WASHINGTON — A ring-shaped satellite carrier the U.S. Air Force developed a decade ago to deploy experiments has evolved into a reliable asset to get small national security payloads to geosynchronous Earth orbit. 

The so-called ESPA ring — short for Evolved Expendable Launch Vehicle (EELV) Secondary Payload Adapter — was created to fill unused capacity on national security space rockets. The newest version of the ring designed by Northrop Grumman, the Long Duration Propulsive ESPA or LDPE, deploys experiments but also more advanced operational smallsats.

Each ring has six ports that can accommodate 320 kilograms of payload mass per port.

“LDPE provides added propulsion, power, and avionics subsystems enabling operations as a fully functional satellite,” Space Systems Command program manager Lt. Col. Michael Rupp, said in a news release.

Under a contract with U.S. Space Systems Command, Northrop Grumman built three LDPE rings for national security missions. One launched in December 2021, the second in November 2022 and the third one will fly on a SpaceX Falcon Heavy in the upcoming USSF-67 mission. A more advanced version of the ring is in the works under a July 2022 $22 million contract.

Space Systems Command said all payloads on LDPE-1 and LDPE-2 were successfully deployed to geostationary orbits. 

The EAGLE, short for Evolved Expendable Launch Vehicle Secondary Payload Adapter Augmented Geosynchronous Experiment, started as a joint development by the Air Force Research Laboratory and Orbital Sciences back in 2012, said Troy Brashear, Northrop Grumman vice president of national security systems. Orbital Sciences was later acquired by Northrop Grumman.

Military customers are seeing the utility of the ESPA ring as a much more affordable option than dedicated launches, and the rings are flexible enough that payloads can be swapped at the 11th hour, Brashear told SpaceNews. 

“An interesting part of this satellite program is the ability to make changes on the fly,” he said. That is not possible with most space missions where the payloads are designed for specific interfaces and substitutions are difficult to make. “On LDPE we’ve been able to show that payloads on any of the six ports can be swapped out as late as at the launch site.”

Northrop Grumman manufactures the ESPA satellites in Gilbert, Arizona. After being shipped to Cape Canaveral, individual payloads in recent missions were changed out right before launch, he said. “And it provided a ton of flexibility to the customer.” 

A form of resilience

Brashear said the ability to add a new payload to the mission on short notice is increasingly important as a form of resilience, giving the Space Force options to deploy experiments or operational satellites in response to emerging needs. 

“The foreign threat environment is changing pretty fast. And for our customers, speed and agility to stay ahead of those challenges is paramount,” he said. “This program is providing that sort of resilient architecture to put things into orbit faster, and cheaper since it’s a very small satellite structure, utilizing empty space on a ride that would go unused.”

The LDPE satellites fly to geostationary orbit on big rockets that typically carry a large primary payload and the ring as a secondary payload. When it reaches orbit, the LDPE is released from the second stage. Once the ring is deployed, the individual payloads can stay attached to the platform permanently or can be dispensed as independent satellites, go off and do their own missions.

“The U.S. government’s investment over the last 10 years in these ESPA products has just timed up very nicely with the threat environment,” he said. “If these investments hadn’t been made 10 years ago, we wouldn’t have this freight train to space where we can take six payloads up in a cost effective manner.”

Another benefit of these rings is that they are interchangeable with any of the national security space rockets the Space Force uses, which are operated by United Launch Alliance and SpaceX. LDPEs have launched on ULA’s Atlas 5 and on SpaceX Falcon Heavy. “There’s obviously different loads and dynamics and testing,” said Brashear. “But both ULA and SpaceX have been fantastic to work with.”

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