Title: Mars Science Laboratory Planetary Protection Landing Site Constraints
1Mars Science LaboratoryPlanetary Protection
Landing Site Constraints
John D. Rummel31 May 2006
2Planetary 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! )
3What 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
4Project 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
5Category 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.
6Definition 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.
7Project 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
8The 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.
9Basis 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
10Failure 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
11Thermo-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.
12General 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
13Viable 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).
14MSL 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)
15PP 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
16PP 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
17PP 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
18For Example A Model of Ice-Depth on Mars
Latitude
Head et al. Nature Dec03
19 20(No Transcript)
21PPAC 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
22PPAC 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
23PPAC 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
24PPAC 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
25PP 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