Implementing A Regenerative Ranging Protocol for Small Satellites

The Global Navigation Satellite System (GNSS) is a collection of satellite constellations, like GPS,
that provide position information on the Earth to an accuracy of 2 - 7 meters. In space the United
States Space Surveillance Network detects and tracks satellites orbiting the Earth. NASA
maintains a database of NORAD two-line elements (TLEs) which can be used to predict the
position and velocity of Earth orbiting satellites to within 1 km.

GPS receivers for small satellites operating in Low Earth Orbit (LEO) costs 10 - 50 times as much
as an equivalent system for ground use. GNSS is not readily available for satellites orbiting higher
than LEO or orbiting another body like the moon or Mars. The NORAD TLEs are also not readily
available for satellites orbiting other planets. Students in the Space Systems Engineering Program
at UAF who are designing the CubeSat Communications Platform (CCP) need to be able to
accurately determine their satellite’s position (range) in order to determine its current link budget
and determine the best modulation and coding protocol to be transmitting.

One of the biggest contributing factors to the ranging signal losses is distance. Distance
exponentially decreases the signal to noise ratio by 1/r^2 where r is the distance. This means that
communications that are received and re-transmitted by a satellite will have losses equivalent to
1/r^4. In Pseudo Noise ranging there are two different ways to process the signal, one of which
involves using regenerative ranging and the other involves a non-regenerative method [1]. Nonregenerative ranging does not process the ranging signal at the satellite, rather the unprocessed
signal is sent back to the ground station. In contrast, Pseudo-Noise (PN) regenerative ranging
processes the signal at the satellite and then sends it back down to the ground station. Using a
regenerative ranging technique will reduce the overall losses down to 1/r^2 as opposed to the 1/r^4
losses. As such this proposal seeks to explore the use of regenerative ranging techniques to
reduce the overall noise and provide better accuracy to accomplish CCP’s mission.