Hubble's new superpowers
Posted: Friday, May 08, 2009 11:50 AM by Alan Boyle
ESA
Click for video: Atlantis grabs hold of the Hubble Space
Telescope in this artwork illustrating the mission plan. Click on
the image for more about Hubble and its new instruments.
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When astronauts from the shuttle Atlantis open up the Hubble Space Telescope for its final extreme makeover, much of the work will be aimed at fixing what's been ailing the world's premier orbiting observatory. It'll get fresh batteries and brand-new gyros, and if all goes well, Hubble's Advanced Camera for Surveys and the Space Telescope Imaging Spectrograph will be back in full working order for the first time in years.
But this is not just a fix-up mission. Two new instruments are due to be swapped into the mix, and those enhancements should give Hubble superpowers it never had before: for example, three-in-one vision that spans the spectrum from ultraviolet to infrared, and the ability to make out the cosmic cobwebs that stretch out between galaxies.
"We're all looking forward to seeing how well the new installations and the instrument repairs go," Ken Sembach, Hubble project scientist at the Baltimore-based Space Telescope Science Institute, told me this week. "We're looking forward to an improved Hubble."
The new instruments, known as the Wide Field Camera 3 (WFC3, or "Wiff-see-three") and the Cosmic Origins Spectrograph (or COS), should open the way for new wonders and speed up the pace of discovery during Hubble's final five years. They're designed to complement the two instruments being repaired - or replace them in case they can't be fixed.
Here's a quick guide to Hubble's future superpowers and how they'll mesh with the space telescope's pre-existing capabilities:
NASA
Computer-generated graphics show where the Wide Field Camera 3 will go.
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WFC3: Superman's three-in-one vision
The $75 million Wide Field Camera 3's superpowers have their roots in its enhanced sensitivity in wavelengths ranging from the ultraviolet part of the electromagnetic spectrum, through visible wavelengths and into the infrared.
"This camera basically is doing the work of two or even three cameras, if you think about the previous generations of instruments," Sembach said. He said its sensitivity to infrared light is 10 to 30 times that of Hubble's old workhorse for those wavelengths, the now-dormant Near Infrared Camera and Multi-Object Spectrometer, a.k.a. NICMOS.
WFC3 takes full advantage of manufacturing standards that just weren't available for earlier instruments - such as the camera it's replacing, the Wide Field and Planetary Camera 2 (WFPC2, or "Wiff-pic-two"). During image processing, engineers usually have to work around the small blemishes caused by imperfections in the camera detectors, but with WFC3, "we can remove almost all of those to very high precision," Sembach said.
Once the camera gets to work, you can expect bunches of eye-popping, color-enhanced images that combine ultraviolet, visible-light and infrared data. "One of the real drivers behind this camera, scientifically, was really wanting to understand what's going on in star-forming regions," Sembach explained.
The infrared detectors can pick up the light that filters through warm clouds of interstellar dust, while the ultraviolet/visible light detectors can spot the hot blue stars that are just crackling into existence. "You can start to build up a more complete picture of how these stars are forming, and how they're interacting," Sembach said.
To get an idea how observations from multiple wavelengths can be put together, check out the Hubble/Spitzer/GALEX image of the galaxy M81, and the Chandra/Hubble/Spitzer/GALEX view of the galaxy M51.
WFC3 also is equipped with "grisms" - grating-equipped prisms that can analyze the spectral signature of light and determine how distant a celestial object is, based on its redshift.
"One of the other things that WFC3 was really designed for is to look back at earlier times of the universe and pick out really red things, as a precursor to what we'll be doing with the James Webb Space Telescope in the 2013-2014 time frame," Sembach said. "It's going to be a very interesting time to look at, when galaxies are just first coming together."
The new camera could help Hubble double or triple the rate of discovery for extremely distant supernovae. Those are just the kinds of observations that can help sort out the mysteries surrounding the accelerating expansion of the universe. For more about that and other WFC3 wonders, check out this NASA Web page.
NASA
An artist's rendition shows an astronaut installing the Cosmic Origins Spectrograph.
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COS: The Flash's speediness for spectroscopy
We've already mentioned how WFC3 can analyze the characteristics of light from distant galaxies to figure out how far away they are. When it comes to ultraviolet wavelengths, the $70 million Cosmic Origins Spectrograph is built to conduct that kind of analysis with far greater sensitivity than WFC3 or the space telescope's other spectrograph could manage.
The Space Telescope Imaging Spectrograph, or STIS, performed a similar duty before it broke down in 2004. But COS is built to handle light far more efficiently. "In STIS, there are many, many bounces before the light gets into the detector. In COS, there's only one bounce. ... You gain a lot just by not absorbing that light," Sembach said.
As a result, COS will be 10 to 30 times more sensitive than STIS was, depending on the brightness of the object you're observing. "If you want to take a spectrum of a star or a quasar or galaxy, what normally would have taken you 10 orbits will just take one orbit," Sembach said.
And when it comes to dimmer objects, COS can do more in two weeks than STIS could do in a year. That opens up whole new vistas in astronomy. Job No. 1 is to chart the ethereal cosmic web that apparently provided the framework for galaxy clusters soon after the universe was born - hence the reference to "Cosmic Origins" in the contraption's name. Learning more about the cosmic web may also tell astronomers more about the mysterious unseen stuff known as dark matter.
"That cosmic webbing can't currently be imaged with Hubble or any other observatory up there," Sembach said. "There's no way to study it other than to observe the light that's processed through it. You're looking for the 'fingerprint' of that stuff on the light, basically."
Eventually, COS' scientists will use hundreds of fingerprint analyses, pointing in all directions into the sky, to build up what they call a "CAT scan of the universe."
But wait ... there's more: COS should be able to track the flow stellar winds and even sample the starlight shining through the atmospheres of alien planets. "For example, you might be able to see whether a planet's atmosphere has hydrogen or carbon or oxygen in it," Sembach said.
COS will be installed in a slot currently taken up by a corrective-optics package known as COSTAR. Spacewalkers installed COSTAR back in 1993 to compensate for Hubble's incorrectly shaped mirror. But now all of Hubble's instruments have their own built-in corrective optics, so COSTAR is no longer needed. It will be brought back down to Earth aboard Atlantis, along with WFPC2.
What's ahead: The League of Extraordinary Instruments
If everything goes right, Hubble will have two cameras, WFC3 (new) and ACS (repaired) ... and two spectrographs, COS (new) and STIS (repaired). Does it sound as if there's some NASA-style redundancy going on? Maybe a little bit. After all, it's by no means certain that ACS and STIS will be repaired.
NASA |
A diagram shows the location of Hubble's instruments after servicing: Wide Field Camera 3 (WFC3), Near
Infrared Camera and Multi-Object Spectrometer
(NICMOS), Space Telescope Imaging Spectrograph
(STIS), Cosmic Origins Spectrograph (COS);
Advanced Camera for Surveys (ACS) and Fine
Guidance Sensors (FGS) for pointing and astrometry.
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Hubble's handlers say the instruments will complement each other instead of duplicating each other. For example, ACS is particularly good at taking pictures in visible-light wavelengths, but not as good at either end of the spectrum. In contrast, WFC3 is optimized for the ultraviolet and the infrared wavelengths.
When it comes to taking pictures of the dusty protoplanetary disks around stars, or even directly imaging planets around other stars, ACS will be the instrument of choice because it has a coronagraph that can block out a star's glare. WFC3, which was designed before ACS went on the fritz in 2007, doesn't have one.
That doesn't mean WFC3 is totally incapable of seeing an extrasolar planet. "If conditions are right, it might be possible to get a direct image with some clever observing techniques," Sembach said. But the example does show that the old instruments can still do some things better than the new ones.
It's the same with STIS: "It's capable of spectroscopy at optical wavelengths, which COS is not," Sembach said. If STIS is returned to working order, it will be the instrument of choice for analyzing alien atmospheres and watching black holes gobble up gas. Generally speaking, COS can gather light more efficiently, but STIS can study areas of the sky in higher resolution.
Having instruments with overlapping capabilities is a good thing, Sembach said: "Being able to do something two different ways provides validation that what you're seeing is correct, or maybe confirmation that it isn't."
Sembach and his colleagues on the Hubble team should find out how much capability they'll have soon after each of the Atlantis crew's five spacewalks. First there'll be an "aliveness test" to make sure all the circuitry is hooked up correctly. If the connections needs tweaking, the job might have to be handled during a later spacewalk. Later, Hubble's engineers will conduct functional tests and calibrate the instruments.
"We'll start interleaving some science observations with the calibration observations sometime in July and August," Sembach said.
Meanwhile, the Hubble team will try to bring NICMOS back online as well. "It relies upon a cooling system that has been off since September of last year, and we've been unable to restart it," Sembach said. "We will try again to restart it this summer."
Look for the first fruits of Hubble's new (and restored) superpowers to be revealed shortly after Labor Day.
More about Hubble and Atlantis' mission:
