Optical links will connect SDA’s Transport Layer to weapons platforms. (SDA)
WASHINGTON — The Space Development Agency recently launched 13 more early-version satellites in its planned communications and missile tracking networks in low Earth orbit.
“Tranche 0 is the demonstration and warfighter immersion tranche. So, we’re looking to show that you can build out sort of a proliferated architecture that allows you to do things like tactical data links, beyond-line-of-sight targeting, and advanced missile detection and tracking,” Mike Eppilito, SDA program director, told reporters last week ahead of the Saturday launch.
The full SDA Tranche 0 constellation will number 28, including 20 in the Transport Layer for data relay and eight in the Tracking Layer for ballistic and hypersonic missile tracking — two of the multiple layers in the agency’s Proliferated Warfighter Space Architecture (PWSA), designed to make it harder for adversaries to negate US space capabilities via the sheer number of satellites available to US commanders.
The first 10 Tranche 0 birds were launched in April, eight built by York Space Systems for the Transport Layer and two built by SpaceX for the Tracking Layer. Of the 13 being launched over the weekend, 11 Transport Layer satellites, 10 are provided by Lockheed Martin, and one from York, Eppilito said.
A third launch will go up later this year that will carry the four Tranche 0 Tracking Layer satellites provided by L3Harris, he added, which has faced some delays caused by supply chain issues. Finally, one York Transport Layer bird will remain on the ground as a test bed.
The agency eventually plans to operate some 300 to 500 Transport Layer satellites in LEO, designed to provide the communications backbone of the Defense Department’s Joint All Domain Command and Control (JADC2) concept for managing operations across the ground, air, sea, space and cyber domains.
Another 200-some satellites will make up the Tracking Layer, which will complement the Space Force’s current Space Based Infrared System (SBIRS) satellites in geosynchronous Earth orbit (GEO) and their follow-on constellation, the Next Generation Overhead Persistent Infrared (Next-Gen OPIR) system with satellites in GEO and polar orbits. The service’s major acquisition command, Space Systems Command, also has initiated plans to rapidly field another set of missile warning/tracking satellites in medium Earth orbit (MEO).
Laser Links Lagging?
Since he took over SDA back in 2019, Director Derek Tournear has been saying both the key enabler, and the long pole in the tent, for the PWSA — especially the Transport Layer that is at the heart of concept — is the use of lasers as data links among the satellites and from the satellites to the ground.
Laser links will allow SDA to enhance the data throughput of its satellites, and lower latency — connecting satellites in the same plane and eventually “across planes in space,” and finally to the ground, Jennifer Elzea, SDA’s chief of strategic engagement, told reporters.
(An orbital plane is a flat, disk-shaped geographical space that connects the center of the object being orbited, in this case the Earth, with the center of the orbiting objects themselves. Thus, for Earth-orbiting satellites this corresponds with inclination angles from the equator.)
The agency has developed a baseline standard for optical inter-satellite links (OISLs) that will allow any provider to simply “plug into” its Transport Layer, and has stood up a lab in concert with the Naval Research Laboratory where any would-be provider can test their own optical terminals for compatibility. The goal is to help spur more entrants into the field and allow strong competition down the road.
Eppilito said that each of the Tranche 0 satellites will carry two OISL payloads. For the satellites now on orbit, he noted, SDA is currently “working through the initialization of those payloads” for both the York and the SpaceX birds. The expectation is to be able to undertake on-orbit tests of each vendor’s ability to link to the other’s satellites “later this year,” he added.
Elzea explained that SDA is trying to push forward the technical maturity of OISLs now commercially available.
“Optically linked satellites are something that commercial industry has done for a little bit of time now, but it’s not something that the military has heavily relied upon, because the market didn’t really support it until recently,” she said. “That’s another example of where we’re taking a concept that exists and then enhancing it.”
But that technology remains in early stages, according to experts.
While four companies were in the initial running to provide OISLs for Tranche 0, the field winnowed down to two, according to industry sources: Tesat-Spacecom, a subsidiary of European aerospace giant Airbus Defence and Space, providing the links for three of the primes, CACI International (which in late 2021 acquired SA Photonics) providing the links for the fourth, Eppilito said.
“The whole thing about optical inter-satellite links is a nightmare,” Tim Farrar, president of Telecom, Media and Finance Associates, told Breaking Defense.
He explained that while some commercial companies, such as SpaceX, are already using OISLs to link satellites in the same orbital plane, the much harder job is to keep the laser beam stable and locked on between satellites orbiting in different planes.
SDA’s Transport Layer will be composed of satellites in at least six planes.
“In-plane [linking] is not very hard because they’re not moving relative to one another,” Farrar elaborated. Satellites in different planes instead are “whizzing past” each other. “These things are moving past each other incredibly fast, and it is very, very hard to maintain a lock and even establish a lock.”
