accuracy that can be obtained with the SGP4 orbit model is on the order of 1 km within a few days of the epoch of the element set. The term "low orbit" may refer to either the altitude (minimal or global) or orbital period of the body. Historically, the SGP algorithms defines low orbit as an orbit of less-than 225 minutes. Two-digit Epoch Years from 57 to 99 correspond to 1957-1999 and those from 00 to 56 correspond to 2000–2056. The maximum number of Satellite Catalog Numbers that can be encoded in a TLE is rapidly being approached with the recent commercialization of space and several key break-up events that have created a massive number of debris objects. Future adaptations of the TLE have been imagined to extend the number of encodable Satellites within the TLE. References Spaceflight concepts Orbits Computer file formats de:Satellitenbahnelement#Das Two Line Elements Format TLE