The habitat uses radio waves to communicate with Mission Control. The habitat radio system, known as CAPCOM, uses amplitude modulation; as it is not affected by the Doppler effect. This method of communication is suitable mainly for audio-video communications, with limited capacity for computer file transfers. This is because the signal loses strength over great distances because of the diffuse nature of radio waves. Radio is also easily affected by interference, reducing the information transfer rate.
For the transfer of large files such as astronaut biomeds, digital pictures and maps, the astronauts use a laser-based communications system to communicate with earth. Known as AUXCOM, this system uses a light emitter and receiver to communicate. The laser beam, usually in the infrared of ultraviolet, carries digital information, which is received by a laser receiver on the other end. One set of light receivers and emitters are on board the habitat, whereas the other set is onboard a satellite orbiting earth. The receiving satellite is used so that the light waves are not affected by the scattering effects of earth's atmosphere. Upon receiving the light signal, the satellite beams down the information to Mission Control via traditional radio waves.
The disadvantage is that the satellite used to relay messages to and from Mission Control orbits the earth. Therefore, AUXCOM may only be used when the satellite's orbit takes it between the habitat and earth. Because of this, AUXCOM is used for biomeds and other such data while CAPCOM is used for continuous communications with Mission Control.
Faster than Light
- Main article: IEST