Travelling to the Moon?

Question

I've been reading quite a bit about the Apollo programme just recently and one question is bugging me. If the spacecraft travelled at 17 000 mph and the Moon is 250 000 miles away, how did it take 3 days to travel from the Earth to the Moon. Surely at that speed it would only take 15 hours. I realise that the craft orbited the Earth a couple of times first before entering TLI, but that wouldn't take up over 2 days!

So what happened with the rest of the time?

By the way, if you're going to say that there were no Moon landings and that it was all a hoax, please don't bother answering. I firmly believe that it all happened as it's been reported over the last 40 years or so. Thanks ;-)

Some great answers, thanks!

Of course, I hadn't thought about 17 000 mph being the max speed (altho they did reach 25 000 mph at re-entry, I believe). So what would have been the average speed?

Answer 1

The 17,000 mph speed was the speed for earth orbit. The trans-lunar injection burn raised the speed to 25,000 mph (escape velocity), which decreased over time as the earth's gravity slowed the craft. At about 210,000 miles out, the moon's gravity became stronger than earth's, and the speed increased to about 5,500 mph. The service module engine was burned to reduce this to the roughly 3,500 mph necessary to be in lunar orbit. The process was reversed for the return trip.

Answer 2

The farther it traveled from the earth, the more it was slowed down by gravity. It didn't go 17,000 mph all the way. Plus, adding to that a bit is the fact that it's not a straight line to the moon. You have to take into account the orbital dynamics. Until the moon's gravity dominates, the craft was still in an earth orbit even though it was a very elliptical one.

Answer 3

Earth escape velocity is 25,000 MPH. The 3rd stage of the Saturn rocket accellerated the ships to that speed, and shut off. From there out, Earth's gravity slowed it down. By mission rules, the spacecraft had to be on a "free return" mission, meaning, if the service module engine didn't fire to slow them down to put them in orbit, the craft would swing around the moon & already be plotted on a course back to Earth.

Now, by the time it reached lunar orbit, the craft was only going about 2,000 MPH. To 'park' the craft in lunar orbit, the service module's engine fired to slow it down further.

When it came time to come home, the reverse happened - they fired the engine once again, to accellerate the craft to escape lunar gravity, then the ship sped up as Earth's gravity took hold - until it hit the atmosphere going around 25,000 MPH.

Answer 4

The craft wasn't going 17000 the whole way. It did slow down during the journey because of the earth's gravitation. Also, the craft did not go in a stright line; that would have taken too much energy (and fuel). Instead it went into an elliptical orbit that took it from the earth to the moon. That orbit was curved and had a length more than just the 238,000 miles to the moon.

Answer 5

Dear Sir:

I realize that the simple math does not compute for this space trip. That is because at Time = Zero you are not traveling at 17,000 Miles Per Hour, and at the instant of landing, you are not traveling at 17,000 Miles Per Hour. So, allowances have to be made for acceleration and deceleration.

Beyond that, several orbits of the Moon were made to locate and precisely identify the landing zone. That added significant miles to the overall trip. You already mentioned several orbits of the Earth prior to actual acceleration into space for the trip. All totaled, the numbers work out okay.
that is especially true when you consider that the most crucial moments of the flight were the instant of blast off for the Moon, and the actual landing on the Moon's surface. If they messed up either of those they would have to use excessive fuel to get back on course (bad blast off sequence), or crashed on the Moon preventing a desireable return to Earth (bad landing). Since there is no atmosphere around the Moon, there were no speed brakes like you see on various jet aircraft. Retro rockets had to be fired to slow their speed and descent to the Moon's surface. Traveling at a very high rate of speed you cannot slow down to landing speed in one or two seconds...you must do it gradually or your guts wind up in your lap,

Answer 6

There are two points to this:

1) Whilst the moon is 250,000 miles away as the crow flies, gravitation pull from other planetary objects had to be taken into account and therefore a more round-about route was taken on the way to the moon

2) 17,000 was its maximum speed however due to fuel and "engine" restrictions most of time was used leveraging the moon and sun's gravitational pull in order to get to the moon rather than the Apollo craft itself

Answer 7

It's because the space ship doesn't travel in a straight line between the earth an where the moon is at take off. It has to travel in an elipse to where the moon will be when the ship gets there. The distance travelled will be far greater than the average distance between the earth and the moon.

Answer 8

you can figure that out add istance of orbits around the earth and moon plus 250000 miles between the two minus the time they were on the moon divide by th total travel hours of the time traveled and youll get a fair estimate.and i think we landed to if not they wouldnt have had to retouch the photos.

Answer 9

When the craft got to the half way point the turned it around and started to slow it down. When it achieved orbit they stayed in orbit for some time while they prepared to descend.
Thus taking more time than seemed they ought.

Answer 10

Going at 90 degrees, you would have to travel 25,000 mph to escape Earths gravity. If they were going at 17,000 mph they would have to take off like an airplane. That would take a fair amount of time.