Agreements for Joint Observations with the NRAO were made before the observatory was split into multiple observatories.  Access to the Joint Observing program will continue for the GBT at least for semester 23A.  Since the arrangements were made through the NRAO, the documentation below does not directly mention the GBO.

By agreement between the NRAO and the Space Telescope Science Institute, STScI will be able to award time on NRAO facilities to highly ranked proposals that request time on both HST and NRAO telescopes. NRAO has offered up to 3% of the available open skies time on its North American facilities, namely the Green Bank Telescope (GBT), the Very Large Array (VLA), and the Very Long Baseline Array (VLBA), for allocation by the HST Time Allocation Committee (TAC), subject to a maximum of 5% of the available time in any given VLA configuration.

In return, STScI has offered 30 orbits of HST time  per year for allocation by the NRAO TAC. Joint HST/NRAO proposals should be submitted to the observatory that represents the primary science facility, not to both observatories.

HST as Primary Observatory: NRAO observing time awarded through the HST Cycle 31 review will be implemented during the 2023B and 2024A observing semesters. The award of time on NRAO facilities will be subject to approval by the NRAO Director, after nominal review by the NRAO TAC to avoid duplication of programs. The important additional criterion for the award of NRAO time is that both the HST and the radio data are required to meet the science goals of the project. It is not essential that the project requires simultaneous NRAO and HST observations. Under this agreement, NRAO time will only be awarded in conjunction with new HST observations (and should not be proposed for in conjunction with an Archival Research or Theory Proposal).

NRAO as Primary Observatory: HST time awarded through the NRAO TAC will be implemented during the course of HST Cycle 31.  Proposals submitted to the NRAO requesting HST orbits must indicate that the proposal is joint with HST and must specify the number of orbits requested. The important additional criterion for the award of HST orbits is that both the HST and radio data are required to meet the science goals of the project. It is not essential that the project requires simultaneous NRAO and HST observations.

Successful proposers will submit Phase II HST proposals at the standard Phase II deadline. Funding will be available to US investigators to support HST data reduction; budgets should be submitted at the standard deadline

Proposers must always check whether appropriate archival data exist, and provide clear scientific and technical justification for any new observations of previously observed targets. Observations awarded time that duplicate observations already approved by HST or NRAO for the same time period may be canceled, or data sharing and cooperation among different groups may be necessary, as determined by the two observatories. This includes triggered proposals with similar trigger criteria, with or without previously known coordinates.

Be aware that some HST targets might not require new NRAO observations because the joint science goals can be met using:

• non-proprietary archival data from the VLA or VLBA that are online
• VLA continuum images from sky surveys at a wavelength of 20cm and at a FWHM resolution of 45 arcseconds or 5 arcseconds.

All scientific data from NRAO telescopes have a proprietary period during which the data are reserved for the exclusive use of the observing team. The NRAO data archive policy and proprietary periods are online, and apply to data taken through the joint HST-NRAO program.