With much fanfare and media hype surrounding the event, the US shot down a dying spy satellite on February 20, 2008. US spokespersons stated that the shoot-down was necessary because the satellite, at the end of its life, was soon to re-enter the earth's atmosphere and break up, posing a greater danger than other similarly disintegrating satellites because it carried a large load of toxic fuel. Some commentators observed that such capabilities could also help protect the earth from meteorites.
But there were clearly other motivations as well. The shoot-down was an opportunity for the US military to test and demonstrate anti-satellite weapons capabilities, an extension of the Reagan-era "star wars" programmes. It was also undoubtedly a response to a similar satellite shoot-down conducted by China just over a year ago, an event sharply attacked by the US and its Western allies as being a provocative action that would trigger an arms-race in space.
With so many possible ramifications, the print and electronic media, not to mention the now ubiquitous internet blogosphere, have been full of commentary and speculation, often misinformed. This article tries to clarify some major issues. Does this represent a technological breakthrough? What is the difference between the US and Chinese shoot-downs? What is the relationship between the weapons systems used and systems currently deployed or under development. What are the implications for militarisation of space? And are we witnessing a new arms race?
The US shoot-down
The dying US satellite was a highly classified 2500 kg National Reconnaissance Office NROL-21 (military designation US-193) satellite that had fatally malfunctioned almost immediately after its launch in December 2006. At the point of impact, the satellite was 247 km above the earth and traveling at 27,000 kmph. It was shot down by a single SM-3 missile fired from the USS Lake Erie, a battleship equipped with the Aegis missile defence system based in the Pacific Ocean near Honolulu in Hawaii. The ship had an additional missile in case the first one missed the target. Another Aegis ship standing by had a missile ready while a similarly equipped third ship monitored the entire exercise from Pearl Harbour. The satellite being shot down was a spy satellite, and anti-missile technology was used to shoot it down. Yet the US Defence Department was at pains to emphasise that the satellite was shot down due to safety concerns alone -- neither to prevent exposure of sensitive technologies if it fell to earth in large chunks, nor to test US anti-satellite capabilities.
Some worry was legitimate. With a decaying orbit, meaning the satellite was getting ever closer to the earth, it would soon have re-entered the earth's atmosphere with some potential dangers. This happens with all satellites at the end of their life, and most of them simply burn up in the atmosphere due to the friction and heat generated. But given the orbital path of US-193, the fact that no controls were available, and that 450kg of toxic hydrazine was being carried, it was decided not to leave the satellite to the mercy of gravity alone. There was a chance that, instead of re-entering the atmosphere, the satellite may have bounced off it, after which its trajectory would have been unpredictable and the consequences of its re-entry uncertain.
Video imagery of the shoot-down showed a large explosion, fairly clear evidence that the fuel tank had been hit, although both the US Defence Department and NASA would not confirm this till further conclusive evidence was received. Some reports said that destruction of the hydrazine was proved by readings from colour spectrometers using the principle that each element or chemical gives off a distinctive colour.
However genuine the reasoning behind the shoot-down, although not everyone is convinced that enough hydrazine would have survived the re-entry to pose a threat, it certainly provided excellent cover for the US military to test its anti-satellite or "asat" systems. The US has been developing asat capabilities since the ‘80s but had last destroyed a defunct satellite in low-earth orbit as far back as 1985 using relatively primitive methods, namely an air-to-air missile fired from an F-15 aircraft flying at an altitude of 80,000 feet (25,000 metres approx). The capability to target and destroy satellites is a major tactical advantage, and data gathered from a real-time test using contemporary weapons systems would be invaluable to the US military.
In the media hype, many commentators described the shoot-down as something out of science fiction. But was it really quite so extra-ordinary?
Technology used to shoot down satellites is the same as in anti-ballistic missile systems: both target fast-moving objects following a predictable path. Contemporary kill missiles do not carry explosive warheads (unlike early precursors which carried even nuclear-tipped warheads to make up for lack of accuracy and absence of precision guidance systems) but physically ram into the targets which are "killed" by the huge quantity of energy released by the collision of the two objects at a relative speed equal to the sum of their separate velocities towards each other.
In the US shoot-down, the missiles used were precisely such anti-missile weapons derived from the US Strategic Defence Initiative or "star wars" programme of the ‘80s. The ship-based Aegis systems are state-of-art integrated tracking, computer control and network communication weapons systems used against targets in the air, on surface or underwater. The basic Aegis systems were subsequently upgraded to Ballistic Missile Defence (BMD) systems designed to destroy short and medium-range ballistic missiles either in the post-boost phase (after their rocket motors have done their job allowing mainly momentum and gravity to complete the task) or just prior to re-entry into the atmosphere, both times when ballistic missile trajectories are most predictable.
In the present case, the systems had to be slightly re-programmed to adjust for the greater speed of satellites compared to ballistic missiles. Even long-range intercontinental ballistic missiles (ICBMs), that reach far higher altitudes and therefore attain greater descent velocities, would reach speeds of around 10,000 kmph whereas US-193 was traveling around three times faster. A missile is also "hot" whereas satellites are "cold" with no source of power and thus more difficult to track by the infra-red sensors in the kill missile.
On the other hand, satellites are relatively easier targets than missiles. Satellites have more predictable trajectories and go around the earth several times a day (US-193 orbited the earth 16 times daily) giving many opportunities for the anti-missile system to track, acquire data and destroy the target. If the target is missed the first time, another try is possible in the next orbit, or the next one.
US & Chinese tests
Given the known level of sophistication in technologies available with space-faring nations, the US anxiety and hostility to China's anti-satellite test was astonishing.
China shot down a defunct weather satellite on January 11 at an altitude of 860km using a land-based SC-19 medium-range ballistic missile. The range was much less than that of ICBMs that China has had for many years, and the missile too is familiar. China has had an anti-missile programme since the early 1970s. Indeed, China had even conducted an anti-satellite test in January 2006, again to US condemnation, although its results were not conclusive, making the 2007 one the first known successful Chinese "asat" test.
The US lodged a formal diplomatic protest. US allies Britain, Japan and Australia also registered protests but were unashamedly silent on the US shoot-down. Japan's concern "from the point of view of security as well as peaceful use of space" obviously did not extend to the US demonstration of anti-satellite weaponry!
To hide its embarrassment at having shot down a satellite within a year of loudly condemning China for the same, US spokespersons tried hard to demarcate the US action from China's. According to the US, its own satellite shoot-down – which was announced in advance – was necessary because of the potential danger, and left very little debris close to the earth's atmosphere where it will soon disintegrate, whereas China's test was conducted without warning, was not prompted by any need other than military testing and was therefore "aggressive", and left considerable debris at much higher altitude where the pieces would be in orbit for several months posing a danger to other orbiting satellites.
These arguments are specious, post-facto justifications and do not merit serious consideration. Having advance warning or not made no difference to other countries and peoples. The Chinese satellite is said by NASA to have broken up into 1600 pieces, but David Wright of the Union of Concerned Scientists in the USA said the US satellite was far larger and its destruction may have produced 100,000 pieces, small but still dangerous to vehicles in space. It should also be noted that there are many tons of dead and defunct satellites orbiting the earth as "space junk". Finally, the US "asat" systems, being ship-based rather than land-based like the Chinese counterpart, are far more deadly and aggressive being mobile across three-fourths of the earth's surface.
Drive for US hegemony
The US posture was simply the global hegemon's frustration at a rival power demonstrating a capability that the US seeks to monopolise, and thus devaluing the threat of overwhelming US military superiority.
Low-earth satellites have now become an integral part of US military structure. Navigation, communication, target acquisition and weapons guidance systems, command and control systems, and real-time surveillance, all based on such satellites, are routinely used by land, sea and air forces of the US military. The Chinese tests highlighted the vulnerability of these satellites and systems that depend on them. One US security analyst, for instance, pointed out that if the US got into a conflict with China over Taiwan, China had now shown that it could quickly knock out US satellites and thus "put out US eyes and ears" and seriously damage the US war machine.
If the US goes to war, that too against a major power, it should certainly expect some opposition! But even here there is some exaggeration. Simple reconnaissance and GPS satellites may be in low orbits, but truly strategic satellites orbit the earth at much higher altitudes. Navigation satellites are 20,000 km above the earth and communications satellites orbit the earth at 40,000 km. At such altitudes, orbiting speeds being much lower, the impact energy would be only about a tenth as high as in the tests under discussion, thus reducing the "kill probability". Weapons systems against such satellites are yet to be developed.
If anti-missile technologies keep advancing, these problems would undoubtedly be solved before long. So the answer surely lies in a global agreement to prevent development and deployment of such weapons and to insulate space from the arms race.
But, as with nuclear weapons, here too the US has asserted its right to possess a class of weapons even while enforcing a structure in which others are denied similar capabilities. The US has therefore been the main obstacle to a comprehensive ban on militarisation of space.
Under a space policy set in place by President George W Bush in August 2007, the US asserts its right to "freedom of action in space" and to "deter others from either impeding those rights or developing capabilities intended to do so." The policy also states that the US would "deny, if necessary, adversaries the use of space capabilities hostile to US national interests."
As recently as February 12, 2008, Russia and China jointly submitted a proposal to the annual UN Disarmament Conference for an international treaty to ban the deployment of weapons in outer space. The draft treaty called for "prevention of the placement of weapons in outer space [and] the threat or use of force against outer space objects." To no one's surprise, the US flatly refused to even discuss such a proposal, with the US spokesperson stating that binding arms control agreements "are simply not a viable tool for enhancing the long-term space security interests [read hegemony] of the United States…"
One doesn't need to look for hidden meanings of smiles by Chinese leaders or of invitations by China to play ping-pong. By conducting its anti-satellite test just prior to the Disarmament Conference, China was sending a clear message: there is urgent need for a global agreement to prevent militarisation of space. Otherwise the next theatre of war will be the heavens!