What is the maximum height could a weather balloon achieve on Mars without rupturing?
Assume that the balloon is adapted for Mars' atmosphere and gravity from standard high altitude balloons used on Earth.
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$\begingroup$ I think "What advantages would a weather balloon provide over a rover?" is a totally different question, the obvious answer is that a rover would make a terrible weather balloon. Why not ask "what advantages and practical limitations would lighter than air craft have over rovers for explanation on Mars?" separately? $\endgroup$– uhohCommented Mar 20, 2019 at 2:48
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$\begingroup$ Why the tag rovers? A rover and a balloon are two very different things. If a balloon is filled with very little gas so that its pressure in a vacuum is well below its burst pressure, it would not rupture. But this balloon would never reach vacuum when started from the surface. Remember the balloon satellite Echo in Earth orbit long ago. $\endgroup$– UweCommented Mar 20, 2019 at 12:04
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2$\begingroup$ If the balloon includes a pressure-relief valve, it won't rupture, no matter how high it goes. The real question is how high can a balloon go in the Martian atmosphere? I.e.at what altitude does the air it displaces weigh the same as the balloon? $\endgroup$– Ray ButterworthCommented Mar 20, 2019 at 12:46
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$\begingroup$ Be back on the Electronics SE tomorrow! :-) $\endgroup$– peterhCommented Mar 20, 2019 at 17:38
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1$\begingroup$ @uhoh I'd even ask, why place one most highest altitude atmospheric balloon in mars atmosphere, when you can stay orbital, LMO or GMO, and save speed, fuel/mass, velocity changes, avoid atmospheric disturbances and instruments related incaccuracies. $\endgroup$– user19132Commented Mar 25, 2019 at 23:28
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Most weather balloons can go up to about 40 km. At that altitude, the pressure is about 2.9 millibars. The Martian atmosphere is about 6 millibars at surface level. At the summit of Olympus Mons (21.25 km) the pressure is about 0.3 millibar. That would set 2.9 millibar at about 9.8 km above the Martian surface.
The record for highest high-altitude balloon is 53 km, where the pressure is only 0.55 millibar. If released on Mars that balloon would pass the top of Olympus Mons going up to 28 km.
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$\begingroup$ I ran the numbers and got 0.55 millibars at 28km. I've seen from 0.3 to 0.72 millibars quoted as the pressure at the top of Olympus Mons. I'm going to chalk that up to seasonal variations and that the measurements are all derived. $\endgroup$– SchwernCommented Mar 21, 2019 at 1:10
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$\begingroup$ This calculation seems to assume that pressure varies linearly with height. I don't believe this is the case in Martian atmosphere. It's more exponential on Earth, and it should occur for the same reasons on Mars. $\endgroup$– JMacCommented Mar 21, 2019 at 12:25
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$\begingroup$ @JMac Yes,
p = 699 * e^(−0.00009∗ℎ)according to NASA orh = -11111 * ln(p/699)(in Pascals and meters). That puts 290 Pa (2.9 mbar) at a bit under 10km. The answer isn't far off. $\endgroup$– SchwernCommented Mar 21, 2019 at 17:02 -
$\begingroup$ But balloons on Mars can obviously go higher than 9.8 km because of the gravity of Mars which is less than half as strong as the Earth's. $\endgroup$ Commented Jun 18, 2020 at 9:23