|Proposed use of balloons on Mars|
Balloons have been flying for decades in Earth's stratosphere, which has an atmosphere as thin as that on the surface of Mars. Conventional stratospheric balloons have lifetimes limited to a few days because of the daily heating and cooling of the balloon. Helium super-pressure balloons, currently under development for the Ultra Long Duration Balloon (ULDB), will fly more than 100 days and perhaps as long as a year here on Earth. Smaller super-pressure balloons carrying payloads of only a few pounds have already flown for as long as a year.
|A Mars settlement|
Using this technology, a future Mars balloon would deploy soon after a spacecraft entered the Mars atmosphere and would then rapidly inflate from a helium tank as it descended beneath a parachute. After inflation, the parachute and tanks would detach and the balloon would fly at a nearly constant altitude both day and night. The balloon's internal pressure would be higher during the day than at night, although the balloon volume would remain the same. Strong, lightweight, leak-proof materials are under development to permit large tool kits of science instruments to be flown on such a balloon. Tests of balloon deployment in the Earth's atmosphere are currently underway as well.
Another kind of lightweight balloon that might be useful on Mars is called a solar Montgolfiere balloon, named after the French brothers who flew the first hot air balloon. It does not have to be inflated with a light gas such as helium. Instead, the balloon would deploy upon entering the Martian atmosphere. An opening at the bottom of the balloon would fill up with Martian "air" while falling to the surface. The balloon would then be quickly heated by the sun, which provides buoyancy. Montgolfieres are attractive because they are not vulnerable to leaks, as any leaking Martian "air" would be quickly replaced and re-heated by the sun. However, the balloon lifetime is limited to a few hours, because it is only buoyant until the sun goes down. However, the Montgolfiere balloon can play two important roles in exploration:
- provide a soft, slow landing for small craft on potentially hazardous terrain, with greater control than a parachute-assisted or rocket landing system.
- go back up into the atmosphere after dropping off the landed craft so that it could image the surface further and gather more science data before nightfall