Project Grab Bag was an air sampling program conducted in the United States for the monitoring in the stratosphere of above-ground nuclear weapons testing in the Soviet Union. As the USA became aware of the loss of key ideas and design concepts, it was important to reassess the state of the Soviet program in fission devices, and to monitor extensions of their program to fusion devices. The objective of the Grab Bag program was to develop a unmanned high-altitude balloon-borne system that would collect air samples at an altitude of typically 80,000 feet and return them to earth for analyses. The air samples would be analyzed for the presence krypton and xenon, which among other specific isotopes were unambiguous markers of fission reactions. These short-lived isotopes were created in the fission process and carried high into the atmosphere by the fireball where they would remain for some days.
Birth of the concept
Early in 1953 the eventual sponsors of the Grab Bag program contacted the Balloons and Meteorological Systems group at General Mills, Inc. in Minneapolis, Minnesota under the direction of Harold E. Froehlich to raise the need to develop a system to obating high altitude air samples containing debris from above ground nuclear weapon tests by the USSR. The information obtained from the samples would be of paramount importance in monitoring progress in the Soviet nuclear weapons program. The sponsors did not discuss specific kinds of debris or isotopes that were of interest. Sizable air samples obtained at high altitude, for example 80,000 feet, were judged to be desirable, that is, samples of the order of 1200 cubic feet at standard temperature and pressure conditions. This meant that samples of approximately 33,000 cubic feet would need to be collected at altitude. The sponsors also conveyed a sense of urgency as an important weapon test was expected to take place at an USSR test range in the latter part of the summer of 1953, in about six months. The Grab Bag team began to develop the concept of suspending an uninflated envelope beneath a large helium filled balloon, and carrying the envelope to high altitude and filling it with ambient air. An autopilot would then initiate the descent of the entire system. When the system had descended to about 10,000 feet the air sample would be transferred from the envelope into an armored vessel that could withstand a variety of landing situations and protect the air sample from loss at the point of recovery. The balloon system would include an electronic controller and autopilot to carry out this sequence of events, and to return the entire system back to ground in a controlled descent.
Development of the system
The first version of the system counted with a high speed blower, the associated power supply and electronic control package that was suspended from the base of the sample balloon, at the lowest point in the load train. The base of the sample balloon was modified to take a cylindrical fitting that was fitted with the blower. The blower would operate at the ceiling altitude of 80,000 feet for of the order of two hours to fill the sample balloon with about 33,000 cubic feet of air. Once completed the task, an auto pilot would release a predetermined amount of helium from the lifting balloon and initiate the descent of the entire system at a rate of about 400 feet per minute. As the system descended to about 10,000 feet, an axial fan located at the top of the sample envelope would be activated to transfer the air sample into a flexible armored vessel located just above the sample balloon and below the lifting balloon and suspended parachute. The transfer of the sample required a short period of time and then a valve at the base of the armored vessel was sealed. The system continued to descend and when the control unit contacted ground, explosive devices severed the connection between the lifting balloon and the parachute marking the end of the flight. The Grab Bag concept resulted in a complex load train with electrical cables running along the entire length of the system, about 300 feet in length.
Launching of this complex balloon system required special handling techniques and the entire process was referred to as a platform launch, a novel concept developed by Harold E. Froehlich, Principal Engineer of the Balloons and Meteorological System Group. In this form of launching the load train, nearly 300 feet in length, was laid out on a ground cloth covered runway with the lowest part of the load train in the upwind direction. The uppermost part of the system, the top of the lifting balloon, would be in the downwind direction. A heavy platform was positioned at a point toward the top of the lifting balloon and the balloon material would pass over the platform and be securely held in place by a large horizontal padded roller about four feet in length. The helium inflation tube was located in the upper portion of the lifting balloon so that the helium source would inflate the section of the balloon beyond the platform.
Launching of the Grab Bag system was initiated by releasing the padded roller on the launch platform. The ascending balloon would then sequentially pick up the lower part of the lifting balloon, the deployed parachute and armored vessel, the uninflated envelope, and lastly the heavy insulated bag containing the controller, blower, instruments, telemetering equipment and power supply. There were variations of this procedure that evolved to facilitate the launching. For example, the heavy instrument bag and blower assembly was eventually mounted on the front of a vehicle that drove under the balloon system as it ascended during launching, and the bag was released from the vehicle using small explosive devices.
Grab Bag flights were typically launched early in the morning and recovered during daylight hours of that same day. The ascent time to 80,000 feet was usually about three hours. Once at float altitude, about thirty minutes were needed to assure that the system was stable. If the system instruments indicated that the altitude was not changing, the blower attached to the sample envelope balloon at the base of the system was initiated by the controller. The sample gathering process typically required of the order of an hour or so to be completed. The blower was then turned off by the controller and a valve closed that sealed the sample envelope from the outside. The auto pilot was then activated by the controller, releasing helium from the lifting balloon and initiating a descent of the entire system. In practice, the descent of the system did not become apparent for of the order of an hour after the autopilot was activated. This was due to the fact that the sample balloon, now containing a large volume of air, would generate lift with any descent due to adiabatic heating of the sample air in the isothermal stratosphere. It could require an hour or two to establish a nominal descent rate of the system. The descent to altitudes of the order of 15,000 feet could take of the order of two to three hours. At this point the axial fan was automatically initiated to transfer air in the sample balloon into the armored vessel. This transfer was usually completed before the system reached an altitude of 4 or 5 thousand feet and a valve in the armored vessel valve just above the axial fan was sealed by the controller. As the system continued to descend and touched down, explosive cutters fired to release the lifting balloon from the lower part of the system and the armored vessel fell the short remaining distance, perhaps fifty feet, to the ground. Usually the recovery crew was at the landing site and immediately began the process of transferring the air sample from the armored vessel into high pressure bottles for transfer to another laboratory for analyses.
Earlier tests and full scale program
A series of test flights were carried out in the Grab Bag development program. The first six flights were devoted to tests various system components: evaluation and further development of the launching procedure; testing of the system controller; adequacy of the power supply and the auto pilot function; a study of the blower function at altitude to evaluate both its function and the volume of air delivered into the sample balloon as compared to the laboratory results; evaluation of the process in which the axial fan transferred the air sample from the sample balloon into the armored vessel and the vessel was sealed; and in each case, further development of logistics for system launching and recovery. The seventh flight performed over the Minneapolis area on August 14, 1953 was the first operational flight of the complete system and succeeded on collecting an important air sample that contained debris from a nuclear weapon test in the USSR, designated Joe-4: it was the first test of a thermonuclear weapon by the USSR that was conducted two days earlier, on August 12, at Semipalatinsk in Kazakhstan. The sample obtained on that flight provided information that was of vital interest to those assessing fission/fusion reactions and test activities around the world.
The program was quickly expanded following that initial success, performing launches in the US from New Brighton (Minnesota), Sioux City (Iowa) and San Angelo (Texas) and also from locations in the Panama Canal Zone, and Sao Paulo, Brazil under operative command of the 1110th Balloon Activities Group, based at Goodfellow AFB, San Angelo, Texas. Until its termination in 1958 almost 1000 missions of the Grab Bag system were performed. The radioactive sampling effort would be continued under program ASHCAN using more efficient collection instruments and shifting from air samples to particulate samplers.
Near five years after the last mission of the program was completed U.S. Patent 3,077,779, for this high altitude air sampling system was assigned to H. E. Froehlich, Roger A. Kizzek, Donald F. Melton, and Richard L. Schwoebel.
GRAB BAG balloon flights list (incomplete)