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Space shuttle descends: Satellite turkey-shoot to commence

US Navy books vast Pacific firing area five days running

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Updated The American military has issued further warning notices to aircraft and shipping in the Pacific, offering further opportunities for US warships to destroy a malfunctioning secret spy satellite before it descends to Earth. Meanwhile, NASA has cleared the space shuttle Atlantis to land as scheduled in Florida this afternoon, allowing the first satellite shot to be attempted above the Pacific in the early hours of tomorrow morning (UK time).

Atlantis, having departed from the International Space Station on Monday, was until lately orbiting higher than the crippled spy satellite, like the ISS. Neither would have been at significant risk should the warships fire, according to the US government.

However, the planned attempt to break up the satellite using ballistic-missile defence interceptors will create a spreading cloud of debris, mostly still travelling at enormous speed above the atmosphere. US officials believe the satellite wreckage will mostly descend and burn up within hours of a hit, but nonetheless have decided to get the shuttle down before firing.

Atlantis needed to land by Friday, as its power supplies would have run out then. If the anti-satellite firing took place first, the shuttle could have been at risk from debris as it descended. At orbital velocities of several miles per second, even a very small fragment of satellite could wreck the shuttle totally; or at least cause enough damage for the heat and stresses of re-entry to be fatal, as in the Columbia disaster. Once the space shuttle commences re-entry, it has no option to abort and return to orbit.

Now, however, Atlantis is carrying out its de-orbit burn on schedule and will be safe on the ground at Cape Canaveral shortly after two in the afternoon UK time. That will leave the skies clear for the flotilla of US warships now at sea west of Hawaii to launch a specially-modified Standard SM-3 ballistic-missile interceptor into the path of the crippled spy sat as it hurtles overhead at approximately 0330 tomorrow morning UK time.

According to the US defence authorities, President Bush has delegated firing authority to defence secretary Robert Gates. Gates is due to commence a nine-day overseas trip tomorrow, but will apparently give firing orders "from the road, if necessary".

An initial warning to airmen blocked off a 1400-mile stretch of the Pacific between the hours of 0230 and 0500 tomorrow morning UK time. The spy satellite will be over the southwest edge of the warning zone at approximately 0328, and departing towards Canada less than three minutes later - perhaps in the form of a cloud of fragments, if an "exo-atmospheric kill vehicle" lofted by a triple-stage Standard rocket has managed to get precisely in the satellite's way.

Since the initial NOTAM (Notice to Airmen) was issued, another has been put out for the same area 24 hours later, indicating a time window for a subsequent shot if the first should miss. A separate warning to shipping specifies that hazardous operations may take place in that area during the same two-and-a-half-hour time slot for the next five days. The air warning will be updated daily, apparently.

The danger area doesn't change, despite the fact that the satellite's track above it will shift gradually westward as the days pass. (Sky-watcher Ted Molczan's pdf plot shows this plainly.) This is because the only hazard in the firing area itself is from falling boosters and so forth from the Standard interceptors - and perhaps from highpowered radars being used to track the satellite and assess the shoot. There is a standing NOTAM in the area warning of X-band emissions from the radar at the Pacific Missile Range Facility on Kauai, which would seem a logical one to use as it will have the satellite in sight as it passes above the firing area.

It has also been reported that the often-troubled radar-golfball-on-an-oilrig sea-based X-band radar (SBX) might be employed. Text purporting to be a NOTAM has been posted on skywatcher sites and (of course) Wikipedia. However, the NOTAM at least appears to be a fake, as it cannot be found on US government channels.

Actual satellite debris is unlikely to come down in the Pacific firing area - rather it will carry on along the spacecraft's original track, spreading and deviating in complex ways. Ten minutes after a hit, the centre of the wreckage cloud will be over Canada. Ten more minutes after that and the cloud will be racing southward above the Atlantic. Owing to the timing of the shot window, the frag cloud will then stay mainly over oceans for much of its predicted two-orbit lifespan - though it will graze western and southern Africa, and pass above Australia twice.

The Bush administration is still sticking firmly to its story that the shoot is aimed at rupturing the satellite's 40-inch hydrazine tank so as to prevent a toxic gas cloud on impact. China and Russia continue to evince boilerplate "concern" over the mission and possible militarisation of space.

Here at the Reg, we're obviously hoping for repeated, spectacular misses (the US Navy apparently only has three modded SM-3s on hand) followed by eventual sale of the secret sky-spy payload on eBay and further sensational revelations.

A Pentagon news conference is expected shortly after the initial firing, at around 0400-0430 tomorrow morning UK time. We'll keep you posted. ®

Update

AP reports that Pentagon spokesmen have said that the Northern Pacific is too rough for satellite-shooting just now, and they may need to wait until Friday to commence firing.

"We don't anticipate the weather being good enough today," said an unidentified military officer. "It has not been enough for us to say 'no' and put the launch mission off ... But it would take improved conditions to proceed."

The spokesman confirmed that everything else is ready, and said the last possible day for sat-shooting would be the 29th. After that the effects of the atmosphere on the descending spacecraft will make it impossible to hit with an SM-3.

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