Space Fission Power Post #2: Abundant Power is the Key to Space Exporation.

On Earth, life and humanity has benefited from the energy of the sun (plants, animals, fuels, heat, etc.), but in space you’re essentially on your own.  Power is the single most important element to the survival of both spacecraft and humans in space, and an abundance of power is essential to providing safe and reliable missions – without power there is no existence. NASA science missions have been extremely successful since the 1960s, but since then there has been no fundamental change in where we can go and how much power we have when we get there. We could increase the benefits of science missions by orders of magnitude with a robust, low-mass source of abundant power. For human exploration, the need for abundant power provides a different paradigm that we’ve come to know on Earth.  An astronaut is not concerned with the over-hyped health effects of radiation (from a reactor, or the sun and cosmic rays); rather, an astronaut’s concern is whether the power system will provide power when it is needed. In addition, these astronauts will want to be “power rich”, a term frequently used by NASA astronauts (e.g. discussion I’ve had with Scott Horowitz, Ed Lu, John Grunsfeld, and Franklin Chang Diaz) when discussing human space exploration.  The most important asset is the one that you’d prefer to be the most in abundance. Power can be binned into three areas when discussing space exploration: electricity, propulsion and heat.

Electricity

Electricity is the most valuable asset that space power systems can provide. Almost all terrestrial technologies have evolved within the paradigm of available electricity, and with enough electricity almost anything can be accomplished.  It is hard to imagine any spacecraft or human outpost in which electricity will not be the lifeblood of the mission.  Nomads and Pioneers could live off the land to explore and settle the Earth; space explorers can potentially do the same thing sans one component: electricity.  Some things can be done more efficiently without our favorite energy “middleman,” but there is almost nothing we can’t do if we have abundant electrical power.  For near-term scientific missions, increased electricity allows more capable instruments, increased instrument duty cycles, onboard scientific analysis, higher data-rate communications, and smaller antennas. For human missions, abundant electricity enables science and exploration, but more importantly it is the foundation of their safety and life support.

Space Propulsion

The first order physics of space propulsion is very simple – throw something off the back off your spaceship and you will go faster (Newton’s third law of motion).  In this respect, the brute force approach to space propulsion is to launch as much propellant as you can into Earth orbit (and if launch costs can be made affordable this is a great option for relatively low delta-V missions, like a conjunction class mission to Mars).  If launch costs are high, and/or you need to get somewhere fast, then the key to making propulsion effective is to gain as much thrust as you can for every unit of mass that you eject (Specific Impulse).    On top of this, the thrust to weight of your propulsion system and spacecraft is very important.  Ultimately, a power source can provide a propulsion system in three ways: the byproducts of the power source are used directly as the propellant (direct propulsion), the power source provides heat directly to the propellant (thermal propulsion), or the power source creates electricity that is used to accelerate an ionized propellant (electric propulsion).  In all cases, abundant energy/power is needed to enable effective human space propulsion (with due concern given to the effort required to place those energy sources and propellants into Earth orbit).

Heat

Heat is needed to keep things warm and to drive chemical processes – these functions can be completed via electricity, but they are done more efficiently without it (because heat generally creates the electricity in the first place).  In space, thermal heating is needed for systems ranging from the smallest spacecraft to large human outposts.  Where adequate sunlight is not available, NASA has routinely used the Radioisotope Heater Unit (RHU) to keep components warm in space, while waste heat from a large thermodynamic power system could keep entire spacecraft or human outposts warm at essentially no “cost” to the infrastructure.  Process heat is very important to create practical and sustainable human outposts elsewhere in the solar system.  Many technologies have been envisioned, and in some cases developed to transform in-situ materials to usable consumables (air, water, rocket fuel) and/or construction materials (ceramics and metals).  Again, if a large-scale power plant is used to create electricity, the process should reject enough “free” heat to meet most of these needs.

In the very long term, we would need to use in-situ resources to power a sustained space-faring existence. These in-situ resources could simply be the materials to fuel our previously developed technologies, or the in-situ resource might provide a unique energy alternative (using site specific chemical or geothermic resources). In all cases, an Earth-based energy technology that can provide abundant power is needed to 1) get us to our destination and 2) establish a semi-autonomous outpost/colony which can eventually evolve to a self-sufficient location.  For more information on the need for, and possible uses of abundant power to enable our expansion into space, I recommend the writings of Robert Zubrin.