In astrodynamics and rocketry, gravity drag (or gravity losses) is a measure of the loss in the net performance of a rocket while it is thrusting in a gravitational field. In other words, it is the cost of having to hold the rocket up in a gravity field.
It is the difference between on one hand the delta-v expended and on the other hand the theoretical delta-v for the actual change in speed and altitude, plus the delta-v for other losses such as air drag, that are experienced by a thrusting spacecraft.
Gravity losses depend on the time over which thrust is applied as well the direction the thrust is applied in. Gravity losses as a proportion of delta-v are minimised if maximum thrust is applied for a short time, or if thrust is applied in a direction perpendicular to the local gravitational field. During the launch and ascent phase, however, thrust must be applied over a long period with a major component of thrust in the opposite direction to gravity, so gravity losses become significant. For example, to reach a speed of 7.8 km/s in low Earth orbit requires a delta-v of between 9 and 10 km/s. The additional 1.5 to 2 km/s delta-v is due to gravity losses and atmospheric drag.
Read more about Gravity Drag: Example, Vector Considerations
Famous quotes containing the words gravity and/or drag:
“Grown beyond nature now, soft food for worms,
They lift frail heads in gravity and good faith.”
—Derek Mahon (b. 1941)
“I know those little phrases that seem so innocuous and, once you let them in, pollute the whole of speech. Nothing is more real than nothing. They rise up out of the pit and know no rest until they drag you down into its dark.”
—Samuel Beckett (1906–1989)