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As we move into the next era of geodetic VLBI, the scheduling process is one focus for improvement in terms of increased flexibility and the ability to react with changing conditions. A range of simulations were conducted to ascertain the impact of scheduling on geodetic results such as Earth Orientation Parameters (EOPs) and station coordinates. The potential capabilities of new automated scheduling modes were also simulated, using the so-called ‘dynamic scheduling’ technique. The primary aim was to improve efficiency for both cost and time without losing geodetic precision, particularly to maximise the uses of the Australian AuScope VLBI array. We show that short breaks in observation will not significantly degrade the results of a typical 24 h experiment, whereas simply shortening observing time degrades precision exponentially. We also confirm the new automated, dynamic scheduling mode is capable of producing the same standard of result as a traditional schedule, with close to real-time flexibility. Further, it is possible to use the dynamic scheduler to augment the 3 station Australian AuScope array and thereby attain EOPs of the current global precision with only intermittent contribution from 2 additional stations. We thus confirm automated, dynamic scheduling bears great potential for flexibility and automation in line with aims for future continuous VLBI operations.

The APOD (Atmospheric density detection and Precise Orbit Determination) is the first LEO (Low Earth Orbit) satellite in orbit co-located with a dual-frequency GNSS (GPS/BD) receiver, an SLR reflector, and a VLBI X/S dual band beacon. From the overlap statistics between consecutive solution arcs and the independent validation by SLR measurements, the orbit position deviation was below 10 cm before the on-board GNSS receiver got partially operational. In this paper, the focus is on the VLBI observations to the LEO satellite from multiple geodetic VLBI radio telescopes, since this is the first implementation of a dedicated VLBI transmitter in low Earth orbit. The practical problems of tracking a fast moving spacecraft with current VLBI ground infrastructure were solved and strong interferometric fringes were obtained by cross-correlation of APOD carrier and DOR (Differential One-way Ranging) signals. The precision in X-band time delay derived from 0.1 s integration time of the correlator output is on the level of 0.1 ns. The APOD observations demonstrate encouraging prospects of co-location of multiple space geodetic techniques in space, as a first prototype.

Inhomogeneous networks and reference frames are an important issue for Very Long Baseline Interferometry (VLBI). In this work we examine the performance of southern stations and baselines in routine VLBI experiments. A positive impact on baseline length repeatabilities of the increased observing effort by the Australian AuScope VLBI antennas is found by analysing three years of global rapid-turnaround VLBI sessions: while worse results are found for southern baselines compared to northern baselines for the first half of the investigated sessions, the northern and southern baseline length repeatabilities are about the same in the second half of the period. In simulations, the actual observing plan with a significantly lower number of observations for southern stations is identified as a major reason for the worse length WRMS for southern baselines, though other factors seem to influence the results as well. Simulating radio source position uncertainties, effects of up to 10 mm are found on baseline length WRMS for long southern baselines. Improving all source position uncertainties through more frequent observations to better than 50 μ as could reduce this effect by up to 30 % .

The first 5 GHz VSOP (VLBI Space Observatory Programme) observation of the quasar 3C279 was conducted on 10 January 1998 with the satellite HALCA and an array of ground radio telescopes. The high dynamic range image presented here reveals that the core and the secondary component ∼3 milli-arcseconds from the core dominate the compact radio emission, but that lower level features at intermediate distances from the core are also evident.

We are using the VSOP spacecraft, HALCA, together with ground-based telescopes, to image six strong GPS sources with compact double structure. Space-ground baselines are needed to achieve the resolution to accurately measure component sizes at the frequency of the spectral peak, an essential requirement in distinguishing between free-free and synchrotron self absorption emission mechanisms. Many of the components of these sources are only just beginning to show signs of any internal structure on the longest Earth baselines and space VLBI is the only technique that permits investigation of their most compact structure at the frequency of the spectral peak.

We present a preliminary report on the high resolution imaging of the nearby southern blazar PKS 1921-293, observed at 18 cm from the VSOP In-Orbit Checkout. The image shows that the source possesss a core-jet structure similar to that seen with ground-only VLBI observations at centimeter wavelengths. However, the addition of data from HALCA has allowed us to clearly identify the core which we find to be partially resolved with a brightness temperature in excess of 10 12 K.