Discussion
A rocket is to be launched from the bottom of a very deep crater on Mars for earth return. The specific impulse of the rocket, measured in seconds, is to be normalized by the acceleration due to gravity at
Answer: C
The specific impulse is normalized by gravity at earth's standard sea level.
Specific impulse in seconds is defined as \(I_{sp} = F/(\dot{m}g_{0})\), where \(g_{0} = 9.80665\ \text{m/s}^{2}\) is the standard gravity at earth's sea level. It is a fixed conversion constant, chosen so that \(I_{sp}\) in seconds equals the effective exhaust velocity divided by the same number everywhere.
Using local gravity at the launch site, on Mars or anywhere else, would make the same engine report a different specific impulse depending on where it is fired, which defeats the point of the figure. So the crater, Mars 'sea level' and a crater-depth value on earth are all wrong.
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