Mars Sample Return Options

[Rakhir]

Next phase reached in definition of Mars Sample Return mission

http://www.esa.int/esaCP/SEMJAGNFGLE_index_0.html

[John Whitehead]

The ASAT missile weighed a ton, more than the lander, MAV, rover, etc. combined (assumed future affordable capability based on the expectation that the 2009 MSL will successfully land almost 1 ton total on Mars).

A popular definition of "space" is expressed in terms of altitude, but achieving orbit is more about velocity. The ASAT missile merely went straight up to about 500-600 km, which needs a very minor fraction of Earth's orbital velocity. Mars orbital velocity is 45 percent of Earth's. The MAV needs to accelerate zero to 9,000 MPH in 5 minutes.

Generally, rocket motors for military missiles have less raw propulsive performance than space motors, because the former have to be cheaper for quantity production, structurally more robust for abuse in the field, etc. We shouldn't pin our hopes on the possibility that something better than existing space propulsion hardware is available from behind the scenes in the military world.

Overall nprev is right that existing technology gives us "only a starting point." The question is when and how and who is going to move forward to develop a MAV? Part of the reason that the aerospace engineering community does not have a cadre of experts who are spooled up to develop a MAV, is that rocket technology development reached diminishing returns circa 1970, and the expertise in the field faded (along with funding cuts). Today's rocket experts implement relatively small evolutionary departures from existing technology.

John

[djellison]

The question is when and how and who is going to move forward to develop a MAV?

When they get paid to do it, by doing engineering, probably JPL/Ames or similar in colab with industry.

It's a huge challenge - no doubt whatsoever, but I don't really get your point. Where's the cadre of experts for a Titan balloon? Where's the cadre of experts for anything...that we've not actually done yet? The answer.... you get that talent and knowledge by doing it. There's barely the money to build and fly MSL. Given that politics is a banned discussion from this forum - what do you want to talk about.

You didn't say 'There simply is no community of people who have experience building miniature launch vehicles of the exact scope and specification that will be required for MAV'.

We wont have...until we've built an MAV. I'm not going to get into an argument about this ( although it seem you really want one ) - but it's chicken and egg. We didn't have Mars EDL experts till after Viking. We wont have MAV experts till after MSR. Someone needs to write a very big cheque, and the problem will thus be solved. Thats all there is to it.


Doug

[John Whitehead]

I don't really get your point. Where's the cadre of experts for a Titan balloon?
... you get that talent and knowledge by doing it... Someone needs to write a very big cheque, and the problem will thus be solved. Thats all there is to it.

Hey Doug, hopefully your comments will help me focus better on what I was trying to explain. I think the whole planetary community would agree that a Titan balloon would be entirely about innovation, and I think that planetary scientists and others planning missions do consider Titan balloons to be interesting. My concern is that the MAV rocket problem does not seem to be viewed similarly. Has anyone met a planetary scientist who finds propulsion systems to be interesting?

Innovation is unwelcome in the development of propulsion systems for planetary missions, and the engineering culture is built around the notion of only using what is already proven. Spacecraft organizations treat this sort of work as an automatic process. People working in the space propulsion discipline have been taught by their experience that a new project won't get funded unless they say existing technology will suffice. But the technical problem that exists is not one of obtaining the "exact scope and specification." Launching from Mars to orbit, with a vehicle the size of a person, is far beyond being a variation of previous capability.

I absolutely agree that you get the talent and knowledge by doing it. The Rover Team is a great example of a major technical talent pool being convened and nurtured to do something totally unique to Mars exploration. It took decades to build the team and then create working flight rovers, and my understanding is that it has not been easy to keep the team together. I suspect that building up expertise of a similar magnitude for a similarly specialized purpose is going to be needed for the MAV.

While I too look forward to seeing the big checque written for MSR, the reality is that the Mars Program budget is constrained. If money flowed freely, then robotoc sample return could be a dry run for a human mission, using the full scale hardware. I wouldn't agree that money can solve any defined technical problem, since physical limits do exist. In many engineering endeavors, the primary difficulty is complexity. For the MAV (built small enough for an affordable mission), the primary difficulty is physical limits related to the strength of materials, miniaturization thickness limits, unfavorable cube-square scaling of drag versus mass (similarly heat flux versus mass), and unfavorable scaling for other things like manufacturing precision and the effects of fluid viscosity. Does everyone in the system appreciate that complexity and physical limits present totally different kinds of difficulty?

mcaplinger, thanks for understanding.

John W.

P.S. to ugordan: Despite Mars's thin atmosphere, the ideal acceleration profile starts at about one earth gee, because the effect of drag is greater for tiny vehicles like the MAV needs to be. Solid motors on the scale of interst inherently have ten times the ideal thrust, hence more drag.

P.S. to zvezdichko: Separate launches from Earth as you suggest has been the nominal notion for MSR since the late 1990's, with rendezvous in Mars orbit at 500 km altitude. Even to only reach Mars orbit, a single-state MAV might be more difficult than a 2-stage MAV. I personally think a single-stage MAV is possible with a hard technology push, and desirable for several reasons.