Launching the James Webb Space Telescope
Perhaps it’s rather timely that the James Webb Space Telescope will be launched in Spring 2019. Once each of these elements - the sunshield, the mirror and instruments - are assembled, it will look a bit like a flower bud waiting to bloom. The sunshield, like petals, will encase the folded up telescope. But once it reaches its destination, the sunshield opens up and springs to life, and the enclosed mirror then follows suit. Well, providing it all goes to plan. Which is where Bill Ochs’s testing comes in, as he explained to Izzie Clarke…
Bill - The kind of challenges we face now are: how do you test this thing that has approximately 180 different elements that either pop up, roll out, pull out, do all sorts of things to deploy and get to the shape that you see on orbit? Obviously, the other part of this testing is the testing to make sure everything can survive in those very cold temperatures at it all too.
Izzie - How can you bring something this massive down to such cold temperatures?
Bill - We actually have to do it in pieces, so we’ll start with the telescope and science instruments. We’ve just completed a major milestone for our product in completing its final, we like to call it cryogenic test, which is where we bring it down to these very cold temperatures. We don’t really have facilities here at Goddard Space Flight Centre so we went down many years ago to Johnson Space Flight Centre and there was a chamber built there during the Apollo era that was about seven stories high - it was built back in the 1960s. We took that chamber, refurbished it and then we went into the chamber with the flight telescope at the beginning of this past summer. It turned out to be 100 day test where we got down to these very, very cold temperatures. Checked the mirrors to make sure you can focus the mirrors, check their alignments to the scientific instruments.
We went through that entire test and then you have to warm them back up. Just the cooling down and the warming up takes about 30 days so we had some challenges in there. I think that the biggest challenge that we had was hurricane Harvey. That hit in the middle of the test; we had approximately 160 people down there but we got through that; we actually did some testing during that. The test has been a huge success. They just had the final data review and in the print that we brought in, the look of that data and say, yes, it looks good. It came out said basically we have a great telescope and a great set of instruments. So that was huge accomplishment.
Izzie - Next step is to make sure that the telescope can survive the violent shaking and the extreme noise of launch.
Bill - We go through what we like to call dynamics testing which consists of vibration and acoustics testing. Vibration simulates the vibration that we’ll see in the rocket with a certain amount of margin, so we actually shake it early on harder than what it would see in the rocket knowing that if it survives that, it can survive the rocket ride. It’s the same thing with acoustic testing, it’s exactly what it sounds like. You put it in a sealed room with two really big speakers and you simulate the sound levels that it would see on the rocket ride.
Izzie - So you actually set these to be even more intense than an actual launch would be?
Bill - Right. You want to make sure it survives so you’ve got to take it up to another level to make sure there are some margins in between what it sees in the rocket and what it can survive. You don’t want that to be the same because then you’re getting too close to maybe damaging something.
What we do is we test things before they go into the vibration and acoustic chambers and then we test it again when it comes out to make sure everything’s working fine.
Izzie - How has that gone? Has it been plain sailing or have there been a few surprises along the way?
Bill - About a year ago we went through and we tested the integrated telescope and science instruments and that packaged together. We found some conditions in there that we didn’t quite understand - we just stopped. As it turns out there was what we call launch release mechanisms… think of it as two pieces of metal that have teeth in it that eventually come apart but it’s to hold them during launch. Those were basically rattling a little bit and that rattling was picking up signatures in all of our sensors that we really needed to understand.
Izzie - This tiny little vibration from a loose latch caused the telescope to shut itself down - but now that’s resolved it’s over to the sunshield.
Bill - We’ve just finished deploying the sunshield for the first time. We had a few little hiccups along the way but it worked very, very well. We were all very happy.
Izzie - What were some of the hiccups?
Bill - Once you deploy the sunshield the five membranes have to be tensioned and we have a unit that makes these sunshields taught. It took a little more force to get it moving than we thought it was going to take. When it finally pulled free we got a little bit of slack inside this tensioning device and the cable got caught. We’re now mitigating that by putting a piece of material that goes around the top of that to make sure that if we have a piece of cable that’s a little loose inside that unit, it can’t get caught on anything.
Izzie - So what’s left before launch?
Bill - On the spacecraft element which is the sunshield and the bus which has all the electronics boxes we then have to put it through it’s environmental dynamics testing, so it has to go through its simulation of a launch environment. In parallel to that the telescope and instruments will show up at Northrop Grumman once the spacecraft element finishes its testing and also go into a thermal vac chamber.
Once it’s done, we then put those two pieces together, so that will take some time. Once those two big pieces are together we do a series of electrical tests to make sure everything’s working fine. It then goes back into dynamics testing. Now the whole integrated observatory will go through vibration and acoustics. But we can’t do any more cold testing because there's no longer a chamber that we would fit in so that’s done once we finish up with the spacecraft element.
Once we’ve integrated our telescope there isn’t a cargo plane that it will fit on so we actually have to go by cargo ship out of Long Beach, California, down through the Panama Canal, and then back around over to French Guiana.
Izzie - And it’s from French Guiana that the James Webb Space Telescope will be packaged into the European Ariane 5 rocket, and begin its 10 year mission as the most powerful time machine, peering back over 13.5 billion years to see the first stars and galaxies forming out of the darkness of the early universe.
But with just over a year to go, there are mixed feelings towards launch…
Gillian - I’m very excited, nervous - I shouldn’t be nervous. I think the engineers have done a superb job on JWST and on my instrument, but you still sort of think well, this thing I’ve spent 20 years working on is going to be strapped on a great big rocket and somebody’s going to fire it up into the sky. And that is a little bit nerve-wracking to think about even if you are very confident of the engineering.
Scott - We always have what I call a healthy nervousness. Nobody should ever be too comfortable with a project this hard because it really is. You’re doing a first of a kind. While we’ve stubbed our toes and things have gone wrong, we’ve never met a challenge that we haven’t been able to solve. And to say we’re sitting here today with a sunshield deployed and the optics completely integrated, we’ve accomplished some of the most significant hurdles in the programme… and it works. I feel great and then I go back to the meetings and I make sure we’re all being worried enough so that we’re prepared for them. It’s good to be worried.
Bill - Oh, I’m very excited. This is going to be an amazing telescope. It’s pretty cool, I started my career on the Hubble Telescope. Hubble, when it was launched, re-wrote the astronomy books and now I’m finishing my career on the James Webb Space Telescope and James Webb is going to re-write them again. It’s not just the things we anticipate seeing but really, just like with Hubble, it’s going to be what we never, ever imagined.
With thanks to Lemoncreme for ambient piano music.