Magellan: A balloon-borne collection technique for large cosmic dust particles

R. WLOCHOWICZ Herzherg Itzstitrrte ofAstroplzysics, Notiotzol Research Corrtzcil ofCrrr~rrrla, Ottnwri, Cnnrtdn KIA OR6

A N D

C. L. HEMENWAY Drirlley Ohser~~rrtoty , Alhriny, New York,

rrtzd Strtte University o f N e ~ v York at Alhrrtly, Albrrny, Neiv York

A N D

D. S. HALLGREN, A N D C. D. TACKETT Drrrlley Ohserr~rrtory, Albany, New' York

Received August 4 , 1975

A new technique for the collection of large cosmic dust particles from balloons is described. Two flights have been completed successfully. Preliminary results are given.

On decrit une nouvelle technique pour la cueillette de grosses particules de poussiere cosmique sur des ballons stratospheriques. Deux lancements reussis ont kt6 effectues. Des resultats preliminaires sont presentis.

[Traduit par le journal] Can. J. Phys.. 54. 317 (1976)

Introduction Various systems have been built for the collec-

tion of cosmic dust from balloons (Bhandari et al. 1968 ; Bigg et al. 1970; Brownlee et al. 197 1 ; Hemenway et al. 1967, 1971) but these were limited by size or geometry to the efficient collec- tion of particles smaller than a few tens of micrometres. Magellan is the name chosen for an experiment designed to collect the large (major dimension 50 to a few hundred micrometres) solid particles falling through the atmosphere at an altitude of about 30 km. Two origins, both extraterrestrial, are postulated for these particles: (1) cosmic dust particles which have partially ablated in penetrating the atmosphere, and (2) fragments of much larger particles or bodies which disintegrate on entering the atmosphere (Verniani 1969). For the first source, the particle flux can be inferred from measurements made with instruments both ground-based and carried on space vehicles (Hemenway et al. 1974); for the second source, the production rate is not well known. It is believed, however, that the influx of the particles, from both sources, in the upper atmosphere is very low. Therefore, the collection of these particles requires an experiment charac- terized by a large collection-area collecting-time product modified by the practical constraint that

the area to be scanned to find the particles must be small. Magellan satisfies these requirements.

Collecting System Funnel

Although the balloon, which carries the experi- ment, is a major component of the experiment's concept, the collecting system is described first. It was developed around the collection surface which is simply a funnel, 7.2 m diameter (40 m2), fabricated from mylar, 12 pm thick, and lightly coated with aluminum to reduce the buildup of static charge. The gore pattern is such that all seams overlap essentially downwards to mini- mize the trapping of particles inside the funnel. The apex of the funnel subtends an angle of 60". The angle was determined following laboratory tests at reduced pressure with samples of aluminized mylar using spherical and irregular test particles greater than 25 pm. For a given slope, humidity is the only identified factor af- fecting the adhesion of particles to clean alumi- nized mylar.

Recovery of test particles of the order of 90 to 100x was achieved in the laboratory. In a test of a fully deployed funnel, 85% of the particles greater than 50 pm were recovered. The implica- tion of these results is that not only will most of

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318 CAN. J . PHYS. VOL. 54. 1976

FIG. 1. Magellan collection funnel in deployed state. FIG. 2. Magellan payload supported by the tow balloon photographed just prior to launch.

the particles falling into the mouth of the funnel be collected at its apex, but that contaminants in the same size range as the collected particles (i.e. > 50 pm) present in the funnel prior to deploy- ment will also be easily shed. Furthermore, to accelerate the shedding of contaminants, a shaker, radio controlled from the ground, was attached to the funnel.

Deployment Mechanisn7 It was both desirable and necessary that the

funnel be collapsed during ascent and deployed at float altitude in order to facilitate the launch, to reduce contamination, and to avoid the destruc- tion of the funnel in its passage through the atmosphere. Two types of mechanisms were de- veloped, each capable of operating with an 80 kg load attached to the apex of the funnel. The first consisted of a ten segment toroid fabricated from a mylar-aluminum lamination 150 pm thick. The segments were pleated and, on com- mand, inflated from a small cylinder of C 0 2 . The possiblility of a faulty deployment due to un- balanced forces in the load lines became evident in the first launch and dictated the need for a

more positive-acting mechanism. Consequently, the second mechanism, shown in Figs. 1 and 2, consisting basically of an inverted umbrella was developed. The deployment is gravity operated. To overcome the tendency of the configuration to remain in the closed position, a pulley system with a mechanical advantage of 4 is built into the stem of the mechanism. The deployment is achieved by sliding the conically-shaped open structure towards the top of the stem; the rate of deployment is governed by an escapement mechanism housed in the sealed square enclosure a t the top of the stem. Bearings of recogniz- able plastics are utilized a t pivot and sliding points to eliminate or, a t worst, to assure the identification of particles which could be gener- ated during deployment. Switches at the pivots monitor the deployment of all arms of the mech- anism.

Sample Collector The collector, Fig. 3, attaches to the apex of

the collecting funnel. Its three sampling pans can be sequentially swung into position below the funnel exposing a clean collection surface,

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WLOCHOWICZ ET AL.: MAGELLAN: A BALLOON-BORNE COLLECTION TECHNIQUE

FIG. 3 Collector with its three sampling pans.

sealed after exposure, and ejected, making room for the subsequent sampling pan. The identical collection units are mounted on three of the four sides of the square frame housing a small stain- less steel funnel which forms the apex of the col- lecting funnel and guides the particles to a 1 cm diameter hole in the bottom face of the frame. This hole is open during launch and the deploy- ment of the funnel and for a short stabilization period at float altitude to allow contaminant par- ticles to fall through the system. The exploded view of the collecting pan identifies the surfaces on which the particles are finally collected. The smaller disc, A, lightly coated with mineral oil, is the primary surface; the larger disc, B, above it, may collect some of the bouncing particles. Other components of the pan are the cover, E, and the slider, D, which is moved by a bellows actuator, C. A bar magnet, G, is cemented to the edge of the slider. When the slider is moved to the right end of the housing, the magnet actuates the reed switch, F, to indicate the sealing of the pan.

In Fig. 3, the first sampling pan is on the left.

On command the cutter, H, separates the sam- pling pan from the arm, I, which is raised, to- gether with the cover, E, by springs, J. Spring K swings the pan clockwise (looking up from the bottom) and, when the hole in the pan coincides with the opening of the small funnel, also raises the pan and seats it on the gasket, R. The pin in the shaft, the slot in the block, L, and the stop, M, guide this motion. The collection is termi- nated by firing the actuators, C, to seal the pan, and the sampling unit is then removed by means of the two cutters, N, releasing the compressed spring. 0 , The removed unit remains attached to the payload by the electrical cable. Sampling pan 2, the center unit, can then be positioned for the next collection. Similarly, unit 3 can be operated after unit 2 is ejected. Switches P and Q respec- tively indicate that the pan is in the collecting position and that the sampling unit has been ejected from the frame.

Pyrotechnic devices are used throughout be- cause of their reliability. To ensure the execution of critical functions, redundancy is provided by using two bellows actuators to seal the pan and

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320 CAN. J. PHYS.

two cutters to eject the units. Furthermore, each cutter comes with two filaments for redundancy.

Reliable mechanical operation at an ambient temperature as low as -75 "C is considered essential. The lubrication problem at low tem- perature was resolved by fabricating the shaft, the block, L, and the slider, D, from an impact- resistant, self-lubricating plastic. Silicone rubber is used for all seals. All other parts are aluminum to minimize weight. The collector weighs 4 kg.

Balloon Practical limitations to the size of the collecting

funnel dictated the need for a balloon capable of long duration flights to maintain a high area- time product for the experiment. An earlier pro- gram, Ghost, established that sealed, or super- pressure balloons, 5 m diameter, could float for months. In January of 1973, our experiment was included on an engineering flight of a 20 m diameter superpressure balloon launched from Australia. Bad weather prevented recovery after the first orbit at which time the balloon was in the vicinity of the launch site. After the next com- plete orbit, the winds carried the balloon north of Australia where it could not be recovered. The balloon survived for 212 days and finally fell into the Pacific ocean without recovery of the pay- load. A superpressure balloon launched a few daysearlier made two complete orbits and was re- covered within 15 km of the launch site. Thus. the technology exists to support the full realiza- tion of the Magellan concept.

Launch When fully deployed, the Magellan experiment

includes, from top to bottom : the balloon, elec- tronics for tracking and cut-down, the main para- chute, a 305 m nylon line to minimize contamina- tion from the balloon and associated hardware, the collecting system, a second electronic package for tracking, controlling, and separating the col- lector from the collecting funnel, and a parachute for the recovery of the collector and associated hardware. The launch technique utilizes a small tow balloon attached to the top of the collecting system to provide for the controlled erection of the system (see Fig. 2) and to lift it at a slow rate. The main balloon, 305 m away and released

VOL. 54, 1976

TABLE 1. Summary of the number of particles collected on two flights of Magellan

Sampling pan 1 2 3

Magellan I1 - 1 Collection time (h) - 16 0.67 Particles collected - 18 3

Magellan 11 - 2 Collection time (h) 3 34 3 Particles collected 6 126 3

:IG. 4. Scanning electron micrograph of collected particle.

simultaneously with the tow bailoon, rises at a FIG. 5. Scanning electron micrograph of collected particle.

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WLOCHOWICZ ET AL.: MAGELLAN: A BAL

faster rate than the tow balloon. When the main balloon eventually begins to lift the collecting system, the tow balloon is cut away. The total weight of the system, excluding the balloon, is 385 kg. The weight of the collecting system alone is 34 kg. On one flight, the deployed funnel was clearly visible through a telescope. The fabric of the funnel was taut, there was no sign of turbu- lence, and a rotation of about 1 turn/h was observed.

Preliminary Flight Data Two successful flights of short duration using

zero-pressure balloons, both launched from Palestine, Texas, have been achieved. The first, on the 6th of May 1974, obtained a main collec- tion of 16 h duration and a control sample of 40 min. The second, on the 17th of October 1974, obtained a main collection of 34 h and two con- trol samples of 3 h each.

Table 1 shows preliminary results for the number of particles collected in each interval. There is a general consistency between collec- tions and with respect to the extraterrestrial flux deduced from the number of craters observed on prepared surfaces exposed on Skylab. Figures 4 and 5 are examples of particles collected during the first two flights. Mg, Al, Si, S, K, Ca, Ti, and Fe have been detected in these particles by energy dispersive X-ray analysis. Although preflight tests led us to conclude that contamination in the system is low, we are analyzing particle types col- lected in relatively large numbers to establish if they originated from some unexpected source of contamination.

.LOON-BORNE COLLECTION TECHNIQUE 321

Acknowledgments Magellan is a joint project involving the

National Research Council of Canada (NRCC) and the Dudley Observatory. The construction of the collectors was the responsibility of NRCC while the Dudley Observatory provided the de- ployment mechanism, the collecting funnel, and the launch. The U.S. effort was supported by NASA Grant NGL 33-01 1-001. The authors are particularly indebted to NASA and the NCAR Scientific Balloon Facility of Palestine, Texas, whose expertise was essential for the successful launching of the complex Magellan payload. NRCC personnel who have contributed signifi- cantly to the design, manufacture, and assem- bly were: Z. Mordasewicz and especially S. Tomkowicz, D. G. Taylor, R. K. Wilke, and J. W. Pygas. Dudley Observatory personnel we wish to recognize for the design and development mechanism and for the field operation are: A. Laudate, J. Tarnawski, and C. Jones.

BHANDARI, N. , ARNOLD, J . R. , and PARKIN, D. W. 1968. J . Geophys. Res. 73. 1837.

BIGG, E. K. , ONO, A,, and THOMPSON, W. J . 1970. Tellus, 22.550.

BROWNLEE, D. E., HODGE, P. W., and BUCHER, W. 1971. IAU Colloquium #13, Albany, N.Y. 1971. NASA SP-319,p.291.

HEMENWAY, C. L., HALLGREN, D. S., and COON, R. E. 1967. Space Res. V11, 1423.

HEMENWAY, C. L., HALLGREN, D. S., LAUDATE, A. T., PATASHNICK, H., RENZEMA, T . S . , ~ ~ ~ G R I F F I T H , O . K. 1971. Space Res. XI. 393.

HEMENWAY, C. L., HALLGREN, D. S. . and TACKETT, C. D. 1974. AIAAIAGU Conf. on Scientific Experiments of Skylab, Huntsville. Alabama 1974. In press.

VERNIANI . F. 1969. Space Sci. Rev. 10,230.

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