Does a heavy NASA rocket require more force initially on liftoff or the stage where it is higher up in the sky?
to reach outer space with zero gravity present there?
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answers:
ANDRE L say: At the time of liftoff, the first stage thrust MUST be greater than the FULL weight of the rocket and it's full fuel and oxidizer tanks. As the first stage, which has the most powerful engines, and thus uses the most fuel per second of firing time than any upper stage, burns, the rocket swiftly loses weight. Plus, the early part of the boost phase involves the most drag from the atmosphere, which tapers off markedly as one gets higher and higher up.

Thus, by the time the first stage is about done, you've likely cut the remaining weight of the climbing rocket by about half, and dropped the air drag by over 98%. Thus, the upper stages have far less weight to push further upwards, and far less drag to fight along the way.

The term 'weightless', when it comes to the conditions while in orbit, does not mean that you no longer need rocket power to further accelerate out of orbit, if your payload is either going to a higher orbit, such as at geosynchronus altitude, or out from the Earth to the Moon or planets. The payload and it's remaining rocket stage still have MASS and the mass of a fixed object (Such as, say, the satellite or payload being carried upwards) doesn't ever drop.

What 'weightless' means is that the object in orbit, once the engines are off, is in free fall balance with the planet it's in orbit of. It's like being in a free falling elevator in a very tall building, only once in orbit, the angle of the fall matches the angles at which the planet's surface drops away, being round.
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Jeffrey K say: Outer space is not zero gravity! Earth's gravity is still pulling on the rocket in space. To feel weightless, it must be in orbit. It must be going 18000 miles per hour. Accelerating up to that speed is what requires the most force and uses the most fuel. Lifting off the ground is the easy part.
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Ronald 7 say: It definitely needs more Power at Lift Off
to break the Inertia of its mass plus the Force of Gravity weighing down on it
The Saturn 5 used One Million Pounds of thrust just to get off the ground
The first Stage took it up to six times the Speed of Sound then it is jettisoned on depletion of fuel, when the second Stage began firing and it took the Rocket up to Orbital Speed, which is 17 500 mph
Even though it resumes weightlessnes because it has broken the power of Gravity, it still is acted upon, no matter of Altitude, from friction through passing through our thin Upper Atmosphere
Which terminates about halfway out to the Moon
Even the ISS has to fire its engines now and again to keep orbital speed up
So do some Satelites, or they would re-enter and get burnt up
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Tom S say: They need more initial thrust, yes, gravity tapers off but never goes to zero.
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CarolOklaNola say: At liftoff Rockets DO have momentum on the ground because the ground is MOVING because the Earth is rotating. Higher up the rocket has lost mass because of loss if fuel. There is NO zero gravity in space. There is microgravity.
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The Taxpayer say: initial. No momentum on ground.
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billrussell42 say: It requires more force on liftoff. The force has to be higher than the weight of the complete rocket in order to overcome gravity.

As it gets higher, the weight becomes less, due to two factors: fuel has been used, so weight is less, and force of gravity decreases with height. Thus the thrust needed becomes less. Or the same thrust prothrustduces more acceleration.

The formula is good old F = ma
where F is the net force, Thrust minus weight. Therefore
a = m/(thrust–weight)
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rick29148 say: more weight = more power needed, yes ..........................
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