Speaker
Ms
Francesca Letizia
(University of Southampton)
Description
When interplanetary missions depart from the Earth, the rocket bodies used for their launch may be inserted into a resonant orbit with the Earth or into trajectories that may cross other orbits. A suite of numerical tools has been developed as part of a European Space Agency contract to study the compliance of the launcher with planetary protection requirements.
For each mission, the launcher injection dispersion, the uncertainty in the spacecraft physical parameters, or potential spacecraft failures are treated with a Monte Carlo (MC) analysis. The uncertainty in the velocity vector components with respect to the nominal manoeuvre is defined and the distribution of velocity is sampled to obtain a discrete number of initial conditions. If required, the dispersion of other parameters (such as the area-to-mass ratio) can be included. Each initial condition is propagated through a high accuracy propagator, which describes the evolution of the launcher trajectory in Cartesian coordinates with respect to the solar system barycentre. Once each trajectory is computed, it is analysed to detect if it enters a planet’s sphere of influence. If so, the b-plane representation is used to characterise the close encounter.
The suite includes several Runge-Kutta propagators (both with adaptive step size strategy and regularised step size), providing also the possibility of dense output and the inclusion of user-provided events in the propagation (e.g. the propagation can be stopped if an impact is registered). Different options in the ephemeris routines (including the NASA SPICE toolkit) are available, which were validated against the data on the JPL Horizon system. In addition, SNAPPShot provides a tool for the analysis of the b-plane to distinguish between conditions of impact, gravitational focussing, and resonances. Fly-bys of different bodies and subsequent close encounters can be handled. The tool can identify the most critical close encounter, which will be used for the statistics generated from the MC analysis. The number of required MC runs to validate the requirements with a given confidence level is automatically estimated Wilson confidence intervals. If impacts are detected, the number of MC runs is automatically incremented.
All codes in the suite have been written in Fortran 90, exploiting the advantages of modern Fortran, such as array operations, dynamic memory allocation, modules and procedure pointers. The possibility of using parallel computations in the MC analysis will be discussed. As an example, an analysis for planetary protection compliance verification for the launcher of the BepiColombo mission requires four hours of computational time on a PC to run a MC analysis with more than 50000 runs.
| Applicant type | First author |
|---|
Primary author
Ms
Francesca Letizia
(University of Southampton)
Co-authors
Dr
Camilla Colombo
(University of Southampton)
Dr
Jeroen Van den Eynde
(University of Southampton)
Dr
Roberto Armellin
(University of Southampton)
Dr
Rüdiger Jehn
(European Space Agency)
