it's my first question here, I'll try to be clear.
I'm creating a story where there is a steampunk style civilization that has to face advanced civilizations in planetary and spatial battles.
I'm trying to create a steampunk army able to fly in an Earth-like planet and in space.
I think a new power source will be necessary for propulsion in the void, but I want to keep the steampunk style, so I'm asking for help in designing a zeppelin able to elevate high in sky till it arrives in space and then uses the alternate power source to get propulsion.
Which material should have the balloon to float thanks to helium but keep the shape in the void?
Thank you all for your answers. Since other civilizations from my story use some kind of magic, I think my steampunk airship could use some magic too.
So I picked the answer @Willk provided and I'll use the hydrogen as a gas while the zeppelin remains in the surface of the planet. Then when it needs to rise into space, the hydrogen gets burned to gain altitude and then used as a rocket propellant to get out from the planet's gravity.
Then, when there is no hydrogen remaining, the balloon cover, displaces thanks to gears, shaping into solar sails as @Joe Bloggs stated to navigate the void since it don't have the need to run very fast.
Finally, when it's time to return to mainland, the sails could transform into some kind of parachutes to land safely, but I'm not 100% sure of this...