Tech Briefs

Explicit Filtering Leading to Grid-Independent and Discretization-Order-Independent Large Eddy Simulation

The re-formulation involves explicit filtering of the conservation equations. NASA’s Jet Propulsion Laboratory, Pasadena, California To validate simulations, one must trust that they are independent of the numerical aspects. A very promising, relatively new methodology for simulating turbulent flows, called Large Eddy Simulation (LES), has some issues in this respect. The issues stem from the aspect that modeling and numerics are totally intertwined, resulting in the fact that the results are grid-dependent and discretization-order-dependent. These issues were described in the preceding article. These issues prevent LES validation with experiments since one can always make adjustments to agree with data, which is not validation.

Posted in: Briefs, Electronics & Computers, Simulation Software


Mars Science Laboratory Second-Chance Flight Software

NASA’s Jet Propulsion Laboratory, Pasadena, California Mars lander spacecraft, beginning with Mars Pathfinder (MPF), have been designed to tolerate flight computer resets during the entry, descent, and landing (EDL) phase despite having only a single flight computer. This capability was enabled by a predictable, non-dynamic EDL architecture. The Mars Science Laboratory (MSL) spacecraft has a highly dynamic EDL architecture as well as dual flight computers, adding more complexity to EDL flight software fault tolerance.

Posted in: Briefs, Aviation, Electronics & Computers


Multi-User Investigation Organizer

Ames Research Center, Moffett Field, California InvestigationOrganizer (IO) is a Web-based information system that integrates the generic functionality of a database, a document repository, a semantic hyper-media browser, and a rule-based inference system with specialized modeling and visualization functionality to support mishap investigations. The semantic hypermedia component includes a customizable ontology that specifies various types of items (people, places, events, causes, systems, and associated information products) relevant to mishap investigations. The ontology also describes important properties of each item type, and details the potential relationships among items.

Posted in: Briefs, Electronics & Computers


Unit Conversion Macro for TecPlot Solutions for CFD

Lyndon B. Johnson Space Center, Houston, Texas The invention is a TecPlot macro, which is a computer program in the TecPlot programming language that processes CFD (computational fluid dynamics) solutions in TecPlot format. The TecPlot data is in SI units (International System of Units) [same as CFD solutions]. This invention converts the SI units into U.S. customary units.

Posted in: Briefs, Electronics & Computers, Mathematical/Scientific Software


Robust Gimbal System for Small-Payload Manipulation

This is a low-mass, small-volume gimbal unit. NASA’s Jet Propulsion Laboratory, Pasadena, California Spaceborne gimbal systems are typically bulky with large footprints. Such a gimbal system may consist of a forked elevation stage rotating on top of the azimuth motor, and occupy a large volume. Mounting flexibility of such a system may be limited.

Posted in: Articles, Briefs, TSP, Motors & Drives


A Phase-Changing Pendulum to Control Spherical Robots and Buoy Sensors

The pendulum adds new flexibility to motion control. NASA’s Jet Propulsion Laboratory, Pasadena, California A novel mechanical control system has been proposed for spherical robots to be used as multifunctioning sensor buoys in areas with ambient forces such as winds or currents. The phase-changing pendulum has been specifically designed for Moballs, a self-powered and controllable multifunctioning spherical sensor buoy to be used in the Arctic and Antarctica, or in other solar system planets or moons with atmosphere, such as Mars or Titan. The phase-changing pendulum has been designed to function in different phases: 1) When used as the spherical buoy, the Moball needs to take advantage of external forces such as the wind for its mobility. With no constraints, it could keep the center of mass in the geometric center of the sphere to facilitate the sphere’s movement. 2) However, as soon as the Moball needs to slow down or stop, the sphere’s center of mass can be lowered. 3) Furthermore, the phase-changing pendulum could lean to the sides, thereby changing the direction of the Moball by biasing its center of mass to the corresponding side. The Moballs could take advantage of such a novel phase-changing pendulum to go as fast as possible using the ambient winds, and to stop or steer away when facing hazardous objects or areas (such as the gullies), or when they need to stop in an area of interest in order to perform extensive tests. It is believed that this is the very first time that a pendulum has been suggested to control a spherical structure where both the length and the angle of the pendulum are adjustable in order to control the sphere. 4) Finally, the phase-changing pendulum could also control the sphere in the absence of wind. The spherical sensor buoys or Moballs could use the stored harvested energy (e.g., from sunlight or earlier wind-driven motions) to move the phase-changing pendulum and create torque, and make the spherical sensor buoys initiate rolling with the desired speed and direction. This is especially useful when the spheres need to get close to an object of interest in order to examine it.

Posted in: Articles, Briefs


Method for Performing GPS L1 C/A Measurements in Wideband Jamming and Interference

John F. Kennedy Space Center, Florida For effective range safety, global positioning system (GPS) metric tracking must be robust to interference with, and jamming of, GPS signals. The conventional approach to mitigating interference and jamming is to use a Controlled Reception Pattern Antenna (CRPA). These few-element phased arrays are used to steer nulls in the directions of interference sources, and/or to point beams in the directions of GPS satellites. The use of CRPAs is limited by their cost and size, as well as the difficulties of integrating the array into a platform. The problems are compounded for a launch vehicle, which must acquire and track GPS signals at high speed and acceleration, and undergo vibration and temperature conditions not common to CRPA use.

Posted in: Articles, Briefs, TSP