Obtaining Time on the VLBA

How to Propose

Observing time on the VLBA is available to all researchers, regardless of nationality or location of institution. However, only 50% of the operational time on the VLBA is available for “open skies” observing. The other 50% is allocated for use by the US Naval Observatory. The allocation of open skies observing time on the VLBA is based upon the submission of a VLBA Observing Proposal using the online Proposal Submission Tool (PST) available via the NRAO Interactive Service web page, at my.nrao.edu. The online tool allows the user to assemble a proposal by specifying the requested observations using online forms, and uploading the required scientific justification. More specific info on using the online tool, and policies related to proposal types, scientific justification page limits, etc., can be found in the NRAO User Portal and Proposal Submission Guide. VLBA-specific details, including capabilities offered for the next proposal deadline, can be found in the current Call for Proposals and the VLBA Observational Status Summary (OSS). For a brief overview of the VLBA, please see the Introduction to the VLBA.

In addition to the general capabilities outlined in the Call for Proposals and the OSS, NRAO offers a VLBA Resident Shared Risk Observing (RSRO) program for those who would like to push the capabilities of the instrument beyond those offered for general use.  Details are available on the web at the VLBA RSRO Program page.

It is also possible to obtain VLBA observing time by proposing to NASA missions, under cooperation agreements established between NRAO and those missions. Such programs exist for the XMM-Newton, Chandra, Fermi, Swift and HST missions. Astronomers interested in those joint programs should consult the relevant mission proposal calls for more information.

Note that it is possible to search cover sheets of proposals previously approved for time since semester 2005C using the Proposal Finder Tool (PFT).

The actual VLBA proposal process consists of the following steps:

  1. Develop rationale: Before writing a proposal, the proposer must develop the scientific rationale for the program, develop a source list, decide on the observing band(s) to be used, and estimate the expected source strengths and their detectability. For spectral-line sources, the proposer also must decide on the desired velocity resolution, and convert that to a spectral resolution.
  2. Create Proposal in the Proposal Submission Tool (PST): After logging into NRAO Interactive Services, click on "Proposals" and then "New Proposal" on the top to the far right of the screen. Then click on VLBA/HSA and "Create" (again on top to the far left). A proposal template will be created for you; click on the proposal number and this will open the proposal for you. There are seven screens to choose from and edit (there is an additional screen where you can find your disposition letter after the proposal has been reviewed).
    1. General: Title, abstract, proposal type, etc.. Edit this page by clicking on the "edit" button to top to the far right.
    2. Authors: List of authors and contact information. You can add an author by clicking on the "Add" button to the right on the page. Then search for your co-authors and if they are not in the database you can add them.
    3. Scientific Justification: Upload a pdf or txt of your scientific justification, no more than 4 pages in length for a Regular or Triggered proposal (including figures, tables and references) with an 11pt font, or 10 pages for a Large (200 hours or more) proposal.
    4. Technical Justification: An important part of the proposal to be submitted is the Technical Justification.  Previously merely a required section in the Scientific Justification, it is now a separate element of each proposal.  Instead of the free format used in the Scientific Justification, we ask proposers to supply information on a number of standard topics, covering the wide range of technical issues of importance.  We have found that this reduces the likelihood that information is left out needed by the Technical Reviewers to judge the feasibility of the project as proposed. Follow the links in the form to obtain more information on the individual topics.  Click here to see an example.  Note that with technical information contained on this page space is freed up in the Science Justification.
    5. Sources: List of sources. One slightly confusing thing here is that you have to create a "New Source Group" to add sources (button on upper right). After creating a group you can either add sources to it by hand or search for them with NED/SIMBAD. Adding sources to this section does not mean any time has been requested for them, they must be linked to a telescope resource in Sessions.  Except for proposals where the sources are not known a priori (e.g. triggered proposals), all target sources must be included in the source list. Calibrators may also be added to this list, but it is not required.
    6. Resources: Resources requested from the VLBA (antennas, frequencies, bit rates, correlator, etc.).  To add a resource click "add" on the right.  If proposing for the VLBA/HSA then the "Socorro-DiFX" correlator should be used. Set which telescopes are being requested and then set the "Observing Parameters" and "Correlation Parameters" based on the scientific goals of the project. For most continuum experiments you will want the highest sustainable aggregate bit rate (currently 4 Gbps; see the relevant section of the OSS), i.e., the largest bandwidth and therefore the highest sensitivity.  For spectral line observations choose the number of baseband channels and their widths based on the expected frequency coverage of the lines, leaving some continuum on either side available for calibration.  If bandwidths narrower than 1 MHz are required, see the spectral resolution section of the OSS.
    7. Sessions: Describes the amount of time requested, and how it should be divided among the various sources and resources. Click on "New Session", this is where you actually request time on your sources at different frequencies.
  3. Examine and Submit: Go back to "My Proposals" and click on the printer icon (looks like a printer) next to the proposal code to see what the proposal will look like to a reviewer.  Once you are satisfied click the submit (large arrow) button to submit the proposal.


Students planning to use the VLBA for their Ph.D. dissertation must submit a Plan of Dissertation Research of no more than 1000 words with their first proposal. This plan can be referred to in later proposals. At a minimum, the plan should contain a thesis time line and an estimate of the level of VLBA resources needed. The plan provides some assurance against a dissertation being impaired by an adverse review of a proposal when the full scope of the thesis is not seen. The plan can be submitted via NRAO Interactive Services. Also see the Plan of Dissertation Research subsection of the NRAO User Portal and Proposal Submission Guide for more details. Students are reminded to submit their plan comfortably in advance of the proposal deadline. New thesis plans must be in PDF format to enable science reviewers to easily access the plans. Students who have not yet graduated, but have active plans on file, should consider updating those plans to a PDF format if they are not already in that form.


Time on the VLBA is scheduled on a 6-month semester basis. Semester A observations typically take place February through July and have an August 1 proposal deadline in the previous year; Semester B observations, take place from August through January and have a deadline on February 1. If the deadline falls on a weekend it is extended to the next working day. The call for proposals typically goes out 3–4 weeks prior to the deadline.

For details on the evaluation of submitted proposals we refer to the NRAO Proposal Evaluation/Time Allocation page. Because of competition, even highly ranked proposals are not guaranteed to receive observing time. Observing time at each VLBA station will also continue to be limited by ongoing testing and maintenance activities; for more information, see the section on Scheduling Considerations in this document.

The Proposal Review Process

Determining who gets time on the VLBA (and VLA, GBT, etc.) involves 6 steps.

  1. Proposal submission: people who wish to use the instruments request time.
  2. Technical review: NRAO scientists and analysts read the Technical Justification (TJ) section of each submitted proposal to determine whether or not the proposed projects are feasible, need adjustments, or are impossible to successfully observe. The science objectives are only considered as they pertain to the requested observations, not their scientific merit.
  3. Scientific review: Science Review Panels (SRPs), made up of experts outside of NRAO, review each proposal for scientific merit.  All the proposals that are considered by a SRP are then ranked.
  4. Time allocation: the Time Allocation Committee (TAC) combines the ranking with the technical reviews to determine which projects are granted observing time, how much time, and at what priority.
  5. Director's review: The observatory Directors, Chief Scientists, the NRAO Assistant Director for Science Support and Research, and other observatory staff review the results from the SRP and TAC to ensure that all NRAO procedures and policies have been followed.  This review may result in some adjustments to priorities.
  6. Disposition letters sent and the TAC report is published: Proposers learn the results of the review process.  The goal is to send the disposition letters at least 2 months before the next deadline.

The entire process, from submitting your proposal to receiving the disposition letter, typically takes between 3 and 4 months.

Director's Discretionary Time

It is also possible to propose for Director's Discretionary Time (DDT).  DDT is reserved for Targets of Opportunity and for Exploratory Time.  DDT proposals may be submitted at any time with the understanding that they should only request for semesters for which the proposal deadline has passed.  The DDT proposals must be submitted through the PST.  DDT proposals are reviewed by the DDT review committee the basis of the proposals' scientific merit, conflict status, LST pressure, and technical feasibility.

A Note on VLBA Observing Semesters

The VLBA observing semesters are always the same.  VLBA Semester A begins February 01 and ends July 31; VLBA Semester B begins August 01 and ends January 31.  Therefore, VLBA observing semesters may not always align with the VLA observing semesters, which vary based on array configuration.

Joint VLBA/VLA/GBT Proposals

Observing programs that require combinations of the VLBA, GBT, and/or the VLA should submit a proposal for each of the requested telescopes, with a clear justification for each, as has been the case to date. The proposals will be reviewed and considered jointly by the Time Allocation Committee. VLBI proposals which request the GBT or VLA (or any other HSA telescope) as elements of the VLBI array do not need separate proposals---those telescopes can be selected as separate VLBI stations from a VLBA/HSA proposal.

For example, a program to monitor a transient source with the VLA and get occasional VLBA observations to look for non-thermal components would need to submit identical proposals to both the VLA and VLBA.