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Fraser
2006-Jun-19, 09:06 PM
NASA's newest visitor to the Red Planet, the Mars Reconnaissance Orbiter, is still in the process of shrinking its orbit, enroute to its final science orbit. When the spacecraft first arrived, its farthest point from the planet was 45,000 kilometers (28,000 miles). After 11 weeks of aerobraking operations, it's reduced this distance to about 20,000 km (12,000 miles). Controllers estimate that the spacecraft will still need to sweep through Mars atmosphere 400 more times over the next 12 weeks to complete its orbital maneuvers. Its final mapping orbit will be approximately 255 to 320 km (160 to 200 mi) above the Martian surface.

Read the full blog entry (http://www.universetoday.com/2006/06/19/mars-reconnaissance-orbiter-continues-to-lower-its-orbit/)

antoniseb
2006-Jun-19, 10:01 PM
Aerobraking is a good thing because it reduces the total fuel required for the mission. The Science Fiction buff in me thinks this is a Rube-Goldberg kind of way to accomplish the mission, and wishes we could just get to Mars and get into the right orbit right away.

Anyway, I'm glad it's going well, and as expected.

saski
2006-Jun-20, 01:16 PM
Allow me a little advocacy.

The prospect which excites me is as follows. Energetically, Deimos is not hard to reach. Work through the delta-v diagram in:

Rockets and Space Transportation; Delta-V in the Solar System
Chris Hirata
http://www.pma.caltech.edu/~chirata/deltav.html

If this is correct, the velocity change from Low Earth Orbit (LEO) to Deimos rendezvous is 5.6 km/s: only a little higher than LEO-to-Lunar surface for 5.5 km/s, and definitely less than LEO-to-Mars-Landing for 10.2 km/s.

For human explorers, the last step down to Mars is expensive and risky, and likewise getting back up and home: 20.4 km/s for the round trip from LEO. In comparison, 11.0 km/s to Deimos and back is comparable with Lunar trips, pound for pound. The catch, compared with Lunar trips, is the travel and supply time together with the supply mass, radiation shielding and perhaps a centrifugal gravity architecture.

Very well, let us aim at a permanent base on Deimos; prepared by a series of uncrewed rendezvous missions to deliver supplies and equipment, and to assay the terrain. (It seems the Russian are planning to begin the last of these in the next few years.) Deimos almost certainly possesses large quantities of surface dust: the several tonne/meter^2 needed for radiation protection are available for very little processing. Deimos' overall density is very low, about twice that of water: if all that is stony material, the satellite is incredibly fragile. Carbonaceous material is very likely, and water ice is plausible.

The obstacles to a human station on Deimos are comparable with our Mir and ISS experiences, except that we have plenty of shielding material. We can rendezvous any amount of material beforehand, at similar cost to soft-landing on the Moon. It would be neither cheap nor risk-free, but it seems comparable in most respects to the current NASA Constellation-based Moonbase plans.

Deimos orbits Mars at 23,460 km distance, at 1355 m/s. A station established on Deimos could assemble vehicles, and perhaps even build parts of them (like ablation entry shields) from local materials. A 1.355 km/s velocity change is all that's needed to transfer a vehicle from Deimos orbit to a vertical fall to Mars. Then, as with the Mars Reconnaissance Orbiter, the vehicle can aerobrake repeatedly to a desired lower orbit, or a desired entry-and-landing trajectory. Plausibly, the initial push from Deimos could be supplied by a small rocket boost, a mass driver, a revolving tether, or enticingly, a magnetized plasma beam as conceived by Winglee, Ziemba et al, as in:

http://www.ess.washington.edu/Space/magbeam/
http://www.niac.usra.edu/files/studies/abstracts/1012Winglee.pdf

It seems to me that with a Deimos base and aerobraking, we could conduct a very thorough robotic orbit and surface exploration of Mars, as well as provisioning a human landing in advance; and this would reduce the human risk factors greatly.

ToSeek
2006-Jun-20, 04:30 PM
Aerobraking is a good thing because it reduces the total fuel required for the mission. The Science Fiction buff in me thinks this is a Rube-Goldberg kind of way to accomplish the mission, and wishes we could just get to Mars and get into the right orbit right away.

We could do it, of course, we just couldn't pack the same massive instrument package on board.