NASA Tests Robotic Orbit-Boost Mission for Aging Swift Telescope
A spacecraft-saving mission for NASA has some unique aspects, as it involves catching the aging Neil Gehrels Swift Observatory with a robotic spacecraft before it descends back to Earth due to orbital decay. Launched in 2004, Swift has spent its mission detecting and studying gamma-ray bursts and other high-energy phenomena, but the satellite’s orbit has decayed from a 370-mile altitude to 230 miles. Left alone, the spacecraft may reenter Earth’s atmosphere in the coming months.
This unusual mission brings attention to another unusual effort, which seeks to maintain a spacecraft in space with more pragmatism than pageantry. NASA has contracted Arizona-based Katalyst Space Technologies to develop a mission centered on their LINK spacecraft, a rapid response vehicle designed to approach, dock with, boost, and release a spacecraft within days or even hours of reaching an operational location. According to current plans, the mission will involve launching LINK, rendezvousing with Swift, docking with the aging spacecraft, raising its orbit by approximately 150 miles, then releasing it in a higher altitude band. The planned launch will occur on a Pegasus rocket released from a Northrop Grumman aircraft over the South Pacific Ocean, with June 27 listed as the date for a successful lift-off.
What makes the mission unique from an engineering standpoint is the complexity of the actual task. While Swift was originally designed to study gamma-ray bursts, it was not engineered to facilitate on-orbit maintenance. Unlike Hubble, it has no docking ports and no onboard systems capable of handling an external craft docking with it. This means LINK has to conduct the operation with the same tools that were available for Swift and none of them are equipped for spacecraft docking.
According to the mission design, LINK must rely on an autonomous docking procedure due to high speed relative to the ground station. Both LINK and Swift will circle Earth at approximately 17,000 mph, so the main challenge is not the speed itself but making sure the vehicles match orbits so accurately that relative velocity becomes negligible. After the spacecraft are launched, LINK is scheduled to undergo several days to a few weeks of phasing maneuvers before attempting capture with Swift. As LINK approaches its target, the plan calls for using rapid imaging to locate and identify Swift, comparing the images to the spacecraft model, and conducting minor maneuvering corrections.
Capture with the spacecraft is a particularly difficult phase. LINK needs to create a full 3D model of the spacecraft because it is unclear what the exterior condition of the satellite will be after two decades of orbiting Earth. Insulation degradation remains a serious possibility and it is impossible to predict ahead of time which portions of the spacecraft structure will provide secure footholds. Finally, once LINK begins approaching Swift, the plan calls for extending metal arms equipped with docking clamps and handing over control of Swift’s attitude to the servicing vehicle.
All of this is crucial for the long-term potential of such missions because this is an example of a spacecraft not designed for in-space servicing. Although NASA has conducted several successful Hubble servicing missions involving space shuttle crews, this will be the first time that NASA tries to save a science satellite from decaying. The fact that future spacecraft will be designed with servicing capabilities in mind is obvious and such satellites will include standard attachment points and features to ensure safe servicing by the robotic vehicle.
However, propulsion will also play an important role in the future development of spacecraft. Orbital raising is simple in principle but complex in practice because it involves balancing thrust levels, available propellant, and the overall time needed for the maneuver. NASA guidelines related to small spacecraft propulsion suggest that chemical engines should be employed for high-thrust maneuvers, while ion thrusters sacrifice thrust levels for sustained operation. Given the time-sensitive nature of the Swift rescue mission, one may assume that orbit raising will require anywhere from one month to several months of constant operation, depending on initial conditions, solar activity, and engine performance. Readers looking to learn more about in-space propulsion can view NASA’s in-space propulsion overview.
Finally, there is the scientific angle to the project. Swift’s mission was supposed to last two years but the spacecraft’s instruments remain functional. It is currently capable of changing its orientation to redirect X-ray and ultraviolet sensors towards afterglow from gamma-ray bursts. At the same time, Swift also has proven valuable in follow-up studies based on data collected by other observatories. To slow its descent, the spacecraft’s operators adjusted its orientation in February to reduce drag and switched off the broad-band detector in April, suspending much of the scientific activity.
But there is also an important program management aspect to consider. At approximately $30 million, this mission will be significantly cheaper than building a brand new telescope. Instead of retiring Swift altogether, NASA will pay less for preserving its capabilities in space and that gives rise to the opportunity to make spacecraft maintenance a common practice in orbit. Kieran Wilson from Katalyst has explained that point as follows: “This is absolutely a model we want to use going forward, where spacecraft are no longer a static asset on orbit they’re no longer stuck with only what they launched with.” Brad Cenko, who represents the scientific side of Swift’s operation, was equally blunt in his characterization of the upcoming procedure as boost era.
Ultimately, LINK could prove successful or fail, but that is not what people will remember from this mission. The true message is that spacecraft maintenance can no longer be considered impossible because it is becoming a distinct engineering field rather than an expensive ritual. And for everyone in the American space community, that is what matters.
David Whitaker — Associate editor for AMI’s aerospace and drone systems desk, translating flight systems, aircraft programs, spaceflight, and UAV developments into accessible technical stories.
