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Mars Science Laboratory Planetary Protection Landing Site Constraints

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Title: Mars Science Laboratory Planetary Protection Landing Site Constraints


1
Mars Science Laboratory Planetary Protection
Landing Site Constraints
John D. Rummel 31 May 2006
2
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! )

3
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
4
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

5
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.

6
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.

7
Project Proposed Options for PP
Categorization Options 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

8
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.
9
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

10
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
11
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.

12
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

13
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).
14
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)

15
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

16
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

17
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

18
For Example A Model of Ice-Depth on Mars
Latitude
Head et al. Nature Dec03
19
  • Questions??

20
(No Transcript)
21
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

22
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

23
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

24
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

25
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
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