Geosynchronous Space Situational Awareness Program surveillance satellites are constrained by limited fuel and propulsion performance.
When the U.S. Space Force sees something suspicious flying around space, it cannot just “saddle up” and go take a look. Operators of orbiting surveillance spacecraft must meticulously plan a route to arrive at the object months later.
Such is the fuel-starved reality of modern spacecraft, which launch at great expense with all their propellant onboard. Lacking the ability to refuel, surveillance spacecraft must make do with what they are carrying.
- New propulsion technology could surprise adversaries
- Current spacecraft have maneuverability akin to World War I Zeppelins, Space Command says
The U.S. Space Force Geosynchronous Space Situational Awareness Program (GSSAP) satellite is no exception, Lt. Gen. John Shaw, deputy commander of U.S. Space Command, said over a livestream at a dynamic space operations event on June 2. The event was hosted on the factory floor of Phase Four, a startup developing radio frequency plasma thrusters for small satellites.
The GSSAP satellites, which launched in 2014, are designed to move around, track and characterize human-made objects around the geosynchronous belt—22,236 mi. from Earth. “We will go look at things that are curious,” said Shaw of the GSSAP satellites. Their performance is limited, however, because they have lifetimes “measured in years,” he added.
“They have a fixed gas tank of a certain amount of Delta-v,” Shaw noted. “We actually have to tell [1st Space Operations Sqdn.], the squadron that flies the satellites, not to operate them too aggressively because I have to save fuel.”
Moving between different geosynchronous orbital planes or inclinations costs a significant amount of fuel, he said. “They actually have to think about six months to a year about the various things [they] want to look at,” Shaw said. “We have to find the easiest traveling salesman [route] to get to each of these objects to really conserve that fuel because it’s got to last a full lifetime.”
The GSSAP satellites also must approach objects gradually. “They can’t just hit the gas from a little ways away—just kind of come in fast and take a look before the object has a chance to realize what angle they’re coming in on,” Shaw said.
The maneuverability of GSSAP satellites and other surveillance spacecraft is akin to the German Zeppelin airships that conducted slow-moving aerial reconnaissance during World War I, he said.
Rapid maneuvers in space often rely on chemical propulsion, a system that uses chemical reactions to release energy and accelerate gases through a nozzle, creating thrust. The type has low specific impulse but high thrust—meaning, it is inefficient but quick.
For longer journeys, spacecraft often use electric propulsion, a system that typically uses electricity generated by a solar panel to positively charge a propellant and then uses electromagnetism to accelerate it out of the thruster. The type has higher specific impulse but lower thrust, so it is an efficient way to travel long distances but not powerful enough for rapid maneuvers.
The Space Force would like the ability “to maneuver without regret” to examine suspicious Russian and Chinese spacecraft in geostationary orbit and beyond. To do this, it needs both long-distance endurance and the ability to sprint rapidly. The U.S. Defense Department has been funding a variety of technologies to achieve that, including nuclear propulsion.
DARPA, for example, is funding the Demonstration Rocket for Agile Cislunar Operations program to test a nuclear thermal rocket in orbit. The technology would use a nuclear reactor to heat a propellant to extreme temperatures before expelling it through a nozzle to create thrust. DARPA says nuclear thermal rockets offer a high thrust-to-weight ratio about 10,000 times greater than electric propulsion and 2-5 times greater specific impulse than in-space chemical propulsion.
In addition to new propulsion technologies, the Space Force is funding development of on-orbit refueling. In October, Northrop Grumman announced it had won a contract from the service to install hydrazine refueling valves on unnamed, not-yet-launched operational satellites.
The ability to top off a spacecraft with propellant would give the Space Force a tactical advantage over its adversaries, Shaw said. “If we had the ability to burn gas almost at will, we would change that current calculation,” he said. “We’d be able to move in a lot quicker and get away a lot quicker, before perhaps there is an awareness that we are even there.”
