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» Hubble looms into view with Earth behind it. |
In
June 1997, NASA made the decision to extend the HST mission
from 2005 until 2010. As a result, the age and condition of
the instruments on board the HST became a consideration that
had to be revisited.
After careful study, NASA decided also to ensure the imaging
capabilities of the HST by replacing the Wide Field Planetary
Camera 2 (WFPC2), with a low-cost, "facility" instrument,
the Wide Field Camera 3 (WFC3).
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As a facility instrument, WFC3 is produced as service to the astronomical
community. The WFC3 developers do not get guaranteed observation
time on HST. While this concept is new to HST and the Space Sciences
community, it has been successfully used by both the Planetary and
Earth Sciences communities in their instrument development projects.
In
addition Wide Field Camera 3 represents a new approach to
the development of HST scientific instruments. The teams of
Government, Academia, and Industry who worked to build the
Wide Field Planetary Camera 1, WF/PC (1), WFPC2, and several
other HST instruments are working together on WFC3, leveraging
their experience to provide a superior instrument at modest
cost.
The WFC3 project is also designed to take advantage of much
of the hardware and software of the previous instruments.
WFPC1 was returned following the First Servicing Mission (FSM),
and many of its assemblies are available for reuse. Flight
designs, and in some cases, spare flight hardware, are available
and can be used in WFC3 for minimal cost.
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» WFCP1 after being removed from Hubble and returned
to Earth - awaiting deintegration so its parts can be used
for WFC3. |
1997 - Extending Hubble's Mission
» An astronaut in space during a servicing mission. |
The
2002 Instrument Selection Review Panel met in June 1997 and
selected the Cosmic Origins Spectrograph (COS) as the instrument
to develop for Servicing Mission 4 in 2003. Servicing Mission
5 (2005) would be the final, "deorbit" mission. Shortly after
this meeting, NASA made the programmatic decision to continue
operation of HST at least until 2010. The last Servicing Mission
for upgrading HST was then changed from late 2002 to early
2003, with the deorbit mission deferred until after 2010.
The current plan is to cancel the 2005 Servicing Mission.
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As a result of the
decision to extend the HST mission, the Project initiated a number
of studies to address the issues of resource availability. Specifically,
to understand how to maximize HST's scientific productivity and
competitiveness until 2010, using available resources. These issues
range from the optimal approach to building state-of the art spacecraft
hardware, to the scientific strategy for HST in its second decade
of operation. The WFC3 project is the result of one such study,
chartered by NASA Headquarters, which addresses the imaging capability
of the HST through 2010.
The study charter recognized that in the period 2002 to 2010,
an adequate imaging capability on HST may not be assured. In 2010,
HST's primary imager, the Advanced Camera for Surveys (ACS), will
be 11 years old. The current imager, the Wide Field and Planetary
Camera 2 (WFPC2) will be 17 years old. The Space Telescope Imaging
Spectrograph (STIS), which has some limited imaging capability,
will be 13 years old. The study addressed the feasibility and
cost of a backup wide-field camera.
1998 - Proposing a Second Channel
» Engineers and scientists working on Hubble's
instruments. |
In
January 1998, the results of the study were presented to the
same 2002 Instrument Selection Review Panel that selected
the COS instrument.
The detailed results of the study were presented as two options.
Option I provided for a backup of the wide-field imaging capability
only. Option II encompassed Option I and added an optimized
coronagraph capability. The panel recommended proceeding with
Option I. |
After a favorable review
by the Origins Subcommittee in March 1998, the HST Project was
directed to begin WFC3 development with Option I. However, in
October of 1998, the Space Telescope Institute Committee (STIC)
formally resolved that "the STIC is convinced that significant
advantages would accrue from the inclusion
of a near-IR channel in WFC3 " and encouraged "STScI
and NASA ...To identify funding sources, perhaps even within the
Hubble Project and the HST User community.
In November, 1998 the Cycle 8 Telescope Allocation Committee (TAC)
asked to be briefed on the WFC3/NIR concept. The TAC made the
following formal recommendation:
| "The TAC
believes that the potential scientific return from adding
this channel is enormous," and "...Is unanimous in its view
that addition of this capability will greatly enhance the
scientific output of HST during the period 2003-2010." |
| "We strongly encourage
NASA to (1) proceed with design and costing of the IR channel
over the next 6-8 months; and (2) to select a design that
achieves an appropriate balance between UV performance and
IR capability," |
| " ...urges STScI
and NASA to explore a wide range of additional creative approaches
to funding WFC3/IR, including the possibility of reducing
the funds available to GO's by 5% over the next 3 years, if
no other options are viable." |
1999 - Approving the Second Channel
» The image shows an infrared study done by Hubble's
NICMOS instrument. |
In
March 1999, the NASA Origins Subcommittee Report strongly
endorsed the scientific case for a near-IR channel for WFC3,
based on a preliminary concept from the project.
The Subcommittee Report stated that the "...inclusion of an
IR channel... would allow HST to address a significantly expanded
range of important problems, including the history of star
formation both within the Galaxy and extending to galaxies
at high redshift." (The image shows an infrared study done
by Hubble's NICMOS instrument) |
WFC3 would use a more
advanced version of the detectors used on the HST Near-Infrared
Camera and Multi-Object Spectrometer (NICMOS) instrument. These
WFC3 detectors would provide a factor of 16 increase in the number
of pixels, and over a factor of two increase in quantum efficiency.
An innovative design would allow the instrument to use simple,
low-cost thermoelectric cooling systems instead of the cryogens
or mechanical cryocoolers that are typical in other IR instruments.
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+ 1999
+ 1998
+ 1997
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