Why did it take Apollo space craft 3 days to get to the moon?

Question

If escape velocity from Earth is 25,000 mph and the moon is 250,000 miles away, shouldn't it only take 10 hours to get there?

To Harith Rahman, it only takes 90 minutes to orbit the Earth and less to orbit the moon. Even if you add many orbits around the Earth, it still doesn't add up. Any NASA employees out there?!

OK thanks to Jordan K, John B, and Justin R. I think I understand it now.

Answer 1

The Apollo spacecraft wasn't traveling at escape velocity. Escape velocity is enough to leave the Earth/Moon and go into solar orbit. They didn't wanna do that, both because of the fuel costs to accelerate that high, plus fuel to decelerate into a lunar capture orbit.

Apollo was traveling at approximately 9,000 feet per second, (which translates into roughly 3,000 meters per second, or 6,300 mi/hr). That translates into about 40 hours to travel that distance. Apollo 11 took roughly 70 hours, additional time for the orbital path is not precisely 250,000 miles.

Answer 2

The spacecraft did not travel at 25,000mph all the way there. Escape velocity is defined as the speed you need to reach to escape with no further active propulsion from the engine. If you have a continually firing engine you can escape at any speed you like. However, fuel economy requires a big boost followed by coasting for the rest of the trip.

The launch used the first two stages and some of the third stage of the saturn V to get up to 17,500mph, orbital speed. After a couple of orbits to check the systems the third stage reignited and accelerated the spacecraft to 25,000mph. It took about ten minutes of firing to do that. After that point the spacecraft was unpowered, and subject to Earth's gravity it began to slow down. By the time it crossed the point at which the Moon's gravity became dominant it was not going anywhere near 25,000mph. From that point on it accelerated again as the Moon pulled it in.

So the straightforward equation in your question does not work because the speed was not constant during the journey.

Oh, and one lunar orbit took about 2 ours, actually longer than Earth orbit, due to the lower orbital speed for lunar orbit.

Answer 3

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I think you have conflated two different stories. Answer 1: Agena Answer 2: Gemini (Gemini VIII in fact) Now here's where things go a little wrong. The only Apollo mission that was meant to land but didn't was Apollo 13 and Jim Lovell was also on Apollo 8, the first mission to fly around the Moon. However the crew of Gemini VIII were Neil Armstrong and Dave Scott. Armstrong of course went on to be the first to set foot on the Moon on Apollo 11. Scott took part in Apollo 9, a fully configured test flight that never left Earth orbit, and Apollo 15 which landed near Hadley Rille on the Moon. Lovell was a crew member of Gemini VII which was a long duration (14 days) flight and also had a rendezevous with Gemini 6A (but no docking). Gemini 6A was renamed and rescheduled when the Agena target vehicle for Gemini 6 suffered a launch failure. The violent spin which necessitated an abrupt end to the spaceflight happened on Gemini VIII. I knew some of this myself but had to look it up on Wikipedia to check details.

Answer 4

This Site Might Help You.

RE:
Why did it take Apollo space craft 3 days to get to the moon?
If escape velocity from Earth is 25,000 mph and the moon is 250,000 miles away, shouldn't it only take 10 hours to get there?

Answer 5

Apollo Speed

Answer 6

The escape velocity is the velocity needed to escape the earth forever. That is not necessary -- you only need enough velocity to get to the point where the moon's pull is greater (That point is called Earth-Moon L1 and is 200,000 miles up).

Also, look at it this way: You don't need to reach escape velocity to get a rocket to an altitude of 10 ft, or 1 mile, or 10 miles, or 100 miles, or 200,000 miles.

Answer 7

no manned space voyage has gone past the 400 mile mark in altitude..satellites sit at 22000 miles up in geosynchronous orbit.

Answer 8

Because they didnt fly straight there, they orbited earth first then went towards the moon, probably did a partial orbit to get to the landing spot, then landed.

Answer 9

also, the have to decelerate in order to enter lunar orbit. if they went all the way there at top speed, they'd shoot right past.

Answer 10

Don't think that these are the scientific answers from NASA but they might help.

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