The Cobol Class Research Vessel is equipped with a simple Ramscoop as a part of its hull design. The Ramscoop will produce 2 KT of Neutronium (fuel) per light-year traveled by the starship. If the starship were to travel 10 light-years (>= 10 and < 11) it would generate 20 KT of fuel. If it used less than 20 KT of fuel to go those 10 light-years the starship would experience a net increase in fuel.
In order to not destroy a towing starship, and the Cobol as collateral damage, the Ramscoop is automatically disabled when a tow beam is locked on the Cobol.
In addition, the Ramscoop is automatically disabled when the Cobol enters a nebula. This is to keep the Ramscoop from being clogged and destroyed by the high level of interstellar matter.
See also: Out of Fuel.