Editing ISS Propulsion Module

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[[Image:ISS Propulsion module.jpg|thumb|right|300px|ISS Propulsion Module (NASA)]]

The '''ISS Propulsion module''' was proposed as a backup to functions performed by the [[Zvezda (ISS module)|Zvezda Service Module]] and [[Progress (spacecraft)|Progress spacecraft]]. Critical ISS functionality such as guidance, [[navigation]], control and propulsion are provided only by Russian (Zvezda and Progress) and the European ([[Automated Transfer Vehicle|ATV]]) spacecraft.<ref>{{cite web|url=http://www.esa.int/export/esaHS/ESAOXX0VMOC_iss_0.html |title=ESA - Human Spaceflight and Exploration - International Space Station - DMS-R: ESA's Data Management System for the Russian Segment of the ISS |publisher=Esa.int |date=2009-01-16 |access-date=2012-01-26}}</ref> A Propulsion Module would have been needed for ISS altitude maintenance and reboost, debris avoidance maneuvers, attitude control and propellant supply in the event the Zvezda Service Module was not available (launch failure, etc.) to the [[International Space Station]]. If the Zvezda had not been available, the [[Interim Control Module]] would have been used at first. It only had a lifetime of three years; then the Propulsion Module would have been necessary.

==History==
The ISS requires an average 7,000&nbsp;kg of propellant each year for altitude maintenance, debris avoidance and attitude control. A Propulsion Module would have provided reserve propellant for one year of ISS orbit life in case of supply interruption. A Propulsion Module would have been attached to the [[Unity (ISS module)|Unity node]] of the ISS.

Multiple supply vehicles are required to satisfy the ISS's 7,000&nbsp;kg annual average propellant need. The then-current plan for six Progress M1 spacecraft per year met that need.

The Propulsion Module would hold 9808&nbsp;kg fuel. Progress M holds 1100&nbsp;kg; Progress M1 holds 1950&nbsp;kg. [[European Space Agency|ESA]] ATV holds 4,000&nbsp;kg. The cancelled U.S. Interim Control Module holds 5000&nbsp;kg of fuel. A [[Space Shuttle|Shuttle Orbiter]] ISS generic reboost had 232&nbsp;kg of fuel available. An Orbiter Max reboost mission had 1626&nbsp;kg of reboost fuel available.  [[Zarya (ISS module)|Zarya]] FGB [Russian: ФГБ - Функциональный Грузовой Блок, English: Functional (or Operational) Cargo Block (or Module)] holds 5,500&nbsp;kg and the Zvezda Service module holds 860&nbsp;kg, however, it is generally preferred to keep the main thrusters on Zarya and Zvezda in reserve, as they have finite lifespans.

The Propulsion Module, besides being part of the backup plan for if the Service Module was not available, was intended to be an American-owned propulsion system for the station and planned as a late addition.  However, the original design was over budget and late. An alternative design, the "Node X" design, which was built around an [[Node 4|improperly fabricated hull]] intended for [[Harmony (ISS module)|Node 2]] or [[Tranquility (ISS module)|3]], was then proposed and tentatively included in the plan, designed with two detachable fuel modules that could be carried up and down in a Shuttle cargo bay for replacement to avoid the problems of transferring propellant between tanks in space. It has subsequently been deleted from the plans, instead requiring the station to rely on the ATV and Progress spacecraft for reboost. Furthermore, in the wake of the Shuttle's retirement, further redesign of the Propulsion Module would have been necessary.

==See also==
*[[Node 4]]

==References==
{{reflist}}
* {{cite news | title=Space Station: The Station Components | url=https://www.pbs.org/spacestation/station/components.htm | work=Houston Public Television | year=1999 | access-date=2009-04-05}}

==External links==
* [http://www.nasa.gov/mission_pages/station/main/index.html International Space Station]
* [https://web.archive.org/web/20090731122359/http://www.onorbit.com/node/1296 A 1999 NASA plan to deorbit the ISS using the Propulsion Module]

{{ISS modules}}

[[Category:Components of the International Space Station]]
[[Category:Cancelled spacecraft]]