony? No. Of the available technologies, GCNR is the best super-engine: It does not require magnetic confinement because it doesn't reach an unmanageable temperature. You keep the engine from melting by spiking the LH fuel with a substance that absorbs the radiated energy, simple carbon black may work, so that it heats the fuel instead of the engine walls. The walls of the engine, cooled by a stream of liquid hydrogen (just like modern chemical engines), do not have to withstand a thermal flux that is far beyond what is achieveable today. CFD will make it easy to design the engine, which theoreticly speaking, is quite simple.

In relation to tether propulsion for unmanned cargo, yes I think GCNR is much easier than trying to mate a cargo (which must be devided up small and built strong, hence $$$) traveling tens of mach numbers at a exact instant in an exact spot and have the catchment mechanism latch on all coreographed perfictly. No "testing" is required to say that this would be very hard to do reliably. Spinning/despinning largely negates its efficency for space cargo and eliminates atmosphere-to-space transfer. Its not as "simple" as its "simple & cheap" label makes it out to be.

If it takes another ten or fifteen years to develop GCNR than MD so be it, as I can say with confidance that using Mars Direct or its children will take reasources away from building a real Mars ship. So we start with GCNR in mind, and use the money that would be spent on Zubrin's lander to build a DC-X style reuseable lander, and so on. This will help bring us closer to the colonization cost and technology threshold, a small price to pay in exchange for wasting billions on a pointless Zubrinesque mad dash to the Red Planet... The second someone puts a footprint in the red soil, its a race against time to build a colony before interest is lost and the plug is pulled, time that cannot be wasted by Mars Direct.

GCNRevenger · 2003-12-18 14:33:41

I also want to reiterate that Mars Direct and its children are also not safe enough for regular manned flights. The artifical gravity scheme is dangerous and heavy, all that redundant cable you use is by no means light-weight, and astronauts will have to do more than walk when they get there; 90 days ought to be the target zero-G limit... and what if your cable doesn't break cleanly?

Dr. Zubrin also underestimates the harm caused by cosmic radiation, which will easily exceed safe dosage without shielding during transit, even without a solar flare. I suspect that he has convienantly shrugged off this hazard to make MD more apealing to Congress. A heavy-duty radiation shield will be needed, more than food/water can provide, which will risk chemical being dangerously overweight and awfully close to the zero-G limit for NTR engines.

For the third time, i'd like to reiterate again how nice it would be to have mass headroom for any Mars ship design; you simply don't have to worry about making the thing so light, which in itself will save signifigant money plus give engineers and the science teams more flexability to make the Mars ship as sturdy and useful as possible. Stronger construction, more spare parts, more instruments, and of course bigger crews and mass for payloads. Chemical can't do this, solid-core NTR can't get it there fast, Ion still can't accelerate quickly enough... you need a super-engine.

MD and other ISPP-return-fuel methods that don't use a super-engine also have no abort option. With propulsive flight round-trip there should be plenty of fuel to simply turn right around if there is somthing wrong. A month into transit and a serious leak is discoverd in the LSS system or a crewman coming down with a virus that was incubating before launch? No problem, turn around and be back to Earth orbit in a week or two. The pure Zubrin MD couldn't even abort the second the Ares SRBs are lit. Use the ISPP to fuel extra lander flights.

Then there is this aerobraking stuff... I think is awfully dangerous because of all the "ifs" involved. With the Martian atmosphere being so thin and gravity being lower, it is harder to predict the depth of the atmosphere in any one spot at any time. The accuracy of the entry angle is so delicate that I have reservations that it can be done reliably. Aerobraking also limits the size of the ship that you can use, since the "hole" you have to punch must extend the length of your rocket, to prevent the superhot air from collapsing back and melting your tail. Your ship must be built strong enough to withstand the sudden deceleration forces, further increasing the mass for a given size instead of a relativly gentle propulsive capture. And best of all, it limits the maximum speed and hence the shortness of your flight. Its a neat trick, and could be used for cargo perhaps, but it will hold us back.

Bill White · 2003-12-18 14:41:43

If it takes another ten or fifteen years to develop GCNR than MD so be it. . .

Setting aside all else, has anyone, anywhere, authorized funding to develop and deploy a GCNR?

10 to 15 years? Where does that come from?

Bill White · 2003-12-18 15:14:49

Speaking for myself, if President Bush stood before Congress in January of 2004 (State of the Union) and called for immediate funding of a robust GCNR program to put American on Mars within 20 years, I believe the Mars Direct plan would die a quick death.

If MarsDirect advocacy rallies public opinion for Mars and if GCNR is as prudent of an investment as you say then the public support for MarsDirect will be readily transferred to GCNR.

MarsDirect advocacy - IMHO - serves a very useful purpose in showing the ordinary person that Mars is feasible NOW.

RobS · 2003-12-18 16:20:41

I am not convinced by any of these arguments in favor of gas core and colonization; furthermore, I can't imagine how the political process would work that would approve "colonization" without an exploration phase first; and the politics and cost of even solid core nuclear still seem impossible to achieve, let alone GCN. The JIMO mission, it seems, is aiming for a 10-30 kilowatt reactor, not something big enough for VASMR or even big enough to run Mars Direct on the surface!

Alas, the result may be like the space shuttle, which necessitated a lie by NASA to get it approved at all (the alternative being no Apollo AND no shuttle). But colonization and gas core? All I can say is, good luck!

-- RobS

Bill White · 2003-12-18 16:46:22

I am not convinced by any of these arguments in favor of gas core and colonization; furthermore, I can't imagine how the political process would work that would approve "colonization" without an exploration phase first; and the politics and cost of even solid core nuclear still seem impossible to achieve, let alone GCN. The JIMO mission, it seems, is aiming for a 10-30 kilowatt reactor, not something big enough for VASMR or even big enough to run Mars Direct on the surface!
Alas, the result may be like the space shuttle, which necessitated a lie by NASA to get it approved at all (the alternative being no Apollo AND no shuttle). But colonization and gas core? All I can say is, good luck!
-- RobS

Sorry! I can get carried away by the whole colonization thing. ???

Yet a one shot MarsDirect could lead to "been there done that" situation and Zubrin plainly intends multiple MarsDirect missions to establish a growing permanent presence.

Children may be 100 or 200 years away (or more) yet sooner or later that becomes a simple choice for our species. Either we learn to bear children at locations other than Earth or we abandon any pretension of becoming a "spacefaring" species.

clark · 2003-12-18 17:07:40

sorry to quibbile...

but is our ability to conceive and raise children on other planetary bodies the only way we can consider becoming a 'space faring' species?

What if we find that the human body is to frail to contend with anything other than 1.0 g? Wouldn't that simply mean that we can only hope to 'settle' empty space in artifical homes? ???

Bill White · 2003-12-18 17:43:23

sorry to quibbile...
but is our ability to conceive and raise children on other planetary bodies the only way we can consider becoming a 'space faring' species?
What if we find that the human body is to frail to contend with anything other than 1.0 g? Wouldn't that simply mean that we can only hope to 'settle' empty space in artifical homes? ???

My definition is about location, not gee forces.

If it proves true that 1 gee is essential for safe conception and birth (and that is a VERY real possibility IMHO) then the deployment of 1 gee habitats to places like Mars or L5-style free floating colonies would NOT deny spacefaring status to our species. Using simulated gravity is not different in principle from bringing a pressure vessel with sufficient oxygen to breathe.

Based on MY definition.

That medical finding would make settling space very much more difficult, yet the definition stays unchanged.

Supplement: If 1 gee is essential for conception and birth then free floating colonies might then be far easier than genuine settlements on planetary surfaces, yet Gerard O'Neill has called for that already.

Enyo · 2003-12-19 02:50:42

Politics will change anything designed to something less functional. We must work against this trend and educate people so they also fight it.
Rather than fighting, let's try to work co-operatively. The politicians control funding to the space agencies, and right now they are the only ones with funding to start space exploration or settlement. Let's get them to work with us, not fight against them.

Huh? I wasn't suggesting we fight anyone. The trend towards reduction of costs and reduction of functionality is the "it" to fight against. We want to educate the politicals and public against wasting energy in this way.

Mars will not make a profit for anyone unless they are really bright...

What Mars currently brings are data points beyond Earth in weather and possibly biology...

Enyo · 2003-12-19 03:08:30

I also want to reiterate that Mars Direct and its children are also not safe enough for regular manned flights. The artifical gravity scheme is dangerous and heavy, all that redundant cable you use is by no means light-weight, and astronauts will have to do more than walk when they get there; 90 days ought to be the target zero-G limit... and what if your cable doesn't break cleanly?
Dr. Zubrin also underestimates the harm caused by cosmic radiation, which will easily exceed safe dosage without shielding during transit, even without a solar flare. I suspect that he has convienantly shrugged off this hazard to make MD more apealing to Congress. A heavy-duty radiation shield will be needed, more than food/water can provide, which will risk chemical being dangerously overweight and awfully close to the zero-G limit for NTR engines.

Cable? What cable? Try Spectra (fishing line). The problem with a tether system is stopping it and restarting it nothing else.
Go check out:Tethers Unlimited for more tethers info.

I've talked with experts beyond Zubrin. Zubrin is not downplaying the radiation problem from cosmic rays and 10 centimeters of water is generally adequate to protect from most solar flares.

If we must shield from radiation and water is not used M2P2 possibly offers a high tech solution.M2P2 as a radiation shield (a PDF)

RobertDyck · 2003-12-19 13:51:05

Try Spectra (fishing line).

I may be guilty of spreading false information. When I worked at the Technology Center of Allied Signal Fibers in Colonial Heights, Virginia, one co-worker pointed out that SpiderWire brand fishing line is made there. He told me that SpiderWire is made from Spectra, which Allied Signal Fibers version of Kevlar. Since then Honeywell bought the Technology Center. Well, after doing some checking I found out SpiderWire is in fact made at the plant I worked in Virginia, and it's made of gel-spun polyethylene fibers. Spectra is high modulus polyethylene fiber, which I think is the same thing. The process for gel-spun polyethylene was originally developed for bulletproof vests. Kevlar is Poly (p-phenylene terephtalamide), which is in the aromatic polyamide (aramid) family. So Spectra and Kevlar are not the same thing. Spectra is more UV resistant, in fact it's as resistant as PET, and has a higher modulus. However, Spectra is slippery so it's difficult to weave into a fabric. It can be scoured in an acid bath to reduce the slipperiness so it can be woven, but it still has a problem with static load. Under static load the fibers tend to creap. That can be reduced with the acid bath treatment, but you still have to keep the static load low to prevent creap. Spectra is great for impact resistance, such as keeping out a bullet or holding a fish that is jerking the line.
References:
Maine Sailing Partners - Sail cloth, Polyester
Iowa State University - Technical Guide for KEVLAR Aramid Fiber
Spectra News
Spider Fishing

Shaun Barrett · 2003-12-19 19:16:56

I haven't looked into this in any detail but maybe someone here has(?).
As I understand it, the Mars Direct Hab weighs some 35 tonnes. Let's assume a situation where the outgoing Hab and spent booster are tethered by a cable some 1800 metres long and rotating around each other at 1 rpm to create 1g of artificial gravity. [I know this was never suggested by Zubrin or anyone else ... except maybe me! .. but it is an extreme case and gives us some upper limits.]
The cable has to take a strain of some 70 tonnes (plus a safety factor).
What thickness of kevlar will support that kind of strain and what will it mass in those quantities?
???

Enyo · 2003-12-19 23:56:46

Try Spectra (fishing line).
I may be guilty of spreading false information. When I worked at the Technology Center of Allied Signal Fibers in Colonial Heights, Virginia, one co-worker pointed out that SpiderWire brand fishing line is made there. He told me that SpiderWire is made from Spectra, which Allied Signal Fibers version of Kevlar. Since then Honeywell bought the Technology Center. Well, after doing some checking I found out SpiderWire is in fact made at the plant I worked in Virginia, and it's made of gel-spun polyethylene fibers. Spectra is high modulus polyethylene fiber, which I think is the same thing. The process for gel-spun polyethylene was originally developed for bulletproof vests. Kevlar is Poly (p-phenylene terephtalamide), which is in the aromatic polyamide (aramid) family. So Spectra and Kevlar are not the same thing. Spectra is more UV resistant, in fact it's as resistant as PET, and has a higher modulus. However, Spectra is slippery so it's difficult to weave into a fabric. It can be scoured in an acid bath to reduce the slipperiness so it can be woven, but it still has a problem with static load. Under static load the fibers tend to creap. That can be reduced with the acid bath treatment, but you still have to keep the static load low to prevent creap. Spectra is great for impact resistance, such as keeping out a bullet or holding a fish that is jerking the line.
References:
Maine Sailing Partners - Sail cloth, Polyester
Iowa State University - Technical Guide for KEVLAR Aramid Fiber
Spectra News
Spider Fishing

All very interesting...but your point was?

A comparison of Kevlar, Spectra and steel

Anyway Tethers Unlimited has used Spectra and find it easy to work with...

But which is used doesn't matter...it not a steel cable, it not heavy...

RobertDyck · 2003-12-20 00:06:43

All very interesting...but your point was?

Spectra is not Kevlar. Fishing line is not made of Kevlar. I'm not sure SpiderWire fishing line is Spectra.

RobertDyck · 2003-12-20 00:43:27

I haven't looked into this in any detail but maybe someone here has(?).
As I understand it, the Mars Direct Hab weighs some 35 tonnes. Let's assume a situation where the outgoing Hab and spent booster are tethered by a cable some 1800 metres long and rotating around each other at 1 rpm to create 1g of artificial gravity. [I know this was never suggested by Zubrin or anyone else ... except maybe me! .. but it is an extreme case and gives us some upper limits.]
The cable has to take a strain of some 70 tonnes (plus a safety factor).
What thickness of kevlar will support that kind of strain and what will it mass in those quantities?
???

Krypton brand ropes use either Kevlar or Spectra. Krypton-K Double Braid uses a Kevlar core with polyester cover. A 3/4" diameter rope has a tensile strength of 33,000 pounds and critical temperature of 350?F; weight for 100' roll is 17.1 pounds. Krypton-S Double Braid uses Spectra core with polyester cover. A 3/4" diameter rope has tensile strength of 30,000 pounds and critical temperature of 150?F; weight for 100' roll is 16.2 pounds.

Safety factor is usually quite high. It's often 4 times, which means the rope can withstand a jerk of 4 times the normal load. 4 * 70 tonnes = 617,294 pounds. To that requires 18.7 lengths of Krypton-K @ 3/4", or a rope with 18.7 times the cross-section area. Rather than try to estimate the weight saving from a single polyester cover, let's just multiply 17.1 pounds by 18.7, then multiply by 59.055 to increase from 100' to 1800 metres. The result is 18,890 pounds or 2.68 tonnes.

Shaun Barrett · 2003-12-20 02:13:16

Thanks, Robert, for coming up with all the relevant detail!
I was just going to celebrate the relatively low figure of 2.68 tonnes when I suddenly thought '18,890 lbs ... 2.68 tonnes ... hmmm! That doesn't sound right.'
Everything looked great up to that point but, tragically, 18,890 lbs is over 8.5 tonnes!! (Don't worry about the last minute slip, I do it all the time.)

What's important is the unpleasantly large mass of cable for a full 1g. Unless we have very capable boosters for this mission and perhaps a more generous budget, I can imagine a lot of people getting very upset over what they might see as an awful lot of mass to provide the unnecessary luxury of a full Earth gravity.
Assuming any attempt at all is made to provide artificial gravity, we need to either aim for a lower figure (Mars gravity has been a popular suggestion) or come up with a more efficient cable.
Does anyone know whether there is any hint of a new material being developed, with a higher tensile-strength-to-mass ratio, apart from carbon nanotubes (cnts) I mean?

Or should we just be waiting for Hi-lift to sponsor cnts as part of their quest for a space elevator, and then just 'borrow' the technology?! Presumably they'll have a viable cnt material in their inventory within 10 years and that should fit in with a Mars Direct timetable fairly well.
I have no figures at all but I can imagine a suitable cnt cable for a 1g rotation of the Mars Hab coming in at a helluva lot less than 8.5 tonnes!

Enyo · 2003-12-20 02:59:18

All very interesting...but your point was?
Spectra is not Kevlar. Fishing line is not made of Kevlar. I'm not sure SpiderWire fishing line is Spectra.

Where did I say Spectra was Kevlar?

I've bought Spectra fishing line to catch fish with. Spectra is used to make tethers. I was talking about tethers.

Spectra fiber for fishing line

RobertDyck · 2003-12-20 08:47:58

All very interesting...but your point was?
Spectra is not Kevlar. Fishing line is not made of Kevlar. I'm not sure SpiderWire fishing line is Spectra.
Where did I say Spectra was Kevlar?
I've bought Spectra fishing line to catch fish with. Spectra is used to make tethers. I was talking about tethers.

Ok, I thought I mentioned using Spectra for tethers once upon a time, and mentioned it is fishing line. I also made the mistake at that time of repeating my co-workers statement that Spectra is Kevlar. If you came up with the idea independently of using Spectra, then my correction is unnecessary and irrelevant. Sorry.

RobertDyck · 2003-12-20 09:11:25

I was just going to celebrate the relatively low figure of 2.68 tonnes when I suddenly thought '18,890 lbs ... 2.68 tonnes ... hmmm! That doesn't sound right.'

Ack! I must have cut-and-paste wrong into the unit converter. I use MegaConverter to convert units such as pounds to tonnes. Oh well, thanks for catching the error.

There are a couple things you can do to reduce the mass. First, instead of multiplying the tensile strength by 4 to deal with bouncing and jerking, get the impact strength of the rope and ensure that can handle the weight. Multiplying the mass by 4 means it can handle a jerk with a 4G acceleration; that is 4 times Earth's gravity. As I mentioned before, the static load and impact strength of Kevlar and Spectra are different. If you just look at the tensile strength to mass ratio of the Krypton ropes, Kevlar appears better; the difference between static load and impact strength may change that. You only need sufficient static load for the 70 tonne mass multiplied by acceleration (1G in this case), and add a small safety factor in case your centripetal acceleration isn't precise; say 10%. Dupont's web page for Kevlar is just sales stuff; unlike their pages for Teflon, it doesn't have technical data. So at this point I don't know static load vs. impact strength.

Another thing you could do to reduce mass is reducing the length. If the astronauts could withstand the coriolis forces without getting dizzy, you could reduce the cable length and increase rotation rate to maintain acceleration.

Shaun Barrett · 2003-12-20 18:25:53

All good points! Thanks again Robert.

All this talk may well be moot, of course, since many people are of the opinion that astronauts can withstand zero-g for 6 months and then perform adequately on Mars (0.38g) for 18 months.
I believe that's probably quite correct, as far as it goes. But then, I look further, at another 6 months in zero-g before a return to full Earth gravity at the end of the mission.
I honestly don't think the astronauts will be able to make the transition back to terrestrial gravity safely after an absence of two and a half years. At least, not without advances in our understanding of human physiology and the development of appropriate medicinal prophylaxis.

I happen to think the mastery of the use of 'tethered-gravity' will be no more difficult to achieve than orbital rendezvous techniques were. Where there's a will ... !
If a suitably low-mass system can be devised, I favour tethered-gravity on both the outward and homeward bound legs of the journey. It was suggested here last year some time that the astronauts could be acclimatised to Martian gravity by slowing the rotation rate in the final stages of the outbound trip. And, conversely, they could be acclimatised gradually to a full 1g during the 6 month flight home by increasing the rotation rate. I believe this is the ideal scenario.

You know, Robert, with your skills and determination, devising a tethered-gravity system might be a way for you to break into the aerospace business. It looks like a doable project which could be approached in a staged and systematic way, so as not to become unwieldy from a financial perspective. Much of the research could be accomplished before any significant expenditures were required and, basically, it's just a mechanical problem that needs fleshing out and refining. The beauty of it, from your point of view, is that nobody else seems to be doing anything with the idea.

Imagine the 'RDyck-Tether-System' becoming standard equipment on crewed Mars missions in the next few decades!!
I, for one, would love to see that happen.

RobS · 2003-12-20 22:14:01

Zubrin's Case for Mars, page 123, says that NASA did experiments in the 1960s and concluded that people could adjust to living in structures rotating at rates as high as 6 rpm. This appears to be the science (assuming the information is correct). Everything else about Coriolis appears to be emotion. As I noted in another posting, sailors have adjusted to living on tiny boats in cramped quarters for months at a time, sometimes in seas with 20 foot waves. This makes living in a tuna can coasting from Earth to Mars, rotating at a couple rpm, to look like a piece of cake. So is everyone advocating spending lots of bucks because they're landlubbers who don't like the idea of coriolis?

The radius of rotation for Mars gravity is: 345 meters for 1 rpm; 86 meters for 2 rpm; 22 meters for 4 rpm; 10 meters for 6 rpm. Why make the tether longer than 22 meters, or maybe about 50 meters for 3 rpm? Or think of it this way: use an 86 meter tether on the return flight, start at 2 rpm, and gradually speed up the rotation to 6 rpm to make earth gravity.

-- RobS

Shaun Barrett · 2003-12-21 02:59:51

Hi RobS!
O.K., O.K. ... So I'm a landlubber, scared of Coriolis effects!
:laugh:

I remember reading somewhere that, while 6 rpm is feasible, 4 rpm is a more realistic limit for most people as far as tolerance of the quite disconcerting Coriolis effects is concerned. Maybe I'm wrong, I don't know.
But, at least on the way to Mars, and even though the crew may have adapted perfectly to either 4 or 6 rpm rotation rates, I have expressed worries about how quickly they might de-adapt. The gist of my argument was only to raise the question of how fast the astronauts would regain their equilibrium after 6 months of rotation. After all, a manoeuvre such as aerobraking into martian orbit may require an A-1-normal vestibular reflex condition and hand-eye coordination. (I'm willing to be proven wrong on any or all of this, by the way. I may well be exaggerating the potential difficulties.)
On the way home, it may not be as critical that the astronauts' inner ear function and coordination are perfect, since they will be closer to home and closer to help when they attempt their orbital manoeuvres. (In this case I'm probably underestimating the dangers rather than overestimating them! )
In any case, may I assume that you favour the tethered-gravity concept for both legs of the journey, or are you simply playing the devil's advocate?

[A couple of very minor points regarding the figures you present, which may be important to Robert Dyck whom I'm trying to persuade to enter the crewed Mars mission infrastructure market (! ), am I right in thinking you're confusing radii with diameters? For martian gravity at 4 rpm, won't Robert need some 44 m of cable for his patented system, depending on the mass of the counterweight?
The 86 m radius cable at 2 rpm will give you a very close approximation to martian gravity as you leave Mars, but this means you'll need some 172 metres of it between the ERV and the counterweight (again depending on the counterweight's mass). And, at a radius of 86 m, increasing the rotation rate to 6 rpm will produce well over 3g! ... It's not a linear relationship.]

Rxke · 2003-12-21 04:02:44

... worries about how quickly they might de-adapt. After all, a manoeuvre such as aerobraking into martian orbit may require an A-1-normal vestibular reflex condition and hand-eye coordination.

De- adapting could be a problem... But not for aerobreaking, etc. As much as we like the mental picture of a 'hot' space-pilot, doing incredible manoevring, it all should be totally automatic. Of course if things go totally SNAFU, there would be some manuall-override capabilities, but i don't think humans are capable to do all that high-precision stuff. The real steerin must be done with computers, some button-pushing by astronauts should be good to give them at least the morale-boosting impression they make a difference, but that'd be merely symbolical.

De-adapting on the surface, OTOH... imagine that all of a sudden you have to de-adapt AND put on your heavy suit, climb off a rickety ladder, and negociate a rock strewn plain... That could be one small stumble for a man, a giant circus for mankind... :laugh:

RobS · 2003-12-21 08:27:12

Shaun, fascinating questions! Research is needed to determine whether people adjust back easily. That' didn't occur to me. Yes, the distances I gave are radii, so the distance to a tethered counterweight would have to be the diameter. I didn't realize the relationship between rotation rate and gravity wasn't linear; thanks for that.

As for my personal thoughts about weightless versus rotational gravity, I think it still largely falls in the realm of personal judgment. The science is not adequate to settle the matter, I think. But Zubrin's judgment strikes me as important. Mars Direct is intentionally as lean a mission as is practical and safe. Some here feel it is too lean and unsafe, in fact. NASA favors weightlessness. I don't think Zubrin would have added the mass for making rotation possible unless he felt it was unavoidable. And his judgment is more informed than mine.

-- RobS

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