Mars Sample Return Options

[Rakhir]

Next phase reached in definition of Mars Sample Return mission

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

[dvandorn]

I dunno, Dan -- the last MSR concept I saw (back in the late '90s) used some leftover, off-the-shelf solid-fuel military missile as its basis for an ascent vehicle. I bet there are at least two or three of them left that haven't been fired in anger yet...

-the other Doug

[John Whitehead]

...leftover, off-the-shelf solid-fuel military missile as its basis for an ascent vehicle.
-the other Doug

Couldn't resist running a quick & dirty trajectory simulation to compare a MAV with military missiles. First verified the flight of a 100-kg MAV by running the trajectory simulation to reach a 500-km circular Mars orbit using about 4150 m/s delta velocity (results match a previous case in the Journal of Spacecraft & Rockets, Nov 2005 p. 1041). Then simulated flight of the same vehicle starting on earth. Had to increase thrust 50 percent so it exceeds earth weight of the vehicle. To reduce the effect of the thick atmosphere on such a tiny vehicle, moved the launch site to 10 km altitude (32,800 feet). The latter seems fair for comparison to air-to-air missiles, which might launch at such an alitude.

The simulation result indicates that a 100-kg Mars ascent vehicle launched 10 km above earth can go more than 500 km downrange. Now, what military missile in this size class has such a capability?

Take a look at www.designation-systems.net, and click Directory of US Military Rockets and Missiles. Note the extensive list available in the selection box. As an example, the latest Sidewinder (AIM-9) is said to have a mass just under 100 kg, but its range is said to be only tens of kilometers. A Navy Standard Missile (RIM-156B or RIM-161) has roughly the same reach as a MAV, but it weighs about 1.5 metric tons. Based on these 2 examples, military missiles appear to offer only a tenth the distance relative to mass, compared to what Mars ascent needs.

While it might be possible to push solid rocket technology toward sufficiently less inert mass to make a solid-propelled MAV, there is no indication that anything off the shelf is capable. If performance details for military missiles and their rocket motors could all be public, there would probably be a more widespread appreciation of just how much harder it is to make a MAV.

John W.

[dvandorn]

Couldn't resist running a quick & dirty trajectory simulation to compare a MAV with military missiles...

...While it might be possible to push solid rocket technology toward sufficiently less inert mass to make a solid-propelled MAV, there is no indication that anything off the shelf is capable. If performance details for military missiles and their rocket motors could all be public, there would probably be a more widespread appreciation of just how much harder it is to make a MAV.

The only corroboration I can find right now that the 2003-2005 MSR concept was to use military hardware is Steve Squyres' comment, in "Roving Mars," that the mini-MAV being planned for use in conjunction with the Athena rovers was "based on a classified Navy program." He also mentions the program had been in existence since 1958.

Squyres says that the payload this mini-MAV was to have lofted into low Mars orbit would have been about the size of a coconut. I imagine this would have weighed significantly less than 100 kg -- maybe only 20 to 30 kg.

The 2003-2005 MSR concept was that two different MSR landers would be flown, each serviced (i.e., loaded with samples) by one of the Athena rovers. An RTE vehicle would then rendezvous with and "gobble up" each of these coconuts and then burn back out of Mars orbit into an Earth return trajectory. (No matter what else happened, this means the two coconuts would have to have been launched into identical orbital planes, or else the RTE vehicle would never be able to carry enough fuel to rendezvous with them both.)

-the other Doug

[John Whitehead]

...Steve Squyres' comment, .... mini-MAV ... was "based on a classified Navy program." ...1958.
Squyres says that the payload .... size of a coconut. I imagine... 20 to 30 kg.
The 2003-2005 MSR concept ... An RTE vehicle would then rendezvous with and "gobble up" each of these coconuts and then burn back out of Mars orbit into an Earth return trajectory...
-the other Doug

The Mini-MAV idea was advanced by Brian Wilcox of JPL, whose father had worked on the noted Navy program circa 1958. The latter was a "hail Mary" attempt at China Lake to put a U.S. object into orbit as a quick response to Sputnik. The main trick was to use several spin-stabilized solid rocket stages, which made the vehicle smaller by deleting guidance & control hardware. Brian explained all this at the AIAA Joint Propulsion Conference in 2001, AIAA paper number 2001-3879.

Later studies of the concept by JPL and contractors resulted in putting the G&C back on. The conceptual design eventually grew from Brian's 20 kg to the latest reference design at 268 kg, too heavy to implement MSR using the MSL 2009 landing system (the largest Mars lander ever developed). The coconut-size sample container has remained the notional payload design for a MAV. Yes, launching a coconut off of Mars with a vehicle smaller than ~200 kg remains THE unsolved problem.

The quote attributed to Steve Squyres is a perfect example of the rampant collective optimism that a Mars ascent vehicle is going to appear from behind a curtain. NASA, JPL, and their contractors have done such a tremendous job of pulling off technological "miracles" for Mars spacecraft, that the implementation of missions is too easily taken for granted.

John W.