At lunar takeoff, this tanker would mass tons, but since it is taking off in lunar gravity, it would effectively weigh only about 62 tons. The composite propellant tanks, similar to what will be used for the BFR, would probably mass only 20 tons, leaving 2 tons for the engines, 2 tons for the landing legs, and 6 tons for the rest of the structure, including the cryo-coolers, sunshade and power system. This provides a structural mass fraction of 8. At this point, we do not know the actual cost of the lunar propellants as delivered to the tanker at the lunar base, including the vehicle development costs, but finally we can compare the relative mass of the delivery propellants.
Radiation design by CGI mesh modeling. Should illustrate the point nicely! I should suggest this to the good people making Kerbal. Could be a cool part of the design experience for nuclear spacecraft.
I've found that a smaller shadow shield diameter is possible by adding truss segments between the shadow shield and the aft end of the radiator panels. Because the truss is lighter than the shadow shield, you realize a mass savings.
He is also using Blender 3D. Click for larger image, and to read William Black's detailed analysis and work logs on the project. Dogmatic Pyrrhonist and I both set about individually setting up a radiation simulation by CG lighting; his results are to be found at links in this thread November 6, Initially, for purposes of approximation, I used a cone, which you strip out of the scene once it has served its purpose, this is used to insure the radiators panels and everything else forward of the shadow shield are completely within the shadow region.
It is a matter of placing the cone so to intersect the aft-most edge of the radiation shadow shield, if all components forward of the shadow shield are properly placed nothing should protrude through the surface of the cone. I realized the technique can be used not only to optimize the shadow shield in terms of placement, but also in terms of diameter.
Previously, using the cone I had realized that increasing the distance between the aft edge of the radiator panels and shadow shield allows a smaller diameter shadow shield. Using this technique allowed me to test that theory, and it in fact worked exactly as anticipated. I rendered the scene against a gray background, then a second time against a completely black background.
I made an attempt which may be laughable to model the plume. I used a bright blue emission shader. I was curious in regards to how much blue emission, representing radiation from the plume, would show up on the structure of the vehicle.
Ron Fischer suggested I attempt this again with volumetric lighting, and I intend to do so at a future date. You might want to check for radiation scatter from the rocket bell to the radiators. Just eyeballing it, it looks like that could happen. Also, from the linked post describing the design — you probably will want a few centimeters of lead fore of the borated polyethylene, for sopping up the gamma rays.
The set of materials that are good at stopping neutrons seems to be orthogonal to the set of materials that are good at stopping gamma rays. By putting the poly between the reactor and the lead, you arrange it so that gamma rays produced by neutron interactions in the poly are also blocked by the lead part of the shield.The American Radio Relay League (ARRL) is the national association for amateur radio, connecting hams around the U.S.
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