Instruments reactivated for a final hurrah before reentry:
NASA's Neil Gehrels Swift Observatory may now be beyond rescue, but the team behind the spacecraft has reactivated its instruments to eke out a final few months of science data before it reenters Earth's atmosphere.
The Ultraviolet/Optical and X-ray telescopes were reactivated last week, and the team hopes to return the Burst Alert Telescope to data collection during September. The former two telescopes were turned off in February to minimize drag and buy time for the reboost effort. The latter was halted in April to reduce power consumption and allow Swift's solar arrays to be positioned to further cut down on atmospheric drag.
The reboost mission failed after control problems with the Katalyst Space LINK spacecraft ruled out an attempt to capture and rescue the Swift observatory. LINK is currently raising its orbit, and there are plans to begin phasing relative to Swift, but there won't be any grappling.
The upshot is that Swift remains set to reenter the Earth's atmosphere in the coming months, perhaps as soon as October. Perhaps a bit later. Whatever the case, mission managers have decided that the potential science return is worth sacrificing a few weeks or months of orbital lifetime.
Swift has spent more than two decades studying the cosmos and remains operational, but lacks the capability to boost itself to a higher orbit. Recent solar activity magnified the effects of drag on the spacecraft, and a high-risk rescue mission was launched a few months ago in an effort to prolong Swift's orbital life.
According to NASA, switching to low-drag operations kept Swift above the critical 185-mile (300-kilometer) threshold until October; below that altitude, the descent rate would accelerate and rescue would no longer be feasible.
"With the resumption of science observations, the team anticipates Swift will reach that milestone sometime in the next one to two months," said NASA.
Previously: Reaction Wheel Failures Leave Swift Rescue Mission Spinning In Orbit
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The Link satellite developed by Katalyst Space Technologies "experienced issues with attitude control" over the weekend, NASA said, causing the spacecraft to spin and resulting in sporadic communications.
Reaction wheels work by discharging momentum to control the pointing, or attitude, of a spacecraft in orbit. They are standard components on many satellites. The Link servicing satellite's cold gas thruster system is used for finer control, particularly as it nears the mission's target: NASA's Swift observatory.
The Link mission began July 3 with a ride to orbit aboard an air-launched Northrop Grumman Pegasus XL rocket. NASA and Katalyst reported good progress in the first weeks of the mission, with successful deployment of the satellite's power-generating solar arrays and stable contact with ground controllers at Katalyst's operations center. The spacecraft's xenon-fueled electric thrusters also completed their first firings in orbit.
The electric thrusters are one of the most critical elements of the rescue mission. They are used for orbit raising to allow Link to rendezvous with the Swift satellite some 200 miles above Earth. Once Link attaches itself to Swift with a set of three robotic arms, the electric thrusters will turn on again to raise Swift's orbit and save it from destruction. Katalyst is now calling upon the electric thrusters to stabilize the Link spacecraft's attitude, something they were not intended to do.
Without a rescue, Swift is on track to reenter the atmosphere and burn up in the next few months. The Neil Gehrels Swift Observatory is nearly 22 years old and is operating well beyond its originally intended lifetime. The spacecraft cannot save itself because it lacks its own propulsion system. NASA officials want to keep Swift going because it is one of the only missions in the agency's fleet tuned to detect gamma-ray bursts, the most powerful explosions in the known Universe. NASA is paying Katalyst $30 million for the rescue service.
Extending Swift's scientific mission was not the only consideration when NASA officials selected Katalyst to build and launch a satellite to boost Swift's orbit. The space agency is using the rescue mission as a technology demonstration and as a way to test the mettle of the commercial satellite servicing industry.
With Swift's orbit rapidly decaying, NASA gave Katalyst nine months to build and launch the Link satellite, an unusually fast timeline for such a complex mission. Katalyst answered the call and delivered the Link satellite for integration with the Pegasus rocket in early June. Poor weather and a technical glitch with the rocket delayed the launch until July 3.
No matter the outcome of the Swift rescue attempt, NASA officials said last month they were already pleased with the results. "From a programmatics standpoint, I consider this a success already, just from the fact that we're even going to try this," said Shawn Domagal-Goldman, director of NASA's astrophysics division.
Katalyst's Link spacecraft is still generating sufficient electrical power in communication with ground teams, NASA said. That gives engineers time to develop a plan to address the reaction wheel problems.
Kieran Wilson, Link's principal investigator at Katalyst, talked about a scenario like this before the launch.
"Our previous programs had issues with power systems and communications," Wilson said. "Those are a lot of the basic things that most of the engineering team gets very concerned about because we're confident that as long as we have spacecraft that can function at a fundamental level, that gives us the freedom and flexibility to work through any issues we find during rendezvous and more challenging dynamical operations."
