9.18 From orbital mechanics, the total velocity change requirement from lunar orbit to lunar landing is 1762 meters/second, or 1938 meters/second with a 10% velocity reserve. Again,assuming the use of space shuttle main engines y may be found to be .5458. The preliminary design criteria determine the lunar landing vehicle fixed masses. Since the engine is a flight-critical i tern, it is a single failure point for crew safety. For this reason,the LLV propulsion is baselined as two space shuttle main engines. Either engine supplies enough thrust to lift 1282 tons against lunar gravity, and thus two engines provide flight redundancy for LLV's with a gross mass less than this figure. Use of two SSME's increases the propulsion mass to 6 tons. It also doubles the mass of thrust structure, which becomes 1 ton. ·Reaction control system and avionic/miscellaneous masses remain · at OTV levels of .5 and 1 ton, respectively. Landing gear mass, based on comparison to aircraft of similar landing mass and sink rate, is 1.5 tons (9.5). The remaining factor contributing to fixed mass is t.!-1 ?.-t 0f the cre~.v P.10'1111'7 . The T.I.V mi ~sions are short,on the order of a day, and while a crew may remain on duty for multiple missions, total mission time for an LLV crew almost certainly remains below two weeks. Assuming a crew of two, it becomes clear that the LLV crew module is closely related in its mission to a Geminf spacecraft. Although weight savings can probably be made due to a lower gravitational environment, the crew module mass is here assumed equal to that of a Gemini: 3 tons (9.6). Total fixed mass of the LLV is the sum of these masses, or 13 tons. The primary mission for the lunar landing vehicle is transporting materials and supplies from lunar orbit to the surface without a return payload. Using the mass matrix equations, it is found that an LLV payload of two space shuttle payloads results in a necessary propellant mass with tankage which is also equal to two space shuttle payloads. The exact numbers may be seen in the mass breakdown of Table 9.3. It is seen from these figures that the total propulsion mass for each mission,consisting of propellant and tank
RkJQdWJsaXNoZXIy MTU5NjU0Mg==