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. Proposals for the Semester Observing Opportunities must be submitted between the announcement of the Call for Proposals and the proposal deadline. The Call for Proposals contains the implementation parameters and procedures and is available online at https://science.nrao.edu/observing/call-for-proposals.

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.

Triggered Proposals

For a Triggered proposal that is not considered Large, users shall specify the proposal type as "Triggered" in the PST. If a proposal is partially Triggered, the entire proposal is considered a Triggered proposal. If the proposal is also Large, users should specify the proposal type as "Large" in the PST and provide clear triggering criteria in the scientific justification.

Joint Proposals

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.

Requests for Future Capabilities

Proposals submitted to a semester call must contain capabilities offered in that semester call. An exception is for a PI who is a graduate student, who may propose up to one semester in advance for capabilities offered on the GBT, HSA, and VLBA. For the VLA, a PI who is a graduate student may propose for any array within one VLA configuration cycle (see Section 7.1 for definition). For other exceptional cases, please seek guidance from the NRAO Science Helpdesk. Submission of such cases will be subject to the NRAO's discretion.

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

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 https://science.nrao.edu/observing/call-for-proposals.

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.

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 https://science.nrao.edu/observing/proposal-types/joint-proposal-opportunities. 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.

^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.