NASA’s Neil Gehrels Swift Observatory has reentered Earth’s atmosphere, closing a mission that spent two decades tracking some of the universe’s most energetic outbursts. The spacecraft made its last sky observations on October 20 while orbiting about 275 kilometers above Earth, NASA ended the mission three days later, and Swift reentered on November 4 over the North Sumatra region of Indonesia. It largely burned up during the descent.
The end came after an attempted commercial rescue mission failed months earlier. A robotic spacecraft called LINK had been sent to raise Swift into a safer orbit, but it reentered in September before it could complete the job. The episode offers a sharp illustration of both the promise and the technical risk of a growing orbital-servicing industry.
Why Swift’s orbit became untenable
By late October, Swift was flying low enough that atmospheric drag was affecting its ability to operate. Even at the edge of space, the thin upper atmosphere creates resistance that steadily reduces a satellite’s altitude. NASA determined that the observatory had dropped to a point where its telescopes could no longer remain sufficiently steady for observations.
Swift’s final active orbit was about 171 miles above Earth. The original rescue plan was intended to move it much higher, to roughly 373 miles, or 600 kilometers. At that altitude, the telescope could potentially have continued making observations for years.
The observatory’s mission had focused on transient and high-energy events, including powerful cosmic explosions. Its reentry therefore marks the loss of an instrument designed not for a single fixed target, but for rapidly responding to unusual signals from across the sky.
A rescue spacecraft became the first loss
LINK was built to approach Swift, capture it with one of three robotic arms, and use its thrusters to boost the telescope’s orbit. That sequence required careful control of a spacecraft operating in close proximity to another aging object in orbit.
In late July, LINK lost two of its three reaction wheels. Reaction wheels are internal spinning devices that spacecraft use to change orientation without consuming propellant. The hardware loss, combined with propulsion-system problems, sent the rescue vehicle into an uncontrolled spin.
Mission engineers used thrusters in an attempt to reduce that rotation. NASA reported in August that the spacecraft’s spin rate had been cut from about 9 degrees per second to roughly 1.5 degrees per second. But using thrusters for control consumes fuel, and the rescue effort did not reach the point of capturing and raising Swift. LINK reentered Earth’s atmosphere in September.
What the failure says about in-orbit servicing
Servicing a spacecraft in orbit is inherently demanding. A repair or relocation vehicle must navigate, stabilize itself, approach its target and execute a capture or connection without damaging either spacecraft. The task grows more difficult when the target is old, operating at a low altitude, or unable to contribute much to the rendezvous process.
The Swift episode also highlights a practical consequence of failure: a servicing spacecraft can itself become another object that must be managed. In this case, the vehicle intended to extend an observatory’s life was lost first, leaving Swift’s decaying orbit unresolved.
That does not eliminate the case for robotic servicing, refueling or relocation missions. Instead, it underlines why propulsion, attitude control, fault tolerance and contingency planning are central to the field. A mission that depends on close-proximity operations must be able to cope with failures in the systems that keep the servicing craft pointed, stable and fueled.
Swift’s reentry was a planned end to a mission whose orbit had become unsustainable, but its path there was shaped by an unsuccessful attempt to intervene. The two losses are now part of the same cautionary case: extending the lives of valuable spacecraft may be possible, but doing so reliably remains a difficult engineering challenge.
This article is based on reporting by Phys.org. Read the original article.
Originally published on phys.org
