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The purpose of this learning module is to enable learners to describe how the Goldstone-Apple Valley Radio Telescope (GAVRT) system functions in support of Apple Valley Science and Technology Center's (AVSTC) client schools' radio astronomy activities.
A magnetic tape recorder developed for the special requirements of radio astronomy and geodesy is described. These requirements include a high bit packing density and long record times. The current version of this longitudinal recorder used by the Very Long Baseline Array (VLBA) records 5.5 Terabits on a 14-in diameter reel of inch-wide tape. A maximum record rate of 256 Mb/s is achieved in the VLBA configuration with one recorder operating at 4 ms and utilizing 32 of the heads in a single stack. The VLBA recorders have been tested using a longitudinal density of 2.25 fr/micron; 448 data + 56 system tracks are recorded in 14 passes, each lasting 50 min, for a total record time (at 128 Mb/s) of 12 h on 14-in diameter reel of inch-wide 13-microns-thick D1-equivalent tape.
A new, fully steerable, decametric array for radio astronomy is under construction at the Clark Lake Radio Observatory near Borrego Springs, California. This array will be a T of 720 conical spiral antennas (teepee-shaped antennas, hence the array is called the TPT), 3.0 by 1.8 km capable of operating between 15 and 125 MHz. Both its operating frequency and beam position will be adjustable in less than one msec, and the TPT will provide a 49-element picture around the central beam position for extended-source observations. Considerable experience has been gained in the operation of completed portions of the array, and successful operation of the final array is assured. This paper describes the results of the tests which have been conducted with the conical spirals and outlines the planned electronics.
A fully steerable, decametric array for radio astronomy is under construction at the Clark Lake Radio Observatory near Borrego Springs, California. This array will be a T of 720 conical spiral antennas (teepee-shaped antennas, hence the array is called the TPT), 3.0 km by 1.8 km capable of operating between 15 and 125 MHz. Both its operating frequency and beam position will be adjustable in less than one millisecond, and the TPT will provide a 49-element picture around the central beam position for extended source observations. Considerable experience was gained in the operation of completed portions of the array, and successful operation of the final array is assured. The results are described of the tests which were conducted with the conical spirals, and the planned electronics and data processing systems are described.
The surce locations of both polariation components of the saturn kilometer wavelength radiation were deduced using Voyager 1 and Voyager 2 planetary radio astronomy data and assumptions about radiation beam geometry. Radio source footprints were compared with the surface locations of saturns ultraviolet aurorae, its polar cap boundary, and its polar cusp.
During both Voyager encounters with the saturnian system, the Planetary Radio Astronomy experiment detected strong discrete episodic bursts of radio emission, termed Saturn electrostatic discharges (SED). An examination of Voyager 2 photopolarimeter data now reveals a narrow feature (possibly a gap) in Saturn's B ring. A single, unique object appears to be responsible for both the SED and this feature.
A new, fully steerable, decametric array for radio astronomy has been built at the Clark Lake Radio Observatory near Borrego Springs, California. This array is a 'T' of 720 conical spiral (teepee-shape) antennas, 3.0 km by 1.8 km. It is capable of operating between 15 and 125 MHz but has best sensitivity in the 25 to 75 MHz range. Both its operating frequency and beam position are adjustable in about 1 msec. A 1024-channel digital correlator has been built and attached to the array. This permits the simultaneous measurement of the complex visibility functions on 512 interferometer baselines between various portions of the array. After Fourier transformation these visibility data yield a 32 x 32 resolution element picture of the area of sky under observation, with frequency-dependent angular resolution ranging from 20 to 2.7 arcsec and a sensitivity of 1 Jy per beam. This system is described, and some initial observations are presented.
The Voyager Planetary Radio Astronomy (PRAD) experiment revealed prominent 'arcs' when the radio intensity at 1-40 MHz was displayed in time-frequency coordinates. These data are consistent with multiple currents flowing along longitudinally separated Jovian magnetic flux tubes, each current radiating conically at angles up to about 90 deg. The spacings between adjacent PRA arcs, and also between adjacent S burst arc segments observed at the Nancay Observatory, were analyzed and found to be so brief, less than 1-3 min, that either these currents and any associated Alfven waves survive for at least a few circulations of Jupiter by Io (a hypothesis independently supported by the observations of arcs at all Io phase angles), or each such Alfven current can radiate at several different cone-angles simultaneously (a hypothesis independently supported by the observation of such behavior in the S burst arcs).
The Voyager planetary radio astronomy experiment detected a bursty, narrow-band radio emission originating in Neptune's magnetosphere. The time of occurrence of nearly all of the episodes of this bursty radio emission can be explained on the basis of a radio source located just above and to the east of the south magnetic offset tilted dipole (OTD) tip (Farrell et al., 1990). However, several episodes of bursty emission do not occur at the usual frequency and planetaray rotation phase for emissions of this type. The occurrences of these rarely seen anomalous episodes are shifted systematically in planetary longitude so as to be consistent with a source of emission to the southwest of the southern magnetic OTD pole. Owing to the proximity of these sources to the magnetic polar region, they are associated with an active auroral region. Therefore, at least from the standpoint of the radio emission, the picture that emerges is of an auroral zone with two emission hot spots approximately diametrically east and west of the south magnetic pole. The possibility of a complete radio-active auroral oval is discussed.
During the inbound and the outbound leg of Voyager 2's encounter with Neptune, the Planetary Radio Astronomy (PRA) experiment aboard the spacecraft detected short radio bursts at frequencies within the range of about 500-1300 kHz, and broad-banded smoothly varying emission patterns within the frequency range from about 40-800 kHz. Both emissions can be described in terms of a period of 16.1 hours determining Neptune's rotation period. Furthermore, just near closest approach, a narrow-banded smoothly varying radio component was observed occurring between 600 and 800 kHz. After giving a brief overview about some general characteristics of Neptune's nonthermal radio emission, the source locations of Neptune's emission components are determined, using an offset tilted dipole model for Neptune's magnetic field. Assuming that the emission originates near the electron gyrofrequency a geometrical beaming model is developed in order to fit the observed emission episodes.
The increasing load on NASA's deep Space Network, the new capabilities for deep space missions inherent in a next-generation radio telescope, and the potential of new telescope technology for reducing construction and operation costs suggest a natural marriage between radio astronomy and deep space telecommunications in developing advanced radio telescope concepts.
Radio JOVE is an education and outreach project intended to give students and other interested individuals hands-on experience in learning radio astronomy. They can do this through building a radio telescope from a relatively inexpensive kit that includes the parts for a receiver and an antenna as well as software for a computer chart recorder emulator (Radio Skypipe) and other reference materials
During the Voyager 2 encounter with Neptune, a narrowbanded bursty radio component was observed between 500 and 1326 kHz by the Planetary Radio Astronomy instrument. Based on the emission occurrence pattern, the radio source has been localized without the explicit use of the Neptunian offset-tilted dipole magnetic field model, which is accurate only at distances greater than 4 R(N) (Neptune radii) from the planet. Only assumptions based upon the general nature of radio wave propagation in planetary magnetospheres were used. A number of different candidate radial positions were sampled. For example, at 1.5 R(N), the derived source location was positioned only about 10 deg from the south magnetic pole. The radiation from this source was beamed into a cone of 77.5 + or - 6.3 deg half-angle that was tilted about 10 deg from the radial direction to the north-northeast. At other sampled radial positions, similar source locations were obtained. Due to its proximity to the south magnetic pole, the kilometric emission radio source is believed to be associated with an active auroral region, similar in nature to those found at earth and Saturn.
Through analysis of available optical spectrophotometric data and radio flux density measurements in the literature, it is demonstrated that a good correlation exists between the radio power and bolometric luminosity of the optically-selected OSOs in the Bright Quasar Sample (BOS) of Schmidt and Green (1983). We have recently used VLBI measurements of a sample of ultraluminous infrared galaxies to infer the likely existence of radio-quiet Active Galactic Nuclei (AGNs) deeply enshrouded in dust within their nuclei (Lonsdale, Smith, and Lonsdale 1993). We employ the radio-bolometric luminosity correlation for the BQS quasars to test whether these hypothetical buried AGNs can be energetically responsible for the observed far-infrared luminosities of the ultraluminous infrared galaxies. The ultraluminous infrared galaxies are shown to follow the same relation between radio core power and bolometric luminosity as the radio-quiet QSOs, suggesting that buried AGNs can account for essentially all the observed infrared luminosity, and raising the possibility that any starburst which may be in progress may not be energetically dominant. The broader implications of the radio-optical correlation in quasars for AGNs and luminous infrared galaxy models and the use of radio astronomy as a probe of the central powerhouse in radio quiet AGNs and luminous infrared galaxies are briefly discussed.
For a 21 day interval beginning on Jan 28, 2007, the radio and plasma wave instruments (S/WAVES) on the twin STEREO spacecraft detected intense impulse-like emissions in both the time-domain receivers and the low end of the frequency-domain receivers. These emissions were much more intense on the STEREO Ahead instrument, but were detected by both. During that interval, the two STEREO spacecraft were only separated by about 0.1deg in heliocentric longitude. All attempts to understand the emissions in terms of electrical disturbances onboard the spacecraft were unsuccessful and, since the impulsive events essentially ceased on Feb 18,2007, the entire study was put on lower priority. However, beginning abruptly on July 20, 2007, a very similar and more intense episode of impulses was detected exclusively by S/WAVES on the STEREO Ahead spacecraft, now separated from Behind by more than 20deg of heliocentric longitude. This new episode lasted nearly as long as the Jan-Feb episode, some 20 days, ending on Aug. 9. On Aug. 13,2007, the STEREO Behind spacecraft arrived at the same heliocentric longitude as the Ahead spacecraft was at on July 20 and the S/WAVES instrument abruptly started detecting impulsive events, although at lower intensities than those on Ahead. The individual waveform of the detected impulses is very similar to signals recorded by the Voyager plasma wave (PWS) and radio astronomy (PRA) instruments and more recently by the Cassini radio and plasma wave science (RPWS) instrument when those spacecraft plunged through Saturn's rings. Those Saturnian signals are attributed to micron-sized dust particle impacts on the spacecraft which creates a temporary plasma cloud which, in turn, induces an electrical signal on the antennas. We reanalyzed the STEREO episodes along the lines of the Saturnian ring plane analyses and have concluded that the STEREO impulses are very likely due to similar dust impacts with bands or clouds of dust of cometary or, more generally, zodiacal light material near 1 AU. The distribution of these clouds of small dust particles is significantly different than theoretical models of interplanetary dust distribution
Progress in the development and operations of the Deep Space Network is reported. Developments in Earth based radio technology as applied to geodynamics, astrophysics, and radio astronomy's use of the deep space stations for a radio search for extraterrestrial intelligence in the microwave region of the electromagnetic spectrum are reported.
During the encounter of the International Cometary Explorer (ICE) with comet P/Giacobini-Zinner, the radio astronomy experiment observed occultation and propagation effects on several distant radio sources. The observations of the partial occultation of the galactic radio source between 360 and 1000 kHz show that the three-dimensional large scale structure of the coma is consistent with the structure determined from in-situ measurements made along the encounter trajectory. In addition, these observations remove a previously existing ambiguity in the position of the galactic source. Between 110 and 360 kHz the earth source is broadened by scattering by the comet random density inhomogeneities. The amount of broadening indicates that the electron density fluctuations measured in situ by ICE along its trajectory (100 pct fluctuations with a scale length of 1000-2000 km over a path length of 100,000 km) exist with the same properties in the perpendicular direction.
A team of engineers and scientists at JPL is currently working on the design of an array of small radio antennas with a total collecting area up to twenty times that of the largest existing (70 m) DSN antennas. An array of this size would provide obvious advantages for high data rate telemetry reception and for spacecraft navigation. Among these advantages are an order-of-magnitude increase in sensitivity for telemetry downlink, flexible sub-arraying to track multiple spacecraft simultaneously, increased reliability through the use of large numbers of identical array elements, very accurate real-time angular spacecraft tracking, and a dramatic reduction in cost per unit area. NASA missions in many disciplines, including planetary science, would benefit from this increased DSN capability. The science return from planned missions could be increased, and opportunities for less expensive or completely new kinds of missions would be created. The DSN array would also bean immensely valuable instrument for radio astronomy. Indeed, it would be by far the most sensitive radio telescope in the world. Additional information is contained in the original extended abstract.