"For bundled shielded missions to nearby star systems, solar sails with thicknesses of 10^−7 m and areal densities of 0.0001 kg/m2 seem feasible, and sail/payload mass ratios of 10:1 will allow exit velocities near the maximum possible for such sails. Sails with about 540 m radius and area of 106 m2 can impart 10 kg payloads with interstellar cruise velocities of 0.0005 c (1.5x10^5 m/s) when launched from 1 au (astronomical unit). At this speed, voyage to the Alpha PsA star will last 50,000 y, and to the Rho Opiuchus cloud, 824,000 years.
At the targets, the microbial payload would decompose into 1011 (100 billion) 30 µm capsules to increase the probability of capture. In the swarm strategy to protoplanetary discs and interstellar clouds, 1 mm radius, 4.2x10^−6 kg microbial capsules are launched from 1 au using sails of 4.2x10^−5 kg with radius of 0.37 m and area of 0.42 m2 to achieve cruising speeds of 0.0005 c. At the target, each capsule decomposes into 4,000 delivery microcapsules of 10^−10 kg and of 30 micrometer radius that allow intact entry to planetary atmospheres."
Reference: Anders, E. (1989). "Prebiotic organic matter from comets and asteroids". Nature. 342 (6247): 255–257. Bibcode:1989Natur.342..255A. doi:10.1038/342255a0.
"For missions that do not encounter dense gas zones, such as interstellar transit to mature planets or to habitable zones about stars, the microcapsules can be launched directly from 1 au using 10^−9 kg sails of 1.8 mm radius to achieve velocities of 0.0005 c to be decelerated by radiation pressure for capture at the targets. The 1 mm and 30 micrometer radius vehicles and payloads are needed in large numbers for both the bundled and swarm missions. These capsules and the miniature sails for swarm missions can be mass manufactured readily.
The panspermia vehicles would be aimed at moving targets whose locations at the time of arrival must be predicted. This can be calculated using their measured proper motions, their distances, and the cruising speeds of the vehicles. The positional uncertainty and size of the target object then allow estimating the probability that the panspermia vehicles will arrive at their targets. The positional uncertainty δy (m) of the target at arrival time is given by equation (1), where α(p) is the resolution of proper motion of the target object (arcsec/year), d is the distance from the Earth(m) and v is the velocity of the vehicle (m/s)"
Reference: Mautner, Michael N. Directed Panspermia. 3. Strategies and Motivations for Seeding Star-Forming Clouds. J. British Interplanetary Soc. 1997, 50, 93-102
δy = 1.5×10−13 αp(d2/v)
Given the positional uncertainty, the vehicles may be launched with a scatter in a circle about the predicted position of the target. The probability Ptarget for a capsule to hit the target area with radius rtarget (m) is the given by the ratio of the targeting scatter and the target area.
Ptarget = Atarget/π(δy)2 = 4.4×10^25 rtarget2v2/(αp2d4)
To apply these equations, the precision of astrometry of star proper motion of 0.00001 arcsec/year, and the solar sail vehicle velocity of 0.0005 c (1.5 × 10^5 m/s) may be expected within a few decades. For a chosen planetary system, the area Atarget may be the width of the habitable zone, while for interstellar clouds, it may be the sizes of the various density zones of the cloud.
Solar sail missions to Sun-like stars can decelerate by radiation pressure in reverse dynamics of the launch. The sails must be properly oriented at arrival, but orientation control may be avoided using spherical sails. The vehicles must approach the target Sun-like stars at radial distances similar to the launch, about 1 au. After the vehicles are captured in orbit, the microbial capsules may be dispersed in a ring orbiting the star, some within the gravitational capture zone of planets. Missions to accretion discs of planets and to star-forming clouds will decelerate by viscous drag at the rate dv/dt as determined by equation (3), where v is the velocity, rc the radius of the spherical capsule, ρc is density of the capsule and ρm is the density of the medium.
dv/dt = -(3v2/2ρc) ρ m/rc
A vehicle entering the cloud with a velocity of 0.0005 c (1.5 × 10^5 m/s) will be captured when decelerated to 2,000 m/s, the typical speed of grains in the cloud. The size of the capsules can be designed to stop at zones with various densities in the interstellar cloud. Simulations show that a 35 micron radius capsule will be captured in a dense core, and a 1 mm radius capsule in a protostellar condensation in the cloud. As for approach to accretion discs about stars, a millimetre size capsule entering the 1000 km thick disc face at 0.0005 c will be captured at 100 km into the disc. Therefore, 1 mm sized objects may be the best for seeding protoplanetary discs about new stars and protostellar condensations in interstellar clouds."
Reference: Mautner, Michael N. (1997). "Directed panspermia. 3. Strategies and motivation for seeding star-forming clouds" (PDF). J. British Interplanetary Soc. 50: 93–102.
The captured panspermia capsules will mix with dust. A fraction of the dust and a proportional fraction of the captured capsules will be delivered to astronomical objects. Dispersing the payload into delivery microcapsules will increase the chance that some will be delivered to habitable objects. Particles of 0.6 - 60 micron radius can remain cold enough to preserve organic matter during atmospheric entry to planets or moons."
Reference: Anders, E. (1989). "Prebiotic organic matter from comets and asteroids". Nature. 342 (6247): 255–257. Bibcode:1989Natur.342..255A. doi:10.1038/342255a0.
"Accordingly, each 1 mm, 4.2 ×10^−6 kg capsule captured in the viscous medium can be dispersed into 42,000 delivery microcapsules of 30 micron radius, each weighing 10^−10 kg and containing 100,000 microbes. These objects will not be ejected from the dust cloud by radiation pressure from the star, and will remain mixed with the dust."
Reference: Morrison, D. (1977). "Sizes and albedos of the larger asteroids". Comets, Asteroids and Meteorites: Interrelations, Evolution and Origins, A. H. Delsemme, ed., U. of Toledo Press: 177–183.
" A fraction of the dust, containing the captured microbial capsules, will be captured by planets or moons, or captured in comets and delivered by them later to planets. The probability of capture, Pcapture, can be estimated from similar processes, such as the capture of interplanetary dust particles by planets and moons in our Solar System, where 10^−5 of the Zodiacal cloud maintained by comet ablation, and also a similar fraction of asteroid fragments, is collected by the Earth."
Reference: Weatherill, G. W. (1977). "Fragmentation of asteroids and delivery of fragments to Earth". Comets, Asteroids and Meteorites: Interrelations, Evolution and Origins, A. H. Delsemme, ed., U. of Toledo Press: 283–291.
"The probability of capture of an initially launched capsule by a planet (or astronomical object) Pplanet is given by the equation below, where Ptarget is the probability that the capsule reaches the target accretion disc or cloud zone, and Pcapture is the probability of capture from this zone by a planet.
Pplanet = Ptarget × Pcapture
The probability Pplanet depends on the mixing ratio of the capsules with the dust and on the fraction of the dust delivered to planets. These variables can be estimated for capture in planetary accretion discs or in various zones in the interstellar cloud."
After determining the composition of chosen meteorites, astroecologists performed laboratory experiments that suggest that many colonizing microorganisms and some plants could obtain most of their chemical nutrients from asteroid and cometary materials. However, the scientists noted that phosphate (PO4) and nitrate (NO3–N) critically limit nutrition to many terrestrial lifeforms. For successful missions, enough biomass must be launched and captured for a reasonable chance to initiate life at the target astronomical object. An optimistic requirement is the capture by the planet of 100 capsules with 100,000 microorganisms each, for a total of 10 million organisms with a total biomass of 10^−8 kg.
"The required biomass to launch for a successful mission is given by following equation. mbiomass (kg) = 10^−8 / Pplanet Using the above equations for Ptarget with transit velocities of 0.0005 c, the known distances to the targets, and the masses of the dust in the target regions then allows calculating the biomass that needs to be launched for probable success. With these parameters, as little as 1 gram of biomass (10^12 microorganisms) could seed Alpha PsA and 4.5 gram could seed Beta Pictoris. More biomass needs to be launched to the Rho Ophiuchi cloud complex, mainly because its larger distance. A biomass on the order of 300 tons would need to be launched to seed a protostellar condensation or an accretion disc, but two hundred kilograms would be sufficient to seed a young stellar object in the Rho Ophiuchi cloud complex.
Consequently, as long as the required physical range of tolerance are met (e.g.: growth temperature, cosmic radiation shielding, atmosphere and gravity), lifeforms viable on Earth may be chemically nourished by watery asteroid and planetary materials in this and other planetary systems."
Reference: Mautner, Michael N. (2002). "Planetary bioresources and astroecology. 1. Planetary microcosm bioessays of Martian and meteorite materials: soluble electrolytes, nutrients, and algal and plant responses" (PDF). Icarus. 158: 72–86. Bibcode:2002Icar..158...72M. doi:10.1006/icar.2002.6841.