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Space Transportation System, Integrated Program Plan

1970 artist's concept illustrating use of a Space Shuttle, Nuclear Shuttle, and Space Tug
Program overview
Country	United States
Organization	NASA Office of Manned Spaceflight
Manager	George Mueller
Purpose	Reusable, low-cost transportation to Earth orbit, cislunar and interplanetary space
Status	Failed to gain political support
Program history
Launch site	Kennedy Space Center
Vehicle information
Uncrewed vehicle	Space tug
Crewed vehicles	Space shuttle Space tug Nuclear shuttle Space station module

TheSpace Transportation System (STS), also known internally toNASA as theIntegrated Program Plan (IPP),^[1] was a proposed system of reusable crewedspace vehicles envisioned in 1969 to support extended operations beyond theApollo program (NASA appropriated the name for itsSpace Shuttle program, the only component of the proposal to survive Congressional funding approval). The purpose of the system was two-fold: to reduce the cost ofspaceflight by replacing the existing method of launchingcapsules on expendable rockets with reusablespacecraft; and to support ambitious follow-on programs including permanent orbitingspace stations aroundEarth and theMoon, and a human landing mission toMars.

In February 1969, PresidentRichard Nixon appointed aSpace Task Group headed by Vice PresidentSpiro Agnew to recommend human space projects beyond Apollo. The group responded in September with the outline of the STS, and three different program levels of effort culminating with a human Mars landing by 1983 at the earliest, and by the end of the twentieth century at the latest. The system's major components consisted of:

• A permanentspace station module designed for 6 to 12 occupants, in a 270-nautical-mile (500 km)low Earth orbit, and as a permanent lunar orbit station. Modules could be combined in Earth orbit to create a 50 to 100 person permanent station.
• A chemically fueled Earth-to-orbitshuttle.
• A chemically fueledspace tug to move crew and equipment between Earth orbits as high asgeosynchronous orbit, which could be adapted as a lunar orbit-to-surface shuttle.
• Anuclear-powered shuttle or ferry using theNERVA engine, to move crew, spacecraft and supplies between low Earth orbit and lunar orbit, geosynchronous orbit, or to other planets in the solar system. A crew module derived from the space station module would be used to send humans to theMoon or Mars.

The tug and ferry vehicles would be of a modular design, allowing them to be clustered and/orstaged for large payloads or interplanetary missions. The system would be supported by permanent Earth and lunar orbitalpropellant depots.^[2] TheSaturn V might still have been used as aheavy lift launch vehicle for the nuclear ferry and space station modules. A special "Mars Excursion Module" would be the only remaining vehicle necessary for a human Mars landing.

The STS was championed by NASA administratorThomas O. Paine until May 1969 and gained Agnew's enthusiastic support. However, asApollo accomplished its objective of landing the first humans on the Moon, Nixon realized that political support for further crewed space activities was beginning to wane, and the Congress would be unwilling to provide funding for most of these extended activities. Based on this, Nixon rejected all parts of the program except theSpace Shuttle, which inherited the STS name. Nixon accepted Paine's resignation in July 1970 and replaced him as administrator withJames C. Fletcher.

As a result of funding constraints, Shuttle was significantly scaled back from its planned degree of reusability. The overall program scheduled was also delayed. The Shuttle first flew in1981, and wasretired in2011.

A second part of the system,Space Station Freedom, was approved in the early 1980s and announced in 1984 by PresidentRonald Reagan. However, this also became politically unviable by 1993, and was replaced with theInternational Space Station (ISS), with substantial contribution byRussia. The ISS was completed in 2011.

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The system was supposed to include a "space shuttle", sometimes also referred to as an "Earth-to-orbit shuttle", for ferrying crew and supplies to Low Earth Orbit. Larger payloads like nuclear tugs or space station modules would be transported by an upgraded version of theSaturn V rocket, specializing the "shuttle" to relatively low-mass, high-frequency payloads like crew rotations, liquid hydrogen fuel, and liquid oxygen oxidizer. This vehicle is arguably the only one that was realized with theSpace Shuttle, albeit significantly scaled back in nearly all aspects, and for most of its operational life left lacking the infrastructure it was supposed to support.

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The MSFC space tug was designed to handle a number of missions including satellite repair, transfer togeosynchronous orbit, and as the name implies, towing payloads to the nuclear shuttle. Its modular design was centered around a cylindrical propulsion module, with an attachable crew module, cargo module, and lunar landing legs to convert it to a lunar orbit-to-surface shuttle. It was supposed to use liquid hydrogen and oxygen as its fuel and oxidizer, carried into orbit by the Earth-to-orbit shuttle.

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Planned uses for NERVA included a visit toMars by 1978 and a permanentlunar base by 1981.^[3] NERVA rockets would be used for "nuclear tugs" or "nuclear shuttles" designed to take payloads from Low Earth Orbit to farther orbits, resupply of severalspace stations in various orbits around theEarth andMoon, and support for a permanent lunar base. The NERVA rocket would also be used in the Saturn S-N, an upper stage for theSaturn V rocket' upgrading the Saturn'slow Earth orbit (LEO) capability to 340,000 pounds (150 t),^[3] as well as be used to propel a pair of Mars expedition vehicles.

The program was supposed to include multiple space stations, built out of standardized space station modules. Those would be emplaced in low Earth orbit, polar Earth orbit, geosationary orbit, and lunar orbit. The Mars-focused aspects of the plan were supposed to use the station modules as crew sections for its Mars Transfer Vehicles.

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• "Report of the Space Task Group, 1969".NASA. Retrieved6 August 2009.
• Compton, W.D. and Charles D. Benson,NASA SP-4208 Living and Working in Space: A History of Skylab (1983) Chapters 5 and 6 mention 1969 Space Task Group's plan leading to a crewed Mars landing by 2000
• Heppenheimer, T.A.The Space Shuttle Decision: NASA's Search for a Reusable Space Vehicle. Washington, DC: National Aeronautics and Space Administration, 1999.
• Wade, Mark."Space Tug".Encyclopedia Astronautica. Archived fromthe original on July 2, 2002. RetrievedJune 15, 2011.
• NASA Report, Technical Study for the Use of the Saturn 5, INT-21 and Other Saturn 5 Derivatives to Determine an Optimum Fourth Stage (space tug). Volume 1: Technical Volume, Book 1, Web Address when accessed:https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810065609_1981065609.pdf
• Dewar, James. "To The End Of The Solar System: The Story Of The Nuclear Rocket", Apogee, December 2003.ISBN 0813122678

• "Beyond Apollo: Five options for NASA's future (1970)". Archived fromthe original on 8 October 2011.
• Report of the Space Task Group, 1969

• NASA programs
• Spiro Agnew

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