by Trouble with one of the Hubble Space Telescope’s three remaining gyroscopes, which are critical to targeting 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 well into the 2030s, officials said Tuesday.
“We still believe there is a very high reliability and probability that we can operate Hubble successfully, doing cutting-edge science, through the rest of the 20s and into the 2030s,” Hubble project manager Patrick Crouse told reporters during an afternoon teleconference.
Meanwhile, Mark Clampin, director of astrophysics at NASA Headquarters, said the agency has, at least so far, rejected a proposed commercial mission. to boost Hubble to higher altitudes using the SpaceX Crew Dragon spacecraft. SpaceX and Crew Dragon veteran Jared Isaacman proposed the flight as a way to extend Hubble’s life.
By reinforcement the telescope to higher altitudes, the subtle effects of “drag” in the extreme outer atmosphere, which acts to slowly but surely pull a spacecraft back to Earth, could be reduced. Isaacman, a billionaire who flew the first fully commercial flight into low-Earth orbit in 2021, is training to lead three more SpaceX “Polaris” missions, including a flight this summer in which he plans to be the first private citizen to stand in it. open hatch and float, if not walk, in space.
But project managers said Tuesday that Hubble is not in danger of falling back to Earth anytime soon. The latest calculations show that the observatory will remain in orbit until at least 2035, giving plenty of time to consider possible options, if necessary, down the road.
“After exploring the current commercial capabilities, we are not going to pursue re-intensification at this time,” said Clampin. “We appreciate the detailed analysis done by the NASA program and (the SpaceX-Isaacman), and our other potential partners, and it certainly gave us a better insight into the circumstances surrounding the development of a commercial booster mission in the future.
“But our assessment also raised a number of considerations, including potential risks such as premature loss of science and some technological challenges. Therefore, although the restart is an option for the future, we believe that we need to do some additional work to determine whether the short-term scientific risk is greater than the long-term scientific risk.”
Hubble’s years of service in space
The Hubble Space Telescope was launched aboard the shuttle Discovery on April 24, 1990, with a famously faulty mirror, the opening chapter of an incredible story in which astronaut repair teams turned a national embarrassment into an international scientific icon.
Hubble was first hampered by an error during the manufacture of the 94.5-inch main mirror, which caused an optical defect known as spherical aberration, which prevented the telescope from bringing starlight into sharp focus.
But engineers quickly figured out a way to correct Hubble’s blurry vision. They designed a new camera equipped with relay mirrors based on a prescription that would precisely counteract the distortion of the main mirror. Another device, called COSTAR, was designed to direct corrective light at Hubble’s other instruments.
During the December 1993 shuttle servicing mission in December 1993, spacewalk astronauts installed the Wide Field Planetary Camera 2 and the new COSTAR. They also replaced Hubble’s solar panels and other critical components.
NASA launched four more servicing missions, installing new state-of-the-art instruments and replacing aging components such as fine directional sensors and gyroscopes, which move the telescope from target to target and then lock on to 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 at a time for normal operation. During the last servicing mission in 2009, all six were replaced. Three of the new units included components that could be corroded by nature, while the other three had improved designs that greatly reduced or eliminated that risk.
In any case, by the time Hubble’s 30th anniversary rolled around in 2020, all six gyroscopes of an older model had failed.
One of the other three units, gyroscope No. 3, acting erratically earlier, and his performance gradually deteriorated. On May 24, the gyroscope was taken offline, putting the observatory in a protective “safe mode”, halting science operations while engineers discussed their options.
Knowing that gyroscope failures were inevitable, engineers had earlier developed software that would allow Hubble to operate with two gyroscopes or even one. The disadvantage was that the telescope could only hit targets in about half the sky at any given time instead of 85% or more with the three gyroscopes.
Although the telescope could be operated more efficiently with two gyroscopes, the engineers concluded that it would make more sense to put one of the two remaining healthy units into standby mode and operate Hubble with one gyroscope, while the other other being held as a 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 extend Hubble’s life,” Crouse said. “There are some limitations. It will take us more time to (transition) from one target perspective to the next and be able to lock onto that science target.
“That will result in lower efficiency for scheduling science observations. We currently schedule about 85 orbits per week and we expect (to be) able to schedule about 74 hours per week, and so about a 12% reduction in scheduling efficiency.”
Additionally, because the movement of the telescope in single-gyro mode is less precise and subject to error, “we don’t have as much flexibility as to where we can look in the sky at any one time. But only over a period of time. year, the whole sky will be available to us.”
One other limitation: the telescope will not be able to lock on and track targets closer than the orbit of Mars, although even in the three-gyroscope mode, observations have been rare.
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 have updated reliability assessments for the gyros … and we still conclude that (we have) more than a 70 percent probability that at least one gyro will work through 2035,” said Crouse.
The infrared-sensitive James Webb Space Telescope is building on Hubble’s legacy, pushing deeper into space and time and producing a steady stream of discoveries as it moves to the forefront of space-based astronomy. But Hubble is still making world-class observations, and astronomers want to keep it operating as long as possible.
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