Balloons ‑ Types, visibility and flight profiles

Altschuler, Martin D., 1968
  1. Types de ballons
  2. Visibilité
  3. Derelicts and cutdown
  4. Mouvement de ballon
  5. Twilight effects
  6. Ballons éclairés
  7. Fréquence des vols
  8. Balloon UFOs
  9. Conclusions

Types de ballons

Three kinds of balloons can give rise to UFO sightings: neoprene or rubber balloons which expand during ascent from six feet to 30 ft. in diameter; polyethylene balloons which are partially inflated on the ground and fill out at float altitude to a diameter of 100 ft. to 400 ft.; and small super-pressure balloons called "ghost" balloons.

Ballons de néoprène

When neoprene or rubber balloons which are used to carry radiosondes begin their ascent, they have a diameter of six feet. They continue to expand as they rise, and the balloons that reach an altitude of 140000 ft. are 55 ft. in diameter. All of these balloons shatter when they reach a volume at which a weakness develops. One of these balloons has flown as high as 156,000 ft., higher than the largest polyethylene balloons. These balloons are used to make measurements of air temperature, humidity, and winds. Approximately 90% of the neoprene balloons reach 80000 ft.; probably 50% of them reach 100000 ft. The neoprene balloon at any altitude has a brighter reflectance than either the polyethylene or the "ghost" balloon. It is opaque on the ground. As it rises and expands, its skin becomes thinner and reflects and scatters light. They are used in quite large numbers in many places for routine observation because of their low cost. About 100000 of these a year are flown in the United States, with most launches at scheduled times from airports and military installations. During their ascent up to 20000 ft., the neoprene balloons are visible to the naked eye during the daytime, but once they attain an altitude of 20000 ft. or higher they cannot be seen from the ground.

Ballons à super-pression

The other small balloons are the super-pressure "ghost" balloons. In general these have payloads of a few grams. The balloons are usually spherical and size is a function of altitude; five feet in diameter at 20000 ft., seven feet at 40000 ft., ten feet at 60000 ft. A few larger balloons have been flown at higher altitudes. Over 300 super- pressure balloons have been flown in the Southern Hemisphere. Several balloons have flown for over 300 days in the Southern Hemisphere with two balloons still flying which have been in the air for more than 11 mo. Not more than 20 long duration flights have been made in the Northern Hemisphere.

Ballons de polyéthylène

At launch polyethylene balloons are filled with a gas bubble varying from 20 - 70 ft. in diameter. Twenty feet of gas will lift a small balloon to 100000 ft. A 70-ft. bubble is required to carry the Stratoscope II with a 7,000-lb. telescope. Scientists flying this type of balloon usually want to attain altitudes between 80000 and 120000 ft. to gather data on atmospheric radiation or composition. The "cosmic ray community" is the largest user of "ghost" balloons. The diameter of these balloons at altitude is anywhere from 60 - 250 ft. The 250-ft. size is for the Stratoscope II system. The largest balloons, those approximating 300 ft., are designed for very high altitudes. The largest balloon that has been flown to date holds 2.6 x 10^7 cu. ft. of gas and-is just under 400 ft. in diameter. There are a large number of 10000000 cu. ft. balloons being flown approximately half from Palestine, Tex. A few years ago the most common balloon was the 3000000 cu. ft. size.


The relative visibility of a balloon depends on its type, size, material, time-of-day, and altitude. The human eye can usually detect a balloon against a bright sky background when the intercepted arc is 0.5 mil or greater. The radiosonde balloon is visible in daylight to a distance of two to four miles. During ascent, the "ghost" balloon is visible against the bright sky background at a distance of about two miles. At altitude the intercepted arc of "ghost" balloon varies from between 0.2 - 0.6 mil. The polyethylene balloon provides a target of one to two mils at altitude.

The large polyethylene balloons absorb about 5% of sunlight; however, they scatter and reradiate as much as 20 - 30% of the inci- dent light. This scattering is very much a function of angle. Polyethylene balloons are always visible at altitude during daylight hours when the sky is clear. It is often difficult to focus the eyes on the balloon, but once seen it is easy to relocate the balloon. The "ghost" balloon is not visible above 20,000 ft. during daylight hours.

Polyethylene balloons are shaped more like a pear than a sphere, although they always appear spherical from the ground to the naked eye. Glass fiber tapes affixed to the gore seams are used to strengthen polyethylene balloons carrying heavy payloads. Observed from the ground through a telescope, a shell effect gives a taped balloon a saucer-like appearance. The tape itself, which is the basic reflecting element, is quite shiny and reflects well. On very lightly loaded systems the balloons are tapeless; heavier loads require the glass fiber tapes. As seen through the telescope, then, the taped balloons appear much shinier and are distinguished by their scalloped appearance.

Derelicts and cutdown

Another phenomenon that might be witnessed by an observer during the day is what is known as the "cutting down" of a balloon. When the decision has been made to terminate a balloon's flight, the tracking aircraft will send a destruct signal to the balloon's control and command mechanism and a squib will fire. This will detach the payload and shatter the balloon. The payload is then tracked by the plane as it parachutes to the ground. Occasionally, however, the balloon will not shatter.

The shattering of a balloon during payload detachment is easily visible (especially in the late afternoon or early morning). However, the entire operation is not. The payload chute is only 60 ft. in diameter so that it is barely visible. The tracking plane which sends the destruct signal may be 30 - 40 mi. away from the balloon. The "cutting down" of a balloon is usually accomplished one or two hours before sunset or just after dawn so that the pilot can visually track the parachute down. When the balloon does shatter, a large part of the balloon comes down in one piece as a flapping mass. There is little side motion or apparent hovering. Its speed of decent depends on how the balloon breaks up.

With improved balloon materials, there were a number of cases in 1966 where the balloon did not shatter but continued its ascent. Normally, if the balloon does not shatter, it should rise so fast after the shock that the gas does not escape rapidly enough to prevent bursting. Occasionally the balloon will begin to stretch, and if there is no weakness in it, the balloon could remain aloft at that higher altitude for four or five days. It might fly at 130000 or 140000 ft. until sunset at which time the gas will cool, reducing the volume by 5%. This causes the balloon to descend a few thousand feet. In daytime, at high altitudes the balloon's skin tends to run colder than the atmospheric temperature. As the balloon cools in the evening, it starts to descend because it has lost its volume. When it gets to approximately 60,000 - 70,000 ft., where the atmospheric temperatures are colder, the balloon is warmer than ambient temperature. It then picks up the 5% lost solar heat and continues to float along at this altitude until the next morning when it warms up and returns. to maximum altitude.

For example, a 1000000 cu. ft. balloon, launched in France came down in Montana in August 1966, after having remained aloft for 27 days. This balloon had been traveling at 60000 to 100000 ft.

Mouvement de ballon

Actual balloon movement during the day is no more discernible than the movement of hands on a clock. At many times a balloon will appear to move if there are clouds in the sky just as a flagpole might seem to fall over when one is looking at it while lying on his back. The moon demonstrates this same phenomenon when it seems to move across fields and jump fences while looked at from a moving automobile. Anytime there are clouds, a balloon may appear to move at extreme speed.

A small balloon observed in the first few thousand feet of ascent, of course, will be quite obviously moving. Our very large balloons climb at a rate of 700 - 1000 ft/mm; radiosonde balloons ascend at 1000 - 1200 ft/min. As these balloons reach higher altitudes, they could encounter strong wind shears (changes in velocity associated with changes in altitude) of the order of 30 knots/1000 ft. Hence, velocity could change by as much as 30 knots in a minute, but even this would not make a large change in position. The angular movement would always be small over any one-minute period.

With respect to daylight sightings, pilots invariably estimate that balloons they see are considerably lower than their true height. For example, a pilot flying at 30000 or 40000 ft. will always report that the balloon is between 10000 and 40000 ft. above him. He will never say it is 100000 ft. above him. The difficulty arises because no one conceives of a balloon 300 ft. in diameter. There is no depth to the balloon and no background which permits an estimate of either size or distance.

A frequent occurrence in Boulder, Cob., when searching for a balloon which has been recently launched, is to focus on the fluffy balls from a cottonwood tree floating 50 - 100 ft. above the observer. The cottonwood ball has been tracked on several occasions for two to three minutes before its motion convinced the observer that it was a one-inch cottonwood ball at 100 ft. and not a 10-ft. balloon at 10000 ft.

Twilight effects

Just after sunset, a balloon may still be in sunlight. At this time the contrast becomes sharp and the balloon is clearly visible. A good bright balloon appears at least as bright as the brightest we ever see Venus when the planet is high in the sky : This "twilight effect" may continue from 20 mm. to two hours.

At high altitudes we have another striking effect for the last few minutes before the sun sets at balloon altitude. This is caused by the sun reflecting off the balloon producing a rosy pink and later bright red color as the sun's rays pass through a hazy atmosphere and only the red end of the spectrum reaches the balloon. This has generated reports of fiery objects in the sky.

The neoprene balloons are also visible at twilight. An Australian scientist made experiments at NCAR for about a year using a new technique for measuring ozone. He flew a neoprene balloon with a little stopper attached which permitted the gas to escape and enabled the balloon to remain aloft for one or two hours at altitude instead of ascending and bursting. To make measurements of the reflectance of the sun on the balloon and determine the ozone concentration, he launched the balloons so that they would reach 100,000 ft. above the observing site just after sunset. These balloons were plainly visible about sunset, continued to become brighter and brighter, and then receded to a faint glow before disappearing.

Ballons éclairés

Small rubber pilot balloons are still being used in many countries. For night soundings these two-foot diameter rubber balloons are tracked by small candles placed under the balloon. A single candle in a little holder has been used. The holder creates an even glow and keeps the candle from going out. The candle has been replaced in most countries by small battery-powered bulbs of approximately two candle power. Although the pilot balloon tracked by theodolite is no longer in common use in the U. S., a light is still used on radiosonde balloons at night to assist the observer to acquire the balloon, particularly if the night is dark and the trackers have had difficulty locking the radar set on the target. The blinking, bobbing light swaying under a pilot balloon or radiosonde balloon produces an exciting and attractive UFO. The FAA requires that large polyethylene scientific balloons carry lights when below 60000 ft. at night. They can provide an awesome sight as they slowly ascend.

Fréquence des vols

About 100 polyethylene balloons are flown each year from Palestine, Tex. San Angelo, Tex. has been an active launch area with as many as 100 - 200 per year. Chico, Calif., during the winter months has about ten flights, and Holloman AFB, N. M. (White Sands), has approximately 50 - 100 per year. Minneapolis remains still a center of balloon activities with 20 - 50 flights per year -- usually of small polyethylene balloons.

In addition, there are other field programs during the year that are undertaken by universities and manufacturers. Ten to 20 flights are made from Cardington, England each summer. A continuing flight program is conducted from Aire sur L'Adior, France. Australia, Russia, India, and Brazil have active flight programs using large polyethylene balloons.

About 100000 of the small neoprene balloons are flown each year in the United States for routine observation. Radiosonde balloon flights constitute a vast undocumented area. They are generally sent up four times a day. Flight schedules are all based on Greenwich time. At some times of the year at some places in the country, the balloons will be going into altitude at twilight. There are approximately 100 sites in the United States that send up radiosondes four times a day. Records of launch time and location for these balloons are kept in Asheville, N. C.

A radiosonde balloon ascending to 100000 ft. at twilight and then shattering can be the source of reports of a fiery object in the skies which disappears in a burst of flame.

Balloon UFOs

Two situations are illustrated that have produced UFO reports. In January 1964, a large balloon was flown from the Glen Canyon Dam area near Pago, Ariz. It was a 6000000 cu. ft. balloon with a light payload. The balloon, which was flying at 135000 ft., had encountered extremely strong winds. About three hours after it reached altitude it was decided to cut the balloon down. By this time the balloon was over Okla. It did not burst during payload detachment, but maintained its integrity and continued to ascend to 140000 ft. When, just after sunset, it came over the East Coast at 140000 ft., a number of pilot reports were received of a balloon sighted at 60000 - 70000 ft. Because it was at twilight on a very clear day, a number of people saw the balloon. This triggered a rash of flying saucer stories. For example, in Va. the people of a small town gathered a posse together to go out into a field to pick up the little green men. The sheriff attempted to halt them, but after a gun-waving encounter was forced to give up. The townspeople then went out into the field and fortunately failed to find their little men.

At altitudes of 5000 - 10000 ft. we fly a different kind of "ghost" balloon. This cylinder-shaped balloon is approximately 20 ft. long and about two feet in diameter. We flew one of these from Boulder on 23 June 1965 at an altitude of 6,500 ft. We lost the balloon after a few hours. It went through some rather heavy showers, and seventeen days later over the Azores a silvery object like a long spear was sighted in the sky. At the same time as the silvery object was seen -- all of the clocks on the Azores stopped. Later investigation determined that an electrician short-circuited the island's clock power supply while he was working on a fuse box.


The public at large and even many scientists are unaware of the great number of balloon launchings that occur every year in all parts of the world. The majority of such launchings are for meteorological studies, but some relate to other atmospheric or astronomical research.

By far most of the balloons launched for whatever purpose go unobserved except by those directly interested in their performance. They perform their missions and are cutdown or burst unnoticed by the public. This is due to the fact that most launchings take place at times and under conditions which make observation -- and misidentification -- of them unlikely or impossible. As a result, when a balloon is observed under unusual conditions by individuals not familiar with the kinds of devices described in this chapter it may be erroneously reported as an UFO.

Balloons ‑ Types, visibility and flight profiles

Altschuler, Martin D., 1968