Launching Cumbria's next balloon to the stratosphere
Holding a YAGI antenna for extended time periods will be tiring, so we created this stand out of wood to hold it for us. In addition, we implemented a payload holder. As you can see, the balloon payload is in it’s final form of creation (without the balloon of course) – and we are now looking for appropriate launch dates on predict.habhub.org
We need to launch our balloon when we have a reasonable chance of recovering it as well as when we can be confident that it will not land in a dangerous or inconvenient location. To accomplish this, we will use several tools as follows: flight predictors (Cambridge and Southampton Universities), BBC weather and jet stream predictors.
Both Cambridge and Southampton Universities use modelling software – you input your information, e.g. altitude, ideal ascent and descent rates and outputs a prediction of your flight path. Cambridge University will give you the most likely path and landing location and Southampton gives a variety of different outcomes by factoring in different variables and adjusting them to create an area of prediction rather than a specific point (this is called the Monte Carlo method).
We also look at ground level weather on the BBC website to avoid high surface wind speeds and rain which helps to reduce the risk of any issues occurring during the launch procedure.
And lastly, look at the jet stream predictor which gives us more accurate representation as to how the balloon will be affected by the jet stream. We don’t want to launch the balloon if the balloon is going to spend a long time in the jet stream as this will cause the balloon to fly further from the launch site (ideally less than 100 miles away).
We will then use our launch criteria check list which outlines conditions that are acceptable and unacceptable to launch in. For example, we won’t launch if the predictions show we are likely to and in large bodies of water, high congested areas, or power lines. There are redlines which cannot be crossed.
References:
http://astra-planner.soton.ac.uk/
http://predict.habhub.org/
There is quite a lot of variability in ascent and descent rates, but typically the balloon follows a steady and linear path both for ascent and descent.
The balloon will ascend rapidly at first, and then settle to a steady 4.6ms-1 to 5.8ms-1 for a typical 1-meter radius helium balloon.
The apex is usually around 25-35km. (approximately 100,000 feet, for perspective, 3 times commercial aircraft cruising altitude)
The balloon’s descent rate can be controlled, but it is recommended to aim for a steady 4 to 5ms-1 rate of descent. (controlled by the parachute)
Assuming the balloon reaches 30km, and ascends and descends at average rates, the ascent time would be approximately 1 hour and 40 minutes, and the descent time would be around 1 hour and 50 minutes, summing to a round-trip time of 3 hours and 30 minutes.
It is important to try and fill the balloon with the correct quantity of helium (considering payload mass) because the flight prediction software relies upon the anticipated ascent and descent rates of the balloon. An underfilled balloon will tend to travel much further. The typical distance covered depends completely on atmospheric conditions e.g. wind speed and jet stream, and could be from a few miles to hundreds of miles.
A typical balloon’s profile:
https://www.whitemountainscience.org/wmsi-blog/2016/11/29/profile-high-altitude-balloon-recovery credit goes to Bill Church