A.8.1.1.1 Avionics Non-Catastrophic Failure *
A.8.1.1.1 Avionics Non-Catastrophic Failure
A vast majority of the electronic components included in our launch vehicle design contribute to the non-catastrophic failure rate. However, the gyro drift rate is the main source of non-catastrophic failure that can be given a specific numerical value from the components selected. This piece of equipment has the most impact on our ability to meet the mission requirement of attaining a 300km orbit.
Gyro drift occurs when very small errors in the collected rate data are integrated in an effort to provide orientation data[2]. There are many things that contribute to gyro drift, but their explanations are complex and are beyond the scope of this section. A gyroscope that is high in accuracy has a drift rate of less than 0.1 deg/hr[2]. According to the Survey of Instrumentation and Measurement, a gyro drift rate of 1 deg/sec is considered acceptable in a warhead seeker or flight control system, but is only tolerable for a short time in stand-alone navigational applications[2].
Electronic components display the gyro drift in terms of the gyro bias. This is the deviation between the ideal output of the gyro and the actual output[1]. Because this parameter is one of the driving forces behind the prices for gyroscopes, we have chosen to accept the use of a gyro with a larger drift rate. The specified drift rate of our system is 0.5 deg/hr. This is a conservative rate for a gyroscope being used for our purposes.
One way to prevent this drift rate from becoming a problem is to periodically reset the gyro output so that it matches the output from other location-sensing devices and thus, eliminate any accumulated error in measurement[1]. The accelerometers have a much smaller error rate and our position data can also be integrated from that data as well as from the positional data of the gyroscope[3].
Other components contributing to the non-catastrophic failure rate include sensor failure, wiring shorts, malfunctions in the range safety equipment, and failure of the telecommunications equipment. These, however, did not impact our ability to meet the mission requirements due to the fact that our sensors are not connected to any system that makes changes to the performance of the launch vehicle.
References:
1 Paniit, Sudhakar M., Zhang, Weibang Modeling Random Gyro Drift Data by Dependent Systems. [online] Michigan Technological University,
URL:http://ieeexplore.ieee.org/iel5/7/4104218/04104235.pdf?isnumber=4104218&prod=JNL&arnumber=4104235&arSt=455&ared=460&arAuthor=Paniit%2C+S.M.%3B+Wwibang+Zhang [cited 26 March 2008].
2Dyer, Stephen A. Survey of Instrumentation and Measurement, Wiley-IEEE, 2001.
3 Wertz, James R., and Wiley J. Larson, eds. Space Mission Analysis and Design, 3rd ed., Torrance, Kluwer Academic and Microcosm Press, 1999.
Author: Nicole Bryan and Danielle Yaple