I spent nearly the entire weekend on the launch system specifications, and compiled a non-standard launch system.  Instead of a conventional rocket launch, I have decided to use a heavy-lift cargo plane as the first stage.  The Russians did research on this during the late 80s for their MAKS program.  MAKS also has a fuel tank and orbiter, giving me what appeared to be an all-in-one solution for a CTV.  However, MAKS can only reach an altitude of 200 kilometers; ISS’ orbit approaches a 400-kilometer altitude.  So, I needed to try to get this thing lighter.

The MAKS system already was the maximum payload the cargo plane could carry, and since the cargo plane is the largest in the world there’s nothing I can do.  So the first thing I concentrated on was the orbiter.  The MAKS orbiter was designed to be a mini-shuttle, complete with payload bay, crew cabin, and remote manipulator arm.  As the CTV has nothing to do with payloads, and the fact that the orbiter weighs nearly 27 metric tons, a new orbiter was needed.

I decided to take another look at the X-38.  It can carry a crew of 6 (MAKS could carry 8 if the payload bay had a pressurized living module installed), yet weighs less than a third of the MAKS orbiter at 8,163 kilograms.  The X-38 lacks engines though, so I added the MAKS’ 2 RD-701 engines to the configuration, brining the orbiter’s mass up to over 15 metric tons.  It was at this point I realized that this nearly doubled the mass, so I went hunting for a new engine.

The Encyclopedia Astronautica CD-ROM has a spreadsheet with detailed specifications concerning every rocket engine ever built.  I created a couple new columns in the spreadsheet that held equations to determine how many engines would be required to meet or exceed the total thrust of the 2 RD-701 engines and give me a mass ratio of the 2 RD-701s vs. the weight of the engines in question.  2 engines came back, one just barely meeting the requirements.  The 2^nd was the RD-261, which provides 15% more thrust while reducing the engine mass by nearly 30%!

The RD-261 engine uses different propellants than the RD-701, which proved to yield more weight reductions.  The RD-701, along with kerosene, used liquid oxygen and liquid hydrogen.  Both of these are very cryogenic, requiring additional hardware in the fuel tank to keep them at their extremely cold temperatures.  They also need to be constantly topped-off prior to launch.  The RD-261’s propellants, UDMH and nitrogen tetra oxide, are not cryogenic and are actually the preferred propellants for ICBMs, which the military likes to have ready to go at any minute in the event of an emergency.  The RD-261 was originally developed to propel ICBMs for the Soviet Union, created in the early 1970s.  The RD-701, however, was designed exclusive for MAKS, and its first test firing occurred in 2001.  Given all of these advantages, and the fact that the RD-261 has a long service record and the RD-701 has none at all, I find this to be an excellent engine to use.       

Mr. Kross also passed my request for an Outside Expert to a Mr. Victor Pritchett at the Marshall Space Center in Huntsville, Alabama.  He has experience with SLI, numerous CTV proposals, and will be working on the NASA’s new OSP program.  He said that he would be delighted to assist me.  I have sent a more detailed report of my CTV draft to him and to Mr. Peters.  During the coming week I hope to determine whether my weight savings will allow this configuration to reach the ISS and revise the draft with Mr. Peters’ and Mr. Pritchett’s recommendations.