NASA’s 3,200-pound Neil Gehrels Swift Observatory is expected to burn up in Earth’s atmosphere, and no established observational replacement is waiting in the wings. Engineers estimate it will become difficult to operate after it drops below 185 miles (300 kilometers) in early to mid-October. Atmospheric drag has already pulled it down to about 200 miles (325 kilometers).
A scientific asset at risk
Swift launched in November 2004 and has worked in low-Earth orbit as an astrophysics observatory. Its instruments were designed to study gamma-ray bursts, the universe’s most powerful explosions, and they’ve also observed cosmic flashes, asteroids and comets. The observatory can quickly turn toward events such as flaring black holes.
Its expected descent comes just shy of the 22nd anniversary of its launch. Solar activity caused the increased drag: intense flares and coronal mass ejections expanded Earth’s atmosphere after the sun reached the peak of its 11-year cycle in 2024. NASA scientists predicted a fall descent as the expanded atmosphere increased drag on the spacecraft.
NASA’s rescue effort failed over the summer. The agency and Arizona-based Katalyst Space Technologies tried to boost Swift’s orbit using LINK, a satellite developed, built and launched in nine months. LINK launched in early July but spun out of control in space.
NASA Astrophysics Division director Shawn Domagal-Goldman said, “Without intervention, Swift was going to re-enter the atmosphere by year’s end.” He called the effort “a high-risk, high-reward mission.”
The rescue attempt
Katalyst went ahead with a planned mid-August rendezvous as a demonstration, not a rescue, because LINK had ongoing orientation issues. Engineers used its thrusters to slow the unexpected spin and uploaded new flight software. The maneuver depleted propellant.
“As a result, Katalyst and NASA together determined that LINK no longer had sufficient fuel to safely execute the planned capture and orbit-raising phase of the mission,” Katalyst said. In the first week of September, the company’s satellite came within 7.5 to 9 miles (12 to 15 kilometers) of Swift, practicing how a future servicing mission might approach a satellite or telescope not designed for servicing in space.
LINK deployed its three robotic arms, originally intended to grab Swift, and fired its three electric propulsion thrusters. Katalyst said LINK operated in space for 85 days before re-entering Earth’s atmosphere on September 25.
What the mission leaves behind
Katalyst Space CEO Ghonhee Lee said, “While we did not accomplish every objective we set out to achieve, in less than a year we went from mission concept to launching and operating the first commercial space robot.” Lee said the company plans to use data and lessons from LINK for its next generation of spacecraft servicing existing space missions. “The future of space will require spacecraft that can do more once they get there,” he said.
NASA and Katalyst said the modified mission advanced U.S. spacecraft-servicing technology, tested how satellites could operate longer in low Earth orbit, and challenged the team to meet unprecedented mission timelines. Domagal-Goldman said the team was “capturing lessons learned to ensure we’re ready to go even farther.”
Swift’s mission scientists have gradually turned its instruments back on to collect data and make observations until the end. The instruments had been off for months to reduce power use and keep the observatory from sinking; restarting them speeds its decline.
A statement from space-tracking company LeoLabs said some hardware may survive re-entry because of the spacecraft’s size, but the probability of debris causing significant property damage or physical harm is very small. It said surviving debris would more likely fall into the ocean or uninhabited land. NASA didn’t respond to a request for comment on potential risks.