WASHINGTON -- A team of scientists published an observational and modeling study showing that water vapor, a common launch byproduct of space traffic, can actively cool the mesosphere and induce the formation of mesospheric clouds.
Since the end of the shuttle age in 2011, 17 countries have created their own space agencies, now totaling more than 72, 14 of which have their own launch capabilities. In 2020, there were 104 successful rocket launches globally that potentially released water vapor. But what are the affects it is having on the earth’s atmosphere?
“Nobody knows how much these smaller launches are contributing; not yet anyway,” said Michael Stevens, Ph.D. from the U.S. Naval Research Laboratory’s Geospace Science and Technology Branch, and a paper co-author. “If you're using these clouds to measure any small multi-decadal changes, then they can become important. We've shown in this study that they could contribute significantly. But we don't know yet whether they do contribute significantly. This study has advanced our growing understanding of the impact.”
Polar mesospheric clouds research at the edge of space serves to test high altitude weather and climate models of the upper atmosphere that is important for the Navy.
“This new understanding of weather, including regions of the ionosphere, is critical for improving models of over-the-horizon-radar propagation,” Stevens said.
NASA funded the “Super Soaker Mission”, a three-year study, which culminated with the experiments Jan. 25-26, 2018 at the Poker Flat Research Range (PFRR) in Alaska. The team created an experiment consisting of three sounding rockets; two rockets carried trimethylaluminum tracers, and a third rocket carried 485 pounds (220 kilograms) of liquid water.
While many American space missions launch in Florida, PFRR is a good location to study their effects in a controlled setting because of the ground-based instrumentation already in place there. PMCs are at an altitude of about 53 miles (85 kilometers) and are thinner than the clouds one sees looking out their windows.
The rocket with the water detonated when it reached altitude and within seconds, a ground-based lidar detected PMCs.
“The fact we saw the clouds form so quickly and the fact that they persisted for about three minutes, was unexpected,” said Stevens. “We saw it on screen and I don't think everyone in the room believed we were going to see that, but we did.”
Stevens was the sole NRL representative on the mission who brought his previous experience with other case studies of this phenomenon conducted over the past 20 years.
“Polar mesospheric clouds appear in the summertime over the poles, and there is evidence they are getting more common. There are also several published papers showing main engine exhaust from the space shuttle can create these clouds, sometimes contributing up to 20% to a PMC season,” Stevens said. “Compared to the overall water budget of the Earth, of course, these contributions are negligible. But compared to the amount of water in these tenuous PMCs it is not.”
“You can only see PMCs near the polar latitudes with the naked eye when the sun is actually below the horizon but still shining up high in the atmosphere in front of you; that’s how thin they are,” Stevens said. “These altitudes where we're working are an arid portion of the atmosphere. So here we come, and we launch a rocket full of water, and we detonate this thing, we're totally soaking it. It's only a bathtub of water, but a bathtub up there is a big deal.”
Stevens has spent most of his career working on satellite missions and said he felt privileged to work with such a great team at NASA and the PFRR science team.
“This was my first rocket mission on which I was actively involved,” Stevens said. “It was a different experience, and it was great, and I hope one day we can do it again.”
A video of the 2018 rocket launches is available at http://bit.ly/3sBs12J. A video of a prelaunch interview is available at http://bit.ly/2Ph0jda.
About the U.S. Naval Research Laboratory
NRL is a scientific and engineering command dedicated to research that drives innovative advances for the U.S. Navy and Marine Corps from the seafloor to space and the information domain. NRL is located in Washington, D.C., with major field sites in Stennis Space Center, Mississippi; Key West, Florida; Monterey, California, and employs approximately 2,500 civilian scientists, engineers, and support personnel.