RADIO observations of the strong, flat-spectrum radio source PKS1830-211 revealed a double structure, with a separation of 1 arcsec, suggesting that it might be a gravitationally lensed object 1. We have now obtained high-resolution radio images of PKS1830-211 from several interferometric radiotelescope networks, which show an unusual elliptical ring-like structure connecting the two brighter components. The presence of the ring, and the similarity of the two brighter spots, argue strongly that this is indeed a gravitationally lensed system, specifically an Einstein ring in which lens and lensed object are closely aligned. Although the source is close to the galactic plane, it seems that both the lens and background (lensed) object are extragalactic. This object is one hundred times brighter than either of the two previously discovered radio Einstein rings, and is among the six brightest flat-spectrum sources in the sky. Its brightness makes it a peculiar object: it must involve either a chance alignment of a lensing object with an unusually bright background source, or an alignment with a less bright object but amplified to an unusual degree.

At the 37th IAF Congress [Levy et al., Acta Astronautica 15, 481 (1987)] we presented the initial results of a demonstration using a TDRSS spacecraft antenna as the orbiting observatory in a very long baseline array. This demonstration established the feasibility of the OVLBI technique. In the beginning of 1987, additional OVLBI observations were made at a radio frequency of 2.3 GHz. Of the 24 sources observed, 23 were detected. These data have been analyzed and the results are presented. After the successful completion of the 2.3 GHz observations, it was decided to attempt to use the 15 GHz capability of the TDRSS for a higher resolution demonstration. Simultaneous 2.3 and 15 GHz observations were successfully conducted in February and March 1988. The radiometric sensitivity of TDRSS at 15 GHz was very much less than at 2.3 GHz. Of the 23 sources observed, 11 were detected.

VLBI observations of the strong radio source 1934 - 638 have been made at 2.3 GHz as part of the Southern Hemisphere VLBI Experiment (SHEVE; see Preston et al. 1989), using five antennas in Australia and one in South Africa. The source was found to be double with a component separation of 42.0 +/- 0.2 mas (84h^-1^ pc for H_0_=100h km s^-1^ Mpc^-1^), a position angle of 90.5^deg^ +/- 1^deg^, and component sizes of about 2.5 mas. Comparison with single-baseline data taken 12 yr earlier (Gubbay et al. 1971) shows no evidence for any significant change in structure within the reported errors, which places a limit of 0.05c +/- 0.2c on the expansion velocity. About 40% of the total flux density is seen only on the shorter baselines and is modeled as an additional elongated component aligned with and between the compact double components. The source's almost equal compact double structure, peaked spectrum, low variability, small polarization, and particle-dominated radio lobes indicate that it belongs to the class of symmetric compact double sources first noted by Phillips and Mutel (1980, 1981, 1982). The relationships between component size, surface brightness, and luminosity as a function of component separation are concordant with other known compact doubles in the evolutionary model of double radio sources presented by Carvalho (1985) and Mutel and Phillips (1988). However, no other known member of this class has a substantial portion of its flux density in an additional extended component.

The Southern Hemisphere VLBI Experiment (SHEVE) program is aimed at producing high-resolution images of southern radio sources. The radio telescopes of the present SHEVE array are described below and some recent results presented.

VLBI observations of the nucleus of Centaurus A have been made at two frequencies with an array of five Australian radio telescopes as part of the Southern Hemisphere VLBI Experiment (SHEVE). Observations were made at 2.3 GHz with all five antennas, while only two were employed at 8.4 GHz. At 2.3 GHz seven tracks in the (u,v) plane with coverage of 6-8 hr each were obtained, yielding significant information on the structure of the nuclear jet. At 8.4 GHz a compact unresolved core was detected as well. We find that the source consists of the compact self-absorbed core, a jet containing a set of three knots extending from 100 to 160 mas from the core, and a very long, narrow component elongated along the same position angle as the knots. The allowable range for the position angle of the jet is 51^deg^ +/- 3^deg^, in agreement with that of the radio and x-ray structure on arcsecond and arcminute scales. The jet has brightened at 2.3 GHz by ~4 Jy, a factor of nearly 3, since the early 1970s, 1.8 Jy of which has occurred in the last 2 yr with no discernable changes in structure.

VLBI observations of the compact, nonthermal radio source at the Galactic center show it to be elongated at 8.4 GHz along a position angle of 82 + or - 6 deg. The source has an axial ratio of 0.53 + or - 0.10 with a major axis of 17.4 + or - 0.5 mas. Examination of VLA maps of the Galactic center region indicate no obvious alignment with this smaller-scale elongation of the nuclear region, nor is the nuclear position angle aligned with the axis of Galactic rotation. Comparison with the size measured at frequencies from 1 to 22 GHz shows that the size follows very closely the lambda-squared dependence expected from interstellar scattering. The alongated nature of the source implies either that the scattering medium is anisotropic or that some remnant of the intrinsic structure remains visible through the scattering medium.

A desire for increased angular resolution at microwave frequencies has led to the development of radio telescopes with very large effective apertures. Very long baseline interferometry (VLBI) has made it possible to synthesize telescopes with effective dimensions of a large fraction of an Earth diameter. By using a satellite-borne radio telescope as part of a VLBI array, the dimensions of the Earth cease to be a limitation. The use of a satellite VLBI telescope puts stringent requirements on the communication links between the spacecraft and the ground. A demonstration was performed to show that the orbiting VLBI (OVLBI) concept is feasible. The Tracking and Data Relay Satellite System (TDRSS) was used as the orbiting element of the VLBI demonstration. Stability tests were made before the observations to determine the suitability of the TDRSS for OVLBI use. The first successful OVLBI observations were performed using the 64-m antenna observatories of NASA's Deep Space Network in Tidbinbilla, Australia, and of the Institute for Space and Astronautical Science in Usuda, Japan in conjunction with the TDRSS. Data from three quasars were successfully correlated at the Haystack Observatory in Westford, Mass.; the results were used to deduce the system performance.