In its first mission since 2021, a Northrop Grumman Pegasus XL rocket is scheduled to be air-launched from the Lockheed L-1011 TriStar Stargazer. Riding aboard Pegasus XL is NASA’s Swift Boost Mission, a mission utilizing a robotic servicing spacecraft from Katalyst Space Technologies to raise, or “boost,” the orbital altitude of NASA’s Neil Gehrels Swift Observatory.
Pegasus XL is scheduled to be dropped from Stargazer on Thursday, July 2, at 09:09 UTC over the South Pacific Ocean. Stargazer will take off from the Ronald Reagan Ballistic Missile Defense Test Site at Kwajalein Atoll in the Marshall Islands. The rocket will ignite its solid motor five seconds after dropping from Stargazer.
NASA’s Swift Observatory and orbital decay
Launched in November 2004 atop a Delta II rocket from Florida, NASA’s Neil Gehrels Swift Observatory, commonly known as Swift, is a space telescope designed to observe gamma-ray bursts and the X-ray, ultraviolet, and visible-light afterglows they produce. Gamma-ray bursts are the brightest and most energetic explosions in the universe and can last anywhere from milliseconds to hours. The bursts are thought to originate most commonly from supernovae, the explosions of high-mass stars at the end of their lives.
A Delta II launches Swift in November 2004. (Credit: NASA)
A successor to NASA’s Compton Gamma Ray Observatory, which operated from 1991 to 2000, Swift features a gamma-ray burst detection rate of 100 per year and has more than double the detection sensitivity of Compton.
When launched, Swift was expected to operate for two years and study only gamma-ray bursts. However, with the spacecraft continuing to operate in good condition after 2006, NASA teams continued to support the mission and alter its scientific scope to include observations of all astrophysical transient events across multiple wavelengths.
Swift detected its 500th gamma-ray burst in May 2010, and then its 1,000th in October 2015. As of publication, Swift has detected 1,760 gamma-ray bursts, having detected 11 in 2026 alone.
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When Swift was launched in 2004, Delta II inserted it into a circular low-Earth orbit (LEO) with a perigee altitude (the lowest point in its orbit) of 585 km and an apogee altitude (the highest point in its orbit) of 604 km at an inclination of 20.60 degrees. However, while LEO is technically above the Karman Line, the very outer regions of Earth’s atmosphere still permeate into the orbital region of LEO. Thus, spacecraft travelling at these altitudes can interact with the atmosphere and have their orbits degraded by atmospheric drag.
Swift, being located in LEO, has seen significant orbital degradation due to atmospheric drag. Over the 21 years it’s been operating in LEO, Swift’s perigee altitude has lowered to 373 km and its apogee altitude to 378 km. The International Space Station, located in a 413 km by 422 km LEO, faces the same issue and uses visiting cargo and crewed spacecraft to raise its orbital altitude to prevent re-entry into Earth’s atmosphere. The Space Shuttles did the same for the Hubble Space Telescope during their servicing missions to the observatory.
However, Swift sees no visiting vehicles to boost its orbit, which has decayed more quickly than expected due to increased solar activity over the last few years. Without an orbital boost, Swift has a 90% chance of reentering Earth’s atmosphere before the end of 2026. With the spacecraft in operable condition and continuing to return useful scientific data, NASA turned to the private spaceflight sector for options to save the telescope.
Artist’s rendering of NASA’s Neil Gehrels Swift Observatory. (Credit: NASA/Chris Smith)
Swift Boost Mission and Katalyst’s LINK spacecraft
Under the agency’s Small Business Innovation Research program, NASA awarded Katalyst Space Technologies a $30 million contract in September 2025 to develop a spacecraft capable of boosting Swift’s orbit. While the mission’s primary goal is to boost the orbit of Swift, the mission will also serve as a technology demonstration for future missions that could service and “save” scientifically important space-based missions.
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“Given how quickly Swift’s orbit is decaying, we are in a race against the clock, but by leveraging commercial technologies that are already in development, we are meeting this challenge head-on. This is a forward-leaning, risk-tolerant approach for NASA. But attempting an orbit boost is both more affordable than replacing Swift’s capabilities with a new mission, and beneficial to the nation — expanding the use of satellite servicing to a new and broader class of spacecraft,” said Shawn Domagal-Goldman, Director of NASA’s Astrophysics Division, in the September 2025 press release.
At the time of its selection by NASA, Katalyst was already developing robotic servicing spacecraft with an anticipated demonstration mission in 2026. The Swift Boost Mission will serve as a demonstration mission for the company’s upcoming NEXUS servicing spacecraft, which will be capable of servicing multiple spacecraft across several different orbits. According to NASA, the mission will “be the first time a commercial robotic spacecraft captures a government satellite that is uncrewed, or not originally designed to be serviced in space.”
For the Swift Boost Mission, Katalyst will use its LINK servicing spacecraft to rendezvous with, inspect, dock with, and boost Swift. LINK’s development was greatly accelerated after the mission contract was awarded, with the spacecraft completing environmental testing in May 2026, just eight months later.
LINK will use three parallel-manipulator robotic arms to interact with Swift, with each of the three arms featuring a lidar sensor and grippers. The spacecraft will be capable of capturing and conducting the mission with just one arm, but will use all three for better control. Given that Swift was not designed with a docking port for servicing, LINK will use ground-handling flanges on Swift’s satellite bus to “dock” to the spacecraft. Ahead of docking, the two spacecraft will coordinate their attitudes so LINK can visually inspect the docking points and ensure they aren’t obstructed.
The exact docking procedure that LINK will follow was tested and validated on an air-bearing table using a mock model of Swift. LINK has the ability to abort a docking attempt and retry.
For the boost itself, LINK is equipped with three Hall-effect thrusters that utilize xenon fuel and 16 reaction control system thrusters. Each of the Hall-effect thrusters is angled to align with the center of mass of LINK and Swift when docked. Following the boost — which, if successful, will return Swift to its original near-600 km LEO — LINK will undock, deorbit, and reenter Earth’s atmosphere.
LINK integrated with Pegasus XL ahead of fairing encapsulation. (Credit: NASA/Ron Beard)
Northrop Grumman’s Pegasus XL rocket was selected as the launch vehicle for LINK due to its ability to launch the spacecraft into Swift’s unique 20.6-degree orbit inclination. Pegasus XL is a three-stage small-lift launch vehicle that is air-launched horizontally from the Lockheed L-1011 TriStar Stargazer. The rocket’s first three stages utilize solid propellants, with an Orion 50SXL as the first stage, an Orion 50XL as the second stage, and an Orion 38 as the third stage.
Pegasus XL is a more powerful variant of the original Pegasus rocket, which first launched in April 1990. Over its career, Pegasus and Pegasus XL have launched 45 missions, with 40 successes, three failures, and two partial failures. Pegasus XL stands 17.6 m tall with a diameter of 1.28 m, and is capable of launching 450 kg to a 200 km LEO.
Pegasus XL was mated to Stargazer at NASA’s Wallops Flight Facility on June 12, with LINK arriving at Wallops on June 5 and Pegasus XL integration completed on June 9. Stargazer and Pegasus XL departed Wallops for Kwajalein Atoll in the Marshall Islands on June 18.
On launch day, Stargazer and Pegasus XL, with the LINK spacecraft encapsulated within its fairing, will depart from the Ronald Reagan Ballistic Missile Defense Test Site at Kwajalein Atoll. After cruising over the South Pacific, Pegasus XL will be released from Stargazer at 09:09 UTC on Thursday, July 2nd. After falling away from Stargazer for five seconds, Pegasus XL will ignite its first stage, beginning the Swift Boost Mission.
Pegasus XL is released from Stargazer on a previous mission. (Credit: NASA)
At T+01:19 minutes, the first stage will burn out and separate, with the second stage igniting at T+01:35 minutes. The second stage will burn for over a minute, with burnout and separation occurring at T+02:50 minutes. Fairing separation is expected during the second stage burn at T+02:17 minutes. Pegasus XL will then coast for several minutes, igniting its third stage at T+06:35 minutes. Third stage burnout is expected at T+07:44 minutes, with LINK deployment at T+12:44 minutes.
LINK checkouts will begin immediately following deployment and last for two weeks. The spacecraft will then spend two to three weeks rendezvousing and inspecting Swift, before spending another one to two weeks docking with the telescope. The boost phase of the mission is expected to last around three months, with the recommissioning of Swift after the boost taking around a month to complete.
The Swift Boost Mission will mark the 46th and presumably final mission for the Pegasus XL rocket. The mission will also mark the rocket’s first since the Odyssey (TacRL-2) mission in June 2021, and the 156th overall orbital launch attempt in 2026.
(Lead image: Pegasus XL mated to Stargazer ahead of the Swift Boost Mission. Credit: Micah Pieczarka for NSF)
