Thursday, October 13, 2011

Solar thruster calcs

Given that 25 kw of electrical power can be created and, assuming that this will lift 25 times 100 kg/kw equals 2500 kg giving a thrust to mass ratio of 1 to 1:

Let's break down the various components to see what we can come up with:

Allow 500 gallon tank, stainless steel for hydrogen storage, plus insulation 1000 lbs or 454 kg,  400 kg hydrogen fuel equals 854 kg for fuel and tank, 35 kg for a suncube 1 square meter times 64 suncubes to generate 25 kwh of electrical power in space.  We don't need as much mass, because it is in space, no weather issues.  So let's assume that you can cut the cubes weight down by 75%.  That gives 560 kg. for the cubes.  Together, the fuel and the power takes up 1414 kg.
Need a heat exchanger and a nozzle, pumps and plumbing.  I am wondering if the heat exchanger and the nozzle can be combined.  That would save mass, hopefully.  Some of the plumbing will be inside the heat exchangers.   This may not be comparable in weight, but this engine here would probably be powerful enough to lift off the moon.   It's mass is 242 kg.  If that is all it weighs, we don't need to worry about exotic new combination of heat exchange and nozzle.  Double the mass for those two.  That gives another 242 kg.

Summing up the two above paragraphs, we arrive at  1898 kg.

That leaves 602 kg.  for all of the rest of your equipment before you even get to crew and crew hab.

But not to worry.  The moon's gravitation is but 1/6 of Earth's, so the thrust to mass ratio can be less than 1 and still lift off.  Perhaps it can be as low as 1/4 to 1.  The Shuttle's thrust to mass at liftoff was 1.5 to 1, so  if you take 1/6th of that, you get about 1/4.  So, we have a lot of room left.  Even if I underestimated by a factor of 2, it would still leave a ratio of 1/2, which is twice 1/4.

This exercise is speculative of course.  I'm not qualified to do a thorough enough and accurate enough job for this, but given the possibility of not being too far off, it would appear that a lunar module could be constructed that would allow you to launch missions off the moon into lunar orbit and beyond.  That could be back to Earth, or to a Lagrangian point where a more capable machine could take you to ???  Mars, maybe?

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