Frequently Asked Questions
The next-generation VLA (ngVLA) is a future centimeter-to-millimeter wave interferometer that builds on the legacy of the JVLA, ALMA and the VLBA, as the next major facility in ground-based U.S. radio astronomy. The ngVLA is optimized for observations at wavelengths between the superb performance of ALMA at sub-mm wavelengths, and the future SKA1-MID at longer (decimetric) wavelengths.
The ngVLA opens a new window on the Universe through ultra-sensitive imaging of thermal line and continuum emission down to milliarcecond resolution, as well as unprecedented broad band high-angular-resolution continuum polarimetric imaging of non-thermal processes. The ngVLA will perform transformative science covering areas of terrestrial planet formation to the first generation of molecules in the early Universe, as detailed in the recently published ngVLA Science Book.
The ngVLA reference design consists of 244 dishes of 18 m diameter and 19 dishes of 6 m diameter. All antennas can operate as a single array, or the array can be divided into subarrays to optimize the use of observing time for specific use cases.
214 of the 18 m dishes are concentrated in the U.S. Southwest and comprise the main array which provides 10x the effective collecting area of the JVLA at 40GHz. Thirty 18 m dishes are distributed at very long baselines up to 9000 km reaching across North America, and are referred to as the Long Baseline Array or LBA.
The 18 m antenna design is an offset-Gregorian geometry, with its feed-arm low, for optimal science and operational performance. The preliminary design is presently being developed and will be prototyped in the 2022-2024 period thanks to a recent MSIP award from the National Science Foundation.
An additional 19 dishes of 6 m diameter will make up a short baseline array (SBA) and will be sensitive to a portion of the larger angular scales undetected by the main array. The SBA can be combined with four 18 m (main-array) antennas (defined above) used in total power mode to completely fill in the central hole in the (u, v)-plane left by the 6 m dishes.
The ngVLA will operate from 1.2 – 116 GHz (25 – 0.26 cm). Technical details about the ngVLA can be found on the Project Documentation page. Key performance parameters of the ngVLA are available on the Performance Estimates page.
The U.S. Low Frequency Radio Community is exploring an option for a co-located array that would use the ngVLA infrastructure to cover 20 MHz to 150 MHz. An option to add a prime focus feed to the ngVLA antennas to cover 150 MHz to 800 MHz is also possible. Funding and design for these options (e.g., ngLOBO) is outside the scope of the ngVLA project.
The resolution of an interferometer is determined by the observed wavelength and its longest baseline. The ngVLA will be designed to implement multiple subarrays, with each subarray covering a range of baselines to provide a resolution and surface brightness sensitivity appropriate for the object under study. With up to ~1000 km baselines, the ngVLA main array will achieve an angular resolution ranging between ~0.5 and 50 mas at 2.6 mm (116 GHz) and 25 cm (1.2 GHz), respectively. Using the full extent of the ngVLA in a configuration including the LBA antennas on continental scales, even higher angular resolution imaging will be possible, achieving ~60 mas and 6 mas at 2.6 mm (116 GHz) and 25cm (1.2 GHz), respectively.
Key performance parameters of the ngVLA are available on the Performance Estimates page.
The ngVLA core will be centered near the location of the VLA site on the plains of San Agustin, with additional mid-baseline stations currently spread over greater New Mexico, Arizona, Texas, and northern Mexico. The 10 long baseline array stations are currently located at five VLBA sites plus five existing radio facilities that will take advantage of present infrastructure: Washington, California, Iowa, West Virginia, New Hampshire, Puerto Rico, the U.S. Virgin Islands, and Canada. New observing sites in Hawaii are under consideration.
The VLA has been the scientific powerhouse of radio astronomy since its inception in the late 1970s, consisting of 27 movable 25 m symmetric antennas, with maximum baselines of 36.4 km. The VLA underwent a major electronics upgrade, completed in 2011, which provided continuous frequency coverage between 1 – 50 GHz. The ngVLA, by comparison, will consist of 214 dishes of 18 m diameter extending up to ~1000 km baselines and an additional 30 (18 m) antennas on scales up to 9,000 km, delivering an order of magnitude improvement in both sensitivity and angular resolution. The ngVLA dishes will not be movable, so different angular scales are achieved using subarray selection. The ngVLA will also extend the operational frequency range from 1.2 – 116 GHz (25 – 026 cm).
ALMA is a radio interferometer optimized to take advantage of the sub-mm (THz) windows that are only accessible at high, dry sites such as the Chajnantor plateau, which is at ~5000 m altitude. While ALMA operates in the 3mm band and above, the ngVLA main array (at an altitude of ~2100 m) can both access the 3mm atmospheric window and will provide a factor of ~10 times better sensitivity and baselines that are ~60x longer than ALMA.
As currently envisioned, SKA1-MID will be the premier radio interferometer at decimetric wavelengths, consisting of up to 133 x 15m (+ 64 x 13.5m MeerKAT) dishes with a maximum baseline of up to ~150 km and eventually covering a frequency range spanning 350 MHz (85 cm) to 14 GHz (2 cm). The ngVLA, on the other hand, is being optimized to cover and complement the frequency range above the highest SKA1-MID band, on continental-scale baselines, providing much higher angular resolution and sensitivity at cm wavelengths.
The scientific and technical differences between the arrays are apparent, with the ngVLA focusing on cm/mm emission, in particular thermal gas/dust emission on milliarcsecond scales and redshifted molecular line emission. SKA1 is planning to observe at meter through centimeter wavelengths, expanding on the scientific legacy of instruments like WSRT, ATCA and the VLA.
The ngVLA strongly complements SKA1 and ALMA by providing enhanced sensitivity and resolution to pursue new scientific goals and interests in the parameter space bridging those facilities.
Yes. The project office is currently in the process of exploring international and domestic (academic and industrial) partnerships. International and domestic collaborating institutions have already contributed to community studies and baseline system designs. They also currently participate in project advisory councils. If you are interested in discussing partnership options, please contact our Project Director. We anticipate a name change for the instrument once the project enters into its design and development phase, allowing our international partners to participate in this activity.
NRAO and its international partners will be building upon their ALMA experience and success in developing the ngVLA project. Many projects undergo scoping revisions before and during construction to address planning shortcomings, changes in assumptions or external conditions, new constraints, etc. ALMA was rebaselined in 2005, eventually completing the project within 0.5% of the revised budget estimate. NRAO has a long tradition of excellence in construction of radio astronomy instruments and facilities.
The U.S. government has never been asked to fund the SKA in any significant way; the SKA was unable to gather scientific community support in the Astro 2010 Decadal Survey due to uncertainties in the scientific requirements and technical definition of the project at that time. NSF’s withdrawal from supporting overall SKA development in the U.S. was a consequence of funding shortfalls in U.S. science early this decade and a recognition that the project was not broadly supported in the U.S. astronomy community. Since 2010, the scientific goals of SKA1 have narrowed, and engagement with the broader U.S. community has further declined. The fact that U.S. science funding agencies are not engaging with the SKA arises from several scientific and cultural differences.
The ngVLA concept has been developed to explore new horizons in cm radio astronomy, synergistic with other existing, under construction, or planned instruments in the U.S. in coming years, and focuses on our PI-driven science interests. Specifically, the ngVLA has been designed to make transformative advancements in each of the three key science priority areas identified by the Astro2020 Decadal Review (i.e., Pathways to Habitable Worlds; New Windows on the Dynamic Universe; and Unveiling the Drivers of Galaxy Growth) resulting in it being given a high priority to be built this decade.
The ngVLA may eventually be considered as a partner with an SKA global program, thereby engaging all parts of the U.S. Radio/Millimeter/Sub-Millimeter community in new opportunities in the 2020s. ngVLA and SKA leadership are currently discussing these possibilities.
The ngVLA is being designed as a proposal-driven instrument. The science program will be determined via a competitive peer review process similar to other large PI-driven observatories (e.g., ALMA, VLA, HST, JWST etc.), adopting best practices for minimizing selection biases. In this way the ngVLA will be a different style of instrument than other facilities on the horizon, such as LSST and SKA1, which have science programs focused on carrying out large surveys. Further details on the facility Science Operations can be found in the Operations Concept document.
Building on the current model for ALMA science operations, we anticipate ngVLA users will be delivered Science Ready Data Products (SRDPs; e.g., images and data cubes), rather than raw data, due to the sheer volume of data and computing resources that will be required to reduce data. However, raw visibilities will still be available upon request. Using ALMA and the VLA as test beds, we are building up our expertise and knowledge base of the best methods/practices/deliverables for SRDPs in preparation for the ngVLA.
The ngVLA data processing implementation will be based on the CASA package, providing continuity with JVLA and ALMA and continuing to provide a flexible data reduction package for experts in the community. As part of the construction project, CASA will evolve both in the implementation of cutting edge algorithms and the infrastructure needed for broad scale parallelization in order to support the ngVLA. We anticipate data processing and analysis features being split out into separate CASA packages, with data analysis capabilities being most commonly used by users at their home institutions.
The Science Ready Data Products (SRDPs) produced by the ngVLA will be available through the NRAO Archive interface, providing a single access point for ALMA and ngVLA data products. After the proprietary period, these SRDPs will be available to the full community, providing a rich archive of images ready for study. Capabilities for inspection and selection prior to download will assist in mitigating download times. This approach is being used successfully already for ALMA science.
As recommended by the Astro 2020 Decadal Survey, we expect to enter the NSF Major Research Equipment and Facilities Construction (MREFC) design phase in 2022 and have a final design completed by late 2025. The National Science Foundation Large Facility Office would conduct a final design review to assess the program before construction, and procurement and construction would then commence in 2026. The project anticipates a 10 year construction and commissioning effort that should be completed in 2035.
With construction commencing in 2025, we would anticipate a notional Early Science start date in 2028, with full array operations beginning in 2034. Prior to early science, the VLA will likely see a period of reduced capabilities as the ngVLA commissioning efforts ramp up. We are currently starting to develop a transition plan in consultation with the broader local and scientific community that will bridge VLA and ngVLA operations.
Current estimates for ngVLA are $2.3B (2018, risk adjusted) for construction, and an operational cost of $93M (2018) per year (i.e., <3x current VLA + VLBA operations). Of the $2.3B in construction, we anticipate the U.S. to be the majority partner (~75%), with the remaining piece covered by a combination of international and multi-agency partnerships that are actively being pursued. For context, construction costs for the ngVLA are anticipated to be comparable to those for ALMA, allowing for inflation.
The ngVLA project includes a Science Advisory Council (SAC) and Technical Advisory Council (TAC) to guide the science case and technical implementation of the array. To date, the ngVLA Science Working Groups (SWGs) have prepared over 80 science use cases that were subsequently prioritized by the SAC. These form the highest-level requirements for the system, and have significantly impacted the design concept as it has matured from 2015 through 2019. Examples of community driven changes are the inclusion of 1.2 – 10 GHz frequency coverage, a Short Baseline Array of 6m apertures plus total power antennas, and the Long Baseline Array.
Likewise, the ngVLA TAC has also influenced key design decisions, including the feed design for Band 1 and 2, the aperture size, and the selection of the optical design for the ngVLA antenna.
If you are interested in providing scientific or technological input to help guide the design of the ngVLA, please contact the respective council chairs.
The ngVLA reference design includes an assessment of the technological readiness of each major element in the system. All ngVLA systems could be built with 2019 technology. The imaging pipeline and archive will require continued advances in processing power and storage technology from 2019 through full operations in 2035 in order to achieve our current science goals within the allowable cost.
For other systems, while they can be achieved with present technology, a core goal with ngVLA development is to find solutions that allow for volume manufacturing, improved performance, increased reliability, and reduced lifecycle cost. There is ample scope for advances in technology to improve the value of the array over the course of the design.
Some enabling technologies for ngVLA are discussed on the Technology page. The technologies and approaches developed for ngVLA will have application well beyond the project, enabling many different futures.
Depending on detailed science interests, processing requirements are often set by the lowest observing frequency (i.e., fully imaging large primary beams); as our primary science missions are at higher frequencies, the processing challenges are much more tractable. We expect to benefit from additional technological development due to the later delivery of the ngVLA. Even if expected improvements fail to materialize by the beginning of operations, because we store the raw visibility data, reprocessing of data with better algorithms or with increased fidelity can be done when the computational resources become available.
The current ngVLA compute size model, based on a set of defined science use cases, is available in the Project Documentation page. The average compute capacity required, inclusive of expected parallelization inefficiencies, is on the order of 60 PFLOP/s. This is comparable to the recently constructed Frontera system at the Texas Advanced Computing Center. Note that ngVLA would not require such capacity until approaching full operations in 2035, when such systems will be more common and affordable.
The average total power load is estimated at 6.5MW for the array, central infrastructure, and off-site buildings combined. This is approximately four times the current VLA load. Significant savings are achieved in the design of the antenna electronics, correlator system, and computing cluster when compared to existing facilities. The main power source on the plains is expected to be grid power provided by the local utility company. Green power sources (photovoltaic and wind turbines) are being considered, and are increasingly attractive to reduce operating costs and environmental impact. Remote ngVLA antennas are being located in part to use local infrastructure (e.g., grid power) but may also benefit from innovations in renewable energy.
NRAO started the ngVLA project as an internally-funded R&D effort in 2015. NSF provided support of order $2M for development in 2015 through 2017. Based on clear community engagement and support in developing the key science goals, NSF reprofiled an additional $11M for 2018 and 2019 which has supported the definition of the ngVLA science case and the development of the ngVLA reference design. In-kind partner contributions of approximately $1M have also been made over the 2016-2018 period.
The NSF awarded NRAO/AUI an additional $10M for 2020-2021 design & development activities, while additionally creating a new cooperative support agreement specifically for ngVLA. Such agreements are long-term funding arrangements, put in place to support existing facilities and key initiatives. Most recently, the NSF awarded NRAO/AUI $23M from 2021-2024 via the competitive MSIP program to support the ngVLA Antenna Development, which includes the construction of a prototype.
Given the strong endorsement of the project from the Astro 2020 Decadal Survey, NRAO will be requesting a ramp up in design funding to complete the design mid-decade.
Yes! The NRAO recognizes the interests and concerns of local and regional communities and that these must be addressed in a respectful and collaborative manner. We also value the unique knowledge, experience and insights of local communities and their critical influence and role in enabling the project to realize its potential. The NRAO is currently developing an authentic and deliberate ngVLA stakeholder engagement strategy, which will open and maintain a number of channels for inclusive, in-depth local and regional engagement during all phases of the project.
Yes! The NRAO is committed to incorporating the potential broader impacts (BI) of our work for society in our planning, and has appointed a BI Lead to research, develop and manage the anticipated multi-faceted BI efforts for the ngVLA throughout the life of the project. The NRAO will invest significant funding in BI projects that promote Collaboration and Partnerships; Education and Diversity; Infrastructure; Natural and Cultural Heritage; and Technology and Commercialization. Implementation plans to use the ngVLA to drive broadening participation by under-represented minorities in STEM, as well for education and public outreach, are included in the BI strategy. Contact firstname.lastname@example.org for more information.
The technical capabilities of ngVLA made it a useful component for receiving radar signals generated at other facilities. Radar observations with ngVLA will support studies of Near-Earth Objects (NEOs) as part of planetary defense, and potentially spacecraft in low/medium/geostationary orbit. Part of the mission of the NSF is to support national defense, so this is not a conflict of interest for NSF. ngVLA participating in such efforts represents an important step forward in these scientific and surveillance activities.
Yes, we are planning to operate the ngVLA as an Open Skies observatory, as is the case for all other NRAO facilities, subject to the general principle of reciprocity outlined by the NSF/NASA-sponsored Astronomy & Astrophysics Advisory Committee. Investigators may be awarded ngVLA time based on scientific merit regardless of institutional affiliation.
While the most impressive scientific goal of the ngVLA is perhaps its flexibility to make transformative discoveries over a wide range of areas in astrophysics, one extremely compelling new piece of scientific parameter space that is opened by the ngVLA’s unique combination of frequency coverage, sensitivity, and angular resolution is its ability to detect and study Earth-like planets that are forming around nearby stars while simultaneously examining the initial conditions for life around forming planetary systems. Similarly, the ngVLA’s observational capabilities will provide completely new insight on the formation and evolution of black holes, including sources of gravitational waves, by being able to both resolve binary black hole systems and measure their proper motions.
ngVLA’s sensitivity and frequency coverage far exceeds and complements that of the currently-planned SKA-1 Mid instrument in South Africa. While the instruments overlap in science interests at lower frequencies (1-15 GHz), they are observing in different hemispheres, which provides important capabilities for the astronomy community to explore the entire sky. At its highest frequencies, ngVLA also has some overlap with the southern hemisphere ALMA telescope. These overlaps, and the all-sky coverage, provide the scientific community with enhanced capabilities to pursue astronomical research, and ngVLA’s role bridging SKA and ALMA as the preeminent centimeter-wavelength radio telescope is critical.
NRAO has worked closely with the broad community to develop ngVLA (and in fact, all projects and initiatives we carry out on our telescopes). We have also supported many smaller non-NRAO projects in the community with resources and expertise. Our mission is to provide facilities beyond the scale possible by university consortia; that said, we have many advisory and oversight committees from which we receive feedback on our strategic direction. The Decadal Survey represents a consensus view of the community’s interest, and NRAO’s goal is to serve those.
NRAO operates in many locations around the U.S. and around the world, and we are increasingly aware of this issue for our facilities. Beyond our own efforts to engage with and support our local indigenous communities, we are currently engaged in a process with NSF to explore this issue for all of our sites. NSF seeks to understand its relationships and responsibilities to the indigenous cultures connected to the many locations it supports in the interest of national scientific research and defense, and we will both follow their lead and go further to address these concerns when opportunities arise.
Pure and applied scientific research is one way in which society can transform itself, both in terms of the technologies and STEM-focused human capital (people) generated by the effort, but also the promotion of scientific literacy in society. These research benefits create new focus and solutions for important problems in society. The average American invests about 1.5 cents per year in astronomy research, and receives images of black holes in the centers of nearby galaxies, technologies that can be found in your cellphones, and a workforce excited by, and trained in, STEM topics. It is important to address and balance all of the efforts needed to solve humanity's issues, including pure research with technological and STEM benefits.
During the development of ngVLA’s antenna locations, we will work with local stakeholders and tribal authorities to seek out areas that are compatible with cultural concerns.
Yes! Over the next few years (Design & Development) we will be growing our Observatory staff in essentially all areas of endeavor (science, engineering, computing, public outreach, administration, etc.), so we encourage people to keep an eye on our Careers webpage.
The Decadal Survey Committee has outlined an exciting scientific program for this decade, including a handful of major instruments requiring significant investment. Over the past few years, several scientific communities (astronomy, geophysics, Polar programs) have been working with the NSF and Congress to increase Major Research Equipment and Facilities Construction (MREFC) funding to support upgrades and new scientific facilities to create or retain U.S. leadership in key sciences. NSF's AST has presented projections of MREFC growth at AAS and AAAC meetings over the past few years that would enable the instruments identified as priorities for this decade (like ngVLA) to be funded. Congress responds to scientific needs and excitement, and the Decadal Survey report has pointed the way forward. ngVLA can be afforded in many scenarios under consideration.
The ranking received from the Decadal Survey by ngVLA indicates the research community is highly interested in the scientific and technical promise of the instrument. The next step for the project is completing the design and development phase for the telescope (anticipated to take four years). During that time, NRAO and the community will work with the National Science Foundation and other potential domestic and international partners to allow construction to begin mid-decade. The community is strongly in support of ngVLA. Now we need to acquire the resources for a construction start.
This Decadal Survey result is an expression of science interests in the future – there is a long way to go with both design/development activities and working with NSF and Congress to identify construction funds for ngVLA. The VLA remains the most powerful and flexible radio telescope on Earth, and will continue its science mission for many years to come in all scenarios. Similarly, the VLBA provides essential observing capabilities necessary for a range or astrophysical and geodetic areas of research. NRAO hopes that late in this decade, ngVLA’s new scientific capabilities eventually will surpass the VLA and VLBA’s current scientific specifications, and they both can be retired.
The current layout of antennas (the Configuration) has been created to explore the real-world implementation challenges to be faced when building the instrument needed to address the science goals. The current configuration meets the scientific and implementation requirements, but can be expected to evolve as discussions about land acquisition, including interactions with local stakeholders and (potentially) indigenous groups, and assessment of the availability of utilities (power, communications) take place. Antennas near the center of the array (e.g. the Plains of San Agustin) cannot be moved far; antennas throughout the desert Southwest, and supporting long baseline sites, can be moved substantially (10s-100s of km).
ngVLA is being developed by NRAO and partners, with centers of interest situated around the globe. The Project Office is based in Albuquerque, NM, with significant engineering work occurring in Socorro and Charlottesville. Over the past two years, NRAO has begun a major teleworking initiative, and building on our ALMA experience in the 2000s, we expect people working on ngVLA to be distributed throughout the U.S.
Yes, operational costs are a driving design constraint and the prototype antenna testing will help bound the array-level estimates for system availability and reliability.
The ngVLA is aiming for approximately a 3x-6x improvement in the mean time between maintenance of an ngVLA antenna compared to the existing VLA antennas. Our operational cost estimates assume the lower end of this range, while the design requirements are based on the more ambitious upper end of the range.
The VLA antennas are approximately 40 years old, so significant improvements are achievable purely based on component age and improvements in component manufacturing techniques. Another significant source of gains is architectural - the ngVLA antenna architecture aims to reduce parts count, which also inherently raises reliability. For example, a VLA antenna has a total of eight cryogenic refrigerators and three cryogenic compressors, while the ngVLA design has two refrigerators and one compressor. Even assuming comparable component-level reliability, the reduced parts count increases the cryogenic sub-system reliability.
As part of prototype testing the antenna will be exercised continuously to determine any components prone to failure and to bound the predicted MTBF of the antenna and antenna electronics with empirical evidence. These improved and substantiated MTBF estimates will allow us to refine our operational maintenance and staffing models, and the resulting operations cost estimate.