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K2 illustration
Despite losing two of its four reaction wheels, NASA’s Kepler spacecraft has found new life—and new planets—with its K2 mission. (credit: NASA Ames/JPL-Caltech/T Pyle )

Two astronomy missions back from the brink

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For all the challenges involved in flying a space astronomy mission, from the technical issues during its development through launch, scientists want to ensure that the missions work as long as possible when (and if) they start operating. In many cases, it may be scientists’ only opportunity in their professional careers to carry out these observations, and use them as the basis for later missions.

“The plane has come back in ‘like new’ condition,” Marcum said of SOFIA. “We have a very healthy observatory.”

Two missions in NASA’s portfolio of astronomy missions, though, recently faced untimely ends, albeit for different reasons. The Kepler spacecraft ran into technical problems in 2013 when the second of four reaction wheels, used to accurately point the spacecraft at a specific region of the sky, failed. Last year, the Stratospheric Observatory For Infrared Astronomy (SOFIA)—not a space mission per se, but an airborne observatory carrying out observations not possible from the ground—was facing cancellation by the agency as a cost-cutting measure.

Today, though, both Kepler and SOFIA have survived their brushes with programmatic death. SOFIA got most—but not all—of its funding back in the final fiscal year 2015 spending bill, enough to keep the airborne observatory flying. Kepler, meanwhile, has found success in an alternative mission, even as scientists continue to analyze the data it collected in its four-year original mission.

“A very healthy observatory”

SOFIA was in the process of being declared operational last year when it was hit with a budgetary surprise. The Obama Administration’s 2015 budget request slashed the project’s budget from $87.4 million it received in 2014 to only $12.3 million. NASA said constrained budgets forced it to make the decision to cut SOFIA funding. “It turned out that we had to make very difficult choices about where we go with astrophysics and planetary science and Earth science, and SOFIA happened to be what fell off the plate this time,” administrator Charles Bolden said last March (see “Aborted takeoff”, The Space Review, March 17, 2014).

A few months later, SOFIA’s fortunes were changing. The House of Representatives passed an appropriations bill in late May that largely restored the project’s budget, back to $70 million. A bill under consideration (but never passed) in the Senate offered $87 million for the project. However, those involved with SOFIA had to wait until Congress passed the omnibus spending bill last month to officially be out of the woods. That bill, like the House version, provides $70 million for SOFIA.

That amount is enough to allow SOFIA to resume science observations later this month (it had been undergoing maintenance for the second half of 2014), although project officials said last week they’re still working to determine the effect the lower funding level—a 20-percent cut versus 2014—will have on operations.

“There will be some impacts due to the cut for this year,” SOFIA project scientist Pamela Marcum said at a SOFIA “town hall” meeting last week at the 225th Meeting of the American Astronomical Society (AAS) in Seattle.

Marcum said the project is assuming that the 2015 funding level is a “transient dip” that will be restored to the earlier, higher level in future budgets. “Therefore, the decisions we are making to address the budget challenge for this year should not have permanent ripple effects for the duration of the program,” she said, although she did not disclose the options under discussion to implement that cut.

For now, the plan is for SOFIA to resume science observations later this month, and begin a new series of competitively-selected observations, called Cycle 3, in March. Among the science planned for Cycle 3 are observations of Pluto as it occults, or passes in front of, a star just two weeks before NASA’s New Horizons spacecraft flies past the distant world, offering an early preview of the state of Pluto’s tenuous atmosphere.

Marcum said the project assumes the lower 2015 budget is a “transient dip” that will be restored to the earlier, higher level in future budgets.

Despite its budgetary troubles, SOFIA is in good technical condition. The aircraft underwent a six-month “heavy maintenance” period in Germany starting in June, overseen by NASA’s partner on the project, the German space agency DLR. The project decided to go ahead with the overhaul when it was clear the project was no longer in serious danger of losing its funding and thus mothballing the aircraft.

The SOFIA aircraft, a Boeing 747SP, returned to California last month. “The plane has come back in ‘like new’ condition,” Marcum said. During the overhaul, technicians also examined the 2.5-meter telescope mounted in the plane’s aft section, looking for any wear and tear. “There was no notable trace of wear or damage,” she said. “We have a very healthy observatory.”

K2 ascending

Kepler, meanwhile, has found new life with a somewhat different mission than its original one. With only two of four reaction wheels working, Kepler is no longer able to precisely point at the same field of the sky as it had done originally. However, engineers found a way to use those two wheels, along with solar pressure and the spacecraft’s thrusters, to point at different fields for about 80 days at a time, changing fields to accommodate changes in the direction of solar pressure as the spacecraft orbits the Sun.

Kepler is now in the third of nine such 80-day campaigns on what’s called its “K2” mission, which won approval last May by a senior review panel that examined NASA’s ongoing astrophysics missions. That K2 mission, project scientist Steve Howell said at a separate town hall meeting during the AAS conference, was going well. “The spacecraft is doing really fine,” he said.

In fact, project officials said the spacecraft is pointing more stably than previously expected, requiring less thruster propellant. As a result, it should be possible to extend the K2 mission once the last of the nine scheduled campaigns is done in mid-2016. “When we first proposed the K2 mission, we thought we had enough fuel to last for two years,” Howell said. “We believe we can go about another year.” That would allow for four more 80-day observing campaigns.

“Most of the new 500 candidates we announced are going to be planets,” said Caldwell of the latest Kepler discoveries.

The K2 mission has also started to generate discoveries. Last month, NASA announced the first exoplanet detected in data collected during the K2 phase of Kepler, a world 2.5 times the size of the Earth closely orbiting its star. While hardly an Earth-like world, it does raise the prospects of finding such worlds, particularly around cooler stars where the habitable zones are closer in, allowing time to detect transits even during the shorter observing campaigns offered by K2.

The K2 mission is continuing although the mission got a 10-percent cut in 2015, according to agency officials. “We are currently in the process of developing the budget profile and finalizing that with the project,” Douglas Hudgins, program scientist for NASA’s Exoplanet Exploration Program, said at a meeting of the Exoplanet Exploration Program Analysis Group held just before the AAS Seattle conference. “Everyone has sharpened their pencils and done a good job of mapping out a plan that will conduct the K2 mission pretty much as proposed.”

As Kepler collects new data, scientists are still pouring through the data from the spacecraft’s original four-year mission, looking at the same region of the sky. At the AAS meeting last week, scientists announced the release of an updated planet catalog, identifying 554 new “planet candidates” that astronomers believe are most likely planets. That update brought the total number of planet candidates in the Kepler data to 4,175.

At the meeting, astronomers announced that they had validated now more than 1,000 of those planet candidates, using other observatories and observing techniques to confirm that the brief, periodic decreases in brightness of the stars seen by Kepler were, in fact, caused by orbiting planets passing in front of the star. Two of the newly validated planets are among the most “Earth-like” to date, based on their size and their orbits in their stars’ habitable zones, where liquid water could exist.

A few of the new planet candidates could be something else—error in the data, variability in the star itself, and so on—but astronomers were confident that the number of “false positives” among the overall pool of planet candidates is low.

“Most of the new 500 candidates we announced are going to be planets,” said Doug Caldwell of the SETI Institute at a January 6 press conference at the AAS meeting. He estimated about 10 percent of the candidates are likely to be false positives.

Scientists expect to continue to study the Kepler data from the original run for the next few years, refining their analysis techniques to tease out potential additional planets in the data, even as they start to go through the data collected by the spacecraft from its series of K2 observing campaigns. No one at last week’s conference expected to run out of exoplanets to study in the Kepler data any time soon.