Hacker News Reader

Comment by xioxox | Hacker News Reader

Cool! I wonder why balloons have not been used much on other planets? Is it the weight of the gas? The USSR had the the Vega 1 and 2 balloons on Venus, but presumably further missions could be pretty useful for studying planetary atmospheres, even for gas giants.

View on HN

I don't think it's viable for Mars; the atmosphere there is only 1% of what the Earth's is, so (amateur armchair maths) to carry the same payload they'd need a balloon 100x as large, plus something to fill it with lighter than the surrounding atmosphere.

Keep in mind that the lifting power of a balloon scales with volume, not diameter - so something with 100x the volume is only about 4.6 times as big as the equivalent balloon on Earth.

The gas has to be lighter than the atmosphere of the target planet. For planets with very thin atmospheres or planets with mostly-hydrogen atmospheres, that is hard to achieve. That leaves basically Venus and maybe Titan?

Of course! Presumably you could use heated gases in the gas giants (like hot air balloons). I found this rather old JPL page which suggests it could be possible: https://www2.jpl.nasa.gov/adv_tech/balloons/outer_jupisat.ht...

Actually, on Mars it's relatively easy to have a gas be lighter than the atmosphere; the atmosphere is mostly CO2, so most common gases, including nitrogen, are lighter than it. The problem is that since the air is very thin, you don't get much lift for a given volume. So for Mars you need a very big balloon, but it can be filled with almost anything.

(Side note: balloons have actually been used on Venus already, on the Vega missions!)

A clarification: technically, filling a balloon with a lighter gas is actually pretty easy: the pressure inside the balloon is almost the same as that outside (if the balloon is made of a non-stretchy material like mylar that doesn't compress the air), so all you need to have the inside be lighter is to use a less dense gas. Mars atmosphere is mostly CO2, so even nitrogen could work as a lifting gas.

The problem of course is that while it's easy to use a gas that's less dense than Mars' atmosphere, it can't be very much less dense because you're starting from a very low density. So, you'd need a huge volume in order to lift anything substantial.

edit: looks like a sibling comment said the same thing first..

Reply on news.ycombinator.com