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Gyro Issues Force Hubble Into Safe Mode

The Hubble Space Telescope as seen from Space Shuttle Columbia during STS-109, also known as Servicing Mission 3B. Its silver thermal foil reflects Earth’s oceans and clouds behind it, while its solar arrays appear dark, and its shutter faces to the left. During the mission, Hubble was upgraded with various new pieces of equipment, and had its orbit reboosted.
Credit: NASA

NASA’s Hubble Space Telescope has suspended science operations for the time being. NASA reported that the space observatory entered safe mode on May 24th. In safe mode, Hubble pauses operations and waits for further instructions while Hubble Mission Team members on the ground at NASA’s Goddard Space Flight Center analyze an encountered fault with the spacecraft. The issue relates to Hubble’s Pointing Control System, a collection of gyroscopes, reaction wheels, and sensors used to aim the telescope at its observational targets. More specifically; one of Hubble’s three operational gyroscopes began giving faulty telemetry readings, this error was automatically detected by Hubble’s computers, prompting the entry into safe mode.

The Hubble Space Telescope launched in April of 1990, 34 years ago, aboard the Space Shuttle Discovery as the primary payload of the STS-31 mission. Shortly after, a major fault in the telescope’s mirror was discovered, rendering Hubble’s imagery fuzzy and its data imprecise. Luckily, despite the flaw, Hubble was built with servicing missions in mind, and in December of 1993, Space Shuttle Endeavour flew Servicing Mission 1 to Hubble with the equipment necessary to correct the fault, leading to a recovery of the telescope’s full intended capabilities. 

Hubble went on to provide revolutionary data for the fields of cosmology and astronomy, providing glimpses of the early universe for the first time via its famous deep field images, and even measuring dark energy, the rate at which the universe’s expansion increases. In more recent years Hubble has even contributed to relatively younger fields such as exoplanetology, becoming the first telescope to observe and characterize the atmosphere of an exoplanet. These are but some of the many monumental contributions the great observatory has made to science, and the telescope has continued to collect vital data to this day. As a recent example, in December of 2023 Hubble completed a three-year study of young stars, where it observed young blue stars in ultraviolet light, a wavelength only Hubble can observe.

The Hubble Space Telescope would be visited four more times by Space Shuttle Orbiters and their crews, and across all missions Hubble saw over a dozen gyroscope replacements, (the telescope originally operated with six gyroscopes), as well as service and swap outs to various other components. However, with the cancellation of the Space Shuttle Program in 2011, the means to service Hubble as originally intended no longer exist. Now, the vital space observatory has not received servicing since 2009, and despite its age the Hubble Space Telescope remains an incredibly high demand scientific instrument; being the largest visible light space telescope in operation. Modern space telescopes like the recently launched James Webb Space Telescope or upcoming Nancy Grace Roman Space Telescope offer their own impressive capabilities, but neither are direct replacements, with JWST being an infrared telescope and NGRST being a survey telescope.

Questions regarding Hubble’s future have become increasingly more common as time goes on. Hubble has previously entered safe mode for different issues in January of 2019 and October of 2021, and without a reboost to its orbit is expected to reenter Earth’s atmosphere in 2034. In 2022 NASA called for proposals to service and reboost Hubble. One such proposal from Jared Issacman, commander of the Inspiration4 mission and organizer of the company’s Polaris Program, to utilize SpaceX’s Crew Dragon spacecraft has been the center of much discussion ever since. However, as recently reported by NPR, Issacman’s proposal is considered potentially risky by NASA personnel. Robotic options, similar to the Mission Extension Vehicle manufactured by Northrop Grumman, are perhaps less risky as they involve no crew and may provide a similar life extension while being a simpler operation. As of the end of May 2024 NASA has not made any commitments to a new Hubble servicing mission.

Hubble affixed to the cargo bay of Space Shuttle Atlantis during STS-125 also known as Servicing Mission 4, Hubble’s fifth and final servicing mission, in 2009. The photo depicts the mission’s fourth EVA, with Astronaut Michael Good seen centerframe on the end of Atlantis’ robotic arm, while astronaut Mike Massimino works in the lower right.
Credit: NASA

With a proper successor left to the distant future, and Hubble hoped to continue operations into the next decade, this latest issue may promote further discussion of NASA’s options in securing the telescope’s future. NASA expects to provide further information on the issue in the first week of June, 2024.

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