[Space] test filling the test balloon

Ed Moore eam52 at cam.ac.uk
Wed Jan 13 15:41:27 PST 2010


Just on the off chance it might save you going down the odd dead end that we did, here's just my 2c, if it's any use:

Helium is a very searching gas. If there's a leak, Helium will find it, whereas you might be none the wiser if you tested it with CO2. We have experienced this directly.

In our experience, the ease of inflation is almost entirely a function of wind speed. Trivial on a still day, and a pig if there's a decent breeze, with the neck twisting up and threatening to snap. Additionally, helium regulators can become unstable (their diaphragm starts oscillating wildly and it makes an awful noise) if there is not enough back pressure on the low pressure side, so we sometimes put a bit of a kink into the low pressure tube to give it something to work against.

Here is a photo that shows our basic setup. It's just a PVC fill tube which we feed with a low pressure hose from one end, and pull the balloon neck over the other end. That's me in the middle.

http://www.flickr.com/photos/jcoxon77/3729673291/sizes/l/in/set-72157621083447545/

Once the balloon is full, we tend to seal it with cable ties whilst it is still on the fill tube:

http://www.flickr.com/photos/cuspaceflight/3740803122/in/set-72157621627845939/

and then tie the payload on, then remove the rest of the neck from the tube, fold it back up on itself, more cable ties, then a couple of turns of duct-tape to stop the sharp edges from the cut cable ties from cutting the balloon.

Here is Henry modelling the fill tube:

http://www.flickr.com/photos/cuspaceflight/3740862214/sizes/l/in/set-72157621752468298/

The 90-degree joint is useful because you can hang stuff off it, like a pre-determined mass which is the mass of the payload + the mass of the free lift you desire. Then we fill the balloon until it is neutrally buoyant with this mass. At least, that is how we used to do it, now we use fish-scales and hook them onto the fill tube to measure the neck lift of the balloon. It's a bit less faff.

Anyway, this is just how we do it, there are obviously lots of far more experienced groups in your part of the world who have it figured out much better. The one single lesson I have learned from launching though, and forgive me if this is teaching granny to suck eggs, but it's caught us out a couple of times, is that inflating the balloon really is the point of no return, so be absolutely sure that the payload is fully working, that you have got a solid GPS lock for several minutes already, before you commit. There's nothing more annoying than having to abandon $150 of balloon and helium because the GPS is being flakey or the flight computer has crashed because the SD card has had some unexpected wait-state about 20 minutes in.


	- Ed

_____________________
Ed Moore,  CU Spaceflight 

On 13 Jan 2010, at 22:59, deleted wrote:

> Bear in mind that filling a gas that's positively buoyant is going to be significantly different logistically than filling a negative or neutral gas.  The only reason I can think of to practice with a neutral gas would be if you're trying to devise an airtight filler seal.  Make sure your whole filling rig can withstand like 20lbs of upward vertical force.
> 
> On Wed, Jan 13, 2010 at 2:14 PM, Christie Dudley <longobord at gmail.com> wrote:
> I think nitrogen might be better for the balloon due to it's inertness and it shouldn't be significantly different from CO2 in price, but I may be wrong.  Praxair, I've heard, is a bit cheaper than airgas.  I vaguely recall hearing about the FLG discount that could be had, too.  I can look into that.
> 
> Christie
> 
> 
>> On Jan 13, 2010 1:59 PM, "Jonathan Moore" <moore at eds.org> wrote:
>> 
>> I would guess airgas. I have bought CO2 there for a reasonable price.
>> On Wed, Jan 13, 2010 at 1:29 PM, Mikolaj Habryn <dichro at rcpt.to> wrote: > Apparently filling balloo...
>> 
> 
> 
> _______________________________________________
> Space mailing list
> Space at lists.noisebridge.net
> https://www.noisebridge.net/mailman/listinfo/space
> 
> 
> _______________________________________________
> Space mailing list
> Space at lists.noisebridge.net
> https://www.noisebridge.net/mailman/listinfo/space



More information about the Space mailing list