(1 porticie per km2-yeor)


(1 porticie per km2-yeor)

_■ ' r.i.J_■ I ".J rJ J I ■ ; Irf J I '' rJ_■ i ..m.1

,„U 15 ,„16 ,„17 IS ,„19 ,„20 ,„31 10 10 10 10 10 10 10 10 10 10 10 10 10

Energy (eV)

Figure 7.19. Cosmic ray energy spectrum.

pessimistic views are expressed in [Choi, 2008]. In fact, this is a key issue in any plan of lunar or planetary colonization: across its spectrum, radiation energy is so high as to result in impractically massive, or energetic, shielding strategies conceivable at this time.

In planning interplanetary manned missions all this argues powerfully for shortening them as much as possible. In light of this conclusion, nuclear propulsion, with its high Isp and reasonable thrust over long periods of time stands out as the prime candidate for a propulsion system.

In the following, the two classes of nuclear propulsion systems, NTR and NER, together with their many variants, will be described and briefly discussed; however, the basics of nuclear fission reactor technology will be first outlined. For generic engineering details the reader should refer to Turner [2005]; three space reactor concepts are discussed and compared in [Lenard, 2008].

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