No air on moon, no sound. How did Apollo measure distance? Geom? Their computer cannot measure lasers in 1969.

Question

Apollo 11 started at 50,000 feet before it's desent. They almost knew to the exact foot even at 12 feet. They could not have used sound waves. Maybe two angles provided their measurements from the lander?

The radar sounds good, but to the exact feet. They were saying 20,.., 15,.. 10.., 8 feet,,. landed..... Radar???? Like for airplanes? Their computer back then was no better than a 1979 calculator. They just want say, but they did land! No hoax!

Radar only sends out a wave... It bounces back. The English invented it for the WWII. It dosn't need air, but it can't tell you that your 50 feet away from the moons surface...... Don't they use angle with multiple radar stations? Anyway there you go.

Okay the radar sounds good.

Sorry but they did call out measurement. Watch the mpgs......
http://video.google.com/videoplay?docid=1813746110244003823&q=apollo+15+moon+landing&total=46&start=0&num=10&so=0&type=search&plindex=8

Answer 1

Radar is limited by its wavelength. In those days, they were still stuck with 10 cm radars, meaning that the best accuracy they could get was a measly 4 inches. This is rotten compared to today's submillimiter radars.

Reading laser distances has been possible since the mid-1960s.

It was also possible to tell distances with accuracy better than a foot (up to about 60 feet) with a stereoscope binocular. This device had been invented for the Navy about a century ago. The closer you are, the more precise it can be. Models with larger baselines could be used up to a few miles. They were used on ships to tell the distance to other ships (or to very sharp coastal features, like lighthouses).

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"Don't they use angle with multiple radar stations?"
no

During WW2, they invented DECCA at about the same time as radar. DECCA is a passive system that receives radio signals from three stations and compares the phase difference between the signals so that the navigator can plot the position of the ship on a special chart (one marked with lines of equal phase difference).

Radar is a system that simply measures the time difference between the emission of an electromagnetic pulse and the reception of its echo. Really low tech. So simple that the computer from a 1969 calculator could have handled it if you had really wanted to do it with a digital computer (radar usually used analog)

Answer 2

Threw a rock out the window and counted how long it took to hit the surface. Well, ok, they didn't, it was just the landing radar. It was mounted on the bottom and was used just to figure out how far they had to go for the last few thousand feet after the pitch-up manuever and they were upright again. It was trouble-prone, but managed to work OK except on Apollo 14 where they had to recycle the circuit breaker before it would give a readout.

Answer 3

They used radar. You don't need a computer to use radar. Radar was invented in the early '40s. Guess what: not everything requires a computer. It can EASILY tell you how far you are away from the surface without a computer. All you need is an analog mixer. just becuase YOU do everything with a computer doesn't mean it CAN'T be done, and more efficiently too, without one.

And it's not altitudes that they are calling out on the radio in the film. It's *number of seconds of fuel remaining*.

Answer 4

The computer used information from several sources. There was inertial guidance data, landing radar data and ground tracking data. It computed an altitude based on things like the rate of decent and the time since some previous fix. It was not simply a raw radar altitude.

Answer 5

They used a combination of radar and a system known as LPD. LPD was literally inscribed on the view ports of the LEM and assisted in measuring the last several feet to the lunar surface. Picture of the LPD here =>http://history.nasa.gov/alsj/lpdin.jpg

Answer 6

Distance Earth to Moon via light off lunar "dust". Landing craft may have already set up reflectors to precisely laser-measure the lunar surface. Future landers will surely do this.

Answer 7

Can you google "LEM radar"?

Tons of interesting stuff pops up!

http://stinet.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=AD0624581

They were obviously worried that the altitude radar might become unusable from the exhaust ionization!

Google "lunar excursion module radar" and you will find

http://lsda.jsc.nasa.gov/books/apollo/S1ch2.htm

http://history.nasa.gov/diagrams/ad013.gif

Shows the control panel of the radars (there are at least two: one for altitude over the lunar surface and one to measure the distance to the Apollo module for docking).

:-)

Answer 8

I don't know the details. My first guess would be some sort of radio reflection, like radar. I wonder how far off my guess is...

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Here's a bit on navigation (but not the radar) ;

http://en.wikipedia.org/wiki/Apollo_PGNCS

Answer 9

There are enough atoms in the space around the moon to use radar. Don't need to have air.

Answer 10

They used radar.