Notes on fabrication of spacecraft, Part VIII

 Speculation alert will apply: Series continued from last post.

This series is similar to the series that I did in 2012 on Infinite ISP.  I called it the MAB, which meant Microwave Air Breathing Booster.  That concept was to use a microwave beam as energy to heat the reaction mass, which was the atmosphere itself.

The main goal behind these speculations is a way to minimize the size of the spacecraft that gets to orbit.  The more reaction mass that won't be carried along, the better, for each pound adds many more pounds that have to be carried as well.

This is the reason for using the SABRE concept of an airbreathing rocket, as oxygen makes up a considerable amount of reaction mass.

As the air gets too thin, however, the onboard reaction mass has to take over.  This is the reason for a nuclear thermal rocket, as the ISP will be up to a thousand.  But we can't use an NTR until we get to the Karman line, so how to deal with that?

Instead of using the SABRE engine in conventional rocket mode, switch to the microwave power to get to the Karman line with an ISP of nearly as good as an NTR.  This saves the need for the heavy oxygen requirement and relies totally upon hydrogen as a reaction mass.

Perhaps the SABRE could be eliminated altogether.  For some folks, they may want to remove the NTR as well and go entirely with the Microwave approach.  But the ISP isn't quite as good, so that won't allow optimization.  Secondly, the Microwave has limited range.  Move outside its effective radius and you lose power.  One other consideration, the Microwave has to be in a dry place with little humidity, as the humidity will foul up the transmission of the energy beam.  This introduces a complexity to combining the NTR with the Microwave.  What to do to overcome that problem?

I was thinking of placing the Microwave complex on top of a mountain in the middle of the Pacific.  Mauna Kea Hawaii to be exact.  Given the right location, desert like conditions can be re-created on the backside of a mountain that is high enough to cause snowfall, which depletes the atmosphere of water.  The thinner air at the summit is also helpful with the projection of an energy beam.

So, in practice, the 747 will carry the X-33 to 30k feet and release it.  Either the SABRE engines take over, or the Microwave, or a combination of both.  The X-33 reaches the Karman line, and then releases the NTR package, which then takes over and goes to orbit.

I'll look at the mass savings in the next post.