Who invented the very large array

These two factors are often contradictory. To capture faint images a telescope needs to collect lots of light over a long time, but this can make images blurry. To capture a sharp image you often need a brighter source. It is similar to the effect of our own eyes, which adapt to brightness. By arranging antennas into different configurations, the VLA can overcome this challenge, allowing it to capture both sharp images and faint objects depending on the needs of astronomers.

There are four primary configurations used by the VLA. They are each assigned a letter A — D, depending on the spread of the antennas.

Configuration A, spanning more than 22 miles, is where the antennas are most widely spaced, and Configuration D is where they are closest together, with the antennas clustered into an area less than a mile wide. The VLA cycles through these configurations, staying in each one for several months. The largest configuration gives the VLA its highest resolution. Each receiver first-stage was mounted on separate circularly polarized feeds located on a 2 meter diameter ring centered on the vertex of the dish.

An asymmetric secondary reflector at the Cassegrain focus was rotated to illuminate each feed and direct the beam along the electrical axis of the telescope. The 6 cm receiver was conventional and included a parametric amplifier followed by a mixer and IF system. For the 18—21 cm system, the signal was up-converted to 5 GHz 6 cm and the 6 cm paramp used as the second stage.

In order to properly illuminate the 18—21 cm sub-reflector and to keep the feed from being prohibitively large, a dielectric lens was placed in front of the feed. The 1. Although the addition of the 1. At each band there were two independent receivers, one each for left and right hand circular polarization. For each polarization, the MHz IF band was split into two 50 MHz bands, which was the largest that the digital electronics of the era could accommodate. In order to optimize the aperture efficiency, the primary and Cassegrain secondary reflectors differed from their canonical parabolic and hyperbolic shape Williams To evaluate the planned fixed position 4-feed system, the Green Bank Foot Telescope was converted to a Cassegrain optics employing a rotating asymmetric secondary reflector.

Unfortunately, the Green Bank prototype did not uncover a problem caused by the offset feed geometry, which resulted in the two circularly polarized beams being displaced by 0. By the time the problem was discovered, six systems had already been purchased, and it was decided not to implement any changes. Although NRAO had experienced considerable issues with the reliability and stability of cryogenically cooled receivers on the Green Bank Foot Telescope, Weinreb made the bold decision that in order to obtain the best sensitivity he needed to use cooled parametric amplifiers on the VLA front ends.

One of the key technical innovations employed during the construction of the VLA, was the use of the newly-developed low loss TE 01 mode circular waveguide to carry the IF signals back from each antenna. The same waveguide carried the common local oscillator reference signal from the central laboratory to each antenna and the extensive monitor and control signals to and from each antenna and the central control building.

It was felt that optical fiber technology was not sufficiently well developed at the time to be used for the VLA. However, when they went to the NRAO business office to get approval to buy the waveguide, Weinreb and Hvatum had to admit that the waveguide was being manufactured only in Japan.

Moreover, the Japanese plant where the waveguide was being fabricated was scheduled to be closed. NSF approval was straightforward, but the US Department of Commerce was not so easily convinced why such a large government contract should go to Japan, especially without an open bidding process.

The TE 01 mode circular waveguide was buried alongside the railway track to transfer the local oscillator and IF signals between the central control building and each antenna. Another important design change from the original proposal, made possible by the rapid development of digital signal processing technology, was to build a digital delay-multiplier system based on custom designed Application Specific Integrated Circuits ASICs to process the four 50 MHz IF bands, two in each circular polarization.

To compensate for the delay of up to microsecs in the differential path length from each antenna, the digital delay system needed to maintain an accuracy of better than two nanoseconds across the 50 MHz band. However, the actual implementation of all four IF bands had to be deferred as the initial computer system was not adequate to handle the full data load.

Although a spectral line capability was not included in the original proposal, the VLA correlator that was finally built employed a technique known as recirculation, whereby an increased number of frequency channels could be obtained at the expense of limited bandwidth.

It was made feasible by using two custom developed integrated circuits which reduced the number of multilayer circuit cards from to A particularly challenging area, the computing hardware and software, was divided into two areas. Recognizing the enormous challenge that the VLA image processing presented, NRAO investigated the feasibility of using analogue optical imaging processing. The original PDP 11s were later replaced by several more cost-effective and popular VAX machines, including one in Charlottesville, and later by Convex C1 mini-supercomputers.

Robert Bob Hjellming led the development of the asynchronous software system and Barry Clark the synchronous system, but they were supported by a growing team of programmers along with a growing software budget. In order to take advantage of the rapid growth in computing power, the initial hardware acquisition was limited to that needed to handle only the 10 antenna continuum system, with the intention of acquiring the rest of the computing hardware closer to the end of the VLA construction.

In the end, this approach gave the best computing power for the money, but severely limited the use of the partially completed VLA. This meant one could observe a hundred or more sources per day instead of the planned two to three sources, with a corresponding increase in the computing load.

Moreover, the VLA proposal assumed a relatively straightforward single data pass of gridding and Fourier transform, but the use of deconvolution techniques and self-calibration led to multiple passes and an interactive data reduction process. NRAO scientists initially assumed that due to the large number of interferometer baselines deconvolution would not be needed for VLA data.

This not only delayed the start of full VLA operations, but the extended production schedule increased the cost due to the then high level of inflation, the loss of quantity discounts for large purchases, as well as the need to maintain the administrative, scientific, and technical support structure over a longer period of time. As it developed, the extra time and increased funding turned out to be a blessing, as it allowed time for prototyping, testing, and, where necessary, design changes with a minimum of retrofitting.

However, as described below, the actual rate of inflation became much higher, which resulted in continual modifications to the construction plan and threatened the successful completion of the VLA. Coincidently, as reported in the Wall Street Journal, the Authorization and Appropriations bills reached the House floor and were each passed on the same afternoon.

With no appropriation, the authorization was meaningless. At the request of the NSF, dozens of other funding arrangements were prepared over the course of the project, with 17 alone in FY But there was still another hurdle to overcome.

The charge to SRI was to 1 determine the proposed system feasibility and ability to meet specifications in the light of existing technology, 2 confirm the cost and time schedules for the construction, development, and operation of the system, and 3 evaluate the method for managing the VLA Project proposed by AUI. SRI convened an ad hoc committee that did not include any astronomers. The committee met five times over a period of three months.

As with other radio arrays, the largest single cost item for the VLA was for the antennas. Reflecting the increasing interest in going to shorter wavelengths, the antennas were specified to have a surface accuracy of 0. The E-Systems contract also included an Antenna Assembly Building to facilitate the construction of the antennas, the installation of instrumentation, as well as ongoing antenna maintenance and repair.

Since the fabrication and erection of the antennas was planned to be stretched out over a number of years, the contract was complex, since there is no guarantee from year to year that Congress will appropriate the needed funds. During FY, E-Systems completed the engineering design, and the first two prototype antennas delivered in met all specifications. This lead to the first serious problem in the VLA construction program. Due to the oil crisis resulting from the OPEC oil embargo following the Yom Kippur War, and the abandonment by Richard Nixon of the US Gold standard and subsequent dollar devaluation, the s experienced a period of extreme inflation.

Within eight months the cost of steel doubled. It was apparent that any attempt to enforce the predetermined prices would result in bankruptcy, leaving NRAO with no path to secure the antennas. However, this meant that by spending an unplanned large fraction of the limited NSF annual funding on the antennas, the instrumentation of the antennas was delayed and the antennas were not available for commissioning or scientific observations at the planned rate.

Unloading surplus rail in Socorro. Crane is unloading Crab Orchard rail from rail cars. The truck in the background is leaving with rail for the VLA site. All of the instrumentation, the front ends, IF systems, digital delays, and the correlator, were designed by NRAO engineers, and for the most part, were fabricated in-house. Other instrumentation, including the monitor and control system, feeds, paramps, cryogenics, and the waveguide distribution system, were fabricated commercially. With a careful system of testing and noting failure rates, redesigns and retrofitting were kept to a minimum.

Not unexpectedly, in view of the problems experienced in Green Bank, the cryogenic systems proved to be the least reliable component until a new manufacturer was found. With the instrumentation of the first completed antenna, and the start of commissioning, the VLA project management, scientists and engineers moved from Charlottesville to temporary headquarters in Socorro, New Mexico, during the spring and summer of It was a one-hour bus ride, each way, from Socorro to the VLA site.

Although on most days most of the staff were not normally needed at the construction site, Lancaster adopted the practice of having everyone—management and administrative personnel, scientists, engineers, and technicians—all ride together to the site on one of two buses. This practice enabled a high level of communication among the disparate groups, which many later agreed was crucial to the successful completion of the VLA.

Throughout the eight-year construction, Heeschen continually stressed that NRAO was committed to meet the agreed budget. If some item came in at higher than the planned price, something else had to go. Numerous such adjustments were made during the process; fortunately, many of the deleted items were restored in the later years. The increase in the Consumer Price Index over the same period was more than a factor of two.

NRAO was able to keep the impact of the unprecedented high inflation modest, due in part to the procurement adjustments made to the fixed-price antenna contract, the more modest rate of inflation for electronic instrumentation, and level or even reduced prices for computing equipment. Characteristically, Congress and the NSF were nervous throughout the construction period. They were mostly concerned about how NRAO was reacting to the potential cost increases resulting from escalation, but also asked about how telescope time would be awarded, how many women were employed on the project, and interestingly, what additions to the array were foreseen for the s.

The NSF responded to the Congressional mandate by appointing a panel of representatives from industry, universities, and government agencies chaired by Cornell University Vice President Robert Matyas.

There were no astronomers on the panel, which met five times during The Steering Committee met monthly to provide continuing advice on the various aspects of the VLA construction program. It contributed significantly to setting the final parameters of the VLA as well as addressing various technical problems as they arose. The Committee also drew attention to the lack of sufficient computer power to deal with making images from VLA data.

When completed in , the VLA was not only the most powerful radio telescope in the world, it was, not surprisingly, the most complex radio telescope ever built. In recognition of its sophistication and complexity, VLA users needed extensive documentation which was initially provided by a widely used user manual known as The Green Book Hjellming The Green Book was an indispensable reference source to observing with the VLA and included detailed instructions for post-observation data calibration and imaging.

One of the advantages of array-type radio telescopes is that they are built in steps, and early observations can begin as soon as there is an interesting number of antennas. Also, being able to test many aspects of the final array after only a few antennas were completed and instrumented meant that debugging and the development of observational procedures could begin early. Even the partially completed VLA far exceeded the scientific capability of any other radio telescope, so the user community got a head start on using the VLA.

A key concept of the NRAO plan was, to the extent possible, to transfer project development personnel, especially the scientists and engineers, to operations, and so minimize turnover and exploit the expertise and experience of the development team for operations.

When ten antennas became operational in , it was becoming clear that VLA operations needed to be separated from the continuing construction activities, but during the several years of overlap, this meant that operations started more slowly than desired. Richard Dick Thompson, who had been the key systems engineer, was placed in charge of the operations phrase.

Thompson had begun his career at Jodrell Bank as part of the team that developed radio-linked long baseline interferometry in the late s Sect. Dave Heeschen had been the energetic NRAO leader for 18 years, and as the VLA approached completion he decided to step down to return to research and to be able to spend more time with his family. Roberts and Wade were longtime friends and colleagues, but they had different approaches to management.

According to Wade, who was concerned that the local staff were underpaid, as a small gesture, he and Lancaster let them use an NRAO van to travel between their home and the VLA.

When he learned of this practice, Roberts instructed them to stop. Incensed, at what he perceived as micromanagement, Wade responded by resigning as VLA Director, but he agreed to stay on until Roberts could find a replacement. However, in defiance of Charlottesville management, Wade informed one of the technicians that he was to be on hour call, so it would be necessary for him to take the van to Datil each night, and that if anyone else wanted to ride with him that would be OK.

Ekers was then a Professor at the University of Groningen in The Netherlands, where he had established himself as an expert in radio interferometry. The expectations of what people would do with the VLA increased tremendously between the time we first submitted the proposal and the time we eventually began building it. When we first designed the computer, we thought it was adequate for what we then thought the thing would do.

Heeschen resisted the temptation to ask for the additional funds that would have enabled the earlier full exploitation of the VLA, particularly for spectroscopic observations. In January , in order to keep up with the flow of data, use of the VLA was reduced to 50 percent of the available observing time, and full time observing was not restored until April Adequate computing power was arguably the single biggest constraint to the VLA scientific productivity, and throughout the early s NRAO struggled with the computing issue.

Combined with the increasing availability of powerful, yet inexpensive work stations, AIPS made it possible for the users to reduce their VLA data at their home institution, thus relieving NRAO of the need to provide a major computing center. Initially, computing resources were so limited that users were normally restricted to making images no larger than x pixels, and needed to specifically request permission if they wanted to make larger images.

Although VLA image processing was initially restricted by the limited computing power available, if NRAO had instead chosen what many argued was a more cost effective optical image processing, it would have excluded the use of CLEAN and self-calibration, which would probably have restricted the VLA imaging capability to that proposed in As mentioned, with the growing use of inexpensive powerful computers, the data processing was no longer an issue, but with time the VLA hardware became outdated.

Other components of the VLA such as the power cables and surplus railroad ties were deteriorating at an alarming rate. Since support of the Voyager encounter required a higher level of reliability than normal radio astronomy observations, NRAO convinced NASA to provide sufficient funding to also replace the backup power generators, deteriorating railway ties, and power cables supporting the inner configurations.

As discussed in Chap. While its designers were most strongly influenced by the opportunities and problems presented by extragalactic radio sources, the need for such an instrument was apparent in all areas of radio astronomy, and the VLA was in fact designed to be used for almost all kinds of radio astronomy studies. The VLA has 10 to times greater resolution and sensitivity than any other existing radio telescope, and its resolution is comparable to or greater than that obtainable at optical and other wavelengths.

Its speed, sky cover, ability to measure polarization, and ability to make high frequency, high resolution spectroscopic observations give it tremendous power and versatility for a wide variety of problems.

NRAO users were expected to do their own calibration and analysis. Student use generally required attentive support from a faculty or in some cases an NRAO staff advisor. The power and complexity of the VLA led NRAO to provide more hands-on support for users, which, in turn, began to attract a broader group of astronomers who needed radio data to enhance their research program.

To support the growing user community, and especially to train the new generation of scientists who would use the VLA, NRAO started the very successful series of synthesis imaging workshops. An unanticipated use of the VLA developed when NRAO received two separate proposals to use the VLA for sky surveys intended to detect and catalogue an unprecedented number of discrete radio sources. A competing proposal came from a group led by Robert Becker from the University of California, Davis, proposing a deeper, higher resolution survey that would reach sources as faint as 1 mJy, but only covered the limited area of the sky corresponding to the Sloan Digital Sky Survey SDSS York et al.

With the higher angular resolution, the proposed Becker survey would give more accurate source positions needed for optical identification with SDSS counterparts, as well as imaging the arcsec structure of detected radio sources.

However, unlike the NRAO survey, it would be insensitive to larger scale radio emission. The two proposed surveys were not only in competition, but each wanted thousands of hours observing time. The NRAO Director, Paul Vanden Bout, polled the user community, who were mostly supportive of the two proposals, so he appointed a small internal committee chaired by Frazer Owen to make a recommendation on choosing which proposal to approve.

But once the observing began, other users, including those who supported the idea of big projects, complained that they were taking up too much observing time. The two projects were each completed, but to minimize the impact to other observers, each was stretched out over a number of years.

Both the Condon et al. The VLA has also helped to propel radio astronomy into the popular media, appearing in several movies and numerous TV ads. The popular movie Contact brought particular attention to the VLA, although it gave a misleading impression that the VLA is used to search for signals from extraterrestrial intelligent civilizations.

Images of the VLA appear frequently in TV advertisements, although mostly for products and services unrelated to radio astronomy. The impact of the VLA was not all positive. Faced with limited operating budgets, the NSF could not support the expensive VLA operations at the same time as the many more modest university-operated facilities.

The reduction of the once vibrant university radio astronomy groups restricted the training of the next generation of technically-skilled observers, further increasing the pressure on NRAO to provide a turn-key observing opportunity at all of its facilities. The VLA is, therefore, proportionally even more influential in world radio astronomy than HST is in world optical astronomy. When built in the s, the VLA receivers, waveguide transmission, and digital correlator were all state-of-the-art.

However, the limited funding made available for VLA operations, combined with the rapid advances in technology, meant that only two decades after its dedication the VLA instrumentation was becoming woefully obsolete. Moreover, the great changes in astronomy over the last few decades of the twentieth century led to new demands for better sensitivity and image quality as well as improved spectral and angular resolution.

Karl G. Jansky Very Large Array rededication, 31 March Top: Attendees at the rededication ceremony. Credit: D. The specification of the dynamic range is a bit subjective as it depends in part on the complexity of the field being imaged. But with the improved sensitivity and larger bandwidths came the need for better interference suppression and improved dynamic range in order to reach the thermal sensitivity limits of the array in long integrations. Although data analysis, especially from the first few years of the JVLA, was rather labor intensive, the publication of a special issue of the Astrophysical Journal Letter s in Vol.

Detailed reviews of synthesis imaging in radio astronomy are given by Taylor et al. The recent implementation of adaptive optics has enabled some ground based telescopes to achieve diffraction limited imaging at near infrared wavelengths. The authors do not elaborate, but presumably they are talking about a conventional 2-element interferometer. Apparently Pawsey had been the first author on this paper, but the author list was rearranged to be alphabetical.

Swenson, G. The design and construction of the Westerbork Synthesis Radio Telescope, including the earlier considerations of the Benelux Cross, are discussed by Raimond In all radio arrays, data corresponding to interferometer spacings comparable to and smaller than the antenna diameter is missing and this results in the inability to observe structures whose angular scale is comparable with the primary beam of the individual elements. Each of the redundant spacings from different antenna pairs sampled the same Fourier component of the sky, so any differences in the measured interferometer response were due to instrumental, tropospheric, or ionospheric effects.

Trexler Naval Research Laboratory. John Bolton, representing Caltech, served as a consultant to the Panel, but returned to Australia before the work of the Panel was completed. DSH to J. Findlay, Ivan Pauliny-Toth, M. Vinokur, C. Wade, and V. Ironically, a few years later the Caltech 90 foot dishes were converted to alt-az mounts.

Morgan, and Allan Sandage. Whitford, A. During this period the Consumer Price Index increased by a factor of 2. The main contributors to the design report were L. Chow, B. Clark, D. Heeschen, D. The paint that we use contains a high concentration of titanium dioxide, which equalizes the temperature over a large area. With less difference in temperature there is less difference in expansion and contraction. An Education Officer manages tours, the Visitor Center and its Gift Shop staff, and educational programs to local schools.

Safety Officer NRAO employs a fulltime safety officer to help ensure the safety of employees, visitors, and the equipment and facilities. Employees are trained on everything from CPR to safe driving to proper lifting techniques. Each person on the antenna must attach a lock to the switch that turns on and off the drive motor circuitry, so that the antenna is disconnected from its primary source of energy.

Servo Mechanics A Servo Shop is responsible for maintaining the electronics on the pound servo motors that point the antennas. These motors generally work against each other to provide precision pointing to less than 10 arc seconds. The VLA motors have been running since the s and are pretty robust.

The VLBA antennas tend to be more sensitive to power glitches and often blow fuses. Our mechanics give the VLBA site technicians technical assistance over the telephone, if they need immediate servo help. The ACUs convert commands from the modcomps computers that control the antennas to electrical motor currents that point the antenna for the observer. They use big machines and move a lot of dirt. Railroad ties must be replaced regularly. Our crew has to lift the rails and ties, dig out the bad clay, and rebuild a more robust drainage system before re-installing the track.

Quality ballast, a heavy gravel material, is one of the most important ingredients in maintaining railroad tracks. It must be replenished, and occasionally totally replaced. Transporter Crew The transporter crew drive and maintain the two giant transporters that gently lift and haul our VLA antennas to new pads throughout the year and for maintenance.

The crew must also coordinate with the antenna mechanics, track crew, servo techs, and others any time an antenna must be moved, whether it is being moved into the barn for routine maintenance, to another location in the array, or on to the support structure to change an azimuth bearing.

The warehouse managers are responsible for keeping up with all of it: shipping and receiving, ordering, organizing, taking inventory. They can also do plasma welding and cutting, if needed. Want to know more about the work done at NRAO? Hear directly from our employees and how they got here in our Role Model Video Series.

The antennas and transporters of the Very Large Array were designed and built in the s. Its 28 meter dishes are kept in excellent working condition, and their performance has not downgraded in the decades of their use. However, modern advances in receiver and computing technology have catapulted over those years.

Scientists here felt that an overhaul of the guts of the antennas and the installation of a fiber-optically fed supercomputer would turn the VLA into a state-of-the-art instrument once again. The receivers are supercooled to keep their materials and electronics from giving off any radio signals of their own that would swamp the weak signals we receive from space.

The cryogenic pumps working constantly, thanks to electricity flowing to the antennas through their concrete pads. The Array The VLA is an interferometer array, using the combined views of its 27 antennas to mimic the view of a telescope as big across as the farthest distance between its antennas.

For the VLA, this can range from less than a mile to over 22 miles across! On a regular schedule throughout the year, the antennas are disconnected from their piers and gently lifted on the back of the antenna transporters.

Drivers carefully haul the antennas along the tracks to new piers. This changes the view of the array: the farther apart the antennas are placed from each other, the more detail they will see when their views are combined.

Receiver Electronics Combining the views of the antennas and their wide range of receiver frequencies requires a series of specialized electronics directly in the receiver rooms of each telescope.

To ensure that combined data align properly, an atomic clock signal gives the data from each receiver a highly accurate time stamp. The incoming radio waves are mixed with this timing signal and amplified, then they are digitized for their travel down the fiber optic cables into the supercomputer.

This computer was designed and built by our partners at the National Research Council in Canada. Skip to content. Basics Science People Tech Visit. Home Telescopes Very Large Array. Such an observatory could hunt for black holes, watch solar systems form, search for the chemical building blocks of life around young stars, and assist in studying gravitational wave events captured by the Laser Interferometer Gravitational-Wave Observatory LIGO.

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