Mars Science Laboratory Planetary Protection Landing Site Constraints

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Mars Science LaboratoryPlanetary Protection
Landing Site Constraints
John D. Rummel31 May 2006
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Planetary Protection Mission Status

• The MSL Project is working to implement a
  planetary protection strategy that meets NASA
  requirementsconsistent with the missions
  science objectivesand 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 Projects 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.
• MSLs expected science objectives will require a
  biologically and organically clean sample
  handling and analysis chain (organics rule! )

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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 area
• where water ice may be relatively near the
• surface, that requires a careful and thorough
• assessment of the projects options for
• meeting planetary protection requirements
• and objectives

Design Concept
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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 policys Category IVc.
• This category since incorporated into NPR
  8020.12C (April 2005)
• But there are multiple options for meeting IVc
  requirements

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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.

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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.

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Project Proposed Options for PP
CategorizationOptions for Meeting IVc
Requirements

• At least three possible approaches to PP
  categorization are outlined
• 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
• 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
• 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

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The Evolving Story Of Martian Water / Ice
Head et al. Nature Dec03
Distribution of examined MOC images gt 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.
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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 Dont 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

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Failure Scenarios and Breakup Sequence During
Entry Descent and Landing (EDL) MSL White Paper
Tumbling
Design Concept

Nominal EDL
Forward
Backward
Parachute Failure
Tumbling
Failure at Entry
-90
-60
-13.8
Descent stage rover Tumbling
Rover RTG DS core Tumbling
Pre-Entry Failure
Descent stage Failure
GPHS modules Tumbling
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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,
  gt4 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 10s of sols.
  Conditions where there is high ice content which
  produces gt40 water by mass could allow for
  mobility which is also considered in the
  analysis.

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General Thermal / Fluid / Bio Scenario MSL
White Paper

• Thermal wave has not reached organism
• Warming of ice and organism
• Liquid H2O present
• Opportunity for microbial multiplication
• Bioavailable H2O has been depleted
• Losses due to sublimation, chemical reaction,
  wicking, and boiling
• Organisms become dormant (e.g., sporulation)
• Heating to sterilizing temperatures depending on
  closeness to the heat source

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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
lt 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).
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MSL Planetary Protection Implementation

• Bottom line
• We dont 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)

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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

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PP Categorization Letter, August 23, 2005

• 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

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PP Categorization Letter, August 23, 2005

• 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

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For Example A Model of Ice-Depth on Mars
Latitude
Head et al. Nature Dec03
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• Questions??

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(No Transcript)
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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

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PPAC Letter, August 15, 2005

• 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 projects
  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 teams 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

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PPAC Letter, August 15, 2005

• 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

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PPAC Letter, August 15, 2005

• 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

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PP Categorization Letter, August 23, 2005

• 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 (gt 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 landers sampling apparatus or any other
  portions of the spacecraft that will be similarly
  processed to contact the martian subsurface