|

Risk and Reliability of an Unmanned Planetary Exploration Mission

In this training model, a hypothetical NASA planetary exploration mission was simulated. The Model simulates all of the major components of the mission as it progresses through its phases: launch, interplanetary cruise, orbit insertion, landing, and exploration. The model simulates failure modes for the various mission components along with dynamic behavior such as consumption of propellant for attitude control and the effects of solar flares.

During the launch boost phase, both the solid rocket boosters and the main engines must perform successfully. The GoldSim model simulates the trajectory of the launch, and if a failure occurs can identify the appropriate coordinates, so that the potential consequences on the ground could be estimated. Unlike a fault tree approach, which is limited to a few discrete outcomes, the simulation results in a continuous range of possible failure locations along with their probabilities.

If the launch is successful, the spacecraft system (an orbiter and lander) separates from the booster rocket, and the 1.5 year long cruise phase starts. During the cruise phase most systems are shut down, but those that are operating are subject to potential events such as micrometeoroid hits and solar flares. The intense radiation from solar flares can affect microprocessors, and the potential effects of this are included in the simulation.

A subsystem of the model simulates the orbital insertion process, with a variable degree of consumption of the propellant for the main chemical braking rocket and for the attitude control system.

If orbit is successfully achieved, the model moves on to simulate the entry of the lander system into the planet's atmosphere and its descent to the surface. Finally, the two years of data collection by the lander's scientific systems are simulated, along with the communication systems that link it to the orbiter, and the orbiter to earth.

This model is discussed in more detail in Development of a Dynamic Simulation Approach to Mission Risk and Reliability Analysis.


 

Making Better Decisions In An Uncertain World