Engineering topics
Chang, Johnny
Publications and source records attributed to Chang, Johnny.
Mars 2020 Lander Vision System Flight Performance 1
The Mars 2020 Entry Descent and Landing (EDL) system delivered the Perseverance rover to the surface of Mars on February 18th, 2021. A large fraction of the Jezero Crater landing site was covered with landing hazards including cliffs, inescapable dune fields and rocks. These hazards were identified or inferred using orbital imagery before launch so that they could be avoided using Terrain Relative Navigation (TRN) which was composed of two parts: the Lander Vision System (LVS) and Safe Target Selection (STS). During EDL, the LVS successfully estimated map relative position by fusing landmarks matched between descent imagery and a map of the landing site with Inertial Measurement Unit (IMU) data. This position estimate was used by STS to identify the safest target for landing that was also reachable given fuel and other constraints. The EDL system then used the powered descent phase to retarget to this location and land safely. The overall error between the targeted location and actual landing location was 5m which was an order of magnitude less than the 60m touchdown error requirement. This paper will describe the final tests of the LVS before launch, the checkout of the LVS during operations and the LVS performance during EDL.
The Lander Vision System for Mars 2020 Entry Descent and Landing
In January 2016, the Mars 2020 project added Terrain Relative Navigation to the project baseline. This new capability helps the mission avoid large hazards in the landing ellipse, which enables the consideration of landing sites that more geologically diverse than before. This diversity should improve the quality of the samples collected by Mars 2020 for possible future return to earth. The Lander Vision System (LVS) is the sensor that provides the position fix that is used to determine where to land between hazards identified in orbital data prior to landing. This paper describes the LVS flight design for Mars 2020, a high-fidelity simulation used as a design tool and the expected LVS performance for Mars 2020.
Performance Evaluation of an Intel Haswell- and Ivy Bridge-Based Supercomputer Using Scientific and Engineering Applications
We present a performance evaluation conducted on a production supercomputer of the Intel Xeon Processor E5- 2680v3, a twelve-core implementation of the fourth-generation Haswell architecture, and compare it with Intel Xeon Processor E5-2680v2, an Ivy Bridge implementation of the third-generation Sandy Bridge architecture. Several new architectural features have been incorporated in Haswell including improvements in all levels of the memory hierarchy as well as improvements to vector instructions and power management. We critically evaluate these new features of Haswell and compare with Ivy Bridge using several low-level benchmarks including subset of HPCC, HPCG and four full-scale scientific and engineering applications. We also present a model to predict the performance of HPCG and Cart3D within 5%, and Overflow within 10% accuracy.
I/O Performance Characterization of Lustre and NASA Applications on Pleiades
In this paper we study the performance of the Lustre file system using five scientific and engineering applications representative of NASA workload on large-scale supercomputing systems such as NASA s Pleiades. In order to facilitate the collection of Lustre performance metrics, we have developed a software tool that exports a wide variety of client and server-side metrics using SGI's Performance Co-Pilot (PCP), and generates a human readable report on key metrics at the end of a batch job. These performance metrics are (a) amount of data read and written, (b) number of files opened and closed, and (c) remote procedure call (RPC) size distribution (4 KB to 1024 KB, in powers of 2) for I/O operations. RPC size distribution measures the efficiency of the Lustre client and can pinpoint problems such as small write sizes, disk fragmentation, etc. These extracted statistics are useful in determining the I/O pattern of the application and can assist in identifying possible improvements for users applications. Information on the number of file operations enables a scientist to optimize the I/O performance of their applications. Amount of I/O data helps users choose the optimal stripe size and stripe count to enhance I/O performance. In this paper, we demonstrate the usefulness of this tool on Pleiades for five production quality NASA scientific and engineering applications. We compare the latency of read and write operations under Lustre to that with NFS by tracing system calls and signals. We also investigate the read and write policies and study the effect of page cache size on I/O operations. We examine the performance impact of Lustre stripe size and stripe count along with performance evaluation of file per process and single shared file accessed by all the processes for NASA workload using parameterized IOR benchmark.
An Application-Based Performance Evaluation of NASAs Nebula Cloud Computing Platform
The high performance computing (HPC) community has shown tremendous interest in exploring cloud computing as it promises high potential. In this paper, we examine the feasibility, performance, and scalability of production quality scientific and engineering applications of interest to NASA on NASA's cloud computing platform, called Nebula, hosted at Ames Research Center. This work represents the comprehensive evaluation of Nebula using NUTTCP, HPCC, NPB, I/O, and MPI function benchmarks as well as four applications representative of the NASA HPC workload. Specifically, we compare Nebula performance on some of these benchmarks and applications to that of NASA s Pleiades supercomputer, a traditional HPC system. We also investigate the impact of virtIO and jumbo frames on interconnect performance. Overall results indicate that on Nebula (i) virtIO and jumbo frames improve network bandwidth by a factor of 5x, (ii) there is a significant virtualization layer overhead of about 10% to 25%, (iii) write performance is lower by a factor of 25x, (iv) latency for short MPI messages is very high, and (v) overall performance is 15% to 48% lower than that on Pleiades for NASA HPC applications. We also comment on the usability of the cloud platform.
Update on Controlling Herds of Cooperative Robots
A document presents further information on the subject matter of "Controlling Herds of Cooperative Robots". The document describes the results of the computational simulations of a one-blimp, three-surface-sonde herd in various operational scenarios, including sensitivity studies as a function of distributed communication and processing delays between the sondes and the blimp. From results of the simulations, it is concluded that the methodology is feasible, even if there are significant uncertainties in the dynamical models.
Mapping Nearby Terrain in 3D by Use of a Grid of Laser Spots
A proposed optoelectronic system, to be mounted aboard an exploratory robotic vehicle, would be used to generate a three-dimensional (3D) map of nearby terrain and obstacles for purposes of navigating the vehicle across the terrain and avoiding the obstacles. The difference between this system and the other systems would lie in the details of implementation. In this system, the illumination would be provided by a laser. The beam from the laser would pass through a two-dimensional diffraction grating, which would divide the beam into multiple beams propagating in different, fixed, known directions. These beams would form a grid of bright spots on the nearby terrain and obstacles. The centroid of each bright spot in the image would be computed. For each such spot, the combination of (1) the centroid, (2) the known direction of the light beam that produced the spot, and (3) the known baseline would constitute sufficient information for calculating the 3D position of the spot.
Columbia Application Performance Tuning Case Studies
This talk will. present several case studies of application performance enhancements on the SGI Altix platform. The enhancements include both explicit (dplace) and implicit (cpubind/cpuset-pin) process-pinning, eliminating memory contention in OpenMP applications, eliminating unaligned memory accesses, and system profiling. These enhancements enabled 2- to 28-fold improvements in application performance.
Three dimensional imaging utilizing structured light
This paper describes a method of remote sensing 3-dimensional structure of the proximity utilizing a laser, a holographic grating, and a single regular CCD camera. Basically, the laser beam is split by a holographic grating to form a regular spaced grid of laser beams that are projected into the field of view of a CCD camera.
System architecture for guided herd of robots exploring Titan
This paper describes a system architecture for an aerorobot blimp guiding and controlling a herd of sondes on Titan's surface.
Dynamics and control of a herd of sondes guided by a blimp on Titan
This paper describes the model and the algorithm developed for an aerobot blimb guiding and controlling a herd of sondes on the surface of Titan. The paper summarizes the derivation of the equations of motion used in simulations, and the features of the simulation model.
Using Modules with MPICH-G2 (and "Loose Ends")
A new approach to running complex, distributed MPI jobs using the MPICH-G2 library is described. This approach allows the user to switch between different versions of compilers, system libraries, MPI libraries, etc. via the "module" command. The key idea is a departure from the prescribed "(jobtype=mpi)" approach to running distributed MPI jobs. The new method requires the user to provide a script that will be run as the "executable" with the "(jobtype=single)" RSL attribute. The major advantage of the proposed method is to enable users to decide in their own script what modules, environment, etc. they would like to have in running their job.