7. Design of Capsule Size(From the Journal of the British Interplanetary Society 1997, 50, 93-102. Michael N. Mautner)
For maximising the probability of success, it is desirable to maximise the number of survivable units for a given total payload mass, and to minimise the size of the life-containing capsules.
In order not to be stopped by drag, the optimal size for penetrating the cloud is 1 mm. However, once in the target region, sufficient drag is in fact necessary for capture, and the capsule size can be reduced further. In fact, it is estimated that only dust particles in the range of 0.6 - 60 mm can survive atmospheric entry and still remain cold enough to preserve organic matter . A median size in this range, would be 30 mm. In the following discussings we consider a mass of mass of 1.1E-10 kg. This requires that the millimeter size capsules will be designed to disintegrate into smaller capsules once within the target protostellar or accretion regions. For example, the 1 mm capsule may be made as a looser aggregate that will disintegrate by collisions with dust particles, or by evaporation of the binding matrix in the relatively warmer target zone, into 30 mm capsules. This particle size is comparable to the <1E-10 kg particles that constitute about 10% of the zodiacal cloud. Significantly, this particle size will not be ejected from the solar system by radiation pressure .
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