Servicing Mission 3B
STS-109 Columbia • March 1-12, 2002
Servicing Mission 3B was actually the fourth visit to Hubble. NASA split
the original Servicing Mission 3 into two parts and conducted 3A in December of 1999. During SM3B a new science instrument was installed: the
Advanced Camera for Surveys (ACS). Several other activities were accomplished as well over a 12-day mission with five spacewalks.
ACS Installation
With its wide field of view, superb image quality, and exquisite sensitivity,
Hubble’s newest science instrument, the Advanced Camera for Surveys
(ACS) has 10 times more discovery power than the camera it replaces.
In other words, ACS can produce 10 times as many science results in the
same amount of time.
ASC sees in wavelengths ranging from visible to far ultraviolet. It is actually a team of three different cameras with specialized capabilities. The
high resolution camera will take extremely detailed pictures of the inner
regions of galaxies and search neighboring stars for planets and planetsto-be. The solar blind camera blocks visible light to enhance ultraviolet sensitivity. Among other things, it will be used to study weather on planets in
our own solar system. With a field of view twice the size of Hubble’s current
surveyor, ACS’s wide field camera will conduct new surveys of the universe.
Astronomers will use it to study the nature and distribution of galaxies in order to understand how our universe evolved. (click for diagram of parts)
Solar Array 3 (SA3) Installation
Four large flexible solar array (SA) panels (wings) provide power to the
observatory.
During SM1, the original arrays were replaced by SA2 and have powered Hubble for over eight years. Radiation and debris have taken their
toll on sensitive electronics, which were replaced to ensure uninterrupted
service for the remainder of the mission.
The new solar arrays (SA3) are rigid arrays, which do not roll up and
therefore are more robust. Hubble got a brand new look with its latest set
of solar wings. Although one-third smaller than the first two pairs, the power
increase was between 20 and 30 percent. They are less susceptible to extreme temperatures and their smaller-sized will reduce the effects of atmospheric drag on the spacecraft.
Power Control Unit (PCU)
As Hubble’s power switching station, the PCU controls and distributes
electricity from the solar arrays and batteries to other parts of the telescope. Replacing the original PCU, which had been on the job for 11
years, required Hubble to be completely powered down for the first time
since its launch in 1990. Hubble’s new PCU has allowed astronomers to
take full advantage of extra power generated by the new solar arrays.
NICMOS Cryocooler (NCC) Installation
Astronauts retrofitted an existing but dormant instrument called the Near
Infrared Camera and Multi-Object Spectrometer (NICMOS) with a new, experimental cooling system to return it to active duty. NICMOS was placed
on Hubble in 1997 but became inactive two years later, after depleting
the ice it needed to cool its infrared detectors. By fitting NICMOS with the
experimental cryogenic system, NASA was able to re-cool the detectors to
-334°F (-203°C or 70 K) to revive its infrared vision.
The super-quiet cooler uses ultra-high speed microturbines, the fastest
of which spins at over 200,000 rpm (over 50 times the maximum speed of a
typical car engine). Hubble’s engineering team successfully demonstrated
this technology in 1998 aboard STS-95 in the first on-orbit test of a high-performance, high-efficiency, mechanical cryocooler.