Moonguy

Consider an unmanned lunar cargo lander that delivers 5,000 kg to the lunar surface. The delta-v for landing from a low lunar orbit is 2,100 m/sec. and the Moon's gravity is .16 Earth's. Now, consider that same lander used to land a payload on Mercury from a low Mercury orbit where the delta-v involved is 3,200 m/sec. Mercury's gravity is .38 Earth's. All of the physical characteristics of the lander must remain the same, only the payload mass can be altered. How much payload must be off-loaded to accomplish the landing? Thank you. . .

Good clarifications, thanks! Regarding the reflector/concentrator, why are they made of anything rigid at all? Solar sail films already exist with 10 GRAM/m2 density. They ;also have 90% reflectivity. The materials available - at least the samples I have held in my hands - are strong enough to be integrated into an inflatable structure or even a mechanical arrangement like that in an umbrella. Adding scrim or other items to strengthen the reflector material is easily accommodated well with in the 1 kg/m2 mass limit. The system you describe has a lot of flexibility. I have to think a solar thermal stage would be easier to develop than a nuclear thermal stage. The higher Isp (1267 vs ~950) sure looks like ample incentive. Sort of gets you to wondering why. . .

This occurred to me while I was reading the earlier posts: Would it not be possible to channel the concentrated light into the thrust chamber through fiber-optic cables? This would make the orientation of the reflectors independent of the thrust vector. The light from the fiber-optics concentrates inside the chamber as in other concepts, but does not require the chamber to be designed with exotic materials in order to allow light through. I have not had time to check it out, but it would seem this could scale sufficiently for use by a manned vehicle. . . especially one going to Mercury (or Venus).

Dude, every time I read one of your posts I get at least 100 ideas to chew on. I'm starting to mutter things like "Inverse square rule at Saturn would yield. . ." at the dinner table. My family is starting to worry. STOP!! Get out of my head!!!

I hope this will be on-topic: Would the extruded panels with corrugations necessarily require an 'outer' skin? Oriented in line with the thrust axis, I would think the corrugations would provide adequate stiffness against panel flutter. For thermal insulation, half of the tank circumference is naked to the air but could easily be protected with spray-on foam. This would also tend to 'smooth' the surface of the tanks and reduce friction losses.