Calculating volume and lifting gas for a zero-pressure balloon

[physicsCU]

For a lab I am working on, we are designing a high-altitude research balloon.

I have some questions though.

1. How do I calculate the volume of a zero-pressure balloon? By taking my mass of the body over the density of the air at altitude, does this give me the volume of gas needed at that altitude? But the zero-pressure has a larger envelope that isn't filled so that the gas expands.

2. From question 1, how would I figure out how much lifting gas i needed at the ground? Is there a formula I can use?

3. How do I compensate for the diurnal cycle to maintain a specific altitude?

Thanks for the help!

 

[lightgrav]

surely you mean "zero gauge pressure" ...
This is P_atm = 10^5 N/m^2 at ground!
buoyant Force is (rho_displaced)(V_displaced)g
As P decreases, V of the gas increases
. . . but not for your payload!
Unless you heat it, lifting effectiveness
will decrease consistently as it rises.

I have only half-baked ideas for T stability!
Good Luck!