Recently, the plan of Selenodesy by use of VLBI (RISE: Radio Interferometry for Selenodesy) is proceeding. In this plan, as the VLBI radio sources both that on the Moon surface and on board of satellites around the moon are considered. As a next step to the selenodesy, we (Hosokawa and Imae at CRL and Kawano and Hanada at NAO) began to examine the planetodesy using counter VLBI technique. The first target of the planetodesy is the planet Mars.
With the progress of these projects, a study group on the mechanics of spacecraft and VLBI has been organized in last fall. Hosokawa is appointed as the contact person of the group in CRL. For the realization of these plans, many new technical developments and analysis methods on VLBI technology will be needed. Let us summarize the technical topics and problems of these plans.
There are two important characteristics in these plans. These are, the radio sources are artificial ones, and they are at the finite distances. Because of the former property we will be able to set the intensity and the frequency characteristics of the sources somewhat freely. The latter demands a new analysis method where the parallactic corrections and the motion of the sources should be taken into account. The sensitivity to the motion of the source will provide a new route to the real time positioning of the space crafts.
In the case of counter VLBI, the former property will be fully applied to the planetodesy plan. In our examination, all radio sources on Mars are equipped with atomic clocks, so that all the signals from these sources should be synchronized. This synchronization would be done by two-way satellite time transfer via the Mars-stationary satellite. As the radio sources, we can choose the carriers or the spectrum diffused ones according to the purpose and possible system of the plan. Then, we will be able to measure the differences among propagation times of the radio signals from the sources on Mars to the observatory on the Earth. On the other hand, interplanetary radio propagation would be affected by many relativistic effects that are caused by the complicated motion of the sources and by the gravitational field by the massive bodies in the Solar system. Hence, we have to make the corrections for these effects.
To summarize, there are many interesting and challenging subjects on
VLBI technology in the plans of Selenodesy and the planetodesy.
Therefore it would be worth paying attention to these plans for us, the
VLBI technical development center.
Figure 1. Figure on Counter VLBI.