Editing Special sensor microwave/imager (section)

== Instrument history ==
The SMMR was flown on [[Seasat]] and NASA [[Nimbus 7]] in 1978.  Seasat operated only for a few months until the satellite suffered an electrical short that ended the mission, while Nimbus 7 unexpectedly operated for 9 years, returning data until 1987.

The SSM/I has been operating almost continuously on Block 5D-2 flights F8-F15 (not F9) since June 1987. Concerns about the radiometer's performance over the full range of space environmental conditions led to the F8 instrument being switched off in early December 1987 to avoid overheating.  The 85&nbsp;GHz vertical polarization channel failed to switch on in January 1988.  Analysis showed inadequate thermal shielding of the sensor's radiometers due to excessive heating at [[perihelion]].  The 85&nbsp;GHz horizontal polarization subsequently had a large increase in radiometric errors and was switched off in summer 1988.

The launch of the next SSM/I, on board the F10 satellite, took place on 1 December 1990, but was not fully successful.  The explosion of the booster rocket left the F10 in an elliptical orbit.  The incidence angle of the F10 SSM/I boresight would vary in relation to the Earth throughout each orbit and this also altered the surface area of the Earth viewed by the radiometer.  The deviations in the incidence angle of up to 1.4° were quite large and would alter the responses of several geophysical algorithms if not taken into consideration.  Further, related changes in the swath width from a minimum of 1226&nbsp;km at perigee to 1427&nbsp;km at apogee altered the amounts of radiation viewed by the F10 SSM/I radiometers.  The non-circular orbit also caused slight precession of the equatorial crossing time of the F10 by 50 seconds per week.

The F12 imager had a delayed launch date (the spacecraft was out of the DMSP build sequence) due to a faulty SSM/I.  The extra time and costs taken to rectify the problem did not, however, help.  The SSM/I failed to ‘spin-up’ after launch, and consequently data were not available from this instrument.  The SSM/Is on F11, F13, F14 and F15 have all produced excellent data.

Before the F8 was decommissioned, it aided investigations into measuring passive microwaves at higher Earth incidence angles (i.e. > 51 degrees).  An increase in angle would allow a greater swath width to be utilised, giving a greater amount of coverage at the Earth's surface.  The F8 Tilt Experiment (see links) was carried out between 25 June and 13 July 1993.

{| class="wikitable"
|+ SSM/I Satellites characteristics (source: DMSP website and http://www.ssmi.com {{Webarchive|url=https://web.archive.org/web/20120826071821/http://www.ssmi.com/ |date=2012-08-26 }}).
|-
! scope="col" | Satellite
! scope="col" | Ascending equatorial time at launch
! scope="col" | Ascending equatorial time (1995)
! scope="col" | Ascending equatorial time (current)
! scope="col" | Descending equatorial time (current)
! scope="col" | Launch date 
! scope="col" | End mission/operational support
|-
| F8
| 6h15
| 6h17
| N/A
| N/A (should be 18h17)
| 1987-06-18
| 1991-08-13
|-
| F10
| 19h42
| 22h09
| N/A
| N/A (should be 10h09)
| 1990-12-01
| 1997/11
|-
| F11
| 17h00
| 18h25
| 19h38
| 7h25 (should be 7h25)
| 1991-11-28
| 2000/08
|-
| F13
| 17h42
| 17h43
| 18h33
| 6h33
| 1995-03-24
| Providing primary support 
|-
| F14
| 20h21
| N/A
| 19h08
| 7h08
| 1997/05
| 2008-8-23
|-
| F15
| 21h31
| N/A
| 20h42
| 8h42
| 1999-12-12
| 2021-08-09
|-
| F16 <br>
(carries new sensor [[SSMIS]])
| 21h05
| N/A
| 21h05
| 9h05
| 2003-10-18
| N/A to research community
|}
F17, F18, and F19 all carry [[SSMIS]].