Actual Flight Hardware Research Articles

Software Reliability Analysis of NASA Space Flight Software: A Practical Experience.

In this paper, we present the software reliability analysis of the flight software of a recently launched space mission. For our analysis, we use the defect reports collected during the flight software development. We find that this software was developed in multiple releases, each release spanning across all software life-cycle phases. We also find that the software releases were developed and tested for four different hardware platforms, spanning from off-the-shelf or emulation hardware to actual flight hardware. For releases that exhibit reliability growth or decay, we fit Software Reliability Growth Models (SRGM); otherwise we fit a distribution function. We find that most releases exhibit reliability growth, with Log-Logistic (NHPP) and S-Shaped (NHPP) as the best-fit SRGMs. For the releases that experience reliability decay, we investigate the causes for the same. We find that such releases were the first software releases to be tested on a new hardware platform, and hence they encountered major hardware integration issues. Also such releases seem to have been developed under time pressure in order to start testing on the new hardware platform sooner. Such releases exhibit poor reliability growth, and hence exhibit high predicted failure rate. Other problems include hardware specification changes and delivery delays from vendors. Thus, our analysis provides critical insights and inputs to the management to improve the software development process. As NASA has moved towards a product line engineering for its flight software development, software for future space missions will be developed in a similar manner and hence the analysis results for this mission can be considered as a baseline for future flight software missions.

A vision-based strategy for autonomous aerial refueling tasks

Autonomous aerial refueling is a key enabling technology for both manned and unmanned aircraft where extended flight duration or range are required. The results presented within this paper offer one potential vision-based sensing solution, together with a unique test environment. A hierarchical visual tracking algorithm based on direct methods is proposed and developed for the purposes of tracking a drogue during the capture stage of autonomous aerial refueling, and of estimating its 3D position. Intended to be applied in real time to a video stream from a single monocular camera mounted on the receiver aircraft, the algorithm is shown to be highly robust, and capable of tracking large, rapid drogue motions within the frame of reference. The proposed strategy has been tested using a complex robotic testbed and with actual flight hardware consisting of a full size probe and drogue. Results show that the vision tracking algorithm can detect and track the drogue at real-time frame rates of more than thirty frames per second, obtaining a robust position estimation even with strong motions and multiple occlusions of the drogue.

AUTONOMOUS FLIGHT CONTROL AND HARDWARE-IN-THE-LOOP SIMULATOR FOR A SMALL HELICOPTER

The paper describes hardware development for a small helicopter and a hardware-in-the-loop (HITL) simulator for flight control system and obstacle avoidance testing and validation. The proposed obstacle avoidance system (OAS) is briefly outlined. The HITL simulator is developed to closely mimic the behavior of the actual flight hardware so as to easily develop, debug, and test the flight control system on the ground thereby minimizing the mission risk. The helicopter in use is a small X-Cell gas turbine retrofitted to achieve high bandwidth control of the helicopter with the ultimate goal of achieving obstacle avoidance once the inner-loop flight control system is tested. The sensor utilized for rigid body attitude and position determination is a navigation-quality Inertial Mesurement Unit (IMU). A specialized dual processor board has been designed and developed for implementation of the control system and the obstacle avoidance algorithm. Furthermore, the HITL simulator includes the actual helicopter itself for purpose of driving the servos on the helicopter and a board for mimicking the IMU output. Preliminary control system designs and testing on the HITL simulator and the path-planning and obstacle avoidance algorithm (GODZILA) are presented in this paper.