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Mission type Solar astronomy
Operator NASA / JPL
COSPAR ID 1999-070B
SATCAT № 26033
Mission duration 7 years
Spacecraft properties
Manufacturer Orbital Sciences
Launch mass 288 kilograms (635 lb)
Power 80.0 watts
Start of mission
Launch date 20 December 1999, 07:13 (1999-12-20UTC07:13Z) UTC
Rocket Taurus 2110
Launch site Vandenberg LC-576E
Contractor Orbital Sciences
Orbital parameters
Reference system Geocentric
Regime Sun-synchronous
Semi-major axis 7,067.28 km (4,391.40 mi)
Eccentricity 0.0029721
Perigee 675 km (419 mi)
Apogee 717 km (446 mi)
Inclination 97.80 degrees
Period 98.54 minutes
Epoch 5 December 2013, 12:18:57 UTC[1]

The Active Cavity Radiometer Irradiance Monitor Satellite, or ACRIMSAT is a dedicated satellite and instrument that is one of the 21 primary observational components of NASA's Earth Observing System program. ACRIMSAT was launched on 20 December 1999 from Vandenberg Air Force Base as the secondary payload on a Taurus rocket along with KOMPSAT and placed into a high inclination, 700 km. sun-synchronous orbit from which the ACRIM3 instrument monitors the total solar irradiance (TSI).

The ACRIM3 instrument has made state of the art measurements of the TSI since the start of its Science Mission in April 2000. It extends the TSI measurement database begun by earlier ACRIM instruments on the NASA Solar Maximum Mission (ACRIM1: 1980-1989) and Upper Atmosphere Research Satellite (ACRIM2: 1991-2001).[citation needed]

Richard C. Willson is the principal investigator for the experiment and leads the ACRIM3 Science Team. Willson designed the active cavity radiometer type of sensor used by self-calibrating satellite TSI monitoring experiments today. The implementation of the ACRIM3 instrument was a collaboration between Willson, the original JPL/ACRIMSAT Project Manager Ronald Zenone and ACRIM3 Instrument Scientist Roger Helizon. The Mission is controlled using the ACRIMSAT tracking station at the JPL Table Mountain Observatory in Southern California. Co-Investigators are: Nicola Scafetta (climate impact of solar variability), Hugh Hudson (solar physics)and Alexander Mordvinov (solar physics).

ACRIMSAT (international designator 1999-070B) is a spin-stabilized, single-purpose satellite constructed by Orbital Sciences Corporation. The end-to-end cost of the ACRIMSAT satellite, the ACRIM3 instrument, launch, ground station, operations and the science team activities during its 13 1/2 year mission to date has been less than $50 million - a good example of the efficacy of NASA's 'Better, Faster, Cheaper' initiative and ample evidence that inexpensive instrumentation and small dedicated satellites are the cost-effective approach for providing state-of-the-art TSI monitoring.[citation needed]

ACRIMSAT/ACRIM3 tracked the TSI during a 2004 transit of Venus, and measured the 0.1% reduction in the solar intensity caused by the shadow of the planet.[2] It also recorded data for the 2012 Transit of Venus.[3]

At 09:43 and at 11:21 on 5 April 2014 ACRIMSAT was rated as having a high risk of collision (<20m) with the newly launched Sentinel-1A. A 39 second burn of Sentinel-1A during LEOP successfully avoided the collision.[4]


  1. ^ "ACRIMSAT Satellite details 1999-070B NORAD 26033". N2YO. 5 December 2013. Retrieved 6 December 2013. 
  2. ^ The Astrophysical Journal v.641 pp.565–571 (2006), Schneider, J. M. Pasachoff, and Richard C. Willson, The Effect of the Transit of Venus on ACRIM's Total Solar Irradiance Measurements: Implications for Transit Studies of Extrasolar Planets
  3. ^ PIA15820: NASA's ACRIMSAT Observes Venus Transit
  4. ^ Sentinel-1A team. "A NIGHT SHIFT LIKE NEVER BEFORE". ESA. Retrieved 17 April 2014. 

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