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The Status of Hungarian Space VLBI
Assistance Software
By S a nd o r F r e y
e­mail: frey@novell.sgo.fomi.hu
FOMI Satellite Geodetic Observatory, Penc, P.O. Box 546, Budapest, H­1373, HUNGARY
A new space VLBI user support software development is going on at the Satellite Geodetic
Observatory (Penc, Hungary). Currently the Japanese VSOP and the Russian Radioastron
satellites are expected to be launched at the end of 1996 and in the first half of 1997 respectively.
The Space VLBI Assistance Software (SPAS) is being developed since 1993. The main purpose
of this program is to help the user community to prepare observing proposals for both missions.
The software gives some insight to the complex conditions of space VLBI missions. It is useful
for approximate scheduling of space VLBI observations taking various restrictions into account.
The first version of the user assistance software will be available at the beginning of 1995. The
first Announcement of Opportunity is expected to be released in the middle of 1995. We show
the capabilities of the software. Some preliminary results achieved so far are also presented.
1. Introduction
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 Announce­
ment 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)).
2. Assistance software development in Hungary
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 inter­compared with the versions of Canadian and USA ones as well as the Russian
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2 Sandor Frey: The Status of Hungarian Space VLBI Assistance Software
program which is being developed as the scheduling software of Radioastron satellite. The
inter­comparisons 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 inter­comparisons 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 develop­
ment 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 inter­comparisons 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.
3. Capabilities and operations of SPAS
SPAS has a windows­like graphical user interface. It allows the user to issue commands
and specify input parameters as easily as possible using either mouse or keyboard. Opera­
tions 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 on­board 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.
ffl SubSat plots the subsatellite tracks and locations of telemetry stations on Earth's
map.
ffl SatVis displays and lists the visibility schedule of satellites from tracking stations.
Gives the tracking time coverage of satellites from telemetry stations.
ffl ObsInt displays and lists the observability schedule of radio source from ground
VLBI stations and space VLBI satellites. Gives the time coverage of observations.
ffl TopoPos plots tracks of radio source and satellites on the sky in horizontal system
as seen from ground stations. Lists the azimuth and elevation values.
ffl UVPlot produces UV­plot for selected baselines.
ffl 3DView shows a 3­dimensional movie of the rotating Earth, the ground VLBI stations
and the satellites as seen from the direction of radio source (or other selected direction).
ffl SpaceView shows a movie of Earth indicating the position of the telemetry stations
as seen from the satellite.
ffl SkySurv creates a survey for a specified area of the sky deciding if certain parts are
observable from ground VLBI stations and satellites or not at a given time.
ffl Access creates a long term survey for a sky area. It shows how long the certain
parts are observable from ground VLBI stations and satellites during a time interval.

Sandor Frey: The Status of Hungarian Space VLBI Assistance Software 3
Figure 1. Main menu of SPAS graphical user interface.
ffl CheckArc gives information about the possible attitudes of space VLBI satellite
when observing a selected radio source during a time interval. It takes the on­board
observing constrains into account.
ffl Beam selects radio sources within the primary beam of space VLBI antenna for phase
referencing purposes.
ffl Sensitivity plots the RMS sensitivity of baselines as a function of integration time;
plots the minimum detectable brightness temperature and the signal­to­noise ratio for
the baselines as a function of time.
ffl Cone selects radio sources in special geometric configurations with respect to the
satellite orbit normal.
ffl Calculator performs basic calculations, unit conversions and coordinate transform­
ations.
The recommended hardware configuration includes IBM PC AT/386 or 486 compat­
ible computer, mathematical co­processor, SVGA graphics card. These tools are widely
available at possible users' site.
4. First results
According to the ESA standards (ESA (1991)) we used a top­down 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 Sensit­
ivity 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.

4 Sandor Frey: The Status of Hungarian Space VLBI Assistance Software
Figure 2. Screen outputs of SatVis, SubSat and ObsInt operations.
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 inter­comparisons between other
space VLBI assistance software developed by other groups independently. SPAS can
only be released after these inter­comparisons.
5. Conclusion
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.
This work is being supported by the Hungarian Space Office under contract MEC
93­0054 and by the Joint Institute for VLBI in Europe (JIVE) under the contract with
Commission of European Communities (CHGECT920011).
REFERENCES
ESA Software Engineering Standards, 1991, ESA PSS­05­0, Issue 2, (ESA, Paris).
Fejes I., Murphy D.W., Taylor A.R., Yakimov V., Young G., 1993, in Proceedings of URSI/IAU
Symposium on VLBI Technology Progress and Future Observational Possibilities, (Kyoto,
Japan).
Frey S., 1994, Space VLBI Assistance Software (SPAS) Development Status Report, 18th Ra­
dioastron Meeting, (Suzdal, Russia).

Sandor Frey: The Status of Hungarian Space VLBI Assistance Software 5
Murphy D.W., Yakimov V. Kobayashi H., Taylor A.R. Fejes I., 1993, in Proceedings of
URSI/IAU Symposium on VLBI Technology Progress and Future Observational Possib­
ilities, (Kyoto, Japan).
Noszticzius I., 1993, in New Space VLBI Assistance Software Package Development in Hungary,
26th Young European Radio Astronomers Conference, (Les Houches, France).