Henry Spencer wrote:

They are, alas, the key systems. It's a propulsion-intensive mission, and
needs precision guidance en route and for landing, and at least a minimum
of guidance for the return trip.

Hmm, 20kg payload. Perhaps: 5kg of packaging, 10kg heatshield, 5kg
parachutes, 5kg main structure, 5kg misc. subsystems. That's 50kg at
reentry. 5kg of electronics, 5kg midcourse maneuvering, 5kg power and
misc. gives 65kg payload for the ascent stage.

5kg engines, 5kg controls, 5kg tanks and general structure, with the
payload handling guidance, gives 80kg dry mass for a pretty light ascent
stage. Assuming unimpressive pressure-fed propulsion, mass ratio is going
to be 3 or so, giving lunar liftoff mass of 250kg.


The Soviet sample return missions had no midcourse correction ability;
the return stage was launched toward the zenith of the Lunar heavens
over where the lander was positioned, and gravity did all the rest to
get it back to mother Russia. The landing sites had to be precise to
allow this to work, and in fact a specific launch time from Earth meant
a specific landing site on the Moon- badly limiting the areas that could
be sampled. The ascent stage carried just gyro stabilization systems
that kept its ascent vertical and accelerometers to permit motor
shutdown at the correct velocity for its return trip Earthwards.
I think this gets discussed in "Challenge To Apollo".
The mathematician who came up with the idea for this mission trajectory
was very well thought of in the U.S.S.R.; AFAIK, the U.S. never
developed this idea independently.

Pat