Using MathWorks\u27 Simulink® and Real-Time Workshop® Code Generator to Produce Attitude Control Test and Flight Code

This paper describes the use of a commercial product, MathWorks\u27 RealTime Workshop® (RTW), to generate actual flight code for NASA\u27s Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) mission. The Johns Hopkins University Applied Physics Laboratory is handling the design and construction of this satellite for NASA. As TIMED is scheduled to launch in May of the year 2000, software development for both ground and flight systems are well on their way. However, based on experience from previous APL missions such as Midcourse Space Experiment (MSX) and the Near Earth Asteroid Rendezvous (NEAR), the designers of the attitude estimation and control system desire a more streamlined approach for analysts to incorporate their algorithms into flight code. Specifically, the attitude control designers want an easier and quicker iteration capability during integration and test that somehow includes their principle development environment, Simulink®. One of the problems is that complete attitude simulations in the Simulink models include both flight and non-flight elements. With a significant initial effort, RTW now separates flight code from the non-flight code, incorporating changes directly from Simulink instead of editing the code after the fact. RTW first converts the Simulink inner workings into a single, all-knowing file. The Target Language Compiler. (TLC) then uses this file to convert the information into actual code. Simulink\u27s RTW product comes complete with canned TLC configuration files that control the generated C code. By editing these configuration files, analysts are able to perform complete estimation and control simulations in Simulink, and then with the click of a button produce code that can be directly compiled and linked onto flight systems. This ease has one caveat, however. By empowering the analysts to generate their own code, they also inherit the class of problems associated with real-time embedded systems, such as concerns with time and space efficiency

Quantitative Experimental Analysis Of Transparency And Stability In Haptic Interfaces

The notion of haptic transparency is used to quantify the fidelity with which virtual object properties are presented to, and perceived by, the human operator. Experimental results are presented quantifying the ability of humans to detect differences in mechanical impedances representing typical types of impedance corruption (loss of transparency) encountered in haptic interfaces due to stabilityenhancing dynamic compensation. In particular, a poor connection is found between the stiffness of virtual walls and their perceptual "hardness", prompting a new definition of hardness which is often dominated by the high frequency dynamics of the rendered impedance. INTRODUCTION Several performance metrics have been used to characterize haptic interfaces, ranging from teleoperation task completion times (Hannaford, et. al.,1991, Vertut and Coiffet, 1986) to achievable virtual stiffnesses and dampings (Colgate and Brown, 1994). In this paper, we use the notion of haptic transparency (Lawrence,..

The SNOE Spacecraft: Integration, Test, Launch, Operation, and On-orbit Performance

The Student Nitric Oxide Explorer (SNOE) was launched on 26 February 1998. Its objectives are to measure nitric oxide density in the lower thermosphere, to analyze the solar and auroral fluxes that create it and cause its variation, and to demonstrate the feasibility of low-cost, University-based missions that include a high degree of student participation. The SNOE spacecraft and instruments were designed and built at the University of Colorado Laboratory for Atmospheric and Space Physics (CU/LASP). It travels in a 580 x 550 km, sunsynchronous orbit with a 10:30 AM ascending node. It spins at 5 rpm with the spin axis normal to the orbit plane. It carries three instruments: An ultraviolet spectrometer to measure nitric oxide altitude profiles on the limb, a two-channel ultraviolet photometer to measure auroral emissions in the nadir, and a five-channel solar soft X-ray photometer. An experimental GPS receiver is also included for orbit determination. This paper describes completion of the SNOE project through integration and test, launch site operations at Vandenberg AFB, the early-orbit campaign, and routine mission and science operations. The on-orbit performance of the spacecraft subsystems is assessed, including the passive thermal regulation system as well as the electrical and computer systems. SNOE is in good health and appears to be headed for a long and successful mission