Robert Navarro

The Commensal Real-Time ASKAP Fast-Transients (CRAFT) Survey

We are developing a purely commensal survey experiment for fast (<5 s) transient radio sources. Short-timescale transients are associated with the most energetic and brightest single events in the Universe. Our objective is to cover the enormous volume of transients parameter space made available by ASKAP, with an unprecedented combination of sensitivity and field of view. Fast timescale transients open new vistas on the physics of high brightness temperature emission, extreme states of matter and the physics of strong gravitational fields. In addition, the detection of extragalactic objects affords us an entirely new and extremely sensitive probe on the huge reservoir of baryons present in the IGM. We outline here our approach to the considerable challenge involved in detecting fast transients, particularly the development of hardware fast enough to dedisperse and search the ASKAP data stream at or near real-time rates. Through CRAFT, ASKAP will provide the testbed of many of the key technologies and survey modes proposed for high time resolution science with the SKA.

A MULTI-BEAM RADIO TRANSIENT DETECTOR WITH REAL-TIME DE-DISPERSION OVER A WIDE DM RANGE

Isolated, short dispersed pulses of radio emission of unknown origin have been reported and there is strong interest in wide-field, sensitive searches for such events. To achieve high sensitivity, large collecting area is needed and dispersion due to the interstellar medium should be removed. To survey a large part of the sky in reasonable time, a telescope that forms multiple simultaneous beams is desirable. We have developed a novel FPGA-based transient search engine that is suitable for these circumstances. It accepts short-integration-time spectral power measurements from each beam of the telescope, performs incoherent de-dispersion simultaneously for each of a wide range of dispersion measure (DM) values, and automatically searches the de-dispersed time series for pulse-like events. If the telescope provides buffering of the raw voltage samples of each beam, then our system can provide trigger signals to allow data in those buffers to be saved when a tentative detection occurs; this can be done with a latency of tens of ms, and only the buffers for beams with detections need to be saved. In one version of our implementation, intended for the ASKAP array of 36 antennas (currently under construction in Australia), 36 beams are simultaneously de-dispersed for 448 different DMs with an integration time of 1.0 ms. In the absence of such a multi-beam telescope, we have built a second version that handles up to 6 beams at 0.1 ms integration time and 512 DMs. We have deployed and tested this at a 34-m antenna of the Deep Space Network in Goldstone, California. A third version that processes up to 6 beams at an integration time of 2.0 ms and 1,024 DMs has been built and deployed at the Murchison Widefield Array telescope.

Arraying performance of a 3-antenna demonstration array for Deep Space communications

NASA provides telecommunications services to its deep space scientific missions by way of its Deep Space Network (DSN) of large antennas Currently this DSN consists of monolithic antennas (34 m and 70 m diameter) located equidistant in longitude around the earth. The use of arraying has been proposed as a cost effective way to replace large antennas and/or add capability to the DSN in the future. A demonstration array was constructed at JPL as part of the study of arraying possibilities. This array consisted of three elements, two of which were 6 m-diameter antennas and one of which was a 12 m-diameter antenna. The array included a real-time FPGA based signal processing system capable of simultaneously operating as an interferometer and a signal combiner. The signal combiner was designed to sum the entire received spectrum from all elements of the array with the resulting signal compatible with the downlink tracking and telemetry system used by the DSN. The system was used to track various spacecraft at both frequencies of interest (X-band near 8.4 GHz and Ka-band near 32 GHz) as well as natural radio sources over broader bandwidths around the same frequencies. Signals from the combiner system were provided to a telemetry receiver where performance measurements could be compared to a single DSN antenna. Detailed results of these demonstrations with the Mars Reconnaissance Orbiter (MRO) and the Cassini Orbiter at Saturn are presented1 2.

Spacecraft-to-earth communications for Juno and Mars Science Laboratory critical events

This paper describes the Entry, Descent, and Landing (EDL) Data Analysis system (EDA). The EDA software supports the real-time interpretation of Multiple Frequency-Shift Keying (MFSK) tones provided by the spacecraft. The objective of this software is to provide communication of status between the spacecraft and the mission personnel on Earth during critical events when low rate telemetry is not possible due to high dynamics and low signal-to-noise ratio (SNR). Although these communications cannot be used to affect the landing due to the length of time required at these distances, this information is important in the case of a mission failure. Mars Science Laboratory will utilize the EDA software during EDL. Juno usage will include Jupiter orbital insertion (JOI), with predicted SNR of 12-15 dB-Hz. Results are presented from the Juno tones test. Simulated signals were also generated for Juno at JOI and Mars Science Laboratory (MSL) EDL and these results are analyzed.

Implementation of a Digital Signal Processing subsystem for a Long Wavelength Array station

This paper describes the implementation of a Digital Signal Processing (DP) subsystem for a single Long Wavelength Array (LWA) station.12 The LWA is a radio telescope that will consist of many phased array stations. Each LWA station consists of 256 pairs of dipole-like antennas operating over the 10–88 MHz frequency range. The Digital Signal Processing subsystem digitizes up to 260 dual-polarization signals at 196 MHz from the LWA Analog Receiver, adjusts the delay and amplitude of each signal, and forms four independent beams. Coarse delay is implemented using a first-in-first-out buffer and fine delay is implemented using a finite impulse response filter. Amplitude adjustment and polarization corrections are implemented using a 2×2 matrix multiplication.

Frequency domain beamforming for a Deep Space Network Downlink Array

This paper describes a frequency domain beamformer to array up to 8 antennas of NASAs Deep Space Network currently in development. The objective of this array is to replace and enhance the capability of the DSN 70m antennas with multiple 34m antennas for telemetry, navigation and radio science use. The array will coherently combine the entire 500 MHz of usable bandwidth available to DSN receivers. A frequency domain beamforming architecture was chosen over a time domain based architecture to handle the large signal bandwidth and efficiently perform delay and phase calibration. The antennas of the DSN are spaced far enough apart that random atmospheric and phase variations between antennas need to be calibrated out on an ongoing basis in real-time. The calibration is done using measurements obtained from a correlator. This DSN Downlink Array expands upon a proof of concept breadboard array built previously to develop the technology and will become an operational asset of the Deep Space Network. Design parameters for frequency channelization, array calibration and delay corrections will be presented as well a method to efficiently calibrate the array for both wide and narrow bandwidth telemetry.

Improved spacecraft tracking and navigation using a Portable Radio Science Receiver

The Portable Radio Science Receiver (PRSR) is a suitcase-sized open-loop digital receiver designed to be small and easy to transport so that it can be deployed quickly and easily anywhere in the world. The PRSR digitizes, down-converts, and filters using custom hardware, firmware, and software. Up to 16 channels can be independently configured and recorded with a total data rate of up to 256 Mbps. The design and implementation of the systems hardware, firmware, and software is described. To minimize costs and time to deployment, our design leveraged elements of the hardware, firmware, and software designs from the existing full-sized operational (non-portable) Radio Science Receivers (RSR) and Wideband VLBI Science Receivers (WVSR), which have successfully supported flagship NASA deep space missions at all Deep Space Network (DSN) sites. We discuss a demonstration of the PRSR using VLBI, with one part per billion angular resolution: 1 nano-radian / 200 μas. This is the highest resolution astronomical instrument ever operated solely from the Southern Hemisphere. Preliminary results from two sites are presented, including the European Space Agency (ESA) sites at Cebreros, Spain and Malargüe, Argentina. Malargües South American location is of special interest because it greatly improves the geometric coverage for spacecraft navigation in the Southern Hemisphere and will for the first time provide coverage to the 1/4 of the range of declination that has been excluded from reference frame work at Ka-band.

Design and implementation of a Deep Space Communications Complex downlink array

This paper describes the design and implementation of an array system that includes a frequency domain beamformer that will coherently combine the downlinked signals from up to eight inputs at each of NASAs three Deep Space Communications Complexes (DSCC). The array signal processor digitizes inputs with an intermediate frequency (IF) bandwidth of 100 to 600 MHz, coherently combines the inputs digitally, and transforms the combined waveform back to analog. Real-time correlation measurements are used for delay and phase calibration, allowing the system to adjust for atmospheric variations. A Downlink Array system is operational at each DSCC. Initial results from passes with the New Horizons spacecraft are presented and system performance is analyzed.

An FPGA-based back end for real time, multi-beam transient searches over a wide dispersion measure range

Isolated, short pulses of radio emission of unknown origin have been reported and there is strong interest in wide and sensitive searches for such events. To achieve high sensitivity, large collecting area is needed and dispersion due to the interstellar medium should be removed. To survey a large part of the sky in reasonable time, a telescope that forms multiple simultaneous beams is desirable. We have developed an FPGA-based transient search engine that is suitable for these circumstances. It accepts short-integration-time spectral power measurements from each beam of the telescope, performs incoherent de-dispersion simultaneously for each of a wide range of dispersion measure (DM) values, and automatically searches the de-dispersed time series for pulse-like events. If the telescope provides buffering of the raw voltage samples of each beam, then our system can provide trigger signals to allow data in those buffers to be saved when a tentative detection occurs; this can be done with a latency of tens of ms, and only the buffers for beams with detections need be saved.

Fast Transient Detection as a Prototypical “Big Data” Problem

The detection of fast (< 1 second) transient signals requires a challenging balance between the need to examine vast quantities of high time-resolution data and the impracticality of storing all the data for later analysis. This is the epitome of a “big data” issue—far more data will be produced by next generation-astronomy facilities than can be analyzed, distributed, or archived using traditional methods. JPL is developing technologies to deal with “big data” problems from initial data generation through real-time data triage algorithms to large-scale data archiving and mining. Although most current work is focused on the needs of large radio arrays, the technologies involved are widely applicable in other areas.