Ballooning activities in Japan

The Scientific Balloon Center of ISAS/JAXA has carried out two balloon campaigns at Sanriku, Iwate, Japan every year. Ten to twelve balloon vehicles are launched annually for scientific and engineering experiments. Since 2005, a Brazilian balloon campaign has also been conducted in cooperation with INPE. In the 2006 Brazilian campaign, large and heavy payloads up to 1500 kg for astronomy will be launched. New generation balloons, such as super-pressure balloons and high-altitude balloons with ultra-thin films, are being developed. The current status and prospect of the Japanese scientific ballooning are discussed.     

Time variations of cosmic-ray helium isotopes with BESS-Polar I

The Balloon-borne Experiment with a Superconducting Spectrometer (BESS) is configured with a solenoidal superconducting magnet and a suite of precision particle detectors, including time-of-flight hodoscopes based on plastic scintillators, a silica-aerogel Cherenkov detector, and a high resolution tracking system with a central jet-type drift chamber. The charges of incident particles are determined from energy losses in the scintillators. Their magnetic rigidities (momentum/charge) are measured by reconstructing each particle trajectory in the magnetic field, and their velocities are obtained by using the time-of-flight system. Together, these measurements can accurately identify helium isotopes among the incoming cosmic-ray helium nuclei up to energies in the GeV per nucleon region. The BESS-Polar I instrument flew for 8.5 days over Antarctica from December 13th to December 21st, 2004. Its long-duration flight and large geometric acceptance allow the time variations of isotopic fluxes to be studied for the first time. The time variations of helium isotope fluxes are presented here for rigidities from 1.2 to 2.5 GV and results are compared to previously reported proton data and neutron monitor data.     

Progress of super-pressure balloon development: A new “tawara” concept with improved stability

The super-pressure balloon (SPB) has been expected to be a flight vehicle that can provide a long flight duration to science. Since 1997, we have developed the SPB. Now we are at the phase of developing an SPB of a practical size. In 2009, we carried out a test flight of a pumpkin-shaped SPB with a 60,000 m³ volume. The undesirable result of this flight aroused us to resolve the deployment instability of the pumpkin-shaped SPB, which has been known as one of the most challenging issues confronting SPB development. To explore this deployment issue, in 2010, we carried out a series of ground tests. From results of these tests, we found that an SPB design modified from pumpkin, named “tawara”, can be a good candidate to greatly improve the deployment stability of the lobed SPB.     

Relay balloon

A relay balloon system for long-duration or large-area observations is described. The system consists of a balloon for scientific observations and a relay balloon for a data-relay terminal between a ground station and the balloon for observation. The system was successfully applied to the observation of electric-power fields (50 and 60 Hz) over the Pacific ocean. The maiximum distance between two balloons was about 1100 km and that between the Sanriku Balloon Center and the main balloon for the observation was about 1300 km.     

A challenge to the highest balloon altitude

Development of a balloon to fly at higher altitudes is one of the most attractive challenges for scientific balloon technologies. After reaching the highest balloon altitude of 53.0 km using the 3.4 μm film in 2002, a thinner balloon film with a thickness of 2.8 μm was developed. A 5000 m³ balloon made with this film was launched successfully in 2004. However, three 60,000 m³ balloons with the same film launched in 2005, 2006, and 2007, failed during ascent. The mechanical properties of the 2.8 μm film were investigated intensively to look for degradation of the ultimate strength and its elongation as compared to the other thicker balloon films. The requirement of the balloon film was also studied using an empirical and a physical model assuming an axis-symmetrical balloon shape and the static pressure. It was found that the film was strong enough. A stress due to the dynamic pressure by the wind shear is considered as the possible reason for the unsuccessful flights. A 80,000 m³ balloon with cap films covering 9 m from the balloon top will be launch in 2011 to test the appropriateness of this reinforcement.     

Development of balloon-borne reel-down and -up winch system

Balloon-borne winches, which can reel down and up scientific instruments repeatedly, have been developed since 1981 in order to observe stratospheric vertical microstuctures. The instrument is suspended by a kevler wire through a traverse-cum ropeguide, and its depth is accurately measured by counting numbers of spool rotations and ropeguide turns. Battery consumption is minimized by utilizing an efficient deccelerator and a hysteresis brake. In 1983 we have successfully performed to reel up and down a 12 kg payload through 1 km for three cycles at 24 km altitude. We are improving the capability of the winch, and have succeeded (May 1984) to reel down a 22 kg payload up to 3 km from a balloon.     

Search for antihelium: Progress with BESS

In this paper, we report searches for antihelium in cosmic rays using two recently flown magnetic rigidity spectrometers. BESS-TeV had extended rigidity with an MDR of 1.4 TV and had a flight duration of one day. BESS-Polar was optimized for collecting power. It was flown for 8.5 days and had an MDR of 240 GV. The former flight allows us to explore a previously unexplored rigidity band and the latter flight yields a factor of three improvement in the overall BESS limit. No antihelium candidate was found in the rigidity ranges of 1–500 GV, and 0.6–20 GV, among 7 × 10⁴ events taken with BESS-TeV, and 8 × 10⁶ events taken with BESS-Polar, respectively.     

Cosmic ray H/H ratio measured from BESS in 2000 during solar maximum

The Balloon-borne Experiment with a Superconducting Spectrometer (BESS) was flown from Lynn Lake, Manitoba, Canada in August, 2000, during the maximum solar modulation period, with an average residual atmospheric overburden of 4.3 g/cm². Precise spectral measurements of cosmic ray hydrogen isotopes from 0.178 GeV/n to 1.334 GeV/n were made during the 28.7 h of flight. This paper presents the measured energy spectra and their ratio, ²H/¹H. The results are also compared with previous measurements and theoretical predictions.