Mars Solar Bag

The heated air inside the bag causes the bag to float.

A Solar Bag is a long plastic bag made from a very thin plastic and colored black to absorb solar energy. The heated air inside the bag provides buoyancy and causes the bag to float. Over the years, it’s become a very popular science demo for teachers to share with their students as they explore the properties of air. You can imagine how surprised we were to learn that scientists from Pioneer Astronautics and Jet Propulsion Laboratory conducted successful tests of its Mars solar balloon inflation system using our Solar Bag. These photos give you a bird’s eye view of what our Solar Bag looks like at about 120,000 feet above the Earth! Keep reading to learn how scientists are conducting tests to develop an actual Mars balloon mission.


Pioneer Astronautics has conducted a successful dynamic test of its Mars solar balloon inflation system. The experiment, performed at an altitude of 116,000 ft over Kuner, Colorado, on September 26, was part of an SBIR phase 2 program supported by NASA’s Jet Propulsion Laboratory in Pasadena, California.

Scientists have yearned for many years to make use of Mars’ thin carbon dioxide atmosphere to enable airborne exploration. Balloon carried instruments would return a bird’s eye view of Mars unequalled by either orbital or surface platforms, and would reveal through their travels the pattern of the planet’s atmospheric motions as well. However attractive such a mission might be, Mars balloon missions have long been stalled by the challenge of autonomously deploying and inflating a balloon from a descending Mars entry capsule.

To address this question, Pioneer Astronautics has developed an innovative balloon inflation system. Instead of using a conventional inflation gas stored in heavy high-pressure tanks delivered to the balloon using complex plumbing and valving systems, the Pioneer technique employs a vaporizable liquid such as methanol as a float fluid. The methanol is stored within a balloon which is colored black to absorb solar energy, and which in turn is stored in a pressurized canister. When the canister is opened under the low-pressure conditions which prevail at low altitudes on Mars or high altitudes on Earth, part of the methanol flashes to vapor, driving the balloon out of canister. Inflation is then completed automatically as solar energy vaporizes the remainder of the methanol.

An alternative solar-heated balloon system being developed by JPL fills a balloon with ambient atmosphere while it is falling. The balloon is then quickly heated by the sun, providing buoyancy. The Pioneer liquid-filled balloon buoyancy technique is similar, but induces less stress on the balloon. Also, because a gas with a lower molecular weight than CO2 is employed, a smaller balloon can be used to lift an equivalent payload.

On August 23, 2000, this system was first successfully tested under non-dynamic conditions. Deployed from a slowly ascending balloon at an altitude of about 97,000 ft, a 25 cubic foot black methanol solar balloon was observed to inflate in less than a minute. Following that successful test, the Pioneer investigators, in consultation with JPL, agreed to address the more formidable challenge of autonomously inflating a balloon under the dynamic conditions that would occur during parachute descent on Mars.

The September 26 flight test was the culmination of this program. The experiment was lifted to altitude by a 141,000 cubic foot polyethylene balloon, with a smaller 19,000 cubic foot balloon used to decelerate the payload to parachute descent type velocities. The flight string below these balloons was fully redundant, including two GPS transponders, two cameras, and two methanol balloon canisters, as well as a small backup parachute and a radio-direction finding beacon. This highly complex launch string was close to 300 ft long. Launch from the Fatton Ranch near Windsor, Colorado, was accomplished using the entire Pioneer Astronautics workforce, assisted by the rancher and a group of Mars Society volunteers. Tracking was provided by two mobile GPS/VHF receiver teams, who were also equipped with radio direction finding (RDF) equipment. These were backed up by volunteers from the Boulder-based Deep Space Exploration Society who followed the flight using their 60 ft radio dish.

The launch took place at about 8:40 AM under clear skies and near windless conditions. Ascent rate was about 700 ft/min at takeoff, rising to 1050 ft/min towards apogee, and the slowly moving payload was visible from the ground throughout almost all of its flight.

One of the GPS units lost lock at 58,000 ft; however, the other continued to give good GPS data. At 10:40 AM, the system reached 115,000 ft and Pioneer radioed a command to cut away the main balloon. This was done with a portable high gain Yagi antenna, causing separation to occur at 119,000 ft at 10:44 AM. The carrier balloon continued to ascend to about 122,000 ft, where its burst panel opened and it began to descend.

Approximately 30 seconds after carrier balloon cutaway, the balloon canisters opened. However, when the upper canister opened, the safety string holding its upper half to the lower half either broke or otherwise came loose. In any case, the entire lower experimental train, consisting of the backup canister, the lower TV camera, and the RDF beacon was lost.

The solar balloon stayed in the upper canister for perhaps ten seconds, then popped forcefully out in a partially inflated condition. Inflation was then completed at an estimated altitude of 116,000 ft and a descent velocity of about 35 miles per hour.

Atmospheric density at 116,000 ft on Earth is equal to that at an altitude of 8 km on Mars. Temperature in Earth’s atmosphere at 116,000 ft is about -26 degrees C, comparable to the -56 degrees C expected at 8 km on Mars. The 35 mph descent velocity could also be attained on Mars using a parachute decelerated Mars entry capsule system. The experiment was thus a good duplicate test for a Mars mission.

Pioneer’s mobile teams managed to keep both the carrier balloon and drag balloon/flight experiment systems in view until shortly before they hit the ground around 11:45 AM. Both landed in a swampy wooded area of state land north of Hardin, Colorado, about 30 miles ESE of the launch site. The solar balloon and camcorder were successfully recovered around 3:15 PM, and the remains of the carrier balloon were recovered around 5:15 PM.

Commenting on the experiment, Pioneer Astronautics president Robert Zubrin said, “This flight was a notable success. We had some subsystem failures, but the redundancy of our overall experimental design carried us through to get the data. The bottom line is that we have now conducted a dynamic autonomous inflation of a balloon under conditions that in almost every way duplicate those that will need to be dealt with on Mars. This knocks down one of the tall poles that has long been standing in the way of a Mars balloon mission.”

“The next steps needed are to reproduce this work with larger craft, and eventually with full-scale replicas of those needed for an actual Mars balloon mission. Let’s do it, and open the skies of Mars.”

Dr. Zubrin served as Principal Investigator for the project at Pioneer Astronautics, with Dr. Gary Snyder and K. Mark Caviezel serving as Pioneer’s lead electronics and balloon systems engineers, respectively. The technical monitor for the program at the Jet Propulsion Laboratory was Jack Jones.

Additional Info

A special thanks to Mark Caviezel from Pioneer Astronautics for providing this information and giving us permission to share the great photographs.

Note: Someone out there is bound to call our office and complain that their Solar Bag just didn’t go up 120,000 feet. Our only reply is… start small and work your way up.

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