Have
you ever wondered how much ground detail an astronaut aboard the
International Space Station (ISS) can see? Here is your chance to
find out, with your own eyes! And not only that, it'll help you to
locate the geocache as well.
BEWARE
OF NETTLES!
Once I
attempted to signal Don Pettit, science officer aboard the ISS at
the time. I used a fairly large mirror to beam sunlight toward his
temporary abode in the sky hurdling along at 16,600 miles per hour.
More of the story is available at my
"Hello ISS!" cache. At the time I wondered what he could see
from above the atmosphere; could he see roads, large buildings, the
Cedar River? When he tried to spot my reflection, he was not
looking straight down, which is what this exercise presumes. To
visualize what would be resolvable at his nadir (straight down), I
developed the following simple
technique.
To
begin with, MAKE SURE TO READ THE
MAGENTA
LETTERING then, (1) copy and paste this
Google Earth image of
Cedar Falls, Iowa to a Word document. Before printing if off,
(2) right click the picture and, under, Format Picture, Size,
Width, scale it to 7.29 inches wide. Once printed, (3) determine
its scale, i.e. what its size is compared to real life. To make
this a lot easier I added a white line that represents a distance
of 10,000 feet (3,048,000 millimeters). I'm leaving it up to you
to figure out how to calculate this. It's a simple ratio. Note:
It's a lot easier to measure the line in mm and do the calculations
using decimals. That's why I've included how many mm 10,000 feet
is.
Record the scale as S in equation
1 below. (4) At
Heavens-Above.com, find the km altitude of the orbit of the
ISS. To locate it click on the blue, "ISS" under, "Satellites, 10
day predictions for: ISS." Now click on the blue word, "Orbit". You
can use either its Perigee Height or its Apogee Height. Use this
online
utility to convert the km value to feet then record this as A
in equation 1. Now work equation 1 to determine the proper viewing
distance to the picture. Record the viewing distance as V.
Round V to the nearest foot. NOTE:
I HAVE DISCOVERED THAT YOUR ANSWER MAY ROUND UP OR DOWN ONE-FOOT
FROM WHAT I GOT. HENCE YOU MAY HAVE TO TRY OUT THREE DIFFERENT
VALUES FOR THIS DISTANCE.
Tape
the picture up, measure out the appropriate distance and have a
look! Please share what you were able to see and anything new you
learned. If you have binoculars, try looking through them to see
how much more would be visible.
What
you have seen from the V distance will give you a good idea what
Pettit could make out when looking straight down through
this window. Imagine what they can see when using binoculars!
Remember, they are not looking at a measly print either. They are
seeing more clearly than what you are. I’ve read that the view is
particularly awesome at night. The only draw back is that are
moving REAL fast so they wouldn't have much time to
look.
How
can they see so much? That will become clear (pun intended) if you
compare the altitude of the ISS with a standard 1 foot globe. So
let’s do it! Go here
to obtain the mean diameter of the earth. Use the unit converter
again to convert the diameter of the earth to feet. Record that
value as E in equation 2. Work equation 2 to find the distance in
inches (G) that the ISS would orbit a 12 inch globe.
Round G to the nearest tenth of an
inch.
Equation
1
S x A =
V
S = the
scale reduction of the print
A = the
altitude of the station in feet
V = the
viewing distance to the print in feet,
[Remember to round to the nearest
foot.]
Equation
2
(1 ÷ E)
x A x 12 = G
A = the
altitude of the station in feet
E =
diameter of the earth in feet
G =
the inches that the ISS would orbit above a 12 inch globe,
[Remember to round to the nearest tenth of an
inch.]
To determine the
latitude of the geocache, use equation 3. Replace the MMM with the
numbers in the answer. Round to the
nearest thousandths
place.
To
determine the longitude of the geocache, use equation 4. Replace
the MMM with the numbers in the answer. Round
to the nearest thousandths
place.
Equation
3
N 42°
28.XXX where MMM = V x 9.042
Equation
4
W 092°
24.XXX where MMM = G x 2263
Good
luck!
-it
PS Just as I
was typing this in came an e-mail listing the latest images that
the astronauts aboard the ISS have taken of the earth. I once
searched that sight and discovered a pretty good image of
Waterloo, Iowa. In fact I use it in my Hello ISS cache. If
interested have a look at The Gateway to
Astronaut Photography of Earth. Here’s their home page. Another searchable
database: Earth
From Space.
.
.