Tuesday, February 1, 2011

ISS conjunction alert cancelled

NASA are reported a conjunction alert for the ISS: A piece of space debris (object 37117 in the tracking database consisting of debris from Russia’s COSMOS 2252 satellite) may pass within 0.115 km of the ISS. ISS mission controllers are now assessing what action to take, including a potential debris avoidance manoeuvre (DAM) as soon as tomorrow.

Just as ESA’s Emilio de Pasquale mentions in our flight dynamics profile video (see post below), the ISS is a big, living object – a moving ‘target’ for the ATV Johannes Kepler. Every change in the ISS orbit – including any avoidance manoeuvre in the coming days – will require recalculations of ATV-2′s planned trajectory. Looks like the flight dynamics teams for both the ATV and the ISS are busy this week!

According to NASA, ISS flight controllers were contemplating a DAM as early as 9:14 CET on 1 February. Full details after the jump.

Tracking data on the object are sparse and the small radial miss distance of the object (0.115 km – just 115 metres) warrant close monitoring.

The predicted time of closest approach for the conjunction is during HTV robotics operation scheduled for Tuesday morning, 1 February. The standard template for performing the manoeuvre as close as possible to the time of closest approach (thus buying time to cancel if not required – no one likes to use fuel unnecessarily). The orbit change would take place at 9:14 CET on 1 February.

Initial coordination with the ISS Flight Control Team has led to an acceleration of the engine ignition time by three orbits to allow the robotics operations to continue as planned. BY coincidence, an ISS reboost of 0.6 m/second was already planned for 9 February. Engineers are investigating if tomorrow’s debris avoidance manoeuvre could replace this reboost meeting the same constraints which ensuring a safe trajectory from the conjunction.

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