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The Forefront of Space Science

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Another important improvement was the exhaust vent. Since the atmospheric pressure decreases as the balloon ascends, the gas within expands and accordingly the balloon gradually expands. When a sealed film is used, the balloon bursts because gas expands beyond its volume and it finally descends. To prevent this, an exhaust vent is provided on typical scientific balloons. Due to the release of expanded gas, the balloon loses buoyancy, enabling it to stay at a certain altitude. Equipping scientific thin-film balloons with exhaust vents, however, results in an increase in weight, which is disadvantageous for breaking the altitude record. From the point of view of balloon users, however, this alteration can offer significant benefits, because experiment opportunities are not limited to the period of balloon ascent. They can also perform their experiments while the balloon remains at its highest altitude.

We also introduced a new method of balloon release using slider release equipment and a collar. The collar is bound onto the balloon during gas filling to prevent expansion of its lower part with no filled-gas, and it is removed just before balloon release. With tests in advance, we confirmed that these methods worked well. Due to these measures, we were able to release the balloons reducing wind influence.

The opportunity to launch the 80,000 m3 volume balloon, incorporating many developmental results and our teamís passion, finally came in September 2013. The balloon we flew was 81 m in overall length and 36.7 kg in weight with a payload of 4.5 kg hanging from the balloon including a paratute and suspending ropes. On an ideal day for a balloon launch ĀEslightly cloudy, no fog, and no wind ĀEthe balloon was smoothly released as shown in Fig.1. Since the balloon was squeezed by the afore-mentioned collar, it did not expand and suffered no wind effect. Fig. 2 shows temporal change of the balloonís altitude. The balloon ascended smoothly, went beyond 53.0 km altitude, and came into the level flight at 53.7 km altitude, breaking the altitude record for the first time in 11 years. Fig. 3 is an image transmitted from the onboard camera, showing that the balloon expanded spherically. The exhaust-vent mechanism is shown at right. The moment of gas emission from it was also observed. The balloon stayed at its highest altitude for 12 minutes until it was punctured by the balloon destruction command.

Figure 1
Figure 1. Balloon release using the slider release equipment and collar
Since the root of the expanded part of the balloon was squeezed by the collar, the lower part did not expand and there was hardly any wind effect.

Figure 2
Figure 2. Temporal change of balloonís altitude
The balloon stayed at an altitude of 53.7 km for 12 minutes.

Figure 3
Figure 3. Fully expanded balloon photographed by onboard camera
At right is the exhaust-vent mechanism.

With this experiment, we can confirm the birth of a flying vehicle that can stay in the mesosphere above an altitude of 50 km, which was our original target. Based on our achievement this time, we now plan to develop a balloon capable of flying a payload of up to around 10 kg and maintaining its highest altitude. We expect that our new balloons will be used for a variety of scientific experiments other than ozone observation. Of course, we will continue our quest to go even higher into the sky.

(Yoshitaka SAITO)

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