Please Note: the e-mail address(es) and any external links in this paper were correct when it was written in 1995, but may no longer be valid.
FOMI Satellite Geodetic Observatory, Penc, P.O. Box 546, Budapest, H-1373, HUNGARY
Two space VLBI missions are under preparation. The Japanese VSOP is scheduled for launch in September 1996 while the Russian Radioastron in 1997. The first Announcement of Opportunity will be issued in the middle of 1995 according to the current plans. By that time the potential users of space VLBI experiments will need assistance software which can help them in preparing observing proposals. The anticipated deadline for the first proposals is 6 months after the first issue of Announcement of Opportunity.
Such assistance programs should meet various requirements. The users would like to prepare observing proposals which are reliable and therefore acceptable for the space VLBI missions. The software should introduce the users to the new technique, enable them to select the optimal radio source, the best time period and ground station network for the observations. In order to carry out these tasks this kind of software should take all the observing restrictions into account including satellite orbit, tracking and on-board technical constraints. Moreover, these programs should be easy to understand and handle.
There are three different space VLBI user support software which still have an initial version. However, they are under further development. These assistance programs are developed in Canada (University of Calgary), USA (Jet Propulsion Laboratory) and Hungary (Satellite Geodetic Observatory) (Fejes et al. (1993)). The space agencies preparing the space VLBI satellites will have scheduling software which perform more or less similar operations than user assistance software. These developments are going on at the Astro Space Center of Lebedev Physical Institute (Moscow, Russia) and the Institute of Space and Astronautical Science (Tokyo, Japan) (Murphy et al. (1993)).
A prototype space VLBI user assistance software has been completed in the Satellite Geodetic Observatory, Penc (Hungary) in 1993. The results provided by this software were inter-compared with the versions of Canadian and USA ones as well as the Russian program which is being developed as the scheduling software of Radioastron satellite. The inter-comparisons showed a good agreement between the different products (Fejes et al. (1993)). New recommendations for the future developments have also been collected.
Adopting the conclusions of the tests and inter-comparisons we decided to develop a completely new version of Hungarian Space VLBI Assistance Software (abbreviated as SPAS) instead of modifying the prototype (Noszticzius (1993)). This new software is intended to follow also the new user requirements. SPAS has considerably refined capabilities concerning the computational models as well as the user interface.
The team chose a new way of development following the ESA Software Engineering Standards (ESA (1991)). It provides us detailed guidelines for each phase of the development from the collection of user requirements to the software release and the maintenance. The Standards also require ``heavy'' documentation which makes the development easier to control. ESA expressed its interest in the software development and helps to keep the requirements. We expect that ESA supervision ensures the good quality of the product. Further inter-comparisons with US, Canadian and Russian software are also anticipated.
The production deadline for the first version of SPAS is the first quarter of 1995. Then the program will be released along with the necessary user documentation. In order to continue the development successfully after the release of the first version we will need close contact with the users. We are ready to collect and implement the new user requirements.
SPAS has a windows-like graphical user interface. It allows the user to issue commands and specify input parameters as easily as possible using either mouse or keyboard. Operations use common data base including radio source, VLBI station, satellite and telemetry station catalogues.
The software can handle a maximum of 20 ground based VLBI antennae, 2 space VLBI satellites and 20 tracking stations together in an observing session. The checking of satellite on-board pointing restrictions is also implemented in SPAS.
We summarize the capabilities of 14 SPAS operations below (Frey (1994)). These operations show the space VLBI measurements from various aspects. They provide the necessary information for scheduling observations using the space VLBI satellites.
The recommended hardware configuration includes IBM PC AT/386 or 486 compatible computer, mathematical co-processor, SVGA graphics card. These tools are widely available at possible users' site.
Figure 1: Main menu of SPAS graphical user interface.
Figure 2: Screen outputs of SatVis, SubSat and ObsInt operations.
According to the ESA standards (ESA (1991)) we used a top-down decomposition method of the software components. After the collection of user requirements the logical model of the software was set up first. Then we defined the structural levels of the program and the interfaces of each module. Now the development is in the so called detailed design phase. The algorithms of program modules (subroutines, functions) have already been defined and documented. The coding of the program and the compilation of User Manual is going on.
The coding of the lower level routines as well as of SubSat, SatVis, ObsInt and Sensitivity subprograms have been completed. We show the main menu of the graphical user interface (Figure 1) and the output windows of some operations completed until now (Figure 2).
The lower level routines have well defined requirements concerning their output values. During the detailed design phase we continuously tested the completed modules. The first test runs of the coded subprograms also show good performance. The numerical results are in good agreement with those of our prototype program.
Of course we will have to perform careful and detailed tests after the completion of SPAS. Tests will include internal validation and also inter-comparisons between other space VLBI assistance software developed by other groups independently. SPAS can only be released after these inter-comparisons.
The coding of Space VLBI Assistance Software (SPAS) is about 50% completed. The software package is being developed in Hungary. SPAS will be completed at the beginning of 1995. After careful tests and validation the user support software will be released by the middle of 1995 when the first Announcement of Opportunity for VSOP satellite is expected to be issued. It will be available free of charge on request for potential space VLBI users who are interested in submitting observing proposals for VSOP or Radioastron missions.