The European Space Agency (ESA) and the Institute of atmospheric physics at the German aerospace center, DLR, teamed up to measure rocket emissions on a suborbital launch that flew on 1 October. Ground-based measurements were combined with measurements recorded from a chaser aircraft that flew through the exhaust plume of a rocket launched from Esrange in Sweden, for the Mapheus-17 mission. The operations show what is possible to record and better understand rocket emissions in the lower atmosphere as space agencies work towards more sustainable space transportation.

Rockets have been launching for over half a century, but what trail do they leave behind? This seemingly simple question is not so easy to answer. How would you sniff the exhaust from rockets as they interact with the changing atmosphere and ascend through the troposphere, stratosphere and into the vacuum of space, higher than any other vehicle can travel? Most research has so far been based on computer models and simulation studies of rocket exhausts and their interactions with the atmosphere, leaving a gap in our knowledge.

This is why ESA suggested a new project ‘Firewall’ with DLR to develop a concept to measure rocket emissions. To learn by doing, Firewall used DLR’s Mapheus-17 solid-propellant sounding rocket mission as a first test case.

Mapheus is a regular series of DLR rocket flights, this mission housed multiple experiments in materials and life sciences, as well as testing technology in microgravity. Mapheus-17 flew almost 300 km upwards before landing back on Earth 16 minutes after liftoff – around 70 km downrange from the launch pad.

The first stage is powered by a solid propellant Red Kite engine, for which combustion products are expected to be hydrochloric acid, water vapour, ice, aluminium oxide, carbon dioxide, nitrogen and soot.

The Firewall campaign relied on DLR’s Falcon 20E research aircraft that is equipped with instruments to measure gases and particles in the rocket’s exhaust plume. The Falcon 20E aircraft took off around 20 minutes before the rocket launch and then flew through the region where the plume drifted at altitudes between 2 and 6 km. As the plume disperses just minutes after liftoff it becomes invisible, adding to the challenge of taking measurements.

A custom-made container packed with an array of scientific measurement systems near the launch site also recorded the emissions at the launch pad, complementing what the aircraft measured.

“The operations we conducted are a proof of concept,” says Valère Girardin, ESA’s technical officer for Firewall, “we need to see what is feasible and reasonable in terms of measurements, operations and coordination. Rocket launches have lengthy countdowns and large no-flight zones. Safely flying aircraft close to a rocket launch is no trivial matter. Similar atmospheric measurement campaigns are needed for when satellites fall back to Earth and burn up, where the interactions with the upper atmosphere are important to measure and chart.”

“Such campaigns give us the critical insights and data needed to optimise design, choice of materials and operations for future engines and satellites from a sustainability point of view,” says Lorenz Affentranger, ESA systems engineer for the Clean space and circular economy office.

NASA were also invited to and participated with carbon dioxide detection instruments on the ground.

The project offered the team important real-world experience in coordinating air-traffic control, flight instruments, the teams working on the rocket operations and how to combine them in a joint campaign. The operations went well, the rocket concluded its flight and the Falcon 20E observation aircraft landed safely after flying through the rocket exhaust. Researchers at ESA and DLR will now analyse the data recorded to see if the setup worked as intended. If so more rocket-sniffing flights could follow.