Balloons on Mars
Balloon History on Earth
The first widely recorded, public demonstration of a balloon took place in June of 1783. On this date, a 105-foot circumference balloon, designed by the brothers Joseph and Jacques Montgolfier, was launched in Annonay, France. It rose to an altitude of 6,000 feet. This balloon or ballon was named for the oblong paper bag used in their early experiments. The brothers made a fire and used the smoke and heated air to fill the ballon. Because the air inside the ballon was warmer than the cooler and heavier air surrounding the ballon, it floated upward.
A few months later, a hydrogen-filled balloon designed by Professor Jacques Alexander Charles was successfully launched in Paris, France. Since hydrogen is a gas that is lighter than air molecules, it displaces the air molecules (or pushes them out of the way) as it rises upwards. By the end of that year, both kinds of balloons were being used to carry passengers.
The invention of the balloon started a new period of explorations. The early "aeronauts" competed with one another to travel higher and farther. Today, balloons are used mostly for sports and recreational purposes or for high-altitude scientific and meteorological research.
There are two main parts of a balloon: the balloon itself which is called the envelope, and the basket or gondola. The gondola is attached to the envelope by strong cables. The envelope is made of a lightweight, gas-tight fabric.
How They Stay Airborne
A balloon gets its lift from Archimedes' Principle. A balloon traps lighter-than-air gases (hydrogen or helium or hot air) in its envelope. These gases then displace the cooler and/or heavier air surrounding the envelope on the outside. This creates an upthrust or buoyancy force that lifts the envelope and gondola (that is, if the weight of gondola, passenger(s) and payload are not heavier than the lift force!)
The air pressure in the atmosphere slowly decreases as one rises in altitude. If the pressure on the top of a balloon could be carefully measured, one would find that the air pressure is slightly less there than at the bottom of the balloon. The greater pressure acting on the bottom of the balloon results in a small lift force pushing up on the ball. The amount of lift force depends on the difference in pressure between the top and the bottom of the balloon. As the difference in air pressure between the top of the balloon and the bottom of the balloon becomes greater, the lift force will become greater. It also depends on how big the surface area of the balloon is. The greater the surface area of the balloon the greater the lift force, also.
The Greek mathematician and engineer, Archimedes, described the amount of buoyancy force on an object as equal to the weight of the fluid that it displaces.
As a simple math problem it looks like this:
Weight of displaced fluid = object's volume x fluid densityThe weight of the fluid displaced is the displaced volume times the fluid density. Since the buoyancy force on an object in the atmosphere is so small, an object must be very large and very lightweight to get enough buoyant lift to be useful.
So what does Archimedes taking a bath have to do with flying balloons on Mars? In order for a hot air balloon to carry two people of average weight in Earth's atmosphere, the envelope would need to be almost 55 feet in diameter. That's a fairly large balloon. This balloon would then displace about 6,200 pounds of air. The hot air inside the balloon would weigh about 5,200 pounds. This means that the hot air balloon could really only lift about 1,000 pounds. If the balloon envelope, basket, fuel tanks, and burner weigh about 600 pounds, that would leave only about 400 pounds of lift to pick up two people. In Earth's atmosphere it would be able to generate enough lift to carry its payload safely.
But what about Mars' atmosphere?
Surprise, a hot air balloon on Mars makes no sense, because there is no air on Mars. The atmosphere on Mars is CO2 but there is so little of it that it is not enough to heat. On Mars a helium balloon would make sense.
Did you ever play with a helium balloon at a birthday party when you were little? Can you imagine a helium balloon on Earth that could carry two people (about 400 lbs.)? If the envelope of the balloon was made of thin mylar, it would be 1/3 of the weight of the fabric that is used for hot air balloons. There would be no propane gas tank or gas burner but there would still be a gondola and there would be a helium tank. The size of the helium balloon would be 30 feet in diameter.
On Mars if you used the same materials for a two person balloon, the diameter of the balloon would have to be 160 feet. That's one enormous balloon! The envelop would weigh 1300 lbs. and if you packed it in a container with no airspace, the container would be 2 feet in diameter and 5.5 feet long. That's a big heavy object to send all the way to Mars. There would be very few benefits for the cost of such a balloon. Not to mention that it would be difficult to control the balloon's flight.
So, how are balloons controlled anyway?
The aeronaut can only control the upward and downward movement of the balloon. To ascend, the aeronaut adds hot air or more lighter-than-air gas into the envelope. To descend, the aeronaut releases the hot air or lighter-than-air gas out of the envelope. A balloon has no means of propulsion. A balloon's side-to-side movement cannot be controlled so it drifts with the wind. To change direction, the aeronaut must ascend or descend to catch a wind current moving in the desired direction of flight.
Hot Air Balloon
These balloons are used mainly for sport and recreation. They use air heated by a burner to give the lifting force to carry the gondola and its passengers and cargo. To rise higher, more hot air is released into the envelope. This is done by pulling on a cord that releases the flow of liquid propane from its storage cylinder through a tube toward the burner. The liquid is heated by a flame which warms it and turns it into a gas. The gas reaches the burner. Flames are released from the burner which warms the air in the envelope. To descend, hot air is released from the top of the envelope. This causes the air inside the balloon to become cooler. The balloon then descends.
A hydrogen balloon works just like a hot air balloon except that it does not use a burner to generate hot air. It uses a gas called hydrogen. The gas is stored in a tank and released into the envelope when the balloon needs to ascend. Hydrogen is lighter than the mixture of air molecules found in Earth's atmosphere. So when the envelope is filled with hydrogen, it naturally rises above the heavier air molecules by pushing them out of the way on the way up.
Compare Balloons on Mars and Earth
Atmospheric Flight Table of Contents
Planetary Flight Home Page