Europe’s ATV-5 cargo ship helped ‘shove’ the International Space Station (ISS) out of the path of a piece of space debris this week. The Pre-Determined Debris Avoidance Maneuver (PDAM) was required after a tracked object – possibly a lens cap/cover – from the Chinese spy satellite, Yaogan 12, became a “repeating conjunction concern” for the orbital outpost.
The requirement of a Debris Avoidance Maneuver (DAM) is not uncommon.
The ISS – a huge structure – is racing around the planet at 17,500 mph, in an orbit that contains threats that are usually tagged under the MMOD (Micrometeoroid Orbital Debris) designation.
The larger pieces of debris – usually originating from expended satellite and rocket hardware – are tracked by Space Command/NORAD, allowing for any threats to spacecraft to be known in advance, providing them a heads up to move into a different path and thus avoid a collision.
Most of the time the threats – known as conjunctions – are evaluated over time and seen to be avoiding the Station. Sometimes they are seen late, with no time to ‘steer’ the ISS out of the debris’ potential track.
One such incident occurred on March 13, 2009 – when a “RED Late Conjunction” threat resulted in NASA’s Expedition 18 Commander Mike Fincke, Russian Flight Engineer Yury Lonchakov, and NASA’s Sandra Magnus being asked to ‘evacuate’ into the “safe haven” of the docked Soyuz, as the ‘25090 PAM-D’ debris closed in on the Station.
Per Flight Rule B4-101, this “late conjunction” call results in the crew being ordered to close the hatches between Station modules and enter the Soyuz vehicles – which serve as lifeboats during their docked stay at the ISS – before TCA (Time of Closest Approach) breaches the 10 minute mark.
The crew will initiate an emergency departure from the Station if the debris threat realizes itself into an impact and causes a breach of the life support environment.
The 2009 threat, which had the capability of puncturing one of the Station’s modules, was a simple ‘yo weight’, originally part of a Delta PAM-D stage used to launch GPS 37 in 1993.
After a tense wait, the threat passed by the Station without making an impact, allowing for the crew to re-enter the ISS and re-open the hatches to the modules.
DAMs can be conducted by a number of docked vehicles, providing a push to move the Station out of the debris threat’s path. The Space Shuttle providing such a role when required by Station, while the Russian Progress also lends a hand on occasion.
The Station can even conduct DAMs on her own, using the thrusters on the Zvezda module.
However, a docked spacecraft can save the use of the ISS’ propellant reserves, as was the case this week.
The vehicle has been assisting the Station with more than just its array of supplies, but also with reboosts and also a PDAM back on October 27. Such requirements are factored into an ATV mission, with a large amount of onboard propellant available.
(ATV-3 Docking Animation created from 70 hi res ATV-3 docking images acquired by L2 – LINK).
This week’s PDAM was more interesting than most, given the debris was identified as from a Chinese spy satellite.
“Pre-Determined Debris Avoidance Maneuver (PDAM): The team performed a Pre-Determined Debris Avoidance Maneuver (PDAM) of 0.5 m/s in order to dodge a repeating conjunction concern with Object 39372 (Yaogan 12 Debris),” noted L2 ISS Status information.
Yaogan-12 was launched back in November, 2011 by a Long March 4B. It is a second generation electro-optical observation satellite equipped with a small angular observation system.
The Chinese media always class this range of satellite as remote sensing birds that are used for “scientific experiments, land survey, crop yield assessment, and disaster monitoring.” However, it is widely known in the West that they are based on the Phoenix Eye-2 satellite platform and used for military purposes.
While the satellite itself was not the debris threat, the early cataloging of the associated debris – known as object #39372/2011-066G, YAOGAN 12 DEB – could be the satellite’s discarded lens cap or cover.
With the Station shoved out of the object’s path, nominal operations are continuing. Also, the timing of the PDAM also killed two birds with one stone – removing the need for a pre-planned reboost, that was also to be conducted by ATV-5.
“The PDAM was completed nominally, and the ISS is back in a nominal Torque Equilibrium Attitude (TEA),” added ISS Status. “Since the PDAM was executed , the reboost that was planned for later is no longer required, and will not be performed.”
(Images: Via ESA, NASA, and L2).
(Click here: http://www.nasaspaceflight.com/l2/ – to join L2 and directly support NASASpaceflight.com).