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Mars Sample Return
nprev
post Jul 26 2007, 09:26 PM
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I get your point, JR. In all fairness, though, there does seem to be some precedent for the strategy. Ranger/LO/Surveyor were all precursors to Apollo, so since Mars is the espoused future goal for US manned exploration it's getting the lion's share of UMSF attention.

Not necessarily saying it's the right way to go, but merely speculating on the apparent reason for the focus.


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Pavel
post Jul 26 2007, 09:42 PM
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I think you missed the "far into the future" part. Mars sample return is going to be harder than the current missions, and it's likely to take a lot of time. And it can fail like any other mission, for technical or monetary reasons. We can get into the situation when specialists are waiting for additional financing, and there are no working rovers on Mars. The sample return mission is just too big for the pipeline now.
A think we need an "entry" strategy - how to implement ambitious missions efficiently, so that we don't end up with another over-expensive and unsustainable Apollo-like program.
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JRehling
post Jul 27 2007, 09:01 PM
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Pavel
post Jul 27 2007, 10:26 PM
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Mars is also special because it the easiest extraterrestrial planet to research. Try getting samples from Mercury or Venus. Now that would be hard!

The Moon and asteroids are easier, but some questions can only be answered by researching planets. Mars is a natural stepping stone for planetary research. We may learn enough about Mars at some point, but the technology developed for Mars will be reused for other celestial bodies.

A massive one-off project would be less useful for further exploration than smaller specialized missions. MER-like robots can be driving on Europa one day.
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Jim from NSF.com
post Jul 29 2007, 02:42 PM
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QUOTE (JRehling @ Jul 27 2007, 05:01 PM) *
I don't think we want a sustainable program. Not a sustainable big program. That implies money pit to me.

The people doing research on liver cancer don't want a sustainable liver cancer research program. They want to cure liver cancer. Research is the means, not the end. I personally would like to see research on liver cancer end -- once they cure liver cancer.

excess quoting removed



Nonsense.
Liver cancer will continue after one cure has been found. The cure may be expensive, lengthy etc
We know how to set broken bones yet research continues and better "cures" are the outcome

Has ocean research finished.

Not until there is a human presence on Mars, will the missions end. Strike that, there may be Martian weathersats.
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spdf
post Aug 1 2007, 03:55 AM
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A question here: If you have a ~30-40 kg small satellite and you want to launch it from mars surface into mars leo, how much energy do you need for it? And how big would be the rocket? Is there any more detailed study on this online?

Thanks
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ElkGroveDan
post Aug 1 2007, 04:16 AM
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QUOTE (spdf @ Jul 31 2007, 07:55 PM) *
A question here: If you have a ~30-40 kg small satellite and you want to launch it from mars surface into mars leo,

not sure, but I think you'd first want to launch it in lmo wink.gif


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helvick
post Aug 1 2007, 06:40 AM
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You can find some of my back of the envelope calculations on that question in an early post in this thread ( here )
The delta-v that you need is 4.1km/sec to from the martian surface to LMO. Assuming you're using an engine with performance similar to an ammonium perchlorate solid motor (ie an Isp of around 280), then you will need at least 135kg of fuel. You will need an actual launch shell to put it all in which would add another 10-20kg + another 30-60kg of fuel to cope with that extra initial mass.
Note I've made no allowances for atmospheric mass here and that will be significant even though the martian atmosphere is not very dense.
Excluding drag you are talking about an initial mass of at least 215kg to get 40kg to LMO.

And finally you need a (martian) ground assembly to hold it all before launch and I've no idea how to estimate how massive that might be.
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nprev
post Aug 5 2007, 01:45 AM
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QUOTE (helvick @ Jul 31 2007, 11:40 PM) *
And finally you need a (martian) ground assembly to hold it all before launch and I've no idea how to estimate how massive that might be.


I would assume that the return stage would be integrally mounted to the descent stage in the proper configuration--pointy end up, propellant loaded-- before Earth departure; physically configuring it for launch on Mars in any significant way seems really risky from a technical standpoint. Still, lots of mechanical complexity needed to put the payload aboard, unless it's a simple scoop...


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JRehling
post Aug 9 2007, 04:37 AM
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monitorlizard
post Aug 17 2007, 08:01 AM
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I'm probably going to get my head handed to me for saying this, but can't a case be made for a Mars sample return with a direct Mars to Earth trajectory, bypassing a rendezvous in Mars orbit with an Earth return stage?

The obvious counter to this idea is that the size/weight of the Earth return rocket on Mars would be MUCH larger than that needed to reach low Mars orbit. OK, agreed. But there are a lot of advantages to direct to Earth launchings from Mars. One: A Mars orbiter to receive the sample canister wouldn't be needed. That eliminates an entire launch from earth and an entire spacecraft. Two: No need for a rendezvous in Mars orbit. This is an extremely complex operation to do unmanned, and I think it is the pacing technology for when a sample return could be done. It also raises the cost of the mission enormously.

The alternative is to launch a single massive spacecraft to Mars, have it collect and store samples by whatever means is preferred, wait until the next alignment of earth and Mars, then launch the sample return spacecraft directly to earth (no orbiting Mars first). This would require the use of a much larger launch vehicle from Earth than a standard sample return scenario, but that cost would be offset by requiring no Mars orbiter launch, and the much greater simplicity of the Mars to earth portion of the mission (which should also reduce costs greatly and, more importantly, give a greater chance of success).

I've made my case, let the carnage begin. biggrin.gif
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djellison
post Aug 17 2007, 08:29 AM
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Well - yes - carnage indeed. Instead of a 5kg litle satellite to launch from the surface - you have to land, and then launch again - a much larger launch vehicle, to launch not only the small sample cache but also a complete, fueled, spacecraft and entry capsule - able to not only enter the Earth's atmosphere at the other end - but navigate with TCM's between Mars and Earth. A full up proper spacecraft - perhaps 100kg (complete guess). Landing and then launching your return capsule is not easier.

You're making the requirements of the MAV an order of magnitude larger - and thus the landing requirements an order of mag larger (when we don't know how to land >750kg on the surface) and thus the first launch vehicle from Earth being an order of magnitude larger....which doesn't really exist

I think from a biohaz perspective (even if it's just paranoia) - taking a small cache from orbit, putting it into another large entry capsule that is then sealed makes a lot of sense. If you have the entry capsule on the surface, you've exposed it to the Martian environment as well.

I can perhaps see the case for single launch - a viking like split between lander and orbiter, and then then a re-rendezvous on orbit for the return to Earth - but taking EVERYTHING you need to get from Mars back to Earth ( a complete spacecraft) all the way to the surface and back makes the entire problem much more difficult than it needs to be. Also- orbit rendezvous and return offers the option for multiple samples collected and launched from multiple sites to be returned via a single orbiter.
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monitorlizard
post Aug 17 2007, 09:03 AM
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Thanks, Doug. I knew I was going to be defeated on this, but reading the details answered a lot of questions I had.
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djellison
post Aug 17 2007, 09:11 AM
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It's not 'defeated' - I mean, there's merit to making as few manouvers in the system as possible. If you could make a spacecraft with the necessary Delta V and entry ability to do the Mars to Earth flight - but <10kg - perhaps it could be done - but I'd want my return vehicle to be very big, very reliable, and packed full of redundent systems.

Doug
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Cugel
post Aug 17 2007, 09:27 AM
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Of course the points Doug mentions are valid and pretty serious drawbacks for the Direct-to-Earth approach.
However, there is (at least) one point in favor for it: ISRU, aka the Zubrin Fuel Processor.
By far the greatest part of the mass of the return vehicle must be fuel, so if you can somehow land with empty tanks and then do a refill the whole plan makes more sense. You probably can't do DTE without ISRU. But even in a split mission approach ISRU could perhaps be an interesting option.

There is also another issue with the split mission architecture. Is it really possible to automatically rendezvous with a completely passive cannister? Something that doesn't have a radio, position control, an energy source, etc... How do you know its orbit with enough accuracy? But if it can't be a passive cannister, how much hardware must be added before you can find it in orbit? What does that do to that 5 Kg mass number?
Actually, I don't believe in such small numbers, it will probably be more like 100 Kg. At least.
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