One of the problems I am going to face when it comes to launch time, is exactly how much helium do I need to get the required lift. To much and the balloon will burst early and not reach a high altitude. Not enough and the balloon could just float aimlessly without ever bursting, and very likely land in the ocean.
You can use various calculators around the internet to get a rough idea, such as the habitat burst calculator. You enter the type of balloon and the altitude your attempting to reach and it will provide a ‘Neck Lift’. This is the weight the balloon should be able to left in order to take the payload to the aimed altitude.
When filling the balloon with helium you need to check how much force it is lifting, by either using some luggage scales , or attaching a weight such as a water filled bottle that is at the predetermined weight.
I purchased a small digital scale to assist with filling helium into the balloon.
I chose this particular model as it has a fairly secure handle that I could attach a rope into. Other models had a hand grip which would have been harder to tie down. I just need to be careful of the hook to ensure it doesn’t penetrate the balloon cutting my mission short.
I most probably will have some pre-filled bottles that are at the required weight as a backup, as its the first launch I don’t know how accurate the scale reading will be.