I would like to take this opportunity to share something with other forum members
A freind of mine, Clive, is an amateur astronomer. a physics and cosmology buff, and all-around very smart man. He mentors school kids in science classes. Clive told me about this student, a 14 year old girl, who made an unusual entry in this year's Cawthron Institute Science Fair.
I have decided to post it here, since we have in this thread a claim from an HB that the ISS is a balloon being flown in the atmosphere. Following is a reprint (with the student and her mum's permission) of her presentation, which was called - SPEEDY SATELLITES.
Question
How many times does the International Space Station orbit the earth in one day?
Hypothesis
I think that the space station will go around the earth 7 or 8 times a day because it seemed to be traveling extremely fast when I saw it.
Method
To time the passes of the space station I needed to set up a datum line that could be used to watch when it passed.
To do this I have found a simple method using a bike wheel on a pole and a stop watch.
Step 1 - I removed the front wheel from a bike and remove the tyre.
Step 2 - I constructed a frame to attach the wheel to that can be adjusted to different vertical and horizontal angles, and attached the wheel to it.
Step 3 - I attached the frame to the top of a solid vertical pole that had a clear view to the sky.
Step 4 - I aligned the axle so that it points to the celestial South Pole. The rim of the wheel will now be closely aligned with the earth’s celestial equator. The space station will pass over this line. The celestial South Pole can be found by extending the vertical line of the Southern Cross and intersecting it with a line perpendicular from the midpoint between the Pointers. This is the position of which all of the stars appear to revolve around in the night sky.
Step 5 - By looking through the plane created by the bike wheel you are able to observe when the space station passes this plane, this can be used to accurately time when the space station passes the same projected plane in the sky.
Step 6 - With my mobile phone logged in to the international atomic clock, I recorded the time that the space station passed through the plane created by the bike wheel. I recorded this time in my log book.
Step 7 - I repeated steps 5 and 6 several times over a number of nights.
Step 8 - I can now use the times to calculate the number of passes between each reading, the average orbit period and calculate the number of orbits in a day.
Fair Testing
1 - I used the International Atomic Clock each time to make sure the timing was accurate.
2 - I made sure that the wheel was protected from bumps and stayed stationary to ensure the timing was accurate.
3 - We aligned the wheel accurately with the Celestial South Pole to be sure that the space station would pass it each time.
4 - I checked the alignment of the wheel with the Celestial South Pole before each pass of the Space Station was timed.
5 - I used two spotters to ensure we identified the space station in the sky with plenty of time to prepare for it passing the wheel.
6 - I used two spotters to accurately identify when the space station crossed the plane of the wheel.
7 - I did multiple time tests over a long period of time so that we could average out the results and reduce errors.
Conclusion
I was really surprised at how close the recorded times were to each other, even with using a basic method to time the space station passes. My testing showed that the International Space Station makes one orbit of the earth every 92 minutes and 32 seconds. This equates to orbiting the earth 15.56 times a day which is many more times than I expected. It must be travelling extremely fast – a lot faster than I thought.
Discussion
I was surprised that the method I used to time the space station passes provided such accurate and consistent results. Measuring the results over a longer period of time gives a longer sample period which helps to reduce differences and the size of errors between individual results. Being able to time at least one set of consecutive passes was critical to the experiment working.
I was also surprised at how fast the space station is travelling. It needs to travel this fast so that as it is falling to earth it is also travelling past earth and never actually gets closer to the earth’s surface.
The method I used can be used to time any satellite that orbits the earth more than once a day – there are thousands of them out there!
Further Learning
I have found out that you can calculate the orbit radius of a satellite from a formula based on Johannes Kepler’s 3rd law which he published in 1619. Using an online calculator the orbit radius for the space station works out at 6777km from the earth's centre. The earth has an average radius of 6371km which means that the space station is 406km high.
You can also work out the speed of the space station using the orbit period and orbit radius. The speed calculates at 7.67 km per second.
All satellites are in orbit around earth’s centre but not all rotate around the earth surface. These satellites appear to be stationary in relation to earth and they need to be a lot further away (thousands of kilometres) so that they are not affected as much by earth’s gravity. The satellite that SKY TV comes from is like this.
Bibliography
Kepler’s Third law (on line orbit calculator):
http://www.1728.org/kepler3a.htm
Heavens above (satellite prediction tables):
http://www.heavens-above.com/
Atomic Clock Time (timing space station passes)
http://www.timeanddate.com/time/internatio
nal-atomic-time.html
This young girl puts all HBs, including Neil Baker, to shame. She has asked a questiion, and set about using real observation, real research and real experimentation (ie. real science) to answer it. Along the way, with just a rudimentary, but well designed contraption and naked eye observation, she has;
1. Measured the orbital period of the ISS as 1:32:32. The actual orbital period was 1:32:41; only 9 seconds error in 5561 seconds, or 0.16%. Her calculation of the orbital speed at 7.67 km/s is very close to the published figure of 7.66 km/s.
2. Calculated the ISS orbital altitude as 406 km. It was actually 399 by 408 km around the time of her observations which corresponds to 403.5 kms... about 0.5%.
Here is the student along side per presentation. You can see a photo of her equatorially mounted bike wheel at the bottom. (Photo courtesy of the Cawthron Institute, Nelson, NZ -
http://www.cawthron.org.nz/Her entry won two prizes...
The Albert Jones Memorial AwardSponsor: Nelson Science Society / Earth and Sky Ltd.
Prize: A fully funded trip to Mount John Observatory
Criteria: The best oral communication of a project during the interview process
The Royal Aeronautical Society AwardSponsor: Royal Aeronautical Society, Blenheim Branch
Prize: $100
Criteria: The best investigation relating to 'flow', including hydro and aero dynamics, vessel building and design.