Space Station to Get a ‘Laser Cannon’

CATS in the laboratory. Credit: NASA/GSFC.

What’s a space station without a laser cannon?

The International Space Station will be getting its very own laser at the end of 2014. And unlike the planet-smashing capabilities of the Death Star of Star Wars fame, this laser will to be enlisted for the purpose of science.

It’s called CATS, and no, it isn’t the latest attempt to put feline astronauts in space. CATS stands for the Cloud Aerosol Transport System. The goal of CATS is to study the distribution of tiny particles of dust and air contaminants known as aerosols.

Developed by research scientist Matt McGill at NASA’s Goddard Space Flight Center in Greenbelt Maryland, CATS is slated to head to the International Space Station later this year on September 12th aboard SpaceX’s CRS-5 flight of the Dragon spacecraft. CATS will be installed on the Japanese Experiment Module-Exposed Facility (JEM-EF) and will demonstrate the utility of state-of-the-art multi-wavelength laser technology to study aerosol distribution and transport in the atmosphere.

Such knowledge is critical in understanding the path and circulation of aerosols and pollutants worldwide. When the Eyjafjallajökull volcano erupted in Iceland back in 2010, many trans-Atlantic flights were grounded as a precaution. These measures are necessary as several flights have suffered engine failures in the past due to encounters with volcanic ash clouds, such as the four engine failure of KLM Fight 867 in 1989 and the British Airways Flight 9 incident over Southeast Asia in 1982. Knowing where these dangerous ash clouds are is crucial to the safety of air travel.

The expanding ash cloud spewing from Iceland's Eyjafjallajökull volcano as seen from space in 2010. Credit: NASA.
The expanding ash cloud spewing from Iceland’s Eyjafjallajökull volcano as seen from space in 2010. Credit: NASA.

To accomplish this, CATS will emit 5,000 1 milliJoule laser pulses a second at the 1064, 532 and 355 nanometer wavelengths.  This represents a vast improvement in power requirements and thermal capabilities over a similar instrument currently in service aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) Earth remote sensing spacecraft.

And it’s that third 355 nanometer wavelength that will make CATS stand out from CALIPSO. This will also allow researchers to differentiate between particle size and measure the horizontal and vertical distribution of aerosol particles in the atmosphere. CATS will also be capable of measuring the number of individual photons being reflected back at it, which will provide a much better resolution and understanding of current atmospheric activity.

“You get better data quality because you make fewer assumptions, and you get, presumably, a more accurate determination of what kind of particles you’re seeing in the atmosphere,” McGill said in a recent press release.

The International Space Station also provides a unique vantage point for CATS. In a highly inclined 51.7 degree orbit, the station passes over a good swath of the planet on 16 orbits daily on a westward moving ground track that repeats roughly every three days. This will assure CATS has coverage over a large percentage of the planet, including known pollutant transport routes across the northern Pacific and down from Canada over the U.S. Great Lakes region.

While the first two lasers will operate in the infrared and visual wavelengths, said third laser will work in the ultraviolet. And while this will give CATS an enhanced capability, engineers also worry that it may also be susceptible to contamination.  “If you get contamination on any of your outgoing optics, they can self-destruct, and then your system is dead. You end up with a very limited instrument lifetime,” McGill said.

Still, if CATS is successful, it may pave the way for larger, free-flying versions that will monitor long-range atmospheric patterns and shifts in climate due to natural and man-made activity. And the ISS makes a good platform to test pathfinder missions like CATS at low cost. “In our current budget-constrained environment, we need to use what we already have, such as the [station], to do more with less,” McGill said.

CALIPSO's LiDAR imaged from the ground by Gregg Hendry in 2008. Used with permission.
CALIPSO’s LiDAR imaged from the ground by Gregg Hendry in 2008. Used with permission.

The advent of a LiDAR system aboard the ISS has also generated a spirited discussion in the satellite tracking community concerning prospects for spotting CATS in operation from the ground. The CALIPSO LiDAR has been captured by ground spotters in the past. However, CALIPSO fires a much more powerful 110 milliJoule pulse at a rate of 20 times a second. Still, the lower power CATS system will be firing at a much faster rate, delivering a cumulative 5,000 milliJoules a second.  CATS won’t be bright enough to show up on an illuminated pass of the ISS, but it just might be visible during darkened passes of the ISS through the Earth’s shadow. And, unlike CALLIPSO — which is part of the difficult to observe A-Train of Earth-observing satellites — the ISS passes in view of a majority of humanity. At very least, activity from CATS will be worth watching out for, and may well be seen either visually or photographically.

We’ll soon be adding CATS to the long list of outstanding science experiments being conducted aboard the International Space Station, and the sight of this “fully armed and operational battle station” may soon be coming to a dark sky site near you!