First US lunar lander in more than 50 years rockets toward moon with commercial deliveries

submitted by neolib from apnews.com

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[–]Alienhunter 2 insightful - 1 fun2 insightful - 0 fun3 insightful - 1 fun -  (3 children)

Again you are simply misunderstanding the third law of motion. No atmosphere is necessary to push against. A jet engine would work fine in a vacuum as a source of thrust assuming you brought your own air to use. (In reality since a Jet engine needs to suck in air from the surrounding atmosphere to work it won't work in space) rockets simply bring everything with them they need to function in space.

You also aren't fighting directly against Earth gravity. Once you achieve orbital velocity which in terms of energy needed is absolutely the biggest hurdle, then you need relatively little energy and thrust to make course corrections as you're in a vacuum condition with no air resistance and therefore no drag. In an orbital velocity that 95% of normal ground level acceleration works to keep you in an orbit and also can be used to gravitationally slingshot you out further if you are smart about how you go about it.

Keep in mind that you are at about 75% of escape velocity in low earth orbit. The amount of energy you need to escape from low earth orbit is far lower than the amount of energy you need to reach low earth orbit in the first place. The amount you need to reach the moon is even less than that as the moon is still in earth orbit.

It's one of the counter intuitive peculiarities of orbital physics we don't consider in terrestrial situations. Same as how the energy required to leave the solar system entirely is much lower than the energy required to go to the sun despite the fact the sun is much closer. If you wished to send a probe to impact the sun you'd have to work against the Earth's velocity to place the probe in an orbit that had the probe lose most of its relative velocity against the sun which is much harder to do than get the probe a bit more velocity to do a slingshot maneuver around the sun and achieve a parabolic orbit that will see it fly out uncontrollably into the void.

[–]Tom_Bombadil 1 insightful - 1 fun1 insightful - 0 fun2 insightful - 1 fun -  (2 children)

Again you are simply misunderstanding the third law of motion. No atmosphere is necessary to push against.

Your premise assumes that the equal and opposite reaction in the third law will apply force in a vacuum.

For a gas to apply force, it has to apply pressure. But had molecules can only apply pressure to one another if they're contained.

The atmosphere functions at a container with back pressure at 14 lbs/(in2).

The inertia of atmosphere (resistance to gaseous expansion), applies back pressure to the exhaust gases, which applies back pressure against the rocket surfaces, and the equal and opposite sequence does work on the rocket and it's is moved.

Combustion in a vaccine doesn't have an enclosure of atmosphere.

In a vacuum, as soon as the molecules ignite and expand they are forced into empty space without resistance.

No inertia of gases in the atmosphere to create back pressure. The gases expand without resistance into the vacuum of space.

No back pressure, and no compression of gases, and no build up of pressure against the surface of the rocket.

No work applied to the rocket. No movement.

There's no way around this reality. The rocket exhaust won't build up back pressure (thrust), which means there's no efficiency.

Bro. This is physical reality. I don't like it either, but there's nothing for it.

[–]Alienhunter 1 insightful - 1 fun1 insightful - 0 fun2 insightful - 1 fun -  (1 child)

This is very easy to prove with a vacuum chamber and some pressurized spray can of any sort. Place the pressurized spray can onto a cart or suspend it from the top of the contained, then depressurize it and see if it moves.

There's no need for back pressure of any sort. The initial push is from expelling the matter in the first place.

[–]Tom_Bombadil 1 insightful - 1 fun1 insightful - 0 fun2 insightful - 1 fun -  (0 children)

There's no need for back pressure of any sort.

This is the error in your assessment.

Here's an exceedingly clever experiment, which stimulates the removal of the atmosphere with a rocket.

Rockets can't work in the vacuum of space science experiment.

Notice how the rocket jumps backwards when the parachute comes out. The equal and opposite reaction that doesn't occur with the rocket.