Pegasus launches Swift reboost mission
A Pegasus XL launched a mission to reboost a NASA astrophysics spacecraft on what may be the final flight of that rocket.
A Northrop Grumman Pegasus XL rocket was deployed from its L-1011 carrier aircraft at 4:36 a.m. Eastern on July 3, after three days of delays caused by weather and technical issues. The rocket placed its payload, the 425-kilogram Link spacecraft from Katalyst Space, into low Earth orbit nearly 13 minutes later.
NASA said in a statement more than seven hours later that controllers had established contact with Link but did not provide any additional information about the status of the spacecraft.
Katalyst Space developed Link under a $30 million NASA contract awarded last September to attempt to save the Neil Gehrels Swift Observatory, or Swift, spacecraft in low Earth orbit. That gamma-ray observatory is in a decaying orbit and in danger of reentering late this year or early next year.
The company repurposed a low Earth orbit technology demonstration of its satellite servicing technology already in development for the Swift reboost mission, delivering a spacecraft ready for launch within nine months of contract award.
"This is an absolutely unprecedented development timeline," said Kieran Wilson, principal investigator for Link at Katalyst, at a prelaunch briefing June 17.
Now in orbit, Katalyst Space will spend the next two weeks performing in-orbit checks of the spacecraft, after which Link will begin its approach to Swift and survey the spacecraft, a process expected to take two to three weeks.
That survey will include examining Swift and determining the best locations on the spacecraft that Link's three robotic arms can grapple. Project officials said before the launch that while they have identified locations on Swift that they think the arms can grapple, they want to inspect the spacecraft to see if they are still suitable for capture.
"We're confident that as long as we have a spacecraft that can function at a fundamental level, that gives us the freedom and flexibility to work through any issues that we find during rendezvous and the more challenging dynamical operation," Wilson said. Swift is projected to remain above an altitude of 300 kilometers, below which the reboost mission is not feasible, until at least October.
Swift will be able to assist that effort by moving in cooperation with Link. "Swift is an unprepared but cooperative partner in the rendezvous," he said. "We'll be moving through a bunch of maneuvers as a tandem team between the Swift mission ops and the Link mission ops teams to perform those inspections at various ranges."
If Link can attach to Swift, it will use its ion engines to raise the orbit, currently at about 360 kilometers, to 550 to 600 kilometers. Link will then detach and use its remaining propellant to lower itself and speed up its deorbit. The reboost process will take three months, and after Link departs, Swift will resume science operations.
NASA has called the Swift reboost mission a "high-risk, high-reward" effort because of the challenges in trying to raise the orbit of a spacecraft not designed to be serviced, as well as Katalyst Space's limited spaceflight experience. However, the agency argues the benefits, if successful, extend to other NASA missions and the broader industry.
"We didn't want to set the precedent that anything that comes out of orbit has to be boosted," said Shawn Domagal-Goldman, director of NASA's astrophysics division, at the prelaunch briefing.
In the case of Swift, extending its mission helps the astrophysics community because of the mission's value in monitoring gamma-ray bursts and other high-energy phenomena.
"This is an observatory with unique capabilities for astrophysics," he said. "So we decided, yeah, we want to go save this one this time because of how special it is."
A successful Swift reboost could enable similar efforts, including for the Hubble Space Telescope, whose orbit is also decaying and could reenter in the first half of the 2030s. Domagal-Goldman said at an advisory committee meeting in June that he would be open to a Hubble reboost mission, provided the telescope's operating costs can be reduced.
The launch is also the last scheduled flight of a Pegasus rocket. The air-launched rocket was developed by Orbital Sciences Corp. and first flown in 1990. The vehicle, which at times in the 1990s launched five to six times a year, has flown only six times in the last 15 years. The launch of Link was the first Pegasus launch since a responsive space mission in June 2021.
Katalyst Space selected Pegasus last November because of the unique orbit Swift is in, with an inclination of about 21 degrees. Northrop reportedly offered Katalyst a Pegasus rocket, in storage after being built for another customer, at a low cost.
At the prelaunch briefing, Wes Collier, vice president of launch systems at Northrop Grumman, left open the door for future Pegasus launches. "We certainly are open to follow-on contracts or new opportunities for Pegasus," he said. "We think that it's a great system for future responsive launch opportunities."
Collier offered a similar sentiment in a Northrop statement after the launch.
"Ready for launch in under eight months, Pegasus is the go-to choice for missions that need to get off the ground now," he said. "Its air-launch design and proven Orion motors mean payloads can get to orbits that are harder for other rockets to reach."
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