To breadboard and demonstrate optical feeder-link technologies using the Technology Demonstration Payload (TDP#1) on the Alphasat satellite. Stray-light and self blinding issues when transmitting and receiving from the same aperture will be addressed by separating the Tx and Rx wavelength by a small amount.

 

The technology demonstration payload (TDP#1) on the Alphasat GEO spacecraft is a coherent optical communication data relay demonstrator for optical inter-satellite links and Ka-band downlinks. It is a precursor development from the German Space Agency (DLR) for the European Data Relay System (EDRS), but not commercially utilized. It is therefore the ideal platform to test optical feeder-link technologies in a representative environment. However, the use of virtually identical wavelengths at 1064 nm makes feeder-link experiments difficult due to stray-light causing self-blinding of the receiver by the transmitter.

 

Analysis of the filter transmissions on TDP#1 have recently shown that a wavelength separation of 2 nm between Tx and Rx would still allow the coarse and the fine acquisition sensors on TDP#1 to receive a signal from a ground station. With highly selective filters (thermally controlled Fabry-Perot) this wavelength difference can be used in an Optical Ground Station (OGS) to sufficiently reduce the stray-light and to demonstrate an important milestone of feeder-link technology, namely the reception and transmission through the same telescope aperture in an OGS. This is a prerequisite for adaptive optic pre-distortion of the feeder-link beam to compensate atmospheric turbulence. This shall be demonstrated in a follow up activity. However, the utilization of adaptive optics (developed in other activities) for transmit beam pre-distortion already in the present feeder-link demonstration with TDP#1 on Alphasat would be considered as bonus.