Tech Briefs

Multi-Antenna Radar Systems for Doppler Rain Measurements

Use of multiple antennas would enable removal of platform Doppler contributions.

Use of multiple-antenna radar systems aboard moving high-altitude platforms has been proposed for measuring rainfall. The platforms contemplated in the proposal would be primarily spacecraft, but, in principle, the proposal could also apply to aircraft. The problem of measuring rainfall velocity from a moving platform is especially challenging because the velocity of the platform (especially in the case of a spacecraft) can be so large that it is difficult to distinguish between the rainfall and platform contributions to Doppler frequency shifts. Furthermore, nonuniform filling of radar beams can lead to biases in Doppler estimates. Although it might be possible to reduce these biases through improved data processing, a potential alternative is to use multiple antennas positioned at suitable alongtrack intervals.

Posted in: Briefs, TSP, Electronics & Computers, Measurements, Antennas, Radar, Antennas, Radar, Weather and climate

Simple, Compact, Safe Impact Tester

Cushioned impact decelerations up to hundreds of normal Earth gravitation are easily produced.

An apparatus has been designed and built for testing the effects, on moderatesized objects, of cushioned decelerations having magnitudes ranging up to several hundred g [where g = normal Earth gravitational acceleration ( ≈9.8 m/s2)]. The apparatus was originally intended for use in assessing the ability of scientific instruments in spacecraft to withstand cushioned impacts of landings on remote planets. Although such landings can have impact velocities of 20 to 50 m/s, the decelerations must not exceed a few hundred g. This requires the deceleration to occur over a distance of as much as 50 cm in a time of tens of milliseconds. This combination of conditions is surprisingly difficult to simulate on the ground. The apparatus could also be used for general impact testing.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Crashworthiness, Test equipment and instrumentation, Entry, descent, and landing, Spacecraft

600-GHz Electronically Tunable Vector Measurement System

The design satisfies a complex set of technical and economic requirements.

A compact, high-dynamic-range, electronically tunable vector measurement system that operates in the frequency range from ≈560 to ≈635 GHz has been developed as a prototype of vector measurement systems that would be suitable for use in nearly-real- time active submillimeter-wave imaging. A judicious choice of intermediate frequencies makes it possible to utilize a significant amount of commercial off-the-shelf communication hardware in this system to keep its cost relatively low. The electronic tunability of this system has been proposed to be utilized in a yet-to-be-developed imaging system in which a frequency- dispersive lens would be used to steer transmitted and received beams in one dimension as a function of frequency. Then acquisition of a complete image could be effected by a combination of frequency sweeping for scanning in the aforesaid dimension and mechanical scanning in the perpendicular dimension.

Posted in: Briefs, TSP, Test & Measurement, Calibration, Measurements, Imaging, Imaging and visualization, Wireless communication systems, Imaging, Imaging and visualization, Wireless communication systems

Modular Architecture for the Measurement of Space Radiation

New architecture developed with improved capabilities adds radiation hardness.

A modular architecture has been conceived for the design of radiation-monitoring instruments used aboard spacecraft and in planetary-exploration settings. This architecture reflects lessons learned from experience with prior radiation-monitoring instruments. A prototype instrument that embodies the architecture has been developed as part of the Mars Advanced Radiation Acquisition (MARA) project. The architecture is also applicable on Earth for radiation-monitoring instruments in research of energetic electrically charged particles and instruments monitoring radiation for purposes of safety, military defense, and detection of hidden nuclear devices and materials.

Posted in: Briefs, Electronics & Computers, Measurements, Architecture, Architecture, Radiation

Smart Data Node in the Sky

A document discusses the physical and engineering principles affecting the design of the Smart Data Node in the Sky (SDNITS) — a proposed Earthorbiting satellite for relaying scientific data from other Earth-orbiting satellites to one or more ground station(s). The basic concept of the SDNITS is similar to that of NASA’s Tracking Data Relay Satellite System (TDRSS). However, the SDNITS would satisfy the needs of the next generation of Earth-observing satellite missions, including, notably, the need to relay data at much higher rates — of the order of 10 Gb/s versus 400 Mb/s for the TDRSS.

Posted in: Briefs, TSP, Electronics & Computers, Data acquisition and handling, Satellite communications, Data acquisition and handling, Satellite communications

Pseudo-Waypoint Guidance for Proximity Spacecraft Maneuvers

A paper describes algorithms for guidance and control (G&C) of a spacecraft maneuvering near a planet, moon, asteroid, comet, or other small astronomical body. The algorithms were developed following a model- predictive-control approach along with a convexification of the governing dynamical equations, control constraints, and trajectory and state constraints. The open-loop guidance problem is solved in advance or in real time by use of the pseudo-waypoint generation (PWG) method, which is a blend of classical waypoint and state-of-theart, real-time trajectory-generation methods. The PWG method includes satisfaction of required thruster silent times during maneuvers. Feedback control is implemented to track PWG trajectories in a manner that guarantees the resolvability of the open-loop-control problem, enabling updating of G&C in a provably robust, model-predictive manner. Thruster firing times and models of the gravitational field of the body are incorporated into discretized versions of the dynamical equations that are solved as part of an optimal-control problem to minimize consumption of fuel or energy. The optimal- control problem is cast as a linear matrix inequality (specifically a secondorder cone program), then solved through semi-definite-programming techniques in a computationally efficient manner that guarantees convergence and satisfaction of constraints.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Spacecraft guidance, Spacecraft guidance

Update on Controlling Herds of Cooperative Robots

A document presents further information on the subject matter of “Controlling Herds of Cooperative Robots” (NPO-40723), NASA Tech Briefs, Vol. 30, No. 4 (April 2006), page 81. To recapitulate: A methodology for controlling a herd of cooperative and autonomous mobile robots exploring the surface of a remote planet or moon (specifically, Titan or Titan-like) is undergoing development. The proposed configuration of mobile robots consists of a blimp and a herd of surface sondes. The blimp is the leader of the herd, and it commands the other robots to move to locations on the surface or below the surface to conduct science operations. Once a target is chosen, the sondes cooperatively aim sensors at the target to maximize scientific return. This hierarchical and cooperative behavior is necessary in the face of such unpredictable factors as terrain obstacles and uncertainties in the model of the environment.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Product development, Robotics

Simulation and Testing of Maneuvering of a Planetary Rover

A report discusses the development of a computational model of a Mars Explorer Rover maneuvering across terrain under varying conditions. The model is used to increase understanding of the rover dynamics. Increased understanding is helpful in planning further tests and in extending the operational range of the rover to terrain conditions that would otherwise have to be avoided in a conservative approach. The model is implemented within MSC.ADAMS®, a commercial suite of computer programs for simulating a variety of automotive and aeronautical mechanical systems. Following its initial formulation, the model has been successively refined in an iterative process of simulation, testing on simulated terrain, correlation of simulation results with test results, and adjustment of model parameters to increase degrees of matching between simulation and test results. In particular, three aspects of the model have been refined, as follows:

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Simulation and modeling, Terrain, Autonomous vehicles

Improved On-Chip Measurement of Delay in an FPGA or ASIC

Input and output buffers and the associated delays are eliminated.

An improved design has been devised for on-chip-circuitry for measuring the delay through a chain of combinational logic elements in a field-programmable gate array (FPGA) or application-specific integrated circuit (ASIC). Heretofore, it has been the usual practice to use either of two other types of on-chip delay-measuring circuits:

A delay chain of inverters is incorporated into the FPGA or ASIC chip along with an input port for feeding the inverter chain and an output port for feeding a signal to off-chip measurement circuitry. The disadvantage of this design is that the measurement is inaccurate because it includes delays in buffers that are parts of the input and output ports. The delay chain is arranged as a ring oscillator. The disadvantage of this design is that the delay chain does not always oscillate as expected.
Posted in: Briefs, TSP, Semiconductors & ICs, Design processes, Electronic equipment, Electronic equipment

VLSI Design of a Turbo Decoder

The design is readily adaptable to diverse applications.

A very-large-scale- integrated-circuit (VLSI) turbo decoder has been designed to serve as a compact, high-throughput, low-power, lightweight decoder core of a receiver in a data-communication system. In a typical contemplated application, such a decoder core would be part of a single integrated circuit that would include the rest of the receiver circuitry and possibly some or all of the transmitter circuitry, all designed and fabricated together according to an advanced communication-system-on-a-chip design concept.

Posted in: Briefs, TSP, Electronics & Computers, Data acquisition and handling, Telecommunications systems, Data acquisition and handling, Telecommunications systems

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