mars science laboratory planetary protection landing site constraints

Mars Science LaboratoryPlanetary Protection Landing

Site Constraints

John D. Rummel

31 May 2006

Planetary Protection

Planetary Protection Mission Status

• The MSL Project is working to implement a planetary protection strategy that meets NASA requirements—consistent with the mission’s science objectives—and that is technically and programmatically feasible

– The MSL project is subject to the COSPAR 2002/NASA 2005 PP policy

– The presence of a radioisotope power source (RPS) is assumed (but will not be official until the Record of Decision is formally signed by NASA, sometime in 2006)

– An MSL Planetary Protection Categorization Justification White Paper provided an analysis to support the Project’s PP categorization request

• Initial conditions for the mission with respect to Planetary Protection:

– MSL is not carrying instruments for the investigation of extant life

– MSL is not intending to target a “special region” (per PP policy definition) directly, although may do so via vertical mobility (arm, drill) N. B.

– MSL’s expected science objectives will require a biologically and organically clean sample handling and analysis chain (organics rule! )


What Makes MSL Different from Other Post-Viking Missions

• Several circumstances are different, and thus more challenging, for MSL compared to other post-1992 Mars lander/rover missions

– Identification of a special region concept and the need to deal with “off-nominal” landings (elements of NASA/COSPAR Category IVc)

– Orbiter measurements, the scientific interpretations of those measurements, and new hypotheses point to the possibility of water-ice being present over a large portion of the Martian surface, “relatively close” to the surface

– Proposed use of a radioisotope power source (RPS)—not used for Mars landers since Viking

• It is the presence of the RPS, a “perennial heat source,” coupled with the possibility of an off-nominal landing in an areawhere water ice may be relatively near thesurface, that requires a careful and thoroughassessment of the project’s options for meeting planetary protection requirementsand objectives

Design Concept


Project Categorization Request (April ‘04)

• Was based on NPR 8020.12B, then applicable

• “Based on our understanding of planetary protection requirements we think that Category IVa with the additional provision that the sample-access hardware that will contact the Martian subsurface should meet the equivalent of Category IVb. This combination is intended to meet the provisions of the current COSPAR planetary protection policy’s Category IVc.”

• This category since incorporated into NPR 8020.12C (April 2005)

– But there are multiple options for meeting IVc requirements


Category IVc

For missions which investigate martian special regions (see definition below), even if they do not include life detection experiments, all of the requirements of Category IVa apply, along with the following requirement:

Case 1. If the landing site is within the special region, the entire landed system shall be sterilized at least to the Viking post-sterilization biological burden levels.

Case 2. If the special region is accessed though horizontal or vertical mobility, either the entire landed system shall be sterilized to the Viking post-sterilization biological burden levels, OR the subsystems which directly contact the special region shall be sterilized to these levels, and a method of preventing their recontamination prior to accessing the special region shall be provided.

If an off-nominal condition (such as a hard landing) would cause a high probability of inadvertent biological contamination of the special region by the spacecraft, the entire landed system must be sterilized to the Viking post-sterilization biological burden levels.


Definition of “Special Region”

A Special Region is defined as a region within which terrestrial organisms are likely to propagate,

OR

a region which is interpreted to have a high potential for the existence of extant martian life forms.

Given current understanding, this is apply to regions where liquid water is present or may occur. Specific examples include but are not limited to:

Subsurface access in an area and to a depth where the presence of liquid water is probable

Penetrations into the polar caps

Areas of hydrothermal activity.


Project Proposed Options for “PP Categorization”

[Options for Meeting IVc Requirements]

At least three possible approaches to PP categorization are outlined:

1. Follow the example of Viking– Based on the Viking experience and a current analysis of the costs

and risks (contained in the White Paper) a system-level dry heat microbial reduction (DHMR) implementation could cost between $60M to $170M. Costs in this range may be beyond the resources available

2. Enables a full coverage of the proposed +/-60 latitude with a pre-Viking-sterilization-level cleanliness requirement for the spacecraft, and a post-Viking-sterilization-level cleanliness for the sampling tool(s)– The PP Categorization Justification White Paper is intended to

provide the strategy and justification for this approach– The costs to implement this approach are within the scope of the

initial project estimates, assuming the successful completion of on-going technology and design work

3. Restrict landing sites to regions where the probability of ice near the surface is acceptably low, with the same cleanliness requirements as #2; validate landing site acceptability at site selection “gate” after MRO data available– A fall-back option with potential scientific ramifications


The Evolving Story Of Martian Water / Ice

Head et al. Nature Dec’03

Distribution of examined MOC images –>

Yellow circles indicate MOC images with dissected mantle terrain, red circles indicate

images with no apparent dissected terrain. The mantle is interpreted to be present

poleward of ~60°, but is not dissected. An albedo mosaic is used as a background.


Basis for Surface Ice Distribution Assumptions

What We Know• The Mars Odyssey Gamma Ray Spectrometer (GRS) suite and HEND data show

large amounts of hydrogen within the top meter of the Martian surface layer poleward of 60° latitude in each hemisphere (and at certain longitudes poleward of 45° latitude) [Boynton et al., 2002; Mitrofanov et al., 2002; Feldman et al., 2002)]

• There is an interpretation of these data suggesting that large volume percentages of ground ice (50-75%) are present at high latitudes, covered by 15-30 g/cm2 (roughly 10-20 cm) of dry regolith

• Lower-latitude features may be due to bound water, adsorbed water, or spatially unresolved patches of ground ice

• Morphological evidence (Head et al., 2003) suggests sublimation of an icy surface may have occurred in the 30º-60º latitude band. No such evidence is present for latitudes equatorward of about 30º (was subsurface ever icy?)

What We Don’t Know (yet)• No near-surface ground ice has been unambiguosly detected equatorward

of ~45º latitude (i.e., over most of the proposed MSL landing area)• No ability to detect ground ice below ~1 m at the present• Spatial distribution / resolution of all elemental / chemical

detections of ice


Pre-Entry Failure

Tumbling

Nominal EDL} Parachute

FailureFailure at Entry

Descent stage + roverTumbling

Rover + RTG + DS coreTumbling

Tumbling

Forward

Backward

GPHS modulesTumbling

Descent stage Failure

-90°-60°

-13.8°

Failure Scenarios and Breakup Sequence During Entry Descent and Landing (EDL) –

MSL White Paper

Design Concept


Thermo-fluid Dynamic Analysis of Heat Source at

Dry / Icy Interface Summary – MSL White Paper

• General results for probabilistic analysis – The transient thermal wave passes quickly at first then slows down

approaching a critical radius beyond which no ice will melt. – Moisture content must be above a critical level, >4% by mass (the

hygroscopic limit for a loam-like soil, very conservative), for reproduction to occur but that level of moisture is transient and a function of the initial ice content (see following page)

– Heat source and dried area around heat source become very hot

• Net result is that there is a very restricted region near the dry/icy boundary where microbes must be initially located in order to be in liquid water and grow. That region is transient and lasts on the order of 10’s of sols. Conditions where there is high ice content which produces >40 % water by mass could allow for mobility which is also considered in the analysis.

Wet layer

Dry layer

Icy soil

Heat Source element

Dry soil

Microbe growth region


General Thermal / Fluid / Bio Scenario – MSL White Paper

A. Thermal wave has not reached organism

B. Warming of ice and organism

C. Liquid H2O present

• Opportunity for microbial multiplication

D. Bioavailable H2O has been depleted

• Losses due to sublimation, chemical reaction, wicking, and boiling

• Organisms become dormant (e.g., sporulation)

E. Heating to sterilizing temperatures depending on closeness to the heat source

Time History

-60

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20

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Time (arbitrary units)

Temperature (deg C)

E

A B

C

D


Viable Zones – MSL White Paper

The colored cells satisfy the criteria of (a) containing more than 4% water by mass at some time, and (b) not exceeding 383K at the indicated time after drying. The scale indicates how long the cell was wet.

No cells meet the criteria for < 30% ice. The 30% case reaches sterilization temperatures by 160 sols, the 40% case by 400 sols. Even after a Martian year, the two deepest “wet” cells remain unsterilized in the 50% case (this was still true nearly a year later).

12

0 c

m

100 cm100 cm

250W, 50% iceDry + 636 sols





100 cm

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m


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Sols


MSL Planetary Protection Implementation

Bottom line

• We don’t know enough about– Ice distribution or quality on Mars

– Nature of the martian subsurface (as reflected in DATA)

– Potential for spacecraft-induced “special regions” to support microbial growth on Mars

– The MSL flight system and its EDL record of success...

• So we are going to be cautious and conservative as we move forward– Limitation on MSL landing sites based on perennial heat-source issues (spacecraft-induced “special regions”)

– Conservative definition of natural “special regions” wrt MEPAG SR-SAG, for subsurface access (OK, but clean tools required)


PP Categorization Letter, August 23, 2005

As requested, the MSL mission is hereby assigned as Category IVc in accordance with

NPR 8020.12C, with the following options for implementation (assuming an RPS is

incorporated into the final design for the landed portion of the mission):

1. Prepare the landing system to meet Viking post-sterilization cleanliness requirements (controlled cleaning and assembly as noted below, followed by a system-level dry heat microbial reduction step in accordance with NPR 8020.12C), with control of recontamination through launch and delivery to Mars

– Under this option no restrictions on landing sites or on horizontal or vertical mobility into martian special regions would be imposed on the MSL mission by my office

Or

2a. Prepare the landing system to meet Viking pre-sterilization cleanliness requirements in accordance with NPR 8020.12C, including the following top-level requirements

– The total bioburden for exposed exterior and interior spacecraft surfaces of the “landed system” shall not exceed 3 x 105 spores at launch, with the average bioburden not exceeding 300 spores per square meter, as measured by the NASA standard microbial assay



2b. In addition, the portions of the sampling apparatus or any other portions of the spacecraft that will contact the martian subsurface must be subject to a sterilizing treatment providing no less than a four-order-of-magnitude reduction in the spore population measured by the NASA standard microbial assay. The required reduction is based on an initial bioburden of no more than 300 spores per square meter

– Dry heat is the approved decontamination method, and specifications for its use are provided in NPR 8020.12C. Alternative methods require a demonstration of effectiveness by the Project and approval by my office

– The Project must provide the facility or equipment and the means to accomplish this decontamination. The facility or equipment will be subject to certification and the means of decontamination and/or bioburden reduction will be subject to approval and monitoring

– Following the final pre-sterilization microbiological assay and microbial sterilization procedure, the Project must demonstrate that the sterilized elements are adequately protected against recontamination. This may require the use of biobarriers. Whatever the means of protection, the Project must provide demonstrated evidence that contamination requirements are not compromised following sterilization treatment



2c. The mission will be limited to landing sites not known to have extant water or water-ice within 1 m of the surface. One-sigma landing ellipses that address failure modes subsequent to parachute opening at Mars need to fall outside such areas

– Later access to martian special regions (as defined by NPR 8020.12C) will be permitted only by vertical mobility, through the use of sterilized sampling hardware, as detailed above

– No horizontal access through mobility by an unsterilized rover will be allowed

– Proposed landing sites will be reviewed by my office for compliance with this requirement pre-launch, and prior to the preparation and presentation of landing site options to the Science Mission Directorate Associate Administrator


For Example: A Model of Ice-Depth on Mars

Head et al. Nature Dec’03

Lat

itud

e


Questions??


PPAC Letter, August 15, 2005

• The Planetary Protection Advisory Committee takes note of two factors important in discharging its responsibilities:

– Planetary forward protection policies exist expressly for the purpose of enabling scientific investigations while guarding the likelihood that the results of such investigations will be of the highest feasible scientific integrity over the course of the period of biological exploration

– In every instance when scientific investigation of a site of potential biological interest is contemplated, it is possible to make the case for delaying until more effective protective protocols may be possible or affordable, or until more information may be available on which to base precautionary measures

– Nonetheless, the PPAC recognizes that facilitating science is a high imperative, and that, while planetary protection is a foremost consideration, there are no zero-risk scenarios other than inaction, which itself is unacceptable

– Each judgment balances the reality of non-zero risk of contamination with scientific value of investigation



– Evaluating the risk of forward contamination is made difficult by the paucity of certain experimental data. As an example, though not a unique example, projects continue to rely on assessments of the “probability of growth” of terrestrial microbes or spores emplaced in extraterrestrial environments (PG). The empirical basis for estimating PG is sparse and limited in the range of experiments that have thus far been carried out and reported. Although the Committee has no specific reason to believe that PG is substantially higher than assumed in, for example, the Mars Surface Laboratory project’s analysis, there is room for debate on the matter. This weakens forward contamination abatement plans that rely on probability of growth estimates

• PPAC did not find arguments based on probability of growth – as put forward by the MSL Project – persuasive as a sufficient basis for shaping an MSL planetary protection plan.

– This conclusion should not be construed as a criticism of the MSL project team’s analysis, but rather as an observation on the state of the art

– This matter is raised to call attention to the need for further research – and for the investments to underwrite that research – to better define parameters crucial to planning for control of forward contamination risks



• The principal difficult-to-control planetary protection risks are those associated with failure to successfully land

• The most important risks involve the possibility that the lander system suffers an uncontrolled impact with the surface under conditions that can create a localized warm and wet zone in which terrestrial organisms carried to Mars with the system could survive and multiply

• Concern focuses especially on failure scenarios that could implant both contaminated spacecraft or lander components and the Radiothermal Power System – or components of it – in such a way as to result in a warm wet zone encompassing the contaminated components, and in which the implanted organisms or spores could subsequently grow and migrate away from the site



• PPAC recommendations on MSL planetary protection measures attempt to balance factors alluded to earlier in this letter

• The Committee was mindful of the need to define requirements in such a way as to be verifiable

– Ideally, given uncertainties cited earlier, such as about probability of growth, arguments could be – and were – made for setting a more stringent requirement on the absence of water and ice from potential entry-failure impact ellipses, down to a level of two meters or more

– The limitations on the availability of data to reliably verify that such stringent requirements are met could place such a heavy burden on the scientific flexibility of the mission – with respect to landing sites and operations – as to compromise the scientific objectives to an extent greater than justified by the uncertainties

– We note that this inability to verify the absence of water to greater depth does increase the attendant risks



For either option, other requirements, including documentation, are as specified in

NPR 8020.12C:

– All flight hardware shall be assembled in Class 100K (ISO 8, or better) clean room facilities, with appropriate controls and procedures.

– The probability of impact of Mars by the launch vehicles shall not exceed 10-4

– The project shall provide an organic material inventory of bulk constituents (> 1 kg) for all launched hardware. In addition, the project should archive a 50 g sample of any organic material of which more than 25 kg is used

– The Project will provide for periodic formal and informal reviews by my office, which I anticipate will include formal reviews to coincide with the ATLO spacecraft readiness review, the pre-ship review, and pre-launch readiness review; and informal reviews, as necessary

– Independent verification bioassays. The Project shall accommodate, on a non-interference basis, independent assays by my office to confirm the spacecraft bioburden before launch. These assays will be conducted while the spacecraft are at the Kennedy Space Center (KSC) spacecraft preparation facilities, and/or prior to the application of the terminal sterilization process to the lander’s sampling apparatus or any other portions of the spacecraft that will be similarly processed to contact the martian subsurface

mars science laboratory planetary protection landing site constraints

Documents

planetary protection

msl different

requirements of category

discussion purposes

feasiblethe msl project

special region concept

martian special regions

equivalent of category