Using inflatable balloons to collect hydrogen from space as a simple solution for radiation shielding

Question

I've seen this video where around the 4:59 mark it states hydrogen is the "best element" to protect humans from cosmic rays:

Even if it's not completely true, we know hydrogen is present in space, albeit in very low quantities. My guess is it has a slightly higher concentration in low earth orbit. So, what if we put a series of huge inflatable balloons around the crew deck of a spaceship? They might collect hydrogen around the Earth for months if needed, prior to the transfer burn to Mars or any other destination. It would be a very simple, yet cost-effective solution for radiation protection. Thoughts?

Answer 1

As the narrator says almost immediately afterward, they're looking at using water as shielding, not gaseous hydrogen; you need to bring water along anyway, might as well store it around the crew spaces to serve as radiation shielding as well. Some groups are also investigating hydrogen-rich polymers as a possible barrier to GCRs.

Answer 2

Such a technique, while possible, is very impractical. This is in part because, in leo and even at the karman line, the atmosphere is so extremely rarified that it no longer acts as a fluid and instead is simplified to the interactions of individual molecules. Gas molecules collide 100,000,000,000 each second and travel 500 times the length of the atoms diameter before colliding, but in space, this collision between two gas molecules only occurs ever few metres. This means that, even if you could design a mechanism light enough to out weigh the cost of simply launching up hydrogen, it would likely just bounce out. There is the idea that you could use some sort of matrix structure like an aerogel to trap hydrogen gas, but such a solution offers far more complexity than cost savings, and again weight is the primary concern.