Bussard ramjet (thing)

By scooping up atoms (mostly hydrogen) and stray particles in the path of the spacecraft and fuel a fusion reactor with the collected matter, thereby generating thrust, the need for onboard fuel will be minimized.

In order to keep the fusion reactor running, enough matter has to be collected. By using a toroidal coil mounted in the front of the craft, a magnetic field is generated that draws matter into the collector, thereby lowering the speed needed by the ramjet to sustain reactor operation. Still, approximately 6-10% of c is considered the minimum initial speed for the ramjet drive.

To attain this speed and to ensure that the ramjet can return to orbiting speeds, fuel has to be stored aboard the ramjet.

Typical flight schedule for a craft with this type of propulsion is:

1. Acceleration to 6-10% of c using onboard fuel.
2. Activation of the fuel scoop. Further acceleration, max speed depends on the density of the surrounding. A low density allows a higher maximum speed but a slower acceleration due to lack of fuel, and vice versa.
3. Initial brake. The fusion reactor is deactivated but the fuel scoop is left running, serving a dual purpose of acting as a brake (using the inertia of particles in the semi-vacuum) and gathering fuel for the final brake and a re-acceleration.
4. Final brake. As the speed of the spacecraft decreases, the efficiency of the initial brake diminishes. To bring the spacecraft to orbiting speed, the thrusters are activated, consuming fuel scooped during the initial brake.