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#51 2012-04-09 03:16:31

Russel
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Registered: 2012-03-30
Posts: 139

Re: Landing on Mars

Where would be the place to discuss general ideas about mars mission concepts? As in a clean sheet of paper type discussion, not talking about Mars direct etc etc.. ?

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#52 2012-04-09 05:45:21

louis
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From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Landing on Mars

Russel wrote:

Where would be the place to discuss general ideas about mars mission concepts? As in a clean sheet of paper type discussion, not talking about Mars direct etc etc.. ?

I suppose it's here...you need to start a new thread I guess. Why not start a thread: "Clean Sheet Discussion of Mars Mission concepts".

Most threads under this heading quickly evolve into general discussions as people come at it from different angles. I favour Space X technology, orbital assembly, lots of pre-landing robot supply missions, no artificial gravity, retro rocekt entry with a small human lander, immediate industrial and agricultural infrastructure with ISRU... there are so many variations!

One big divide I think is between those who are thinking of an isolated mission and those who want permanent settlement from the get-go. I favour the latter: if you can do one mission you can do two back to back and begin the permanent settlement of Mars.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#53 2012-04-09 06:50:20

Russel
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Re: Landing on Mars

Ok well I'll just go off in all directions smile

I like Space X. So far they've done pretty good work. Remains to be seen how successful they will be commercially and that's important if they're keen to go any further. I'm still searching for more details on some of their stuff - especially the capabilities of the super-draco.

I like orbital assembly. It surprises me how much people shy away from it, considering we've now got a wealth of experience with the space station. In particular I dream of some things you just can't launch direct - large heat shields - large solar arrays and so on.

Lots of things done robotically.. sure.

Don't have a problem with aritifical gravity. Its not that hard to put a spin on things.

I'm not entirely convinced of the merits of trialing stuff that's really about colonisation. Exploration is one thing, but I personally think the human race needs to get a bit more civilised before we go messing up other planets.

As far as missions go, if you take a step back and try to see the thought-process involved, its sometimes easy to see a pattern. Certain paths being taken. Certain principles being emphasised over others. What I don't see is enough attention to mindless detail - enough trial and error of random ideas.

For instance. In situ propellant. On the surface sounds like a good idea. In practice, you just need to send a test mission without humans first. Does that rank against the fuel saving? Not sure here.

For instance. If you take in situ propellant production for granted, where do you produce it? Where do you refuel, and what?

I'll give you a concrete example. Lets suppose that space-faring vehicle (the space hab as some call it) hangs out in Mars orbit. But the propulsion is logically a separate issue. Ok then. How about this. You land first a propellant lab. Could be a rover in its own right. Could be nuclear. Could be solar. Doesn't matter for the purpose. Ok, next thing is the propulsion unit that gets you back home. Somewhere in the process the propulsion unit mates with the lab and gets fueled. Its all done robotically. Next the propulsion unit takes off for Mars orbit and sits there waiting.

So you could work a mission rather like this.

Everything you'd expect gets landed on Mars.. habitat.. ISPP.. propulsion unit. Propulsion unit takes on fuel, goes into orbit. All systems check out.

Skipping over the details, the humans launch, fly to Mars, leave a space hab in orbit, that robotically docks with the propulsion stage. On Mars their capsule refuels using the same propellant lab.

Anyhow, I left out a lot of details. I'm just posing this to point out the many permutations that I don't think have been considered yet.

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#54 2012-04-09 14:40:20

louis
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From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Landing on Mars

Russel wrote:

Ok well I'll just go off in all directions smile

Don't have a problem with aritifical gravity. Its not that hard to put a spin on things.

Hmmm...excuse my scepticism on that one. If AG is so easy to achieved, why hasn't it been done, especially for the space station where people spend such extended time in space? 
The benefits of AG are clear, but I am not convinced that it is cost effective, especially if we are travelling to a planet with substantial gravity, where we can supplement that gravity with strategically placed body weights (on the main joints, head and shoulders.

Russel wrote:

   I'm not entirely convinced of the merits of trialing stuff that's really about colonisation. Exploration is one thing, but I personally think the human race needs to get a bit more civilised before we go messing up other planets. .

I think the argument for a "sufficiency first" strategy is that then everything else you want: exploration, science and so on follow on. 

It's a bit precious to start talking about "messing up other planets". If there were complex ecosystem on Mars then I agree we would have an ethical responsibility not to destroy it. But as far as we know all there is dirt and ice.  Besides, we have to go there to find out if there are any ecosystems there. 

There are billions of planets in the cosmos. We've got to start somewhere, learning about how to live on other planets. Now is the time to go because now we have the technology. For me this is an existential challenge which we should rise to.

Had we had a sufficiency first strategy on the moon,  we might well have permanent bases their now which would have yielded huge scientific advances.


Russel wrote:

 

As far as missions go, if you take a step back and try to see the thought-process involved, its sometimes easy to see a pattern. Certain paths being taken. Certain principles being emphasised over others. What I don't see is enough attention to mindless detail - enough trial and error of random ideas.

For instance. In situ propellant. On the surface sounds like a good idea. In practice, you just need to send a test mission without humans first. Does that rank against the fuel saving? Not sure here.

For instance. If you take in situ propellant production for granted, where do you produce it? Where do you refuel, and what?

I'll give you a concrete example. Lets suppose that space-faring vehicle (the space hab as some call it) hangs out in Mars orbit. But the propulsion is logically a separate issue. Ok then. How about this. You land first a propellant lab. Could be a rover in its own right. Could be nuclear. Could be solar. Doesn't matter for the purpose. Ok, next thing is the propulsion unit that gets you back home. Somewhere in the process the propulsion unit mates with the lab and gets fueled. Its all done robotically. Next the propulsion unit takes off for Mars orbit and sits there waiting.

So you could work a mission rather like this.

Everything you'd expect gets landed on Mars.. habitat.. ISPP.. propulsion unit. Propulsion unit takes on fuel, goes into orbit. All systems check out.

Skipping over the details, the humans launch, fly to Mars, leave a space hab in orbit, that robotically docks with the propulsion stage. On Mars their capsule refuels using the same propellant lab.

Anyhow, I left out a lot of details. I'm just posing this to point out the many permutations that I don't think have been considered yet.

Yes, there are a lot of permutations. One thing I would say in defence of my own approach: the smaller you make the lander/ascent vehicle (the more like the Apollo lander), the less propellant you have to use, the less propellant you have to make or take.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#55 2012-04-09 15:31:36

RobS
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Re: Landing on Mars

I think there are good reasons why we don't have centrifugal gravity for the International Space Station. Things have to dock with it, and often, and there have to be several docking ports. Furthermore, to spin the place, the masses have to be balanced. Finally, you can't do zero-gee research if ISS is spinning, and no one yet knows how to build a station part of which is spinning and part od which isn't. One engineering requirement of ISS is a minimum of vibration, and it part isn't spinning there will always be vibration.

A 3-day moon flight doesn't need gee.

A 6-month flight to Mars probably would benefit from gee, though. The crew won't have an adjustment period on the surface before they can work. And since nothing has to dock to the vehicle while in transit to Mars, and it isn't performing zero-gee research, I can't think of reasons it shouldn't be spun. The spinning won't prevent communications or mid-course corrections.

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#56 2012-04-09 20:18:48

Russel
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Re: Landing on Mars

I concur with RobS. The ISS has a bunch of things that don't like spin - including I might add the solar power system.

What I don't know about journeys that last (say) 6 months, is exactly how *much* AG you need. Personally I'd just love to have at least a little - enough to stop things floating around. But the really interesting science is whether or not you need it over the whole trip, or whether its good enough to ramp it up over the last week or so before you land.

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#57 2012-04-09 21:02:43

RobS
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Re: Landing on Mars

Bones need more artificial g than toilets, you might say! But maybe enough for toilets, cooking food in ordinary ways, and other routine tasks is all you need. Right now we know very little about the entire matter. We don't even know how many revolutions per minute are too much for human health. My guess, for what it is worth, is that if people can adapt to living on pitching ships without getting seasick, they can adapt to rotating habitats.

The other issue is that any vehicle designed for artificial g also has to be designed for weightlessness, because there will be times when there won't be any gravity. So you will always need a zero-gravity toilet, even on a hab designed for rotation. And in a way that's the strongest argument against artificial gravity; it requires that everything be designed to work in two very different modes.

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#58 2012-04-09 21:45:01

Russel
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Re: Landing on Mars

Ok, how about this for a bit more detail.

The return vehicle comes in 3 main parts. The space-hab itself - nothing special, its just a tin can with everything you'd expect including shielding. Then you have a propulsion module sufficient to the task of getting the space-hab and landing capsule back to Earth. Again, nothing special, and you're talking circa 40 tons of propellant. Third is a landing/ascent module - which is actually a larger and more capable rocket in its own right.

The propulsion module dovetails into the landing/ascent module. They share a heat shield and other EDL gear.

Initially you have an unmanned flight. You've got the space-hab, propulsion module and landing/ascent module mated. They arrive at mars and aerocapture into orbit The landing/ascent and propulsion module then undock and head for a landing. Somewhere you've managed to store the necessary seed hydrogen.

The propulsion module and landing/ascent module land near to the ISPP unit and (probably over time) tank up. Then the landing/ascent module carries the propulsion module into orbit. The propulsion module docks with the space hab and together the return vehicle sits there waiting as a back up. The landing/ascent module could sit around in orbit waiting for reuse. I'm going to assume that for now.

Now we're ready for humans. They turn up in another space hab. Which brings with it another propulsion module (which is handy because you need one to get there). And of course the landing capsule. The landing capsule splits off and heads for a landing. The space hab together with the propulsion module aerocapture as before. Then the space hab (you've got plenty of time here) undocks from the propulsion module. The propulsion module docks with the landing/ascent module that happened to be hanging around from the last flight, and the cycle repeats. They go down to pick up fuel, return, reassemble. All done robotically.

When the humans leave they pick up the original return vehicle, leaving a new one ready and waiting.

Point is at no stage are you left without a plan B. There's a fully fueled and ready return craft in orbit around Mars at all times. There's also an abort to surface option. And you get the most reuse out of every part (until things wear out). For instance the space-hab can aerocapture into earth orbit, refurbish, restock. So too does the propulsion module - assuming its worth mucking around with refueling in earth orbit. And of course the landing/ascent module could last you through a number of missions.

Of course you're now going to be looking for a ISPP unit that's capable beyond one mission too.

One other detail I left out. You also need to figure out how to give the landing capsule enough tankage to get it back into mars orbit. You could in theory time it right and lift it onto the landing/ascent module but I'd rather the freedom to take off at any time.

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#59 2012-04-10 08:54:33

GW Johnson
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Re: Landing on Mars

As regards artificial gravity,  I think you'll find we actually do have some idea of what spin rates are tolerable.  Aircraft and early astronautic work defined it.  That boundary is a bit fuzzy,  but 4 rpm seems to be a good rule of thumb for a top rotation rate. 

What we don't know is how much gee is enough.  That research has never been done,  and I for one do not trust people's lives and health to surrogate studies like enforced bed rest.  It's just not the same. 

Our only direct experiences are at 1 gee and zero gee,  with the result that in zero gee bad things start happening to the body that cannot really be reversed,  after somewhere in the vicinity of a year.  Again,  a fuzzy boundary. 

Most missions to Mars involve a one-way transit time of 6-9 months,  plus some extended stay on the surface.  Total mission times are around 2 years.  Mars has 0.38 gee,  but we have no data whether that's "enough gee",  precisely because those studies were never done in a spinning lab in LEO. 

So,  it looks to me like it's one full gee at no more than 4 rpm.  Period.

That's a 56 meter radius.  If you build the vehicle long and narrow and put the habitat on one end,  you can just spin it end-over-end for gee.  De-spin for maneuvers.  Easy.  No battlestar-galactica,  no extended space truss structures,  no complicated cable-connected anything. 

Think around a dozen-and-a-half to two-dozen docked 30-50 ton modules,  mostly propellant tanks,  each one around 5 m diameter and 15-20 meter long,  or something in that vicinity.  1 full gee at way under 4 rpm.  I'd put a Skylab-like module up there for 6 folks,  at one end,  and a NERVA-type nuclear rocket on the other.  (We know how to build those engines,  by the way.  They all but flew 4 decades ago.)

The "Skylab" could be 3 or 4 inflatables docked together.  Just provide lots of open space inside,  in which to live sanely for several months at a time. 

Don't count on ISRU return propellant on the first trip,  it's an untried technology as yet.  Losing a crew is simply more "expensive" than carrying the return propellant with you.  It is crucial to design-in a "way out" for the crew at every single phase.  These people must return alive if there is ever to be another trip. 

You can send the landers and their propellants and surface supplies separately,  and then rendezvous in LMO with it when you get there.  It's the surest way,  one we already know works.  "KISS" is how to ensure it all works. 

So,  we're looking at assembly of a small "fleet" in LEO.  We know how to do that,  we built the ISS that way.

Once you're in the shuttle payload range of 25+ tons,  it no longer really matters very much what the module size is.  What matters is cost per kg delivered to LEO.  With Falcon-Heavy up to 53 tons priced at about $2000/kg,  what do we need with a big,  expensive government rocket development anymore?

Just thinking out loud,  and trying to raise some very pertinent questions.....

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#60 2012-04-10 10:20:43

Russel
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Registered: 2012-03-30
Posts: 139

Re: Landing on Mars

One point about AG is that whilst on Mars you're stuck with .38 of a G and there's really only one way to find out what that will do to a human.

Given that, I suspect that its really a case of that's what you've got so that's what you'll have to adapt to.

I also suspect that after 2 years on Mars you're probably not going to cope too well with going directly back into 1G. So it would be handy to gradually increase over time.

Btw, I did some rough calculations on the above scenario. Turns out you could get away with the 130-160 ton IMLEO for the space hab, and return vehicle - the stuff you have to directly launch with your crew.

In situ propellant production makes a big difference, but its a real pain in terms of the fine details - the plumbing and procedure.

Turns out that by the time you launch a ascent/descent vehicle - purely a fuel ferry from the surface of Mars, you're talking around 130 tonnes on the surface of Mars before launch. Ouch. Still its cheap.

On the point about cheaper launch costs, you're quite correct. Two things.

One is that with launch costs down at $2,000 a Kg or less, another hundred tonnes or so, whilst that might seem like a lot of money, is cheap compared to development costs and risks. Meaning, I'm still quite happy with strapping on a shitload of tanks and flying there and back (well to orbit anyhow) without messing with ISPP.

Having said this, where I'm comfortable with ISPP is like in the scenario I gave above, where you have a fully fueled and ready return vehicle waiting in orbit around Mars even before you send anyone out there.

Two is that if you're free to throw another hundred million at another 50 tons into low earth orbit, then my attitude is do it with style! Make the shielding right. Take your extra rovers and your fluffy toys too.

Many times I've approached this problem and always come up against that trade-off between re-use and elegance and safety. The above scenario is close to what I feel is a pretty good idea - though I'm not sure about the fine details - in particular about slowing down something the wrong side of 10 tonnes.

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#61 2012-04-10 12:47:26

RobS
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Re: Landing on Mars

Regarding Martian gravity: At my height, I should weigh about 175 and I have been as high as 235. I suspect I could get my weight down to 140 and be healthy. So my bones can handle a wide range of weight.

If I weighed 175 on Earth and went to Mars, I'd weigh 70 pounds. If I walked around 8 hours a day with 70 pounds of lead in my pockets--not difficult to do--my bones would feel 140 pounds of weight and I'd be getting some good exercise. If I wanted more exercise, a pogo stick would do it; as long as one is jumping up and down, Martian gravity is plenty to stress your bones (you might jump three times as high, but the vertical stress on your bones would be the same as on Earth). Basketball would probably be a great form of exercise on Mars. (Can someone please figure out how high the basket would need to be, though?)

So my intuition or guess is that Martian gravity would be plenty. Lunar gravity may be fine, too, but I'd have to carry a lot more lead in my pockets and the exercise areas would need really high ceilings!

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#62 2012-04-10 13:19:01

RobS
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Re: Landing on Mars

GW Johnson: It's fun to figure out ways to get people to Mars, isn't it? And there are a thousand ways to do it.

The space-hab itself - I wouldn't make it from a "tin can" but an inflatable. I think Zubrin's Falcon Semi-Direct plan is quite useful this way: send the crew in the return capsule, which can also serve as the aerobrake and the solar storm shelter, and use an inflatable for interplanetary cruise. If the capsule is large enough (say, 5 to 10 cubic meters per passenger) it can serve as a work area, can have the galley and waste treatment, and would have plenty of room for storage of equipment and consumables. The inflatable would provide two things: large public spaces and fairly small private spaces. Neither requires much mass, either; a lounge requires chairs and screens, maybe a table; an exercise area requires a treatmill or elliptical; either space could be used for handball or pingpong, perhaps; private cabins need a bed, desk, clothing storage, a screen, maybe a porthole. I am not as optimistic as Zubrin that the inflatable could be stored during aerobraking, but if it weighs a few hundred kilograms, as he says, one could haul two along.

"The propulsion module and landing/ascent module land near to the ISPP unit": I wouldn't separate these things. Zubrin says the in-situ pripellant plant would mass only 500 kilograms, so for the first two or three missions, every lander would carry its own. That way you'd have back up as well.

"Then the landing/ascent module carries the propulsion module into orbit": This is another important question to settle. From a high elliptical orbit around Mars, every tonne of payload needs about a third to half a tonne of fuel for trans-Earth injection. So if you are pushing a 15-tonne hab back to Earth from that orbit, it needs 5 to 8 tonnes of methane and oxygen (I don't recall exactly the amount at the moment, and it depends on the orbit, anyway). Not too much, actually, to haul from Earth. But if you want to get 5 tonnes of propellant into that orbit from the Martian surface, you need about four times as much propellant; 20 tonnes to get the 5 tonnes into such a high orbit around Mars. Do you want to haul the 5 tonnes from Earth, or build a bigger ISP plant, haul more solar panels and more hydrogen to the Martian surface, and lift the extra mass to orbit from Mars? For your third or fourth mission, you'd want to send it from Mars; your transportation system should be well developed by then, you'd have plenty of solar panels, and you would probably have a local hydrogen source (water). But do you want to launch it from Mars for the first mission? Maybe or maybe not.

"The propulsion module docks with the landing/ascent module that happened to be hanging around from the last flight, and the cycle repeats. They go down to pick up fuel, return, reassemble. All done robotically": I'm not sure we need to do anything in this sentence robotically. A simple transportation system just needs a docking to work.  But we may need robotic efforts to deploy solar panels. I suspect one can set up a system that will self-deploy using compressed Martian air.

"Point is at no stage are you left without a plan B. There's a fully fueled and ready return craft in orbit around Mars at all times. There's also an abort to surface option.": Yes, ideally you always want this.

"And you get the most reuse out of every part (until things wear out). For instance the space-hab can aerocapture into earth orbit, refurbish, restock. So too does the propulsion module - assuming its worth mucking around with refueling in earth orbit. And of course the landing/ascent module could last you through a number of missions.": This seems to be what Musk plans to do. If he can develop a system to reuse stages from low Earth orbit back to the earth' s surface, he may be able to do the same with Mars.

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#63 2012-04-10 14:18:21

louis
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Registered: 2008-03-24
Posts: 7,208

Re: Landing on Mars

Russel wrote:

Turns out that by the time you launch a ascent/descent vehicle - purely a fuel ferry from the surface of Mars, you're talking around 130 tonnes on the surface of Mars before launch. Ouch. Still its cheap..

Not sure what you are talking about here - are you talking about how much mass needs to be landed in order to be able to launch an ascent to LMO vehicle from the Mars surface? Can you break down the 130 tonnes for us?  I think Apollo got off the surface of the moon with about 10 tonnes mass.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#64 2012-04-10 19:20:16

Russel
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Re: Landing on Mars

louis, sorry, that wasn't clearly expressed.

What I meant was this. If you're flying home from Mars orbit you need roughly as much mass in fuel as the mass you're trying to get home. So I figured around 30 tonnes of fuel.

Now to get that fuel from the surface of Mars to orbit, you need even more fuel. In that case with a DV of 4.1 and methane/lox you're now adding twice your mass in fuel.

Add to that the ascent stage itself, leave it with enough fuel to return to surface, and add margins, and you're talking about 130 tonnes of vehicle launching from the Mars surface.

Mind you, nearly all of that mass is essentially free.

Btw, the thing that is annoying me is the sheer size of the hydrogen tank.

I'm well aware that you can cut this down by shaving mass of the space-hab. As I said before though, the minimum mass would be set by shielding requirements so I doubt you'd get that below 20 tonnes.. unless you did something real clever.. used fuel tanks for shielding.. and took some risks. You've still got the mass of the return capsule and other junk.

Oh and an aside. Since your largest threat is one off events - solar storms - I wonder if anyone's looked into taking the obvious cheat. Putting more shielding in one direction.

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#65 2012-04-10 19:35:42

Russel
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Re: Landing on Mars

I'm not that familiar with how people propose to actually make inflatables work. And whatever you build it is by its nature going to provide little shielding to the background. That's why I'm more comfortable with that sort of thing in LEO and on Mars itself.

A tin can wouldn't just be the usual aluminium alloy shell. You'd probably want to build it in layers using polyethylene composite and then a conventional outer layer. And that's just for a start.

And you'd still need a storm shelter and yes all the usual ideas apply, including surrounding yourself with whatever mass you have on hand. Personally I'd like a couple of metres of stuff between me and the outside world - even if its arranged more in one direction. I'd also give some thought to using the external structure and even the heat shields as part of the picture - even to the extent of the whole arrangement looking ugly. Remember also that radiation shielding has to be done as a layered defense - the integrity of the outer layer still counts.

So yeah.. I'm still skeptical of inflatables. To my mind some of this is a response to people backing away from thinking about roomy structures because they are either obsessed with launching it direct from the surface of Earth, and thus are limited to a fairing, or else are too intent on saving the last bucket of kerosene.

Personally, I could cope with a capsule hotel type space provided they promised me that that meant getting me there (and getting me out of a hostile radiation environment) as fast as possible.

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#66 2012-04-10 19:57:34

Russel
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Re: Landing on Mars

"I wouldn't separate these things." (referring to the landing/ascent module and the propulsion module)

Yes, I did that for clarity. Actually there's a bunch of spins on this, including issues of which tanks go where. I'm still pondering it. You've essentially got two masses you don't really want to carry back and forth from Earth to Mars and back on every trip.

One is the landing structure. The other is extra engines you need purely for ascent from Mars. In orbit you don't need nearly as much thrust.

The answer to the former might mean more space junk - well more Mars junk. Meaning the landing structure stays there along all the EDL gear. Its just that well, you know how much junk ends up Everest and how expensive it is to do garbage patrol there.. on Mars?

If you can engineer an engine that has 500KN of thrust and it doesn't weight more than a tonne then you're doing fine.

The fun part is that if you have an engine that can get 130 tonnes off the surface of Mars, and then you attach it to something much lighter in orbit, you're in for a serious "get us the hell outa here" experience smile

And this is the thing that intrigues me. The talk is SpaceX has got its super draco to do 67KN. Now what I don't get is, does that make sense in terms of the nozzle size - would something like that fit under the skin of a dragon without sticking out too much? Obviously someone knows something I don't (grumble).

And then there's that damned hydrogen tank - which roughly would be the same volume as your methane and oxygen tanks put together (yes, even seed hydrogen)

So, here's one permutation.

You've got yourself a propulsion/landing/descent module all in one. So I'll just call it a propulsion module.

It sets out from Earth as a package, complete with hydrogen tank (ick) and its own EDL gear. The whole darn thing descends to Mars surface, fuels up, takes off - but ditches the hydrogen tank, the shield, the legs etc. It goes and finds a space hab, attaches and there you go.

As for integrating the propellant processor. OK, my thinking is that real unsolved problem is the power source. A nuclear source isn't going to be light so you really want to leave it on the ground, and you probably want to give it wheels, so its safely out of the way most of the time. A solar source could work - but you'd end up with maintenance issues with solar carpets. Again, probably heavier than the actual propellant lab itself.

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#67 2012-04-10 20:20:17

SpaceNut
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Re: Landing on Mars

Russel wrote:

Where would be the place to discuss general ideas about mars mission concepts? As in a clean sheet of paper type discussion, not talking about Mars direct etc etc.. ?

You could also visit the MarsDrive Human mission planning design group as they would like the help http://tech.groups.yahoo.com/group/marsdrivemission/

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#68 2012-04-10 20:25:35

SpaceNut
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Re: Landing on Mars

Russel wrote:

Ok well I'll just go off in all directions smile

I like orbital assembly. It surprises me how much people shy away from it, considering we've now got a wealth of experience with the space station. In particular I dream of some things you just can't launch direct - large heat shields - large solar arrays and so on.

Sure putting up smaller piece makes it easier to use existing launch capability but that also adds complexity to each piece depending on wait state time to mating to the next piece as well as for more dead weigh being needed to couple the stages, more fuel plus thrusters or engines, power supply parts in either solar or batteries ect....

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#69 2012-04-10 20:35:02

SpaceNut
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Re: Landing on Mars

RobS I would tend to make the Mars surface habitat an inflatable as that would reduce the mass would be about 30% less aiding for a lower heatshield heating and smaller size for decelleration...The in space habitat can be smaller if it is linked to the ERV as that makes it a shared space area and because it is in orbit before reuse I favor a tin can for its purpose...

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#70 2012-04-11 10:14:11

Russel
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Registered: 2012-03-30
Posts: 139

Re: Landing on Mars

"Sure putting up smaller piece makes it easier to use existing launch capability but that also adds complexity to each piece depending on wait state time to mating to the next piece as well as for more dead weigh being needed to couple the stages, more fuel plus thrusters or engines, power supply parts in either solar or batteries ect...."

I think the answer to that is to use in orbit assembly judiciously. And to be clever with the way things self assemble. There's really only a few things that present a real challenge.. I'll go through those.

If its a space hab, it can launch from Earth, and simply dock in orbit.

Likewise the pieces for a propulsion vehicle don't in and of themselves have to be particularly large - at least in diameter. 

Similarly for various other things that can be launched direct.

The two main things I have an eye on are these:

1. Big heat shields. I think these will become inevitable. And lend themselves to an assembly line of sorts.

2. Mars habitat itself.

Btw, if you design a mars habitat to integrate with (structurally) and sit on top of a large heat shield (40m dia) then you suddenly have lots of design freedom (you can even throw in a central inflatable space). And you can do it on one level, and by its nature (since you have to assemble it in orbit) its compartmentalized.

Last edited by Russel (2012-04-11 10:30:19)

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#71 2012-04-11 10:16:32

Russel
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Registered: 2012-03-30
Posts: 139

Re: Landing on Mars

Thanks for the suggestion about marsdrive. I'll lurk a little there.

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#72 2012-04-11 12:33:41

RobS
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From: South Bend, IN
Registered: 2002-01-15
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Re: Landing on Mars

Regarding the issue of radiation, you can't protect against cosmic rays without meters of stuff, and that's way too much for any time soon. Putting the crew next to the fuel tank will help, at least. Solar storms, when they hit, produce anisotropic radiation; in other words, the radiation comes from lots of directions, not just from the sunward direction. But according to Zubrin's The Case for Mars, the consumables packed around a radiation storm shelter will shield the crew adequately. The metal ERV provided only a little of that; most of it was consumables. So I think a roomy capsule with consumables and all the zero-gee equipment could serve as a radiation shelter and a light inflatable could provide the housing during the rest of the flight. I think inflatables can be used on the surface and in space; in fact, maybe one inflatable will serve for both places.

A 40-meter heat shield: Wow, that would be big, and very heavy. It'd probably mass more than the retrorocket fuel it saves, too, and it'd have to be assembled in orbit.

Dropping the hydrogen tank: You could do that if you don't need the volume. If it isn't destroyed by the launch, you could alwaqys use it later for fuel storage.

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#73 2012-04-11 17:24:45

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 29,303

Re: Landing on Mars

Heat shield mass is dependant on the materials...
http://en.wikipedia.org/wiki/Atmospheric_reentry#PICA

mars-science-lab-msl-heat-shield-bg.jpg

http://en.wikipedia.org/wiki/SpaceX_Dragon
SpaceX announced that its chosen heat shield material, PICA-X (a proprietary variant of NASA's phenolic impregnated carbon ablator (PICA) material), had passed heat stress tests in preparation for the Dragon's maiden launch

http://nextbigfuture.com/2009/07/pica-a … defined,0_

PICA is a modern TPS [Thermal protection systems] material and has the advantages of low density (much lighter than carbon phenolic) coupled with efficient ablative capability at high heat flux. Stardust's heat shield (0.81 m base diameter) was manufactured from a single monolithic piece sized to withstand a nominal peak heating rate of 1200 W/cm^2

THE RACE TOWARDS LAUNCH: QUALIFYING THE MARS SCIENCE LABORATORY HEATSHIELD IN UNDER TEN MONTHS

THERMAL PROTECTION SYSTEM CHALLENGES FOR THE MARS SCIENCE LABORATORY HEATSHIELD

LockMart Completes Mars Science Laboratory Heatshield

Heavy-duty heat shield prepares for launch to Mars

Last edited by SpaceNut (2012-04-11 17:27:18)

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#74 2012-04-11 18:10:27

MatthewRRobinson
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Registered: 2012-04-11
Posts: 16

Re: Landing on Mars

I'm sorry if it's a little off-topic, but I can see my thread here might get focused on this one particular issue, seeing how much concern there is on it right now. So that all the discussion on that thread doesn't get centered on that one issue, I want to ask it here.

What the plan calls for is aerocapture of a surface habitat (~20 ton mass range), and separately, an ERV (~20-30 ton range).

The re-entry and landing method of the habitat isn't important, and it lands on a low-energy trajectory.

However, the ERV must be fully reusable and land on a slightly higher-energy trajectory. Would PICA-X, a ballute (down to at least mach 2.5), and powered descent be sufficient?
For the PICA-X part, I want to cite that it can potentially survive hundreds of Earth-orbit re-entries (*source, 2), perhaps making it possible for a PICA-X heatshield to survive a few, or even ten or more Trans-Mars EDL's?

Last edited by MatthewRRobinson (2012-04-11 18:12:36)

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#75 2012-04-11 19:48:20

RobS
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From: South Bend, IN
Registered: 2002-01-15
Posts: 1,701
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Re: Landing on Mars

No one has tested a ballute yet, so I don't know how much is known about their properties or what will work. Does anyone have references to them?

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