# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: It's Moon-landing Monday
Date: 2009 Jul 20, 09:37 -0400

```The distance (900 miles) is an easy one.  Use your sextant to measure the
diameter of the moon, and since you know the true diameter, you can calculate
the distance to the moons center, using simple triangles similar to HP.  Use
your sextant like a stadimeter.  As a check, you can also perform the same
calculation using the diameter of the earth.

In terms of the RA and declination, use the earth as a nadir point and
determine where you are relative to the star patterns shown.  Nominally, in
celestial navigation, we use the zenith, but because it is easy to look down
at the earth and see the star patterns, look at your nadir.  Since the star
patterns will not shift in parallax for an orbit within the earth-moon
system, this will provide a very reasonable RA and declination.

Finally, since we can assume you are "out of earth orbit" for 6 hours, you are
generally pointed in the correct direction anyway.  As a result, the time to
fire the rocket is most dependent on the distance and not so much on the RA
and declination.

Best Regards

-----Original Message-----
From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of frankreed@HistoricalAtlas.com
Sent: Monday, July 20, 2009 7:36 AM
To: NavList@fer3.com
Subject: [NavList 9150] It's Moon-landing Monday

To celebrate the fortieth anniversary of the Apollo 11 landing on the Moon, I
propose a navigation brain game...

You are on your way to the Moon in the year 2029, sixty years after the first
moon landing, to begin a six-month stay as part of a team of five at the tiny
"International Moon Base". You have been granted a twenty kilogram allowance
for personal effects, and navigation-fanatic that you are, you have chosen to
bring along a beautiful, well-adjusted, perfectly-aligned, traditional marine
sextant manufactured way back in 1999. You also carry a laptop computer in a
radiation and EMP-shielded case containing whatever databases of astronomical
information suit your fancy (you've got at least a terabyte to spare so have
no fear --if you can imagine it, you can load it on that laptop!). Then, just
six hours out of Earth orbit on-course for the Moon, in a terrible accident,
a solar flare, or an electrical fault, or just plain old gremlins wipe out
your spacecraft's electronics leaving you no navigational capabilities, no
automated spacecraft control, no communications with the Earth or GPS-like
satellites or any astronauts in Earth orbit, lunar orbit, or already on the
Moon. Life-support is functioning for a few days, and you can still fire your
rockets and thrusters manually, but everything else is dead. So what could
you do? You dig out your sextant from your luggage... You fire up your laptop
with its detailed databases of astronomical data... Can you get to the Moon?
If not to the Moon's surface, can you get yourself to within, let's say, 100
nautical miles of some spot in lunar orbit? In short, could you become "Buck
Bowditch in the 25th Century" and use traditional celestial navigation tools
and skills, plus a laptop full of data and software, to save you and your
comrades? Just to make things specific, your job is to fire your rockets at
their standard thrust along a vector pointed at 6 hours RA and 20 degrees
Declination (+/- 0.1 degrees in both coordinates) at an exact specified
distance of 900 miles (+/-10 miles) from the Moon's surface on your current
trajectory. If you do that, you will be able to rendezvous with an orbiting
rescue spacecraft and win the game. Ready to go?? :-)

-FER
PS: The spacecraft's windows are just windows. They are not optically flat.

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