How the Balloons Will Work

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 superpressure balloons, currently under development for the Ultra Long Duration Balloon (ULDB), will fly more than 100 days and perhaps as long as a year. Smaller superpressure balloons carrying payloads of only a few kilograms have already flown for as long as a year.

This technology is now being applied to Mars. The Mars balloon would be deployed soon after the spacecraft enters the Mars atmosphere and would be rapidly inflated from a helium tank as the payload descends beneath a parachute. After inflation is complete, the parachute and tanks would detach and the balloon and its science payload would then fly at a nearly constant altitude for 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 material is under development to permit large payloads to be flown on Mars by such a balloon and tests of balloon deployment in the Earth's atmosphere are underway. Payloads would include imaging, magnetometers, spectroscopy and any technique that can benefit from surface proximity.

Another kind of lightweight balloon, called a solar Montgolfiere, named after the French brothers who flew the first hot air balloon, does not have to be inflated with a light gas such as helium. Instead, the balloon deploys upon entering the Martian atmosphere and an opening at the bottom of the balloon fills up with Martian "air" while falling to the surface. The balloon would be quickly heated by the sun and provide buoyancy. The balloon lifetime is limited to a few hours, because it is only buoyant until the sun goes down. However, the balloon can then play two roles in exploration.

Two Important Roles for Balloons

First, the balloon can be used to provide a soft landing for small payloads on potentially hazardous terrain. The landing should be slower and more controlled than a parachute-assisted or rocket landing system. Montgolfieres are attractive because they are not vulnerable to leaks since leaking "air" would be quickly replaced and re-heated by the sun. Second, once the Montgolfiere drops off its payload, the balloon could go back up into the atmosphere with a small gondola that would perform imaging and gather other science data for the rest of the day. These images would show greater detail than orbiters, which are so far above the surface.