Two Houston aerospace companies — Intuitive Machines and Venus Aerospace — have reached testing milestones for equipment they’re developing.

Intuitive Machines recently completed the first round of “human in the loop” testing for its Moon RACER (Reusable Autonomous Crewed Exploration Rover) lunar terrain vehicle. The company conducted the test at NASA’s Johnson Space Center.

RACER is one of three lunar terrain vehicles being considered by NASA for the space agency’s Artemis initiative, which will send astronauts to the moon.

NASA says human-in-the-loop testing can reveal design flaws and technical problems, and can lead to cost-efficient improvements. In addition, it can elevate the design process from 2D to 3D modeling.

Intuitive Machines says the testing “proved invaluable.” NASA astronauts served as test subjects who provided feedback about the Moon RACER’s functionality.

The Moon RACER, featuring a rechargeable electric battery and a robotic arm, will be able to accommodate two astronauts and more than 880 pounds of cargo. It’s being designed to pull a trailer loaded with more than 1,760 pounds of cargo.

Another Houston company, Venus Aerospace, recently achieved ignition of its VDR2 rocket engine. The engine, being developed in tandem with Ohio-based Velontra — which aims to produce hypersonic planes — combines the functions of a rotating detonation rocket engine with those of a ramjet.

A rotating detonation rocket engine, which isn’t equipped with moving parts, rapidly burns fuel via a supersonic detonation wave, according to the Air Force Research Laboratory. In turn, the engine delivers high performance in a small volume, the lab says. This savings in volume can offer range, speed, and affordability benefits compared with ramjets, rockets, and gas turbines.

A ramjet is a type of “air breathing” jet engine that does not include a rotary engine, according to the SKYbrary electronic database. Instead, it uses the forward motion of the engine to compress incoming air.

A ramjet can’t function at zero airspeed, so it can’t power an aircraft during all phases of flight, according to SKYbrary. Therefore, it must be paired with another kind of propulsion, such as a rotating detonation rocket engine, to enable acceleration at a speed where the ramjet can produce thrust.

“With this successful test and ignition, Venus Aerospace has demonstrated the exceptional ability to start a [ramjet] at takeoff speed, which is revolutionary,” the company says.

Venus Aerospace plans further testing of its engine in 2025.

Venus Aerospace, recently achieved ignition of its VDR2 rocket engine. Photo courtesy of Venus Aerospace