[35] As DISCUSSED IN THE PREVIOUS SECTION, NASA lunar policy was changed from one of sterilization, or attempted sterilization, of the space vehicles involved to one of an attempt to minimize and localize contamination. The policy on planetary missions remained unchanged, save for the fact that it was stated in probability terminology rather than in absolute terms. Sterilization may be an absolute term, but there is always some probability as to whether this absolute condition is achieved in any particular case. Because of this difference in policy the accomplishments of the lunar program and the planetary program will be discussed separately.
The effectiveness of the lunar program can best be summed up in a simple statement. No microorganisms were recovered from the lunar samples returned during the Apollo program. This was true of both in vitro and in vivo tests (Holland and Simmons, 1973) at the Lunar Receiving Laboratory. This was a result both of the efforts to limit contamination in the earlier unmanned launches and of the effort to take the samples under aseptic conditions in the Apollo manned landings, in spite of the fact that the lunar surface was indeed contaminated. An estimate of the amount of contamination which the Moon received was made (Dillon, et al., 1973), as was required under NASA Policy Directive 8020.7. The Sandia Laboratory investigators who conducted this analysis took into consideration the spacecraft bioburden at launch, the bioburden change in cislunar space, the [36] distribution of organisms on the lunar surface, and the changes in the terrestrial density on the lunar surface subsequent to its original dispersal. They estimated that the number of viable microorganisms per square meter of lunar surface at the times the Apollo samples were taken was between 1 x 10-4 and 1 x 10-5.
Another interesting study (Flory and Simoneit, 1972) was concerned with the maximum amount of terrestrial organic chemical contamination which might be expected to be found on the returned Apollo samples. It should be noted that while it was considered unlikely that live microorganisms would be found on the Moon, the organic geochemists expected to find organic chemicals there, as they had found them in meteorite samples which had landed on the Earth. In these latter cases, the question of whether the organic compounds found had come from terrestrial contamination upon impact and retrieval had always been raised. It was hoped that the origin of organic compounds recovered from the lunar samples would be free of such doubt. The study reported only on Apollo 11 and Apollo 12 samples, but concluded,
There was one flurry of excitement on returned lunar samples which should be discussed. Apollo 12 landed near the site where Surveyor 3 had achieved a soft landing and had left instruments on the lunar surface. The astronauts brought back several of these instruments for examination of what had happened to them after 31 months of exposure to the lunar environment. One of those returned was a section of the electrical cabling of the Surveyor's TV camera. This cabling was known to have a high level of internal contamination associated with its wiring bundles. Moreover, the surface wrappings of this cable had been deliberately contaminated with several thousand Bacillus subtilis spores. No organisms were recovered from the wrapping or the internal section of the cable (Knitter, et al., 1972). However, one of the returned instruments was the camera itself; though not sterile at launch it had not been deliberately contaminated as had the cable wrappings. This too was examined microbiologically, and one microorganism was recovered from a part of the polyurethane foam insulation in the camera interior (Mitchell and Ellis, 1972). After much investigation, in which several microorganisms were recovered from the backup camera [37] which had remained on Earth, the organism recovered from the camera which had remained on the Moon was identified as alpha hemolytic Streptococcus mitts. The investigators concluded that it was of terrestrial origin and had survived the lunar exposure and return trip, but other scientists challenge that conclusion. The question remains unresolved.
The NASA planetary quarantine provisions for missions to the planets are much more rigorously controlled than were the lunar missions, which were considerably relaxed after the issuance of NASA Management Manual 4-4-1 in September 1963. They follow the directive of NPD 8020.10, September 1967, that allocated a basic probability of 1 x 10-3 that a planet of biological interest would be contaminated and the requirements of NHB 8020.12 that quarantine plans for unmanned planetary missions be submitted to the Planetary Quarantine Officer for approval. The NASA PQ Officer suballocates the basic probability of 1 x 10-3 to each unmanned planetary mission based upon the type of mission and the total number of flights estimated to be conducted during the period of biological interest.
On the basis of these plans, an initial estimate is made of how much of this suballocated probability is needed by that particular mission. Following the flight, a revised calculation is made and a value given to the probability that the planet was contaminated by that particular mission and, thus, how much of the allocation had been used. The evolvement of the basic formula for these calculations is discussed in Werber's companion volume. The formula currently used is
where
[38] A simplified model which combines the survival factors into the probability of the release of an organism in a viable state is
It is evident that some of these values such as m and P(r), can be derived from laboratory data. P(r) is the probability of release of microorganisms from the spacecraft hardware and is determined on the basis of experimental data for similar hardware and simulated planetary environmental conditions. The value for the microbial burden, m, is derived by taking into consideration sampling of the assembled spacecraft for viable organisms and determining from laboratory experiments how much this number was reduced by the known effectiveness of the subsequent sterilization or decontamination treatment to which the spacecraft was exposed. The value assigned to the probability of growth after release on a particular planet, P(g), has to be, of necessity, much more of a value judgment. In either case the PQ Officer officially assigns numbers to these values, depending upon recommendations made to him by his various consultants, particularly AIBS. These assigned values, of course, are subject to revision as new information becomes available. The latest compilation of these approved parameters appears in a looseleaf notebook entitled "Planetary Quarantine Parameter Specification Book." It was especially prepared for the information of the international community and was made available at the COSPAR meeting in Constance, West Germany, May 1973. Each volume is serially numbered, issued to a specific individual, and kept up to date by periodic revisions and supplements.
Two of the services performed by Exotech Systems, Inc., for the PQ office are maintaining a data bank for the information acquired by that office and keeping the Planetary Quarantine Status Board up to date by summarizing all the information on the probabilities of contamination by those missions already flown and the projected allocations of Pc to those missions in the planning stages.
This status board is a rather complicated compilation and will be summarized here, rather than reproduced in full. There have been six Mariner Missions to Mars (Table III). For the first two of these, the initial allocations of Pc were 4.5 x 10-5. The initial allocations for the next two were reduced to 3 x 10-5. These were all flybys, and the post-flight calculation indicated no probability of contamination. The same was true of Mariner 8, a planned orbiter which failed. Mariner 9, now in orbit around Mars, was given an initial allocation of 7.1 x 10-5; the post-launch estimate of Pc was 1.6 x 10-5, and this value [39] stands as the probability that Mars has been contaminated to date by U.S. missions (Fox, Hall, and Bacon, 1972). A revised estimate of the allocation for each of the two Viking lander missions planned for 1975 is 1 x 10-4.
The story is similar for Venus. Three flyby missions were attempted; two were successful. Estimates are that no contamination was made by the U.S. in these missions. A planned Mariner (MVM) flyby later in 1973 has been given an initial allocation of Pc of 7 x 10-5 for both Venus and Mercury.
Two Pioneer spacecraft intended to fly by Jupiter have been launched. Should the first provide acceptable scientific data, the second may be placed on a trajectory to Saturn after swinging by Jupiter. Their initial allocation of a Pc is 6.4 x 10-5.
The Viking mission to be launched in 1975 and designed to orbit and land on Mars in 1976 has been given an initial allocation of 7.2 x 10-5, with a supplement of 2.8 x 10-5 recovered from the previous successful missions to Mars. Currently the Viking project has chosen to assign allocations of 3.2 x 10-5 to the orbiter and 2 x 10-5 to the lander, with 2.8 x 10-5 allowed for ejecta, and the 2 x 10-5 held in reserve for assignment in ease of unforeseen need.
In summation, the biological aspects of the U.S. space program can, in spite of all its initial difficulties, be considered a success. The space missions have been accomplished without compromise of the planetary quarantine restraints.
