obtained from the assumption that the entire EOTV vehicle is used on its last or 20th flight to carry out disposal missions. Thus taking one twentieth of the cost of an EOTV, $690 million, an estimate of $34.5 million is obtained for satellite modifications. The final cost, that of mission operations, is a time dependent cost. It is assumed here that the mission operations costs for the disposal mission are equal to mission operations costs for EOTV flights. This amount is $4.8 million per year. Using the EOTV thruster packs, it requires about 62 days to impart a velocity increment of 1 km/s to the SPS satellite. Thus the mission operations costs, assuming continuous thrust operation, amount to about $818,000 per kilometer per second of velocity increment. Combining the above costs leads to a velocity-dependent cost estimating relationship for SPS disposal cost as follows: Disposal cost = $(34.5 + 18.0 AV) million. This cost is given in 1977 dollars, comparable to the SPS cost estimates. It is the cost presented in Table 1.3. In order to compare these costs to the satellite capital investment cost, they must be discounted back to the initial operation date of the satellite. This discount factor is (1 + p)~L where is the discount rate and L is the satellite lifetime. Taking P = 0.04 and L = 30 years, (1 + p)~L = 0.308. Thus the present value of disposal costs referenced to the initial operation date of the satellite are on the order of $30 million or 0.3 percent of the capital cost of the satellite.
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