CRISP (Cosmic Ray Ionization Spectrograph Experiment)

CRISP, an acronym for the Cosmic Ray Ionization Spectrograph Program, was an experiment carried out by the Cosmic Ray Physics Branch, Space Physics Division of the NASA Manned Spacecraft Center in Houston, Texas, to measure the intensity and properties of cosmic radiation in the upper atmosphere.

The image on the left depicts the instrument mounted on its gondola before a flight. This gondola, an oddly shaped structure measuring 13.3 x 8.3 x 5 feet, housed the detectors and electronic systems. It maintained a constant internal pressure of approximately 14.7 psia using a dedicated gas system.

The CRISP detectors were composed of the Charge Identification Module (CIM) and the Ionization Spectrograph (IS). The CIM identified the charge of incoming cosmic ray particles, their direction and path of incidence, and ensured that only one particle entered the system at a time. It included two spark chambers, a plastic Cerenkov detector, and two plastic scintillation detectors. The IS measured the total energy of an incident particle by recording the energy deposited in the form of ionization. This spectrograph consisted of tungsten and steel modules. The tungsten module distinguished between electrons and protons by exploiting the marked difference in the development of an electron-photon cascade (produced by electrons) and a nuclear cascade (produced by protons) in tungsten.

The detector electronics included high-speed logic electronics and a digital system. The logic electronics classified the cosmic rays into categories and initiated the data acquisition sequence, while the digital system converted the data into a format suitable for the Data Acquisition System (DAS). The DAS featured a VHF telemetry system and an onboard magnetic tape recorder. Additionally, the payload included an analog data system and a UHF digital command system for monitoring and controlling the performance and status of all gondola systems.

The instrument's primary power source came from four parallel packs of silver-zinc batteries. Each pack, sealed in watertight containers, consisted of 18 cells connected in series.

The Data Acquisition Van, which was flown aboard a C-130E aircraft that closely followed the balloon's path, contained telemetry receiving equipment, real-time electronic monitoring tools, data display equipment, and command systems for both the balloon (HF) and gondola (UHF).

The instrument's significant weight -9,500 pounds- necessitated the use of the largest balloon available at the time, which had a volume of 34 million cubic feet. This two-part interconnected system included a main balloon, surmounted by a smaller launch balloon. Both balloons were constructed of laminated Mylar plastic film reinforced with Dacron fibers. At launch, the smaller balloon was filled with 500,000 cubic feet of helium. As the system ascended, the expanding helium passed through a transfer duct (a collar-like ring connecting the two balloons) to fill the main balloon, which expanded to a final diameter of 731 feet.

Despite its ambitious goals, the CRISP project ultimately failed as all flight attempts ended unsuccessfully due to balloon failures, leading to the program's abandonment in 1971.

Balloon launched on: 8/26/1970
Launch site: Holloman Air Force Base, Alamogordo, New Mexico, US  
Balloon launched by: Air Force Cambridge Research Laboratories (AFCRL)
Balloon manufacturer/size/composition: Zero Pressure Balloon Winzen - Natural shape, taped, capped - 38.190.000 cu ft (Stratofilm 1.5 mil)
Flight identification number: H70-50
End of flight (L for landing time, W for last contact, otherwise termination time): 8/26/1970
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 2 h
Landing site: Balloon failure at 48.000 ft.
Payload weight: 9.500 pds
Overall weight: 13.800 pds

The balloon flight was attempted on August 26th, 1970 from the Holloman Air Force Base in Alamogordo, New Mexico. Everything went as per schedule and procedure. Althought the scientific payload was intended to reach an altitude of 108,000 feet, the balloon failed at approximately 48,000 feet. The failure was traced to a circumferential tear about a foot long at the apex close to the apex plate. This tear apparently resulted from a concentrated high-tensile load during inflation and/or let-up and launch.

• Polyethylene balloon fabrication and specifications Final report Winzen Research Inc - 1971