# Attitude requirements for inter-satellite laser communication

Previous questions have address the beam divergence angles and the expected signal attenuation for laser communication between spacecraft.

However, I was wondering what is a typical receiver aperture for a laser comms receiver, and whether these are usually fixed to a spacecraft or mounted on a set of gimbals. The ERDS equipment seems to be mounted on a one-axis gimbal.

Ultimately, I would like to determine the attitude pointing accuracy needed for a LEO to LEO laser inter-satellite communication. Inter-satellite radio communication has a number of strict requirements on the frequency used, making it difficult to develop and test in a lab without a large amount of funding (23 GHz oscillators are not that cheap).

The linked image is a 125mm telescope in a coarse-pointing hemispherical (two axis) mount. It has a field of view of about 2.5mrad in acquisition mode, which drops to 0.5mrad for data transfer. It’s backed up by fine-pointing optics with sub-10$\mu$rad pointing and sub-$\mu$rad co-linearity, consistent with a diffraction limited beam.