There are many simple and great Raspberry pi projects out there, but few are as impressive as the words "atmospheric satellite". It sounds difficult, scientific, confusing. But actually, it can be very easy. For under 100 pounds, you can take high quality photos, record air pressure, and much more. The scientific side of things is when using the airPi, with which you can detect levels of nitrous oxide and other gases in the air, as well as basic measurements like temperature. You can even detect the weather, using humidity sensors and LDRs, to name two. The more casual approach is using the raspberry pi camera module.

I have never been interested in the weather, but I love electronics. I'm always looking for a simple, practical and fun project involving things I have lying around the house. A couple weeks ago, I ordered some parts for an atmospheric satellite I was interested in building, inspired by the new breed of cheap, powerful satellites like the Cubesat. The only problem was, it didn't do anything. I needed a function. And so I used a camera, to take breathtaking photos. This instructable should help you to make an inexpensive, functional fly-and-collect atmospheric satellite, capable of doing whatever you wish. I will also show you how to install an atmospheric sensor, known as the airPi, onto your satellite.
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List of Parts (links supplied):
Raspberry Pi Model A (B works as well, but higher energy consumption) http://www.rs-components.com/raspberrypi
Tracking Device, in this case, Loc8tor GPS (A phone can be used, see 'Extras' for more): http://www.loc8tor.com/uk/loc8tor-gps-tracker.html
External Battery:http://www.amazon.co.uk/Ultra-Compact-Lipstick-Siz...
Sports Parachute: http://www.amazon.co.uk/Power-Chute-Speed-Training...
Balloon (The stronger the material the longer the flight): http://www.amazon.co.uk/meter-Professional-Weather...
Function Part- whatever you want to use the satellite for, in this case the airPi): https://www.tindie.com/products/tmhrtly/airpi-kit/ NOTE: I do not recommend buying the airPi, it is very overpriced. It is easy and much more cost efficient to build your own, instructions are on the website.
Enclosure: http://www.otterbox.com/OtterBox-Drybox-1000/OTR3...

Step 1: Why You Need Each Part

This instructable covers building with both the airPi and raspberry pi camera module, but not in much detail, as this would have to be very long to fit in all the instructions, and irrelevant to someone using the other function. I recommend googling any queries you have before asking me, though I am happy to answer any questions.
The sports parachute is used to prevent the satellite from smashing into bits on impact. Shown on the next page.
The raspberry pi can be used with the airPi or the Raspberry pi camera module. The camera module is inserted as shown above. See page 3 for the Linux code.
The Otterbox works well as you never know where your satellite may land, and some peace of mind is never a bad thing. An enclosure is required,
The balloon is the most important part of the satellite. This is the driving force, the thrust. Of course, helium is required for it to float.
The gps module allows you to locate the satellite. Launching the satellite in an urban area is not recommended, though the more remote the area, the higher the chance of the gps signal being weak.
The external battery is obvious. The raspberry pi requires power. The shorter the flight, the lighter the battery required. The model B uses 400 milliamp in an hour, while the model A uses considerably less than that. Judge the size of the battery against the length of recording.

Step 2: Code and Construction

If you choose to use the camera module, you'll want to use the code: raspistill -tl This is of course, after having inserted and enabled the camera module in the pi settings. So if I wanted to take a photo every 10 seconds, I would type: raspistill -tl <10000>
If you choose to use the airPi, after inserting the board to the pi, the results will come through, but will not be visible, as you have no screen. Do not worry, as these results will be clear once you have collected the raspberry pi and connected it to a monitor, and you can forecast the weather, test your atmospheric CO2 levels, and use as many sensors as your heart desires.
The most difficult part, in my opinion, is the GPS module, depending on which one you have chosen. If using a mobile phone, make sure you are in a reasonably urban, but not too built up area. Of course, make sure the app is active and that the external battery is charging the phone as well as the pi. In any case, make sure nothing could be blocking the GPS signal when you launch the satellite. With the Loc8tor, everything is very easy. You are shown the exact location on request, via an easy-to-use application. With other GPS trackers, the difficulty varies. The main cause of failure for atmospheric satellites is the lack of GPS signal, and the inability to retrieve the payload.
Once you've got your functional part set up, you've done the hard part. The rest is very easy. Place your functional part (including the raspberry pi!) into your enclosure. Connect the power cord to the external battery, and make sure you're receiving whatever you want to receive. Place the gps module inside, making sure it is on and showing the current location. Close the enclosure and tape the parachute's strings to the underside of the enclosure (or use glue, or do whatever secures your parachute to the satellite). Now fill as many balloons with helium as you can (unless using a weather balloon, like the one in the link, in which case one should be fine), and make sure they are securely connected to the box. You're done! Wait for around 8 hours, before checking the gps location. You can now collect your satellite, connect the pi to a monitor, and enjoy the breathtaking photos or atmospheric measurements you collected.

Step 3: Extras

It is often said that to save power, you should shut off the video inputs on the pi. This is not a great idea, considering you'll want to see your photos or data, and there's not much hope of that when you can't see what you're doing.
Mega pixels are not important. The pi may run out of memory by the end of the flight, depending on the time lapse you set, but as any professional photographer will tell you, anything above 4 megapixels doesn't noticeably affect the image quality. Which is fortunate, considering the raspberry pi has a 5 megapixel camera.
If you have faith in your satellite, and are on a budget, a phone can be used as a GPS tracker. This is risky, but ideal when deciding whether High Altitude Weather Ballooning (HAWB) might be of interest to you. If using an iPhone, the app "Find my iPhone" can be used, or if on android, "GPS Tracking Pro" is recommended.
I recommend you write a phone number, or some kind of contact address on the enclosure, as someone may find it and, not knowing the owner, dispose of it. The risk of theft is small, considering you have a GPS tracker installed, but of course the risk is larger if you are using a smartphone.
And pretty much all there is to it, on the simple side of things. With all parts ordered, this project can be completed in a day, but can be repeated as many times as your number of balloons will allow you.
This instructable has no license, so please send me any photos or information if you build your own, and feel free to base your own instructables upon this one. No credit required. Good luck!

Photo Credits - Pi enclosure and Earth shot: Dave Akerman
Tag: Build My Lab