Space science gets big at NASA
The future of NASA’s planetary exploration plans may rest on larger missions and nuclear technologies
by Jeff Foust
|The pendulum now seems to be swinging back in the direction of larger, more capable, and costlier missions.|
None of those planned or proposed missions, though, have attracted as much attention as Project Prometheus. The project was unveiled earlier this year as a multi-year, multi-billion effort to develop nuclear power and propulsion technologies, and put those technologies to use on space science missions. The cornerstone mission for Prometheus is a spacecraft descriptively, if unpoetically, called Jupiter Icy Moons Orbiter (JIMO). JIMO would putter among the three large icy moons of Jupiter—Callisto, Europa, and Ganymede—studying them in detail not possible before by Voyager or Galileo.
It’s not surprising, then, that when Women in Aerospace convened a panel discussion about NASA space science policy, the focus was not on the small missions but on larger missions, most notably Prometheus. The consensus of the panel, composed of NASA officials, Congressional staffers, and outside experts, is that Prometheus is a worthwhile and achievable project for NASA, but also one with its share of titanic hurdles to overcome.
What Project Prometheus offers to scientists and spacecraft designers can be summarized in a single word: power. It sounds simple, but power, along with mass, cost, and schedule, are the key variables that shape spacecraft design. The amount of power available determines what and how many scientific instruments a spacecraft can carry, as well as the rate at which those instruments can transmit their data back to Earth. Depending on the propulsion system used, power can also determine where and how fast a spacecraft can travel.
|“Power is the wellspring for everything else required on a spacecraft,” said Hartman. “If you’re going to go to multiple targets in the outer solar system, you have to use fission for power.”|
If successful, Prometheus can provide JIMO and future missions with a nuclear reactor that can generate far more power than the radioisotope thermoelectric generators (RTGs) that have been standard issue on outer solar system missions since Pioneer 10. “We’re not talking about a couple of light bulbs to power a spacecraft, we’re talking about stadium-style lighting,” said Colleen Hartman, director of the solar system exploration dividision of NASA’s office of space science.
That additional power can make all the difference in planning a mission to Jupiter’s moons. As currently envisioned JIMO will carry a large suite of instruments, likely including a radar sounder to measure the depth of the ice crusts on the three moons, a laser altimeter, and a camera, among others. Most of these instruments typically have large power and/or data transmission requirements that make them difficult to include on power-constrained budgets. “Power is the wellspring for everything else required on a spacecraft,” said Hartman. “If you’re going to go to multiple targets in the outer solar system, you have to use fission for power.”
JIMO is the successor to Europa Orbiter, a mission NASA was planning in the late 1990s but eventually cancelled because of cost overruns. The RTG-powered spacecraft would have performed only a handful of flybys of Callisto and Ganymede before entering orbit around Europa, where it would be able to spend, at most, a month or two studying the moon with a radar sounder and a few other instruments before radiation irreversibly damaged the spacecraft. JIMO will be able to spend months orbiting Callisto and Ganymede, studying them in detail before venturing into the harsher radiation environment around Europa. A goal of JIMO, Hartman said, is to provide 10-meter resolution images of virtually the entire surfaces of all three moons, something that would not have been possible with Europa Orbiter.