A proposed new policy for planetary protection

In order to control contamination of planets by terrestrial microorganisms and organic constituents, U.S. planetary missions have been governed by a planetary protection (or planetary quarantine) policy which has changed little since 1972. This policy has recently been reviewed in light of new information obtained by planetary exploration during the past decade and because of changes to, or uncertainties in, some parameters used in the existing quantitative approach. On the basis of this analysis, a new planetary protection policy, with the following key features, is proposed: deemphasizing the use of mathematical models and quantitative analyses; establishing requirements for target planet/mission type (i.e., orbiter, lander, etc.) combinations; considering sample return missions a separate category; simplifying documentation; and imposing implementing procedures (i.e., trajectory biasing, cleanroom assembly, spacecraft sterilization, etc.) by exception, i.e., only if the planet/mission combination warrants such controls. Interpretation of the new policy for missions like Galileo, Mars Surface Sample Return, Saturn Orbiter with Twin Probes, and missions to comets are considered. In general, the new policy proposes elimination of all but documentation requirements for most planetary missions and simplification of the remaining compliance procedures.     

Planetary protection and the search for life beneath the surface of Mars.

The search for traces of extinct and extant life on Mars will be extended to beneath the surface of the planet. Current data from Mars missions suggesting the presence of liquid water early in Mars' history and mathematical modeling of the fate of water on Mars imply that liquid water may exist deep beneath the surface of Mars. This leads to the hypothesis that life may exist deep beneath the Martian surface. One possible scenario to look for life on Mars involves a series of unmanned missions culminating with a manned mission drilling deep into the Martian subsurface (approximately 3Km), collecting samples, and conducting preliminary analyses to select samples for return to earth. This mission must address both forward and back contamination issues, and falls under planetary protection category V. Planetary protection issues to be addressed include provisions stating that the inevitable deposition of earth microbes by humans should be minimized and localized, and that earth microbes and organic material must not contaminate the Martian subsurface. This requires that the drilling equipment be sterilized prior to use. Further, the collection, containment and retrieval of the sample must be conducted such that the crew is protected and that any materials returning to earth are contained (i.e., physically and biologically isolated) and the chain of connection with Mars is broken.     

Critical issues in connection with human missions to Mars: protection of and from the Martian environment.

Human missions to Mars are planned to happen within this century. Activities associated therewith will interact with the environment of Mars in two reciprocal ways: (i) the mission needs to be protected from the natural environmental elements that can be harmful to human health, the equipment or to their operations; (ii) the specific natural environment of Mars should be protected so that it retains its value for scientific and other purposes. The following environmental elements need to be considered in order to protect humans and the equipment on the planetary surface: (i) cosmic ionizing radiation, (ii) solar particle events; (iii) solar ultraviolet radiation; (iv) reduced gravity; (v) thin atmosphere; (vi) extremes in temperatures and their fluctuations; and (vii) surface dust. In order to protect the planetary environment, the requirements for planetary protection as adopted by COSPAR for lander missions need to be revised in view of human presence on the planet. Landers carrying equipment for exobiological investigations require special consideration to reduce contamination by terrestrial microorganisms and organic matter to the greatest feasible extent. Records of human activities on the planet's surface should be maintained in sufficient detail that future scientific experimenters can determine whether environmental modifications have resulted from explorations.     

Planetary environment protection ID no: F3.3-M.1.05 implications for the development of a network of surface stations on Mars.

The European Space Agency's studies of a Comet Nucleus Sample Return mission (ROSETTA) as its Planetary Cornerstone in its long-term programme 'Horizon 2000' and the Marsnet mission, a potential contribution of the Agency to an international network of surface stations on Mars, has revived the interest in the present state of Planetary Protection requirements. MARSNET was one of the four candidate missions selected in April 1991 for further Design Feasibility (Phase A) Studies. Furthermore, of all space agencies participating in planetary exploration activities only the United States National Aeronautics and Space Administration had a well established Planetary Protection Policy on Viking and other relevant planetary missions, whereas ESA is considering the feasibility and potential impact of a planetary protection policy on its Marsnet mission, within the framework of a tight budgetary envelope applicable to ESA's medium (M) class missions. This paper will discuss in general terms the impact of Planetary Protection measures, its implications for Marsnet and the issues arising from this for the implementation of the mission in ESA's scientific programme.     

载人火星探测的行星保护

行星保护是影响载人火星探索任务的重要问题之一。载人探测的行星保护包括3个方面,即防止来源于地球的微生物污染目标星球的正向污染防护、防止外来生物对地球的潜在危害的逆向污染防护,以及确保航天员的健康和安全。国际宇航界已经开始针对载人火星探测的行星保护制定政策法规和开展技术研讨。本文介绍了行星保护的定义和法理依据,简要回顾了美国国家航空航天局在“阿波罗登月”中的行星保护措施,并对未来载人火星探测中的主要污染物、污染途径以及污染防护策略进行了初步探讨。     

U.S. planetary protection program: Implementation highlights

The implementation of planetary protection in the United States space program has reflected the trend in policy from an absolute to a probabilistic prohibition of the contamination of the celestial bodies of the solar system. The early emphasis on spacecraft sterilization (e.g. Ranger) was replaced by the imposition of contamination control procedures on later missions such as Pioneer, Viking, and Voyager. Similarly, analytical and laboratory techniques were developed to demonstrate compliance with probabilistic requirements. Microbial burden reduction methods that are not hazardous for spacecraft reliability supplanted the abstract concept of sterilization. The United States implementation of planetary protection has been completely successful. In an exploration program that has included Mercury, Venus, Mars, the Jovian system, and the Saturnian system, there have been no accidental impacts or detection of false positives (terrestrial microbes). Further, the contamination control and microbial burden procedures have proved beneficial to spacecraft systems and on-board science instruments. We review in this paper the implementation of planetary protection procedures by the Pioneer (10 and 11), Viking and Voyager projects.     

Interstellar planetary protection

In the coming decades the detection of Earth-like extrasolar planets, either apparently lifeless or exhibiting spectral signatures of life, will encourage design studies for craft to visit them. These missions will require the elaboration of an interstellar planetary protection protocol. Given a specific dose required to sterilize microorganisms on a spacecraft, a critical mean velocity can be determined below which a craft becomes self-sterilizing. This velocity is calculated to be below velocities previously projected for interstellar missions, suggesting that an active sterilization protocol prior to launch might be required. Given uncertainties in the surface conditions of a destination extrasolar planet, particularly at microscopic scales, the potential for unknown biochemistries and biologies elsewhere, or the possible inoculation of a lifeless planet that is habitable, then both lander and orbiter interstellar missions should be completely free of all viable organisms, necessitating a planetary protection approach applied to orbiters and landers bound for star systems with unknown local conditions for habitability. I discuss the case of existing craft on interstellar trajectories – Pioneer 10, 11 and Voyager 1 and 2.     

Planetary protection issues in advance of human exploration of Mars.

Current planetary quarantine considerations focus on robotic missions and attempt a policy of no biological contamination. The presence of humans on Mars, however, will inevitably result in biological contamination and physical alteration of the local environment. The focus of planetary quarantine must therefore shift toward defining and minimizing the inevitable contamination associated with humans. This will involve first determining those areas that will be affected by the presence of a human base, then verifying that these environments do not harbor indigenous life nor provide sites for Earth bacteria to grow. Precursor missions can provide salient information that can make more efficient the planning and design of human exploration missions. In particular, a robotic sample return mission can help to eliminate the concern about returning samples with humans or the return of humans themselves from a planetary quarantine perspective. Without a robotic return the cost of quarantine that would have to be added to a human mission may well exceed the cost of a robotic return mission. Even if the preponderance of scientific evidence argues against the presence of indigenous life, it must be considered as part of any serious planetary quarantine analysis for missions to Mars. If there is life on Mars, the question of human exploration assumes an ethical dimension.     

Planetary protection issues for Mars sample acquisition flight projects.

The planned NASA sample acquisition flight missions to Mars pose several interesting planetary protection issues. In addition to the usual forward contamination procedures for the adequate protection of Mars for the sake of future missions, there are reasons to ensure that the sample is not contaminated by terrestrial microbes from the acquisition mission. Recent recommendations by the Space Studies Board (SSB) of the National Research Council (United States), would indicate that the scientific integrity of the sample is a planetary protection concern (SSB, 1997). Also, as a practical matter, a contaminated sample would interfere with the process for its release from quarantine after return for distribution to the interested scientists. These matters are discussed in terms of the first planned acquisition mission.     

Planetary protection issues related to human missions to Mars

In accordance with the United Nations Outer Space Treaties [United Nations, Agreement Governing the Activities of States on the Moon and Other Celestial Bodies, UN doc A/RES/34/68, resolution 38/68 of December 1979], currently maintained and promulgated by the Committee on Space Research [COSPAR Planetary Protection Panel, Planetary Protection Policy accepted by the COSPAR Council and Bureau, 20 October 2002, amended 24 March 2005, http://www.cosparhq.org/scistr/PPPolicy.htm], missions exploring the Solar system must meet planetary protection requirements. Planetary protection aims to protect celestial bodies from terrestrial contamination and to protect the Earth environment from potential biological contamination carried by returned samples or space systems that have been in contact with an extraterrestrial environment. From an exobiology perspective, Mars is one of the major targets, and several missions are currently in operation, in transit, or scheduled for its exploration. Some of them include payloads dedicated to the detection of life or traces of life. The next step, over the coming years, will be to return samples from Mars to Earth, with a view to increasing our knowledge in preparation for the first manned mission that is likely to take place within the next few decades. Robotic missions to Mars shall meet planetary protection specifications, currently well documented, and planetary protection programs are implemented in a very reliable manner given that experience in the field spans some 40 years. With regards to sample return missions, a set of stringent requirements has been approved by COSPAR [COSPAR Planetary Protection Panel, Planetary Protection Policy accepted by the COSPAR Council and Bureau, 20 October 2002, amended 24 March 2005, http://www.cosparhq.org/scistr/PPPolicy.htm], and technical challenges must now be overcome in order to preserve the Earth’s biosphere from any eventual contamination risk. In addition to the human dimension of the mission, sending astronauts to Mars will entail meeting all these constraints. Astronauts present huge sources of contamination for Mars and are also potential carriers of biohazardous material on their return to Earth. If they were to have the misfortune of being contaminated, they themselves would become a biohazard, and, as a consequence, in addition to the technical constraints, human and ethical considerations must also be taken into account.     

Implementing planetary protection requirements for sample return missions.

NASA is committed to exploring space while avoiding the biological contamination of other solar system bodies and protecting the Earth against potential harm from materials returned from space. NASA's planetary protection program evaluates missions (with external advice from the US National Research Council and others) and imposes particular constraints on individual missions to achieve these objectives. In 1997 the National Research Council's Space Studies Board published the report, Mars Sample Return: Issues and Recommendations, which reported advice to NASA on Mars sample return missions, complementing their 1992 report, The Biological Contamination of Mars Issues and Recommendations. Meanwhile, NASA has requested a new Space Studies Board study to address sample returns from bodies other than Mars. This study recognizes the variety of worlds that have been opened up to NASA and its partners by small, relatively inexpensive, missions of the Discovery class, as well as the reshaping of our ideas about life in the solar system that have been occasioned by the Galileo spacecraft's discovery that an ocean under the ice on Jupiter's moon Europa might, indeed, exist. This paper will report on NASA's planned implementation of planetary protection provisions based on these recent National Research Council recommendations, and will suggest measures for incorporation in the planetary protection policy of COSPAR.     

Overview of current capabilities and research and technology developments for planetary protection

The pace of scientific exploration of our solar system provides ever-increasing insights into potentially habitable environments, and associated concerns for their contamination by Earth organisms. Biological and organic-chemical contamination has been extensively considered by the COSPAR Panel on Planetary Protection (PPP) and has resulted in the internationally recognized regulations to which spacefaring nations adhere, and which have been in place for 40 years. The only successful Mars lander missions with system-level “sterilization” were the Viking landers in the 1970s. Since then different cleanliness requirements have been applied to spacecraft based on their destination, mission type, and scientific objectives. The Planetary Protection Subcommittee of the NASA Advisory Council has noted that a strategic Research & Technology Development (R&TD) roadmap would be very beneficial to encourage the timely availability of effective tools and methodologies to implement planetary protection requirements. New research avenues in planetary protection for ambitious future exploration missions can best be served by developing an over-arching program that integrates capability-driven developments with mission-driven implementation efforts. This paper analyzes the current status concerning microbial reduction and cleaning methods, recontamination control and bio-barriers, operational analysis methods, and addresses concepts for human exploration. Crosscutting research and support activities are discussed and a rationale for a Strategic Planetary Protection R&TD Roadmap is outlined. Such a roadmap for planetary protection provides a forum for strategic planning and will help to enable the next phases of solar system exploration.     

A consensus approach to planetary protection requirements: recommendations for Mars lander missions.

Over the last several years, the nature of the surface conditions on the planet Mars, our knowledge of the growth capabilities of Earth organisms under extreme conditions, and future opportunities for Mars exploration have been under extensive review in the United States and elsewhere. As part of these examinations, in 1992 the US Space Studies Board made a series of recommendations to NASA on the requirements that should be implemented on future missions that will explore Mars. In particular, significant changes were recommended in the requirements for Mars landers, changes that significantly alleviated the burden of planetary protection implementation for these missions. In this paper we propose a resolution implementing this new set of recommendations, for adoption by COSPAR at its 30th meeting in Hamburg. We also discuss future directions and study areas for planetary protection, in light of changing plans for Mars exploration.     

An empirical model of the plasma environment around Mercury

Since the flyby observations by Mariner 10 in 1974 and 1975, Mercury has been one of the most interesting objects for space physics and planetary exploration. The MESSENGER and BepiColombo missions now plan to revisit this planet. In order to design plasma instruments for the BepiColombo mission, we have estimated electron and ion fluxes around Mercury with an empirical model, which has been developed for the Earth’s magnetotail. The solar wind data needed as input parameters are derived from Helios observations. The result shows that our predicted electron fluxes at aphelion agree well with the Mariner-10 data. It is also noted that ion instruments must cover a very wide dynamic range of proton fluxes. However, the applicability of the Earth’s magnetospheric model to Mercury is, in itself, an important issue for comparative magnetospheric studies.     

Penetration testing for the Optical Probe for Regolith Analysis (OPRA)

The Optical Probe for Regolith Analysis (OPRA) is a spike-shaped subsurface analytical probe that will be delivered to a planet, asteroid, or cometary body by a lander and/or rover. OPRA will be pushed down into the subsurface to record near infrared spectra as a function of depth down to maximum of 50 cm. Therefore, knowledge of the required penetration force to specific depths can be helpful in estimating the length of the probe. Test probes covering the anticipated diameter (2.5, 1.9, 1.2 and 0.9 cm diameter) and tip angle (T.A. = 30°, 60°, 90° and 120°) of OPRA were inserted mechanically into dry playground sand. The results showed that tip angle does not have a major effect, while probe diameter and density of the regolith are the most important parameters. Increasing probe diameter from 0.9 to 1.9 cm (i.e. a factor of 2) leads to an increase in penetration force from 200 to 1000 N (i.e. a factor of 5) at 20 cm depth. An increase in bulk density (B.D.) from 1550 to 1700 kg m⁻³ leads to an increase in penetration force from 10 to 200 N at 20 cm depth. Bearing capacity theory was used to explain the downward movement of the penetrometer through regolith and showed good agreement with the experimental results. This model was then used to take into account the effect of gravity on other planetary bodies. We observed a good agreement between the theoretical model and results from penetration testings on the Moon by the Apollo missions. Since the maximum allowed force for penetration is the weight of the lander/rover on their targeted planetary surface, our results put a strong constraint on the maximum reachable depth without endangering the whole mission.     

Planetary protection, legal ambiguity and the decision making process for Mars sample return.

As scientists and mission planners develop planetary protection requirements for future Mars sample return missions, they must recognize the socio-political context in which decisions about the mission will be made and pay careful attention to public concerns about potential back contamination of Earth. To the extent that planetary protection questions are unresolved or unaddressed at the time of an actual mission, they offer convenient footholds for public challenges in both legal and decision making realms, over which NASA will have little direct control. In this paper, two particular non-scientific areas of special concern are discussed in detail: 1) legal issues and 2) the decision making process. Understanding these areas is critical for addressing legitimate public concerns as well as for fulfilling procedural requirements regardless whether sample return evokes public controversy. Legal issues with the potential to complicate future missions include: procedural review under National Environmental Policy Act (NEPA); uncertainty about institutional control and authority; conflicting regulations and overlapping jurisdictions; questions about international treaty obligations and large scale impacts; uncertanities about the nature of the organism; and constitutional and regulatory concerns about quarantine, public health and safety. In light of these important legal issues, it is critical that NASA consider the role and timing of public involvement in the decision making process as a way of anticipating problem areas and preparing for legitimate public questions and challenges to sample return missions.     

Societal issues as Mars mission impediments: planetary protection and contamination concerns.

Societal and non-scientific factors represent potentially significant impediments for future Mars missions, especially in areas involving planetary protection. This paper analyzes public concerns about forward contamination to Mars and back contamination to Earth, evaluates major areas where lack of information may lead to uncontrollable impacts on future missions, and concludes that NASA should adopt a strategy that actively plans both the generation and subsequent management of planetary protection information to ensure that key audiences obtain needed information in a timely manner. Delay or avoidance in dealing with societal issues early in mission planning will increase the likelihood of public opposition, cost increases and missed launch windows. While this analysis of social and non-scientific considerations focuses on future Mars missions, the findings are also relevant for RTG launches, nuclear propulsion and other NASA activities perceived to have health, safety or environmental implications.     

Thermal protection system development,testing, and qualification for atmospheric probes and sample return missions: Examples for Saturn,Titan and Stardust-type sample return

The science community has continued to be interested in planetary entry probes, aerocapture, and sample return missions to improve our understanding of the Solar System. As in the case of the Galileo entry probe, such missions are critical to the understanding not only of the individual planets, but also to further knowledge regarding the formation of the Solar System. It is believed that Saturn probes to depths corresponding to 10 bars will be sufficient to provide the desired data on its atmospheric composition. An aerocapture mission would enable delivery of a satellite to provide insight into how gravitational forces cause dynamic changes in Saturn’s ring structure that are akin to the evolution of protoplanetary accretion disks. Heating rates for the “shallow” Saturn probes, Saturn aerocapture, and sample Earth return missions with higher re-entry speeds (13–15 km/s) from Mars, Venus, comets, and asteroids are in the range of 1–6 KW/cm². New, mid-density thermal protection system (TPS) materials for such probes can be mission enabling for mass efficiency and also for use on smaller vehicles enabled by advancements in scientific instrumentation. Past consideration of new Jovian multiprobe missions has been considered problematic without the Giant Planet arcjet facility that was used to qualify carbon phenolic for the Galileo probe. This paper describes emerging TPS technologies and the proposed use of an affordable, small 5 MW arcjet that can be used for TPS development, in test gases appropriate for future planetary probe and aerocapture applications. Emerging TPS technologies of interest include new versions of the Apollo Avcoat material and a densified variant of Phenolic Impregnated Carbon Ablator (PICA). Application of these and other TPS materials and the use of other facilities for development and qualification of TPS for Saturn, Titan, and Sample Return missions of the Stardust class with entry speeds from 6.0 to 28.6 km/s are discussed.     

Legal aspects of planetary protection for Mars missions.

The planning and execution of manned and robotic missions to Mars present a wide range of jurisprudential issues. Provisions to prevent the disruption of natural celestial environments, as well as damage to the environment of Earth by the return of extraterrestrial materials, are important components of the law applicable to mankind's activities in outer space, and have been supplemented by scientifically instituted planetary protection policies. However, divergent legal regimes may exist, as the space treaties in force are neither uniform in their provisions, nor identical as to the states which have signed, ratified, or adopted the international agreements. The legal requirements applicable to a specific mission will vary depending on the entities conducting the program and specific mission profile. This article analyzes the divergent international legal regimes together with the factors which will influence the determination of the standards of conduct which will govern manned and robotic missions to Mars.     

Planetary penetrators: Their origins,history and future

Penetrators, which emplace scientific instrumentation by high-speed impact into a planetary surface, have been advocated as an alternative to soft-landers for some four decades. However, such vehicles have yet to fly successfully. This paper reviews in detail, the origins of penetrators in the military arena, and the various planetary penetrator mission concepts that have been proposed, built and flown. From the very limited data available, penetrator developments alone (without delivery to the planet) have required ∼$30M: extensive analytical instrumentation may easily double this. Because the success of emplacement and operation depends inevitably on uncontrollable aspects of the target environment, unattractive failure probabilities for individual vehicles must be tolerated that are higher than the typical ‘3-sigma’ (99.5%) values typical for spacecraft. The two pathways to programmatic success, neither of which are likely in an austere financial environment, are a lucky flight as a ‘piggyback’ mission or technology demonstration, or with a substantial and unprecedented investment to launch a scientific (e.g. seismic) network mission with a large number of vehicles such that a number of terrain-induced failures can be tolerated.