ANIMAL CAPSULE

The objective of these series of balloon flights was to study cosmic radiation effects on biological systems using mice to examine how heavy cosmic ray particles interact with brain tissue, while simultaneously gathering nuclear emulsion data to calibrate electronic radiation detectors for future space missions and potentially capturing solar flare events to assess astronaut radiation hazards. Bemidji, Minnesota was chosen as the launch site due to its high geomagnetic latitude (58°N geomagnetic), which minimizes Earth's magnetic field interference with low-energy charged particles, particularly solar protons, thereby maximizing detection opportunities for solar radiation and its biological effects under near-space conditions.

Several institutions colaborated in the balloon flight series. NASA Langley Research Center constructed fiberglass animal capsules for biological exposure studies, while the Armed Forces Institute of Pathology analyzed tissue samples from exposed mice to investigate cosmic ray particle effects on brain tissue. The Air Force Cambridge Research Laboratories, prepared and analyzed nuclear emulsion plates, while the Aeromedical Laboratory at Holloman Air Force Base contributed animal payloads and particle counters. The School of Aviation Medicine supplied biological test subjects including black mice, algae, Neurospora fungi, and seeds, while the Air Force Special Weapons Center provided ionization chambers for measuring radiation dose rates.

In the image at left we can see a typical payload in the series. The animal capsules used in the balloon flights were thin fiberglass spheres, 24 inches in diameter, designed to serve as life-support systems for mice during high-altitude stratospheric balloon flights. Their essential purpose was to ensure that internal environmental conditions remained within safe physiological limits for the duration of the flight. The capsules maintained an internal temperature between 68°F and 78°F, although temperatures tended to drop to the low 60s during the early flight stages and rose to the low 80s later on. Internal pressure was regulated to approximate atmospheric sea-level pressure at 760 mm Hg. Before launch, each capsule was flushed with 100% oxygen for 45 minutes, a procedure intended to saturate the internal atmosphere sufficiently to meet the oxygen needs of the animals during the flight. Additionally, carbon dioxide levels were regulated with internal CO2 and moisture controlled via lithium chloride-lithium hydroxide and a battery-powered fan mounted within a central cylinder.

Inside each capsule, twelve mice were flown, divided into three groups of four. Each group was confined within a plastic holder measuring 4 by 6 inches. Each mouse was housed in its own compartment within these holders, which were designed to restrict body movement while keeping the head almost completely stationary. Above each group of mice, a nuclear emulsion plate measuring 4 by 6 inches was mounted precisely 78 millimeters above the heads of the animals. These plates served to monitor the passage of cosmic particles by capturing their trajectories, allowing researchers to determine whether and where particles penetrated the brain tissue below. The three mouse holders were arranged in a ring around the centrally located cylinder that housed the environmental control system. This configuration ensured that each set of animals was exposed evenly to environmental and cosmic radiation conditions.

The emulsion plates, were doubly coated to allow accurate determination of the trajectory of ionizing particles by capturing two distinct points of intersection on either side of the plate. Each emulsion unit was composed of two Ilford G5 plates, bonded together with a 3% gelatin solution. The plates were preconditioned at high humidity to reduce internal stress, and after bonding and curing, they were sealed in parafilm and black polyethylene rubberized tape to render them moisture-proof. All wrapping bonds were positioned on the upper face to ensure the lower face, which was in contact with the lucite animal cage, remained thin and flat.

Balloon launched on: 7/23/1960 at 04:34 CST
Launch site: Bemidji Regional Airport, Minnesota, US  
Balloon launched by: Raven Industries Inc.
Balloon manufacturer/size/composition: Zero Pressure Balloon Raven - 17.000 m3
Flight identification number: GHI
End of flight (L for landing time, W for last contact, otherwise termination time): 7/23/1960 at 18:34
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): ~ 15 h
Landing site: Near Malta, Montana, US
Payload weight: 588 lbs

• Balloon launch at Bemidji (MN) Newsclipping from Brainerd Daily Dispatch, July 23, 1960
• Bioastronautical Measurements Of Ionizing Radiations In Space: Nuclear Emulsion Monitoring Report Air Force Cambridge Research Labs Hanscom AFB Ma
• Brain Study of Mice Exposed to Cosmic Rays in the Stratosphere, and Report of Nuclear Emulsion Monitoring In Four Balloon Flights from Bemidji, Minnesota, July-August, 1960 Military Medicine, Volume 128, Issue 7, July 1963, Pages 655–672