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As discussed in Infrared space interferometry - Why isn't it being done? the space-based radiotelescope Spektr-R has been used in Very Long Baseline Interferometry or VLBI. See also What are Spectr-R's major contributions to radio astronomy that could not have been done from Earth? for more info.
Is it the only space-based receiver to be used for VLBI observations, or have there been others?
KRT-10 radiotelescope in July 1978
The world's first VLBI-experiment was conducted with a KRT-10 space-based radiotelescope and a RT-70 radiotelescope in Evpatoria, Crimea.
https://ru.wikipedia.org/wiki/КРТ-10 (in Russian)
See also Space VLBI
The first space VLBI experiment was on Salyut-6 orbital station with KRT-10 (ru:КРТ-10), a 10-meter radio telescope, which was launched in July 1978.
I found a 2008 citation of space-based VLBI 'by using a radio antenna in earth orbit. This has indeed been accomplished with the Japanese satellite "HALCA" (Highly Advanced Laboratory for Communications and Astronomy, Hirabayashi et al. 2000)'. There were two papers cited for this instance: SUB-MILLIARCSECOND IMAGING OF QUASARS AND ACTIVE GALACTIC NUCLEI by K. I. KELLERMANN, et al and "Space-VLBI polarimetry of the BL Lacertae object S5 0716+714: rapid polarization variability in the VLBI core"
That was found on a Caltech website (although the authors were German) and I noticed that Katie Bouman, who as a graduate student was a leader in the Event Horizon Telescope effort to image M87, is now an ass't prof at Caltech.
JAXA had a radio telescope mission named HALCA:
HALCA was launched by M-V-1 on February 12, 1997. As a radio astronomy satellite, it conducted various engineering experiments including deployment of large antenna and VLBI interference experiments before successfully making VLBI observation. It is now a mainstay of the VSOP program, a large-scale international collaboration project.
HALCA operations ended in 2005.
