The Space Force's LDPE mission launching later this year will use the ESPAStar bus to host several smallsats and hosted payloads. Credit: Northrop Grumman

WASHINGTON — The U.S. Space Force plans to demonstrate later this year two approaches to provide rides to space for small satellites and hosted payloads, including a version of a common adapter equipped with a propulsion system.

The Space Test Program 3 mission, scheduled to launch later this year on an Atlas 5, will carry the first Long Duration Propulsive ESPA (LDPE) payload. LDPE uses the EELV Secondary Payload Adapter (ESPA), a ring-shaped adapter for secondary smallsat payloads, as a bus equipped with power and propulsion systems to maneuver after launch and carry payloads to their final orbits.

The Space Force’s Space and Missile Systems Center (SMC) sees LDPE as a pathfinder for a series of future missions to enable frequent launches of smallsats and hosted payloads. “We call the LDPE our ‘freight train to space,’” said Col. Heather Bogstie, senior materiel leader of the rapid development division at SMC, in a video presentation at the Small Satellite Conference. “The general concept is we hope to launch these once a year, funding permitting, and get capabilities on orbit in a rapid fashion.”

LDPE uses Northrop Grumman’s ESPAStar bus, which is optimized for use in geostationary orbits but can also be used for low and medium Earth orbit. It can accommodate 1,920 kilograms of payload in its six docking ports for smallsats or hosted payloads, and its propulsion system provides more than 400 meters per second of delta-V.

Three LDPE missions are scheduled for launch in the next 18 months, Bogstie said. SMC will then transition to a program called Rapid On-orbit Space Technology Evaluation Ring (ROOSTER). She said SMC is planning to award contracts for two ROOSTER missions in the near future, with the potential for more to follow.

Future contracts for similar systems across the Space Force may be consolidated to be under a single program office, she said, lowering costs and increasing efficiency.

One challenge in the development of LDPE has been meeting a goal of rapid integration of payloads. SMC wanted the ability to replace payloads as close as a month to launch if a payload suffered technical problems or if a higher-priority payload needed to fly. However, Bogstie said the coupled loads analysis needed for launching spacecraft requires creating a finite element model of the ring and its attached payloads more than a year in advance.

“If there’s an issue with development or a problem with the integration and test phase, we cannot make modifications to the spacecraft after we deliver that finite element model,” she said.

To address that problem, SMC has adopted what’s known as a modular open systems approach to the development of LDPE. Using an approach similar to cubesat deployers, SMC is developing digital models to identify payload volumes within which payloads can be replaced without extensive reanalysis.

“It creates a model-based environment that, as long as we can stay within the model, we can more quickly ingest and change out those individual payloads,” said Stanley Straight, chef engineer for the innovation and prototyping directorate at SMC, in the conference talk.

A complementary effort to LDPE is Tetra, a series of smallsats under development at SMC. Each satellite is designed to host a range of payloads and be capable of launching on LDPE and similar payload adapters.

The first Tetra satellite, Tetra-1, was built by Millennium Space Systems is scheduled to launch as part of the USSF-44 mission no earlier than October on a SpaceX Falcon Heavy. Tetra-2 is under construction by Blue Canyon Technologies to demonstrate “interesting maneuverability options,” Bogstie and Straight wrote in a paper accompanying their presentation.

Tetra-3 and -4 will be bult by York Space Systems as part of a “two for one” deal, they wrote. The missions those two spacecraft will fly are still being defined.

While LDPE and Tetra are designed primarily to support technology demonstration missions, Bogstie said she could eventually envision LDPE and ROOSTER supporting operational missions. “Once we get the commodity buys in place and we have an architecture of rings,” she said, “we can see benefits in communications, on-orbit servicing, on-orbit logistics, refueling. The opportunities are really endless.”

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...