After being grounded last year, some of the nation's smaller rockets, such as the Atlas and Delta, are again ready to send payloads into space.

NASA created Hitchhikers to provide customers with a way to send small payloads into orbit on the space shuttle.

Hit hard by the post-cold war decline in military spending, the Lockheed Corporation said Tuesday that it would build midsize rockets to send both military and civilian payloads into space.

But the capability of the new rocket is limited - it can send payloads of only 3,500 pounds into geosynchronous orbit.

They involve two or more rockets stacked on top of each other, designed to launch while in the air, much like the multi-stage rockets that are used to send payloads into space.

The dispute is fueled by the continuing repercussions of last year's space disasters, which temporarily ended the nation's ability to send large payloads into space.

The 21-ton, 42-foot-tall, one-third scale prototype made three test flights last year, and proponents say it could lead to a vehicle that could send payloads into orbit at perhaps a tenth of current costs.

The chosen orbital altitude is a trade-off between the delta-v needed to counter-act the air drag and the delta-v needed to send payloads and people to the station.

The rocket, the X-33, they said, would test advanced technology that could lead to low-cost, reusable rockets that greatly reduced the cost of sending payloads into space.

Just as such services let the car send data to the outside world, malware writers could try to use those wireless conduits to send destructive payloads into cars.