Why is the Oberth Effect still applicable when reaching interplanetary space? in Science & Spaceflight Posted Thursday at 02:13 PM · Edited Thursday at 02:14 PM by RCgothic Rockets are constant thrust devices. It doesn't how fast you're going, they push the same regardless. Work is force times distance. If you apply 10N to a stationary block and it doesn't move, you've done no work. If you apply 10N to a trolley going 1m/s, you've done 10J of work. If you apply 10N to a rocket going 10,000m/s, you've done 100kJ of work. Rockets are therefore more efficient when they're going fast. The fastest part of an orbit is deep in a gravity well. Only velocity parallel to the direction of motion counts, so burning sideways is equivalent to a standing start.