Forum: Space / Science

on Tue 20 of July, 2010 14:58 PDT, by Jeff-Wash

There's some news on the net that ESA and NASA mat combine forces, and budgets, for two separate martian missions.

Firstly, to send a Sample Collection Mission to the martian surface around 2017-2018. That mission will basically involve a rover collecting interesting dust-rock samples and stockpiling them for another Mars mission 25 months later. That later mission will involve a lander 'supposedly' landing nearby to load up the precious samples into its upperstage for return to Earth.

I can't see this working. The accuracy required for the actual Sample Return Spacecraft to accurately land near the stockpiled samples for it to gather up just doesn't appear to be there. All Mars landers so far have had relatively large landing ellipses that indicate a large degree of inaccuracy in landing on the martian surface. Landing on the Red Planet appears to remain a crap shoot with a lot of luck involved.

on Thu 22 of July, 2010 07:54 PDT, by Delbert

You might recall that the Viking launders were attached to the orbiters and waited awhile before they were detached and landed. I don't recall if that improved their landing accuracy or not.

on Tue 20 of July, 2010 17:17 PDT, by TB

I don't know. Apollo 12 managed to land within walking distance of an old Surveyor.

on Tue 20 of July, 2010 20:44 PDT, by Nick H

Tom, beware of comparing apples and oranges.

Lunar missions generally gain accuracy because the vehicle is inserted into a stable Lunar orbit, from which a de-orbit manouevre can be conducted very accurately, especially with the relatively nearby ranging and location facilities of Earth.

Mars missions generally go for direct landing from an interplanetary transfer orbit, with only one shot at the landing and less local triangulation (though that situation is beginning to improve with the number of live orbiters still circling the Red planet).

In addition, the Apollo and Surveyor missions had rocket guidance during the landing phase, rather than a more passive landing system, but future Mars missions are beginning to go back to Rocket-guided landing systems after the post-Viking economy era.

A pin-point landing is NOT going to be as simple as the Surveyor/Apollo tie up, but I'm sure it CAN be done, if needed...

on Wed 21 of July, 2010 10:21 PDT, by mcfly

Which is simpler: putting the craft into orbit, then descending once everyone's caught their breath, or plunging directly from interplanetary travel into the Martian atmosphere to a relatively pinpoint landing?

Obviously both are possible, but with different demands and risks. If I were a mathematician, I'd relish the challenge of the latter option.

on Wed 21 of July, 2010 09:28 PDT, by TB

Good points. How much distance would the sample rover have to cover to make up for landing error by driving to wherever the return lander is?

on Wed 21 of July, 2010 15:18 PDT, by Jeff-Wash

The sample rover may have to cover many kilometers depending on the accuracy or inaccuracy of the landing of the return lander.

I think braking into an initial parking orbit might help the accuracy of the 2020 MSR lander, but that might require a large braking rocketmotor package. That might shrink the actual lander to a size that would put further limits on what it can do.

on Thu 22 of July, 2010 09:06 PDT, by TB

A lander might have an easier time navigating to a specific point on Mars' surface if a previous lander was sitting down there broadcasting a navigation signal at the landing site.

on Thu 22 of July, 2010 19:09 PDT, by Nick H

But then you need the sample return component to have a propellant package that can wait on the Martian surface till the rover arrives. Solids and Hypergolics are probably fine but liquids are problematical, unless you're doing an in-situ fuel manufacture like Zubrin advocates, but this has its own weight and complexity issues.

Another detail is that if either half of a split mission lands inside a patch of terrain that cannot be exited/entered, or the wrong side of a terrain barrier, then the whole mission is compromised. To avoid this, we tend to get focussed onto "safe" (i.e boring) locations with limited interest in the gelogy and topography.

My forecast is, however, for a medium-to-long distance rover to be directly landed via aerobraking and rockets in mission year 1, and then a return lander to be again directly injected, but with significant effort for terminal guidance, in mission year 3.

My best alternative option is to land the whole damn package in one go, and have a short-to-medium range rover pop out locally and get some rocks and dirt, then load them back to the return capsule on the landed base all within a 30-90 day mission, and return in the same martian year while the transfer orbit is still near-optimum. It needs a heavier mission, but cuts out a lot of the "what ifs".

Oh, and why not have a small drill on the lander to collect a local sample AND emplace a seismometer? (yeah, I know it add weights and complexity, but I hate landing a dumb base station when we could be putting a string of long-term sensor stations like the Apollo ALSEP)

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Forum: Space / Science

Mars Sample Collection Mission, 2018? Mars Sample Return Mission, 2020? It won't work.

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