Translating the incremental velocity data and specific impulse data into weight ratio yields Figure 5.8. The weight ratio for the four propulsions systems described in Table 5.3 is indicated in the legend. The weight ratios for the LEO to GSO orbital altitude change are: 4.00 for the hypergolic engine, 2.39 for oxygen/hydrogen, 1.55 for solar electric and 1.11 for nuclear electric. The acceleration specified for the chemical rocket powered OMV is 0.5 "g". For the electric thruster-powered OMV the acceleration is 0.1 "g". The gross weight of the one-way OMV is straightforward, and the sizing program balances the propellant required versus the capacity of the propellant tank that determines the operational empty weight (OEW). The sized OMV for each of the propulsion systems transporting a 5,000-lb (2.268-ton) satellite given in Table 5.6 that follows. The gross weight for the one-way mission is:
Gross weight = WR (OEWomv + WSatemte)
Note that the Operational Empty Weight (OEW) is essentially constant. It is greater for the electric propulsion configurations because of the solar panels for the solar electric and radiators for the nuclear electric. As in the case for the launchers, the primary difference in the weights and thrusts is a result of the carried propellant. The propellant mass for the hypergolic rocket is 34 times greater that for the nuclear electric rocket. The propellant load is reduced by the increasing specific impulse of