Sending a camera to the edge of space and recovering the wreckage from the children who found it
Send a digital camera as high as possible, have it take photos (and collect atmospheric data), and retrieve everything after it parachutes back down to earth.
With digital cameras and smartphones becoming ubiquitous, sending and retrieving a camera from space has become a fairly common hobbyist project. This means there is plenty of useful reference material and planning software we can take advantage of.
Our process will be:
We want to achieve two goals: capture photographs, and collect atmospheric data. A maximum altitude of 90,000ft will be our target, which will guide much of our design.
We need a compact digital camera with intervalometer functionality for taking photos at regular intervals. Thanks to the open-source CHDK (Canon Hack Development Kit) project, any Canon digital camera can be modified to work.
We will use an old Canon Powershot SD1100 IS, which has the added bonus of having built-in image stabilization.
Installing CHDK allows us to use the KAP UAV Exposure Control script, designed specifically for our purposes. Beyond intervalometer functionality, it intelligently controls shutter speed, aperture, and ISO settings to ensure sharp images with consistent exposure.
We aren’t constrained by space as much as we typically are, so an Arduino Uno R3 will work fine as a microcontroller:
For measuring barometric pressure and temperature, we will use the BMP085:
For measuring humidity we will use the DHT22:
For recording the direction the camera is facing, we will use a HMC5883L magnetometer / compass module:
For detecting acceleration (g-force, orientation), we will use the ADXL345:
For power we will use two 3.7V Li-Po batteries in series:
For GPS location tracking we can use an old iPhone. We can setup a program which responds to an SMS query with its current GPS coordinates. We will lose service after a few thousand feet of altitude, but this doesn’t matter as we will only need to ping for the payload location during its descent.
At our desired maximum altitude of 90,000ft, the temperature will be approximately -50C - cold enough to cause problems with some of our electronics. The camera, batteries, and most of the electronics will need to be kept warm in an isolated compartment. We will design our enclosure using foam, separating any components whose performance may suffer at low temperatures in a foil-lined section.
Just prior to launch we will throw in some glove warmers to keep this compartment warm.
The sensor modules need to be exposed to atmosphere, so they will be housed outside the isolated compartment. So will the phone which needs cell reception in order to provide us with GPS coordinates.
Throwing it all together, we have our enclosure:
This will all be taped together tightly before launch.
With our payload completed, we can now work on getting it into the air and back down again safely.
From a safety perspective, we should build a radar reflector to ensure that our balloon and payload are not invisible to passing planes. To return our payload quickly but safely, we will need a properly sized parachute, stowed appropriately so that it does not deploy before the weather balloon bursts. And lastly the balloon we use will need to be appropriately sized to lift all of this, ensuring we reach our desired height before bursting.
The layout will be the following:
We will use bright orange Mil-Spec 550 paracord for the tether/suspension line:
A lightweight radar reflector can be easily made using cardboard and foil tape.
We build one approximately as large as the enclosure:
Tallying up our weights so far:
We are already at 624.32g, and still need to add a parachute which could be up to 100g. The standard weather balloon used for a payload of 1-2lbs is the Kaymont HAB-600:
It seems ideal for our purposes:
Using a balloon burst calculator, we can figure out how much helium we will need in order to achieve our desired height of 90,000ft. We want the balloon to reach its burst diameter as close to 90,000ft as possible.
With 90.3 ft^3 (2557L / 2.56m^3) of helium, the balloon will rise for 81 minutes with an ascent rate of 5.65m/s, before bursting at 90,000ft.
The helium canister will come with a regulator, so we must design an adapter for connecting the neck of the balloon for filling:
We will use ripstop nylon to build our parachute. This is commonly done in the amateur rocket community, and a useful guide is available.
To keep our payload from drifting too far from our launch site, we want our payload to return to the earth as quickly as possible. We also want it to land without suffering significant damage. NASA typically uses 5m/s as a descent rate for their payloads, but we should be able to get away with a descent rate of 6m/s.
Tallying up our final weights:
We get a total of 1304.32g. Using a parachute descent rate calculator, the following parameters will result in a descent rate of 6m/s:
From 90,000ft this will result in a descent duration of 4589s (76.5 minutes).
Knowing our ascent rate, descent rate, total weight, and helium volume, we can use flightpath prediction software to identify the ideal location (and conditions) for launch.
For convenience, we will aim for a landing site less than 125km from the launch site. For safety we will also avoid airports, highways, and large cities.
We play with our launch times to achieve the ideal flightpath:
With a launch location and time determined, we are ready to send our balloon up.
The helium is picked up:
The payload is assembled:
The parachute is prepared:
The camera is tested:
The balloon is inflated:
Time to launch:
We have liftoff:
After a 2 hour journey up and down, we ping for a GPS location one last time. The payload’s final resting place was the backyard of a farmhouse:
A long drive and we’ve found it:
How it ended up in the backyard was a fun story: some kids saw the balloon coming in for a landing in a nearby forest, and chased it down on their ATVs. They took it home, tore it apart, and started looking at the photos, thinking it may be of military origin. They were disappointed to learn the truth.
The balloon reached a maximum altitude of 66,000ft (20,140m), taking 1h4m to ascend and 37m to descend. This is short of our design goal of 90,000ft, which means the balloon was overinflated at launch.
Photos:
Flight Path:
Looking at the final moments, we can see where the payload initially ended before being brought into the backyard:
Data:
