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

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

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

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

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)

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)

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

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

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

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

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

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!