Full GaAs Solar Array for Spacebus

Status date

As part of the global roadmap and development logic to implement GaAs Solar Arrays on the overall Spacebus™ 4000C range, this project covers the establishment of the full design and justification file of a 4-panels wing (CDR level) and its qualification for next Spacebus™ application programs (PFM wing qualification).

It follows the elementary qualification of GaAs networks for next Telecom Solar Arrays generation, which has been performed under ARTES 3/4 contract.

The development is based on:

  • The newly, such developed, GaAs network with 3G28 Azur Space cells,
  • The use of large Solarbus solar arrays heritage.

The final aim of this project is to provide the Spacebus™ 4000C family with full GaAs Solar Arrays in line with the present market needs in terms of global competitiveness and improved power to mass ratio compared to existing silicon cell solar arrays.

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It comes logically after the previous ESA project consisting in the choice and qualification of a GaAs cell network.

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This study covers the first step with:

  • The establishment of the full design & justification file for next application programs using a 4-panels wing configuration fully covered with 3G28 GaAs cells,
  • And the achievement of its qualification.

Together with the results of a 3-panel wing qualification tests, it will allow to get a large overview of the new GaAs wings performances and their associated justification file.

The trigger of options could, in a second step allow, to extend further the GaAs solar array product family to other points of the Spacebus™ 4000C family in line with application program awarding.


The Solarbus products family was initially a Silicon based family that will be progressively replaced by a GaAs family for competitiveness reasons including mass saving. The technical improvement obtained by the GaAs instead of Si network is power to mass efficiency increase.

This network change challenges the accommodation of the new network on an existing wing architecture with the best filling factor while keeping all rules to get an ESD safe design. From a mechanical point of view the impact of the mass increase due to the GaAs technology has to be verified and minimized.

This project objective is to introduce the first full GaAs GEO SOLARBUS in the family as a “core application” and then to introduce all the extensions toward other products of the Spacebus range.


The W41S4 solar array has been developed and tested in the frame of a first application program foreseen to be launched before end 2012. A second program is running with this W41S4 configuration.

Together with the already available W31S3 configuration, Thales Alenia Space is able to cover the previous Silicon Solar Array wings up to 7 panels per wing with a more competitive and safe product.

Beyond that, it contributes to Spacebus™ competitiveness.


W41S4 Solarbus

Wing Architecture

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4 in line panels with transfer deployment function
Full GaAs Network 100V Bus
Standard SPACEBUS 4000C Interfaces

Electrical Parts Solar Array

Wing layout:

  • 2 Wings
  • 4 Panels
  • Bare Cell: 3G28%/150-8438 GaAs Triple Junction

Blocking diodes at string level,
Redunded grounding network.

Thermal sensor.

Mechanical Parts Solar Array


Technology : CFRP Skins + Aluminium Honeycomb Sandwich

Size : 3660*2216mm²

High Modulus CFRP Skins
20mm thick honeycomb
Kapton front layer

Optimized reinforcements GaAs higher areal mass support.

Hold down points : 8
Hinge I/F : 4 (incl 2 transfer)
Handling I/F : 2 zero G + 4 handling
Transfer harness supports : 4
Synchro cable interface : YES


Technology: RTM Carbon Fibre Rods with new geometry including qualified parts and processes from previous yokes

Hold down points for yoke: 3
Handling I/F : 2 zero G
Transfer supports : YES
Synchro cable interface : YES

Hold down points Technology:
Carbon Fibre Rods Pods
Redunded release devices.
Mechanisms set

Guiding: Ball Joints
Latching: Logarithmic cam

  • Inter-panel: Spiral Spring
  • Root hinge: Brush Motor

Speed regulation: Brush Motor (Eddy current reverse behaviour)



The project is the issue of a new GaAs solar array based on technological qualification inputs from previous contract for GaAs qualification under GEO conditions.

This project is the issue of one of the numerous solar array needed to replace the complete Silicon Solarbus family. This project is the first for full GaAs application on large panels of 8.1sqm. It will be nevertheless helped by first mixed configuration on 4000 B2 with GaAs+Si or full GaAs export program network that helped to initiate the basic local designs for network.

Major milestones are:

EQSR in January 2011 (18/01/2011)
CDR in May 2011 (25/05/2011)
TRR in December 2011 (15/12/2011)
TRR closeout in March 2012 (29/03/2012)
TRB in July 2012 (05/07/2012)
FR in July 2012 (26/07/2012)

Current status

All Project Plan milestones have been achieved successfully. The CDR level design file and justification file has been established following with Spacebus™ system level requirements. 4 panels - PFM wing underwent successfully its qualification sequence and is now delivered to system AIT on first application program.

Furthermore, a first 3-panels Full GaAS Solar array is operational in orbit since end of March 2012.