Linguofreak
Well-known member
I was thinking it might be interesting to design an addon for a mission that involves landing a lunar inhabitant on the Earth and returning him safely to the moon with approximately 1960's or 70's technology. (Before the decade is out, if possible. )
The challenge of this is that it would involve finding some way to soft-land a surface to LEO launcher (Something about the size of a Mercury-Atlas for one man to Earth, or Gemini-Titan for two men) on an unprepared field (thus ruling out "airplane style" landings) on Earth. We'll probably have to ignore/handwave the logistics aspect, since such a launcher would require a pretty massive crew to prepare for launch, and just landing it and getting it up again should be a pretty big challenge without worrying about whether our surface team could actually prepare the rocket for launch.
Our tech assumptions:
The empty mass of each stage/vehicle involved is equal to engine+structure+crew quarters (if that stage has any)
Crew quarters mass 1000 kg of life support + living space + occupant per person carried.
Engine mass is determined by power/mass ratio, with the limit being somewhere around 3 Megawatts per kilogram. (Power is equal to isp*thrust). The J-2 is 3.024 MW/kg, so that high is fine, but don't push it too much higher.
Structure is 5% of crew quarters + engine mass + fuel. This is subject to review by those with more engineering experience than myself. Structural mass will probably be a fairly high percentage for Earth stages (since they have to withstand 1 g on the surface, and more than that during launch, as well as a bit of a jolt during landing), and a fairly low percentage for space stages and lunar liftoff and landing stages.
Engine types should be limited to nuclear thermal and chemical. ISP's and propellant densities should be within reason for the engine type selected (propellant density should probably have some effect on structural mass, but I'm not exactly sure what effect). For nuclear thermal, the ISP limit is 10000 m/s for hydrogen, 7800 m/s for methane, and 6300 m/s for ammonia.
Anybody interested in trying?
The challenge of this is that it would involve finding some way to soft-land a surface to LEO launcher (Something about the size of a Mercury-Atlas for one man to Earth, or Gemini-Titan for two men) on an unprepared field (thus ruling out "airplane style" landings) on Earth. We'll probably have to ignore/handwave the logistics aspect, since such a launcher would require a pretty massive crew to prepare for launch, and just landing it and getting it up again should be a pretty big challenge without worrying about whether our surface team could actually prepare the rocket for launch.
Our tech assumptions:
The empty mass of each stage/vehicle involved is equal to engine+structure+crew quarters (if that stage has any)
Crew quarters mass 1000 kg of life support + living space + occupant per person carried.
Engine mass is determined by power/mass ratio, with the limit being somewhere around 3 Megawatts per kilogram. (Power is equal to isp*thrust). The J-2 is 3.024 MW/kg, so that high is fine, but don't push it too much higher.
Structure is 5% of crew quarters + engine mass + fuel. This is subject to review by those with more engineering experience than myself. Structural mass will probably be a fairly high percentage for Earth stages (since they have to withstand 1 g on the surface, and more than that during launch, as well as a bit of a jolt during landing), and a fairly low percentage for space stages and lunar liftoff and landing stages.
Engine types should be limited to nuclear thermal and chemical. ISP's and propellant densities should be within reason for the engine type selected (propellant density should probably have some effect on structural mass, but I'm not exactly sure what effect). For nuclear thermal, the ISP limit is 10000 m/s for hydrogen, 7800 m/s for methane, and 6300 m/s for ammonia.
Anybody interested in trying?