Navigation & GNSS-R

Our Track Record

SSTL developed and delivered the first operational payload for Galileo, Europe's satellite-supported navigation programme, as part of its GIOVE-A mission launched in 2005.  

Since then SSTL has supplied 22 navigation payloads for the deployment phase of Galileo, and we are now manufacturing a further 12 payloads that will form the heart of the navigation system.

SSTL’s GNSS receivers are highly regarded for quality and robustness and have flown on many missions, including SSTL’s DMC constellation, ESA’s PROBA-1, USAF STPSat, JAXA SLATS, RemoveDEBRIS, and the International Space Station.

SSTL has also pioneered the new field of GNSS-R with successful payloads on board TechDemoSat-1, DoT-1 and the NASA CYGNSS constellation, and is continuing to develop the technology and data analysis in pursuit of this new science.


Galileo Navigation Payloads

We have designed, manufactured and supplied 22 navigation payloads for the deployment phase of Europe's satellite-supported navigation system, Galileo, and we are now manufacturing a further 12 payloads for delivery to our partners, OHB-System in Germany. 

Our payload solution is based on European sourced atomic clocks, signal generators, high power TWTAs and Antennas.


We designed and manufactured GIOVE-A, the pathfinder satellite with a mission to secure the Galileo frequency filings at the International Telecommunications Union (ITU). GIOVE-A  was designed, built and tested in a rapid 30 month programme and launched on schedule on 28th December 2005, allowing ESA to claim the frequency filings for the Galileo programme three months before the licence expired. 

The satellite also played a crucial role as the test-bed for the Galileo payload units, providing a representative signal-in-space for ground-based experimentation with Galileo signals as well as characterising the radiation environment for the Medium Earth Orbit used by all future Galileo satellites.

On the 2nd May 2007 GIOVE-A successfully transmitted the first European navigation message from space, containing the information needed by users' receivers to calculate their position. 

In 2012 SSTL's experimental GPS receiver on-board GIOVE-A successfully achieved a GPS position fix at 23,300km altitude - the first position fix above the GPS constellation on a civilian satellite.

GPS is routinely used via Low Earth Orbit satellites to provide the orbital position and offer a source of time to the satellite.  Spacecraft in orbits higher than the 20,000km of the GPS constellation however can only receive a few of the signals that "spill over" from the far side of the Earth, meaning that the signals are much weaker and a position fix cannot always be secured.

With the support of ESA and the ARTES programme of funding, we included the SGR-GEO receiver on the GIOVE-A satellite to prove that a receiver could achieve a position fix from a higher orbit.  The SGR-GEO is adapted from our SGR range of receivers and incorporates a high-gain antenna and a precise oven-controlled clock.  It demonstrates special algorithms to allow reception of weak signals and an orbit estimator intended to allow a near continuous position fix throughout orbit. 


GNSS Reflectometry (GNSS-R) is an Earth observation technique that uses GNSS signals as L-Band radar sources, allowing the satellite to take measurements of ocean wind speeds, polar ice and hydrological land parameters at a higher spatial resolution and an order of magnitude lower cost than other methods. 

SSTL has pioneered the development of GNSS-R with a payloads on UK-DMC1 (2003), TechDemoSat-1 (2014), DoT-1 (2019) and the NASA CYGNSS Constellation (2016).  GNSS-R data from SSTL’s satellites is available via the MERRByS website.

Data from the SSTL GNSS-R instruments on-board the CYGNSS mission have demonstrated the potential for soil moisture measurement by GNSS Reflectometry, and preliminary work shows that GNSS-R also has good sensitivity for Freeze-Thaw sensing in the active zone of permafrost. Unseasonal changes in the permafrost cycles could potentially release larger quantities of methane, which risks exacerbating global climate change.  GNSS-R can also be used to assess biomass, a measure of forest density which acts as a vital sink for removing carbon dioxide from the atmosphere. In addition to longer term climate observations, soil moisture and inundation measurements from GNSS Reflectometry can provide important information for short term operational purposes, for example, towards Numerical Weather Prediction and flood warnings following rainfall events.

SSTL is also developing an ESA Scout Mission Concept called HydroGNSS which comprises two 40kg satellites that collect data continually in near-polar orbits, taking hydrological measurements over the whole globe. The HydroGNSS mission concept makes advanced use of new GNSS Reflectometry techniques such as Galileo signals, dual polarisation, and coherent signal acquisition to measure 4 Essential Climate Variables (ECVs) over land: Soil Moisture, inundation, permafrost freeze/thaw, and biomass. HydroGNSS has been down-selected by ESA for a concept study, and the finally selected Scout mission will commence in 2021.


Our  Space GNSS receivers (SGRs) are highly regarded for quality and robustness and are flying on most of our own satellites and many other spacecraft.

Space GNSS Receivers routinely provide position, velocity and time information to satellites in low Earth orbit, and more than 70 orbiting satellites have used receivers and antennas provided by SSTL, on missions from UKSA, ESA, NASA, USAF, JAXA and on the International Space Station.  SSTL’s receivers are based on COTS components, with radiation mitigation and quality processes to suit small satellite applications. 


SGR-Axio – A dual antenna GNSS receiver with multi-constellation and dual frequency options

SGR-Ligo – A low power Cubesat-format GNSS receiver

SGR-ReSI – Remote Sensing Instrument (contact us for details)

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