Inmarsat-4A F4

Inmarsat-4A F4, also known as Alphasat and Inmarsat-XL, is a large geostationary communications I-4 satellite operated by UK based Inmarsat in partnership with the European Space Agency. Launched in 2013, it is used to provide mobile communications to Africa and parts of Europe and Asia.[2]

Inmarsat-4A F4
Full scale mockup Alphasat at Le Bourget Airshow 2013
Mission typeCommunications
Technology
OperatorInmarsat
European Space Agency
COSPAR ID2013-038A
SATCAT no.39215
Mission durationExpected: 15 years
Elapsed: 7 years, 21 days
Spacecraft properties
BusAlphabus
ManufacturerEADS Astrium
Thales Alenia Space
Launch mass6,649 kilograms (14,659 lb)
Start of mission
Launch date25 July 2013, 19:54:07 (2013-07-25UTC19:54:07Z) UTC
RocketAriane 5ECA VA-214
Launch siteKourou ELA-3
ContractorArianespace
Orbital parameters
Reference systemGeocentric
RegimeGeostationary
Longitude25° east
Perigee altitude35,771 kilometres (22,227 mi)
Apogee altitude35,801 kilometres (22,246 mi)
Inclination0.14 degrees
Period23.92 hours
Epoch29 October 2013, 17:07:36 UTC[1]
 

Inmarsat-4A F4 has been constructed by EADS Astrium and Thales Alenia Space based on the Alphabus satellite bus. It was the first Alphabus spacecraft to be launched, and as such it carries several experimental communications systems in addition to its commercial payload. The spacecraft had a launch mass of 6,649 kilograms (14,659 lb), and is expected to operate for at least fifteen years.[2]

Arianespace had been contracted to launch Inmarsat-4A F4, with an Ariane 5ECA rocket, flight number VA-214, delivering it and INSAT-3D into geosynchronous transfer orbit.[3] The rocket lifted off from ELA-3 at Kourou at 19:54:07 UTC on 25 July 2013,[4] with Inmarsat-4A F4 separating from the rocket around 27 minutes later.[5]

The spacecraft operates in a geostationary orbit at a longitude of 25 degrees east. As of 29 October 2013, it is in an orbit with a perigee of 35,771 kilometres (22,227 mi), an apogee of 35,771 kilometres (22,227 mi) and 0.14 degrees inclination to the equator. The orbit had a semimajor axis of 42,157.20 kilometres (26,195.27 mi) and eccentricity of 0.0003552, giving it an orbital period of 1,435.75 minutes, or 23.92 hours.[1]

European Data Relay System test

The satellite was used as part of a in-orbit verification of the ESA European Data Relay System. In 2014, data from the Sentinel-1A satellite in LEO was transmitted via an optical link to the Alphasat in GEO and then relayed to a ground station using a Ka band downlink. The new system can offer speeds up to 7.2 Gbit/s in the future.[6]

gollark: You could probably run a long cable to a separate access point.
gollark: Networking issues, particularly wireless networking ones, are horribly eldritch and intractable.
gollark: That looks very* non-hypothermic.
gollark: Isn't torture not actually very good at getting information?
gollark: I always found pencil erasing to be annoyingly smudgy and/or imperfect and/or slow.

References
  1. "ALPHASAT (INMARSAT 4A-F4) Satellite details 2013-038A NORAD 39215". N2YO. 29 October 2013. Retrieved 29 October 2013.
  2. Krebs, Gunter. "Alphasat (Inmarsat-4A F4)". Gunter's Space Page. Retrieved 29 October 2013.
  3. Bergin, Chris (25 July 2013). "Ariane 5 ECA successfully deploys Alphasat and Insat-3D". NASASpaceFlight.com. Retrieved 29 October 2013.
  4. McDowell, Jonathan. "Launch Log". Jonathan's Space Page. Retrieved 29 October 2013.
  5. Clark, Stephen (25 July 2013). "Mission Status Center". Ariane Launch Report. Spaceflight Now. Retrieved 29 October 2013.
  6. "Laser link offers high-speed delivery". ESA. 28 November 2014. Retrieved 5 December 2014.
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