The US Air Force Research Laboratory (AFRL) is working on a Navigation Technology Satellite-3 (NTS-3) to be sent to geostationary orbit as an add-on to the GPS satellites already present in Medium Earth Orbit (MEO).
The satellite will be used to enhance the positioning, navigation, and timing (PNT) services that are currently provided by Global Positioning System (GPS) satellites.
A medium Earth orbit (MEO) is an Earth-centred orbit with an altitude above a low Earth orbit (LEO) and below a high Earth orbit (HEO) — between 2,000 and 35,786 km above sea level.
“We wanted to look at how to use a constellation that has a hybrid architecture,” Joanna Hinks, NTS-3 deputy program manager at AFRL, told reporters on April 7 at the Space Symposium in Colorado Springs.
In 2018, L3Harris won an $84 million contract from AFRL to build NTS-3. The 1,250-kilogram satellite is being assembled at an L3Harris facility in Palm Bay, Florida.
Initially, the AFRL was considering sending NTS-3 into the MEO, according to Hinks, but later it was decided that Geostationary Earth Orbit (GEO) would be a better location for NTS-3 for the researchers to assess the possible advantages of having a multi-orbit PNT architecture.
“The idea here is that we already understand how navigation works from MEO,” Hinks said.
Pentagon growing weary
One of the objectives for NTS-3 is to test new software-defined radio technologies which can be used to reprogram the signals to confuse jammers. Parsons Corp is developing a ground system that will integrate the GPS and NTS-3 signals to assess the network’s performance in a jamming environment.
In recent times, Pentagon is growing weary of the threat of electronic devices that can interfere with the signals from GPS satellites in MEO.
The US Space Force operates a constellation of 31 satellites orbiting Earth at an altitude of 20, 000 km for PNT services. These satellites in six orbital planes circle the Earth twice per day broadcasting PNT signals that are essential not only for military operations but also for the daily functioning of the civilian economy.
According to the National Institute of Standards and Technology, GPS technology has a $1 billion a day economic impact on the US. Such reliance on GPS makes it an attractive target for adversaries.
During the hearing of the House Appropriations Committee’s defense subcommittee in May 2021, the chief of space operations of the US Space Force Gen. John Raymond pointed at China and Russia as the primary actors pursuing technologies aimed at “robust jamming of GPS and communications satellites.”
In late 2019, Bjorn Bergman, an analyst with SkyTruth, a nonprofit environmental watchdog, analyzed a large data set of Automatic Identification System (AIS) associated with ships.
Bergman discovered at least 20 locations near the Chinese coast where GPS spoofing took place with GNSS [Global Navigation Satellite System] locations of ships operating in the area were replaced with fake coordinates.
These included the ports of Shanghai, Fuzhou (Huilutou), Qingdao, Quanzhou (Shiyucun), Dalian, and Tianjin.
The timing of the spoofing coincided with observations of Iranian oil being received by China in defiance of US sanctions on Iran suggesting that some of the spoofings may be designed to help conceal these transactions.
This phenomenon was first documented by the MIT Technology Review which described how the Captain of a US-flagged container ship noticed the apparent malfunctioning of the vessel’s AIS — vessels on the navigation screen appeared and disappeared without explanation and appeared to move when they were in fact stationery.
Bergman identified GPS spoofing rings or circles that were about 200 meters in diameter indicating that the actual spoofing device may be located at the center of each of these rings
Alternative PNT technologies
While the Defense Department uses several alternative PNT technologies to complement GPS or to serve as a backup if GPS is unavailable, such as an inertial navigation system that uses inertial sensors and clocks that allow a platform to identify its position and keep track of time without an external signal.
Other technologies rely on celestial and magnetic navigation to determine position. Also, there is a growing number of satellites in low Earth orbit (LEO) that transmit PNT information.
However, according to a report by the Government Accountability Office (GAO), none of these alternatives, have reduced the US military’s heavy reliance on GPS.
“There are known vulnerabilities and military officials talk about the need for alternatives,” said Jon Ludwigson, GAO’s director of contracting and national security acquisitions. “But when it comes down to funding programs, by default they choose GPS.”
Therefore, the concept of adding another layer of PNT could be a significant offset of the U.S.’s overreliance on GPS.
The NTS-3 is projected to launch on the USSF-106 mission planned by the U.S. Space Force to be launched in 2023 It will be the first national security mission to fly on United Launch Alliance’s new Vulcan Centaur rocket.