1. Planetary Protection Category III
Case Study
Planetary Protection Category III
Presented by Dr. Gerhard Kminek, COSPAR

2. Table of Content Planetary protection category III description
Case study for planetary protection category III
Requirements for case study
Implementation of requirements for case study
Things to remember

3. Category III description
Flyby (i.e. gravity assist) and orbiter missions to a target body of chemical evolution and/or origin of life interest and for which scientific opinion provides a significant2 chance of contamination which could compromise future investigations
2Implies the presence of environments where terrestrial organisms could survive and replicate, and some likelihood of transfer to those places by a plausible mechanism
Applicability: Mars, Europa, Enceladus
Credit: ESA/Mars Express
Credit: NASA/JPL/Galileo
Credit: NASA/JPL/Cassini
However, if an orbiter mission is looking for life, the mission will have to meet requirements for a life detection mission (i.e. avoid compromising the life detection measurement)
Credit: NASA/JPL/Cassini

4. Case study ExoMars Trace Gas Orbiter (TGO) Target body: Mars
Propulsion: Chemical
Transfer: Deterministic Deep Space Manoeuvre (DSM) with several 100 m/s and stochastic Trajectory Correction Manoeuvres (TCMs) with several m/s
Orbit acquisition: Mars Orbit Insertion (MOI) manoeuvre with several 100 m/s and aerobraking
Final orbit: 400x400 km, 373:30 repeat pattern
Credit: ESA/ExoMars

5. Requirements for case study
Launcher upper stage
The probability of impact on Mars by any element not assembled and maintained in ISO level 8 conditions shall be  1x10-4 for the first 50 years after launch
Note: This requirement also applies if a launch service is provided to another customer, e.g., launch of the Emirates Mars Mission (EMM) on H-IIA
Spacecraft
One of the following conditions shall be met:
The probability of impact on Mars by any part of a spacecraft assembled and maintained in ISO level 8 cleanrooms, or better, is  1x10-2 for the first 20 years after launch, and  5x10-2 for the time period from 20 to 50 years after launch (e.g., Mars Express, TGO)
The total bioburden of the spacecraft, including surface, mated, and encapsulated bioburden, is  5x105 bacterial spores (e.g., MRO, Maven)

6. Implementation of requirements
Launcher upper stage
The probability of impact on Mars by any element not assembled and maintained in ISO level 8 conditions shall be  1x10-4 for the first 50 years after launch*
*Relevant requirement needs to be reflected in Launcher Interface Requirements
Trajectory analysis based on Monte Carlo method to achieve a one-sided 99% level-of-confidence
Trajectory analysis covers all reference trajectories for the launch window (i.e. >1)
Number of Monte Carlo runs depends on the detected number of impacts (iterative)
Analysis includes:
Gravity potential of Earth and Mars and 3rd body perturbation by Sun, Moon, Jupiter and Saturn
Solar radiation pressure (SRP) with un-controlled attitude
Propellant blow-down as directed contribution, outgassing as spherical contribution
In case there is a manoeuvre of the upper stage after the release of the spacecraft (e.g., for Breeze-M and Centaur), the reliability of this manoeuvre (from flight records) has to be part of the overall analysis
In case impact probability is too high  increase launch bias away from Mars (effect on delta-v budget for spacecraft)

7. Implementation of requirements
Spacecraft
One of the following conditions shall be met:
The probability of impact on Mars by any part of a spacecraft assembled and maintained in ISO level 8 cleanrooms, or better, is  1x10-2 for the first 20 years after launch, and  5x10-2 for the time period from 20 to 50 years after launch
The total bioburden of the spacecraft, including surface, mated, and encapsulated bioburden, is  5x105 bacterial spores

8. Implementation of requirements
Spacecraft
One of the following conditions shall be met:
The probability of impact on Mars by any part of a spacecraft assembled and maintained in ISO level 8 cleanrooms, or better, is  1x10-2 for the first 20 years after launch, and  5x10-2 for the time period from 20 to 50 years after launch
The total bioburden of the spacecraft, including surface, mated, and encapsulated bioburden, is  5x105 bacterial spores

9. Implementation of requirements
Credit: ESA/ExoMars
Analyse the stability of the final science orbit  stable for >50 years 
Numerical propagation of orbit with atmospheric variation (driven by solar cycle); evaluate right ballistic parameter and proper parameters from the atmospheric model
Analyse the impact probability of the spacecraft before the DSM  no impact >50 years 
Monte Carlo method to achieve a one-sided 99% level-of-confidence
Necessary input is the launcher dispersion matrix (injection conditions)
Gravity potential of Earth
3rd body perturbation by Sun, Moon, Jupiter and Saturn
Solar radiation pressure (SRP) with controlled and un-controlled attitude
Credit: ESA/ExoMars
Analyse the impact probability between the DSM and reaching the final science orbit
Assume trajectory impact probability of ‘1’ after DSM (conservative)
Reliability of the flight hardware necessary to control the spacecraft and reliability of operation
Atmospheric variation for Mars aerobraking phase; ignore chance for recovery (conservative)
Micrometeoroid impact and effect analysis (details next)
Credit: ESA/ExoMars
Probability of impact: PHW failure + POP failure + Pmeteoroid kill 1x10-2

10. Implementation of requirements
Micrometeoroid model definition
Selection of micrometeoroid flux model (e.g., Grün), velocity distribution (e.g., 20 km/s), micrometeoroid density (e.g., 2.5 g/cm3), and average impact angle (e.g., 45)
Analysis of consequences
Selection of critical units necessary to control spacecraft (see reliability analysis)
Assess protection based on presence of MLI, panels, honeycomb panels, etc. in terms of equivalent thickness; take into account view factors
Assess protection based on distances between different elements to select use of proper ballistic limit equation (BLE from IADC)
Assess the failure modes of critical hardware
Typical problematic hardware e.g., tanks, star trackers, propulsion lines, UHF RFDN waveguides
Credit: ESA/ExoMars
MLI CFRP SLI
Bumpers
Rear Wall
Credit: ESA/ExoMars

11. Implementation of requirements
The approach used for the TGO is conservative in many ways but also easier to evaluate
This approach can be used for orbiter missions and for cruise stages delivering a lander
In case this approach is not sufficient to demonstrate compliance with the probability of impact requirements, other approaches could be used (but do not guarantee compliance)
Replacing the fixed micrometeoroid velocity with a velocity distribution (e.g., Taylor)
Replacing the trajectory impact probability value of 1 during part of the cruise phase with a value based on a trajectory analysis and allowing recovery manoeuvres
Allowing recovery manoeuvres during aerobraking
PI: prob. of impact during this phase
pi: prob. of impact due to the ith manoeuvre
qi+1: prob. that the next manoeuvre to remove the impact fails
PI = ipiqi+1
PI = i(orbit)[pi(non-recoverable)+pi(recoverable)qi]+j(manoeuvre)[pj(non-recoverable)+pj(recoverable)qj]+P(safe mode)+Q(t1, t2)
i(orbit)[pi(non-recoverable) + pi(recoverable)qi]: prob. of impact of a healthy spacecraft due to random variations of the atmosphere
j(manoeuvre)[pj(non-recoverable) + pj(recoverable)qj]: prob. of impact of a health spacecraft due to tracking, manoeuvre & operational issues
P(safe mode): prob. to enter a safe mode
Q(t1, t2): prob. of impact due to hardware reliability and micrometeoroids

12. Things to remember
Probability of impact requirements can have an effect on the qualification of hardware (e.g., solar arrays for aerobraking), the trajectory design, the delta-v budget (re-targeting), and spacecraft design (e.g., location of tanks, additional micrometeoroid protection)
To accommodate these effects, have a first analysis ready for the PDR
This first analysis should not be too simplistic – otherwise late changes in the spacecraft design or operation might become necessary
There is a trade-off in the aerobraking design between more gentle and longer aerobraking (negative for micrometeoroid effects and reliability) and more aggressive and shorter aerobraking (negative for hardware qualification and operation)
Ensure good interface with launcher system for upper stage impact analysis
All activities necessary to perform a probability of impact analysis are interdisciplinary and require the interactions between different engineering disciplines!