Benefits of LEO Satellites
GPS and other GNSS operating mostly in medium Earth orbit (MEO) are the primary domain for PNT services. Out-of-domain solutions such as LEO satellites, terrestrial wireless infrastructure, network time transfer, and signals of opportunity are required as an essential contingency capability to protect the operations of PNT-dependent systems, ensure the survivability and resilience of our national critical infrastructure, and preserve the continuity of government.
STL is an out-of-domain PNT solution in the LEO satellite category. LEO constellations have different operational features and performance characteristics than MEO systems in the primary domain, such as increased signal strength and enhanced security. LEO-based solutions are also by their very nature global, bringing coverage to every spot on the planet and offering 2-D/3-D positioning in addition to precise timing.
High Power Signals
STL signals are sent using a unique high-power channel, which combined with the proximity of LEO satellites (compared to GPS satellites in medium Earth orbit) and signal coding gain, produces a signal that is 1,000 times (30 dB) stronger than any GNSS signal.
Continuous Signals from Everywhere in the Sky
LEO satellites travel at speeds of approximately 17,000 mph (an eight-minute horizon-to-horizon transit), resulting in carrier frequency variations due to Doppler effects. Look angles in the sky are continuously changing due to the satellites’ rapidly traversing orbits, making it possible for the STL transmission to reach receivers in the even the most challenging locations. Furthermore, Iridium satellites’ polar orbits ensure global coverage, including at the poles (where the GPS signal is weak).
With multiple satellites in a LEO constellation, Satelles is able to provide 3-D location information along with precise timing. Whereas wide-area ground-based PNT systems — most notably those that rely on terrestrial wireless infrastructure — only have the potential to deliver 2-D positioning and doing so typically requires the deployment of supplemental infrastructure.
Not Susceptible to Terrorist Attack
Unlike land-based systems, satellite systems are effectively impervious to terrorist attack, and are far less vulnerable to state actor attack.
Protection from Space Phenomena
At their lower orbit altitude, LEO satellites are well protected from space disturbances (e.g., solar storms), and they are far less susceptible to the deleterious effects of internal charging and surface charging that can cause permanent damage to the electronic components of space vehicles operating in MEO or GEO orbits. LEO satellites are better shielded from these phenomena because they orbit below the Earth’s magnetosphere and inner Van Allen Belt (planetary radiation belt).
Protecting GNSS as the Primary Domain of PNT