Encyclopedia Astronautica
Millenium Express

American SSTO VTOVL orbital launch vehicle. General Dynamics Space Systems Division proposal for the 1990 SDIO competition was a VTOL SSTO named Millennium Express. The final vehicle was a 15 degree cone with a 20%-length Rocketdyne aerospike engine. Payload was specified as 4500 kg into a polar low earth orbit. The Express could carry on its nose a payload module, a small Apollo-type two-crew seperable manned capsule, or a six-crew module that remained attached to the vehicle for recovery. The similar Douglas Delta Clipper was selected by the USAF for further development.

The proposed subscale 'x-plane' version (equivalent to the Douglas DC-X) was dubbed Pathfinder. GD estimated that the Pathfinder version could be flying by 1993, with the prototype of the orbital version working up to orbital speed in a series of flights in 1995-1998. Production vehicles would fly from 1999. Derivatives of the basic vehicle could be combined with upper stages to support lunar bases, provide landing craft for lunar or Mars expeditions. The vehicle was to be designed for 500 flights, and have a ground turnaround time of 104 hours, using only 50 people.

General Dynamics and its partner Rocketdyne went through a series of iterations to arrive at the final design. The Model 106 of December 1990 was powered by RL10 engines (four in the small Pathfinder X-vehicle). This was replaced at the time of final proposal by the SX-107 pressure-fed plug nozzle. It was felt that if a Phase II contract had been received, the actual solution to fly would be the SX-109 with a pump-fed aerospike. In the event the aerospike technology did not provie itself in the test or prototype vehciles, fall-back designs using conventional RS-44 engines were drawn up.

LEO Payload: 4,500 kg (9,900 lb) to a 300 km orbit at 90.00 degrees. Payload: 9,000 kg (19,800 lb) to a LEO 28 deg.

Status: Study 1991.
Gross mass: 576,000 kg (1,269,000 lb).
Payload: 4,500 kg (9,900 lb).
Height: 32.00 m (104.00 ft).
Diameter: 4.70 m (15.40 ft).
Span: 16.30 m (53.40 ft).
Apogee: 300 km (180 mi).

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Associated Countries
See also
  • SSTO Category of launch vehicles. Single Stage To Orbit. More...
  • VTOVL The concept of a reusable single-stage-to-orbit Vertical Take-Off Vertical Landing (VTOVL) launch vehicle that would reenter and return to its launch site for turnaround and relaunch was first proposed by Philip Bono in the 1960's. The appealing simplicity of the concept has been offset by the technological risk in developing it. The problem with any single-stage-to-orbit concept is that if the empty weight of the final vehicle has been underestimated it will not be able to deliver any payload to orbit, or even reach orbit. Since weight growth of up to 20% is not unknown in aerospace projects, this is a very real threat which has made both NASA and private investors reluctant to invest the billions of dollars it would take to develop a full-scale flight vehicle. More...

Associated Manufacturers and Agencies
  • Convair American manufacturer of rockets, spacecraft, and rocket engines. Convair, USA. More...

  • Miller, Ron, The Dream Machines, Krieger, Malabar, Florida, 1993.
  • Hudson, Gary C, History of the Phoenix VTOL SSTO and Recent Developments in Single-Stage Launch Systems, AAS 91-643, included in Proceedings of 5th ISCOPS, AAS Vol. 77, pp 329-351, November 1991.

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