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The infrared performance of the Hubble has limitations since it was not designed with infrared performance as an objective. For example, the mirror is kept at a stable and relatively high temperature (15 °C) by heaters.
<blockquote>HST is a warm telescope. The IR background flux collected by cooled focal plane IR instruments like NICMOS or WFC3 is dominated, at rather short wavelengths, by telescope thermal emission rather than by zodiacal scattering. NICMOS data show that the telescope background exceeds the zodiacal background at wavelengths longer than λ ≈ 1.6μm, the exact value depending on the pointing on the sky and on the position of the Earth on its orbit.<ref>{{cite journal |title=The Performance of HST as an Infrared Telescope |last1=Robberto|first1= M.|display-authors= 4|last2= Sivaramakrishnan|first2= A.|last3= Bacinski|first3= J.J.|last4= Calzetti|first4= D.|author4-link= Daniela Calzetti |last5= Krist|first5= J.E.|last6= MacKenty|first6= J.W.|last7= Piquero|first7= J. |last8= Stiavelli|first8= M. |url=http://www.stsci.edu/hst/wfc3/documents/published/spie4013386.pdf
Despite this, the combination of Hubble's mirror and NICMOS offered never-before seen levels of quality in near-infrared performance at that time.<ref name="spaceflightnow.com">{{Cite web | url=http://www.spaceflightnow.com/news/n0206/06nicmos/ | title=Spaceflight Now | Breaking News | Hubble's infrared camera brought back to life}}</ref> Dedicated infrared telescopes like the [[Infrared Space Observatory]] were ground-breaking in their own way, but had a smaller primary mirror, and were also out of service at the time of NICMOS installation because they ran out of coolant. NICMOS later overcame this problem by using a machine chiller like a refrigerator, which allowed it operate for years until it went offline in 2008.
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==History of NICMOS==
NICMOS was installed on Hubble during its second servicing mission in 1997 ([[STS-82]]) along with the [[Space Telescope Imaging Spectrograph]], replacing two earlier instruments. NICMOS in turn has been largely superseded by the [[Wide Field Camera 3]], which has a much larger field of view (135 by 127 arcsec, or 2.3 by 2.1 arcminutes), and reaches almost as far into the infrared.
[[File:STS-82 crew.jpg|thumb|NICMOS was installed by the crew of STS-82, this [[Space Shuttle]] mission in 1997 also installed the STIS instrument on Hubble Space Telescope, a scale model of the telescope is shown with this crew photo]]
[[File:STS-82 Discovery on Mobile Launcher Platform.jpg|thumb|NICMOS's ride to space heads to the launchpad, January 1997]]
[[File:Hubble Redeployment (9458246017).jpg|thumb|Hubble Space Telescope held by the Space Shuttle robotic arm]]
[[File:STS082-323-017.jpg|thumb|Shuttle crew EVA with Hubble Space Telescope]]
When conducting infrared measurements, it is necessary to keep the infrared detectors cooled to avoid having infrared interference from the instrument's own thermal emissions. NICMOS contains a cryogenic [[Dewar flask|dewar]], that cooled its detectors to about 61 K, and optical filters to ~ 105 K, with a block of [[solid nitrogen]] ice. When NICMOS was installed in 1997, the [[dewar flask]] contained a 230-pound (104 kg) block of nitrogen ice. Due to a thermal short that arose on March 4, 1997, during the instrument commissioning, the dewar ran out of [[nitrogen]] coolant sooner than expected in January 1999.
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A new software upload in September 2008 necessitated a brief shutdown of the NICMOS cooling system. Several attempts to restart the cooling system were unsuccessful due to issues with the cryogenic circulator. After waiting more than six weeks for parts of the instrument to warm up, and theorized ice particles to sublimate from the neon circulating loop, the cooler once again failed to restart. An Anomaly Review Board (ARB) was then convened by NASA. The ARB concluded that ice or other solid particle migrated from the dewar to the circulator during the September 2008 restart attempt and that the circulator may be damaged, and determined an alternative set of startup parameters. A successful restart at 13:30 EST on 16 December 2008 led to four days of cooler operations followed by another shutdown.<ref>{{cite web|url=http://www.stsci.edu/hst/nicmos/newsItems/Nicmosncs_status_01232009|title=NICMOS/NCS Status|date=January 23, 2009|publisher=[[Space Telescope Science Institute]]}}</ref> On 1 August 2009, the cooler was restarted again;<ref>{{cite web|title=Hubble Space Telescope Status Report|date=August 5, 2009|publisher=[[NASA]]|url=http://www.nasa.gov/mission_pages/hubble/servicing/SM4/news/HST_update_5Aug2009.html}}</ref> NICMOS was expected to resume operations in mid-February 2010<ref>{{cite web|title=NICMOS Late Breaking News Page|date=December 16, 2009|publisher=NASA|url=http://www.stsci.edu/hst/nicmos/localNews?display_type=all#NICMOS_NCS_status_12162009|archive-url=https://archive.today/20120805163354/http://www.stsci.edu/hst/nicmos/localNews?display_type=all%23NICMOS_NCS_status_12162009|url-status=dead|archive-date=August 5, 2012}}</ref> and operated through October 22, 2009, at which point a lock-up of Hubble's data handling system caused the telescope to shut down. The circulation flow rate to NICMOS was greatly reduced during this operating period confirming blockage in the circulation loop. Continued operation at reduced flow rates would limit NICMOS science so plans for purging and refilling the circulation system with clean neon gas were developed by NASA. The circulation loop is equipped with an extra neon tank and remotely operated solenoid valves for on-orbit purge-fill operations. As of 2013, these purge-fill operations have not yet been performed.{{update after|2014}}
[[Wide Field Camera 3|WFC3]], installed 2009, was designed to partly replace NICMOS.<ref name=aas>{{cite
On June 18, 2010, it was announced NICMOS would not be available for science during the latest proposal Cycle 18. As of 2013, a decision as to whether the purge-fill operations will be performed and whether NICMOS will be available for science in the future has not been made.{{update after|2014}}
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