July 17, 2024
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Space

Despite gyroscope failure, NASA says Hubble Space Telescope still falls short of world-class science – Spaceflight Now

The Hubble Space Telescope is seen after its launch from the space shuttle Columbia during a maintenance mission in 2002. Credit: NASA

Problems with one of the Hubble Space Telescope's three remaining gyroscopes, critical for pointing and locking targets, have led mission managers to switch to a backup control mode that will limit some observations but keep the iconic observatory operating until 2030s, officials said 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 20s and into the 2030s,” said Hubble project manager Patrick Crouse. to reporters during an afternoon conference call.

At the same time, Mark Clampin, director of astrophysics at NASA headquarters, said the agency had ruled out, at least for now, a proposed commercial mission to boost Hubble to a higher altitude using a SpaceX Crew Dragon spacecraft. The flight was suggested by SpaceX and Crew Dragon veteran Jared Isaacman as a way to extend Hubble's lifespan.

By raising the telescope to a higher altitude, the subtle “drag” effects in the extreme outer atmosphere, which act to slowly but surely draw spacecraft back to Earth, could 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 occupy the position. open a hatch and float, if not walk, in space.

But project managers said Tuesday that Hubble is in no danger of falling back to Earth anytime soon. The latest calculations show that the observatory will remain in orbit at least until 2035, allowing time to consider possible options, if justified, in the future.

“After exploring current commercial capabilities, we are not going to pursue a restart at this time,” Clampin said. “We greatly appreciate the in-depth analysis conducted by NASA and the (SpaceX-Isaacman) program and our other potential partners, and it has certainly given us a better understanding of the considerations for developing a future commercial restart 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 re-boosting 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.”

The Hubble Space Telescope was launched aboard the shuttle Discovery on April 24, 1990, with a famously defective mirror, the opening chapter in an unlikely story in which spacewalk repair crews turned a national embarrassment into an international icon of science.

Hubble was initially hampered by an error during the manufacturing of the 94.5-inch primary mirror that resulted in an optical defect known as spherical aberration, which prevented the telescope from sharply focusing starlight.

But engineers quickly discovered a way to correct Hubble's blurry vision. They designed a new camera equipped with relay mirrors adjusted to prescriptions that would exactly counteract the aberration of the primary mirror. Another device, known as COSTAR, was designed to direct corrected light toward other Hubble instruments.

During a crucial shuttle servicing mission in December 1993, spacewalking astronauts installed the new Wide Field Planetary Camera 2 and COSTAR. They also replaced Hubble's solar panels and other critical components.

The Hubble Space Telescope photographed during the last space shuttle maintenance mission in 2009. Credit: NASA

NASA would launch four more maintenance missions, install new, state-of-the-art instruments and replace aging components, such as gyroscopes and critical fine guidance sensors, which move the telescope from one target to another and then anchor it with rocks. Solid stability for detailed observations.

Gyroscopes are critical to Hubble's longevity. The telescope was launched with six ultra-stable gyroscopes, but only three are needed at a time for normal operation. During the last maintenance mission in 2009, all six were replaced. Three of the new units included hair-thin “flexible cable” power and data lines susceptible to some form of corrosion, while the other three featured an improved design that greatly reduced or eliminated that risk.

In any case, by the time Hubble's 30th anniversary rolled around in 2020, all three of the previous model's six gyroscopes had failed.

One of the three remaining units, gyro number 3, began acting erratically earlier and its performance progressively worsened. On May 24, the gyroscope was taken offline, putting the observatory into protective “safe mode,” halting scientific operations while engineers discussed their options.

Knowing that gyroscope failures were inevitable, engineers 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 percent or more with the three gyroscopes.

Although the telescope could be operated more efficiently with two gyroscopes, engineers concluded that it would make more sense to put one of the two remaining units into standby mode and operate Hubble with a single gyroscope, keeping the other in reserve for use. . as necessary.

“Our team first developed a plan for single-gyro operations more than 20 years ago, and it is the best way forward to prolong the life of Hubble,” Crouse said. “There are some limitations. It will take us more time (to move) from one objective attitude to the next and to be able to set that scientific objective.

“That will lead to lower efficiency in scheduling scientific observations. We currently schedule about 85 orbits per week and expect to be able to schedule about 74 hours a week, which means a reduction of about 12 percent in scheduling efficiency.”

At first glance, this image is dominated by the vibrant glow of the swirling spiral at the bottom left of the frame. However, this galaxy is far from the most interesting sight: behind it lies a galaxy cluster. Galaxies are not randomly distributed in space; They swarm together, brought together by the inflexible hand of gravity, to form groups and clusters. The Milky Way is a member of the Local Group, which is part of the Virgo Cluster, which in turn is part of the Laniakea Supercluster of 100,000 galaxies. The galaxy cluster seen in this image is known as SDSS J0333+0651. Clusters like this can help astronomers understand the distant and therefore early universe. Credit: ESA/Hubble and NASA

Additionally, because the telescope's movement in single-spin mode is less precise and subject to error, “we won't have as much flexibility in where we can look in the sky at any given time. But within a year we will have the entire sky at our disposal.”

Another limitation: The telescope will not be able to lock on to or track targets closer than Mars' orbit, although such observations were rare even in three-gyroscope mode.

Meanwhile, engineers plan to implement a gyroscope control mode in the coming days and return Hubble to scientific operations by the middle of the month.

“We updated the gyro reliability assessments… and still concluded that (we have) a greater than 70 percent chance of operating at least one gyro through 2035,” Crouse said.

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

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