Actarus Project

Open Source Arduino & Android-based High Altitude Balloon with Gps Assisted auto "Return To Launch"

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Actarus XI – Final goal of the mission

We are just 18 days away to the launch of Actarus XI (this is the final name of the mission), and it is time to publish the details of the mission, in terms of objectives and the equipment used.
With this post we begin to analyze the objectives of this first launch that will serve mainly to collect data and photos, useful for subsequent missions.
In particular, in addition to performing shooting photos and video will be logged (saved in a log file on sd card), the following information:

  • Latitude
  • Longitude
  • GPS Altitude
  • Internal temperature
  • Outside temperature
  • Atmospheric pressure
  • Acceleration in three axes x, y and z

The processing of these data make it possible to understand and evaluate a range of essential information for subsequent missions, in particular:

  • reliability of the prediction on the trajectory
  • rate of climb
  • rate of descent
  • lateral acceleration (so in essence the strength of winds)
  • capacity of the thermal insulation
  • battery life

It will then be temporarily excluded from the objectives of the mission, for weight problems, the assessment of the impact of low temperatures on the servomotor (which will control the direction of the drone) and solar radiation suitable for the production of energy.


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How it works – a little theory

How does the balloons fly in near space work?
The idea is quite simple.
The helium gas is lighter than air. The air density is in fact 1,225 kg/m3 while the helium is 0,1785 kg/m3. This roughly means that 1 liter of helium, weighs “-1 gram”,  namely that a liter of helium is able to lift approximately 1 gram.
In this way, if we fill a balloon with about 2,000 liters of helium, we have an upward thrust of about 2,000 grams. Without the weight of the balloon that is 1,200 grams, there are another 800 grams of weight to be lifted. If the payload will be 800g, the situazione would be stable, so in order to have a little push we need to leave at least 550 grams free. There are so 250g of weight to be lifted. In these 250 grams we have to put strings, the camera, the GPS tracker and the onboard computer.
That said, at what speed will lift our balloon?
The calculation to be done is quite complex, because we have two conflicting forces. One is graviity force upwards caused by helium, and the other is the friction of the balloon against the air that increases as we go up due to the increase of volume of the balloon (which will be discussed shortly).
Using an online calculator, we can say that the average speed with the parameters above, is about 5.3 m/s.
How do we know at what altitude will go the balloon?
Here too it is to do two calculations. Because the higher you climb, the more the atmospheric pressure decreases, our balloon will get bigger according to the physical law on the gas, so halving the pressure doubles the volume. In this way the balloon we inflated with 2,000 liters (and therefore with 2m3 of volume), arrived at 5000 meters above sea level will double the volume (4m3), according to an exponential progression…  Arrived at about 33,000 meters, the volume will be so high (approximately 130 times the initial volume), the balloon will burst, and at this point our payload will begin to fall. At what speed?
Also here we have to calculate the two forces, the gravity that “pulls” downward and that of friction of our parachute … The calculations are quite complex, but even here there is a usefull online calculator. For a payload of 250g and with a parachute of 40cm in diameter, the speed of fall will be about 6.5 m/s.
At this point we just have to calculate the trajectory of our ball, and here will help us a site that using the predictions of the winds, gives us a fairly accurate path with landing point, once specified the starting point, the ascent and descent speed and altitude of bursts.
Et voila!!! 🙂

The Actarus Project

What is Actarus Project?
The project aims to launch a payload with GPS, camera, sensors and communications to an altitude of more than 38km (125000ft) with the help of a helium inflated balloon, and then get it back with a autonomous paraglider drone so that the payload can return to the launch site.
The final goal of the project is to take pictures, videos, weather data and to prove that is possibile to design and build a simply “Return To Launch” system, suitable for other similar projects.
In fact, although we have seen that it is fairly easy to launch these balloons at high altitudes, the problem of recovering the payload, it is not always easy, especially if you live in an inaccessible and wild area as the one in which we live.
So the main difference between our project and ohter similar projects, is the way the payload will come back to the earth.
Also we would like to try to beat the 53km world record.
All the project is open source, so all information about the hardware and the software used for the missions, will be available to everyone through our website.
We think the technological work behind this project, which is based practically on the Arduino and Android platforms, made available to everyone will mark a step forward in the search for near space, and can be a source by other scientists or hobbist around the world.

Who are we?
We are two friends with a passion for electronics, adventure, and science (and of course make the impossible possible…) 🙂
So we have been playing with some projects (this is not the only one!!!) based on these three passions.
All the projects are designed by us, taking inspiration from other projects that we have found on the net.
The starting points are Arduino, Android based smartphones, and a touch of madness… 🙂

All began in late 2011 when we saw a hobby high altitude baloon on a magazine, so we asked each other if we would be able to do something like that.
In some days we had all the stuff for the first very low altitude test launch, and so began the “Actarus Era”.
These tests aims to become familiar with the all the calculations and the necessary tools, and they have produced positive results.
The reasons why we didn’t make high altitude test are economic and legal: before start with a high altitude project we need some more funds (in the test launches we used standard party balloons and low resolution old smartphones) and some permissions issued by E.N.A.C. (sort of Federal Aviation Administration).

The future
So after a break of about a year, during which we continued to work in the background and study the details of our project, we are almost ready for final launches.
This will be through a series of successive launches in which each will provide information for the next launch.
These launches would take place from the month of June 2013.
Now we  just need some funds to realize our project.
If you want you can contribute with just little money: please take a look at this post, or contribute through Indiegogo platform at
Thank you

L & A