AFRL’s NTS-3 Satellite Experiment Tinkers with GPS But Doesn’t Really Fix America’s PNT Problem

The American military is almost wholly reliant on a constellation of 34 Global Positioning Satellites to perform just about any mission. The military writ-large says they understand the vulnerability of GPS but the first of the USAF’s priority Vanguard programs does little to address the risk to the crucial navigation system.

The Air Force Research Laboratory (AFRL) is leading the effort to launch and put an experimental satellite called NTS-3 (Navigation Technology Satellite-3) through its paces with more than 100 different PNT (position, navigation, timing) related technology experiments once the satellite launches later this year.

AFRL director, Major General Heather Pringle laid out the obvious motivation for NTS-3 during a 2022 space symposium. “We know that the way of warfare has changed,” she said, “and we’re going to be having difficulties with jamming, and having difficulties getting our position, navigation and timing signals to our warfighters.”

L3 Harris Technologies is building the satellite and integrating its subsystems under an $84 million contract granted in 2018. In 2019, the Air Force designated NTS-3 as one of the first three “Vanguard” programs to deliver “innovative, game-changing capabilities to the warfighter at an accelerated pace”.

The high-flying language used by the Air Force to describe its Vanguard programs has a corollary in the tag line that L3 Harris uses to tout its role in NTS-3 which it says is “Transforming PNT to meet 21^st century warfighter needs”.

NTS-3 may evaluate a range of different GPS techniques and procedures but it is not going to “transform PNT” nor be a “game-changing capability”. Put plainly, it merely tinkers with the GPS operating scheme the U.S. has had in place for the last 35 years.

The path to our current GPS constellation was paved in the early 1970s by the Naval Research Laboratory’s NTS-1 and NTS-2 spacecraft which were revolutionary game-changers.

Instead, NTS-3 will evaluate GPS signal augmentation technologies that will likely be integrated into forthcoming GPS III Follow-on satellites (GPS IIIF). In 2018, the Space Force awarded Lockheed Martin
LMT
a contract to build up to 22 GPS IIIF satellites which, unlike the current Medium Earth Orbit (MEO) constellation, are expected to fly in a higher Geostationary Orbit (GEO). This will allow a relative handful of satellites to provide global GPS coverage the thinking goes.

NTS-3 will also launch to the higher altitude. There, it will trial a new phased array antenna which is expected to enable higher-power GPS beaming signals which can be targeted to regions of the globe where U.S forces are facing GPS jamming and other adversary-generated interference. The fact that the GEO altitude can allow for multiple spot beams at the same time is one of its advertised advantages.

NTS-3 will also experiment with on-demand M code – a more secure anti-jamming GPS signal designed to be autonomous, meaning that a user can calculate their position using only this particular signal. The satellite will further experiment with on-orbit re-programable capability, essentially allowing NTS-3 to broadcast GPS signals in different, frequently changing waveform guises like a software-defined radio.

A complementary ground segment called the Global Navigation Satellite System Test Architecture, or GNSSTA (developed by the MITRE Corporation in partnership with the AFRL), is a reprogrammable software-defined receiver allowing users to receive both legacy GPS and advanced signals generated by NTS-3. GNSSTA will lay the groundwork for future operational receivers to provide the Space Force and Air Force with options to respond quickly to GPS jamming and spoofing.

L3 Harris actually depicts NTS-3’s operational capabilities in a graphic on its website which sums up the projected benefits of its additive technologies in space and on the ground. The trouble is, the efforts being made heretofore by AFRL, L3 and others don’t really break significant new ground, a reality U.S. adversaries surely recognize.

As described, NTS-3 doesn’t leverage any new approaches like using on-orbit assets to aid with magnetic or photonic navigational techniques or bolstering inertial navigation using quantum sensing.

When pressed, Kelle Wendling, L3 Harris’ space systems sector president, acknowledged the incremental nature of the capabilities NTS-3 is supposed to test.

“We have not focused on a wholesale regroup of what are we going to do for PNT,” she says. “Some of that could be vendor-lock and some of that could be things going on with the current system. Our approach has been that if we have the opportunity – and the opportunity right now is going to be evolutionary vs. revolutionary – we’ll take these technologies and make incremental changes that do give us some flexibility but certainly don’t re-invent PNT.”

They do potentially make for on-orbit GPS assets that might be able to survive the opening stages of a high-intensity conflict more flexible.

“We don’t have on-orbit test yet but all indications in the [ground] testing that we’ve done,” Wendling says, “are that [NTS-3] will be incredibly agile from a waveform, re-programmability, and autonomy perspective.”

The coverage achieved by a GPS satellite at GEO altitudes may also represent cost savings since fewer satellites can cover the globe. L3 Harris has worked to further reduce the cost of NTS-3 by using a reusable commercially available bus, Northrop Grumman’s
NOC
ESPAStar-D. “We build it three times faster and it’s significantly lighter and cheaper [than current GPS satellites],” Wendling affirms.

The capability that NTS-3 will showcase may also come cheaper because the government currently envisions placing as few as three satellites with its baseline payload into GEO orbit. While they may offer better coverage, anti-jamming, timing and autonomous waveform-hopping to better reach U.S. forces in-need of PNT, they will also be vulnerable to the ground and space based anti-satellite weapons of China and Russia as well as to the on-orbit jamming, grappling and other capabilities such adversaries are believed to possess.

Targeting three to four satellites, even satellites in GEO, is not a hard problem I suggested. Ms. Wendling responded that, “There are some things that we have capability-wise on the platform that allow it to not be such a target.”

Presuming these are defensive capabilities, I asked if they will form part of the testing/experimentation that NTS-3 will undertake?

“They are part of the discussions of the experiments we are having to ensure we have comprehensive capabilities,” Wendling replied stressing the potentially classified nature of possible self-protective sensors and maneuvering capability NTS-3-derived sats could integrate.

But “discussions” are not experiments nor do they represent defensive capability. Classification concerns are also too often used by the government/DoD and industry to duck answering uncomfortable questions. Another of these turns on the vulnerability of GEO located satellites to space congestion. AFRL and L3 Harris have asserted that placing additional navigation satellites in LEO makes them vulnerable to space junk and debris-creating exploits.

This suggests that plugging NTS-3-like payloads into other low-flying constellations like the Starlink internet network, Iridium’s 66-satellite communications constellation (a network that features a little-known GPS alternative called “STL”) or Aireon’s ADS-B air traffic control satellite constellation isn’t a good idea.

“The conversation right now is ‘let’s not proliferate in LEO“, Wendling says. “The number of systems and debris there is going to be a challenge. We’re not seeing LEO as the most defensible, persistent or resilient orbit.”

But as far back 2017, an analysis found that the threat posed by space debris to satellites in geosynchronous Earth orbits was much greater than had been assumed. Likewise, AFRL and L3 Harris fail to mention the possibilities that LEO navigation constellations represent beyond greater numbers of smaller satellites less susceptible to being wiped out.

The same clutter that is said to be a risk to LEO satellites raises the possibility of hiding in plain sight. A set of smaller PNT satellites could leverage the possibility of hiding in the band of LEO congestion spanning the circumference of the earth, offering coverage that GEO altitude GPS III sats could provide without standing out like beacons.

LEO also offers the possibility of employing “virtual” PNT satellites – sleeper satellites which look like debris. Separate parts of a PNT sat payload could be launched independently and dispersed into LEO and other orbits. Sensors could be in one location, an amplifier in another, a processor in yet another, all orbiting relatively immersed in space debris.

And as for coverage for American troops in far flung global locations, it should be remembered that the proximity of LEO satellites (25 times closer to the Earth than GNSS satellites) with high power signals like Iridium’s STL could offer PNT broadcasts up to 1,000 times (30 dB) stronger than GPS, allowing them to penetrate deep into GPS-challenged environments where signals are obstructed or degraded, including indoors.

Kelle Wendling does stress L3 Harris’ tradition of placing payloads in hosted environments, adding that the company is capable and willing to place NTS-3 type technologies on a varied range of space platforms but the company simply isn’t getting a signal to do so from the government.

As the first of the Vanguard programs the NTS-3 experiment would not appear to be in the vanguard of advance space-based PNT at all. It’s much more of a default as L3 Harris’ Wendling acknowledges.

“We can’t do nothing. Absent [the Office of the Secretary of Defense] saying we really want to re-think PNT and are going to put billions into a new architecture, this is the current opportunity to experiment [with PNT] and that’s how they’ve chosen to move forward. We’re responding to the appetite that the government has now.”

When it comes to facilitating the U.S. military’s basic way of fighting, tinkering with GPS just isn’t good enough.