Sustainable Access to Mars: Interplanetary Transportation Architecture

GW Johnson · 2013-02-03 10:08:34

I think the basic trade is schedule time vs the number of new technologies to develop. It's an experience thing. The only way to do rapidly something that is challenging, is to use only currently-ready-to-use "tinkertoys" (meaning technologies and hardware).

The more new stuff you want to use, the longer it takes to get everything working. That stretches your program out greatly, and that stretch makes it far more expensive. So, experience shows long schedules are inherently expensive. It's as true for building highways as it is for doing space missions.

A pushed-back date is almost as unattractive as a big budget, when trying to "sell" a space project to the voters/congress.

GW

Void · 2013-02-03 11:48:13

I don't want to interupt your worthwhile conversation, but I have a notion of an item of hardware to propose which might be useful to an interplanetary mission where water is a large source of propulsion mass.

Here is my simple cross section diagram for it:

The notion is to use a "Bigelow Expandable Activity Module, or BEAM" as a rigid container.

http://abcnews.go.com/Technology/inflat … d=18240124

Inside a flexable/foldable/elastic bag filled with air. Inside of that a pole or a pannel to attach equipment or sleeping persons to.

As the water gets used up as propellant, the area filled by air gets larger.

Upon a refueling, it gets smaller.

I think the circular Bigelow BEAM might be quite good, if it is not too mass heavy. That is something I do not know.

I do not expect that the travelers will have only this to dwell in, but would have an attached crew compartment. However for various reasons it might be useful to be able to habitate the air filled volume as well at times.

-Cramped space in a crew module.
-Radiation storm.
-Radiation protection during sleeping.
-Crew module becomes temporarily marginal for habitation.

I have indicated two modes of use, the pure water mode would be where you do not want to monkey with purifying the water in the volume before using it for propulsion.

The other mode would allow you to grow plants in the water if the air bag was transparent. This would allow you to use LED's mounted on the pole or pannel to illuminate the interior, and that would be to produce Oxygen, purify Urine, and just maybe grow food. That whole process would be an additional complecation, and would require also that the water be purified, perhaps by distillation before being processed for propellant.

It is worth noting that one of these would be a novelty, but several joined as a unit could be a space station around Mars, and also a propellant depot.

Anyway, it is a direction to consider perhaps.

Russel · 2013-02-04 04:21:41

I went back and did a bit of a comparison.

On the one hand we could use an expendable LH2/LOX stage to Mars. Then an expendable methane/LOX stage back to earth. Aerobraking is assumed on Mars.
Turns out the initial mass in LEO is around the 160 tonnes. Remember we're just talking about the space hab here.

On the other hand we could use water and an MET, with a small LH2/LOX engine for (part of) the TMI/TEI boost.
That works out as around 90 tonnes all up in LEO terms.

So basically the benefit of MET is about halving the launch mass. And I'm making some allowance there for the difference between one rocket having a large solar array and the other not.

Is it worth it in terms of launch costs? maybe $1 to $2 Billion (if spacex delivers). It all depends on what the rest of the program costs and how many times you want to fly as to whether the fuel bill is a big issue relatively speaking.

Looking back on all those technologies.

1. A big solar array. Pretty well understood technology and no doubt someone will want to test one at some point for some reason. The real problem at least for me is combining this with being able to aerobrake. And there are several solutions to that one.

a) Storing the array for aerobraking. That could mean simply having a tough, moderately temperature tolerant framework, and simply stowing the more fragile solar panel units. Yes, that means a space walk once in Mars orbital capture.

b) Going for a very gentle aerobrake. The price to be paid is possibly weeks of aerobraking passes.

2. The MET engine. Again my main concerns are efficiency and reliability. But I'm pretty sure that someone's going to go ahead and try out the technology and its a good candidate for use on precursor missions (sample return, testing means of harvesting water etc).

If its a non starter then we're back to conventional or nuclear for the long haul. Conventional means a couple of spare billion launching fuel. Nuclear has its own development issues.

Now, what I'd *like* to see, is a nuclear alternative to a 500KW solar array. If you could get the radiators down in size you might be going somewhere. Nuclear also lends itself to artificial gravity because you're going to end up with a long boom to keep those pesky neutrons away.

3. A "hollow" heat shield - with steam as coolant. And perhaps air brakes. Completely new technology. But the key here is that we simply need a breakthrough on the front of landing on Mars. Without that every other mass doubles and redoubles. The technologies could be tested from Earth suborbital and orbital flights - and doesn't have to be done on a huge scale. Its also inevitable there are going to be Mars sample return and robotic missions before we send humans - so why not test such technologies on the way.

4. CO/LOX engines. I frankly can't see any showstoppers here. Its just a matter of stepping up to the plate and doing the engineering, and lots of testing.

5 In situ propellant production. Everyone has this problem. I'm just reducing it to the simplest possible reaction.

And there's no reason why such technologies cannot be developed concurrently. So what are we looking at here? Given some require flights to Mars and back there's an inherent and unavoidable delay - but everyone's got this problem. So what do you think? 10 years? About that?

Yes, there are ways to hurry.

While we're at it let me step back and give you some idea of where I come from. I'm Australian. So I can afford to be a little aloof when it comes to US politics. (But I'm well versed in it). I'm here because getting to Mars and back, and doing it well, is a problem worth solving.

I'm no huge fan of colonisation. My view of the human race is a bit different to most people. I think we need to be a bit more civilised (and less prone to trashing the place) before we start "reaching out". But I do think that we need "vision".

So my attitude is to hasten in developing new technology. Getting out there both with precursor missions to Mars and also testing appropriate things on the moon (it has its place).

And in the end solving the problem elegantly and leaving plenty of margin. Or to put it another way do it in comfort and style through good design.

Russel · 2013-02-04 04:25:18

Void,

Interesting concept that. I'm waiting to see how robust those inflatable modules are and if they stand up to the test of years in space. I'm still tossing and turning as to the merits of parking large stores of water as refueling depots. Have you considered the idea of an inflatable like you've drawn as a "storm shelter" module?

Void · 2013-02-04 19:08:36

That's a notion to consider. Be useful if you can. That's pretty much the requirement to play ball.

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#76 2013-02-03 10:08:34

Re: Sustainable Access to Mars: Interplanetary Transportation Architecture

#77 2013-02-03 11:48:13

Re: Sustainable Access to Mars: Interplanetary Transportation Architecture

#78 2013-02-04 04:21:41

Re: Sustainable Access to Mars: Interplanetary Transportation Architecture

#79 2013-02-04 04:25:18

Re: Sustainable Access to Mars: Interplanetary Transportation Architecture

#80 2013-02-04 19:08:36

Re: Sustainable Access to Mars: Interplanetary Transportation Architecture

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