Imagine you were planning to hike the entire Appalachian Trail — all 2,181 miles from Georgia to Maine — without stopping to replenish supplies. What would you set out with in your backpack? The answer is obvious. Almost everything you carried would be food or water, because that’s what you would need to generate the energy for the trek.
Going to Mars or anywhere else interesting beyond low-earth orbit presents a similar logistical challenge. The chemicals required to provide energy for propulsion use up almost all of the available space on your rocket. Remember, once you get into space, you will need propellants not just for speeding up but for slowing down, and every time you make the slightest change in direction, more of that precious cargo will be expended. That’s why we sometimes wind up retiring satellites that still seem to be in good working order — they’ve simply run out of the propellant needed to stay in useful orbits.
This is a tough challenge for any human spaceflight mission to Mars, because so much propellant is needed to get out and back that there’s little space left onboard for anything else. NASA will face the same dilemma no matter what design it picks for its next heavy-lift launch vehicle. But what if there were a way around the problem, a new approach to powering spacecraft that could reduce the amount of mass that needs to be lifted into space by 50 percent or more? Think of the billions of dollars and years of effort that could be saved.
There’s a good chance the solution already exists. It’s called solar-electric propulsion, and it uses the same kind of solar arrays to collect energy that are already installed on hundreds of spacecraft. The basic idea is to turn energy radiated by the sun into a form that can be used to move spacecraft around. The spacecraft would be slower than the chemical rockets NASA uses today, but most of what a manned mission to Mars needs could be dispatched to the Red Planet long before astronauts are, the same way soldiers deploy by air to war zones while their supplies come mainly by ships.
This simple division of labor could drastically reduce the cost of any human deep-space mission, while providing new technology in the near term for maneuvering or servicing satellites already in orbit. The technology not only exists, but was recently used to move a billion-dollar military communications satellite into the proper orbit after its main launch vehicle malfunctioned. All NASA needs to do is provide the money for a modest demonstration project that verifies the concept will work in a scaled-up version. There is already a line item in NASA’s budget for such research, and solar-electric propulsion is the most mature option available for meeting both civil and military needs.
I’m not talking about big money here — maybe fifty cents per taxpayer every year for five straight years. That’s around $400 million total to generate a demonstrator that could provide near-term value while allowing the space agency to shave many billions of dollars off the cost of any Mars mission. It’s a huge bargain that could completely rewrite the calculations for what a Mars mission would cost. Incidentally, it would also keep America ahead of other nations in the development of space technology while consuming less than one-percent of NASA’s budget. Sounds like a no-brainer to me.
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