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A problem with one of the Hubble Space Telescope’s three remaining gyroscopes, critical for pointing and locking onto targets, has prompted mission managers to switch to a backup control mode that will limit some observations but keep the iconic observatory running until 2030, they said. employees Tuesday.

“We still believe there is a very high reliability and probability that we can operate Hubble very successfully, doing groundbreaking science, for the rest of the 20 years and into the 2030s,” Hubble Project Manager Patrick Kruse told reporters during an afternoon conference call.

Meanwhile, Mark Clampin, director of astrophysics at NASA headquarters, said the agency has ruled out, at least for now, a proposed commercial mission to raise Hubble to a higher altitude using a SpaceX Crew Dragon spacecraft. The flight was proposed by SpaceX and Crew Dragon veteran Jared Isaacman as a way to extend Hubble’s life.

By amplification the telescope to a higher altitude, the subtle effects of “drag” in the extreme outer atmosphere that act to slowly but surely pull a spacecraft back to Earth can be reduced. Isaacman, a billionaire who chartered the first fully commercial flight to low Earth orbit in 2021, is training to lead three more SpaceX “Polaris” missions, including a flight this summer in which he plans to become the first private citizen to stand in hatch open and swimming, if not walking, in space.

But project managers said Tuesday that there was no danger of Hubble falling back to Earth anytime soon. The latest calculations show that the observatory will remain in orbit until at least 2035, giving time to consider possible options, if warranted, further down the line.

“Having explored the current commercial opportunities, we will not be pursuing another increase right now,” Clampin said. “We greatly appreciate the in-depth analysis performed by NASA and the (SpaceX-Isaacman) program, as well as our other potential partners, and it certainly gave us a better understanding of the considerations for developing a future commercial launch mission.”

“But our assessment also raised a number of considerations, including potential risks such as premature loss of science and some technological challenges.” So while restarting is an option for the future, we believe we need to do additional work to determine whether the long-term scientific return will outweigh the short-term scientific risk.”

Hubble’s Decades of Service in Space

The Hubble Space Telescope was launched aboard the space shuttle Discovery on April 24, 1990, with a notoriously faulty mirror, the opening chapter of an incredible tale in which space repair crews turned a national embarrassment into an international icon of science.

Hubble was initially hampered by an error during the manufacture of the 94.5-inch primary mirror, which resulted in an optical defect known as spherical aberration, preventing the telescope from bringing starlight into sharp focus.

But engineers quickly devised a way to correct Hubble’s blurred vision. They designed a new camera equipped with prescription-ground relay mirrors that would precisely counteract the aberration of the primary mirror. Another device, known as COSTAR, is designed to direct corrected light at Hubble’s other instruments.

During the shuttle servicing mission in December 1993, the new Wide Field Planetary Camera 2 and COSTAR were installed by spacewalk astronauts. They also replaced Hubble’s solar panels and other critical components.

NASA will continue with four more servicing missions, installing new, state-of-the-art instruments and replacing aging components such as critical fine-aiming sensors and gyroscopes that move the telescope from target to target and then anchor with rock-solid stability for detailed observations.

The gyroscopes are critical to Hubble’s longevity. The telescope was launched with six ultra-stable gyroscopes, but only three are needed for normal operation at a time. During the last servicing mission in 2009, all six were replaced. Three of the new modules include components susceptible to a form of corrosion, while the other three feature an improved design that greatly reduces or eliminates this risk.

In any case, by Hubble’s 30th anniversary in 2020, all three of the six older model gyroscopes had failed.

One of the remaining three units, gyro no. 3, began to act erratically earlier and its performance progressively deteriorated. On May 24, the gyroscope was turned off, putting the observatory into a protective “safe mode,” halting science operations while engineers discussed their options.

Knowing that gyroscope failures were inevitable, engineers had previously developed software that would allow Hubble to operate with just two gyroscopes, or even one. The downside was that the telescope could only reach targets in about half the sky at any given time instead of 85% or more with the three gyroscopes.

Although the telescope could be steered more efficiently with two gyroscopes, engineers concluded that it would make more sense to put one of the two remaining robust modules in standby mode and steer Hubble with just one gyroscope, keeping the other in reserve for use as needed.

“Our team first developed a plan for single-gyro operations more than 20 years ago, and this is the best way forward to extend Hubble’s life,” Kraus said. “There are some limitations. It will take us longer to (move) from one target attitude to the next and be able to stick to that scientific target.

“This will lead to less efficiency for planning scientific observations. We currently plan about 85 orbits per week and expect (to be able to) plan about 74 hours per week, so about a 12% reduction in planning efficiency.”

Also, because the telescope’s motion in single-gyro mode is less precise and subject to error, “we won’t have as much flexibility in terms of where we can observe in the sky at any given time. But over the course of a year we’ll have the whole sky to ourselves.”

One other limitation: the telescope will not be able to lock on and track targets closer than the orbit of Mars, although such observations are rare even in three-gyro mode.

Meanwhile, engineers plan to implement the single-gyro control mode in the coming days and return Hubble to science operations around the middle of the month.

“We’ve updated the gyro reliability estimates … and we still conclude that (we have) a greater than 70 percent probability of operating at least one gyro by 2035,” Kraus said.

The infrared-sensitive James Webb Space Telescope builds on Hubble’s legacy, reaching deeper into space and time and producing a steady stream of discoveries as it moves to the forefront of space astronomy. But Hubble is still making world-class observations, and astronomers want to keep it running as long as possible.