2016 Sep 29
Thursday, Day 273
Planning The Event
In the autumn of 2000, Yuri Koptev, head of the Russian Space Agency indicated that the preferred re-entry location for Mir was around 2000 kilometres to the East of Australia. Using that information is was possible to make a first stab at calculating the ground track (the Koptev Corridor) - see the "De-orbit-1" article on the index page, and also get a view of the time of day it would likely happen. 2001 mid-January, Russia let it be known that the target point for the major pieces of surviving debris was near to 47 degrees South, 140 degrees West longitude.
An earlier study undertaken by Spaceflight Control Centre in Moscow (TsUP) concluded that the de-orbit manoeuvres could be undertaken by a docked Progress spacecraft but that Mir's orbit would have to have descended to approximately 200 x 225 kilometres. A fully-loaded Progress tanker would then be able to provide the necessary retro-thrust.
The task of Progress would be to get Mir down to approximately 220 x 160 kilometres with perigee over the southern Pacific Ocean, and then a final burn of the Progress engines would ensure re-entry. This final Progress engine burn would need to be of ten minutes duration using the main thrust chamber firing in parallel with the smaller orbit correction thrusters. The smaller thrusters would then continue to fire for a further three minutes, making thirteen minutes of burn time in total.
The precision with which Progress would be able to bring Mir in along the target re-entry track would be dependent on controllers being able to steer the orbit into exactly the right position with respect to the Earth. The original parameter published by Russia as determining the ground track on re-entry day was the first orbit ascending node to the West of 20° East longitude (nominally an ascending node at 2.5° west). Once the date was set for March 23, Mission Control settled on re-entry from an orbit with an ascending node at 5 degrees West longitude. For comparison the originally described "Koptev Corridor" resulted from an ascending node at 19° West.
Addendum - Execution
2001 March 23, Mir was brought down from orbit by three firings or burns of the Progress M-1-5 propulsion system. Two of them, at approximately 90 minute intervals, were used to bring Mir's perigee down to an altitude of 160 kilometres above the Earth's surface.
Two circuits of the Earth later, a final firing pushed perigee down to about 80 kilometres to ensure that the complex entered the atmosphere to burn up. According to Mission Control, the main impact area was near to 40° South, 160° West with debris falling in the area 1,500 kilometres before this point and 1,500 kilometres beyond it. The scatter of debris was estimated to be 100 kilometres either side of the track.
Mission Control's issued times for the re-entry burns as estimates before the event and actuals after it. Data in both cases was incomplete. The "best guess" as to the actual timings is listed below.
For those with satellite tracking computer programs, the Twoline Orbital Element set below will generate a good approximation to Mir's final half circuit of the Earth.
MIR 1 16609U 86017A 01082.20581073 .00000000 00000-0 00000-0 0 04 2 16609 51.6441 249.7498 0105148 239.7414 119.3179 16.51075923 07
Significant contact with the atmosphere occurred at 100 kilometres altitude when some of Mir's lighter external elements were torn off as a result of the rush through the rarified air. At 90 sufficient heating for Mir's hull to start burning and enclose itself in a glowing sheet of hot plasma. The orbital complex broke apart about that time and the main modules and other large fragments, each surrounded by a glowing sheet of plasma, were visible from Fiji against the evening sky. Television pictures were transmitted around the world within a few minutes of the event.
An eleventh hour decision led to the final burn of the Progress M1-5 engine being lengthened. It was allowed to continue until it ran out of propellant, resulting in a velocity change of 28 metres per second against a planned 23.5 metres per second. This moved the main impact location further north than the 44.2° South, 150.5° West location given on March 22. Fiji, which enjoyed a good view of the event, is the group of islands southward down the track from the 90 kilometre point on the map below.
The planning version of the map, and estimates of the re-entry timings and heights, were available through this web page for several weeks prior to the re-entry. They were worked out from a combination of Russian information and data from other sources. A major, useful, piece of information came from when NASA presided over the re-entry of the 14-tonne Compton Observatory in 2000. A study was made of the burn-up and fall of debris. Compton started to burn just above 90 kilometres and broke up around 70 kilometres high. Pieces then fell into the Pacific. Another useful piece of information was TsUP's original estimate that debris would fall into an area from 1,800 kilometres before the aiming point to 2,600 kilometres beyond it.
The Last Moments
The timings of the very last events were roughly as below. The main impact point was somewhat short of the 47° South, 140° West announced in January. The location announced after re-entry was 40° South, 160° West with a debris spread of +/- 1,500 kilometres along track and +/- 100 kilometres laterally, reduced from the earlier estimate due to the steeper re-entry angle.
Local Solar Time is listed to give an indication of from where events might be visible. Sunset in this area of the southern Pacific on March 23 was at about 18:20 Local Time:
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