At the beginning of March, NASA announced that the Hubble space telescope had gone back into safe mode “due to a software error on board”. The telescope’s scientific systems were not affected at all, but all related applications were interrupted while crews on Earth tried to fix the problem. The space agency did not disclose details of what exactly the breakdown consisted of, what caused it, or what was done to repair it.
There is probably no cause for concern. Room systems like Hubble always go into secure mode as soon as an anomaly occurs. Safe mode means that the telescope will stop aiming at desired targets and then collect the desired data. Instead, it just makes sure that the solar panels keep powering it. This makes the troubleshooting process easier and more seamless (especially for a software problem that can affect multiple parts of the plant).
Hubble was last put into safe mode in 2018 when there was a problem with two of its gyroscopes that it needs to orientate safely in orbit. The telescope was online again within three weeks, without any permanent problems. The shutdown is another reminder that Hubble is getting on in years. Its three decades of service outlast anything anyone would have expected, and the era of the space telescope is drawing to a close. How much time does the observatory have left and what happens when it is no longer there?
Greiser jack of all trades
Hubble’s aging hardware was last serviced by space shuttle astronauts in 2009. At the time, engineers estimated that it could last until 2016. “After a few years on the fly and with all the renovations, developers have reevaluated the viability and reliability of the instruments and started revising all the information,” said Tom Brown, director of the Hubble Space Telescope Mission Office at the Space Telescope Science Institute in Baltimore. “The latest estimates suggest that we have an excellent chance of being able to work with it scientifically until at least 2026, maybe for the whole decade. It is currently looking very good.”
Hubble has been used in pretty much every kind of astronomical study in the last few decades: studies of planets and moons in our solar system, the view of distant stars, galaxies, supernovas, space nebulae and other astrophysical phenomena. It traces the origins of the universe. The work done in exoplanet science over the past decade has been particularly surprising when you consider that when the telescope was launched in 1990, it would be five years before the first exoplanet orbiting a sun-like star would be discovered.
Hubble is of little use in finding actual exoplanets, but it does help with follow-up observations that can characterize planets and their atmospheres once they are found. When the James Webb Space Telescope (JWST) goes into operation later this year, the combined power of the two observatories could help scientists identify an Earth-like world where life is possible.
Hubble can partially compensate for failures
The JWST is often referred to as the successor to Hubble, but that’s not entirely true. Hubble can observe the universe in visible and ultraviolet wavelengths, while the JWST focuses on infrared observations, which can help study objects from the early universe and characterize the chemical makeup of other worlds. Since Hubble is in space, the influence of the earth’s atmosphere is not a problem, even if the UV radiation pollutes it.
This is particularly critical if one wants to take a closer look at phenomena that have hardly been investigated. Take, for example, the gravitational waves discovered in 2017 that were created when two neutron stars collide. Hubble was able to observe the aftermath of the event and was able to provide data outside of the infrared spectrum that could be used to provide amazingly sharp detail.
Four major scientific instruments are currently active aboard Hubble. So even if one or two of these stop working, there are still a lot of science projects the rest of the observatory can do. The telescope is also built with a lot of redundancy, so that the failure of individual hardware or software components does not necessarily mean that other instruments also give up the ghost.
Succession in sight?
There are currently no plans for a major service mission. Should there be a catastrophic outage that takes Hubble completely offline, it would be hard to imagine NASA approving a repair mission for a three-decade-old observatory. So what will Hubble replace when it finally retires? Brown says other nations have initial plans to launch missions that could take over the visible and ultraviolet observations that Hubble is currently conducting. The Astrosat space telescope from India is currently making UV observations from space, but it is much less powerful. China plans to launch a space telescope called Xuntian in 2024. State media says it will be able to observe an area 300 times the size of Hubble’s.
The real Hubble successor could be NASA’s long proposed “Large Ultraviolet Optical Infrared Surveyor” space telescope (LUVOIR for short), a general-purpose observatory capable of observing multiple wavelengths (including infrared, optical and ultraviolet). But even with secured funding, LUVOIR would not be launched until 2039 at the earliest.
It is therefore quite possible that Hubble will remain active until it can actually be replaced. Most astronomers, however, expect a large knowledge gap when it actually stops working. “Hubble really is best for ultraviolet and optical astronomy,” says Brown. “So much research, especially when it comes to understanding temperature data and chemistry in space, depends on the information it provides. I’m afraid the space community will really feel the loss if Hubble stops working. “