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Mars Sample Return
djellison
post Aug 17 2007, 09:36 AM
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I think a sample cache cannister would have a small battery and a beacon radio.. It'd be interesting to know how much intelligence was required on the 'dumb' part of the recent DARPA orbit rendezvous demos when doing the automated undocking and redocking.

Here's a thought. You could make your sample cache a derivative of a cube sat.

Doug
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Cugel
post Aug 17 2007, 02:05 PM
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A cube-sat? Hmmm, I believe at Delft University (Holland) they actually are developing something like that called a nano-sat. As I recall it was 30 cm. (12 inch) on each side, or something. (And it carried a radio) I will see if I can find some more information on it.
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djellison
post Aug 17 2007, 02:28 PM
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Cubesats are a well established and popular platform ( you'll even find extensive info about them here )

It's 10 x 10 x 10 cm and no more than 1kg

You can extend the platform into a double or triple cubesat ( 10 x 10 x 20 and 10 x 10 x 30 , 2 and 3kg respectively) for added performance.

Doug
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Cugel
post Aug 18 2007, 01:08 PM
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So I guess the 'cannister' could look something like the Delfi-C3 nano-sat

This one doesn't have active attitude control, but that's basically all it's missing for being a perfect MSR cannister. Work is also being done to develop autonomous rendezvous, where nanosats would catch up with big satellites for maintenance or repair. This cube-sat development could really be extremely useful for MSR architectures!

So, I'm willing to lower my bid to 10 Kg! rolleyes.gif
2 Kg of samples.
5 Kg for the standard cubesat bus
3 Kg for attitude control, thrusters and a docking mechanism.
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nprev
post Aug 19 2007, 04:09 AM
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This may be WAY off base, but has anyone considered a purely ballistic MSR mission profile?

What I'm thinking of here is a single-stage (or two at the most, if the upper stage has robust thrusters & agile nav capability) DTE reentry vehicle from the surface of Mars...minimal course correction requirements, tight launch window, maybe even solid-fueled at least for the initial boost phase. Advantages: Relatively simple G&C. Disadvantages: (1) very tight launch window, (2) probably high velocity wrt Earth for entry phase. Don't know without a formal risk analysis how these very coarse factors would play out, nor whatever other dragons there may be.

(BTW, thinking of grams, not kilograms, in terms of sample return quantities: even a very little bit of Mars would go a long. long way in terms of answering fundamental/nagging questions such as the presence or absence of superoxides, carbon abundance/source, iridium ratios, etc., etc., ...)


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The Messenger
post Aug 19 2007, 05:37 AM
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Good question. Solid fuels have a great track record in space...I think there has been one possible failure in 300+solid propellant motor ignitions in the vacuum of space.
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tty
post Aug 19 2007, 07:01 PM
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QUOTE (The Messenger @ Aug 19 2007, 07:37 AM) *
Solid fuels have a great track record in space...I think there has been one possible failure in 300+solid propellant motor ignitions in the vacuum of space.


I gather you aren't including the spin/despin rockets of the early Corona recce satellites which went bang in a disconcerting number of cases.
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djellison
post Aug 19 2007, 07:48 PM
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Or the CONTOUR kick stage smile.gif

Doug
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Jim from NSF.com
post Aug 20 2007, 11:36 AM
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Or the two HS-376's on PAM's of STS 41-B

Or the IUS on STS-6
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nprev
post Aug 21 2007, 02:52 AM
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Hmm. Doug & Jim, if you had to shoot from the hip, would you favor liquid or solid propellant for an MSR return vehicle? Expanding on that, do you think that a DTE strategy would be better than, say, a Mars orbit rendezvous with a return vehicle? Seems as if there might be some significant risk analyses needed to make the best possible decision, but interested in your thoughts.


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John Whitehead
post Sep 19 2007, 12:07 AM
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Here are some comments about "how to get off of Mars" for an affordable sample return mission. We really are talking about a miniature launch vehicle. Mars ascent is far more difficult than any rocket maneuver ever done except earth launch, while Mars ascent needs to be done with about one thousandth the mass of earth launch vehicles.

A Mars ascent vehicle needs to be about 75 percent propellant, e.g. 4200 m/s at 310 seconds Isp. If the rocket stage without payload is 80 percent propellant, then the whole vehicle has to weigh 16 times the payload (12 parts propellant, 3 parts stage hardware, and 1 part payload has the 75% and 80% ratios). If the rocket stage can be as good as 90 percent propellant, then the whole vehicle weighs only 6 times the payload (4.5 parts propellant, 0.5 parts stage hardware, 1 part payload). Much better.

For example, a 20 kg Mars ascent payload means that 80-percent rocket stage technology results in 320 kg launching off Mars, while 90-percent technology needs only 120 kg. That's likely the difference between "not possible" and "possible," given forseeable sizes for Mars landers. I believe the latter can actually be done, if the avionics and batteries can be squeezed into the 20-kg payload allocation -- the rocket engineer perspective on what constitutes payload smile.gif .

So the scale (and therefore cost) of the entire Mars sample return mission depends very strongly on the relative masses of propellant and stage hardware, which in turn is limited by the strength of metal and the difficulty of miniaturization. Whole stages of earth launch vehicles are 90 percent, but there is no precedent for achieving such high numbers in the 1-ton range, let alone on a 100-kg scale. While the above analysis assumes one stage, and multiple stages make it easier in theory, the miniaturization challenge is even more difficult for an upper stage.

Existing flight-qualified solid rocket motors on the scale of interest (~100 kg) are about 90 percent propellant, so it is very tempting to think the problem is solved. However, it is necessary to add directional control. The extra parts could easily over-burden a Mars ascent vehicle. A useful technology development effort might be to build and test-fly a series of small solid rocket stages, all the while working to reduce the auxiliary weight.

For liquid propellants, entirely new custom hardware would have to be developed, because liquid propulsion parts used on satellites and spacecraft are too large and heavy. One possibility for reducing hardware weight is to use a pump-fed engine like launch vehicles do. The principle is to reduce tank weight by making the walls thinner (low pressure), while making the engine more compact (and less massive) by running it at high pressure.

The organizations that build spacecraft propulsion systems have not been asked to design rockets completely from scratch since about 1970 (perhaps a few exceptions), and launch vehicle organizations only build big things. A learning curve should be expected. A bit of good news is that building a Mars ascent vehicle promises to be a very exciting project to inspire the next generation.

John W.
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monitorlizard
post Oct 14 2007, 02:15 PM
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mepag.jpl.nasa.gov/Announcements/Stern_MEPAG_Summary.pdf

The above has a summary of a meeting between MEPAG scientists and Alan Stern on September 24. It sheds a little new light on Stern's thoughts about an MSR, as well as the MSL descopes, and the 2013 Mars Science Orbiter. He actually makes a 2020 MSR mission seem feasible, even affordable, with the sacrifice of one Mars opportunity mission. Both sides brought out new points I hadn't heard officially before. Worth checking out.
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John Whitehead
post Oct 16 2007, 03:25 AM
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Thanks to monitorlizard for pointing out the Sep24 MEPAG meeting notes with Alan Stern. To summarize the key points that I noticed regarding MSR:

1. The notion is that skipping one Mars launch opportunity next decade would save enough money to develop and launch MSR in 2020.

2. Planning for science, mission architecture, and curation (sample handling in Houston) are proceeding.

My analysis:

MSR needs two large spacecraft: a lander that carries the Mars Ascent Vehicle (MAV), and an orbiter that carries the Earth Return Vehicle (ERV). Either of these alone is most likely a heavier and more expensive spacecraft than the one single science spacecraft that would be sacrificed in order to pay for MSR. It doesn't appear to compute financially.

Maybe it will be affordable if the 2009 MSL lander works like a charm, and is just copied without new lander development. Then the challenge is back to building a very small MAV, and likely also a new ERV that is small enough to send to Mars orbit in the first place.

All this says that aggressive innovation in down-sizing propulsion technology is needed. Meanwhile, mission architecture studies (number 2 above) can easily have big errors in the estimates of mission mass (and cost) in the absence of the rocket technology.

We have to hope that the science community will appreciate the need for high-risk rocket technology work. There's essentially nothing out there that can be bought and modified or adtapted in order to successfully launch off of Mars.

John W.
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Jim from NSF.com
post Oct 16 2007, 11:09 AM
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QUOTE (John Whitehead @ Sep 18 2007, 08:07 PM) *
One possibility for reducing hardware weight is to use a pump-fed engine like launch vehicles do.


Not viable. Losses from inefficiencies would be too great. Pressurized systems is the way to go
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monitorlizard
post Oct 16 2007, 12:34 PM
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"There's essentially nothing out there that can be bought and modified or adapted in order to successfully launch off Mars"

That may very well be true, but there's one possiblity I can think of that might just barely do the job: the ASM-135 ASAT antisatellite weapon that was successfully tested in 1985. It was a two stage (solid propellant?) rocket, with a third stage that I think was just the kinetic warhead itself. The first stage was taken from the Boeing AGM-69 SRAM cruise missile (specifically the Lockheed SR75-LP-1), and the second stage was the Vought Altair III. The third "stage" featured a hydrazine attitude control system to allow a direct hit on the target. Such a control system seems to fit well with the requirements for a rendezvous in Mars orbit with the Earth-return vehicle. (all facts taken from Wikipedia)

The ASAT missile was launched from an F-15 at around 85,000 feet, which is like having an extra stage for your rocket, but I'm wondering if the lower gravity at Mars might make it possible to launch from the surface without an extra stage. The ASAT was described as being able to reach altitudes greater than 350 km (the satellite it hit in 1985 was at 555 km), which seems more than adequate if used at Mars. The weight of the entire ASAT missile was 1180 kg, which seems within the range of possibility for an MSR mission.

I have no idea if such a rocket could actually be used for an MSR, and it might need to be so highly modified that starting from scratch might be better, but I think this is the only already-built system that could meet the weight and performance specs needed. It would be a great sword-to-plowshare moment if it could be used. If MSR is a joint mission with ESA, it could be an ITAR nightmare, but this is supposedly a retired system.
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