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.
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.]
(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.
N 42° 28.XXX where MMM = V x 9.042
W 092° 24.XXX where MMM = G x 2263
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.