“Our GREAT² supply chain produced its first prototypes at the start of this year,” said Andrew Barnes, GREAT² technical officer of ESA’s Product Assurance and Safety Department.

“At the same time, Proba-V was offering slots for technology demonstration payloads. We’ve therefore been able to obtain a valuable early opportunity for in-flight testing.”

V for Vegetation

Proba-V

Proba-V is the latest in ESA’s ‘Project for Onboard Autonomy’ small satellite series, offering early flight demonstration opportunities to new technologies from European firms.

The mission will host a cut-down version of the multispectral Vegetation instrument flying on France’s Spot-4 and Spot-5. Proba-V will maintain the flow of land vegetation imagery to the Vegetation instrument’s well-established user community.

Tracking daily vegetation growth across all of Earth’s land, Proba-V will deliver three times greater image resolution than previous generations of the Vegetation sensor. This should yield a vast amount of data for such a small satellite – Proba-V will be less than a cubic metre in volume.

Proba-V’s communications antenna and transmitter are strictly limited in size as a consequence, presenting a potential bottleneck in getting imagery down from orbit into the hands of users. The mission will avoid this by using a compact, highly efficient X-band transmitter, along with onboard storage capacity and data compression techniques.

Putting GaN technology to work

“Proba-V had a couple of ‘guest technology’ slots free, but we decided to do something different,” explained Mr Barnes.

“Among the GREAT² prototype designs is an X-band integrated circuit design. We proposed that we could, with various refinements, add an extra X-band transmitter incorporating a GaN amplifier sourced from GREAT2 to Proba-V’s initial pair of standard GaAs transmitters.”

GaN amplifier

A prototype was rapidly put together for initial testing, with a prototype amplifier incorporated into an existing X-band transmitter developed for Proba-V in collaboration with the French space agency, CNES.

Follow-up testing on electrical and qualification models will follow before the transmitter’s flight model is integrated onto the satellite in about a year, for a launch scheduled in 2012.

“It’s a good result for Proba-V because it keeps room for an additional guest technology while boosting our overall communications robustness,” said Karim Mellab, Proba-V Mission Manager.

“As another advantage, this new transmitter has an adjustable power output. This will help optimise power consumption, a very important consideration for a satellite our size.”

Proba-V taking shape

The mission’s guest technology slot is being filled by a new space radiation detector, with a remaining slot due to be allocated later in the year. Proba-V itself is fast taking shape: Proba-V’s Structural and Thermal Model underwent testing last month at Intespace in Toulouse.

Gaining early flight experience through in-orbit demonstration on missions such as Proba-V is essential to accelerate the technology readiness level of GaN systems, and open the way toward employing them operationally on future space missions.