Why We're Shooting Another Rocket Into the Northern Lights
Auroras heat the Earth's upper atmosphere, like a giant celestial toaster—causing satellites to drift.
Aurora actually heat the Earth's upper atmosphere, like a giant celestial toaster. Photo: Moyan Brenn/Flickr
For the next two weeks, the northern lights won't be the only thing keeping the Alaskan night sky alight. NASA is launching five sounding rockets from its Poker Flat Research Range, one of which is intended to measure how auroral events, or geomagnetic storms, cause satellites to drift.
Though sounding rockets have been launched into aurora now for decades, the Auroral Spatial Structures Probe (ASSP) mission is unique in that it will attempt to map the structure of magnetic and electrical fields within the aurora, of which we currently know very little about.
During periods of heightened geomagnetic activity, aurora actually heat the Earth's upper atmosphere—a result of electrical currents encountering the Earth's magnetic field—sort of like a giant celestial toaster. This process, called Joule Heating, causes the thermosphere to expand, and this expansion of the Earth's thermosphere is what increases satellite drag.
ASSP will attempt to measure electrical and magnetic fields from inside the aurora during an auroral sub-storm, data that scientists will hopefully be able to use to predict when and where the Earth's upper atmosphere will heat and expand as the result of increased geomagnetic activity.
Charles M. Swenson, an associate professor of electrical and computer engineering at Utah State University's Space Dynamics Laboratory, and the principal investigator for ASSP, likened previous attempts at measuring such activity to measuring the height of waves on a lake.
"If you're travelling at the same speed as one of the waves, you might just measure the peak or the trough and it would never change, and you would just have a constant signal," Swenson explained in an interview. "But if you happened to measure in the other direction, going against the waves, then you would see peaks and troughs happening really, really, really quickly."
The challenge for Swenson's team has been figuring out how to determine whether the structure of the aurora's electrical and magnetic fields are relatively constant, or rapidly changing—something that has previously proven difficult with just a single probe. This is why ASSP's payload is actually seven payloads in one—a main payload, and six sub-payloads—which will detach and fly together in an airborne constellation. The solution, Swenson and his team determined, was to send five probes, one after the other, tracing the same path, with two additional probes offset to either side. Because each sub-payload is equipped with GPS, they can track changes in the magnetic and electrical fields across time and space.
Being able to accurately predict these changes when geomagnetic storms occur is the goal. According to Swenson in a press release, "This expanded gas can increase the drag on satellites (those under or about 620 miles altitude) by 1,000 per cent or more for a few days which shifts their orbits significantly." If you're a company that depends on knowing exactly when and where a satellite will be at any given time—say, for surveillance or communication needs—having the ability to model this drift and compensate would be useful.
Swenson says that the sounding rocket is on the launch pad right now, and it's possible it could launch as early as tonight, if conditions are good. If not, the team will try again the next day, and if not then, the next—over and over for the next three weeks until the conditions are perfect for launch. That means a cloudless night, good for the cameras, but also a period of geomagnetic activity. A perfect auroral sub-storm.
"Otherwise I'm just stuck up here every night," Swenson said with a chuckle, "watching the beautiful aurora and waiting for conditions to be right."