# Presentation: 075178

## Science Priorities Related to the Organic Contamination of Martian LandersPaul Mahaffy and David Beaty (co-chairs), Mark Anderson, Glenn Aveni, Jeff Bada, Simon Clemett, David Des Marais, Susanne Douglas,  Jason Dworkin, Roger Kern, Dimitri Papanastassiou, Frank Palluconi, Jeff Simmonds, Andy Steele, Hunter Waite, Aaron ZentNov. 24, 2003

*Note:  This is the presentation version of the white paper “**Report of the Organic Contamination Science Steering Group**”.  If there are any discrepancies between the two documents, the white paper should be judged to be superior.*

## OCSSG Charter

- _Problem Definition_.  What is the best way to define the issues regarding the impact of organic contaminants on future lab-related scientific investigations at Mars?  (We need to define the problems clearly before we can mount a serious attempt to solve them).
- _Problem Priority_.  What is the degree of importance the science community assigns to the issues defined above in #1?
- _Approach to Problem Solution_.  Recommend an approach to resolving any defined, high-priority problems.

**OCSSG Charter**

## Problem Definition

- We need to establish a _definition of “clean”_ that applies to _molecular organic contaminants_, taking into consideration their expected detection limits by various missions.  This is a prerequisite to systematic application of the general methods of molecular biology at Mars.
_*Solution*_
- We propose the structure of a new definition of “clean”, which is from the perspective of the _sample_ as it is delivered to the instruments, rather than from the perspective of _spacecraft surfaces_.
- For the science community this definition is simple and gets to the heart of the matter.
- However, for spacecraft engineers, the approach is non-traditional.

**Problem Definition**

## Problem Definition

- We do not have a scientific consensus on the _organic contaminants of importance_ to in-situ lab instruments in general, their general relative priority, and agreement on concentration levels that are achievable by the spacecraft engineers and useful to the instrument PIs.
- 	*Note:  Each PI can form his/her own judgement on contaminant priorities.  However, what has been missing is the development of a community-based consensus which can be used in a pre-competitive environment.*
_*Solution*_
- An interim consensus solution is presented in this study.

**Problem Definition**

## Problem Definition

- In order to achieve definitive scientific results in an in-situ sample analysis mission, it is necessary to be able to _distinguish contaminants from natural signal_.  For organic molecular contaminants, the design of the procedures necessary to achieve this have not been established.
_*Solution*_
- The OCSSG offers several possible approaches (in priority order) to mission design teams and to the science community.  These solutions range from definitive to helpful.  OCSSG defers to the future mission science/engineering teams to select an approach that is most appropriate for their circumstances.

**Problem Definition**

## Problem Definition

- For NASA’s missions that are planning measurements of in-situ organic geochemistry (including Phoenix, MSL, and future), there has not yet been enough planning on how to _achieve an initially clean sample system_ AND to _maintain its cleanliness_ throughout all measurement operations.
_*Solution*_
- The OCSSG offers several possible approaches to mission design teams and the science community.  OCSSG defers to the future mission science/engineering teams to select an approach that is best for them.

**Problem Definition**

## The four problems described above are of very high priority to the Mars exploration science community.  For astrobiology-related landers, these issues can lie at the heart of their science logic, and can make the difference between the eventual results being definitive, or merely being suggestive.

**Problem Priority**

## Starting AssertionsNature of contaminants and priority 

- For the scientific objectives of missions with an in-situ lab, the _primary contaminant issue_ is the quantity of organic contaminants which will _transfer_ to a sample on its way to a detector.  The portion of the contaminant load which does not transfer to the samples is, for this kind of experiment, irrelevant.
- Earth-sourced and Mars-sourced contaminants need to be considered separately.
- Until organic carbon is definitively discovered on Mars, preventing ANY sample from receiving _Earth-sourced organic contaminants_ above the level of detection is the highest priority.
- Once Mars-sourced organic material has been proved, minimizing cross-contamination of _Mars-sourced organic material_ between samples, so that its variation can be studied, will become critical.
- Both issues _MAY_ become relevant for the same mission (most notably, MSL).

## Approach to SolutionDefinition of “Clean” 

- Contamination control engineers traditionally define clean from the perspective of spacecraft surfaces.

_**Proposed New Approach**_
_**Definition**_**:  A **_**clean sample**_** (or sample split) is one which has been delivered to an instrument with less than a specified amount of contaminants.  **
- Will require a _further specification_ of the amount and nature of allowable contaminants (which will likely differ for each mission).  We recommend the specification be by mass fraction (I.e. ppb).
- This definition incorporates the concept of _transferability_, which distinguishes potential from actual contaminants.
- Requires understanding the overall _system-level performance_ of the sample system.

**Approach to Solution**Definition of “Clean”** **

*Note:  The particulate surface cleanliness is a unitless value that incorporates size bin and number of particles per unit surface area based on an analytical slope.  The specifics are stated in IEST-STD-CC1246D*

## Approach to SolutionProposed General Hierarchy of “Clean” Requirements 

_***Primary Requirement***_
- TBD mission shall have the capability to acquire and deliver clean samples of martian materials to its instruments.
_***Derived Requirements (examples only)***_
- Design.
- Minimize the use of organic materials within the sealed volume.
- Spacecraft manufacture, assembly.
- The general surfaces shall meet or exceed Cleanliness Level 1.
- The general sample acquisition and processing facility surfaces shall meet or exceed Cleanliness Level 2.
- The spacecraft surfaces that will come in direct contact with samples shall meet or exceed Cleanliness Level 3.
- Operations
- Keep the clean parts of the system warm.
- Flush the system with a cleansing sample prior to collecting data.

**Approach to Solution**Proposed General Hierarchy of “Clean” Requirements** **

## Approach to Solution“Clean” Definition and Timing 

_*Pre-competitive Environment*_
- In a pre-competitive environment, it is important that a flight project commit to a certain promised state of sample cleanliness _in advance_ of its instrument competition.
- The ability of the instruments to make use of the specified level of cleanliness may become a selection criterion, and thus must be known in advance.
- The nature of the allowable concentrations of contaminants needs to be general enough to allow for meaningful competition.
_*Post-competitive Environment*_
- In a post-competitive environment, each flight project will _negotiate with its selected investigators_, consistent with any pre-competitive agreements, to define mutually acceptable contamination specifics.

**Approach to Solution**“Clean” Definition and Timing** **

## Approach to SolutionInitial Priorities on Contaminants of General Interest 

- Benzene and more complex aromatics
- Organic molecules with carbonyl or hydroxyl groups.
- non-aromatic hydrocarbons
- amino acids, amines, amides
- DNA
_*Concentrations*_
*A general guideline is that samples need to be clean with respect to these contaminants at approximately the 1-10 ppb level.  These values will be different for different missions.  A specific recommendation for MSL is presented in Slide #18. *

**Approach to Solution**Initial Priorities on Contaminants of General Interest** **

## Approach to SolutionDistinguishing Contaminants from Natural Signal

_*NECESSARY TO ADDRESS POTENTIAL AMBIGUITY*_
- Carry several splits of at least one _standard of known “zero” composition_ in a form and position that they can be introduced as far upstream as possible into the sample chain.
- The nature of the standard(s) needs more discussion—this should be worked with the PSG, once it is formed.
- Before launch, contaminants should be measured both by the mission instruments where feasible _AND_ by terrestrial instruments with higher sensitivity.
- Collect _witness plates_ during ATLO, and archive for later analysis.
_*EXTREMELY VALUABLE*_
- Construct a _duplicate of the critical sample/analysis systems_, which can be held in pristine state (on Earth), and on which tests can be made during mission operations.

**Approach to Solution**Distinguishing Contaminants from Natural Signal

## Approach to SolutionMitigation and contamination control strategies

- In general, establishing an initially clean surface _can be done_ through a combination of precleaning wipes, a series of solvent washes, and vacuum bakeout.
- We need to validate that current methods to clean the _contaminants of specific mission interest_ are sufficient.
- The following ideas are suggested to engineering design teams.
- Hardware should be “designed to clean”, modular and robust enough to be compatible with standard cleaning facilities.
- Select fabrication materials for demonstrated cleanability.

**Approach to Solution**Mitigation and contamination control strategies

## Approach to SolutionMitigation and contamination control strategies

- During the interval between cleaning and sample analysis at Mars, the state of contamination can change, and it _must be monitored_.  The following are suggestions:
- Pre-launch monitoring consisting of residual analysis of constituent species and their amounts through hardware closeout.
- Post-launch contamination monitors (e.g. QCM, calorimeter) which operate in space during flight de-contamination cycles and on Martian surface prior to sampling.
- Flight experiments use of controlled data.

**Approach to Solution**Mitigation and contamination control strategies

## Approach to SolutionMitigation and contamination control strategies

- Maintaining the cleanliness of a surface can be done by controlling the movement of molecular contaminants in the sensitive parts of the system after cleaning.  The following design ideas are offered for engineering teams to use as appropriate.
- Seal and pressurize the sample contact hardware after cleaning.  It must specifically be isolated during cruise.
- Keep the internal surface area and the total volume as small as possible. (This one is_ really_ important!!)
- Minimize, or eliminate, the use of organic materials, and lubricants, within the sealed volume.
- Design in and install getters sensitive to the contaminants of interest.

**Approach to Solution**Mitigation and contamination control strategies

## Approach to SolutionMitigation and contamination control strategies

- Minimize the size of the opening into the most sensitive areas.
- Keep the temperature of the clean parts of the system higher than that of the surrounding sources of contaminants.
- Use a vapor proof biobarrier that can be temporarily removed to protect the most sensitive portions of the clean system.
- Include the capability to bake out the system either during cruise or on Mars.
- Prior to running unknown samples, send a synthetic sample through the system which has getter properties with respect to the contaminants of interest.

**Approach to Solution**Mitigation and contamination control strategies

## Possible MSL Requirements

- MSL shall implement procedures that will allow any organic detection to distinguish a terrestrial contaminant from a martian source.

**Possible MSL Requirements**

## Technology Development

- Technology for _biobarriers_ that are effective against molecular contaminants is judged to be insufficient.
- We have insufficient knowledge on _contaminant transferability_, which is necessary to predict the system performance called for in our overall definition of “clean”.
- The state of the art in _measuring_ the level of general residual molecular organic contamination (on Earth) appears to be sufficient without new basic** **technology development.  However it is expected that the methodologies for assaying certain specific compounds will need to be improved (e.g. benzene, amino acids, nucleic acids (DNA and RNA)).  These assay methodologies will need to be “ATLO-friendly”.
- We need new technologies for sterilization and the monitoring of efficency and effects of sterilisation procedures on spacecraft materials.

**Technology Development**

## External Validation

- Multiple requests for our white paper in progress—very significant interest in this topic by the community.

**External Validation**