Lockheed Martin's VentureStar programme president Jerry Rising has confirmed that flights of the X-33 sub-orbital technology demonstrator will "definitely not" begin in July.

If the decision is made to build aluminium propellant tanks for the vehicle, to replace those made of experimental lightweight composite materials, the delay will be at least 18 months, he says.

The length of the delay depends on the results of an investigation into the breach of a composite liquid hydrogen tank for the X-33 during testing at the NASA Marshall Space Flight Center, Alabama, in November.

An X-33 flight in 2002 would be three years later than originally planned. The demonstrator was to be an identical scale model of the proposed VentureStar fully reusable single-stage-to-orbit vehicle, incorporating most of the VentureStar features.

As the project has stumbled through technical difficulties, including those with the craft's linear aerospike rocket motors, the two craft have become different vehicles - the X-33 fitted with composite tanks to save weight and the VentureStar with heavier aluminium tanks.

The VentureStar will now have an external payload bay pod instead of an internal one.

The objectives of the flight profile for the X-33 sub-orbital demonstrator had already been reduced before the latest tank problem.

The additional weight of the metal tanks on the X-33, which would replace the troublesome composite tanks, will increase the mass of the vehicle and result in further reduced performance.

Source: Flight International