Mars Sample Return |
Mars Sample Return |
Apr 7 2006, 07:32 AM
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Member Group: Members Posts: 370 Joined: 12-September 05 From: France Member No.: 495 |
Next phase reached in definition of Mars Sample Return mission
http://www.esa.int/esaCP/SEMJAGNFGLE_index_0.html |
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Oct 16 2007, 11:50 PM
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#2
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Junior Member Group: Members Posts: 99 Joined: 17-September 07 Member No.: 3901 |
"Jim from NSF.com" noted earlier today that a pump-fed minature launch vehicle may not be viable due to inefficiencies. That's probably true if miniaturization is attempted for centrifugal pumps powered by turbines (aka turbopumps).
Tests on a positive displacement miniature pump indicate that only 2% of the total propellant would provide enough power to run fuel and ox pumps, which is efficient enough. See JPL's Mars Technology Program website for a synopsis at (hope it's still there): http://marstech.jpl.nasa.gov/content/detai...amp;TaskID=2289 It's agreed that pressure-fed propulsion is nice and simple and reliable, but you end up having to make tank walls thicker and heavier than you would like them to be, and also engines larger than you would like them to be. For decades, people have envisioned pressure-fed liquid launch vehicles to get off of earth (Bob Truax, "Big Dumb Booster," Beal Aerospace, Microcosm, etc.), but so far none has succeeded. Even using the strongest materials (carbon fiber), the stages end up being closer to 80 percent propellant than 90 percent, and that makes all the difference (in displacing payload with rocket hardware, or in requiring the whole vehicle to grow huge for the same payload). Regarding monitorlizard's comment about the 1985 ASAT test rocket, the altitude it reached does not necessarily indicate capability to attain orbit (earth or Mars). Reaching orbit requires velocity in addition to altitude. NASA's goal for Mars sample return is to park the sample package in a circular orbit at 500 km altitude. Given only a quarter of orbital energy (half the velocity), it's possible to launch straight up to 500 km (sort of like the ASAT rocket did), but then you fall straight back down again. "Soviet engineer in the 1960's," is an especially appropriate comparison since their return vehicles that launched off the moon (Luna 16, Luna 20, and Luna 24) weighed about a metric ton. The Mars ascent vehicle has to be a tenth that mass, and just to get to Mars orbit it needs a much higher velocity (4200 m/s) than going from the moon all the way to earth (2800 m/s, which the Soviets did nicely using only one rocket stage). Great discussion! John W. |
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Lo-Fi Version | Time is now: 26th September 2024 - 04:37 PM |
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