The International Space Station (ISS) conducted a Pre-Determined Debris Avoidance Maneuver (PDAM) on Monday, dodging part of a spent Minotaur rocket body. The space shove was provided by the engines on the docked Progress M-26M spacecraft, with the burn lasting over five minutes – in turn providing some light entertainment to the Station’s crew.
The requirement of moving the Station out of the path of a potential debris threat is not uncommon.
The huge structure of the ISS, racing around the planet at 17,500 mph, is routinely threatened by what are called conjunction threats, usually from items 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.
This was the situation for Monday’s PDAM requirement, after tracking showed debris relating to an expended rocket stage from an old Minotaur launch was threatening to enter a corridor that could have resulted in a very small chance of an impact.
The Minotaur debris in question was, according to NASA, from a 2013 launch, meaning it was either the ORS-3 mission for the US military, which utilized a Minotaur I rocket with a 29 satellite haul, or the Minotaur V launch with the Lunar Atmosphere and Dust Environment Explorer (LADEE).
Thanks to good orbital tracking, most of the conjunction threats 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 order would be to 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 with this event.
ISS controllers decided to utilize the docked Progress M-26M spacecraft, which executed a 5 minute, 22 second firing at 19:58 pm GMT to slightly raise the station’s orbit and distance it from the conjunction threat that was projected to pass within three statute miles of the complex later in the day.
The vehicle behaved without issue, following a previous reboost that suffered from a false start.
The maneuver raised the station’s altitude by just 106 feet at apogee and 7/10 of a mile at perigee, resulting in an ISS orbit of 254 x 244.8 statute miles.
NASA noted the maneuver will have no impact on the scheduled landing later this week of Expedition 43.
Commander Terry Virts of NASA, Soyuz commander Anton Shkaplerov of Roscosmos and Flight Engineer Samantha Cristoforetti of ESA are completing preparations for their return to Earth and a parachute-assisted landing in Kazakhstan in their Soyuz TMA-15M spacecraft at 13:43 pm GMT this Thursday.
The PDAM provided the crewmembers with some amusement for these final days of their expedition, with the astronauts staging a visual demonstration of the acceleration provided during the firing of the Progress’ engines.
The ISS loop noted Samantha was filmed slowly drifting out of view as ISS accelerated out from under her. The crew also joked about their hair “blowing in the wind” during the PDAM…..for everyone except Scott Kelly.
(Images: Via ESA, NASA, and L2).
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