Over the last 30 years the U.S. has developed and refined an astronaut transportation system and a space station that allow this country to routinely ferry men and women between Earth's surface and low Earth orbit. The importance of this capability is multi-fold:

+ The Space Shuttle is a reusable, available and proven human transporter. It provides ascent to the International Space Station (ISS) and deals with the extremes of reentry. Furthermore, the achievement of low Earth orbit equates to roughly half or more of the needed energy to explore near-Earth regions of the solar system.

+ The ISS can be used as an assembly and test station for solar system exploration. Astronauts on the station have proven abilities in assembling large space structures while performing Extra-vehicular Activities (EVAs). They can receive, store and prepare flight hardware for short or extended missions to the moon, asteroids or Mars.

Current Constellation architecture requires discarding this capability and replacing it with a far inferior architecture, i.e., one requiring the development of a very limited and costly launch system that uses a 1960s' astronaut capsule design.

With such a convenient ferry and space assembly system already in place the U.S. is presented an opportunity, not to replace it, but to build on it. Use the Space Shuttle to ferry astronauts and valuable cargo to the ISS and use expendable launch vehicles to transport consumables and low-value cargo to low orbit.

Take advantage of the ISS as an assembly, integration and test facility for a modular reusable solar system Human Exploration Transfer Stage (HETS). Several valuable advantages present themselves:

+ The HETS concept is a dedicated vehicle for solar system exploration that need not carry huge weight penalties associated with atmospheric ascent and reentry.

+ It can be optimized for the vacuum flight of space, leading to performance and cost advantages that are significantly superior to those of Constellation's architecture.

+ HETS takes advantage of a modular design approach in order optimize its shape, size and design for short, medium and long flights to the moon, asteroids and Mars.

+ Robotic flights of HETS can allow safe check out and testing of the vehicle and its systems during short flights, e.g., lunar circumnavigation trips from the ISS.

In order to satisfy funding constraints, HETS can be an evolving vehicle. In the early years a rather simple HETS can be used for flybys of near-Earth points of interest such as asteroids and the moon. In the later years HETS could evolve into an Earth-Mars transport vehicle.

The HETS architecture could take advantage of many existing technologies, both U.S. and international. For example, during the return leg from Mars, HETS could rendezvous with a space tug at high Earth altitude in order to conserve propellant for Earth capture, allowing the tug to tow HETS back to the ISS. From there, the crew could transfer to the Shuttle for reentry and return to Earth.

This approach allows the continued use of already existing and proven systems for achieving low orbit, and it eliminates the requirement for an exploration vehicle that would have to carry a great deal of added mass to survive atmospheric reentry. The only required new systems would be those elements needed to explore space above low Earth orbit.

NASA and the Augustine Panel - please don't miss this opportunity!

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