NASA - National Aeronautics and Space Administration

Go to a mountain top or into the countryside at night, and you get a clear, bright view of the starry skies. That view is the reason large telescopes and observatories are located in remote areas far away from city lights. But even sophisticated instruments cannot eliminate the effect of the atmosphere, which distorts the light from stars and galaxies.

The Hubble Space Telescope will soon get a visit from the STS-125 space shuttle crew. Image Credit: NASA

NASA's Hubble Space Telescope is the length of a large school bus and weighs as much as two adult elephants. Hubble flies about 550 kilometers (342 miles) above Earth, far above the dusty haze of the planet's atmosphere. With a clear view of the universe, the telescope can take sharp images of the solar system's planets as well as faraway stars and galaxies. It has taken vivid pictures of the birth and death of stars, comet pieces crashing into Jupiter's atmosphere, and the most distant known galaxies in the universe that are billions of light years away.

For 18 years, Hubble has been orbiting Earth and helping scientists understand intricate secrets of the universe.

In its lifetime, Hubble has made many important contributions to science and astronomy. Scientists have used Hubble to measure how far away galaxies are and how quickly they are moving away. This information tells them how fast the universe is expanding, which in turn has helped them to calculate the age and size of the cosmos. Hubble has also given scientists evidence of intriguing phenomena, such as planets revolving around sun-like stars, and of regions in space called black holes, which suck in everything, including light.

Over the years, Hubble has needed some periodic tuneups. Astronauts will make one last trip to service the spacecraft later this year. If all goes as planned, they will replace key parts, repair existing instruments and install new ones that will advance Hubble's ability to peer into the universe and keep the telescope going for at least another five years.

Servicing Mission 4 is scheduled to lift off in October. On the third day of the flight, the space shuttle will meet up with the telescope. Astronauts will use the shuttle's robotic arm to grab the telescope and attach it to the shuttle's cargo bay.

With equipment bay doors open, a crew member prepares to work inside of the Hubble mock-up in the Neutral Buoyancy Lab near Johnson Space Center in Houston, Texas. Image Credit: NASA

Over the course of five spacewalks, the astronauts will install two new instruments on Hubble and try to repair two others. They will also replace the telescope's six batteries and its six gyroscopes, which keep the telescope stable and pointed in the right direction.

The high-tech optical instruments are what have made Hubble's groundbreaking science and astronomy discoveries possible. The instruments detect light at wavelengths, or colors, ranging from near-ultraviolet through visible to near-infrared.

Stars and galaxies emit light in this range of colors. For instance, nearby galaxies, which are younger with bursts of new star formation, emit ultraviolet and visible light. This light becomes redder and shifts to near-infrared the farther away, or older, the galaxy. By observing a galaxy's light emissions, scientists can find out when and how it formed, how it has evolved, and its chemical composition.

Some of the optical instruments now need an upgrade. Astronauts will put in two new instruments:

--Wide Field Camera 3: This will be Hubble's main new imaging camera that spans wavelengths from near-ultraviolet to the near-infrared. It will study everything from the formation of distant galaxies to the planets in Earth's own solar system.

--Cosmic Origins Spectrograph: This instrument is designed to split light into its individual wavelengths. This spectrograph is especially sensitive and efficient at detecting ultraviolet signals. It will be useful to study how stars, planets and galaxies formed and evolved, as well as how elements such as carbon and iron, which are necessary for life, first formed.

The astronauts will also attempt to repair two instruments:

--Space Telescope Imaging Spectrograph: This instrument, which complements the Cosmic Origins Spectrograph, covers most of the ultraviolet range of light, the entire visible range and some wavelengths of the near-infrared. The imaging spectrograph stopped working in August 2004 because of a power supply failure.

The Hubble Space Telescope captured this image of a planetary nebula 6,500 light years away from Earth. Image Credit: NASA

--Advanced Camera for Surveys: With its wide field of view and sharp images, this imaging camera took some of the most impressive pictures of deep space. It suffered a power supply failure in January 2007.

In addition, astronauts will replace the telescope's rechargeable batteries. Hubble orbits Earth once every 97 minutes, spending a third of this time in darkness. While in the sun, Hubble is powered by its solar panels. The solar panels also recharge the batteries, which take over during nighttime orbit. The batteries, which went up with Hubble on board space shuttle Discovery in 1990, are now starting to lose their capacity.

Scientists hope that prolonging the telescope's life will help uncover even more of the universe's secrets.


Related Resources
NASA's Hubble Mission Page
Servicing Mission 4
HubbleSite   →
Amazing Space   →

Prachi Patel-Predd, Institute for Global Environmental Strategies