For immediate release
US and Japanese physicists are cooperating in a research project which aims to fly balloon-borne cosmic ray detectors around the South Pole from McMurdo Station, Antarctica. Participants in the project include physicists from NASA/Marshall Space Flight Center, the University of Alabama at Huntsville, Louisiana State University, the University of Washington in Seattle, and a group of institutions in Japan led by the Institute of Cosmic Ray Research at the University of Tokyo.
A research balloon carrying an unmanned scientific gondola was launched from Williams Field, near McMurdo Station, on 22 December 1994. The balloon flew above 120,000 feet, and took over 300 hours to go completely around Antarctica and return to the vicinity of the launch site. Today (1/11/95), the balloon gondola was recovered from its landing site in Victoria Land, and returned to McMurdo Station, the main American base in Antarctica, where the scientific equipment will be prepared for return shipment to the USA.
The purpose of the project is to carry a cosmic ray detector above most of the earth's atmosphere for 10--20 days, a flight duration much longer than routine balloon flights in the continental US. Balloon flight operations are being performed by the NASA-operated National Scientific Balloon Facility, in collaboration with the US National Science Foundation, which operates all Antarctic research programs. The scientific payload was prepared and will be analyzed by a team of physicists from all participating institutions. If successful, the amount of data collected in this single operation could increase by 50% the information collected in 11 previous flights performed over a period of 14 years.
Cosmic rays are radiation reaching the earth from outer space. Cosmic ray measurements must be performed via balloon or space flights because of the shielding effect of the earth's atmosphere. The intensity of cosmic radiation is very weak, comparable to starlight in terms of the amount of energy striking the earth. Moreover, the number of particles observed above a given energy (the energy spectrum) drops off sharply with increasing energy. Thus long exposures of large detectors are required to obtain a significant measurement. Physicists from the US and Japan organized the JACEE collaboration (Japanese-American Cosmic-ray Emulsion chamber Experiment) in 1979. The project uses a detector called an "emulsion chamber", which is a stack of lead and plastic sheets, interleaved with photographic emulsion plates. The photographic emulsion material is similar to that used in making black and white film, but has been supersensitized to record the tracks of individual subatomic particles. The photographic plates are used to record the tracks of incoming cosmic ray particles, and also the tracks of secondary particles produced when the cosmic rays collide with a nucleus in the detector itself.
By studying cosmic ray interactions, physicists can learn about the nature of fundamental forces at energies higher than those available at particle accelerator laboratories. Some theorists predict a that new state of matter, called the Quark-Gluon Plasma (QGP) may be observed as a result of the extremely high energy densities produced in cosmic ray collisions. Formation of QGP would be signalled by new forms of energy release in cosmic ray collisions, for example by production of an unusually large number of secondary tracks.
In addition to the particle physics aspects, one of the main goals of the balloon flight project will be to provide valuable data on the relative abundances and energy spectra of different types of cosmic ray particles. Such information is essential for astrophysicists attempting to understand the structure of our Galaxy of stars and the nature of the processes that produces cosmic rays, such as stellar explosions called supernovas, or violent processes in compact binary stellar systems.
Seven previous JACEE balloon flights have been performed in the US, using the services of the National Scientific Balloon Facility, in Texas. The earlier flights typically carried a total scientific payload of about 1500 lbs, with an average flight duration of 30 hours. Flights in the US are of relatively short duration because for safety reasons the balloon must be brought down before it approaches a region of high population density. Longer duration flights were performed in the southern hemisphere in part to avoid this problem. In 1987 and again in 1988, JACEE balloons flew from Australia to South America, logging about 120 hours at the top of the atmosphere in each flight. Each of the Antarctic flights will provide 200--400 hours of exposure. A small JACEE test package was flown in Antarctica in 1990, as part of a balloon flight carrying several other projects. Full-scale JACEE flights were performed in Antarctica in 1993-94, but one of the payloads landed in the ocean and could not be recovered. The present flight is intended to replace the data lost in that incident.
For this year's Antarctic flight, the balloon used had a fully-inflated volume of 29 million cubic feet, and was made of a special polyethylene plastic material which is only 0.0008" thick. In previous flights in the US and Australia, the scientific payload was limited in weight because it was necessary to carry a great deal of ballast. Each sunset, the balloon's gas cools and contracts, losing buoyancy and requiring a ballast drop to maintain altitude. In Antarctica, where it is now mid-summer, the sun never sets and so ballast requirements are minimal. As a result, nearly 2300 lbs of cosmic ray detectors can be flown at altitudes up to 130,000 feet for several weeks.
The gondola was tracked using the Global Positioning Satellite (GPS) navigation system, which provides its position continuously. In addition, the onboard telemetry system relayed altitude, temperature and equipment status data from the balloon. The data will be received and processed at the NSBF base station at McMurdo Station, Antarctica, and will be relayed via satellite computer communications channels to NSBF headquarters in Texas. The PI (R. J. Wilkes, UW) and Co- Investigators (Y. Takahashi, UA/H, T. A. Parnell, NASA/MSFC, and M. Cherry and J. P. Wefel at LSU) are in daily communications with the JACEE field team in Antarctica, led by Co-Investigator J. C. Gregory of UA/H, via computer mail and telephone.
After going around the Pole, the balloon returned close to its launch site. The balloon was separated from the gondola by a radio command, and a parachute attached to the gondola controlled its descent. Members of the NSBF field team joined Navy aircraft crews to recover gondola and prepare it for shipment back to the USA, where the photographic plates will be unpacked. Processing of the photographic plates and films will take place in Huntsville. Analysis of the data is expected to require 1--2 years. The project is supported by grants from the National Science Foundation (Division of Polar Programs) and NASA. Further updates will be provided as the balloon flights proceed.
Contact: R. J. Wilkes Dept. of Physics, FM-15 University of Washington Seattle, WA 98l95 (206) 543-4230 email@example.com