Extended Timetable for Decision on New Horizons Extended Mission

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LAUREL, Md. — A final decision on an extended mission for NASA’s New Horizons spacecraft, one that would take it past a small Kuiper Belt object (KBO), won’t come for more than a year, although the project will be taking steps in the coming months to prepare for such a flyby.

The New Horizons project had long held out the prospect of an extended mission for the spacecraft after it completed its flyby of Pluto. The mission team has worked to identify objects in the Kuiper Belt — the disk of small, icy bodies in the outer solar system, of which Pluto is one of the largest members — that the spacecraft could fly past on its way out of the solar system.

Scientists used the Hubble Space Telescope to search the space in the spacecraft’s flight path, finding three KBOs that would be in range of the spacecraft. One of those objects was later dropped from consideration, but the mission team believes the other two are still feasible targets that that the spacecraft could fly by in 2019.

The successful Pluto flyby July 14 leads engineers to believe that a later KBO flyby is technically feasible. “Every indication is that the spacecraft is in great shape,” Chris Hersman, New Horizons mission systems engineer, said at a briefing at the Applied Physics Laboratory here July 15. “That bodes well for the departure phase, as well as the Kuiper Belt object flyby.”

A bigger challenge for the KBO flyby, though, is winning funding. An extended mission would require the project to see additional funding beyond what was allocated for the Pluto flyby. The project would seek that funding in the next senior review of planetary science missions, in 2016.

“That whole process will take a year,” Jim Green, director of NASA’s Planetary Science Division, said in a July 12 briefing here. The results of the senior review, he said, should be announced in August or September of 2016.

Artist's concept of Kuiper Belt object. Credit: NASA
Artist’s concept of Kuiper Belt object. Credit: NASA

Green appeared to leave open the possibility of a different extended mission for New Horizons than a KBO flyby. “There are quite a few things that it could do,” he said of its possible extended mission, without elaborating. Any extended mission decision, he said, would depend not just on the mission’s proposal but available funding for the agency’s overall planetary science program.

However, celestial mechanics requires the mission to take steps well before the senior review to keep open the possibility of a KBO flyby. In a June 29 interview, New Horizons principal investigator Alan Stern said he will make a recommendation to NASA this August on which of the two KBOs the spacecraft should visit. “We can only go to one or the other, since they’re in different directions,” he said.

That will be followed in October and November by a series of trajectory correction maneuvers by the spacecraft to put it on course for a flyby. Waiting much later than November would require the course change greater than what the spacecraft is capable of performing with its remaining propellant.

Hersman said July 12 those maneuvers will be done in a series of four or five shorter thruster burns, similar to earlier spacecraft maneuvers, rather than one long one. “We don’t want to go and do a big burn that we’ve never done before” while the spacecraft is still returning data from the Pluto flyby, he said.

The velocity change needed for the maneuver is approximately 100 meters per second, which requires 20 to 25 kilograms of hydrazine. Hersman said July 15 he estimated New Horizons will have 33 kilograms of hydrazine available for those maneuvers.

While both NASA officials and those directly involved with the mission declined to speculate about the odds of getting an extended mission approved, the successful Pluto flyby has made others increasingly optimistic.

“Given the success of the New Horizons flyby, I think we have every confidence that the team will write an excellent proposal to NASA and that there will be an extended mission to go on to another Kuiper Belt object,” Heidi Hammel, a planetary astronomer and executive vice president of the Associations of Universities for Research in Astronomy, said here July 15.