Mission SammyOne

The Parachute



I did not want my payload to return to earth at terminal velocity, shattered to a thousand pieces on landing. Besides that, the Dutch government sets certain limits on what is the desired descent rate for the payload from a free balloon.

I needed a parachute. But how big and where to buy? I researched the web and quickly found shops that sold rocket parachutes. They come in all sizes, colors and strengths. As my parachute would only have to carry a bit more than a kilo of weight to earth, I thought that the cheapest brand would do good enough. Now I only had to know the size.

I created a spreadsheet for that. With formulas from the internet and ICAO standard atmosphere charts I was able to calculate the descent rate given the weight from the payload, the air density, the chutes drag factor and the diameter. I calculated that at 100,000ft my payload would drop to earth at a whopping 150 km/hr slowing down to only 18km/hr at sea level!

Here is what I calculated:

Diameter: 1.25 m

Payload in Newton: 14.2

Drag coefficient: 0,75 (round parachute with no holes in it)

Estimated descent rates at altitude:

landing - 18 km/hr

1000ft - 18 km/hr

10,000ft - 21 km/hr

20,000ft - 25 km/hr

30,000ft - 30 km/hr

40,000ft - 36 km/hr

100,000ft - 153 km/hr  

The Excel sheet can be found here. Use it at your own risk :-)

I got a green one with a 1.25 meter diameter.

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The Parachute

One of the first images captured