SDA Considers Signals, Technical Tradeoffs for Alternative Satellite GPS Payloads

WASHINGTON – Space Development Agency wants to include colocated payloads on its future data relay satellites, which could be an alternative to GPS positioning, navigation and timing services, but has yet to determine exactly how — something officials hope the industry’s responses to the agency’s recent request for information, due today, will help clarify.

“The goal is to roll out an additional PNT service that can increase the number of DOD PNT users by providing enhancements to military GPS users,” Jennifer Elzea, SDA spokeswoman, told Breaking Defense, meaning users “could use both GPS and SDA signal.’

What form that SDA signal will take is yet to be determined, Elzea explained, and is subject to a number of trade-offs — not least size, weight, power and cost (SWAP-C) — to install a payload on the agency’s fleet of transport-grade satellites. which is due to launch in 2026, is called Tranche 2.

Tranche 2, which has about 250 satellites, is planned to provide users with global access to the transport layer, which is being developed as the basis of satellite communications for the Pentagon. The concept of joint all-domain command and control (JADC2). Overall, SDA envisions an orbital mesh network of more than 500 transport-grade satellites connected to each other via laser communication links, as well as directly to weapons platforms via various types of downlinks.

In recent years, the military has been exploring alternatives to GPS, anticipating that in a future conflict it will operate in contested environments where GPS signals could be jammed, or the satellites that transmit them to soldiers would themselves be subject to cyber or kinetic attack.

“SDA deals with signals different from GPS but offered in the same frequency bands. If the military service PNT SDA is within existing GPS frequency bands, it minimizes the cost of integrating new antenna systems into ground weapons systems. We are exploring multiple uses to determine the greatest impact on the fighter,” Elzea said.

Traffic regulations November 9 The RFI specified that the agency is considering a “low-cost L-band PNT service” based on the two main frequencies used by GPS: L1 (1575.42 +/- 12.276 MHz) and L2 (1227.6 MHz +/- 12.276 MHz) .

Another question is whether the payloads should be carried by highly encrypted ones M-code signal, a stronger signal to help military users overcome obstacles and protect against false GPS signals used to deceive users by misdirecting them. Space forces is fighting to deploy the ground system needed to manage the use of M-code on current and future GPS satellites, and the DoD has been bogged down for decades in field radios and other devices through services that can access it.

“The M-code is under consideration, but the exact signal and its characteristics have not yet been determined. SDA is investigating other signals as well,” Elzea said.

She noted that the SDA’s planned National Defense Space Architecture for Large Constellations in Low Earth Orbit is generally being designed to provide cyber resilience, although “new PNT signal designers are considering the weight of jamming resilience against other potential threats to DoD PNT systems.”

SDA is also testing alternative PNT technologies as well as other high-risk experimental payloads. The National Defense Space Architecture Experimental Testbed, or NExT. Last month, the agency awarded Ball Aerospace a $176 million NExT contract to design, manufacture, deploy, launch and operate a suite of 10 spacecraft and ground systems for flights beginning in 2024.

The NDSA includes seven levels of both in-orbit and ground capabilities. It includes not only the LEO satellites that SDA itself develops and launches — such as the transport layer and the tracking layer of missile warning/missile tracking satellites — but also the ability to integrate and combine data from other military satellites as well as commercial groups.