That’s where B612 wants to step in. In addition to its primary mission, Sentinel is expected to detect many of the smaller Tunguska-size asteroids. “Our goal is to find as many of the dangerous asteroids as possible,” Lu says. If an asteroid on a collision course with Earth is found and tracked early enough, it might be possible to launch a mission to deflect the object.
In 2002, when B612 was co-founded by Lu, Apollo 9 astronaut Rusty Schweickart, Princeton University astrophysicist Piet Hut, and asteroid expert Clark Chapman from the Southwest Research Institute in Boulder, Colorado, it was to pursue ideas for a deflection mission. Among them is the “gravity tractor” maneuver, where a spacecraft hovers near the asteroid, and over the course of several years or more, its relatively tiny gravitational field nudges the asteroid just enough to move its trajectory off a collision course with Earth. B612 assumed that NASA would eventually get a handle on identifying the potential NEO threats.
“It’s very clear that we can deflect an asteroid,” says Schweickart, now chair emeritus of B612’s board of directors. “The prerequisite, of course, and we’ve known this for many years, is adequate early warning…. What was clearly happening within NASA was that this was not being picked up and championed.”
There are some ground-based projects, such as the University of Hawaii’s Panoramic Survey Telescope and Rapid Response System—Pan-STARRS—and small-telescope networks like the Catalina Sky Survey (see “Pint-Size Sky Watchers,” Oct./Nov. 2012), whose primary goals are to search for NEOs.
Sentinel, surveying from space, will complement these projects by covering more of the sky, says Harold Reitsema, Sentinel’s mission director and a retired director for science mission development at Ball Aerospace & Technologies Corporation in Boulder, Colorado. “In order to get a good orbit for [the asteroid], you need to be able to see it many times…and the longer you watch it, the better understanding you have of the orbit,” Reitsema says. Having many instruments dedicated to searching for NEOs, both on Earth and in orbit around the sun, will mean more opportunities to track objects, he says. The time-consuming process of “orbit determination gets very much better.”
Once the B612 leadership decided to build Sentinel, things started to move quickly. The foundation assembled a team of engineers and administrators, among them Reitsema; project architect Scott Hubbard, former director of NASA’s Ames Research Center; and Tom Gavin, former associate director for flight projects and mission success at the Jet Propulsion Laboratory in California.
Ball, which has extensive experience working on the Hubble, Spitzer, and Kepler space telescopes, as well as the Deep Impact mission to comet Tempel 1 in 2005, has bid a fixed-price contract for the development of Sentinel and is currently negotiating the details, including cost, with B612.
Unlike negotiating an arrangement with NASA, working for a private foundation frees Ball from many of the regulatory and accounting rules imposed on taxpayer-funded space projects. The result will save B612 up to 30 percent, Hubbard says. That’s how B612 can keep the total cost of the mission, including plans to launch aboard SpaceX’s Falcon 9 rocket, to something in the neighborhood of $400 million, he adds.
John Troeltzsch, Ball’s designated program manager for Sentinel, has also worked for the company on Hubble, Spitzer, Kepler, and Deep Impact. Sentinel will need a deep space communications system like Deep Impact, a wide field of view and onboard processing power (so it doesn’t waste bandwidth sending data on known asteroids) like Kepler, and infrared detector systems like Spitzer.
Keeping Sentinel’s detectors adequately cold will be a challenge, particularly because the spacecraft will be much closer to the sun than other space telescopes. Unlike Spitzer, which relied on a large tank of liquid helium coolant, Sentinel will use a cryocooler—a mechanical refrigeration device—to keep its detectors cold and free from thermal interference. Imagine a much more elaborate version of the compressor underneath your refrigerator.