Space blog

SSTL has won a contract worth €1.6 million from Astrium GmbH, Germany to proceed with work on a new contract to develop and supply the Multi-Spectral Imager (MSI) for the European Space Agency’s (ESA) EarthCARE Mission.

Earth Explorer Missions are part of the Earth Observation Envelope Programme (EOEP). They are missions led by the European Space Agency to address primary research objectives. The EarthCARE Mission has been approved for implementation as the third Earth Explorer Core Mission. The mission will be implemented in collaboration with Japanese Aerospace Exploration Agency who will provide one of the core Instruments. The EarthCARE mission has been specifically defined with the basic objective of improving the understanding of cloud-aerosol-radiation interactions so as to include them correctly and reliably in climate and numerical weather prediction models.

The EarthCARE mission aims to improve the understanding of the Earth's radiation balance and to minimize uncertainties in climate change prediction models by acquiring accurate vertical profiles of clouds and aerosols, as well as measurements of top of the atmosphere radiance. The Multi Spectral Imager produced by SSTL will provide information on the horizontal structures of clouds, such as cloud type and cover, and cloud optical and microphysical properties. The instrument's 150 km swath will be used to extend to three dimensions the validity of the aerosol, cloud and radiance measurements made by the active EarthCARE instruments which are all directed towards the satellite ground track.

This contract is for the first stage of the Phase B design study; the full Phase B is a 15 month programme. This will be followed by a Phase C/D leading to mission launch in 2013. SSTL is supported in the MSI programme by TNO from The Netherlands who are acting as subcontractors to SSTL.

SSTL’s Group Executive Chairman, Sir Martin Sweeting stated in a press release today that he believes the increased competition resulting from the June proposal by the European Commission to fund the Galileo satellite navigation system through the public sector will reduce the cost and risk involved.

”The increased competition will have significant benefits,” stated SSTL’s Group Executive Chairman, Sir Martin Sweeting. “The public sector will soon be in a position to place contracts that give the European taxpayer better value for money and step up the pace of delivering the system”.

SSTL aims to support the European Commission and European Space Agency (ESA) by building on its experience gained through the successful GIOVE-A mission, to provide best value in the operational phase of Galileo. GIOVE-A was developed under a €28M contract signed with ESA in the second half of 2003. The mission’s primary aim was to broadcast Galileo signals from space so that Europe could claim the frequencies filed for Galileo with the International Telecommunications Union (ITU). The satellite was designed, built, tested and launched before the end of 2005 – on-time and on-budget. GIOVE-A has transmitted Galileo signals for over 18 months and remains the only Galileo spacecraft in operation. Following the success of GIOVE-A, ESA placed a further contract with SSTL in March 2007 for a second satellite named GIOVE-A2.

Sir Martin added:

“It’s clear that a second source of operational satellites is needed, both to provide healthy competition and to reduce risk to the schedule of the Galileo system. SSTL has begun discussions with other key European suppliers, with the aim of forming a team capable of supplying a significant portion of Galileo whilst maintaining the winning formula employed on GIOVE-A. We expect these discussions to be finalised in October, in time to provide the public sector with a much needed competitive option”.

Galileo is a joint initiative between ESA and the European Commission. When fully deployed in the early years of the next decade, it will be the first non-military positioning system to offer global coverage.

Earlier this week, the SSTL built GIOVE-A satellite successfully transmitted its first navigation message, containing the information needed by user receivers to calculate their position. Prior to reaching this milestone, the satellite had been broadcasting only the data needed for measuring the receiver-to-satellite distance.

The first Galileo navigation message was created by the navigation signal generator unit on board GIOVE-A, using content prepared by the GIOVE Mission Segment. This week-one navigation message was uplinked to GIOVE-A on 2 May from the Guildford ground station operated by Surrey Satellite Technology Ltd (United Kingdom) and then transmitted from the spacecraft to the users. The objective of the test was to demonstrate an end-to-end link between the Mission Segment and the user receivers. The navigation message is being generated for demonstration purposes only – no service guarantee is provided.

The complete radio transmission from GIOVE-A carries a navigation signal and a navigation message. The navigation signal contains the information needed to accurately measure the distance from the satellite to the user receiver. The navigation message provides the timing and spacecraft orbit data needed to calculate the time and exact position of the satellite. One of the main tasks of the GIOVE Mission Segment is the generation of this navigation message.

GIOVE Mission Segment

The GIOVE Mission Segment comprises two main elements, a world-wide network of 13 Galileo experimental sensor stations and the GIOVE Processing Centre (GPC) located at ESA’s European Space Research and Technology Centre (ESTEC) in Noordwijk, The Netherlands.

Note: The GPC is operated by European Satellite Navigation Industries (ESNIS) – the new name for Galileo Industries.

In order to generate the navigation message, the sensor stations track the signal-in-space from GIOVE-A and send the tracking information to the processing centre. The GPC computes, among other things, the precise satellite flight path and on-board clock model. It then generates a prediction of the orbital path and clock performance for the near-term future, which is the basis of the navigation message. Next, this message is transmitted to GIOVE-A which retransmits it to the user.

Aside from navigation message generation, the primary tasks of the GIOVE Mission Segment are performance characterisation of the on-board clocks, orbit modelling, and operations planning & telemetry analysis for the navigation payload.

Another validation step completed

On 12 January 2006, GIOVE A transmitted the first Galileo signals, thereby securing the frequencies allocated to Galileo by the International Telecommunication Union. Now, the transmissions are carrying a navigation message – this means that the satellite is providing information that is needed by a receiver to calculate its position.

Although the navigation message structure of GIOVE-A is slightly different, the GIOVE-A navigation transmissions are fully representative of those that will be sent by the operational Galileo system. The operating principles are identical and the achievement of the first navigation message is another important step in the validation of the Galileo system design.

GPS interoperability

Following this successful test, in the near future GIOVE-A will begin to continuously broadcast the navigation message, with the message content being updated whenever the satellite is visible from the Guildford uplink station. Additionally, the message content will be extended to include the time offset between GPS and the experimental Galileo system. Knowing this offset, the Experimental Galileo-GPS Time Offset (E-GGTO), will allow the user to build a position fix using GPS satellites and GIOVE-A.

Galileo is a joint initiative between ESA and the European Commission. When fully deployed in the early years of the next decade, it will be the first civilian positioning system to offer global coverage.

ESA press release: GIOVE-A transmits first navigation message

What next?

SSTL were awarded a second contract on March 5th 2007 for initial activities leading to the construction of a second spacecraft for the Galileo satellite navigation system. Named GIOVE-A2, the new satellite (estimated total value 25 to 30 million Euros) will be based on the company’s proven GIOVE-A technology. From now on, there will always be a European navigation satellite in space.

ESA press release: GIOVE-A2 to secure the Galileo programme