Date:31 December 2008
Galaxies from the early universe. The birthplaces of planets. Dark matter. Dark energy. Since its launch in 1990, the hubble space telescope has brought these mysteries into focus, its powerful gaze scanning the universe for details far beyond the capabilities of planet-bound instruments. It’s now due for its fifth and final servicing mission – and expectations are running high.
Far above the Earth’s surface, Hubble floats clear of the planet’s light-distorting atmosphere, beaming back images that have transfixed humanity and changed the scientific world. The telescope’s triumphs continue to accumulate, thanks to a unique design that allows astronauts to repair and upgrade the telescope while it remains in orbit. Repairs keep the telescope functioning smoothly, while upgrades to the instruments bring a slew of new discoveries and useful science.
During the next servicing mission, designated SM4, astronauts will install two new instruments, repair two inactive ones, and perform the component replacements that will keep the telescope functioning at least into 2014. The bad news: Nasa managers announced recently that they would not be able to meet the February 2009 launch date. The good news: they have a “very good” plan in place.
Part of this plan involves serious preparation. Astronauts train at Nasa’s Johnson Space Centre in Texas, where they learn to deal with weightlessness in a giant water tank in the Neutral Buoy-ancy Lab, and at Goddard Space Flight Centre in Maryland, where they enter Goddard’s huge intensively filtered “clean room” to work with the actual equipment they’ll use and install aboard Hubble. Goddard prepares and tests instruments and hardware, while Kennedy Space Centre in Florida prepares the space shuttle for the mission.
At Goddard, where the Hubble programme is administered, the Space Telescope Operations Control Centre controls the telescope itself, giving the commands that prepare it for the astronauts’ activities and test the newly installed equipment. Goddard’s Control Centre will close the door that protects the telescope’s delicate optics and manoeuvre Hubble into position as the shuttle Atlantis approaches.
When the shuttle is about 60 m away from Hubble, Goddard will command the telescope to execute a roll that brings it into position for grappling. Astronauts use the shuttle’s robotic arm to capture Hubble and dock it in the cargo bay. Next, the astronauts begin their series of five six-and-a-half-hour spacewalks. Two astronauts work outside on Hubble at a time. One mainly handles the free-floating tasks; the other is connected by a foot restraint to the robotic arm, which is operated by a third astronaut from within the shuttle.
To keep themselves from accidentally floating away, the astronauts attach safety tethers to a cable that runs along the cargo bay. (Hubble was built with handrails that also make it easy for astronauts to cling to the telescope.) Many of the telescope’s components, especially the instruments, were designed to be easily removed and replaced during servicing missions.
This mission’s primary scientific priority is the installation of Hubble’s new instruments, Wide Field Camera 3 (WFC3) and the Cosmic Origins Spectograph (COS). WFC3 will be the power behind studies of dark energy and dark matter, the formation of individual stars and the discovery of extremely remote galaxies that were previously beyond Hubble’s vision. WFC3 sees three different kinds of light: nearultraviolet, visible and near-infrared, though not simultaneously. The camera’s range is much greater than that of the instruments currently aboard.
Astronauts will remove Hubble’s Wide Field and Planetary Camera 2 (WFPC2) to make room for WFC3. WFC3 has a higher resolution and a larger field of view than its predecessor.
Galaxy evolution, the formation of planets, the rise of the elements needed for life, and the “cosmic web” of gas between galaxies will be some of the areas of study for the Cosmic Origins Spectrograph (COS). A spectrograph is an instrument that breaks light into its component colours, revealing information about the object emitting the light. COS sees exclusively in ultraviolet light and will improve Hubble’s ultraviolet sensitivity at least 10 times, and up to 70 times when observing extremely faint objects.
COS will take the place of the device installed in Hubble during the first servicing mission to correct Hubble’s flawed mirror, the Corrective Optics Space Telescope Axial Replacement (COSTAR). Since the first servicing mission, all of Hubble’s replacement instruments have had technology built in to them to correct Hubble’s marred vision, making COSTAR no longer necessary. Advanced Camera for Surveys (ACS) and the Space Telescope Imaging Spectograph (STIS), are in need of repair. ACS, which partially stopped working in 2007 due to an electrical short, is the “workhorse camera” responsible for some of Hubble’s most spectacular images. STIS is a spectrograph that sees ultraviolet, visible and near-infrared light, and is known for its ability to hunt black holes. While COS works best with small sources of light, such as stars or quasars, STIS can map out larger objects such as galaxies. STIS suffered a power failure in 2004 and was put into hibernation to preserve the possibility of its repair.
Astronauts plan to fix both – a challenging prospect, since these repairs are beyond the scope of Hubble’s serviceable design. Hubble’s creators envisioned astronauts swapping components, not performing delicate surgeries during spacewalks.
An interior electronics box of ACS that supplies power for ACS detectors contains equipment affected by an electrical short. However, its location makes it inaccessible to astronauts. So instead of trying to reach the problem area, astronauts will attempt to bypass those power-shorted components entirely.
As each of Hubble’s instruments and components is repaired or installed, Goddard performs tests to ensure that everything is working correctly. But before it can try out its new equipment, the telescope needs maintenance. Hubble’s batteries store the energy that powers the telescope during the “nighttime” portion of its orbit, when the Earth blocks the Sun’s rays.
Astronauts will replace all six of Hubble’s 56 kg batteries with new, more effective versions. The telescope’s six gyroscopes are part of the system that points the telescope. When all six gyroscopes are functioning, three are used for pointing and the other three are held in reserve. Time has degraded the gyroscopes to the point where three have failed, two are in use, and a third is turned off to be used as an emergency backup. Astronauts will install six new gyroscopes.
Hubble’s Fine Guidance Sensors (FGS) lock on to guide stars, helping the telescope point. They can also be used as instruments to measure the position of stars in relation to other stars. Astronauts will replace one worn-out FGS with a refurbished model that was removed during a previous servicing mission.
Hubble’s insulating blankets, which maintain the telescope’s normal operating temperature, eventually break down because of their exposure to space. Astronauts will cover key Hubble equipment bays in fresh insulation, also called a New Outer Blanket Layer (NOBL).
Finally, they will install a new device, the “soft capture mechanism”. This simple component will allow a robotic spacecraft to attach itself to Hubble some day, once the telescope is at the end of its life.
When the astronauts have finished all of their tasks, they will use the robotic arm again to release the telescope, and Goddard will issue the commands to bring the telescope back into operation. But before Hubble’s science mission can resume, the telescope will undergo a severalmonth- long testing and calibrating period.The first new images from the telescope will be released early this year.
Restored and updated, Hubble will continue on its journey around the Earth, its new components merging seamlessly with the old, a rejuvenated telescope ready for years of groundbreaking revelations from the Universe.
Just the facts
* Hubble's latest solar arrays (installed during Servicing Mission 3B) cover 36 m2, equal to the area of a highway billboard.
* The telescope's 18-plus years of observations have produced more than 30 terabytes of data, equal to about 25 per cent of the information stored in the US Library of Congress.
* Hubble weighs 11 100 kg . as much as two full-grown elephants.
* Its primary mirror is 2,4 m across and 13,3 m long, about the length of a large school bus.
* During its lifetime, Hubble has made about 800 000 observations and snapped about 500 000 images of more than 25 000 celestial objects.
* Hubble does not travel to stars, planets and galaxies. It snaps pictures of them as it whirls around Earth at 28 000 km/h. The telescope has made just more than 100 000 trips around our planet, racking up over 3,8 billion km. That mileage is slightly more than a round-trip between Earth and Saturn.
* Each day, the orbiting observatory generates about 10 gigabytes of data, enough information to fill the hard drive of a typical home computer in two weeks. The Hubble archive sends about 66 gigabytes of data each day to astronomers around the world.
* Astronomers using Hubble data have published nearly 7 000 scientific papers, making it one of the most productive scientific instruments ever built. About 4 000 astronomers from all over the world have used the telescope to probe the universe.