China's satellite shoot-down isn't just a provocative, dangerous act, writes veteran space analyst Jim Oberg. It also marks the rise of a new kind of satellite-killing technology -- one in which a weapon is shot directly from the ground, to the orbiter up on high.
Previous anti-satellite weapons tests, conducted during the Cold War, involved either co-orbiting killer satellites (the Soviet approach) or an air-launched anti-satellite missile (the U.S. approach, also considered by the Soviets but never attempted). Some tests involved shooting ground-based anti-missile missiles toward satellites, but those missiles never hit their mark.That's because it's hard to nail an orbiter, traveling hundreds of miles up at thousands of miles per hour, from the ground. The fact that the Chinese were able to do it could have troubling repercussions beyond space, as one commenter to the FPSPACE list notes:
Assuming the [Chinese target satellite] was on the order of 3 meters in size, and assuming the kill was made in direct ascent mode as opposed to co-orbiting mode, this test demonstrates the capability to achieve a velocity error on the order of 3 meters / ~1000 seconds, i.e., way less than 1 cm per second. This has obvious implications for their CEPs [Circular Error Probables, the accuracy] of Chinese ballistic missiles.Now, Beijing seems to have cheated just a bit in this test, Oberg observes.
The last orbital data released by NORAD seem to show one end of the [Chinese target] satellite's orbit being raised by about 20 miles (32 kilometers). Such tweaking is characteristic of a satellite lining up its orbital path for a rendezvous with a ground-launched visitor. The international space station does this in preparation for Russian spacecraft visits.In fact, the reason the U.S. Air Force chose the air-launched anti-satellite system is that it does not have to have its target line up with a ground-based missile pad. Naturally, a real target in the real world would never make such a helpful maneuver.Without the targets maneuver to make itself easier to kill, a ground-based shot would likely have to be made from the side or out of plane, in space navigation parlance. With such a geometry, the final approach for physical contact occurs under much higher rates of angular change, making terminal guidance much more difficult. It can be done, but with less reliability.But even with some fudging, this remains a very serious technical accomplishment. Oberg's piece has lots more -- including some possible (repeat, possible) countermeasures to a satellite strike. Be sure to read the whole thing.Of course, for a long time, directly attacking the orbiter with another piece of metal seemed like the least likely, least effective way to knock a satellite out. Since 2004, the U.S. Air Force has had in its arsenal a series of radio frequency jammers, to interfere with satellite operations. Three or four times a year, small groups of junior officers gather at an Air Force Research Laboratory facility in New Mexico to figure out how to take American satellites off-line using nothing more than sweet talk and off-the-shelf gear.Then there are the lasers. Not only did China recently light up an American orbiter with a ground-based laser. But, as Dan Dupont reminds us, the U.S. military spent much of the 90's testing out a satellite-shooting beam weapon of its own: the Mid-Infrared Advanced Chemical Laser, or "MIRACL.""In October 1997, the Air Force commissioned a test of an ASAT [anti-satellite] system based on the MIRACL laser," the Union of Concerned Scientists notes. "This system was directed toward a satellite orbiting 420 km above the Earth. The MIRACL laser apparently had technical difficulties, but the results of the test were startling."
A lower-power (30-watt) laser intended for alignment of the system and tracking of the satellite was the primary laser source used during the test, and it appeared that this lower-power laser was sufficiently powerful itself to blind the satellite temporarily, although it could not destroy the sensor. That a commercially available laser and a 1.5 m mirror could be an effective ASAT highlighted a US vulnerability that had not been fully appreciated. Although the Pentagon described the test as defensive (i.e., to learn about the vulnerability of US satellites to laser attack), manyin particular the Russiansexpressed concern about the offensive capabilities of this system and whether it constituted a breach of the ABM [anti-ballistic missile] Treaty, and formally requested negotiations on an ASAT weapon ban.(Big ups: AT)ALSO:* China Tests Satellite Killer?* China Space Attack: Unstoppable* Satellite Killer's Broad Impact* Why Did China Smack the Sat?* China Sat-Killer Not Yet Weapons Grade?* Who Ordered the Satellite Strike?