NRAO and GBO Users' Policy

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1. Introduction

1.1. Purpose and Scope

Associated Universities, Inc. (AUI) conducts its management and operations of its corporate functions and Research Centers, including the National Radio Astronomy Observatory (NRAO) and the Green Bank Observatory (GBO), collectively referred to as “the Observatory.” This document defines the core policies for use of the AUI’s operational research facilities of the Karl G. Jansky Very Large Array (VLA), the Very Long Baseline Array (VLBA), and the Robert C. Byrd Green Bank Telescope (GBT). The policies concerning the Atacama Large Millimeter/submillimeter Array (ALMA) are maintained independently. Users of ALMA should refer to the documents available online at

The long-term policies set forth in this document supersede other documents in circulation. The Call for Proposals contains the implementation parameters and procedures for the call; however, when in conflict with the policies defined in this document, the NRAO Users’ Policies takes precedence unless explicitly stated.

2. Observatory Users

2.1. Registering with the Observatory

Unauthenticated users (unregistered users, or users who are registered but have not logged in) have access to non-proprietary data from Observatory facilities, documentation, tools (e.g., sensitivity calculator, Archive Access Tool), and the NRAO Science Helpdesk Knowledgebase articles describing solutions to common questions and problems.

Authenticated users, i.e., those who register for a NRAO account and are logged in, may participate in Observatory proposals, access their proprietary data through the Archive Access Tool, track the progress of their projects, and submit tickets to the NRAO Science Helpdesk.

Anyone can register for a NRAO account through the online portal. A user may have one (1) NRAO account, which is identified by a unique, user-selected username. Users are required to provide their first and last names, their affiliation, a street address, an email address, and a phone number. The fields requesting demographic information, such as career stage, gender, and graduation year, are voluntary. User information follows the Observatory’s Confidentiality of Information Policy in Section 2.2. If a duplicate user profile exists or is mistakenly created, please contact the NRAO Science Helpdesk for assistance.

Users are responsible for ensuring that their profile information is correct and up-to-date. The Observatory strongly encourages users to check the spam folder of their email in case official communication is mistakenly directed there.

2.2. Confidentiality of User Profile Information

With the Proposal Submission Tool, any authenticated NRAO user has access to the following information: title, first and last name, preferred name, email address, phone number, affiliation, student status, and username of registered users. All other user information is available only to the user themselves and Observatory staff. With regard to the demographic information requested in the user profile, this information is collected to allow the Observatory to analyze systematics in the proposal review process, which include but are not limited to gender bias and prestige bias. No personal, identifying information will be disclosed as a result of this analysis. The Science Helpdesk Knowledgebase articles will not contain any information which would identify users or reveal confidential proposal information. The full Information Privacy Policy is available online at

2.3. User Support

For all questions related to proposing, observing, data reduction, etc. with Observatory facilities, users are required to use the NRAO Science Helpdesk. During the ticket submission process, please select the appropriate department related to the query. If users have specific questions about observing with the GBT, please email .

3. Proposals: Call, Preparation, and Submission

3.1. Eligibility and Responsibility

All registered users agree to act according to Observatory policies and procedures, as defined in this document and in the Call for Proposals documentation. In particular, all users accept the limitations of the observing capabilities and operational restrictions applicable for the call for which they submit a proposal. Any registered user may submit a proposal for the supported facilities.

Each proposal must identify an individual who will serve as Principal Investigator (PI). Proposals submitted by a consortium are not valid. Instead, a person within the consortium should submit the proposal and act as PI and any other consortium members are co-Investigators (co-Is). The PI or a co-I is required to be specified as the official contact between the Observatory and the proposing team for all proposal correspondence. By default, the PI is the official contact. The PI and all co-Is are responsible for ensuring that their respective profiles registered for the NRAO user account are correct (e.g., email address, affiliation). Proposals may include any number of co-Is.

By submitting a proposal, the PI takes full responsibility of its contents. The PI is responsible to ensure that all co-Is have agreed to be included on a proposal. Including a user as co-I in a proposal without their consent may lead to the proposal being canceled. Co-I names cannot be added to or be withdrawn from the proposal after the proposal deadline.

PIs and co-Is may all view, edit and submit proposals in the PST. Additionally, they all may create, modify, and submit Scheduling Blocks in the relevant workflow (e.g., Observation Preparation Tool; OPT). They are all entitled to receive help from, or discuss project details with, Observatory staff and receive the outcome of the review process.

3.2. Proposing Opportunities

There are two types of calls for proposals at the Observatory: semester and Director’s Discretionary Time (DDT).

3.2.1. Semester Observing Opportunities

Semester proposing opportunities are announced through a Call for Proposals. The observing proposal submission deadlines for Observatory facilities are the closest date to 01 February and 01 August that fall on a Wednesday1 each year. The February deadline applies to requests for observing time from 1 August–31 January; the August deadline applies to requests for time from 1 February–31 July. The Call for Proposals contains the implementation parameters and procedures and is available online at

In response to a semester Call for Proposals, three proposal types can be submitted for the standard semester deadlines each year:

  • Regular proposals are for modest total time requests on Observatory facilities. The Call for Proposals specifies the maximum number of hours a Regular proposal is allowed, which may depend on the capabilities of a facility.
  • Triggered proposals are for pre-planned observations of transients whose event times are unknown a priori.
  • Large proposals are for large total time requests on Observatory facilities. The Call for Proposals specifies the maximum number of hours a Large proposal is allowed, which may depend on the capabilities of a facility.

Joint proposals with non-AUI facilities and commensal observing are proposed for within the scope of these proposal types, see Section 3.2.3 and Section 7.4, respectively. Note, Large proposals can have triggering criteria; users should specify the proposal type as “Large” in the PST.

When determining whether a joint proposal qualifies for as a Large Proposal, the total time requests are evaluated per facility and not as an aggregate sum. When a facility, such as the VLA or GBT, is requested as part of the VLBI/HSA or GMVA, its time is categorized under the VLBI/HSA or GMVA facility for the purpose of meeting the criteria of a Large Proposal. However, if the same facility (like VLA or GBT) is simultaneously requested as a joint resource apart from being an element of the aforementioned facilities, their respective time requests remain distinct and are not compounded when assessing against the Large Proposal threshold.

1 The exact call period will be announced in the Call for Proposal.

3.2.2. Director’s Discretionary Time

DDT may be requested at any time and is appropriate for the following cases:

  • Target of Opportunity (ToO) proposals are for unexpected or unpredicted phenomena such as, but not limited to, extreme X-ray or radio flares. ToO proposals are evaluated rapidly, with scheduling done as quickly as possible and as warranted by the nature of the transient phenomenon.
  • Exploratory Time proposals are normally for requests of small amounts of time, typically a few hours or less, in response to a recent discovery, possibly to facilitate a future submission of a larger proposal. In general, there will not be a need for immediate scheduling with these proposals but, for example, they may need to be observed in the current VLA configuration rather than waiting 16 months.
  • Proposals may be submitted for the purpose of education and public outreach - for example, to image an iconic source or to support a educational opportunity for students. These proposals must involve the Observatory’s Education and Public Outreach program.
  • Proposals for other science opportunities deemed sufficiently urgent to justify prompt action.
  • Proposals may be submitted in response to a Special Call announced by the Observatory. The announcement for the Special Call is available online at

While there is not an a priori limit to time that can be requested via DDT, it is expected that no more than 5% of the Open Skies time on each facility will be allocated for this purpose. DDT proposals cannot be joint proposals that request external telescope time; however, joint proposals between the Observatory’s facilities are allowed. For example, a DDT proposal cannot request HST orbits, but a DDT proposal can request joint observations with the VLA and VLBA.

3.2.3. Joint Proposing Opportunities

There are a number of opportunities for joint proposals with external (non-Observatory) facilities and between the Observatory’s facilities. The time will be awarded only for proposals that require use of both observatories and shall not apply to usage of archival data. The observations are not required to be coordinated or simultaneous, and the programs may be subject to basic feasibility reviews. All joint proposals submitted through the PST must indicate the joint facility, specify the requested time for the joint facilities, and additional details. The Call for Proposals contains the most up-to-date opportunities and requirements for joint proposals.

Joint proposals between the Observatory’s facilities consist of observing programs that require combinations of the GBT, VLBA, and/or the VLA. For such requests, proposers should submit a proposal for each of the requested telescopes. The same Scientific Justification should be submitted with each proposal, and it should contain a clear justification for each telescope requested. VLBI proposals which request the GBT or VLA (or any other HSA telescope) as elements of the VLBI array do not need separate proposals as those telescopes can be selected as separate VLBI stations from a VLBA/HSA proposal. When determining whether a joint proposal qualifies for as a Large Proposal, the total time requests are evaluated per facility and not as an aggregate sum. For example when a facility is requested as an element of the VLBI array, its time is categorized under the VLBI facility for the purpose of meeting the criteria of a Large Proposal. However, if the same facility is simultaneously requested as a joint resource apart from being an element of the aforementioned facilities, their respective time requests remain distinct and are not compounded when assessing against the Large Proposal threshold.

For joint proposing opportunities with external facilities, one proposal should be submitted to the facility where more observing time is being requested; authors should not duplicate their request across the observatories in this case. Authors may re-submit the proposal if their previous submission was rejected (partially or fully), or if the outcome of the previous submission is unknown.

If the latter and a positive disposition is eventually received, it is expected that the duplicate proposal be withdrawn promptly. Proposing teams that are awarded time through an external Telescope Time Allocation Committee (TAC) must adhere to the policies of this document when applicable. If the policies of this document conflict with that of another facility, the Observatory will work with the proposing team and external facility to reach a suitable resolution.

Detailed information about the external joint proposing opportunities can be found within their corresponding Memorandum of Understanding. These documents are accessible online at Note, the agreements for Joint Observations with external facilities were made at different times across the boundaries when the Observatory was split into multiple observatories (NRAO, GBO, and LBO) in 2017, and when the Long Baseline Observatory (LBO) was reintegrated back into the NRAO in 2019. Therefore, the Memorandum of Understandings will sometimes mention various combinations of the NRAO, GBO, and LBO.

Table 2.1 summarizes the amount of time that may be awarded from either the Observatory TAC or the External TAC to an external joint proposal. Column 2 gives the amount of time an External TAC may award on an Observatory facility, and column 3 gives the amount of time the Observatory TAC may award on the external facility. Proposing teams should consult the Call for Proposals for the specific guidelines when preparing a joint proposal.

Table 2.1: Summary of Joint Proposing Opportunities
External Facility External TAC (Observatory Time)a Observatory TAC (External Time)
ALMA 5% 50 hrs per cycleb
Chandrac 3% 120 ks per year
Fermi 5%d 300 ks per year
HSTe 3% 30 orbits per year
JWST 5% 50 hrs per year
NICER 5%f 250 ks per year
Swift 5%f 300 ks per year
XMM-Newton 3%

150 ks per year

a Percentage of observing time that is considered Open Skies.
b The Observatory can award up to 50 hours on the ALMA 12-m array, 50 hours on the 7-m array, and 50 hours on the Total Power array per cycle.
c Chandra ToO proposals are not supported under the Chandra-NRAO joint program.
d A maximum of 5% or up to 200-325 hours of Open Skies observing time per year is available on each telescope.
e HST Snapshots observations are not supported under the HST-NRAO Joint program.
f A maximum of 5% or up to 200-300 hours of Open Skies observing time per year is available on each telescope.

3.3. Proposal Preparation

3.3.1. Proposal Requirements

Proposals for observing time at any of the Observatory’s facilities must be submitted through the PST. In addition to the VLA, VLBA, and GBT facilities, observing proposals for the following non-AUI telescopes are required to utilize the PST: the VLBI-High Sensitivity Array (HSA) and the Global 3mm proposals (GMVA). A detailed guide for the PST is available online at

Proposal preparation in the PST consists of a number of components that must be specified by the user and in compliance with following requirements.

General Information

  • The General Information of a proposal includes the title, abstract, author list, proposal type (DDT, Regular, Large, etc), proposal sponsor, scientific category, declaration of a joint proposal, observing type, and related proposals.
  • A single science category is required per proposal. Proposals that span multiple categories should be split into multiple proposals.


  • All authors should be listed on the proposal at the time of submission, as it is not possible modify a proposal after submission. As stated Section 3.1, including a user as co-I in a proposal without their consent may lead to the proposal being canceled.
  • If the proposed observations are part of a PhD dissertation, a “Plan of Dissertation Research” is required to be submitted with the proposal. If the observing semester occurs after the student intends to graduate, then it is not appropriate to indicate that the proposal is for a dissertation. See Section 7.2 for more details.

Scientific Justification

  • The Scientific Justification is required to be a Portable Document Format (pdf).
  • There should be a minimum of one inch margins on all sides and pages are US letter sized.
  • The minimum font size is 11 point, which includes the font in figure captions, table captions, table headers, content, and references. Fonts in rescaled figures should be legible.
  • The maximum number of pages includes figure captions, table captions, table headers and content, and references:
    • Regular proposals are allowed a maximum of four (4) one-sided pages.
    • Triggered proposals are allowed a maximum of four (4) one-sided pages.
    • Large proposals are allowed a maximum of six (6) one-sided pages.
    • DDT proposals are allowed a maximum of two (2) one-sided pages.
  • For a Large proposal, a plan for data management and data release is a mandatory part of the Scientific Justification.
  • For a DDT proposal requesting Exploratory Time, proposals must include a clear description of why the proposal could not have been submitted for normal review at a previous semester proposal deadline, and why it should not wait for the next proposal deadline. The possibility that a proposer forgets about or misses a proposal deadline, or just discovered that they were granted time for a particular source on some other telescope, will not constitute sufficient justification for granting observing time by this process.
  • For a DDT proposal requesting time for educational purposes should clearly justify the requirements for the requested time allocation and observing mode on any given instrument and should describe the anticipated impact of the observation.
  • For joint proposals, the Scientific Justification must clearly justify the need for each requested facility.
  • For joint proposals between the Observatory’s facilities, the same Scientific Justification must be submitted with each of the joint proposals.

Technical Justification

  • The PST provides prompts for the author to enter their technical justification. The relevant prompts are required to be fully specified and are required to include any additional requested materials, such as the output from a sensitivity calculator and/or a mapping calculator.


  • The Observatory requires proposers to specify their source lists in full. It may be the case that the final source list has not been selected at the time a proposal is submitted. In such cases, all potential sources should be listed. The only exceptions to this requirement are for Triggered proposals to observe sources that are unknown a priori. Note, calibrators should not be specified in the source list.


  • In the PST, proposers are required to specify their requested resources. Depending on the resources requested, additional materials may be required (e.g., spectral line resources), which will be noted in the interface of the PST.


  • Proposers are required to specify the Local Sidereal Time (LST) range, which should take into account constraints from calibrators and in addition to sources.

Proposers should also consult the online documentation for guidance and more information about preparing their proposals:


3.3.2. Compliance in Proposal Preparation

Proposals that are not in compliance with Observatory policies may be rejected or be reduced in scheduling priority. The following is a non-exhaustive review of common cases of non-compliance.

  • A Regular proposal that is determined to be incorrectly submitted as a Triggered proposal.

  • A Scientific Justification that is not compliant with the formatting requirements described above.

  • Relevant information is missing from the Technical Justification. This includes the additional materials such as the output of the sensitivity calculator or mapping calculator.

  • The information in the output of the sensitivity calculator, mapping calculator, spectral line configuration, etc. is incomplete or incorrect.

  • Proposals that intentionally propose for inaccurate source coordinates with the purpose of obscuring the true positions of the sources.

  • A Large proposal that fails to provide a data management and data release plan.

3.3.3. Filler Programs

There are opportunities for so-called “filler” programs on all telescopes. Observing programs that exploit frequencies below 10 GHz, do not have scheduling constraints, and could benefit from short scheduling blocks are eligible to be considered for “filler” time. The proposal should make clear in the abstract and in the science justification that “filler” time is being requested. If “filler” time is requested, the proposal will be ineligible for scheduling priority A or B. A proposal requesting filler time should not require fixed time or guaranteed monitoring periods.

3.3.4. Proposal Science Categories

Proposal science categories are defined to group proposals with similar science intents for consideration by reviewers who are familiar and/or experts in the field. The categories can change, though generally, the science categories do not fluctuate frequently. Currently, proposals for the use of Observatory facilities are organized according to one of the following scientific categories:

SSP Solar system, stars, planetary systems: Sun, planets, comets, IPM; exoplanets; main sequence stars; active stars; stellar winds; AGB and post-AGB stars; PNe; novae
GWT Gravitational waves and energetic transients: supernovae, gravitational wave sources, gamma-ray bursts, tidal disruption events, fast radio bursts, exotic/unknown transients
PCO Pulsars and compact objects: millisecond pulsars, cataclysmic variables, black hole and/or neutron star x-ran binaries, pulsar timing, pulsar proper motion
SFM Star formation: young stellar objects; protostars; jets, outflows; T Tauri stars, circumstellar disks; protoplanetary systems; astrochemistry
ISM Interstellar medium: galactic HI and OH; ISM magnetic field, SNRs; HII regions; astrochemistry
NGA Normal galaxies, clusters, and groups: Galaxies (continuum), including galaxies in groups and clusters: disk emission; star formation; magnetic fields; galactic winds; starbursts; intracluster emission and ICM astrophysics
EGS Extragalactic structure: Galaxies (lines): galaxy structure; galaxy kinematics and dynamics; galaxy chemistry; gas in galaxies
HLA High-Luminosity AGN: AGN, high-luminosity: FR II radio galaxies, quasars, QSOs, blazars, BL Lacs
LLA Low-Luminosity AGN: AGN, low-luminosity: FR I radio galaxies, FR 0 radio galaxies, Seyfert galaxies, quiescent SMBG, Sgr A
HIZ High redshift and source surveys: High-z objects; extragalactic source surveys; galaxy formation; gravitational lenses; large-scale structure and clusters (as cosmological probes); CMB; early universe

Observatory staff reserve the right to change the user selected science category of a proposal to a more appropriate one if warranted without consulting with or notice to the PI.

3.4. Proposal Submission and the Close of the Call for Proposals

3.4.1. Compliance in Proposal Submission

Only proposals that are submitted via the online PST, that comply with the technical constraints and restrictions described in the Call for Proposals, that conform to the policies stated in this document, and that are received before the submission deadline will be considered. The Observatory reserves the right to reject proposals that do not adhere to the policies in this document.

For semester proposals, the proposal deadline is strictly enforced: no modifications to the proposal can be made by the author after the close of the call. If before the proposal deadline, it is possible to withdrawal a proposal and submit a new version (see Section 3.4.3). Requests to the Helpdesk for modifications to the proposal after the deadline will not be considered. Such requests include, but are not limited to, modifying the author list, the contents of the proposal, and modifying the requested items, such as source coordinates, requested time, or facility resources. Users should not submit duplicate proposals during a single Call for Proposals with the intention of acquiring a more favorable review.

3.4.2. Extension of the Close of Call for Proposals

The Observatory encourages users to leverage the NRAO Science Helpdesk and Knowledgebase in preparing their proposals. The Helpdesk is actively monitored to provide timely responses to inquiries, particularly near the close of the Call for Proposals. If an inquiry to the NRAO Science Helpdesk is made sufficiently ahead of the deadline but the issue is not resolved by the deadline, the Observatory will work with the proposers to reach a reasonable solution. The Observatory is not ultimately responsible, however, for late proposal submissions that are a result of inquiries with the Helpdesk - particularly last minute requests. The Observatory encourages users to consult Helpdesk resources far ahead of the deadline and to submit their finished proposals well in advance of the deadline.

There are many third party applications and services (e.g., Overleaf, Google Suite) that may aid a proposer in preparing their proposal. In the event that such a third party application experiences an outage or is otherwise unavailable, the Observatory is not responsible for the impact on a user’s ability to submit a timely proposal.

It is not the policy of the Observatory to extend the deadline for the Call of Proposals without sufficient cause. It is at the discretion of the Assistant Director for Science Support and Research if such an extension is warranted. If an extension is deemed necessary, a banner message will appear on the PST portal to indicate the new deadline.

3.4.3. Changes to Submitted Observatory Proposals

For semester proposals, proposers have the ability to withdraw their proposal directly through the PST without needing to contact the NRAO Science Helpdesk. If this action is taken prior to the proposal deadline, a new proposal can be submitted. Note that the PST currently permits proposal withdrawal only if it’s initiated a minimum of fifteen (15) minutes before the deadline. Beyond this time frame, proposers will need to contact the NRAO Science Helpdesk to withdrawal a proposal. After the proposal deadline, a submitted proposal may be withdrawn but no longer modified. Requests for withdrawal should be made via the NRAO Science Helpdesk. It is at the discretion of the Observatory to permit withdrawal however; if the review process has begun, the proposal will not be withdrawn.

4. Proposal Review Process

4.1. Overview

Proposals are evaluated on the basis of scientific merit. Proposals may also be reviewed for their feasibility by Observatory staff. A feasibility review may include a technical review, a data management review, or both. Unless otherwise noted in the Call for Proposals, semester proposals utilize the Panel Proposal Review process and DDT proposals utilize the Observatory Site Review process. The review process for special calls will be provided in the notice for the special call. Details about the Panel Proposal Review process are available online at The Observatory Site Review process is a less formal review process whereby primarily Observatory staff will provide information for the scientific, technical, and/or data management components of the proposal review.

For the Panel Proposal Review Process, the Observatory is responsible for recruiting reviewers for the Science Review Panels (SRPs) and TAC. The Observatory is committed to the principles of equity and inclusion in the peer review process. As such, it is a goal of recruiting that the demographics of the review panels and TAC reflect the gender demographics of the astronomical community4.

The Observatory welcomes volunteers to be a science reviewer for the Panel Proposal Review process. To apply to volunteer, please submit the online form at For more information about the volunteering and the review process, see online at

Membership of the SRPs is kept confidential by the Observatory, but SRP members are welcome to note their participation (in their curriculum vitae, for example). Membership of the TAC is made public by the Observatory. For the most current semester, the TAC membership is available online

4 The specific recruitment goals are determined by the demographics of the Observatory’s user base, which relies on users to provide their information. Gender-related reports are available at

4.2. Proposal Assessment

The purpose of the proposal-selection process for Observatory telescopes is to select the proposals that potentially are most valuable for the advancement of scientific knowledge. This does not necessarily mean giving high marks to those proposals that will provide sure results; it also includes a careful consideration of well-reasoned proposals that may be unconventional, but provide opportunities for new discoveries. In the evaluation of proposals, reviewers consider how best to exploit the full capability of the unique scientific instruments that the Observatory operates for the community. Reviewers may also consider other factors such as

Publication record

Due recognition should be given to teams who have an established publication record for past related proposals. In contrast, some observers may have considerable data that clearly has not been analyzed and published yet.

Possibility of acquiring more appropriate data

Reviewers may also wish to consider the possibility that other data may be more appropriate for reaching the scientific goals of the proposal. For instance, the relevant data might already exist in the Archive (available through the Archive Access Tool).

Selection of resources

Reviewers may judge whether the requested observations are an appropriate approach to meeting the stated science objectives.

Resource requirements

Reviewers may take into account the amount of resources requested. For example, a particular proposal or scientific goal may be viewed as a valuable use of 4 hours of telescope time, but may not be as valuable if it requires 80 hours of time.

Student status

The Observatory encourages the use of its facilities for student research, particularly for PhD dissertations. In this case, it is most helpful if the proposal will say in some manner how the proposed observations will be used in the dissertation, and whether they are a sidelight or a main focus of the thesis. Reviewers are encouraged to comment on this topic and may choose to support proposals more strongly if there appears to be a well-thought-out program of student research.

4.3. Outcomes and Disposition Letters

A Disposition Letter is sent to the PI and co-Is for semester and DDT proposals. Disposition Letters are also available in the PST for proposers to review. For the semester proposals, this letter contains comments from the cognizant SRP, a linear-rank score from the SRP, comments from the feasibility review (if available), comments from the TAC (if available), and the scheduling priorities. For DDT proposals, this letter contains a brief notice of approval or justification if declined.

A scheduling priority is assigned to each session of a proposal, which is guided by the outcome of the SRPs (e.g., linear-rank score) or the Observatory Site Review, and takes into account the time available on a facility. It is the policy of the Observatory to not allocate all of the available observing time in any LST/GST range during any semester to a single proposal; this includes Joint Proposals. There are five different scheduling priorities:

Priority A This is the highest scheduling priority; the observations will almost certainly be scheduled. For the GBT and the VLBA, the observations will be considered for scheduling for up to two semesters. For the VLA, the observations will be considered for scheduling for two VLA configuration cycles5.
Priority B This is the next highest scheduling priority; the observations will be scheduled on a best effort basis. For the GBT and VLBA, the observations will only be considered for scheduling for one semester. For the VLA, the observations becomes ineligible when the associated configuration ends.
Priority C A lower scheduling priority; the observations are not guaranteed to be scheduled and are used to supplement gaps (e.g., filler time) in LST/GST ranges not filled by higher priority proposals. For the GBT and VLBA, the observations will only be considered for scheduling for one semester. For the VLA, the observations becomes ineligible when the associated configuration ends.
Priority D The lowest scheduling priority; the observations have a low probability of being scheduled and are used as secondary filler when higher scheduler priorities cannot be scheduled. For the GBT and VLBA, the observations will only be considered for scheduling for one semester. For the VLA, the observations becomes ineligible when the associated configuration ends.
Priority N The observations will not be scheduled.

The scheduling terms described above apply unless explicitly stated otherwise in a Disposition Letter. Disposition Letters may include a Scheduling Priority marked with an asterisks (; e.g., N); this is used to indicate that there are specific comments from the SRP, TAC, or Observatory Staff to the proposing team regarding the requested resources. Proposers should review the comments that are returned in the Disposition Letter before proceeding to observation preparation (Section 5.1). In the event that clarification is needed about technical comments, please submit a ticket to the NRAO Science Helpdesk and select the “VLA/GBT/VLBA Proposal Review” topic.

The outcome of the proposal review process is final. If an unfavorable disposition is received, the Observatory strongly encourages authors to prepare a new proposal for a future semester that addresses the returned comments. It is the policy of the Observatory to not allow communication between science reviewers and authors, even mediated through a third party such as the Observatory staff.

In case of questions about details in the Disposition Letter, please submit a ticket to request clarification through the NRAO Science Helpdesk and select the “VLA/GBT/VLBA Proposal Review” topic. However, in no case will such a request lead to a revision of the linear-rank or scheduling priority assigned to the proposal as a result of the review process.

 5 See the definition of a VLA configuration cycle in Section 7.1

4.4. Conflicts and Confidentiality in the Review Process

The review process relies on the scientific community to evaluate proposals based on their scientific merit and to make recommendations regarding time allocation. The process must be robust and free of real or perceived conflicts of interest and must maintain confidentiality. This section details conflicts of interest and confidentiality policies associated with the proposal evaluation and time allocation process.

For the purposes of the Observatory proposal evaluation and time allocation process, an individual is considered to have a potential conflict of interest if one or more of the following is true:

  1. They are a PI or a co-I on a proposal under consideration.

  2. They are affiliated with the same department as the PI or a co-I on a proposal under consideration. This may be relaxed depending on the nature of the relationship between the reviewer and PI/co-I (e.g., a large department with little interaction).

  3. They are a spouse, partner or other family member of a proposal author.

  4. They are a current or recent collaborator of a proposal author (within the last five years).

  5. They are a former student or advisor of a proposal author (within the last five years).

  6. They have any other reason to believe they cannot render a fair and impartial judgment on the scientific merit of the proposal.

In order to ensure that all proposals are treated fairly and without bias, such potential conflicts must be identified and declared. The response to a conflict depends on the role of the participant. The details are available online at

4.5. Proposal Conflicts Policy

With the increasingly flexible capabilities being offered on Observatory facilities, there may more frequently be partial conflicts between proposals in terms of source(s), spectral line(s), array configuration (VLA), observing band, correlator/spectrometer set-up, and science goals. For proposals submitted on the semester submission deadlines, proposal conflicts are handled by the normal proposal evaluation and time allocation process. Proposals for DDT, however, may be submitted at any time and may conflict with a proposal that has already been approved through the standard time allocation process, or has previously been observed with the data still proprietary. Under these circumstances, for the overlapping science goals,

  • Any proposal that has been previously approved through the normal time allocation process with priority A or B, but has not yet been observed, will take precedence over the DDT proposal.

  • Proprietary data that have already been observed, including that for priority C and D projects, at the time of the DDT proposal submission will also take precedence over the DDT proposal.

The DDT proposal will be evaluated only on the part of its science goals that cannot be derived from the observations associated with the previously-approved proposal or previously observed proprietary data conflicted with the DDT proposal. If a DDT proposal is approved on these grounds, the DDT team may be given the option of either:

  • employing an observing set-up that does not conflict with the previously-approved or previously-observed proposals, or

  • to use the previously-approved proposal’s proposed set-up; in this case the conflicting/overlapping data will be made immediately available to the proposers of the previously-approved proposal.

The definition of the conflicting/overlapping data is defined in Appendix A.3, and the Observatory utilizes the source list and resources provided in the proposal to determine potential conflicts.

There may be cases where more than one DDT or ToO programs are triggered on the same object nearly simultaneously. Should such a situation arise, the NRAO Director or designee will take the final decision on which program will be observed. Typically, it will be based on the order of proposal submission, with priority given to the first received proposal. Other factors may be considered, including the requested observing frequency and the prevalent weather conditions.

5. Preparation and Execution of Observations

5.1. Observation Preparation

If a proposal’s Disposition Letter indicates that time is allocated at a scheduling priority of A, B, C, or D then Observatory staff will convert the proposal to a project which is eligible to compete for time in the dynamic queue. All observations on Observatory facilities are executed using the concept of Scheduling Blocks (SBs), although the blocks may not be specifically called Scheduling Blocks. An accepted proposal might require tens or hundreds of Scheduling Blocks to gather the data necessary for exploring that project’s objectives.

It is the responsibility of the proposing team to prepare for observations. Proposers should review the technical and science comments that result from the review process when preparing their project for observation. Failing to create Scheduling Blocks will result in the awarded time to be forfeited. At any point in the project preparation process, a project may be withdrawn, and a NRAO Science Helpdesk ticket should be submitted in such an event.

Each facility may have unique requirements for preparing a project for observation. It is the responsibility of the proposing team to familiarize themselves with the requirements and resources that are relevant to their project. Users should submit a ticket to the NRAO Science Helpdesk if they have questions. The links below to should also be reviewed by users.


For specific policies concerning observer responsibilities, remote observing, observer assistance, student observing, and non-standard instrumentation and software, see and for observing preparation.


The proposing team is responsible for creating SBs ahead of the observing configuration. The Observation Preparation Tool (OPT) is the required online tool to prepare VLA observations. Observers should consult the references online when preparing for VLA projects:


All VLBA observations begin with the program SCHED. When a satisfactory SCHED input file has been achieved, observers should email that input file to . Further resources are available online:

5.2. General and Shared Risk Observing

VLA, VLBA, and GBT observing are classified into two categories: General Observing (GO) and Shared Risk Observing (SRO). The GO category includes the standard capabilities of VLA, VLBA, or GBT whereas the SRO program accommodates those who seek to utilize the facilities beyond their regular capacities. The Call for Proposals provides a detailed outline of what constitutes these categories for each facility.

The Observatory expects that most SRO programs will have no or only minor problems that can be corrected quickly. If an SRO program fails, however, and it becomes clear that detailed testing with additional expertise is needed, then the project must make an experienced member from their team available to help troubleshoot the problem. In some cases, this may require the presence of that experienced member. If adequate support from the project is not given, then the time on the telescope still will be forfeited. The additional effort is to be determined based on discussions with the Observatory staff and management and the project team.

VLA or VLBA SRO proposals will not be carried over if they cannot be scheduled for reasons associated with the shared risk component(s) of the observations, even if awarded priority A. VLA or VLBA RSRO proposals will not be awarded priority A, but would be subject to the same conditions on carry-over as SRO proposals. Those projects in the VLA or VLBA Shared Risk and Resident Shared Risk categories may not be re-observed if they fail due to problems with the shared risk/resident shared risk component(s) of the observation. If observers believe that an observation should be failed after inspecting their data they should submit a ticket to the NRAO Science Helpdesk as soon as possible and in all cases prior to the expiry of the period of eligibility for scheduling.

For GBT SRO, the proposing team may be asked to provide a "backup" receiver if the original one is not available. In such cases, the observation may proceed with the backup receiver, as long as the observation is not considered a duplicate observation, as defined in Section 7.3.



5.3. Observation Scheduling, Project Completion, and Carry-over

Science observations will be scheduled taking into account many factors, including, for example, the weather and proposal grade. The individual SBs of approved projects will remain in the observing queue until one of the following two criteria are met:

  1. The allocated time of a project has been executed.
  2. The potential scheduling period has ended.

For semester proposals, Section 4.3 defines the relevant scheduling periods for Regular, Triggered, and Large proposals. VLA DDT proposals remain in the observing queue for the configuration they request or until the end of the observing semester, whichever occurs first. VLBA and GBT DDT proposals remain in the observing queue until the end of the observing semester. If a project is not completed within these time frames, the project is considered terminated and the proposers should consider submitting a new proposal in the appropriate Call for Proposals.

For both semester and DDT proposals that are dynamically scheduled observations, if the dynamic constraints are no longer satisfied, they may be returned to the scheduling queue, provided the project is in the General Observing category. Re-observation is not guaranteed in such a case.  If observers believe that an observation should be failed after inspecting their data they should submit a ticket to the NRAO Science Helpdesk as soon as possible and in all cases prior to the expiry of the period of eligibility for scheduling. Please contact the NRAO Science Helpdesk for clarification concerning specific projects.

Generally, approved Large proposals are accepted in their entirety for the duration of the program; that is, the Observatory will commit the resources required to discharge the proposal within the constraints imposed by scheduling guidelines even though it may take multiple semesters to do so. The Observatory requires annual progress reports from all Large proposals and reserves the right to revisit allocations made to a given Large proposal if insufficient progress is demonstrated. Specifically, the following aspects of the proposal are considered:

  • A project connected to a Large proposal is required to maintain and provide timely updates to their online resources, otherwise their project may be terminated or future proposals rejected. An approved Large proposal must provide a web link for the Large proposals page7 before observations are scheduled. Initially, this can be a simple web page that describes the project but this page is expected to be kept up to date.

  • A project connected to a Large proposal is required allocate sufficient resources (e.g., observers) for successfully completing the project, otherwise their project may be terminated or future proposals rejected.

As much as 25% to 50% of available Open Skies observing time on Observatory telescopes is allocated to Large proposals. The final percentage will depend on proposal pressure and scientific merit, as determined by peer review. Large proposals will be further constrained to a maximum of 50% of the available Open Skies observing time in any LST range during any semester (or array configuration for the VLA).

The Observatory allocates telescope time and therefore does not guarantee that a specified sensitivity will be obtained. For qualifying programs, the data are run through the Science Ready Data Product (SRDP) pipeline and the proposers are notified of the available pipeline datasets; see the resources online for more information.

Further details pertaining to scheduling are available online: 

VLA and in memorandum “A Brief Description of the VLA Prioritizer”

7 For VLA and VLBA Large proposals, see For GBT Large proposals, see

5.4. PI Errors in Preparation and Execution

The Observatory is not responsible for errors in tuning or pointing (e.g., wrong or outdated ephemerides) due to incorrect information provided by the PI. If unexecuted parts of the project are found to contain similar (or any other) errors before the project execution has been completed, the PI should immediately adjust their prepared scheduling blocks in the relevant tools (e.g., OPT).

5.5. Data Delivery and Data Rights

5.5.1. Data Property

The original contract between the National Science Foundation (NSF) and AUI states that

All scientific information which the Contractor deems to be of record value, prepared by, or otherwise under the control of, the Contractor, in connection with the performance of work hereunder, shall remain the property of the Government, but the Contractor shall have the right to use, disseminate and publish such information, subject to all the provisions of the Articles entitles “Security Requirements” and “Patents”.

5.5.2. Data and Metadata

Proposal data, proposal metadata, observational data, and observational metadata are defined as follows.

  • Proposal data consist of material submitted by the PI (title, abstract, author information, scientific and technical justifications, source/resource information and related sessions) and a disposition letter, which contains scheduling priorities and review feedback.
  • Proposal metadata consists of source positions, observation frequencies, and integration times.
  • Observational data include visibility data and all resulting data products.
  • Observational metadata include the positional and sky coverage information, frequency settings, frequency coverage and resolution, angular resolution, uv-coverage, antenna lists, source and calibrator names, polarization, observation date(s) and start/end times, time on source and sampling rate, weather information and PI name.

For projects with scheduling priorities of A, B, C, or D the name of the PI, proposal ID, title, hours awarded, proposal type, expiration date for Trigger proposals, and the aggregate time observed for Large proposals are made public immediately in the relevant observatory Science Program. This information plus the list of co-Is and the abstract is made available from the Proposal Finder Tool (PFT). The information submitted as part of proposals that are rejected or not observed will remain confidential. The scientific and technical justification, figures, references, and review rankings and reviews are never made public for any proposal.

While proposal source lists are not made public directly, proposal metadata are available publicly from the Archive Access Tool once the data for a proposal have been collected. Observational metadata will be made available without restrictions when an observation is archived. Additionally, Operator Logs are made available once the data have been collected at

5.5.3. Confidentiality of Proposal Data

Both Observatory staff and external members of the scientific community participate in the Observatory proposal evaluation and time allocation process. They will regularly be exposed to confidential information and proprietary data and ideas. The information, data, and ideas must be held in confidence and not disclosed to others. However, several exceptions apply according to the role of the individuals in question.

  • Members of a given Science Review Panel may disclose and discuss the contents of any proposal assigned to them with one another, consistent with the conflicts of interest policy.
  • Members of the Time Allocation Committee may disclose and discuss the contents of any proposal under consideration with each other, consistent with conflicts of interest policy.
  • Observatory staff serving as technical reviewers may need to consult with each other to ensure a fair and complete assessment of technical elements of the proposal. Hence, technical details may be disclosed and discussed internally by relevant Observatory staff as needed.
  • Observatory staff members that participate in the Director’s Review may disclose and discuss the contents of any proposal under consideration with each other, consistent with the conflicts of interest policy.

5.5.4. Proprietary Periods and Observational Data Access

The observational data are reserved for the exclusive use of the proposing team for a fixed period of time, after which they become publicly available. The proprietary period for Regular, Large, and Triggered proposals is normally a maximum of 12 months after the last observation. For data acquired by the VLBA, HSA, or GMVA, the nominal proprietary period begins when the correlated data are entered into the data archive by Observatory science operations. At its discretion, the TAC may recommend a proprietary period that differs from the nominal 12 month period. For Large proposals, the proposing team is encouraged to make their data available to the public after a shorter proprietary period. The TAC recommendation regarding any change in the normal proprietary period is considered as part of the Director’s Review. If the recommendation is accepted, the proposers will be informed and the reason will be provided.

The proprietary period for data acquired by DDT proposals will normally be no more than 6 months and may be waived entirely; i.e., under certain circumstances, the data will be available to other teams or the public as soon as they are acquired. The proprietary period for data obtained by ToO proposals will be assessed on a case-by-case basis but will be no more than 6 months. An example where this option might be exercised is when the announcement of a transient event by one team triggers an active proposal of another team. The data would be made available to both teams immediately. The relevant Director’s office, in consultation with the NRAO Director or designee, will assign a proprietary period for the data based on scientific and programmatic considerations.

The Observatory staff will have access to observational data at all times as necessary for technical analysis and performance tuning. In addition, if a project qualifies to be run through the Science Ready Data Products (SRDP) pipeline, then Observatory staff can download and reduce project data for this purpose. Until the proprietary period expires, Observatory staff may not disclose or scientifically use the observational data from projects for which they are not a PI or co-I, including projects they support, without explicit recorded permission from the PI.

For the VLA and VLBA, the observational data is released to the PIs soon after the data are collected via the Archive Access Tool. Users must log-in to access their data. Qualified datasets are run through the SRDP pipeline and can be accessed through the Archive Access Tool as well. For the GBT, the observational data are immediately available.

5.5.5. Extension of Proprietary Periods

Requests for extensions will be considered for extenuating circumstances outside the control of the PI. The most common circumstances where proprietary time extensions have been approved include parental/personal leave, sick leave, or military service. PIs may submit their request through the NRAO Science Helpdesk and justify that the approved leave takes significant time away from the office. Decisions on requests for an extension of the propriety period are made by the Assistant Director for Science Support and Research. The length of the extension will be considered on a case-by-case basis based on the conditions of the approved leave. For these cases, the extensions must be requested at least one month before the end of the proprietary period. An extension will not be granted if requested within 30 days before the data are scheduled to become public. Vacation, science, sabbatical leaves will not be considered for an extension. The proprietary period of Large proposals will not be extended in the cases of approved leave. The proprietary period may be extended without PI consultation if errors are found in the data by Observatory staff or extenuating circumstances occur (e.g., Archive Acess Tool is unavailable for a long period of time).

5.5.6. Calibration Data

Standard calibration data are observations of calibrators needed to perform the correct calibration of the scientific data. They include the flux, bandpass, amplitude, phase and polarization observations taken during PI observations. This definition extends to data that are resultant from the Accurate Position Service (see Section 5.1).

All standard calibration data have no proprietary period even if they are the result of PI observations. However, there does not yet exist a mode independent of the Archive Access Tool to acquire calibration data that is associated with proprietary data. In the future, the Observatory may make such data accessible separately from the Archive Access Tool. If the Accurate Position Service (Section 5.1) is leveraged, the results will be public domain immediately and source positions, and in many cases, even images will appear on the geodetic web sites.

5.5.7. Test and Science Verification data

Data obtained during commissioning, engineering tests or science verification (SV) activities will be used to characterize and develop the facility systems, including hardware and software. The data will be released through the archive, technical memos, or publications.

Science Verification projects may not duplicate an approved PI or DDT proposal that is in the observing queue or during their proprietary period. If a PI proposal is approved that duplicates a SV observation planned after the proposal submission deadline, the corresponding SV project must be changed to avoid duplication. DDT proposals that duplicate a SV observation already planned and announced on the relevant observatory Science Program before the submission of the former will be rejected.

6. Related Provisions

6.1. Acknowledgement of Observatory Facilities

Users of data acquired with Observatory facilities are responsible for acknowledging the use of Observatory data in their publications. Consult the “Publication Support Policy” section available on the Observatory’s library:

6.2. Visiting the NRAO and the GBO

The Observatory welcomes short- and long-term visits to Socorro, New Mexico; Charlottesville, Virginia; and Green Bank, West Virginia from investigators of successful Observatory programs or archival researchers for expert assistance with processing and analyzing data. Visits for data reduction have to be requested at least one month in advance and are expected to last about a week. Novice visitors are required to be accompanied by an experienced investigator, e.g., a collaborator. Resources for visitors are available online at; GBO specific policies and information can be found at

6.3. Final Provisions

Any situation that is unforeseen or for which ambiguity exists in this Users’ Policies document or in the associated Call for Proposals material will be referred to Assistant Director for Science Support and Research, whose decision is final.

The Observatory reserves the right to change the policies defined in this document at any time. Barring unforeseen emergencies, such changes will apply at the start of the observing semester following the date of their introduction. These changes will be published in the Users’ Policies document at the Call for Proposals and the proposers should review the policies with each proposing cycle.

6.4. Acknowledgements

This Users’ Policies document attempts to maintain consistency with the ALMA Users’ Policies Document when applicable; however, it is independent from the ALMA version and should be treated so.

The majority of these policies and guidelines are taken from the existing online documentation available at, which has been maintained diligently by Observatory staff over the years. As noted earlier, this information and policies in this document supersede the online content and other documents if conflicts exist.

7. Appendices

7.1. Abbreviations, Acronyms, Definitions, and Useful URLs

AAT Archive Access Tool;
DDT Director’s Discretionary Time
LBO Long Baseline Observatory
LST Local Sidereal Time
NRAO Science Helpdesk
Open Skies Open Skies observing time is when any scientist, regardless of nationality or residence, can apply for time on an instrument through a peer-reviewed process. The percentage of time that is considered Open Skies depends on the facility.
OPT Observation Preparation Tool;; requires login
PFT Proposal Finder Tool;
PI Principal Investigator
PST Proposal Submission Tool;; requires login
RCT Resource Catalog Tool;; requires login
SCT Source Catalog Tool;; requires login
Science Program and
SRDP Science Ready Data Products
SRP Science Review Panel
TAC Telescope Time Allocation Committee
TTA Telescope Time Allocation
ToO Target of Opportunity
VLA Configuration

The antennas in the Karl G. Jansky Very Large Array (VLA) are placed in specific configurations. There are four basic antenna arrangements, called configurations, whose scales vary by the ratios 1 : 3.28 : 10.8 : 35.5 from smallest to largest. These configurations are denoted D, C, B, and A, respectively.

VLA configuration cycle; The VLA completes one cycle through all four configurations in an approximately 16 month period. See for current and up-to-date configuration schedules and associated proposal deadlines.

7.2. Student Proposals and Dissertation Plans

The “Plan of Dissertation Research” should be submitted with their first proposal. This plan can be referred to in later proposals; instructions for how to upload or replace a plan are available here.

The Plan of Dissertation is important in the proposal review process and should be well written; it is not a placeholder and should not be a replica of the proposal. The plan must be compliant with the follow requirements:

  • It must follow the Observatory's Plan of Dissertation Research template. The template is available below in word or latex formats:
  • The section headers in the template should not be changed but the instructional text within the template should be replaced.
  • It must be uploaded as a Portable Document Format (pdf).
  • It is a maximum of two (2) pages.
  • There is a minimum of one inch margins on all sides and the pages are US letter size.
  • The minimum font size is 11 point, which includes the font in figure captions, table captions, table headers, content, and references. Fonts in rescaled figures should be legible.
  • All sections of the plan must be authored by the student.

The plan provides some assurance against a dissertation being impaired by adverse referee comments on one proposal, when the referees do not see the full scope of the project. Students should keep their expected graduation date in the user profile (Section 2.1) and in the thesis time line updated, as the date of data acquisition must fall within the timeline of the PhD. If the observing semester occurs after the student intends to graduate, then it is not appropriate to indicate that the proposal is for a dissertation. While not a guarantee, the Observatory allows reviewers to consider elevating the proposal in the rankings if it is associated with an acceptable Plan of Dissertation. This is given in consideration to the time constraints students typically operate under, as having to resubmit a proposal due to minor criticisms may not be possible within the scope of their studies. Therefore, it is advantageous for students to provide a thoughtful and thorough Plan of Dissertation if their PhD research is reliant on the proposal data.

Note, the PST does not validate Plans of Dissertations.


7.3. Definition of Duplicate Observation

A proposed observation is considered a duplicate of another observation if all of the following conditions are met:

  • Target field location
    • For a single-field, the proposed position coincides within the half-power beam width of the
      other observation. Moving objects (e.g., Solar System objects) will be identified by name.
    • For mosaic observations, more than 50% of the proposed pointings are within the half-power beam width area covered by the other observation.
    • For evolving or variables sources, the duplication is not scientifically justified.
    • For GBT monitoring programs, no two active programs can monitor the same proposed position that coincides within the half-power beam width of the other observation. Moving objects (e.g., Solar System objects) will be identified by name.
  • Angular Resolution
    • The proposed angular resolution differs by a factor of ≤ 2 from the other observation.
  • Spectral Windows
    • For the VLA and VLBA,
      • Continuum: The requested sensitivity (rms) for the aggregate bandwidth is better by a factor of ≤ 2 from the other observation and the requested frequency is within a factor of 1.3.
      • Spectral line: If the central frequency in any requested correlator window is encompassed by the other observation and the sensitivity per spectral channel, after smoothing to the same spectral resolution, is better by a factor of ≤ 2. Or, if the spectral resolution, as justified by the science case, is better by a factor of ≤ 2.
    • For the GBT,
      • Continuum: The requested sensitivity (rms) for the aggregate bandwidth is better by a factor of ≤ 2 from the other observation and the requested frequency is within a factor of 1.3.
      • Spectral Lines: Within the largest beam size of two receivers with overlapping frequency ranges, any spectral line being the same while taking into account velocity/redshift.

Solar observations will not be checked for duplication.

7.4. Commensal Observing

Commensal observations can be an effective way to maximize observing hours on Observatory telescopes, by allowing multiple experiments or systems to run simultaneously, when resources allow. The Observatory may support two kinds of commensal observing: commensal observing projects, and commensal systems.

Commensal observing projects refer to peer-reviewed, PI science projects which can be done simultaneously on Observatory telescopes using Observatory backends to conduct two different experiments concurrently. Investigators wishing to carry out commensal observing projects submit independent science proposals as separate primary and secondary proposals, which go through the normal time allocation processes, and are subject to standard data policies.

Commensal systems may be backends or data pipelines which have been approved to run on Observatory telescopes while some PI science experiments are running. Commensal observing systems which are currently on the VLA are described at the proposing page.

A primary proposal controls the telescope pointings and requests the full amount of telescope hours required to fulfill the science objectives detailed in the proposal. Secondary proposals are to run commensally with the primary pointings but make no formal request for an allocation of telescope time. However, when preparing a secondary commensal proposal, please ensure that a nominal amount of time is requested for a session (e.g., 0.1 hrs), even if it is a dummy session. Each proposal must contain estimates of the full resources needed (correlator setup, data rates, etc.) to carry out their specific part of the project.

During the proposal review and time allocation process it will be determined if the combination of the observing set-up and the positions by the primary or secondary proposals conflict with any approved projects. In the case of a conflict, some data restrictions may be applied to the primary and/or the secondary commensal proposal. If the primary and secondary proposals use the same back-end resources (e.g., VLA-WIDAR) it may be necessary for technical reasons to require that the investigators on both primary and commensal projects be given full access to all data.

The Observatory wishes to ensure that peer-reviewed, open-skies PI science projects which are approved via review processes are protected, and that ownership of data is defined. The concept of a “PI science project” includes the science goals and the data produced from PI-specified observing setups. The operation of all commensal systems on Observatory telescopes is subject to the below policy:

Peer-reviewed, open-skies PI science, and the associated output from standard observatory backends, take priority over commensal observing systems. Commensal observing systems may run at all times during open-skies PI science, except when they conflict directly with such science, or cannot run because of technical incompatibility. Conflict is defined by a commensal system reproducing, or being able to reproduce, any part of the PI data approved by the Observatory’s Telescope Time Allocation Committee. The Observatory requires that all commensal systems provide sufficient technical information so that determinations can be made as to whether they will conflict with PI science. The primary project science PI may choose to allow a conflicting commensal system to run; in this eventuality, the commensal system may run alongside the PI science project, subject to technical compatibility. The data produced by a commensal system are controlled by the associated commensal project team.

Observatory telescopes and backends are sufficiently flexible in many cases to allow two experiments to run commensally. To the degree that this enhances science return from the telescopes, Observatory wishes to support commensal projects subject to resource and scheduling constraints. The operation of commensal systems during other (non-open-skies) observing time is subject to the details of relevant contracts or agreements. Groups wishing to carry out commensal observations should submit independent science cases as separate primary and secondary proposals.