The Sample Analysis at Mars Instrument Simulator (SAMSIM) is a numerical model dedicated to plan and validate operations of the Sample Analysis at Mars (SAM) instrument on the surface of Mars. The SAM instrument suite, currently operating on the Mars Science Laboratory (MSL), is an analytical laboratory designed to investigate the chemical and isotopic composition of the atmosphere and volatiles extracted from solid samples. SAMSIM was developed using Matlab and Simulink libraries of MathWorks Inc. to provide MSL mission planners with accurate predictions of the instrument electrical, thermal, mechanical, and fluid responses to scripted commands. This tool is a first example of a multi-purpose, fullscale numerical modeling of a flight instrument with the purpose of supplementing or even eliminating entirely the need for a hardware engineer model during instrument development and operation.

SAMSIM simulates the complex interactions that occur between the instrument Command and Data Handling unit (C&DH) and all subsystems during the execution of experiment sequences. A typical SAM experiment takes many hours to complete and involves hundreds of components. During the simulation, the electrical, mechanical, thermal, and gas dynamics states of each hardware component are accurately modeled and propagated within the simulation environment at faster than real time. This allows the simulation, in just a few minutes, of experiment sequences that takes many hours to execute on the real instrument.

The SAMSIM model is divided into five distinct but interacting modules: software, mechanical, thermal, gas flow, and electrical modules. The software module simulates the instrument C&DH by executing a customized version of the instrument flight software in a Matlab environment. The inputs and outputs to this synthetic C&DH are mapped to virtual sensors and command lines that mimic in their structure and connectivity the layout of the instrument harnesses. This module executes, and thus validates, complex command scripts prior to their up-linking to the SAM instrument. As an output, this module generates synthetic data and message logs at a rate that is similar to the actual instrument.

The mechanical module simulates the actions of a number of mechanical components of the SAM instrument. This module contains the valves, the pumps, and the Sample Manipulation System (SMS). The response of each of these elements is modeled to produce outputs of state variables (velocity, position, force, etc.) that duplicate the behavior of the real elements.

The thermal module simulates the action of ≈60 heaters and their local thermal impact on the instrument. It also predicts the individual temperatures sensed by ≈70 thermistors and transmitted to the C&DH.

The gas flow module simulates the gas dynamics (time-dependent pressures and gas flows) in the Gas-Processing System (GPS) of SAM. The conductance of each gas transfer element (pipe, manifold, leak, pump, etc.) is dynamically computed as a function of the component dimension, gas composition, pressure, and temperature.

The electric module captures the electrical behavior of motors, control boards, Bayard-Alpert gauges, detectors, valves, heaters, and all components that contribute to the instrument power profile.

The behavior of each element of the SAMSIM model is reconstructed by accounting for all the relevant modules to that element. Complex components like pumps integrate contributions from modules to simulate the evolution of their command logic, rotor speeds, currents, temperatures, and throughputs.

This development was conducted by Mehdi Benna of the Center for Research and Exploration in Space Science & Technology (CRESST) at Goddard Space Flight Center and Tom Nolan of Nolan Engineering, LLC. GSC-16566-1

NASA Tech Briefs Magazine

This article first appeared in the August, 2013 issue of NASA Tech Briefs Magazine.

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