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Planetary Protection Systems
The goal of Planetary Protection is to enable the exploration of planetary bodies in our solar system without introducing terrestrial contamination into those that may harbor life. The discipline includes both the protection of the object being studied (forward protection), as well as the protection of life on Earth from potential extraterrestrial contamination (backward protection).
Without adequate forward planetary protection precautions, we risk contaminating other planetary bodies to the detriment of our science and possible future resources. Furthermore, the possible consequences of inadequate backward planetary protection include introduction of material that is potentially hazardous to living systems on Earth.
Engineers work on Opportunity in a cleanroom at Kennedy Space Center. A very important part of planetary protection is keeping contaminants from humans from riding aboard spacecraft. The pictured engineers are donning "bunny suits" that only allow their eyes to be exposed.
Planetary protection requirements for each mission are scaled, based on the type of encounter (flyby, orbiter, or lander) and the potential of the mission's destination to provide insight into the origin of life in our solar system.
JPL engages in missions to areas of particular sensitivity to planetary protection. Our missions include the search for life and regions of past or present habitability in the solar system. Three proposed future missions provide particular challenges to planetary protection: Mars Sample Return, Europa Orbiter and/or Lander, and a Titan Orbiter (or lander). These missions are all likely to take place in the long-term.
Existing planetary protection approaches make these missions extremely difficult. Improved technology and better methods are desperately needed in order to provide adequate safeguards to protect both life on Earth and potential life on other planetary bodies visited by spacecraft.
To implement future planetary protection requirements, we need to advance current technologies to satisfy planetary protection requirements for surface, subsurface and atmospheric missions, as well as those technologies that allow sample acquisition for in-situ life detection or sample return.
Planetary Protection Technologies
Sterilization, Cleaning, and Validation
New approaches to sterilization, cleaning, and validation require a system-level approach to affordable flight systems. Unless JPL plays an active role in developing this system approach, future missions might prove to be impractical. Such capabilities would strengthen JPL’s capability to carry out missions on behalf of NASA.
The current state-of-the-art in Mars contamination studies is to identify organisms commonly found on spacecraft surfaces and/or in assembly facilities, as well as to investigate their survival under dry heat, UV radiation and other sterilization technologies.
Manifold apparatus for studying dry heat survival of multiple samples under different humidity and pressure regimes.
Dry Heat Microbial Reduction
An extensive study of the dry heat survival of resistant bacterial spores, recently performed at JPL, might allow expansion of the scope of the current Viking-era NASA specification. Application of this new knowledge, of how much heat is needed to kill the most resistant of terrestrial organisms and under what conditions, would allow engineers to take credit for pre-assembly manufacturing processes on their spacecraft hardware. This would reduce or eliminate the requirement for a separate planetary protection sterilization step. Alternatively, for example in the case of complex assemblies, the sterilization process could be optimized to accommodate the most sensitive materials in the design and still allow the hardware to meet the planetary protection requirements.
New methods in cleaning to achieve sterility would help NASA to meet its planetary protection goals at lower costs and with greater effectiveness. With the goal of removing all particles larger than two microns in size, three state-of-the-art cleaning systems are currently being studied to determine how well each would remove microbes, biological materials, and biological spores from spacecraft structures. The three systems being tested are: Precision (JPL), Ultra Pure Water (JSC’s White Sands Testing Facility), and the Liquid Boundary Layer Disruption System (HyperFlo Corporation). Preliminary studies indicate that cleaning to the two micron level creates surfaces that are effectively sterile, removing the need for dry-heat sterilization. This simplification of the process would enhance Planetary Protection capabilities, and allow flexibility in the implementation of Planetary Protection requirements, potentially reducing the overall mission cost.
Genetic Inventory of Spacecraft
Current planetary protection requirements are based on detection and counting of a resistant proxy organism using classical microbiology methods. This approach means a level of conservatism must be applied to account for the presence of unknown undetected organisms which may be even more resistant than the proxy.
The advent of molecular biology means that it is theoretically possible to detect the DNA of all the organisms present on a spacecraft. Studies are under way to adopt and adapt this technology for application in Planetary Protection. At the present time, research is to determine the inventory, or potential “passenger list” of organisms associated with spacecraft. For the future, this technology might allow Planetary Protection approaches to be tailored to the organisms present on a spacecraft and the sensitivity of a particular target body to those organisms.
Control of Backward Contamination
Future NASA missions are expected to continue to seek to return samples to Earth for further processing and analysis. These potential sample return missions would have the objective of searching for evidence of life in our solar system, as well as preparing for the subsequent human exploration. There are already several methods of sampling that are in use or in advanced development stages with a relatively high Technology Readiness Level (TRL). However, these methods do not yet fully address the issue of sealing, seaming, and return of a sample container, for example of the type that would be needed to receive a returned sample from Mars.
Modern molecular methods, such as DNA microarray, allow concurrent detection of many thousands of organisms from a single sample.
One challenge of returning a sample from Mars is to demonstrate that a terrestrial hitchhiker organism (live or dead) on an outbound spacecraft would not contaminate the sample collected at Mars. The dispersion of such debris is another subject of research:
Multiphase flows are flows of two or more thermodynamic phases moving together but not necessarily at the same velocity, and not necessarily at the same temperature. Each phase may contain several chemical species. In multiphase flows there is typically a carrier flow, and one or more dispersed phases carried by the flow. The volume of the dispersed phase divided by the total volume is called the dispersed phase volume fraction.
Multiphase flows naturally occur in many situations; examples are: tornadoes; volcanic plumes; avalanches and sand dunes. They are also important in many industrial and commercial systems; examples are: fuel sprays in liquid rocket, gas turbine and automotive engines; household sprays; medical dispenser sprays; agricultural sprays; ink jet printer sprays; paint sprays; fluidized beds; pipe flows in the context of underwater and other type of oil extraction, as well as sewage disposal; and centrifugal separators.
Present understanding of these flows is insufficient for prediction or control. Specific aspects not currently understood include:
the behavior of multiphase flows at moderate and high dispersed phase volume fraction
the dynamic and thermodynamic coupling between a moderate/high volume fraction dispersed phase and a high turbulence intensity carrier flow
the interactions among the condensed phase entities of a high volume fraction dispersed phase when carried by a high turbulence intensity flow.
Some of the projects listed below address particular aspects of these unresolved issues.
Spacecraft Design for Planetary Protection
JPL's Biotechnology and Planetary Protection Group has had a longstanding involvement in planetary projection and space biology, and has a more recent focus on non-space-related biotechnology research. As implementers of planetary protection, the BPP Group ensures that spacecraft meet stringent cleanliness requirements, which protect other solar system bodies from Earth life, and protect Earth from extraterrestrial life that might be brought back by returning space missions. In support of this implementation role, the BPP Group seeks to advance spacecraft cleanliness, sterilization, and validation technologies for NASA's solar system exploration missions. For future space missions, there is a need to advance current planetary protection technology in order to significantly reduce the microbial burden of the spacecraft and to reduce the risk, time, and complexity associated with planetary protection. Complying with planetary protection requirements for missions now in fabrication (e.g., MSL, Juno) is challenging. For the next generation of even more complex missions - following the water in the search for life, meeting planetary protection requirements is expected to stretch resources and drive new technologies, designs, and methods. A planetary protection-enabling spacecraft design would require exploration of innovative system architectures that facilitate PP implementation and development of methods and procedures for engineering implementation in affordable flight systems.
The development plan given in the table below identifies some of the specific key production and capabilities needed for improved planetary protection. Successful completion of new methodologies and technologies would provide new or improved capabilities to meet planetary protection requirements for future missions.
Key Products and Capabilities
2005 State-of-the-art
2005-2008
2009-2012
2013-2016
Thermal Sterilization of Subsystem / Full Spacecraft
Skill lost since Viking
Design principles and procedures in place
Relearning of methodologies for modern spacecraft
Application to future mission set
Knowledge of Microbes Associated with Particles
2 orders of magnitude uncertainty
Acceptable uncertainty
Application to future mission set
----
Knowledge of Dry Heat Effects on Microbial Populations
Application limited to NASA specification
Knowledge expanded to 200° C for resistant organisms
Application to future mission set
----
Particle Transport Modeling
Primitive model for launch; moderately acceptable model for Mars
----
Acceptable model for launch; robust model for Mars
Application to future mission set
Microbial Diversity
Inadequate knowledge
Adequate analysis with modern techniques
Complete analytical capability
Application to future mission set
Cleaning / Validation of Organics
Marginal cleaning, poor validation
Adequate cleaning and validation
Complete solution available for cleaning and validation
Application to future mission set
Selected Ongoing Projects
Cleaning To Achieve Sterility
We are evaluating three state-of-the-art cleaning systems for their efficacy in the removal of microbes, biological materials, and bacterial spores from spacecraft surfaces - an essential element of planetary protection. These advanced cleaning systems are used on progressively more complex materials and structures, such as materials coupons, components, and subsystems, to determine their ability to clean to achieve sterility: the removal of all particles greater than 2 microns in size.
Evaluation images of three candidate cleaning systems: Precision (JPL), Ultra Pure Water (JSC’s White Sands Testing Facility), Liquid Boundary Layer Disruption System (HyperFlo Corporation).
Rapid Single Spore Enumeration Assay
RapidSSEA couples the demonstrated methods of bacterial spore detection based on dipicolinic acid (DPA)-triggered terbium (Tb) luminescence and lifetime-gated imaging. Lifetime-gated imaging eliminates background fluorescence, which has obviated the use of fluorescence assays to enumerate single spores with particulate-laden environmental samples.
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