Is it possible to repair the Hubble telescope without astronauts?

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Is it possible to repair the Hubble telescope without astronauts?







On Friday, October 5, 2018, the Hubble Space Telescope (HST) suffered a failure of one of its six gyroscopes and immediately the astronomical community panicked. Actually the problem, even if it is permanent, is not crucial. Hubble uses its gyroscopes to measure the rotation speed of the telescope around its three axes and thus optimize its scientific observations. These data, together with those provided by other sensors, are used to move the telescope using flywheels. At one point, Hubble uses only three gyroscopes, although I could continue to study the universe with only one (yes, not the same as now). After the failure, the telescope only has two operational gyroscopes, so probably only one is used to extend the life of the other. In fact, between 2005 and 2009 Hubble was running with only two gyroscopes. But beyond this specific problem, what is crystal clear is that it is only a matter of time before the telescope stops working and leaves us orphans ... astronomically speaking (we hope that by then the James Webb is already in orbit). So a recurring question that we will see more and more frequently is whether it is possible to repair this venerable telescope in orbit.



The Hubble Space Telescope seen from Atlantis on the STS-125 (SM4) mission of 2009 (NASA).



The question may seem absurd because all the spacewalkers know that Hubble has been visited by five shuttle missions that have repaired more or less serious problems and installed new equipment and instruments. And is that the Hubble was designed to allow maintenance operations in orbit (the main reason for its high cost). The last of these missions was the SM4 (Servicing Mission 4), carried out by the astronauts of the STS-125 Atlantis in May 2009. Precisely, during this mission the six gyroscopes were replaced by totally new units. What happens is that, obviously, the shuttle has been retired for seven years and there is no manned ship in service that can repair or maintain the Hubble telescope. The private ships CST-100 Starliner and Dragon 2 simply are not enabled for extravehicular activities -not even have EVA suits- nor carry robot arms, while the Orion ship will only carry out missions beyond low orbit. With the manned ships out of the equation, is there any chance?



One of the Hubble gyroscopes disassembled (NASA).





Location of one of the three pairs of gyroscopes (NASA).



Yes there is. In the SM4 mission of 2009 the astronauts installed a coupling system to the rear of the Hubble to allow the visit of a space vehicle. The system is an androgynous mechanism of LIDS type (Low Impact Docking System) of 1.8 meters in diameter similar to the APAS used in the Mir and the ISS. The idea was -and is- to attach a propulsive module at the end of the telescope's useful life to perform a controlled re-entry (this module has not been designed or approved yet). With eleven tons of mass and a slightly inclined orbit (28.5º), Hubble will not be a major threat to humanity, but neither is it a small satellite and the best thing to do is avoid unnecessary risks. Obviously, this system can also be used to couple a robotic ship in order to maintain or repair the telescope.



Hubble coupling system (NASA).





Location of the coupling system (NASA).



The concept, as often happens with everything related to space, is not new. NASA studied it seriously after the Columbia catastrophe in 2003. In the aftermath of the tragedy, it was decided that the space shuttle would only perform the minimum number of missions necessary to assemble the ISS. This decision left out any maintenance mission to Hubble, located in a different orbit than the ISS. The SM4 mission would only be authorized in extremis when an alternative rescue plan was approved. If there was a problem with the STS-125 Atlantis, the STS-400 Endeavor emergency mission would have taken off with four astronauts to approach the Atlantis and rescue its seven crew members. This LON emergency mission scheme (Launch on need) was used in almost all missions of the shuttle from the STS-107 Columbia, although in the case of the SM4 it was more important because the Atlantis could not use the ISS as a refuge in case of emergency.



The ICM (NASA).





The ICM coupled to the Zaryá and Unity modules (NASA).



But before NASA decided to take a risk with the SM4, several scenarios were proposed in which a ship would be coupled with Hubble to repair it remotely. For this purpose the ship had to be equipped with one or several robot arms that would play the role of the astronauts. Some of these proposals made use of the ICM module (Interim Control Module), built by NASA in the late 1990s to keep the ISS in orbit as a result of the delay of the Russian module Zvezdá. Finally the ICM was not necessary and remained on the ground, but it was thought to adapt it for a mission to Hubble. The ship based on the ICM would have been able to replace all the equipment and instruments planned for the SM4. At that time Hubble was not equipped with the LIDS coupling system, so the coupling maneuver had to be much more complex (the astronaut's securing rails would be used for that purpose). The ICM would remain attached to the Hubble and would take care of its controlled reentry at the end of its useful life. In the more modest versions of this proposal the ICM would be coupled with the Hubble without repair and would limit itself to raising its orbit until the end of the mission.



A ship based on ICM is coupled with Hubble for its maintenance (David Akin / NASA).



A more elaborate version of this project, and with an inverted disposition, was the HRV (Hubble Robotic Vehicle) of 2004. This vehicle would be made up of three modules: the EM (Ejection Module), the DM (De-orbit Module) and a robotic system. The EM would carry all the equipment to repair and upgrade the Hubble and would include a 12-meter-long robotic arm, as well as an additional precision manipulator similar to the Dexter of the ISS for the most delicate operations. Interestingly, the DM module would be located between the EM and the Hubble. Once the robotic maintenance was completed, the EM module would be separated and the DM would remain coupled to raise the telescope's orbit and, when the time came, perform its controlled reentry.



Mission HRV (Jiegao Wang et al.)





Elements of the HRV (Jiegao Wang et al.)





Maintenance detail of the HRV mission (Jiegao Wang et al.).



At the end of the past decade, a hybrid mission with manned flights was also proposed in which a series of modules, including pressurized elements to allow the temporary presence of astronauts, would be coupled to Hubble. The astronauts would travel on board of commercial manned ships that, in addition, would elevate the orbit of the complex. These missions would use the LIDS port added in 2009, which would facilitate capture and coupling operations. This mission scheme would be feasible today using the future Dragon 2 and Starliner ships, but the budget of a manned mission compared to a purely robotic one would be incredibly higher.



Proposal for maintenance of the Hubble with pressurized modules and manned ships (in this case a first generation Crew Dragon) (NASA).





Elements of the DSM module for Hubble maintenance (NASA).



All these proposals were discarded, mainly for their high cost, but they show that it is perfectly possible to maintain and repair the Hubble without the shuttle if necessary. I am very much afraid that if the James Webb and the WFIRST continue to accumulate delays, something not unreasonable, in the coming years we will see new reincarnations of these projects to avoid the loss of the only large space observatory in the visible spectrum available to our species.

References:



Jiegao Wang et al, Modeling and Simulation of Robotic System for Servicing Hubble Space Telescope, Proceedings of the 2006 IEEE / RSJ International Conference on Intelligent Robots and Systems October 9 - 15, 2006, Beijing, China.

https://spacecraft.ssl.umd.edu/publications/SM4R_white_paper_r1.pdf

https://sspd.gsfc.nasa.gov/images/nasa_satellite%20servicing_project_report_0511.pdf

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