Hylas-1 advances European telecom technology

With a launch mass of a little over 2.5 tonnes, and based on an Indian platform, Hylas-1 is on the small side as telecom satellites go, but the new technologies it carries enable it to pipe the Internet through the sky to hundreds of thousands of paying customers across Europe.

This first ‘Highly Adaptable Satellite’ is ESA’s first public–private partnership to result in an operational mission: UK operator Avanti Communications has put up the majority of the budget, with ESA’s contribution focused on Hylas-1’s advanced communications payload. Avanti gains a more capable satellite while Europe’s advanced technologies reach orbit much more rapidly than would otherwise be the case.

Telecom R&D has always been a priority for ESA, acting through its Advanced Research in Telecommunications Systems (ARTES) programme. When it comes to space, this is where the money is – the telecom sector is by far the most commercially mature. It is no exaggeration to say that Europe’s continued success within this market forms the economic underpinning for the rest of its space endeavours.

Telecom also offers pronounced social benefits, with satellites proving a versatile tool to extend the global reach of communications networks, from broadcasting to telephony and now broadband Internet.

Putting flexibility into orbit

In a conventional telecommunications payload, a transponder’s receive frequency, bandwidth and transmit frequency are all fixed during the satellite design phase, typically several years before entering into service.

During the lifetime of a satellite, however, the operational requirements on the payload, in particular for broadband satellites, may change with evolving markets beneath them. With the expected lifetime of current commercial satellites exceeding 15 years, the ability to adapt to these changing needs should be highly advantageous.

“Hylas-1 allows its operator to adjust the bandwidth, frequency and output power of its communications payload,” said Andrea Cotellessa, Hylas-1 Project Manager.

“This is a quite new capability, and is due to a payload concept called the Generic Flexible Payload (GFP), developed by Astrium UK through a series of ESA contracts.”

The satellite has a separate antenna on each side of its structure – one transmitting a wide Ku-band beam for TV broadcasting and other standard satellite services, and the other transmitting in higher-frequency Ka-band for broadband services, directing eight spot beams onto key European markets, maximising its efficiency by reusing its given allocation of radio frequencies between spot beams.

“The operator can fine-tune how much bandwidth and power to put in each beam,” explained Mr Cotellessa. “For an operator it is very important to have this flexibility, because you are able to match changes in data demand as they happen - effectively ‘future-proofing’ the satellite against market changes.

“It also means that even with a small satellite you can support large numbers of widely dispersed customers.”

Evolving the GFP

The GFP concept owes its existence to many years of cooperation between ESA and Astrium in payload technological research, Mr Cotellessa added: “The mainstream of research and development by ESA’s Directorate of Telecommunications and Integrated Applications, working through the ARTES programme, has been to look at various next-generation telecom systems and our involvement with the GFP concept was part of that.”

This effort began life in 2003, with ESA supporting a research project by Astrium to develop ‘Modular Microwave Hybrid Technology’ (MMHT).

Typically with telecom satellites their repeaters – the units that amplify, refine or otherwise condition signal inputs for output – are designed and built on an individual, bespoke basis, which adds considerable time and cost to their construction.

Instead, the MMHT approach sought to apply the principle of standardisation to repeater production, creating a portfolio of building blocks for given tasks, such as frequency converters or amplifiers. Known as ‘hybrids’, these circuits can then be combined as required to meet the particular needs of a given mission.

A second stage project, beginning the following year, produced MMHT modules with increased integration and functionality, known as Hi-MMHTs (for High Integration), containing around 2000 separate connections between layers.

The technologies and capabilities developed under these contracts have now been applied to developing the Hylas-1 payload units that together form its Generic Flexible Payload.

Setting the standard

Based on their chosen function, telecom satellites operate in a range of frequency bands, such as C-band for telephony and cable-TV distribution, Ku-band for television broadcasting and ‘very small aperture terminal’ networks, or Ka-band for broadband access.

Rather than satellite makers having to design separate payload systems for each frequency band, the GFP architecture translates the frequency of signals received by the satellite to a standard ‘intermediate frequency’ (IF) at C-band, where all signal conditioning and routing is performed.

This frequency conversion is performed by an electronic device called the Agile Integrated Down-converter Assembly (AIDA), which was the first unit to be developed using Hi-MMHT technology.

On Hylas-1, this signal is then passed to a solid-state matrix called the Routing and Switching Equipment (RASE). While doing away with the need for mechanical connections, RASE can establish connectivity between any pair of satellite uplink and downlink beams.

The signal then passes to an item of equipment that is the heart of the GFP architecture, the Single Channel Agile Converter Equipment, or SCACE.

SCACE allows the channel bandwidth to be adjusted – for example, to respond to changing demand levels from within a particular geographic region, and to be converted to the desired transmit frequency.

The flexibility that the GFP delivers to Hylas-1 is increased by another pioneering piece of technology, developed with ESA support by Tesat-Spacecom in Germany: the In-Orbit Adjustable Microwave Power Module (IOA-MPM) allows the transmit power signal to be adjusted to match demand while maintaining near-constant efficiency, preventing power being wasted in the form of heat.

Qualified for space

One last innovation is the most visible: Hylas-1’s larger, double-sized antenna, which had to be carefully optimised for high-frequency Ka-band operations, the responsibility of EADS Casa Espacio in Spain.

The antenna’s radiating surface accuracy had to be high while resisting any deforming effects due to the temperature extremes of Earth orbit, with high surface reflectivity to prevent undesirable heating.

“The various components of the Hylas-1 payload emerged through co-funded projects with the companies in question,” said Mr Cotellessa. “Then, once the Hylas-1 public–private partnership was agreed, ESA agreed to develop them up to the level they were ready for integrated use within a mission, then to qualify them for space.

“This required the most rigorous qualification programme imaginable: a very long series of ever-more demanding tests, much more demanding in fact than the actual mission requirements.

“But at the end of the process we are left certain that the technology is ready for operation in orbit.”

Even before Hylas-1 is launched on 26 November it has already proven influential. Astrium is already offering GFP technology to its commercial telecom customers, while another IOA-MPM will be flying on ESA’s Small GEO mission, demonstrating a new small geostationary orbit platform.

And a full-sized commercial satellite, Eutelsat’s Ka-Sat, will soon be following Hylas-1’s advance into Europe’s emerging Ka-band broadband market.