Case Study
Planetary Protection Category II
Presented by Dr. Gerhard Kminek, COSPAR Table of Content
Planetary protection category II description Case study for planetary protection category II Requirements for case study Implementation of requirements for case study Things to remember Category II description
All types of missions (gravity assist, orbiter, lander) to a target body where there is significant interest relative to the process of chemical evolution and the origin of life, but where there is only a remote1 chance that contamination carried by a spacecraft could compromise future investigations
1Implies the absence of environments where terrestrial organisms could survive and replicate, or a very low likelihood of transfer to environments where terrestrial organisms could survive and replicate
Applicability: Moon (with organic inventory),
Credit: NASA/Apollo 11 Credit: NASA/Magellan Credit: ESA/Rosetta Credit: NASA/JUNO Credit: NASA/Cassini Venus, comets, carbonaceous chondrite asteroids, Jupiter, Saturn, Uranus, Neptune, Ganymede*, Callisto, Titan*, Triton*, Pluto/Charon*, Ceres, Credit: NASA/Voyager 2 Credit: NASA/Voyager 2 Credit: NASA/Voyager 2 Credit: NASA/Galileo Credit: NASA/Cassini Credit: NASA/Voyager 2 KBO >½ size of Pluto*, KBO <½ size of Pluto
Credit: NASA/New Horizons Credit: NASA/New Horizons Credit: NASA/DAWN *The mission-specific assignment of these bodies to Category II must be supported by an analysis of the remote potential for contamination of a liquid-water environment that may exist beneath their surfaces, addressing both the existence of such environments and the prospect of accessing them Case study
Credit: ESA/JAXA BepiColombo BepiColombo (2 orbiters)
→ Target body: Mercury (Cat. I)
→ Propulsion: Electrical for cruise (transfer module
jettisoned before arrival at Mercury), chemical
around Mercury
→ Transfer: Multiple Earth, Venus (Cat. II), and
Mercury gravity assists mission level Cat. II Requirements for case study Requirements for Cat. II missions are limited to documentation → Planetary Protection Plan due at CDR (draft at PDR useful) → Pre-Launch, Post-Launch, and End-of-Mission Reports at the respective milestones
HOWEVER…
…all missions leaving Earth orbit must demonstrate compliance with impact probabilities or bioburden limits for Mars and probability of contamination limits for Europa & Enceladus → For the specific case study of BepiColombo there is no plausible trajectory leading to the outer solar system within 50 years after launch (the same applied to Hayabusa-2)
Credit: JAXA/Hayabusa-2 Applicable Mars impact probability requirements
→ The probability of impact on Mars by any element not assembled and maintained in ISO level 8 conditions (i.e. launcher upper stage) shall be ≤ 1x10-4 for the first 50 years after launch → 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 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 (Wilson interval) → 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: → Gravitational perturbation by Sun, Earth, Moon, Venus, Mercury, Jupiter and Saturn → Solar radiation pressure (SRP) with un-controlled attitude → In case there is a manoeuvre of the upper stage after the release of the spacecraft, the reliability of this manoeuvre (from flight records) has to be part of the overall analysis currently a trade-off between no upper stage disposition manoeuvre and a dedicated disposition manoeuvre are evaluated based on the impact probability analysis Implementation of requirements
Spacecraft 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
1. Analyse the trajectory impact probability of the spacecraft during cruise from Earth to Mercury • Cover nominal and off-nominal flight conditions and resulting trajectories of the spacecraft, incl. jettisoned modules • Monte Carlo method to achieve a one-sided 99% level-of-confidence (Wilson interval) • Necessary input is the launcher dispersion matrix (injection conditions) • Gravitational perturbation by Sun, Earth, Moon, Venus, Mercury, Jupiter and Saturn • Solar radiation pressure (SRP) with controlled and un-controlled attitude In case the trajectory impact probability is higher than the requirement ⇒ 2. Analyse spacecraft failure probabilities and combine with trajectory analysis • Reliability of the flight hardware necessary to control the spacecraft and reliability of operation • Micrometeoroid impact and effect analysis (details and consequences in Cat. III case study) • Combine the spacecraft failure probabilities with the trajectory impact probabilities (details and consequences in Cat. III case study)
Credit: ESA/ExoMars Things to remember
Requirements for Cat. II missions are limited to documentation and reviews Additional analysis and consequences on flight system design and mission operation can be necessary in particular for missions crossing the orbit of Mars, going to the outer solar system, or performing gravity assist manoeuvres Probability of impact requirements can have an effect on 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 trajectory analysis ready for the PDR This first trajectory analysis should not be too simplistic – otherwise late changes in the spacecraft design or operation might become necessary 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!