NUCLEAR POWER IN SPACE

Although nuclear power must eventually replace much of our present energy mix, its inevitability is perhaps even more clearly demonstrated for the needs of space technology.

All space missions need electric power, but communications and industrial processing generally need more than others. Beyond this need for powering internal equipment, flights to other planets will need propulsion energies that neither chemical fuels nor solar energy can supply. And it is safer than chemical fuels.

The shuttle disaster and NASA's bureaucratic difficulties aside, space technology has been laboring under inherent technological constraints since its inception: no space mission has ever used more than about 40,000 kWh of electrical energy.

What's wrong with present sources, and who needs all that power, anyway?

First, what's wrong. What's wrong with solar, we already know from earth: it is too dilute to deliver much power. For example, to provide an output of 100 kW, no less than 2,800 sq.yards of col-lecting area would be needed. But there is an additional difficulty not met on earth: as the collector area increases, so does the mass increase, and more power still is needed to maneuver it, leading to a vicious circle that results in a stagnant power plateau as the collector size is increased. This diminishing power-to-size ratio has only one advantage: it delivers me from dealing with further drawbacks in-volving energy storage and the folding of these enormous areas into the launching rocket.

Chemical fuels (in fuel cells for direct conversion to electricity) are not, like solar cells, limited by area and volume (nor in short-term peak power); but in energy delivered per unit weight, they are even worse than solar cells.

[The owner of the impaired heart is not, however, admitted to Hawaii, Berkeley, and other places ruled by backward barbarians who have declared their fief a "nuclear-free zone" or have otherwise fouled it with superstitious ordinances. The forward-looking sen- sitives of Berkeley, for example, spend much time defending the rights of the AIDS-afflicted; but the low-down outcast who has heart disease is banished from this progressive city if he uses plutonium to keep his heart going. Neither will the Hawaiian witch hunters permit such satanic contraptions in their realm; however, when a hurricane, some years ago, put their fossil-fired power plants out of action, the Honolulu city elders did not mind using nuclear power supplied by the US Navy from its ships anchored in Pearl Harbor, which is federal territory. What is it about Pearl Har- bor that deprives its commanders of perspicacity? On this occasion, the commander was ill-advised enough to give it to them.]

For power in space, however, radioisotopes are limited to minor special applications requiring low power to be consumed within a very small volume for long durations. If that is not the case, solar power is preferable.

Nuclear power inferior to solar? Is it possible?

And why not, in this context? I have never advocated nuclear power for pocket calculators or for growing tomatoes. Engineering, thank God, is not a matter of political opinions, but of demonstrable, observable and calculable facts.

What? Reactors safer at 1,000 kW than isotopes at 10 W?

That's right. But before we ask why, let me put you on hold with another point I owe you. Meanwhile the figure (based on the 1984 paper referred to below) will summarize what is usable at what power level for how long.

[DIAGRAM of MW vs Duration

of use, for four energy sources: chemical fuels, nuclear reactors, solar, radioisotopes. Indicates that each fuel is suited to a specific power level AND duration of use. chemical fuels: low to high power for short duration, solar: low power for long periods, radioisotopes: low power for long periods, nuclear reactors: high power for any duration.]