Hubble Gyroscope Issues: How NASA Keeps the Legend Alive

The Hubble Space Telescope is arguably the most famous scientific instrument in history, but its age is beginning to show. In mid-2024, NASA made a significant operational shift following persistent issues with the telescope’s pointing system. By transitioning to a new operating mode, engineers have ensured that Hubble can continue its observation of the universe despite hardware failures.

This article explains the specific gyroscope problems Hubble faced in 2024, the mechanics of the “one-gyro mode,” and what these changes mean for future scientific discoveries.

The 2024 Gyroscope Crisis

On May 24, 2024, the Hubble Space Telescope automatically entered safe mode. This is a protective state where the telescope stops scientific operations and orients its solar panels toward the sun to maintain power while awaiting instructions from the ground. The cause was a faulty reading from one of its three active gyroscopes.

This was not an isolated incident. The specific unit, designated as Gyro 3, had been providing erroneous telemetry for months. It repeatedly sent “saturation” readings, indicating that the telescope was slewing (turning) at the maximum possible rate when it was actually stationary.

Prior to June 2024, NASA engineers successfully reset the electronics on Gyro 3 multiple times to restore normal function. However, the failures became more frequent and disruptive. After the May 24 incident, NASA officials decided the instability was unsustainable. On June 4, 2024, the agency announced a permanent transition to a contingency plan known as “one-gyro mode.”

Understanding Hubble’s Pointing System

To understand the fix, you must understand the hardware. Hubble uses gyroscopes to measure the speed at which the telescope is turning. They help the computer understand where the telescope is pointing and how stable it is.

The Hardware History

During the final Space Shuttle visit to Hubble (Servicing Mission 4 in 2009), astronauts installed six brand-new gyroscopes.

  • Design: These are mechanical gas-bearing gyroscopes. Inside each unit, a wheel spins at 19,200 revolutions per minute.
  • Redundancy: The system was designed to use three gyroscopes at a time for maximum efficiency, with three kept as spares.
  • Attrition: Over the last 15 years, three of the six gyroscopes failed completely. This left Hubble with exactly three operational units until Gyro 3 began failing in late 2023.

Currently, Hubble has two functional gyroscopes remaining. NASA has activated one for daily operations and placed the other in reserve to extend the telescope’s lifespan.

How One-Gyro Mode Works

Switching to one-gyro mode is not a desperate improvisation. It is a well-engineered contingency plan developed over 20 years ago to account for exactly this scenario.

In standard three-gyro operations, the telescope can determine its orientation in 3D space purely using the gyro data. In one-gyro mode, the flight computer combines data from the single remaining gyro with other sensors on board:

  • Magnetometers: These measure the Earth’s magnetic field to provide rough orientation data.
  • Sun Sensors: These track the position of the sun to orient the solar arrays.
  • Star Trackers: Once the telescope is roughly in position, it locks onto guide stars to fine-tune the pointing.

This method allows Hubble to maintain the same level of pointing accuracy as before. The images it captures will be just as sharp, and it can still look deep into the early universe.

The Trade-Offs: Efficiency and Limitations

While the image quality remains pristine, the operational change does introduce limitations. The transition essentially trades speed for longevity.

Reduced Efficiency

Because the telescope must rely on magnetometers and star trackers to establish its position, it takes longer to slew (turn) from one target to the next. NASA estimates this will reduce scheduling efficiency by roughly 12%.

  • Weekly Orbits: Previously, Hubble could perform science observations during about 85 orbits per week.
  • New Capacity: In one-gyro mode, this drops to approximately 74 orbits per week.

Tracking Moving Targets

The most significant loss involves objects within our own solar system. In one-gyro mode, Hubble cannot track fast-moving targets that are closer to Earth than the planet Mars. This means it can no longer observe:

  • Asteroids passing near Earth.
  • The Moon.
  • Comets inside the orbit of Mars.

However, it can still track Mars, Jupiter, Saturn, Uranus, Neptune, and objects in the Kuiper Belt without issue.

The Exclusion Zone

Hubble has always had an “exclusion zone”—a part of the sky it cannot observe because it is too close to the sun. This prevents sunlight from damaging the optics. In one-gyro mode, the telescope requires more flexibility in how it turns, so this exclusion zone has expanded slightly. However, NASA confirms that essentially the entire sky remains accessible over the course of a full year.

Future Outlook: Operations into the 2030s

The decision to keep the second healthy gyroscope in reserve is strategic. Based on reliability data from the last 15 years, NASA engineers believe this configuration will allow Hubble to continue science operations through the late 2020s and potentially into the mid-2030s.

Patrick Crouse, the project manager for the Hubble Space Telescope at NASA’s Goddard Space Flight Center, stated during the June 2024 update that the team does not view this as the telescope being on its “last legs.” Instead, it is a new phase of operations that stabilizes the observatory.

By the time Hubble eventually retires, it will likely have operated alongside the James Webb Space Telescope (JWST) for over a decade. This is crucial because the two telescopes view the universe differently. Hubble sees primarily in visible and ultraviolet light, while Webb sees in infrared. Using them together provides a more complete picture of astronomical events than either could provide alone.

Frequently Asked Questions

Can NASA send a mission to fix the gyroscopes? No. Since the retirement of the Space Shuttle in 2011, there is no vehicle capable of capturing Hubble and allowing astronauts to perform repairs. While private missions (such as the Polaris Program funded by Jared Isaacman) have studied the feasibility of a re-boost mission, NASA currently has no plans to pursue a commercial servicing mission due to technical risks.

Will the pictures look different? No. The pointing stability in one-gyro mode is identical to three-gyro mode. The breakdown of the image quality will not change.

What happens if the last two gyroscopes fail? If both remaining gyroscopes fail, Hubble can theoretically operate in a “zero-gyro” mode, but the scientific capabilities would be severely degraded. It would be difficult to point the telescope accurately enough for high-value research.

Is Hubble falling out of orbit? Slowly, yes. Atmospheric drag causes Hubble to lose altitude over time. Current estimates suggest it will re-enter Earth’s atmosphere sometime in the mid-to-late 2030s unless a propulsion mission boosts it to a higher altitude.