on the Hubble 25th Anniversary

Last Friday, the Hubble Space Telescope turned 25. That’s an incredible achievement, exceeded only (off the top of my head) by the Voyager space probes for longevity of space vehicle. Hubble is now probably older than some of the people using it.

Aside from being very long-lived and renowned the world over for its stunning images of space (NASA and others organized competitions to find the best ones), Hubble has also been an exceedingly productive scientific instrument. There are hundreds of thousands of images and spectroscopy that the world never sees, obtained for the purpose of shedding light into various astrophysical phenomena… Hubble is, I believe, the most productive space mission ever, in terms of the number of scientific papers that have been published using it.

It wasn’t always that way, though. Hubble launched with a faulty mirror, and that held back a lot of the science that could be done with the instrument. It was considered (for at least a brief period) a failure – a fact I was most recently confronted with when rewatching “The Naked Gun 2 1/2”: Frank Drebin visits the Loser’s Bar, and the Hubble Space Telescope is one of the pictures on the wall, alongside the Hindenburg, Sir Neville Chamberlain, and others.

The problem with the mirror meant images weren’t as sharp as they should have been, and this was rectified during the first servicing mission in 1993 by installing a corrective lens (COSTAR) in place of the High Speed Photometer. Over the years, Hubble was visited four more times (for servicing missions 2, 3a, 3b, and 4). Over time, ALL of the instruments have been replaced and upgraded, including COSTAR (now that all the instruments have corrective optics built in). So, in a sense, we’re now looking at the sixth (and probably final) Hubble Space Telescope configuration.

That repairability plays a large role in the continued functioning of the Hubble Space Telescope. Servicing Missions 3a effectively found themselves repairing an otherwise-unusable telescope. Things do break, and it’s a testament to the skill of astronauts and our space program that Hubble was designed with such repairs in mind (and, in the case of the STIS spectrograph repair from Servicing Mission 4, could be repaired even when not designed for it).

It’s largely because of one of those breakdowns that I got to use the Hubble Space Telescope, and it’s actually a pretty interesting story. Back in 2008, the telescope’s instrument data system failed. Controllers couldn’t talk to the actual cameras or spectrographs, because that system was dead. In all other respects, the Telescope was fine… it could talk to the ground, it could move, it could do all the basic things a satellite orbiting Earth needs to be able to do… and that lead to a very interesting situation.

One of the things the Hubble Space Telescope has to do is point itself, very very accurately. To do so, it has three instruments called Fine Guidance Sensors positioned around the edges of the telescope that measure and provide corrections to the pointing systems of the telescope. In actual construction, they’re an interferometer. They take light from the sides of the telescope, and interfere the beams with each other to get very very precise positioning information. And if you know what you’re doing, you can do astrometry (the study of the positions of stars) with them. And THEY are attached to the spacecraft control bus.

Fortunately, Servicing Mission 4 was already planned (and due to launch just over two weeks later), so there was SOMETHING already in the works, with a crew trained to work on telescope repair. They just had to go back to the drawing board and add instructions to replace another damaged system, while others made the spare unit flight-ready.

But from late September 2008 through late October when NASA switched over to the backup system, the Fine Guidance Sensors were the only available way of doing science. Very few people use (or have used) the Fine Guidance Sensors for science, but two of the professors at my institution were. And so when NASA needed SOMETHING to do while they waited for the servicing mission to be re-worked, they called up my department. I was a third-year graduate student at the time, and ended up (by virtue of living the closest to campus, I think) going in over a weekend to basically put together a proposal of all of the targets everyone was interested in. I think I’d had plans that weekend, but you can’t turn down free Hubble Space Telescope time, even if it was an exhausting whirlwind of activity. Meanwhile, one of my friends may be the only person who got an ENTIRE WEEK of time on the Hubble Space Telescope entirely to herself… all because her program had been the only FGS program in the queue at the time of the incident.

So that was an incredible stroke of luck for me, it was even better when Hubble was back up and running, with all repaired parts, all new instruments… and it’s now better than it’s ever been.

Since we no longer have the Space Shuttle, and because James Webb has to be (by requirements) far from Low Earth Orbit, Servicing Mission 4 may be the last time a space telescope is repaired. Hubble has overcome a LOT in its 25 years, and it’s still releasing stunning pictures like this one:

NASA Unveils Celestial Fireworks as Official Hubble 25th Anniversary Image
Source: Hubblesite.org

It’s certainly right to treasure what we have, because Hubble is an amazing achievement that we may not see again any time soon… but for now, it’s a heck of a ride.


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