Figure 10.4.9 Basic Orbit Transfer Options The Hohmann transfer coupled with a plane change at apogee requires a total AV of 4330 m/s. Using a cryogenic chemical propulsion system with a specific impulse of 450 m/s leads to the following ratio of fuel mass to spacecraft dry mass: 1.65. Hence, for a spacecraft dry mass of, say, 50 t, the mass of propellant is 82.5 t giving a total mass of 132.5L This is very large and would necessitate, for instance, two Energia launches. Similar analysis can be done for the purely electric propelled spacecraft in a spiraling trajectory, with optimal plane changing as an integral part of the maneuver. This calculation is summarized below: So, electric propulsion has considerable advantages in terms of propellant mass saving, but significant disadvantages in terms of the power requirement and the transfer time. The latter suggests that long durations are spent traversing the Van Allen radiation belts with the serious risk of solar cell degradation (specially for a low cost a Si option) and damage to on board electronics. To account for the advantages and disadvantages of both propulsion systems, a possible solution may be to design a ‘hybrid propulsion system for the maneuver. This would use chemical propulsion for the first stage of the maneuver in order to
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