Sen—The Hubble Space Telescope was launched into space 25 years ago today, on April 24, 1990. NASA, which jointly runs the telescope with the European Space Agency, has marked the anniversary with a display of fireworks—the latest spectacular image from the veteran observatory to be released.
Hubble’s silver anniversary image is of a star cluster called Westerlund 2—a giant grouping of around 3,000 stars, 20,000 light-years away in the southern hemisphere constellation of Carina, the ship’s keel.
The whole region around the cluster is a giant stellar nursery where new stars are being born. Those in the cluster are young at around two million years old, and are particularly hot and massive. A mix of ultraviolet light and hurricane-force winds from the largest stars creates the features in the surrounding cloud of hydrogen gas.
While the image was taken primarily as a “pretty picture” for the purpose of public outreach, Hubble is still working hard as the most important scientific tool available to astronomers. More than 13,000 scientific papers using Hubble data have been published since its launch, and the telescope is still going strong.
However, it is more than five years since the last time the space telescope was serviced, in 2009, and the retirement of the Space Shuttle means that is a less simple—in fact impossible—operation to carry out again in the foreseeable future.
Just like your car, Hubble is bound to deteriorate without servicing, in the inhospitable void of space. As well as suffering extremes of temperature as its orbit carries it in and out of sunlight, its bodywork is being peppered by meteoroids. And one of the six gyros that keep it oriented properly has failed. This is not a problem in itself as only three are needed for navigation, but it is another sign that Hubble, while in pretty good shape for its age, will not keep operating for ever.
The good news is that the end is not nigh. Hubble’s main equipment and instruments are all working well and seem to have at least another five years left in them. The bad news is that its orbit, 560 km (350 miles) above the Earth, will gradually decay with time, due to drag from the tenuous upper fringes of the atmosphere, bringing it lower.
Latest projections suggest that that is unlikely to cause Hubble to re-enter until about 2037, due to the reduced effects of solar activity on the atmosphere—earlier forecasts had predicted it could happen as soon as 2024.
NASA has not yet decided quite what to do with this historic observatory. Current most likely option is that the telescope will be allowed to re-enter and burn up. But the possibility has been left open for it to be retrieved one day, because the telescope has been adapted to allow it to be lifted into a higher orbit where it could effectively be parked. (It could also be used to steer it safely into the Pacific Ocean.)
But missions cost money and many think that money spent saving Hubble would be better spent on new projects. Sen asked two key figures working with Hubble what they thought should happen.
Tony Darnell, astronomy software engineer and social media manager at the Space Telescope Science Institute, in Baltimore, told us: “You're touching on a subject that I hear a lot about, I am always fielding questions about this and I think it will reach a crescendo in the coming years.
“If we do nothing, then in time the orbit of Hubble will decay enough to cause it to fall to Earth. During the last servicing mission, one of the last things done was astronaut John Grunsfeld placed a black grappling ring on the back end of the telescope to allow something (a robotic satellite maybe), to easily grab onto it. That means it's possible now for a robotic mission to go up there and maybe push it higher.
“Sadly though, as far as I know, no one is talking about doing anything like that. Bringing it back to Earth intact would be extremely expensive as it was designed to fit in the space shuttle and it is huge! No spacecraft exist right now (from any country) that could house it and it's hard to justify the cost for the sake of sentiment so I doubt anything will be done ultimately.”
Heidi Hammel has worked closely with Hubble and is now one of the key scientists involved with its successor, the James Webb Space Telescope. She told Sen: “Our goal is to help Hubble be as productive as long as possible, hopefully through 2020 to ensure a few years of overlap with the James Webb Space Telescope.
“In the eventuality that instruments or spacecraft do begin to fail (and they will—space is a harsh environment), our community will certainly have to discuss next steps for this beloved facility. Its disposition has to be balanced with the vibrant new missions we hope to launch. Our goal is to enable the best astronomical science.”
Hammel added: “If, after the facility becomes non-functional, the decision is made to deorbit Hubble, then I hope to be on a cruise ship to watch it return to Earth with a cadre of fellow Hubble Huggers, to celebrate the telescope’s long life and many wonderful achievements.”
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