# Calculating thrust using only weight

How do you calculate minimum thrust for a rocket ship using just the weight of the rocket? How do you chose what engine you need to use for your rocket?

• You don't. Just weight with no context is meaningless. DO you want to liftoff from the ground? Or just slightly change orbit? What planet/gravity? Even if assuming liftoff from Earth, how do you define "minimum thrust"? If you just want to hover, then thrust must == gravitational force on the rocket i.e. thrust in Newton = (mass in kg) * (gravity of 9.81) Nov 7, 2021 at 17:31
• In other words, "minimum thrust for what purpose?" What do you hope to achieve by "thrusting?" Nov 7, 2021 at 18:38
• Just lift off from the ground and hover. Nov 7, 2021 at 23:13
• Re, "lift off from the ground and hover." In order for your rocket to remain stationary near the surface of the Earth but not touching the Earth (i.e., in order for it to hover), then something other than the Earth must support the rocket's weight. And, it must be exactly the rocket's weight because otherwise, the rocket would accelerate upward or downward as seen by somebody standing on the Earth nearby. Nov 10, 2021 at 17:12