A newly released plot of the Hubble Space Telescope’s altitude shows just how quickly the observatory has descended in recent years.
The post on Bluesky by astronomer Jonathan McDowell is a stark reminder that Hubble is heading back to Earth, possibly sooner than previously thought, as its orbit decays.
Hubble was launched into low Earth orbit in 1990, carried in the payload bay of Space Shuttle Discovery. While it remains capable of pointing its instruments and has returned breathtaking imagery over more than three decades in orbit, it cannot raise its altitude.
The observatory was serviced by a succession of Space Shuttle crews over the years, and engineers worked around hardware failures as the observatory aged. However, no amount of ground-based cleverness will stop the spacecraft from eventually re-entering the atmosphere.
The plot from McDowell makes the orbital decay clear. From an initial altitude of more than 600 km, Hubble is now well below 500 km. The more rapid descent in recent years is at least partly due to increased solar activity, which has caused Earth’s atmosphere to expand, but it also highlights the need for a reboost in the next few years before the telescope becomes unrecoverable.
NASA is attempting to rescue the Swift observatory and has paused most science operations after the 21-year-old spacecraft’s altitude dropped below 400 km, in order to buy extra time for a reboost mission later this year.
Jared Isaacman, now NASA Administrator, mooted boosting Hubble in 2022, but was ultimately rejected. Unlike Swift, Hubble was designed to be captured and serviced in space, and the last Space Shuttle servicing mission left an adapter attached to the vehicle for a future visiting spacecraft.
In 2025, Dr John Grunsfeld, former astronaut and retired associate administrator of NASA’s Science Mission Directorate, told The Register that Hubble faced death by a thousand cuts, decaying orbit notwithstanding. Its budget has been relatively flat for years, which means, accounting for inflation, “we’re already down about 30 percent in funding for Hubble.”
“They’re just trying to whittle away at it,” he said.
Hubble transitioned to a single-gyro mode in 2024. It has six of the devices, which are used to point the telescope, but three have failed, and a fourth is showing signs of degradation. The plan was to eke out a few more years of operational life from a spacecraft that had outlived all initial expectations.
However, without a reboost, the telescope could re-enter the atmosphere as early as 2028, according to McDowell’s analysis. His plot suggests it is already on that trajectory. ®