System Overview
Overview Diagram
This diagram shows a very basic overview of what space laser communication looks like. It is very similar to the RF transmission currently employed except for now instead of using radio or microwaves lasers are used. There are a few main points of interest to take note on:
Optical ground station
This is the main communications transfer point from earth to space. From here a high powered laser terminal transmits and receives data from satellites. These ground stations include sophisticated adaptive optics to accommodate atmospheric spreading and diffusion. If cloud coverage is too great at the specific ground station sending the signal the signal may be held for transmission at a later time or sent to another ground station via ground lines for transmission.
GEO satellite & LEO satellite
Geosynchronous orbit satellites (GEO) and low-earth orbit satellites (LEO) are both needed when constructing an effective space communications system. Each platform is mainly provided in our diagram to illustrate that laser terminals would provide adequate communications coverage between satellites of any orbit type.
Below this diagram we have some of the pieces that are essential to laser communication explained.
Laser Terminals
The laser terminals outfitted to the satellites provide the means for laser communications. They generally include a laser beam device for transmission along with an acquisition channel and sensor for receiving transmissions accurately. These terminals are currently being outfitted for newly launched satellites and have been developed for near earth and deep space operation. Current commercial builds have transmission distance ranges from 2,500km to 80,000km with larger ones in development.
Pointing and tracking systems
Without advanced tracking systems getting laser alignment is like pointing a small laser pointer at a small target on the moon with your hand. Pointing and tracking systems are a necessary part of laser communication. These tracking systems are generally accurate within the micro to milliradian range depending on the sophistication and range needed for the application (i.e. deep space vs. satellite-satellite communication).