Hubble Telescope Gyroscope Issues Continue

For over three decades, the Hubble Space Telescope has provided humanity with its deepest views of the cosmos. However, recent hardware malfunctions have forced NASA to change how the observatory operates. Following a series of technical glitches involving its gyroscopes in mid-2024, engineers have transitioned the telescope into a new operational mode to preserve its lifespan. Here is what is happening with Hubble’s pointing system and what it means for the future of space astronomy.

The Recent Malfunctions

In late May 2024, the Hubble Space Telescope automatically entered “safe mode.” This is a protective state where the telescope pauses all scientific observations and orients its solar panels toward the sun to maintain power while awaiting instructions from the ground. This event marked the third time in just a few months that the observatory halted operations due to the same component: a faulty gyroscope.

The specific issue involved one of the three remaining active gyroscopes sending erroneous telemetry readings back to Earth. The sensor was “saturating,” meaning it was reporting the maximum possible slew rate (turning speed) even when the telescope was relatively still. This confusion forced the onboard computer to stop operations to prevent the telescope from drifting off target or damaging itself.

NASA engineers attempted to reset the electronics and troubleshoot the specific unit, but the errors persisted. On June 4, 2024, NASA leadership, including Patrick Crouse, the Hubble project manager, announced that they would stop trying to fix the faulty gyro and instead transition the telescope to a new way of flying.

What Are Gyroscopes and Why Do They Fail?

To understand the problem, you must understand the hardware. Gyroscopes are devices that measure the speed at which the telescope turns. They are essential for:

  • Determining exactly where the telescope is pointing.
  • Moving from one target to the next.
  • Locking onto a specific star or galaxy with extreme precision (needed for long-exposure photography).

Hubble was originally launched with six gyroscopes. During the final servicing mission in 2009, astronauts aboard the Space Shuttle Atlantis replaced all six units with new hardware. Since then, three of those units have failed completely due to age and wear. Until May 2024, Hubble was operating on the remaining three.

The primary cause of failure in these devices is often corrosion on the thin wires, known as flex leads, that carry power and data in and out of the fluid-filled float inside the gyro. Over time, the fluid can degrade or the wires can corrode, leading to the noisy or saturated data that caused the recent safe mode events.

The Transition to One-Gyro Mode

Because the problematic gyroscope is no longer reliable, NASA has switched Hubble to “one-gyro mode.” While the telescope is technically capable of operating with just one gyroscope, the standard procedure for years was to use three for maximum efficiency and precision.

The new plan works as follows:

  1. The Shutdown: The faulty gyro has been disabled.
  2. The Spare: One of the two remaining healthy gyros has been placed in reserve. It is turned off to preserve its remaining operational life.
  3. The Active Unit: The entire observatory now runs on the single remaining active gyro.

This might sound risky, but NASA prepared for this scenario nearly 20 years ago. To compensate for the missing gyroscopes, Hubble now relies heavily on its magnetometers (which measure the Earth’s magnetic field) and Sun sensors to determine its rough orientation. Once it is close to the target, it uses its Fixed Head Star Trackers and Fine Guidance Sensors to lock on visually.

Impact on Scientific Capabilities

The shift to one-gyro mode ensures that Hubble remains functional, but it comes with specific trade-offs regarding efficiency and capability.

Reduced Efficiency

The most immediate impact is speed. In three-gyro mode, Hubble could slew (turn) and lock onto a new target very quickly. In one-gyro mode, the process requires more time for the telescope to figure out exactly where it is pointing and stabilize. NASA estimates this will result in a 12% reduction in scheduling efficiency. Essentially, the telescope will spend more time moving and less time taking pictures.

Limited Tracking of Moving Targets

Hubble is famous for tracking objects within our own solar system, such as comets and asteroids. With only one gyro, the telescope loses some agility. It can no longer track fast-moving targets that are closer to Earth than the orbit of Mars. While it can still observe Mars, Jupiter, Saturn, and distant asteroids, it cannot track a fast object zipping past Earth.

The Exclusion Zone

The telescope has strict rules about where it can point to avoid looking at the sun. In one-gyro mode, the constraints on pointing are slightly tighter. The telescope will have less flexibility in observing targets at certain times of the year, though NASA states that virtually the entire sky remains accessible over the course of a full year.

The Future of Hubble

Despite these issues, the outlook for Hubble remains positive. NASA officials have stated that the hardware, even in this reduced mode, is robust enough to continue high-value science operations into the mid-2030s.

The observatory continues to work in tandem with the James Webb Space Telescope (JWST). While JWST observes the universe in infrared light, Hubble observes in visible and ultraviolet light. This partnership allows astronomers to view the same celestial objects across different spectrums, providing a complete picture of the universe.

There are currently no funded plans for a servicing mission to fix Hubble. While private billionaire Jared Isaacman proposed a private mission to boost Hubble’s orbit and potentially repair it, NASA ultimately declined the offer in 2024 due to risks associated with touching the aging vehicle. For now, Hubble will continue its watch on a single gyroscope, remaining one of humanity’s most important scientific instruments.

Frequently Asked Questions

Is the Hubble Telescope shutting down? No. Hubble has resumed scientific operations. It is simply using a different control mode that relies on one gyroscope instead of three. It continues to take images and gather data.

How much longer will Hubble last? NASA engineers simulate that, with the current one-gyro operational plan, Hubble has a high probability of operating through 2035. The limiting factor will eventually be atmospheric drag pulling the telescope lower in orbit, or the failure of the final two gyroscopes.

Can astronauts fix the gyroscope? Not currently. The Space Shuttle program, which was used to service Hubble, retired in 2011. There are no current government vehicles capable of capturing Hubble and allowing astronauts to perform repairs.

Does this affect the quality of the images? No. The image quality remains identical. Once the telescope locks onto a target using its Fine Guidance Sensors, the stability is just as good as it was with three gyroscopes. The only difference is that it takes longer to set up the shot.