SARAL

SARAL (Satellite with ARgos and ALtiKa) is a cooperative altimetry technology mission of Indian Space Research Organisation (ISRO) and Centre National d'Études Spatiales (CNES). SARAL performs altimetric measurements designed to study ocean circulation and sea surface elevation.[2][4]

SARAL
An artist's rendering of SARAL satellite
NamesSatellite with Argos and ALtiKa
Mission typeEarth observation
OperatorISRO
COSPAR ID2013-009A
SATCAT no.39086
Websitehttps://isro.gov.in/
Mission duration5 years (planned)
10 years, 7 months and 15 days (in progress)
Spacecraft properties
SpacecraftSARAL
BusIMS-2
ManufacturerIndian Space Research Organisation / CNES
Launch mass407 kg (897 lb) [1][2]
Dimensions1 m x 1 m x 0.6 m
Power850 watts
Start of mission
Launch date25 February 2013, 12:31 UTC[3]
RocketPolar Satellite Launch Vehicle-CA, PSLV-C20
Launch siteSatish Dhawan Space Centre, First Launch Pad (FLP)
ContractorIndian Space Research Organisation
Entered service25 June 2013
Orbital parameters
Reference systemGeocentric orbit
RegimeSun-synchronous orbit
Perigee altitude790 km (490 mi)
Apogee altitude791 km (492 mi)
Inclination98.54°
Period100.54 minutes
Instruments
Advanced Data Collection System ("Argos-3") (A-DCS)
Ka-band Altimeter (ALtiKa)
Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS)
Laser Retroreflector Array (LRA)
 

Mission

A CNES / ISRO MOU (Memorandum of Understanding) on the SARAL mission was signed on 23 February 2007.[5] The SARAL mission is complementary to the Jason-2 mission of NASA / NOAA and CNES / EUMETSAT. It will fill the gap between Envisat and the Sentinel-3 mission of the European Copernicus Programme (Global Monitoring for Environment and Security - GMES programme). The combination of two altimetry missions in orbit has a considerable impact on the reconstruction of sea surface height (SSH), reducing the mean mapping error by a factor of 4.[5]

Instruments

The SARAL payload module was provided by CNES: ALtiKa (Ka-band altimeter), Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), Laser Retroreflector Array (LRA), and ARGOS data collection system. ISRO is responsible for the satellite bus (Indian Mini Satellite-2), launch (Polar Satellite Launch Vehicle), and operations of the satellite.

ARGOS Advanced-Data Collection System (A-DCS)
Main article: ARGOS (system)

Argos-3 of French National Space Agency (CNES), manufactured by Thales Alenia Space (TAS). ARGOS contributes to the development and operational implementation of the global ARGOS Advanced-Data Collection System. It will collect a variety of data from ocean buoys to transmit the same to the ARGOS ground segment for subsequent processing and distribution.[5]

Ka-band altimeter (ALtiKa)

ALtiKa, the altimeter and prime payload of the SARAL mission, is the first spaceborne altimeter to operate at Ka-band.[6] It was built by the French National Space Agency, CNES. The payload is intended for oceanographic applications, operates at 35.75 GHz.[1] ALTIKA is set to take over ocean-monitoring from Envisat. It is the first to operate at such a high frequency, making it more compact and delivering better performance than the previous generation.[7]

While existing satellite-borne altimeters determine sea level by bouncing a radar signal off the surface and measuring the return-trip time, ALtiKa operates at a high frequency in Ka-band. The advantage of this is twofold. One, the atmosphere of Earth slows down the radar signal, so altimetry measurements are skewed and have to carry additional equipment to correct for this error. Since ALTIKA uses a different system, it does not have to carry an instrument to correct for atmospheric effects as current-generation altimeters do. ALtiKa gets around this problem by operating at a high frequency in Ka-band. Another advantage of operating at higher frequencies is greater accuracy. ALtiKa will measure ocean surface topography with an accuracy of 8 mm, against 2.5 cm on average using current-generation altimeters, and with a spatial resolution of 2 km. The disadvantage, however, is that high-frequency waves are extremely sensitive to rain, even drizzle. 10% of the data is expected to be lost. (Although this could be exploited to perform crude measurements of precipitation).[7]

DORIS

DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite): DORIS is a dual-frequency tracking system (400 MHz and 2 GHz) based on network of emitting ground beacons spread all over the world.[5]

Laser Retroreflector Array (LRA)

LRA is provided by CNES. The objective of LRA is to calibrate the precise orbit determination system and the altimeter system several times throughout the mission. The LRA is a passive system used to locate the satellite with laser shots from ground stations with an accuracy of a few millimeters. The reflective function is done by a set of 9 corner cube reflectors, with a conical arrangement providing a 150º wide field of view over the full 360° azimuth angle.[5]

Applications

SARAL data products is useful for operational as well as research user communities in many fields like:[1]

  • Marine meteorology and sea state forecasting
  • Operational oceanography
  • Seasonal forecasting
  • Climate monitoring
  • Ocean, Earth system and climate research
  • Continental ice studies
  • Protection of biodiversity
  • Management and protection of marine ecosystem
  • Environmental monitoring
  • Improvement of maritime security

Secondary payloads

The six secondary payloads manifested on this flight were:[5]

• BRITE-Austria (CanX-3b) and UniBRITE (CanX-3a), both of Austria. UniBRITE and BRITE-Austria are part of the BRITE Constellation, short for "BRIght-star Target Explorer Constellation", a group of 6.5 kg, 20 cm x 20 cm x 20 cm nanosatellites who purpose is to photometrically measure low-level oscillations and temperature variations in the sky's 286 stars brighter than visual magnitude 3.5.

• Sapphire (Space Surveillance Mission of Canada), a minisatellite with a mass of 148 kg.

• NEOSSat (Near Earth Object Surveillance Satellite), a microsatellite of Canada with a mass of ~74 kg.

• AAUSAT3 (Aalborg University CubeSat-3), a student-developed nanosatellite (1U CubeSat) of AAU, Aalborg, Denmark. The project is sponsored by DaMSA (Danish Maritime Safety Organization).

• STRaND-1 (Surrey Training, Research and Nanosatellite Demonstrator), a 3U CubeSat (nanosatellite) of SSTL (Surrey Satellite Technology Limited) and the USSC (University of Surrey Space Centre), Guildford, United Kingdom. STRaND-1 has a mass of ~4.3 kg.

The University of Toronto arranged for the launch to carry three small satellites for universities as part of its Nanosatellite Launch Services program, designated NLS-8: BRITE-Austria, UniBRITE and AAUSat3. The three NLS satellites used the XPOD (Experimental Push Out Deployer) separation mechanism of UTIAS/SFL for deployment. The STRaND-1 nanosatellite was deployed with the ISIPOD CubeSat dispenser of ISIS (Innovative Solutions In Space).

Launch

SARAL was successfully launched into a Sun-synchronous orbit (SSO) on 25 February 2013, at 12:31 UTC.[8][3]

References
  1. "SARAL". ISRO. Archived from the original on 31 July 2017. Retrieved 6 March 2013.
  2. "Proposals Sought For Studying India-French Satellite Data". Space Mart. 4 January 2010. Archived from the original on 7 January 2010. Retrieved 12 May 2021.
  3. "Rocket PSLV-20 successfully puts seven satellites in orbit". Zee News. 25 February 2013. Retrieved 12 May 2021.
  4. "SARAL". NASA. Archived from the original on 5 July 2012. Retrieved 12 May 2021. Public Domain This article incorporates text from this source, which is in the public domain.
  5. "SARAL". ESA Earth Observation Portal. 11 May 2021. Retrieved 12 May 2021.
  6. Steunou, N.; Desjonquères, J. D.; Picot, N.; Sengenes, P.; Noubel, J.; Poisson, J. C. (10 September 2015). "AltiKa Altimeter: Instrument Description and In Flight Performance". Marine Geodesy. Informa UK Limited. 38 (sup1): 22–42. doi:10.1080/01490419.2014.988835. ISSN 0149-0419. S2CID 129770765.
  7. "GP - ALTIKA - Call for proposals until 15 February". CNES. 18 January 2010. Retrieved 29 April 2011.
  8. "Indo-French satellite SARAL set for launch on February 25". The Economic Times. 15 February 2013. Retrieved 12 May 2021.
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