The venerable Hubble Space Telescope is running out of gyroscopes, and when there are none left, the instrument stops doing meaningful science.
To preserve the telescope, which has been in space for nearly three and a half decades, NASA announced Tuesday that it will limit the Hubble’s operation to a single gyroscope. This will limit some science operations and take longer to point the telescope at and focus on new objects.
But in a conference call with space reporters, Hubble officials stressed that the beloved science instrument isn’t going anywhere anytime soon.
“I personally don’t see it as a major limitation on his ability to do science,” said Mark Clampin, director of the astrophysics division at NASA headquarters in Washington, DC.
From six to one
The Hubble Telescope was launched on a NASA space shuttle in 1990, and since then the space agency has conducted five servicing missions to repair and upgrade the complex instrument. To this day, it offers mankind the best view of the Universe in the visible light region of the spectrum.
The last of these shuttle service missions Atlantis made numerous upgrades in 2009, including replacing all six gyroscopes that help orient and steer the telescope. However, in the 15 years since then, three of the six gyroscopes have failed. In the last six months, another one, “gyro 3”, is increasingly returning erroneous data. This caused Hubble to slip into safe mode several times, halting science operations.
As a result, the space agency only has two fully functional gyroscopes. One of them, gyro 4, worked a total of 142,000 hours. Another, gyro 6, has accumulated 90,000 hours. NASA’s plan now is to operate the telescope on a single gyroscope, keeping the other as a “backup” option.
NASA has stated that operation on a single gyroscope is feasible, with relatively modest implications for observing capabilities. It will be less efficient and will require more time to direct. This will result in a loss of about 12 percent of the observation time. The telescope will also not be able to observe objects closer than Mars, including Venus and the Moon.
However, by taking this step now, the space agency believes it can extend Hubble’s operational life by another decade. The telescope’s project manager, Patrick Crouse, said there is a 70 percent chance that Hubble can sustain science operations with a single gyro until 2035.
“We don’t see Hubble being on its last legs,” he said Tuesday.
From a scientific point of view, it is important that Hubble continue to operate. Now that the powerful James Webb Space Telescope is operational, the two instruments are a formidable duo. Thanks to Hubble’s visible-light observations and Webb’s infrared observations, astronomers can gain valuable new insights into the nature of the universe.
Another service mission? No, thanks
In addition to aging science instruments and a dwindling number of gyroscopes, NASA also faces some other instrument life challenges. The telescope usually operates at an altitude between 615 km and 530 km above the Earth’s surface. However, the telescope is likely to drop below 500 km sometime this year. At lower altitudes, some telescope observations are affected by other satellites in low Earth orbit.
Clampin said Tuesday that telescope operators don’t expect Hubble to re-enter Earth’s atmosphere until the mid-2030s. This, combined with the gyroscope limit, appears to represent a hard limit on the remaining maximum lifetime of the HST.
However, in 2022, Jared Isaacman, the billionaire who flew the first fully commercial human mission to orbit aboard Crew Dragon, approached NASA about conducting a servicing mission to the Hubble Space Telescope. He proposed to fund most of the mission, which would at least boost the Hubble Space Telescope by at least 50 km.
After NASA and SpaceX conducted a feasibility study later that year, it was recommended that the space agency continue to investigate the possibility of a commercial mission. At a minimum, this could restart the telescope safely, but there were also options that included attaching star trackers and external gyroscopes to compensate for the telescope’s ailing targeting system.
But NASA decided not to use this option.
“Our position at this time is that, having examined the current commercial options, we are not going to pursue a re-enforcement at this time,” Clampin said on Tuesday.
Asked about the study, which NASA declined to make public for proprietary reasons, Clampin said, “It was a feasibility study that helped us understand some of the issues and challenges we might face,” he said. “There were options like being able to make improvements by adding a gyroscope to the outside of the telescope, but they were really just fictional concepts.”
NASA evidently decided it was safer to let Hubble age alone than to risk private hands touching the hallowed telescope. We will see how it goes.