AAS #1: Hubble Servicing Mission update

Contributed by
Jan 8, 2008

I am reporting from the American Astronomical Society meeting in Austin, Texas. I'll be attending press conferences and talking to astronomers, and blogging madly about all this.

Unlike most satellites orbiting the Earth, the Hubble Space Telescope was designed to be periodically upgraded, serviced by the Space Shuttle. This allows astronomers and engineers to keep the technology on the grand old 'scope up to date. This year, NASA plans on servicing the Hubble Space Telescope for the very last time. A full suite of upgrades and fixes are planned, and it's a very ambitious mission. In fact, it's the only non-space station International Space Shuttle flight planned; every other Shuttle flight will be to help construct the ISS.

The last time Hubble was serviced was in 2002, so it's high time for it to be renovated.

At this first AAS press conference, the servicing mission was reviewed. Astronaut John Grunsfeld gve the meat of it; he will lead the activity on the Shuttle. This is his third mission to Hubble, adn his fifth to space.

The major upgrades in this mission are the installation of two cameras -- the Wide Field Camera 3 and the Cosmic Origins Spectrograph. Two cameras already on Hubble will be repaired - the Advanced Camera for Surveys (ACS) and the Space Telescope Imaging Spectrograph (STIS). New parts to be installed include six new gyroscopes (which keep the telescope pointed once it locks onto a target) six new batteries, a new Fine Guidance Sensor (which tells it precisely where it's pointed), new outer blanket (insulation) layers, and a Soft Capture Mechanism.

New Cameras

WF3: Hubble itself is a telescope, able to take light from the sky and bring it into a sharp focus. There are several cameras on the back end of the 'scope, each with their own capabilities. One of the original Hubble cameras was the Wide Field Camera. It was a great instrument for its time, but as tech progressed the detectors got better, so it was replaced with WFPC2 a few years later. The original camera was brought to Earth, and the bus (the framework) was reused to put in all new optics and electronics... creating the WFC3, the most advanced camera to ever go on board Hubble. It will vastly increase the capabilities of Hubble, allowing deeper images to be taken, which manes it will see fainter objects than ever before.

COS: Spectrographs break light up into each individual wavelengths (that is, colors; think of it like a rainbow), which can reveal all sorts of cool information about astronomical objects, including their temperature, composition, distance, rotation, and lots of other things that allow astronomers to understand objects trillions of miles away. COS will do this with ultraviolet light, where hot objects dominate: massive stars, exploding supernovae, gas clouds where stars are being born, and far more. COS will give us far more detailed spectra than we have been able to do before. This must be done from space, because UV light is almost totally absorbed by the Earth's atmosphere.

Cameras to be fixed

STIS: When it was installed, STIS was the most technically advanced camera ever flown in space. It could take images in ultraviolet, visible, and infrared light, and it also could take spectra: it After several years of amazing service, a circuit board on STIS shorted out. In this mission, the astronauts will have to remove 111 (yes, one hundred eleven) tiny screws to open up the camera and replace a fried electronics board. This is an incredibly difficult task; the screws are small (bigger than watch screws, but not by much) and were not designed to be removed at all, let alone using astronaut gloves.

ACS: This camera was installed on Hubble in 2002, but it an electronic short killed it a few years later. Much like STIS, there are many dinky screws to remove, keep track of, and then reinstall. ACS takes amazingly beautiful (and of scientifically interesting) images, and has a key component called a coronograph. If you want to see something dim (say, a bird flying in the sky) next to something bright (say, the bird is near the Sun), you block the bright light so you can see the faint one. That's what a coronograph does; it blocks the bright light from a star so that we can look at the environment around the star. ACS can point at bright young stars and see the disk of gas and dust that still surround them, allowing us to investigate what forming solar systems are like.

Components to be replaced:

Gyroscopes are among the few moving parts of Hubble. Once Hubble locks onto a target, the gyroscopes keep it fixed there. These wear out after a few years, and when all is working well there are at least three gyros working, and three are kept as backups. Right now Hubble has

only one four working gyros and is operating on two; the others have since died. If that last one goes, Hubble will have to be shut down. All six gyros will be replaced on this mission.

Batteries: Hubble runs on solar power, but uses batteries when it is in the Earth's shadow for roughly half its orbit. Over time, batteries lose their ability to hold a charge, so new ones will be put on board; it's the only time they will have been replaced.

Fine Guidance Sensor: these are small telescopes in their own right, which lock onto a bright star with incredible accuracy and tell Hubble when it is pointed accurately at its target.

Insulation blanket: Every time Hubble moves into or out of the Earths shadow, the amount of heat it absorbs from the Sun changes dramatically, and that can strongly affect the cameras on board; as the metal expands and contracts it can change the pointing and focus of the cameras. The insulation blanket helps minimize this. Over time the blanket gets damaged from solar radiation, and will be replaced.

Soft Capture Mechanism: As time goes on, drag with the very thin atmosphere a few hundred miles up lowers Hubble's orbit. If we do nothing, Hubble will re-enter the atmosphere and burn up in an uncontrolled manner. I doubt anyone wants a multi-ton 8 foot piece of glass falling on their house. The astronauts will attach a mechanism on the bottom end of Hubble so that an unmanned rocket can rendezvous with it, and bring Hubble down in a controlled manner over the Pacific ocean, minimizing the risk. I'd love to see us either reboost it again or bring it back down to put in a museum, but there is no money to boost it and keep using it forever, and it's too heavy to bring down safely. And let's face it: every space flight is risky, and sending astronauts up just to bring Hubble back is too big a risk.


I'm personally torn about this mission. I'm really glad NASA is finally reservicing Hubble. I used it for a decade, working with it even before it launched. I got my PhD with Hubble data, and then worked on STIS for several years. I am really hoping they can bring my old camera back up to speed; I wrote a lot of software for STIS and I'd like to see it get more use!

But I'm sad it's the last mission to Hubble. There just isn't enough money to keep Hubble working forever, and even though this mission is to keep the 'scope alive for a few more years, it's hard not to look at it with a little bit of wistfulness. Hubble changed the way the public sees the Universe, showing everyone just how beautiful and awesome astronomy is. But I'm also happy, thrilled, that we'll get a few more years out of the lady, and I hope -- and there's plenty of experience to back this hope up -- that we'll get a lot more beauty, a lot more science, and a lot more surprises from Hubble in her remaining years.

After all as Alan Stern, NASA's Associate Administrator of Science (NASA's top banana for science) said, the goal of this mission is:

When the astronauts leave Hubble for the last time, it will be at the apex of its capabilities-- better than it ever has been before.

What more can we ask for?

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