How Big does a MSR return rocket have to be?

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bad_drawing

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I often lurk in the M&L Threads and I tremendously enjoy the insights and info provided by those here. Today I feel compelled to come out of my hole and ask a question:<br /><br />Today I was reading an article posted on SDC about a Mars Sample Return mission. <br /><br />http://www.space.com/businesstechnology/060301_msr_overview.html<br /><br />My question is this: How big does the return rocket need to be? <br /><br />I realize the payload will be small, Mars gravity well is smaller then Earths, plus the suns gravity should provide some pull... but still I can't quite wrap my head around the idea that a rocket that [in the graphics] appears to be the size of a fat sounding rocket - can escape the gravity well of Mars. All that being said, I realize that the graphics are made by graphic artists who do the best they can with the info as they understand it... so sometimes the Proposal graphic will not match the end product. But still I'm curious as to a ballpark figure on the size and power requirements of the return rocket<br /> <br />Thanks in advance for any info.<br />John<br /><br />
 
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henryhallam

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It's a bit tricky to get a sense of scale from that picture, and as you say it is only an artist's impression, but I think that something that small would use a Mars Orbit Rendezvous mode, i.e. it will meet up with an dock with another stage that had been left in Mars orbit. This would provide the dV, guidance and perhaps reentry shielding necessary to get the sample back to Earth.
 
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mlorrey

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Mars escape velocity is 5 km/sec, which is less than half the 11.2 km/sec escape velocity of Earth. It should be easier to achieve this, as the gravity drag is less, as is the atmospheric drag (almost non-existent). Orbital velocity is 3.5 km/s. Required fuel fraction for an ascent stage to reach orbit, using the same fuel/Isp as the lunar module is 3.2 times the dry mass. The fuel fraction for the original LM was 2.0, so it needs to have a bit higher mass fraction than the LM (this is a ratio, not an amount), but nowhere near the 20 fuel ratio of the Saturn V.<br /><br />If the methane/lox fuel combination is used, fuel ratio drops to 2.82 due to higher Isp.
 
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bad_drawing

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"I think that something that small would use a Mars Orbit Rendezvous mode, i.e. it will meet up with an dock with another stage that had been left in Mars orbit. This would provide the dV, guidance and perhaps reentry shielding necessary to get the sample back to Earth." <br /><br />This makes a lot of sense. Thank you!
 
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mikejz

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For a first MSR I would think that a solid rocket would be the best bet for the lander. 3.5km/s is something a sounding rocket could easly do. I'm willing to bet the CSXT Rocket had that velocity too. <br /><br />Once in orbit, another spacecraft would collect the sample and encase it in a heat shield for its return back.<br />
 
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bad_drawing

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Great information. I forgot to consider the ultra-thin atmosphere.<br /><br />"Required fuel fraction for an ascent stage to reach orbit, using the same fuel/Isp as the lunar module is 3.2 times the dry mass. The fuel fraction for the original LM was 2.0, so it needs to have a bit higher mass fraction than the LM (this is a ratio, not an amount), but nowhere near the 20 fuel ratio of the Saturn V. "<br /><br />Wow. I assumed the difference would be somewhat substantial...but that is huge! <br /><br />Another question: Would there be any benifit/downsides to the lander-to-orbiter rocket being solid fueled? Or is a liquid prop rocket the only way to go in such a situation? <br /><br />*edited for clarity*
 
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j05h

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The main question is what is the dV involved for Mars-orbit or Mars-TEI? Second is size of sample return. My personal view is that a long-duration "collector" that takes many samples from Phobos would give us a good sampling of all three body's material - in some ways it would offer better preserved rocks than those sampled from Mars. Also doesn't involve nasty atmospheric EDL. <br /><br />If we had a good candidate site for life (or something equally important) on Mars, the various ISRU proposals (Zubrin, others) have made the most sense. The lander makes methane while several small rovers collect and deliver samples from the landing area. Proposals for in-orbit docking with a return vehicle introduces more risk than direct return, IMHO. <br /><br />Mars to Mars orbit is 4100 m/s dV, and if i'm reading this right, it's around 6900 m/s total for Earth-return. http://www.pma.caltech.edu/~chirata/deltav.html<br /><br />Here is an old article that claims a 200 lb, 3 ft solid rocket could do it. Nice plan, too, several landers over the years, each launches samples to be collected by an Earth-return orbiter. Payload isn't specified, perhaps several ounces to several pounds of payload?<br /><br />http://www.gsreport.com/articles/art000038.html<br /><br />An interesting idea: which commercially available upper stages could handle segments of the sample return?<br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>
 
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mlorrey

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Zubrin has also proposed sending it prefueled with Diborane.<br /><br />As there is little atmosphere, there isn't much need for reducing atmospheric drag by focusing on high density. You'd want a fuel that is stable for long term storage in various conditions, but has both throttlability and high Isp. Methane is a pretty good choice, as is diborane.<br /><br />The big bill is the booster required to send a Mars probe big enough to have a useful science package AND an ascent stage for sample return. Outside of the throttling issue, sending solid launchers is very KISS, which may be a paramount concern for the remote launch of all remote launches. On the other hand, I have my doubts about sending a rocket with premixed fuel/oxidizer through an atmospheric reentry. That sounds like a recipe for fireworks. If there is a stable liquid oxidizer for hybrid engines, perhaps that is the route to take.<br /><br />As for available motors, a Sparrow AA missile rocket motor is 211 lbs. Fuel is aluminized CTPB. I suspect it has a very fast burn grain pattern. Length 59 inches, dia 8 inches. One of these can be modified with a round grain and a nozzle optimized for a 10 millibar atmosphere.<br /><br />The Thiokol Star 15G retro/separation motor is 15" dia by 31" length. 175.5 lb fuel, 206 lb fully loaded. Isp 285.9. Total impulse 50,210 lbf-sec. Assuming a 15 lb guidance/payload/telemetry unit, fuel ratio is 3.87. This could carry another 5-10 lb of rocks.
 
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mikejz

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I would think that the on-mars fuel generation would work more for a mars 'hopper'.
 
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willpittenger

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I would rather send a few hundred pounds of fuel than a fuel making plant massing several tons. Zubrist's proposal to make fuel mainly makes sense, to me anyway, for a manned lander. Perhaps if your sample return vehicle was going to return a few tons of samples, then it might make sense. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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gunsandrockets

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Interesting link. Thanx. I'd never heard of the beryllium/oxygen rocket propellent combination before, very interesting - an ISP of 710! I could see that having a lot of potential in a hybrid rocket engine.
 
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gunsandrockets

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"I would rather send a few hundred pounds of fuel than a fuel making plant massing several tons."<br /><br />The original goal of the Zubrin proposal was to reduce the launch vehicle required for an MSR mission to one the size of a Delta II. Using a conventional fully fueled MSR lander would require a much larger and much more expensive booster. I believe the total sample returned was supposed to be 0.5 kg.
 
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willpittenger

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The more I think about it, unless the rover associated with MSR will return to the lander, it needs to carry the sample return rocket with it. <br /><br />OK. It's common sense, but no one else mentioned it. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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willpittenger

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Before we attempt MSR, we should do a practice rendezvous in Martian orbit. Why? It takes 20 minutes for signals from Earth to reach Mars. So one of the vehicles must be able to analyze approach data for itself. Waiting for Earth to help out would be fatal.<br /><br />My suggestion would be to use MGS or Mars Odyssey they get older and run low on fuel. You use an probe that has little left to offer science in case of a collision. For the same reason, the other part of the rendezvous should be a probe that is already default. Mariner 9 and the Viking orbiters come to mind. Are they still in orbit? Do we have a fix on their location? If you answer yes to both, we could use them. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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henryhallam

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The most reliable ways of doing automatic rendezvous require active systems on both ends, i.e. a transponder and radar, perhaps as well as visual systems. I don't think any of those are present on the existing Mars orbiters.<br /><br />It is easy to practice automated rendezvous and docking in Earth orbit, the only difference between that and Mars are a couple of numerical constants which are easy to change in software.
 
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mikejz

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I think DART did a lot of in terms of covering the base development of needed systems.
 
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j05h

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>I believe that most theories say that the moons of Mars are caputured bodies, not from Mars at all. <br /><br />That is not my point at all. My point is that Phobos has been Mars' "garbage collector" for at least many million years. Every time an impact blows material off Mars (not even on escape velocity), it has a pretty good chance of getting scooped up by Phobos. Same for down-orbit (?) impacts from Deimos. The rocks that it has collected from Mars would offer us a broad index from Mars' history, without the weathering and other interactions those rocks would suffer on Mars' surface. Similiar to how researchers have proposed finding ancient Earth DNA frozen on Luna.<br /><br />A collector probe would only have to dig/collect and be able to roughly identify each targetted rock. A fairly simple spectrometer and brush (per MER rovers) should do that trick. It would spend months or years poking Phobos for secret rocks, then burn for Earth. Sound good? <br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>
 
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j05h

Guest
>I would rather send a few hundred pounds of fuel than a fuel making plant massing several tons. Zubrist's proposal to make fuel mainly makes sense, to me anyway, for a manned lander. Perhaps if your sample return vehicle was going to return a few tons of samples, then it might make sense.<br /><br />Pioneer has demonstrated suitcase-sized ISRU prototypes, so the potential weight is much lower than you guessed. Zubrin has said several tons of hydrogen, plus a few hundred pounds of equipment for a manned mission. Using sample-return as a demo for ISRU makes some sense, if you think it through, but only in the context of manned follow-ons. <br /><br />I'm all for multi-ton Mars missions, though. If you can come up with the funding, of course. 8)<br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>
 
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