BOULDER, Colo. — Satellite operators need better space weather models to maximize the life of their satellites and to avoid collisions in low Earth orbit.
The growth in the population of satellites and debris in orbit, driven by megaconstellations like SpaceX’s Starlink, has provided a new impetus to efforts to better model how space weather events can increase the density of the upper atmosphere and thus the drag satellites in low orbits can experience.
That was evident during a major solar storm in May 2024, known as the Gannon Storm. While best known for creating brilliant aurora at unusually low latitudes, it also caused a spike in atmospheric density that affected the accuracy of orbits used for predicting potential collisions.
That resulted in errors ranging from 1 to 1,000 kilometers over a day, said Dan Oltrogge of COMSPOC during a talk at the Space Weather Workshop here March 18. By contrast, human spaceflight safety requires accuracies of 100 to 200 meters. “We’re talking hundreds of kilometers of error that really invalidates doing spaceflight safety,” he said.
Recovering from those errors is further complicated by difficulties tracking objects whose orbits have shifted more than expected. “Not only are you mismodeling the drag, you are not getting the observations to help you recover from that,” he said.
Satellite operators, he concluded, need space weather models that are “accurate, predictive and timely,” as well as atmospheric models that can incorporate those space weather predictions to model density and drag.
The Gannon Storm also revealed behavior like “mass migrations” of thousands of Starlink satellites that performed automated maneuvers to raise their orbits to compensate for the increased atmospheric drag. That can also adversely affect space safety.
“These are all unplanned maneuvers,” said William Parker of the Massachusetts Institute of Technology in a talk at the workshop, upsetting forecasts made 12 to 24 hours in advance. “When you have half of all the active satellites maneuvering at one time, you can basically throw all of that analysis out the window.”
“Satellite collision avoidance is really not very robust to geomagnetic storms,” he said, due to those maneuvers as well as the errors in orbital positions caused by atmospheric drag from the storms. “We basically have no ability to do collision avoidance in low Earth orbit during a storm.”
He said the space weather community needs to work with satellite operators on ways to improve the accuracy of forecasts or, at least, provide better information on the uncertainties in those forecasts.
In addition to space safety concerns, space weather can lead to reduced lifetimes of spacecraft because of higher atmospheric drag. That is what Capella Space, a company that operates a constellation of radar imaging satellites, found when drag much higher than forecast shortened the orbital lifetime of its Whitney series of satellites.
The design of the Whitney satellites was based on predictions made of the current solar cycle made in 2019 by the Space Weather Prediction Center. Those forecasts turned out to underestimate solar activity and thus atmospheric drag, said Scott Shambaugh, a former senior engineer at Capella who documented the challenges the company faced in a paper published last year.
The higher solar weather increased atmospheric density by a factor of two to three, with decreased satellite lifetime by a corresponding amount. Capella’s satellites were particularly vulnerable because of their large deployable radar antennas.
He noted in a talk at the workshop that the projected lifetimes of the satellites had dropped from three years to just nine months. Six satellites reentered in 2023 because of atmospheric drag.
Capella took several steps to respond to the problem, including purchasing dedicated launches of satellites to place them in higher orbits than what rideshare missions offered as well as redesigning propulsion systems to provide more thrust to counteract drag. “It was an enormous effort,” he said.
He cited problems satellite companies face in getting accurate space weather and atmospheric models. Spacecraft engineers “are not space weather experts,” he said. “This represents a gap between the academic community and the operators in industry.”
Shambaugh announced at the workshop he’s started a company called Leonid Space that will support satellite operators by providing more detailed, accurate estimates of satellite lifetimes. An example he developed is for the four NASA TROPICS cubesats, launched in 2023 and initially expected to remain in orbit for up to nine years. The Leonid Space analysis instead predicts the cubesats will reenter this summer.
“The real answer we’re trying to get it is the answer to the question, ‘How long do I have before my satellite burns up?’” he said. “My goal here is to bridge the gap between the space weather community and satellite operators.”