20B TAC Report

by Dana Balser last modified May 15, 2020


A total of 239 proposals were submitted to NRAO's North American facilities for semester 20B.  These include the Very Long Baseline Array (VLBA)/High Sensitivity Array (HSA) and the Karl G. Jansky Very Large Array (VLA).  Proposals are reviewed on a competitive basis with a panel review system (see Proposal Review System).  Below are the statistics by proposal count and hours.  The oversubscription is the ratio of the number of submitted proposals to the number of approved proposals.  The pressure is the ratio of the requested time to the available time in hours.  Here we only include proposals submitted for the 20B semester that have been reviewed by the NRAO TAC.  We count HSA proposal hours that request the VLA as a VLBI station.

Statistics by Proposal Count
Submitted 38 201
Approved 19  69
Filler  5  47
Rejected  14  85
Oversubscription 2.0 2.9
Statistics by Proposal Hours
ProposalsVLBAVLA (A)
Requested   1399.60 4442.38
Available     506.10 1576.50
Approved     746.00 1344.13
Filler     251.40 1067.22
Rejected     402.10 2068.75
Pressure       2.8     2.8

For the 20B semester, the NRAO had agreements with the Hubble Space Telescope (HST), the Swift Gamma-Ray Burst Mission, the Chandra X-ray Observatory, and the XMM-Newton Telescope to submit joint proposals whereby the NRAO TAC could allocate time on these external facilities (see the 20B Call for Proposals).   The table below summarizes the results for all AUI North American facilities that are included in the joint program: GBT, VLBA, and VLA.  The time available on the external facilities is per year, whereas the time requested and approved is only for semester 20B.


Joint External Proposals

HST (Orbits)

Swift (ks)Chandra (ks)XMM-Newton (ks)


30.0 300.0 120.0 150.0
Requested 26.0  116.0    60.0   87.6
Approved  2.0   36.0    31.0   57.6



Telescope Pressure Plots

Pressure plots show the total hours of allocated time as a function of LST (or GST).   Also shown are how the hours are divided with respect to weather conditions and observing priority.  Click on the plot to enlarge


VLBA pressure plot as a function of GST. The black line with squares is 52% of the wall-clock time available (after removing time for maintenance and sponsored time). Note that the approximate Pie Town LST is shown on the top axis. The colors correspond to pre-committed time (green), priority A (dark blue), priority B (light blue), priority C (yellow), and priority N (red).


VLBA Pressure Plot 20B




VLA Pressure plot as a function of LST. The VLA has two weather categories: high frequency (above 12 GHz, light shading) and low frequency (below 12 GHz, dark shading). The figure below shows the pressure for the A-configuration.  The black lines indicate the total time available for science (solid), the time available for K-band and higher frequencies (dashed), and the time available for Q-band (dotted).  The letters A, B, C, and N correspond to the priorities assigned by the TAC where A and B are approved time, C is filler time, and N is rejected time.


 VLA Pressure Plot 20B (A)


Observation Preparation



Unless otherwise stated in the TAC comments, proposals approved for priority A time will be eligible for scheduling in semesters 20B and 21A, and proposals approved for priority B or C time will be eligible for scheduling only during semester 20B.

IMPORTANT:  Those allocated dynamic time should begin their .key file preparation about two weeks before 2020 August 1,  the start of semester 2020B. Completed observing files, or preliminary ones, should be sent to the data analysts at vlbiobs@nrao.edu, for checking and possible iteration.  Those proposals with fixed-date allocations (e.g. HSA proposals) will be informed of the date/time of observation about one month prior and their schedules will be due two weeks prior to observation.

Any approved time tabulated above may be divided into multiple scheduling blocks as appropriate, considering the scheduling priority, observing frequency, GST range suitable for the target(s), and GST pressure. For advice on preparing your scheduling blocks, please consult the VLBA Observing Guide or use the helpdesk.



In semester 20B, daytime maintenance activities peak at about 19 hours LST for the A-configuration, so observing pressure is highest there. For status of the VLA and links to the monthly schedules please see the schedsoc home page.  Proposals approved for priority A, B or C time become ineligible when the associated configuration ends, unless explicitly stated otherwise in the Comments from the TAC. Those allocated dynamic time should begin their scheduling block preparation about two weeks before the planned start of the configuration (see Configuration Plans).

Any approved time may be divided into multiple scheduling blocks as appropriate, considering the scheduling priority, observing frequency, LST range suitable for the target(s), and LST pressure. For advice, please consult the VLA Observing Guide.

Unless stated otherwise, any time allocated is only for the identified proposal, and no modification in the project should be made without obtaining permission from NRAO scheduling staff.  To seek permission, submit a ticket to the Proposal Review department of the NRAO Helpdesk.