[X] My Assistant

[Rakhir]

Next phase reached in definition of Mars Sample Return mission

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

[nprev]

Might be worth considering & contrasting US & old Soviet-era (SE) design approaches when thinking about MSR. From what I gather, most SE flight hardware was very rugged, implying that functional modules were optimized for their specific performance, and holistic system interfaces/dependencies were minimized in order to reduce risks. The US approach was almost diametrically opposite, relying instead on a robust C&DH capability to adaptively sequence critical events, which in turn allowed more trade space with respect to subsystem performance margins.

Wonder if there just might be a truly optimal middle ground, here...

[John Whitehead]

Might be worth considering & contrasting US & old Soviet-era (SE) design approaches when thinking about MSR. ...functional modules were optimized for their specific performance....

I was recently fascinated to learn how the Soviet Luna (16, 20, & 24) achieved its ascent and earth return. Yes, it was functionally very simple engineering, tailored to the particular physical situation. The moon's small size (compared to Mars) permitted a direct return. Not going into lunar orbit meant no circularization (orbit insertion) burn, and the fact that the target (earth) was gravitationally large and nearby meant no midcourse corrections either. No need for any engine restarts or staging. A single propulsive burn from the 1-stage ascent vehicle was simply timed (both moment of launch relative to the calendar, and burn duration).

Guidance consisted of flying a vertical trajectory off the moon. The vernier engines were controlled by a local vertical sensor, a pendulum! Site selection was limited to the east side of the moon, where a vertical ascent reduced the geocentric velocity compared to the moon's, so it was effectively just a deorbit burn with respect to the earth. Velocity would have been less than lunar escape velocity, since the earth was sitting there pulling it home. The return stage had a transmitter that could be switched on and off by commands from earth, and the resulting signals received on earth were used to predict the landing point accurately enough to go out and find it.

All this is explained in a paper by Boris Girshovich, presented at the National Space Society's 26th International Space Development Conference, Dallas Texas 2007May25-28. See isdc.nss.org/2007/index.html.

My notes from reading the above paper say that the earth entry capsule was 3 feet in diameter, while the above posting from PhilCo126 a couple days ago says 30 cm. I suspect both numbers are from memory or word of mouth, so does anyone have any solid references to cite here? Has anyone been to Russia where the capsule is presumably in a museum somewhere?

Mars ascent is MUCH harder to do, considering the need for a smaller size, higher delta velocity, double the thrust-to-weight, and more complicated navigation to orbit.

John W.

[AndyG]

The vernier engines were controlled by a local vertical sensor, a pendulum!

Hi John - I'm rather wondering how that would work. If you're accelerating considerably above the level of local gravity, the pendulum will react to the centre of thrust as the local vertical. I could see a long, lazy arc being described back into the regolith.

Andy

[mcaplinger]

I'm rather wondering how that would work. If you're accelerating considerably above the level of local gravity, the pendulum will react to the centre of thrust as the local vertical.

Regardless of the acceleration, the pendulum will always react to the vector sum of the gravity vector and the acceleration vector, so if you want to fly antiparallel to the gravity vector, this should work fine.