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Mission Control to begin manoeuvres to adjust ISS orbit

October 19, 2011, 17:44 UTC+3

“Two powerful corrective (propulsion) engines of the Zvezda service module will be used for raising the orbit,” according to the MCC

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MOSCOW, October 19 (Itar-Tass) — The Mission Control Centre (MCC) on Wednesday will conduct the first of two operations to adjust the orbit of the International Space Station (ISS) in order to create favourable conditions for docking with the Progress cargo spaceship and the manned Soyuz spacecraft that will take into orbit the next expedition to the ISS.

The MCC outside Moscow told Itar-Tass that “according to the ISS ballistic support program, the ISS orbit adjustment is planned for October 19.” The purpose of this operation is the formation of the station’s working orbit in accordance with the strategy of maintaining the height of its flight and ensuring the conditions for docking with the cargo spacecraft, the MCC reported. A second similar manoeuvre is scheduled for October 26.

“Two powerful corrective (propulsion) engines of the Zvezda service module will be used for raising the orbit,” according to the MCC. The engines’ ignition is scheduled for 20:06 MSK, he said. For 106 seconds of their work the ISS will receive an additional impetus of 1.7 m/s and rise for about 2.8 kilometres.

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.

The ISS orbit gradually loses its altitude – several dozen metres daily under the influence of Earth’s gravity and other factors.

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 launch of the Progress M-13M cargo spacecraft is scheduled for October 30, and the Soyuz TMA-22 spaceship, which will take into orbit crewmembers of the ISS Expedition 29/30 will be blasted off on November 14.

The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes. The ISS serves as a research laboratory that has a microgravity environment in which crews conduct experiments in many fields including biology, human biology, physics, astronomy and meteorology. The station has a unique environment for the testing of the spacecraft systems that will be required for missions to the Moon and Mars. The station is expected to remain in operation until at least 2020, and potentially to 2028. The ISS is a joint project between the five participating space agencies, the American NASA, the Russian Roskosmos (RKA), the Japan Aerospace Exploration Agency 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).


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