the nature of ion engines, which have very low thrust but very high specific impulse, or thrust per unit mass of propellant, this is a very slow vehicle, which takes 130-160 days to go from LEO to GEO, and perhaps 30 days for the return trip. Thus the COTV cannot be used for transporting people because the radiation dose during this very slow passage through the earth's radiation belts would just be too great. Accordingly, there is a POTV for people and priority cargo, which uses ^“O? chemical rockets and takes only several hours for the trip. The scale of the operation is very large: Figure B.l gives the construction scenario for both the more conservative (Si) and the more advanced (Ga) options, which are described in more detail in RSR, 1978. The two options have been developed, respectively, by Boeing using Si solar cells and greater total mass (50,000 metric tons per unit) and more conservative technology (I = 7000 sec for the ion engines, etc.), while the more advanced technology developed by Rockwell uses GaAlAs photocoltaic cells, lighter weight (37,000 metric tons per unit) and even higher impulse ion engines (I ■ 13,000 sec). The injection model used here, in Table 3, comes from tRi Boeing scenario (see RSR, 1978, p. B-100). Table B.2 supplements the data of Fig. 1 in presenting the emission of the main burn of the HLLV.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==