== Space Balloon Photography ==
Photography from a Balloon in Space
As such it would be depressing to have your balloon reach space, but the camera system failed to take any good shots. And that's the point of this tutorial: to make you aware of the issues you may encounter.
Camera Spin and Rocking
Even if the resultant video doesn't give you motion sickness, it still plays havoc on the cameras' auto-brightness and auto-contrast features: a rocking camera swaps between pointing at the darkness of black space, occasionally the bright sun, and the whiteness of the clouds on Earth. Depending on the camera this may also cause issues with auto-focusing. Some video compression formats aren't very good with handling fast motion, either.
There are four ways to prevent spin and rocking:
String Length is the distance between the balloon and your package. If the balloon is spun or pushed at the top by wind, that action is translated down to the package by the string. A long string can dampen the twisting effect by storing the twist in the string. It also provides for a longer pendulum arm, reducing the maximum rocking angle of the package as wind pushes the balloon. A longer string is also great if your parachute gets stuck in a tree, allowing you to reach the package and cut it loose.
The one disadvantage to a long string is after your balloon reaches space, where there is little wind, that string may still have twists stored up. The rotations might not stop before the balloon pops - it's a trade off.
My recommendation is a string no less than 50 feet, and preferably ~100 feet. I based these numbers subjectively from results of previous launches.
Use a rotating swivel so that balloon spin doesn't translate down to the package. It should be relatively frictionless even under strain. Heck, use two of them in series just to make sure. More info on choosing a swivel can be found on the space balloon assembly page.
Rotational Moment of Inertia is a measure of an object's resistance to changes in its rotation. There are two ways to increase the RMoI: increasing mass, and moving the mass further away from the center of rotation.
For a balloon, increasing mass is bad as it results in a lower maximum altitude, and at some point exceeds the legally permissible weight limit. The other method to increase RMoI without increasing mass is to make your package in the shape of a donut, as this moves as much mass as possible away from the center of rotation.
The disadvantage do this is that it's much easier to make a cubic-shaped package.
I've seen other teams attaching long poles with small masses at each end, far from the center of rotation to increase RMoI. They've had good results.
Decreasing Wind Resistance . . . If you don't want your package blown around by the wind, make it aerodynamic. Enough said.
An active Control System is the final option to ensure steady video. This could be a multi-access gyro stabilizer, or two servos to form a pan and tilt. The issue of course is the added weight and complexity, plus the difficulty of determining orientation when your motion sensors are being tossed violently in the air.
Post Processing Manipulation
If you search online you can find other video stabilization software packages. More recently Youtube added a video stabilization feature. You push a button and it does it automatically for you. But I personally find this feature distorts the video too much so I rarely use it.
Lastly, if your camera filmed at a high frame rate (~50fps or above), you could put the video in slo-mo. This creates a false impression that it isn't rocking and swaying nearly as much as before. For video above the clouds I find this works really well.
Test your camera and memory card combination for the entire expected flight time beforehand at home. Do this test in a realistic situation, such as while in the insulated package - to test for thermal shutdown due to overheating.
You can also use this test time to figure out what software you need to open such large video files - so you can watch the video immediately after retrieval.
Using Two Cameras
The camera which takes the still images is programmable. We've tried playing around with the various light settings, but haven't had much success on improving average image quality beyond default settings.
These are the cameras we've flown:
The Kodak camera had serious overheating issues. We had two of this model - the first took more than an hour to overheat and the other failed almost immediately. We've since ditched it.
Live Video Transmission
To receive SSTV, you'll need a receiver. You can then attach it to your laptop and view the video using the following software.
note: Transmission of any video requires having a HAM license.
Calculating Distance to Horizon
distance in miles = sqrt( 1.5 x altitude)
You can also calculate Earth's angular diameter using this equation:
angular diameter of the Earth = arcsine[Re / (Re + altitude)]
Re is the radius of the Earth (3963 miles or 6378 km).
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