On February 19, 2018, Aviation Week published U.S. Military Pursues GPS Alternatives in its Aerospace Daily & Defense Report by Eric Tegler. The report detailed Satelles’ Satellite Time and Location (STL) system as a viable option to augment GPS for critical position, navigation and timing (PNT) applications. The article interviewed Satelles CTO, Dr. Greg Gutt and Satelles CEO, Dr. Michael O’Connor. Some key highlights from the article are as follows:
- STL is functioning across Iridium’s constellation of 66 low Earth orbit (LEO) communications satellites.
- STL is in use by the services in space and ground C4ISR applications and in a significant number of embedded systems. Private operators of critical infrastructure from utilities and telecom providers to stock exchanges and data centers are using STL as well.
- STL was developed to augment GPS and GNSS more broadly and essentially, the service turns Iridium satellites into GPS satellites. It provides an independent timing and location capability similar to what GPS provides.
- GPS is provides position accuracy down to less than 10 meters (33 ft.). STL is accurate from 20-50 meters. Combined GPS/STL use provides still-greater resolution.
- STL benefits range from its affordable use of an extant (and the world’s largest) constellation to its capacity to resist jamming and spoofing, and to provide continuous global coverage including the Polar regions.
- STL’s use of robust L-Band frequencies means it is not susceptible to the line-of-sight issues affecting GPS and it can provide PNT to users indoors or under cover with a signal about 1,000 times stronger than GPS signals.
- STL has a level of resiliency inherent in the Iridium network, which spreads risk across 66 satellites (with 10 more as backup) that can communicate with one another via Ka-band inter-satellite links. Unlike GPS satellites, which require individual uplinks for instruction or information transmission, a command sent to one Iridium satellite can be passed to every other satellite in the constellation
- A GPS/STL combination complicates offensive anti-satellite operations for U.S. adversaries not only by increasing the number of PNT hosts to over 100 but by virtue of different orbital altitudes. GPS satellites are at a harder-to-reach, mid-earth orbit while Iridium’s LEO sats cross the horizon in approximately eight minutes, making them more difficult to track.
- The STL system is hosted exclusively by the Iridium constellation. STL reformulates existing signals from Iridium satellites, altering their modulation and developing proprietary coding to give them the highly exacting measurement characteristics necessary to make them useful for PNT.
