Chapter 17 - Comparative Space Power Baselines
Notes by David A Roffman on Chapter 17 of
FRONTIERS IN PROPULSION SCIENCE
Chapter by Gary L. Bennett,
Director, Metaspace Enterprises, Emmett, Idaho
This chapter discusses spaceship power sources and energy storage options. We mostly use chemical approaches to space travel. However, there are ways to improve. Free radical propulsion utilizes neutral atomic fragments produced by dissociation of molecules. Another version of propulsion is metastable, which has excited atoms or molecules with a radiative lifetime of more than a microsecond. Multiple kinds of propulsion systems may be needed for a long mission. There is a proposal to use the sun as a slingshot for extra-solar missions.
A common space power system employs solar panels. NASA has the goal of increasing solar panel efficiency. Solar panels will not work well at distances past Mars. Panels around Jupiter would have to be 25 times bigger to work the same as they do around Earth. For the Dwarf planet Pluto, they would have to be over 1500 times as large.
Considering temperature, radiation fields, and light are important. Batteries can help for short term power boosts, while rechargeable ones are weaker and steadier. Radioisotope power relies on converting heat into electrical energy, via a nuclear reaction. Nuclear power has been used in space for quite some time including in the first military GPS satellites, weather satellites, Apollo lunar data collectors, voyagers, the Mars rovers, and Galileo. Some of these reactors were so great that they lasted decades after they should have stopped working.
The New Horizons mission is currently on route to Pluto, and uses nuclear power. Its mission will rely on this power source all the way up to certain parts of the Kuiper Belt. Nuclear power has been used for decades (since the 60’s in space), and will continue to be used for probes to explore our solar system (and perhaps beyond that). For the record, the first nuclear reactor in space was for the SNAP-10A in 1965.
When spacecraft do fail, a significant amount of malfunctions are due to other system errors, not power shortage. America wasn’t the only country to have used fission power. The former Soviet Union launched perhaps as many as 33 space craft using this power source (31 have been confirmed). For nuclear propulsion, the standard proposed method is to heat hydrogen gas (using the nuclear reactor) and shoot it out the back end of the craft.
Nuclear propulsion promises to be between two to three times faster than chemical propulsion, although materials may limit its efficiency. There are a variety of designs, but those were discussed in earlier chapters. While fusion and antimatter processes are best for space travel, they are currently out of reach. A common misconception is that rockets push against something to move. In reality Newton's 2nd Law is F = dp/dt = dV/dt + Vexhaust*dm/dt. Rockets move because of the change in the mass of the rocket due to the exhaust velocity of the propellant.