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Assignments for Servicing Mission 3B

Assignments for Servicing Mission 3B

New solar panels

Hubble's new Solar Panels in a clean room before launch.

The new Solar Panels during 'space testing' in the test-facilities at ESA's ESTEC laboratories.

Hubble's second set of ESA built solar panels was replaced during SM3B. The first set of solar panels was replaced in December 1993 during the first Servicing Mission. This second set served with honour for more than eight years and were replaced by more robust, rigid arrays that do not roll up. This has reduced vibrations and made it possible to point Hubble even more precisely in space for longer periods and thus produce sharper images. The new arrays are also smaller and will slightly reduce the effects of atmospheric drag on the spacecraft. Even more importantly, these new panels are more efficient and enables scientists to use more instruments on Hubble at the same time.

Replacement of the Power Control Unit

Astronauts preparing for the challenging tasks to be performed during Servicing Mission 3B.

The Power Control Unit (PCU) controls and distributes electricity from the solar arrays and batteries to other parts of the telescope. The original PCU has been on the job for 11 years and to replace it Hubble was completely powered down for the first time since its launch in 1990. Hubble's new Power Control Unit allows astronomers to take full advantage of the extra power generated by the new solar arrays.

Nicmos returns!

The very advanced Nicmos CryoCooler designed to cool Nicmos onboard Hubble.

Astronomers all over the world are already eagerly anticipating the return of Nicmos (Near Infrared Camera and Multi-Object Spectrometer), the sharpest definition infrared instrument in existence, after more than two years of enforced rest.

Nicmos was originally installed onboard Hubble during the second Servicing Mission (SM2) in February 1997. Designed to operate at infrared wavelengths, Nicmos had to be cooled so that its own heat did not interfere with the infrared detectors. In the case of Nicmos, cooling is produced by solid nitrogen at -196 °C, encased in an advanced thermos flask system.

Unfortunately Nicmos' lifetime was reduced from the expected 4.5 years to about 2, due to a problem in the cooling system. The sides of the thermos flask touched and as a result the solid nitrogen inside heated up and evaporated, so that by January 1999 all the coolant nitrogen had disappeared and Nicmos could no longer operate.

Once the problem was recognised the Space Telescope scheduling was adjusted in such a way that Nicmos observations were assigned to as much as 40-50% of the total observing time during the first period of observations after the instrument was installed. In this way the Nicmos science programme was completed despite the instrument's dramatically shortened lifetime.

But at last, after this enforced shutdown, Nicmos has been revived. Astronauts retrofitted it with a new, experimental cooling system that returned it to active duty. By fitting Nicmos with this refrigerator-like cooling system, it is again possible to re-cool the detectors to -196 ºC (77 K), thereby reawakening their infrared vision and extending the instrument's life by several years.

The super-quiet cooler (called the Nicmos CryoCooler - NCC) uses ultra-high-speed microturbines, spinning up to more than 400 000 rpm (revolutions per minute)- over 100 times the revolutions of a typical car engine). Hubble's engineering team successfully demonstrated this technology in 1998 during another Shuttle mission in the first on-orbit test of this high-performance, high-efficiency, mechanical cryocooler.

In the past Nicmos has produced excellent science and astronomers are looking forward to working with this top class instrument again.

A new coat for the telescope

Pieces of Multi Layer Insulation protect the telescope. They look like ordinary household aluminum foil.

The thermal blankets covering Hubble's exterior (called Multi Layer Insulation - MLI) are beginning to show some damage and deterioration, due to debris orbiting the Earth.

Space debris has both a natural and an artificial origin. Naturally arising space debris has dimensions ranging from a thousandth of a millimetre to a few centimetres and resembles tiny stones. The artificial debris is of human origin and includes used rocket parts, small pieces of old satellites and fragments from explosions. To protect critical systems, Hubble and other satellites are placed at safe altitudes that minimise the risk of microcollisions.

Nevertheless, some deterioration is inevitable, so the Multi Layer blankets must be repaired to keep the telescope thermally insulated and protected. The Multi Layer Insulation has flaked in places and there is some concern that the particles might find their way into the telescope and cause a contamination problem. Repairs to this blanket began during Service Mission 3A and continued during Service Mission 3B.

A little boost

Graph showing how Hubble was re-boosted twice during the first and second Servicing Missions. The top of the graph corresponds to 615 km, the bottom to 580. The first re-boost in 1993 was 8 km and the second re-boost in 1997 was 15 km.

Although the atmosphere is quite thin at satellite altitudes (Hubble sits in an orbit about 600 km above the Earth), it is not a perfect vacuum. Over time, all Low Earth Orbiting (LEO) satellites feel the effects of atmospheric drag and lose altitude. If the altitude is not restored, the satellite will eventually re-enter (deorbit).

Hubble has no on-board propulsion, so the only way to restore lost altitude is by the creative use of Shuttle jets during servicing missions. Hubble's altitude was increased before the last spacewalk during SM3B, as it was done during both SM1 and SM2.

The Servicing Mission 3B astronauts

Michael J. Massimino, who will be making his first space flight, will join three veteran astronauts, John M.Grunsfeld, James H. Newman, and Richard M. Linnehan. Scott Altman, a two-time shuttle veteran, will command the mission. Pilot Duane Carey, making his first space flight and flight engineer Nancy Currie will join him on the flight deck. Currie has three previous space flights to her credit.

Left: A group of astronauts are training with a realistic Hubble model for the upcoming tasks.

Below: Underwater training with a simple Hubble model. The underwater environment simulates the absence of gravity in space.

Last Update: 1 September 2019
17-Jul-2024 16:27 UT

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