Hubble Has Transitioned to New Observing Mode, Continuing Science (Updated)

Updates:

(June 18, 2024) The Hubble Space Telescope returned to science operations after transitioning successfully to the new "one-gyro mode" on June 14th. Within a few days, NASA released some of the new images in a press release.

The original story continues below.

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The Hubble Space Telescope needs instruments known as gyroscopes to slew, point, and track objects. But these critical instruments are also the most vulnerable element of the venerable observatory. For months, one of the telescope's three remaining gyroscopes has been acting up. Now, NASA engineers are working to operate the telescope with one less gyro.

Hubble originally launched 34 years ago with six gyroscopes. Five repair missions, flown on U.S. Space Shuttles, allowed for the telescope's upkeep over the years, including replacement of gyros as needed. The last of these missions (STS-125) was in 2009, with Space Shuttle Atlantis. During that mission, the telescope received six brand-new gyros. However, three of those gyros have failed in the intervening years. And on May 24th, after intermittent problems over the previous months, Hubble once again entered "safe mode" when one of the remaining three began relaying faulty telemetry to ground control.

The faulty gyro is experiencing what’s known as saturation: It shows that it has reached its maximum slew value, no matter how fast it’s actually moving. Engineers have tried resetting the faulty gyro, only for the problem to return. Fortunately, Hubble can operate on a single gyro, a capability tested briefly in 2008; however, having two is optimal. The plan for now is to place one of the remaining good gyros in hibernation as a backup and operate the telescope in this "one gyro" mode.

Star trackers, magnetometers, and Sun sensors will take up the slack for the dormant gyro. The magnetometers, for example, can help out by sensing the telescope's orientation relative to Earth’s magnetic field.

“NASA anticipates Hubble will continue making discoveries throughout this decade and possibly into the next, working with other observatories, such as the agency’s James Webb Space Telescope for the benefit of humanity,” the agency stated in a recent press release. Mission operations currently cost some $95 million annually, although the fiscal year 2025 budget request calls for a decrease to $89 million.

However, there are drawbacks to this new mode of operations: It will limit the telescope’s slew rate and won’t allow it to track targets closer than Mars, though those sorts of observations are rare for Hubble. Slewing the telescope to nab transient events and new objects is also now, for the most part, off the table. Perhaps more importantly, the observing efficiency of the telescope overall will drop 12%, from 85 orbits of observation every week to 75. (Each orbit is about 90 minutes long.)

The telescope has been in safe mode since late May and will remain so until the team can transition it to its new one-gyro mode by mid-June.

Hubble’s Legacy

Of course, as is true with any long-lived space mission, Hubble is no stranger to problems. The telescope famously revealed faulty optics to the world shortly after launch in 1990, necessitating the installation of the Corrective Optics Space Telescope Axial Replacement (COSTAR) corrective lens system in 1993.

After COSTAR's implementation, though, Hubble went on to become an icon of modern astronomy, helping mint a whole new generation of professional astronomers. The cultural value of Hubble has seen images such as the Pillars of Creation and the Hubble Deep Field adorn everything from sci-fi vistas to coffee mugs.

"Hubble is expected to operate through the remainder of this decade," says Claire Andreoli (NASA's Goddard Space Flight Center) "It is not expected to enter the Earth's atmosphere until the mid-2030s."

SpaceX had proposed sending a Crew Dragon mission to boost the space telescope's orbit, as part of the company’s Polaris Program. Astronauts installed a docking bracket during the final servicing mission for just such a future contingency, and NASA even studied the feasibility of this option in the Space Act Agreement signed in 2022. However, NASA representatives have stated the agency is not currently considering any plans to conduct such a mission.

“Our assessment for Hubble still concludes a very high reliability,” says Patrick Crouse (NASA's Goddard Space Flight Center) in Wednesday’s press briefing. “We do not see Hubble as being on its last legs; we do think it’s a very capable observatory, poised to do exciting science.”

Hubble has proven to be the original “comeback kid.” Despite this setback, you can still expect to see more science from the Hubble Space Telescope in the years to come.