12 Leonardo Times DECEMBER 2009

BALLOON-BASED OPERATION VEHICLEScienti� c balloons have been launched in Japan by ISAS/JAXA since 1965, and JAXA currently holds the world record for the highest altitude reached by a balloon (53km). Prof. Hashimoto’s group has been developing a system to provide a long duration, high quality microgravity envi-ronment based on a capsule that can be released from a high altitude platform [2].

MICROGRAVITY RESEARCH USING A BALLOON-BASED OPERATION VEHICLE

Since 1981 on average 100 million dollars are spent every year on microgravity research by space agencies in the US, Europe and Japan [1]. There are many ways to achieve microgravity conditions such as, in order of experiment duration: drop tow-

ers, parabolic � ights, balloon drops, sounding rockets, space shuttle, recoverable satellites and the international space station. The order of the previous summation

is also approximately the order of increasing experiment cost (table 1), with the exception of the balloon-drop. From the table, it is apparent that a balloon-based

system could be the most cost-e� cient microgravity environment. Another advan-tage of such a system is that no large acceleration is required before the experiment

can be performed. In this article we will describe a balloon-based system.

TEXT Tatsuaki Hashimoto, Shujiro Sawai, Shin-ichiro Sakai, Nobutaka Bando, Shigehito Shimizu, JAXA-ISAS, Japan Peter Buist, Sandra Verhagen, MGP, DEOS, Delft University of Technology, the Netherlands

Platform Duration [s] Gravity level [10-x g] with x

Cost [$ /kg]

Drop tower 2-9 2-5 3000 Parabolic flight 25 2-3 3000 Balloon-drop 60 2-5 750 Sounding rocket 360 3-4 10000 Space Shuttle < 14 days 3-5 30000 Space station >months 5-6 >30000 Recoverable satellite

>months 5-6

10000-200000

 

Table 1. Available Microgravity Research Platforms (adapted from [1])

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The capsule, coined: Balloon-based Op-eration Vehicle (BOV) and shown in � g. 1, has a double shell drag free structure and is controlled so it does not collide with the inner shell. The � ight capsule consists of a capsule body (the outer shell), an ex-periment module (the inner shell) and a propulsion system. The inner shell is kept in free-fall conditions after the release of the BOV from the balloon, and no distur-bance forces are working on this shell or the microgravity experiment it contains. The outer shell has a rocket shape to re-duce aerodynamic disturbances. The dis-tance between the outer and inner shell is measured using four laser range sensors and besides the attitude of the BOV, the propulsion system ensures that the two shells don’t collide. It incorporates sixteen dry-air gas-jet thrusters providing 60N of thrust each, providing control not only in vertical direction but also in the horizon-tal direction to compensate for distur-bances caused by, for example, wind. The procedure of a typical � ight with the BOV is shown as follows: � rst the BOV lifts o� due to the balloon. Then the vehicle sepa-rates from the balloon and measurements are performed during free fall. Finally, a safe landing is assured by the deployment of a parachute.

BALLOON FACILITIESIn the north of Japan’s main island Hon-shu, the Sanriku Balloon Centre was opened in 1971 and since then 413 bal-loons have been launched from this site. In order to facilitate the launch of larger balloons and utilize better meteorological conditions, the Balloon base was moved to Taiki in Hokkaido in 2008. One impor-

tant challenge for balloon launches is the gusty wind during gas in� ation that can cause damage to either the balloon or the payload. At the new facility, the in� a-tion of the balloon can be performed in-doors in a huge hangar. A so called sliding launcher is used to launch balloons with a volume up to two million cubic meter.

MICROGRAVITY EXPERIMENTSWithin the � eld of � uid physics, material science, combustion, biology, and colli-sion dynamics researchers have identi� ed the need for micro gravity experiments. Speci� cally they required longer and higher quality micro gravity conditions and a shorter time of return for the results of their experiments. A Balloon-based Op-eration Vehicle could potentially be used for this kind of experiments, but a heavy lifting balloon would then be required. To reach a su� ciently high altitude (neces-sary for long-duration microgravity condi-tions) a balloon must be light enough and thus made of ultra thin � lm. But as the payload is very heavy, this � lm should also be incredibly strong. To cope with these con� icting requirements, a � lm based on 2.5 micrometer thick Polyethylene was developed. A multilayer � lm was applied for the top of the balloon where the stress is concentrated; the rest of the balloon consists only of a single layer in order to minimize weight.

GPS EXPERIMENT The Mathematical Geodesy and Position-ing Section of the Faculty of Aerospace Engineering of Delft University of Technol-ogy is involved in a precise GPS-based rel-ative positioning and attitude determina-

tion experiment onboard the BOV and the gondola of the balloon. The BOV and the gondola provide a challenging environ-ment, because of the rather rapidly vary-ing attitude (due to wind and rotation) and high altitude. For a GPS experiment, the altitude of around 40 km is interest-ing as not many experiments have been performed at this height, which is higher than the altitude reachable by an aircraft but below Low Earth Orbits for spacecraft. Furthermore the antennas are placed un-der the balloon, which will a� ect the GPS signals. More information about the GPS experiments can be found in [3][4].

IN-FLIGHT QUALIFICATION OF THE BOV’S MAIN BODY, THE ATTITUDE DETERMINATION PACKAGE AND GPS SYSTEMFlight experiments with the BOV were car-ried out in 2006 (BOV1) and 2007 (BOV2) and a � ne micro-gravity environment was established successfully for more than 30 seconds. To achieve a longer period of micro-gravity conditions and, in the long term, safe horizontal landing, usage of an air-breathing engine to surmount air resistance has been investigated and is now under development for the next � ight experiment. This will be performed on BOV3, a wing type version of the BOV (� gure 3), for which the attitude will be ac-tively controlled to maintain the safety of � ight, i.e. the � ight direction oversea and away from inhabited areas. The main goal of this next experiment is to achieve su-personic horizontal � ight.

An altitude of about 40km is a harsh en-vironment for electrical devices because

Figure 1. BOV Overview Figure 2. The balloon used to lift o� the vehicle

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the pressure is about 1/1000atm and the temperature ranges from -60 to 0 de-grees Celsius. Therefore in September 2008, we performed a test for the atti-tude determination system of BOV3 and a GPS system containing two GPS receiv-ers. The purpose of this � ight was to test the equipment on the gondola without launching the BOV. By this test, nominal performance of some of the sensors in the real environment was con� rmed (for a more detailed description see [4]).

FLIGHT OF BOV4In May 2009, the third � ight of the BOV took place (this � ight is called BOV4 and is launched before the wing-type BOV: BOV3). The balloon reached an altitude of more than 41 kilometers from which the BOV was subsequently dropped. The BOV maintained micro gravity condition for about 35 seconds. The BOV and gondola landed in the sea using their own para-chutes. The BOV, including the micrograv-ity experiment, was successfully recov-ered from the ocean by a helicopter and the gondola was picked up by a vessel.

During this balloon � ight, a second test of the attitude determination package (ADP) and a GPS system was performed on the gondola to con� rm the nominal performance of all the sensors. For the purpose of this experiment, we acquired a new GPS receiver, which is able to collect data from three antennas simultaneously. Using this new equipment we are able to

calculate the full attitude of the gondola, and the nominal performance of the ADP package could be con� rmed by the at-titude determined by the GPS system. Furthermore, we used a ground station to demonstrate the combination of GPS-based attitude determination and relative positioning between the platform and the ground station (more information on this approach can be found in [5]). Therefore this � ight was an example of a fruitful co-operation bene� cial for both JAXA and Delft University of Technology.

FUTURE PLANSAfter the � ight of BOV3 (planned for next year), the system is quali� ed for utiliza-tion and could be used for micro gravity experiments in a cost e� cient way. In or-der to do so we plan to increase the size of the inner shell in which the experiment is contained and to further reduce the cost of system.

ACKNOWLEDGMENTS Peter Buist: His research on precise rela-tive positioning and attitude determina-tion for formation � ying is supported by the MicroNed-MISAT framework.

References:

[1] V.A. Thomas, N.S. Prasad, A.M. Reddy, Microgravity Research Platforms – A study, Special Section: Microgravity Materials Science, Current Science, Vol. 79, No3, 10 August 2000

[2] T. Hashimoto, S. Sawai, S. Sakai, N. Bando, H. Kobayashi, K. Fujita, Y. Inatomi, T. Ishikawa, T. Yoshimitsu and Y. Saito, Progress of Balloon-based Micro-gravity Experiment System, 26th International Symposium on Spacecraft Technology and Science, Hamamatsu, Japan, 2008.

[3] P.J. Buist, S. Verhagen, T. Hashimoto, S. Sakai, N. Bando: GPS Field Experiment for Balloon-based Operation Vehicle, Proceedings of the Astrodynamics and Flight Mechanics Symposium, Sagami-hara, Japan, 2008.

[4] S. Shimizu, P.J. Buist, N. Bando, S. Sakai, S. Sawai, and T. Hashimoto. Design of Multi-sensor Attitude Determination System for Balloon-based Operation Ve-hicle. Proceedings of the 27th ISTS (Inter-national Symposium on Space Technol-ogy and Science), Tsukuba, Japan, 5-12 July 2009, 2009.

[5] P. J. Buist, P. J. G. Teunissen, G. Giorgi, S. Verhagen, Instantaneous GNSS-based Kinematic Relative Positioning and Attitude Determination using Multi-An-tenna Con� gurations, 2009 International Symposium on GPS/GNSS, Jeju, Korea, 4-6 November 2009

Figure 3. 3D-CAD drawing of BOV3

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