# Satellite data unit

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A **satellite data unit** (SDU) is an [avionics](/source/Avionics) device installed in an aircraft that allows air/ground communication via a [satellite network](/source/Satellite_network). It is an integral part of an aircraft's SATCOM (satellite communication) system. The device connects with a satellite via ordinary [radio frequency](/source/Radio_frequency) (RF) communication and the satellite then connects to a ground station or *vice versa*. All satellite communication whether audio or data is processed by the SDU.[1]

The SDU communicates with an onboard MDDU (multi-purpose disk-drive unit) which maintains an updatable table of ground stations near the aircraft's position and the order of preference for selection of which ground station to use which thus guides the choice of satellite. Along with analysing data continuously sent from all ground stations (such as station status and the error rate of signals from each station) the SDU receives information on the aircraft's position and orientation from another onboard system (ADIRU, [air data inertial reference unit](/source/Air_data_inertial_reference_unit)) which it passes to the BSU (beam-steering unit) to direct the signal beam from the aircraft to the chosen satellite.[1]

With the advent of cellphones and the Internet a separate or integrated SDU can be used to offer telephone and Internet services to passengers.[1][2][3]

Logs of satellite communication have been used to inform [search and rescue](/source/Search_and_rescue) agencies of locations of missing aircraft, like [Malaysia Airlines Flight 370](/source/Malaysia_Airlines_Flight_370) whose position was unknown due to loss of [radar](/source/Radar) contact and other communications. Automated SATCOM transmissions suggested it flew about 1,600 km (1,000 mi) off its designated flight path having flown approximately [south-southwest](/source/Points_of_the_compass) rather than the intended approximately north-northeast.[4]

## References

1. A330 TECHNICAL TRAINING MANUAL MECHANICAL & AVIONICS COURSE, pages 58 - 69, copyright Airbus S.A.S, published before 2014, but copyright date not given

1. ["Satellite backhaul for In-Flight connectivity for Wi-Fi and Cellphones"](http://www.radio-electronics.com/articles/satellite-technology/satellite-backhaul-for-in-flight-connectivity-for-85). *www.radio-electronics.com*. 14 Apr 2010. [Archived](https://web.archive.org/web/20140726011315/http://www.radio-electronics.com/articles/satellite-technology/satellite-backhaul-for-in-flight-connectivity-for-85) 26 July 2014 at the Wayback Machine. Retrieved 2023-06-14.

1. ["SDU-7310 Satellite Data Unit"](https://web.archive.org/web/20121009003458/http://www.cobhamsb200.com/SDU7310.aspx). Archived from [the original](http://www.cobhamsb200.com/SDU7310.aspx) on 9 October 2012. Retrieved 2023-06-14.

1. "Information provided to MH370 by AAIB: Information provided to MH370 investigation by UK Air Accidents Investigation Branch (AAIB)". Department of Civil Aviation Malaysia. Retrieved 6 May 2014.

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Adapted from the Wikipedia article [Satellite data unit](https://en.wikipedia.org/wiki/Satellite_data_unit) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Satellite_data_unit?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.