The Active Cavity Radiometer Irradiance Monitor Satellite, or ACRIMSAT was a satellite carrying the ACRIM-3 (Active Cavity Radiometer Irradiance Monitor 3) instrument. It was one of the 21 observational components of

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

's Earth Observing System program. The instrument followed upon the ACRIM-1 and ACRIM-2 instruments that were launched on multi-instrument satellite platforms. ACRIMSAT was launched on 20 December 1999 from Vandenberg Air Force Base as the secondary payload on the Taurus launch vehicle that launched

KOMPSAT KOMPSAT or Korean Multi-Purpose Satellite is a series of South Korean multipurpose satellite for Earth observation satellite, Earth observation, Communications satellite, communications, Weather satellite, meteorological, Biophysical environment ...

. It was placed into a high inclination of 98.30°, at 720 km.

Sun-synchronous orbit A Sun-synchronous orbit (SSO), also called a heliosynchronous orbit, is a nearly polar orbit around a planet, in which the satellite passes over any given point of the planet's surface at the same local mean solar time. More technically, it is ...

from which the ACRIM-3 instrument monitored total solar irradiance (TSI). Contact with the satellite was lost on 14 December 2013.

History

ACRIM-3 made measurements of the TSI since the start of its mission in April 2000. It extended the TSI measurement database begun by earlier ACRIM instruments on the NASA

Solar Maximum Mission The Solar Maximum Mission satellite (or SolarMax) was designed to investigate Sun, Solar phenomena, particularly solar flares. It was launched on February 14, 1980. The SMM was the first satellite based on the Multimission Modular Spacecraft bus ...

(SolarMax) (ACRIM-1: 1980–1989) and

Upper Atmosphere Research Satellite The Upper Atmosphere Research Satellite (UARS) was a NASA-operated orbital observatory whose mission was to study the Earth's atmosphere, particularly the protective ozone layer. The satellite was deployed from Space Shuttle ''Discovery'' durin ...

(UARS) (ACRIM-2: 1991–2001). ACRIMSAT/ACRIM3 tracked TSI during a 2004

transit of Venus frameless, upright=0.5 A transit of Venus across the Sun takes place when the planet Venus passes directly between the Sun and a superior planet, becoming visible against (and hence obscuring a small portion of) the solar disk. During a trans ...

and measured the 0.1% reduction in the solar intensity caused by the planet's shadow. It also recorded data for the

Transit of Venus, 2012 The 2012 transit of Venus, when the planet Venus appeared as a small, dark spot passing across the face of the Sun, began at 22:09 UTC on 5 June 2012, and finished at 04:49 UTC on 6 June. Depending on the position of the observer, the exact tim ...

Team

Richard C. Willson was the

principal investigator In many countries, the term principal investigator (PI) refers to the holder of an independent grant and the lead researcher for the grant project, usually in the sciences, such as a laboratory study or a clinical trial. The phrase is also often us ...

and led the science team. Willson designed the

active cavity radiometer Active cavity radiometer is an electrically self-calibrating, cavity pyrheliometer A pyrheliometer is an instrument for measurement of direct beam solar irradiance. Sunlight enters the instrument through a window and is directed onto a therm ...

type of sensor used by self-calibrating satellite TSI monitoring experiments. The ACRIM3 instrument was a collaboration between Willson, original JPL/ACRIMSAT

Project manager A project manager is a professional in the field of project management. Project managers have the responsibility of the planning, procurement and execution of a project, in any undertaking that has a defined scope, defined start and a defined f ...

Ronald Zenone and ACRIM3 Instrument Scientist Roger Helizon. The mission was controlled using the ACRIMSAT tracking station at the

Jet Propulsion Laboratory The Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center in the City of La Cañada Flintridge, California, United States. Founded in the 1930s by Caltech researchers, JPL is owned by NASA an ...

(JPL)

Table Mountain Observatory Table Mountain Observatory (TMO) is an astronomical observation facility operated by NASA's Jet Propulsion Laboratory (California Institute of Technology). It is located in Big Pines, California, in Angeles National Forest near Wrightwood, north- ...

Southern California Southern California (commonly shortened to SoCal) is a geographic and Cultural area, cultural region that generally comprises the southern portion of the U.S. state of California. It includes the Los Angeles metropolitan area, the second most po ...

. Co-investigators were:

Nicola Scafetta Nicola Scafetta is a research scientist at the University of Napoli Federico II. He was formerly at the ACRIM Lab group and an adjunct assistant professor in the physics department at Duke University. His research interests are in theoretical ...

(climate impact of solar variability), Hugh Hudson (solar physics) and Alexander Mordvinov (solar physics).

ACRIMSAT instrument

The ACRIMSAT instrument and spacecraft represent a unique, new capability for NASA research. The instrument is lighter and more compact than its predecessor by a factor of more than two. This allows the radiometer to be flown in a small, dedicated spacecraft like the ACRIMSAT. The satellite/

radiometer A radiometer or roentgenometer is a device for measuring the radiant flux (power) of electromagnetic radiation. Generally, a radiometer is an infrared radiation detector or an ultraviolet detector. Microwave radiometers operate in the microwave w ...

combination is small enough to be easily launched as a secondary payload on any of an array of boosters, providing its sponsors with the flexibility of numerous launch opportunities while keeping launch costs to a minimum. The active cavity radiometer instrument is designed for precise, continuous measurements of total solar irradiance in spaceflight experiments and is capable of measuring solar energy in the

far-ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...

to far-infrared wavelength range. The instrument includes three identical active cavity radiometers that are used in different cycles. One monitors the Sun all the time. Data from the second instrument will be compared to data from the first instrument once every few months. The third sensor's data will be used as a comparison with the first and second instruments' data once every two months. With this rotating system of data comparison, anticipated slow changes in the first sensor, caused by exposure to the Sun and space, will be calibrated and removed from its measurement results.

Technology

ACRIMSAT was a spin-stabilized, single-purpose satellite constructed by

Orbital Sciences Corporation Orbital Sciences Corporation (commonly referred to as Orbital) was an American company specializing in the design, manufacture, and launch of small- and medium- class space and launch vehicle systems for commercial, military and other governmen ...

. Its total cost, including the instrument, launch, ground station, operations, and science team activities during its 14-year mission was less than US$50 million.

End of the mission

In December 2013, ACRIMSAT suffered a mission-ending failure when its degrading batteries could no longer sustain operations. The spacecraft has not responded to ground commands since on 14 December 2013. After several unsuccessful recovery attempts and extensive failure analysis, the mission was determined to be unrecoverable and officially terminated on 30 July 2014. The spacecraft will remain in orbit for approximately 64 years before returning to

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

References

External links

AcrimSat Launch

ACRIM Science Team homepage

ACRIMSAT Project homepage

Fact sheet on the mission

ACRIMSAT: NASA Science Missions
{{Orbital launches in 1999 Satellites orbiting Earth NASA satellites Spacecraft launched in 1999 Earth observation satellites of the United States