Preparing for Hubble's Fifth
Servicing Mission ("SM4")


Third mission, SM3A:
Astronauts replace parts
Long before NASA was formed and the first satellite was launched into space, a young American scientist named Lyman Spitzer, Jr. proposed that a visible light telescope should be placed in space. A space telescope, he wrote, would reveal much clearer images of far-off objects than any ground-based telescope. Ground-based telescopes are hampered by our Earth’s atmosphere, which blurs light from stars and makes them appear to twinkle.

Spitzer worked for more than 50 years to make his dream come true. On April 24, 1990, he watched NASA launch the Hubble Space Telescope (HST) into orbit around Earth.

Hubble was not only the first space telescope to snap images in visible light, it also was the first space observatory designed to be serviced in space. Periodic servicing missions, scientists believed, would extend the telescope’s operating life and would keep the observatory up-to-date. Astronauts visiting the telescope would replace aging parts and would install science instruments with advanced technology.

Visitors to Hubble


Fourth mission, SM3B:
New solar panels installed
Astronauts, in fact, have visited Hubble four times during the telescope’s 16-year lifetime. Now, NASA is planning a fifth service call to Hubble. The visit, called Servicing Mission 4 (SM4), is planned for late 2007 or early 2008. This servicing mission will help keep Hubble operational until at least 2013.

Hubble is about 380 miles (611 kilometers) above Earth, just above our planet’s atmosphere. It is the size of a school bus (43.5 feet, or 13.3 meters long) and weighs more than 12 tons (11,000 kilograms). The telescope’s primary mirror is 94.5 inches wide (2.4 meters). Hubble is named after U.S. astronomer Edwin P. Hubble who, early last century, discovered galaxies beyond our Milky Way galaxy and determined that space is expanding.

Hubble gets a tune-up

Astronauts aboard the space shuttle will make several spacewalks to install six batteries, six gyroscopes, and a Fine Guidance Sensor. Normally, Hubble’s instruments run on sunlight collected by its twin solar panels, which make the observatory look like it has wings. The batteries power Hubble’s science instruments when the telescope is in Earth’s shadow. The gyroscopes help keep Hubble steady as it orbits Earth and allow scientists to point the telescope at celestial targets. Hubble has three Fine Guidance Sensors, which also help in pointing the telescope at objects.

Making Hubble even better

Another part of the fifth servicing mission is to boost Hubble’s scientific power by installing two state-of-the-art science instruments: the Cosmic Origins Spectrograph (COS) and the Wide Field Camera 3 (WFC3).

COS will examine the ultraviolet light streaming from distant objects. The new instrument will allow Hubble to study galaxy formation and the births of stars and planetary systems. COS will complete observations much faster than Hubble’s previous spectrograph.