Hubble Space Telescope Servicing Mission 3B
Camera for Surveys
Advanced Camera for Surveys, Hubble's new scientific instrument,
will give astronomers the opportunity to discover celestial objects
far beyond the reach of current instruments in a fraction of the
time, unlocking more of the universe's secrets. The new camera,
which is also known as ACS, is a large phonebooth-sized instrument
consisting of three different, specialized channels. Each channel
plays a unique imaging role, enabling ACS to contribute to many
different areas of astronomy and cosmology. It will become Hubble's
new workhorse, surveying far regions of the universe, searching
for extra-solar planets and observing weather and other features
on planets in our own solar system. With its wider field of view,
superb image quality and exquisite sensitivity, ACS will take
full advantage of Hubble's unique position as a space-based telescope.
fourth spacewalk, Mission Specialists James Newman and Michael Massimino
will install ACS into the location currently held by the Faint Object
Camera -- the last of Hubble's original instruments.
Hubble's New Solar Arrays
visits Hubble, spacewalkers will install new solar arrays that will
give the orbital observatory a new look and boost its power. STS-109
astronauts will install the new arrays during the mission's first
first two pairs, which are so flexible that they roll up like
window shades, Hubble's newest solar arrays are flat, rigid and
they fold up. The new arrays have one-third less solar cell area,
but produce at least 20 percent more power than the current set.
The added power enables all the science instruments to be powered
and ready to operate simultaneously, allowing for more discoveries
in less time.
new arrays, which are made of aluminum-lithium, are easier for
the astronauts to work around during servicing missions. In addition,
their smaller size decreases on-orbit drag and slows the rate
at which Hubble's orbit decays. Over time, all low-Earth orbiting
satellites feel the effects of atmospheric drag and lose altitude.
Space Agency (ESA) built Hubble's first two sets of solar arrays.
For the newest pair, ESA designed, developed and tested the Solar
Array Drive Mechanisms, which maneuver the arrays to keep them
constantly pointed at the Sun.
The NICMOS Cryocooler
STS-109, the Near Infrared Camera and Multi-Object Spectrometer
(NICMOS), which has been dormant since January of 1999, will receive
a new cooling system called the NICMOS Cryocooler.
Installed on Hubble in February 1997, NICMOS used infrared vision
to explore dark, dusty regions of space with precise optical clarity.
Since NICMOS operates at cold temperatures, it was encased in
a container filled with solid nitrogen ice to keep the detectors
cold. A small heat leak caused the nitrogen ice to consume more
quickly than planned.
and engineers at NASA's Goddard Space Flight Center in Greenbelt,
Md., devised the NICMOS Cryocooler, a state-of-the-art cryogenic
cooler that is expected to return NICMOS to active duty and re-cool
the NICMOS infrared detectors to about minus 203 degrees Celsius
(minus 334 degrees Fahrenheit or 70 degrees Kelvin).
system, which uses non-expendable neon gas as a coolant, delivers
high cooling capacity, extremely low vibration and high reliability.
It uses a miniature cryogenic circulator to remove heat from NICMOS
and transport it to the cryocooler.
technology was successfully demonstrated in 1998 aboard the Space
Shuttle Discovery on STS-95.
Power Control Unit, or PCU, is Hubble's power switching station.
As the central controller of the telescope's electrical system,
it regulates and distributes the power Hubble needs to operate.
The new PCU
that will be installed in Bay 4 during STS-109's third spacewalk
is going to replace Hubble's original PCU, which has degraded with
age. A fresh PCU will enable Hubble to remain healthier and more
productive throughout its lifetime. The new PCU is the original
flight spare built for Hubble, but this unit has been modified and
retested to ensure optimal performance and to enhance ease of installation
by the astronauts.
One of four
reaction wheel assemblies, or RWAs, is scheduled to be replaced
during STS-109's second spacewalk. RWAs are an important part of
Hubble's Pointing Control Subsystem that use rotational momentum
to move the telescope from one target to another and to keep it
pointed steadily once the target is acquired in the aperture of
the observing scientific instrument. Even though only three RWAs
are required for scientific operations, it was decided to add a
spare RWA to the manifest of STS-109 because of the importance of
the RWAs to the telescope's performance and the amount of time between
this servicing mission and the next.