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ISS orbit raised 6km to make favourable Soyuz landing conditions

November 18, 2011, 9:51 UTC+3
The manoeuvre was conducted in an automatic mode with the help of two correcting engines of the Zvezda service module
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MOSCOW, November 18 (Itar-Tass) — Russia’s Mission Control Centre (MCC) on Friday conducted an operation to correct the orbit of the International Space Station (ISS), aimed at creating favourable conditions for the landing of the station's crew and docking with the next manned Soyuz spacecraft.

The MCC told Itar-Tass that the “orbit adjustment passed normally.” The manoeuvre was conducted in an automatic mode with the help of two correcting engines of the Zvezda service module. “The use of powerful engines is much more effective from the viewpoint of fuel consumption,” the MCC explained.

The engines were fired at 08:07 MSK for 217 seconds. During this time, the average altitude of the station’s orbit, according to expert estimates, increased by about 6 kilometres and reached about 399.3 kilometres. The average altitude is a virtual value used by ballisticians. It is an imaginary circular orbit with the period of revolution around the Earth equal to the station’s elliptical orbital period, the MCC said.

The combined 6-men crew of the ISS Expedition 29 that from Wednesday has been on the orbital station’s mission had been warned in advance about the manoeuvre conducted on a command from the Earth. As the orbit correction operations do not require the participation of astronauts they were sleeping during that time (their reveille on Friday is scheduled for 10:00 a.m.

The ISS orbit adjustment manoeuvres are usually carried out in order to bring the station to the desired orbit for docking with cargo or manned spacecraft, to create conditions for a successful landing, as well as to avoid collision with space debris - small meteorites, fragments of old satellites and ships. For example, it so happened less than two months ago, on September 29, when the station had to be quickly moved from the dangerous proximity to a fragment of a carrier rocket.

At the low altitudes at which the ISS orbits there is a variety of space debris, consisting of many different objects including entire spent rocket stages, dead satellites, explosion fragments—including materials from anti-satellite weapon tests, paint flakes, slag from solid rocket motors, coolant released by RORSAT nuclear powered satellites and some of the 750,000,000 small needles from the American military Project West Ford. These objects, in addition to natural micrometeoroids, are a significant threat. Large objects can destroy the station, but are less of a threat as their orbits can be predicted. Objects too small to be detected by optical and radar instruments, from approximately 1cm down to microscopic size, number in the trillions. Despite their small size, some of these objects are a still a threat because of their kinetic energy and direction in relation to the station. Spacesuits of spacewalking crew could puncture, causing exposure to vacuum.

Space debris objects are tracked remotely from the ground, and the station crew can be notified. This allows for a Debris Avoidance Manoeuvre (DAM) to be conducted, which uses thrusters on the Russian Orbital Segment to alter the station’s orbital altitude, avoiding the debris. DAMs are not uncommon, taking place if computational models show the debris will approach within a certain threat distance. Eight DAMs had been performed prior to March 2009, the first seven between October 1999 and May 2003. Usually the orbit is raised by one or two kilometres by means of an increase in orbital velocity of the order of 1 m/s. Unusually there was a lowering of 1.7 km on 27 August 2008, the first such lowering for 8 years. There were two DAMs in 2009, on 22 March and 17 July. If a threat from orbital debris is identified too late for a DAM to be safely conducted, the station crew close all the hatches aboard the station and retreat into their Soyuz spacecraft, so that they would be able to evacuate in the event it was damaged by the debris. This partial station evacuation has occurred twice, on 13 March 2009 and 28 June 2011. Ballistic panels, also called micrometeorite shielding, is incorporated into the station to protect pressurized sections and critical systems. The type and thickness of these panels varies depending upon their predicted exposure to damage

The previous orbit correction manoeuvre was conducted on October 26. The ISS orbit gradually loses its altitude – several dozen metres daily under the influence of Earth’s gravity and other factors.

The landing of the Soyuz TMA-02M digital spacecraft, which will return to Earth Russian cosmonaut Sergei Volkov, Japanese astronaut Satoshi Furukawa and American astronaut Michael Fossum is scheduled for November 22. The launch of the next Soyuz spacecraft with the ISS Expedition 30/31 crew is scheduled for December 21.

The ISS is a joint project between the five participating space agencies, the American NASA, the Russian RKA, the Japanese JAXA, the European ESA, and the Canadian CSA. The ownership and use of the space station is established in intergovernmental treaties and agreements which divide the station into two areas and allow the Russian Federation to retain full ownership of Russian Orbital Segment (ROS)/(RS), with the US Orbital Segment (USOS) allocated between the other international partners. The station is serviced by Soyuz spacecraft, Progress spacecraft, the Automated Transfer Vehicle and the H-II Transfer Vehicle, and has been visited by astronauts and cosmonauts from 15 different nations.

The ISS provides a platform to conduct scientific research that cannot be performed in any other way. Whilst unmanned spacecraft can provide platforms for zero gravity and exposure to space, the ISS offers a long-term environment where studies can be performed potentially for decades, combined with ready access by human researchers over periods that exceed the capabilities of manned spacecraft. Kibo is intended to accelerate Japan’s progress in science and technology, gain new knowledge and apply it to such fields as industry and medicine. The Alpha Magnetic Spectrometer (AMS), which NASA compares to the Hubble telescope, could not be accommodated on a free flying satellite platform, due in part to its power requirements and data bandwidth needs. The Station simplifies individual experiments by eliminating the need for separate rocket launches and research staff.


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