An Air Force microsatellite successfully completed a series of orbital rendezvous maneuvers with another satellite, program officials said Friday, in the first key test of the XSS-11's mission. If future tests are equally successful, the U.S. military hopes to modify the design of the microsatellite for a wide array of space missions.
The exercises so far have been made around the derelict upper stage of the Minotaur rocket that launched XSS-11 (Experimental Small Satellite #11) five months ago. Program manager Vernon Baker said XSS-11 made its first approach in late July at a distance of 1.6 kilometers, and has since done "several others," coming as close as half a kilometer.
More approaches are planned in the coming months, he continued. “We have certain demonstration objectives for each one,” he explained, “using different sensors, different guidance algorithms, and so forth.”
The accomplishment is a significant one. This spring, a similar attempt by NASA to deploy a space rendezvous robot ended in an embarrassing flop, when its DART spacecraft crashed into the object it was supposed to be approaching.
So far the XSS-11 microsatellite has been flown manually, with each engineers on the ground making course corrections based on computer calculations. Eventually, the microsatellite should be able to make its own course corrections, without assistance from the ground. “We’re running the autonomous planner in the background,” Baker said, and later tests will let the spacecraft fly itself in an entirely hands-off mode.
Although space experts recognize at least half a dozen valuable practical applications of so-called autonomous rendezvous, by far the most controversial possible use would be to attack another country’s satellite. Lobby groups in the West, and spokesmen for foreign governments such as Russia and China, have denounced the XSS-11 mission as a prelude to deploying space weapons to attack foreign satellites.
But other space experts pooh-pooh such ideas as unrealistic. “A weapon needs fast response times and high kill probability,” one expert said privately. "Creeping up on a target for weeks only to have to carry along a howitzer to kill it is a stupid design.”
Program manager Baker said the test flight was designed to specifically avoid any physical contact with the rendezvous object. “Ninety-five percent of our work is designed around creating passively safe trajectories,” he said. “If we hit, we fail.”
The Lockheed Martin-built XSS-11 is a roughly cubical dishwasher-sized spacecraft and weighs only about 300 pounds, tiny by spacecraft standards.
Managed by the Air Force Research Laboratory’s “Space Vehicles Directorate Integrated Space Experiments Division” at Kirtland AFB in Albuquerque, N.M., and operated by the Air Force Space and Missile Systems Center's Detachment 12 there, the satellite was launched by a modified Minuteman missile on April 11. It spent the next several months activating and exercising its sensors and guidance computers.
Small spacecraft with autonomous rendezvous capabilities are now being developed in at least half a dozen projects, some governmental and some corporate. A small British satellite and a pair of Japanese microsatellites have already conducted space tests.
Among the commercially important missions for such vehicles would be the delivery of consumables, such as propellant, to other satellites, adding small modules for supplemental electrical power or other faltering services and resupplying the international space station.
NASA’s plan for the Hubble repair envisioned a robot spacecraft that carried a manipulator arm to perform complex hardware changeout, and although that idea has now been dropped, a Russo-German project called TECSAS is attempting to develop the same ability. In another application, a canister carrying soil and rock samples could be fired into orbit by a Mars lander and then be picked up by a robot ship that would return it to Earth.
Baker said the Air Force project meshes well with the capabilities being developed elsewhere. “Like XSS-11, they are all about how do we connect, replenish, replace and repair in space,” he said. “And in a broader scope,” he added,” it’s about how do you operate safely around another object in space.”
The Air Force is studying these basic capabilities as well as more specific military applications, senior Defense Department scientists said on condition of anonymity. Two potential military missions in particular are worth considering for follow-on testing, they suggested.
First, the U.S. needs a means of inspecting its own military satellites for external damage, either from accidental breakdown or from hostile activity, and a small "scout satellite" capable of detaching, flying around and reattaching itself could provide critical insights in diagnosing — or even warding off — such damage.
Secondly, a U.S. spacecraft near a foreign spacecraft could perform a number of highly valuable but entirely passive functions. Aside from a detailed physical inspection with a resolution far better than possible from a distance, an object in such a location would be able to intercept narrow-beam communications — radio, laser beam, whatever — that otherwise might elude ground-based sensors.
Such applications (and a few others that experts would not describe in detail) are of a fundamentally military nature, but are not "weapons" in any practical sense. They are neither illegal nor in any way destabilizing, the experts insist.
“It is not designed nor is it a U.S. objective to develop hit-to-kill systems or any direct interference,” a senior Defense Department space expert said. “These experiments are designed to do things in close proximity of other satellites. ... This is much different, and far more complicated , than hitting or disabling satellites.”
One top Russian defense analyst agrees with this assertion. Russian Maj. Gen. Vladimir Dvorkin, a senior scientist at the Russian Academy of Sciences’ Center for International Security, told journalists in June that Russian saber-rattling about “responding” to alleged U.S. space weapons was unnecessary because “in the near future as there are no such projects in the world.”