Mesospheric Slingshot

I would like to take forward the idea of "SpinLaunch" (https://www.spinlaunch.com). SpinLaunch's idea is to slingshot a small satellite to space by accelerating it to very high speeds in a special accelerator on the ground. My proposition is to use a very high altitude hydrogen filled balloon for the slingshot. The giant balloon will be at an altitude higher than 50km (Mesosphere). Top surface of the balloon will be covered with high efficiency solar panels which will power the accelerator (hydrogen fuel cells can also assist the solar panels). The thin atmosphere at that altitude will decrease the need for expensive heat shields and loss of energy due to atmospheric drag. The satellite would have a very small rocket on board which can be powered by liquid hydrogen and oxygen. Therefore the launch would be Carbon neutral. The satellites to be launched would be transferred to the balloon by transporting balloons like Zeppelins that utilize hydrogen. The ground launch site would be close to the ocean where hydrogen and oxygen would be generated using wind farms and ocean water.