Redwire will use a smaller version of its SabreSat spacecraft to test propulsion technology where the upper atmosphere still exerts substantial drag. The company announced the new $20 million contract from the U.S. Defense Advanced Research Projects Agency on November 5. The agency’s Otter program aims to use the thin air surrounding a spacecraft as a source of propellant.
The award adds a precursor flight to an existing full-scale mission. Under a $44 million contract announced in November 2025, Redwire is responsible for finishing the full-scale spacecraft and delivering it for launch. The two announced awards total $64 million. Redwire serves as the prime mission integrator, bringing the spacecraft and its onboard systems together for flight.
How the Air Can Both Slow and Propel a Satellite
DARPA’s Otter program concerns very low Earth orbit, which the agency defines for this work as altitudes from 90 to 450 kilometers. A spacecraft moving through the rarefied gas at these heights repeatedly collides with atmospheric particles. Those collisions create drag and remove orbital energy. Thrust applied in the direction of travel can offset the loss.
A conventional electric thruster draws propellant from an onboard supply. Otter’s proposed system would collect gas through an inlet as the spacecraft travels. Using electrical energy, the system would give particles in the gas an electric charge and accelerate them out of the thruster. Sending that material backward produces forward thrust on the spacecraft.
This distinction explains the term air-breathing in Otter. The surrounding gas supplies the material expelled by the thruster. The spacecraft supplies the electrical energy used to accelerate it.
What the Flight Adds to Ground Tests
On the ground, engineers can test an inlet or thruster under selected conditions. In orbit, the inlet, propulsion system, and spacecraft body encounter the same atmospheric flow at the same time. The scaled SabreSat flight is intended to collect data on how those elements behave together before the full-scale mission.
DARPA plans to compare flight measurements with ground-test data and use the results to update simulations of spacecraft at these altitudes. Its objective for the full demonstration is to operate an orbital test platform for more than a year, observing propulsion performance as the surrounding atmospheric conditions change.
