Satellite navigation (GNSS) experts from SSTL are contributing remote sensing and satellite know-how to a pioneering UK-led project that aims to improve forecasting of adverse weather conditions at sea.

Using satellite data to measure ocean roughness has been an area of interest for SSTL since an experimental GNSS receiver payload was launched onboard its UK-DMC satellite. During the past few years, the GNSS receivers team has investigated the use of GNSS reflectometry – the use of reflected navigation signals from space to characterise ocean weather – with promising results, and produced a prototype instrument in collaboration with partners in the UK that will be developed into a payload for the TechDemoSat-1 technology demonstration satellite.



Smarter shipping
In addition to shipping, many marine operations such as offshore oil platforms and renewable energy projects depend on high quality information on sea-state (wave height, period, direction, steepness) for economic and safety decision making. However, the information currently available is based on atmospheric/ocean models and lacks sufficient temporal and spatial resolution.

Martin Unwin, Principal Engineer commented,

Wave conditions are always changing and can vary tremendously over just 100km, or over a period of two hours. This also makes modelling and forecasting very difficult, so the most immediate use of this data is more likely to be what we call ‘nowcasting’ – assessing current conditions thoroughly before commencing an operation.

Another problem with conventional methods is that the use of buoys provides good information around the coast and shipping lanes, but is simply not economical nor practical for charting the vast oceans of Earth. This is one area where satellites, with their global view, are ideally equipped.

All hands on deck
Recognising the opportunity for an improved system, the UK’s Technology Strategy Board has provided co-funding for the WaveSentry project. WaveSentry will address shortcomings on two fronts:

• By exploiting new data sources that include SSTL’s novel satellite remote measurements of wave steepness.


• By integrating data from all sources in a single system (including real-time buoy and ship data).

This multi-disciplinary project will bring together partners from all areas to develop and apply techniques to substantially enhance the integration of diverse data sources to offer improved data about adverse sea-states to a number of markets. SSTL and its partner National Oceanographic Centre, Southampton, are investigating the potential for spaceborne GNSS Reflectometry measurements to contribute towards knowledge of sea state in combination with other data sources.

You can keep up to date with the WaveSentry project on the the Marine Southeast website.

SSTL has taken delivery of a Search and Rescue Antenna (SARANT) for use to support the development of the fully operational satellites that will power Europe’s new satellite navigation system.

An important milestone, this is the first payload equipment to be delivered to SSTL since it was selected by the European Space Agency to deliver the navigation payloads for the first 14 satellites in the system just over a year ago. SSTL’s partner OHB-System in Germany is prime contractor, building the satellite bus for these satellites.

As part of a Global navigation satellite systems (GNSS), Europe’s new sat-nav service will provide highly accurate, guaranteed global positioning, including specialised rescue services. Consisting of 30 satellites in 56 degrees inclined circular Medium-Earth-Orbits, the baseline is a constellation with 9 equally spaced satellites (plus one spare) per orbit.

The newly delivered Search & Rescue antenna will be used by SSTL in the full engineering model of the payload.

The Search and Rescue Payload on the satellites will relay distress and co-ordination messages from the COSPAS-SARSAT Search and Rescue service. The diagram below shows a fully operational satellite with the SARANT visible on top.

Continue reading "SSTL receives first payload equipment for European Sat-Nav"

It’s now five years since Space Blog reported on GIOVE-A transmitting its first signals for the European GNSS system. The first validation satellite GIOVE-A, was launched in December 2005 by a Soyuz rocket from Baikonur in Kazakhstan, and is still working well five years after the satellite payload was commanded 'on' from the SSTL Mission Control Centre.

With a design lifetime of 27 months, the five-year-old has exceeded all expectations. Part of its long lifespan can be put down to design margins, though luck comes into it as well, according to GIOVE manager at ESA, Valter Alpe. The satellite has been orbiting through an exceptionally quiet time in the 11-year solar cycle, meaning it has accumulated lower radiation doses than originally anticipated.

GIOVE-A was built by SSTL in just 30 months and carries a prototype rubidium atomic clock designed for the European GNSS constellation. In 2008 GIOVE-A was joined by GIOVE-B, equipped with an ultra-precise passive hydrogen maser design as well as a second rubidium clock. Operational European GNSS satellites will carry both clock designs for maximum reliability.

During the Farnborough Airshow, a contract was signed for the provision of the Passive Hydrogen MASER (PHM) atomic clocks that will provide an essential timekeeper reference for the navigation payloads that SSTL is building for the Galileo navigation system, a programme of and funded by the European Union.

The PHM atomic clocks will be provided by SELEX Galileo, a Finmeccanica Company, for installation on each of the 14 satellites in the Galileo system, under a contract of more than 30m Euros.

The Passive Hydrogen MASER is the most stable clock ever produced for space applications with a frequency stability better than 10-14 day, and is currently demonstrating outstanding performance on board the Galileo GIOVE-B satellite. It is used as reference timekeeper to measure distance and positions in navigation systems. Its stability is better than 0,00000036 seconds in one year, equivalent to 1 second every 3 million years.

Timing is fundamental to Galileo and is essential for all services. It is best illustrated in positioning calculations, where a timing deviation of 1ns could result in a positioning error of 30cm on Earth.

Continue reading "Super accurate atomic clocks for Galileo"