Figure 1. The Ulysses trajectory for the prime mission
On 30 September 1995, Ulysses completed its prime mission to
explore the high-latitude regions of the heliosphere, becoming
the first spacecraft to truly escape from the confines of the
ecliptic plane. The spacecraft's scientific payload has returned
unique and continuous data throughout, covering the in-ecliptic
transfer orbit to Jupiter, the flyby of the giant planet, the
descent to the south pole of the Sun, and the subsequent ascent
over its north pole. With approval from the funding agencies to
extend the mission for a second solar orbit, the complete set of
Ulysses measurements will provide an invaluable source of data
for space scientists, as well as being of interest to the wider
scientific community.
The ESA archive for Ulysses data provides public access to the
measurements made by the spacecraft, together with the
documentation needed for their correct interpretation. Plots of
selected parameters have been generated and are available on-line
for viewing or downloading. The archive, which takes advantage
of the infrastructure of the Internet made available through the
World Wide Web, will become the central repository in Europe for
measurements made throughout the mission's lifetime.
The joint ESA/NASA Ulysses mission, launched on 6 October 1990 to explore the heliosphere at high latitudes for the first time, recently completed its prime mission (Fig. 1) and has now embarked on a second solar orbit. The spacecraft has provided continuous scientific measurements during its in-ecliptic transfer to the Jovian system (see ESA Bulletin No. 67), its flyby of the giant planet (see ESA Bulletin No. 72), its descent to the south solar pole (see ESA Bulletin No. 82), and its ascent over the north solar pole.
Figure 1. The Ulysses trajectory for the prime mission
After a proprietary period during which the Ulysses investigators have exclusive rights to analyse and publish their observations, the data enter into the public domain. The ESA archive for Ulysses data provides public access to measurements made during the mission and the documentation needed for their correct use. It will also be established as the permanent archive in Europe for all Ulysses data. These activities are performed in the United States by the National Space Science Data Center (NSSDC) and (for the subset of data taken at Jupiter) by the Planetary Data System (PDS), and are coordinated with ESA activities where appropriate.
Unlike NASA, ESA did not explicitly include archiving activities in the Ulysses mission plan, and work in this area only commenced in mid-1993, following approval by the Agency's Science Programme Committee.
Initially, data were defined and generated for the Ulysses Data System (UDS) which provided Ulysses investigators with access to measurements from all instruments within the framework of a computer network restricted to the Ulysses science community. The primary intention of the UDS was to encourage correlative studies between the Ulysses teams by facilitating the exchange of data. Having established the UDS, the data sets were used to form the basis of a public archive, at first by NSSDC, and more recently by ESA.
The ESA archive makes full use of the infrastructure of the Internet provided through the increasingly popular World Wide Web (WWW), taking advantage of the HyperText Markup Language (HTML) for designing graphical user interfaces, the File Transfer Protocol (FTP) for file transfer, and software to browse the contents of web sites (such as Mosaic and Netscape, or Lynx for platforms not supporting graphics and windows applications).
This article describes in detail the data sets held on-line by the ESA archive and the information necessary to access them. Additional applications, such as a simple plotting package to view the data, and a search of a database storing an up-to-date list of references to scientific papers written using Ulysses data, are also reported.
The scientific payload of Ulysses comprises (Fig. 2):
Figure 2. The Ulysses spacecraft in launch configuration, showing
the locations of the various instruments
Radio-science experiments have also been performed (SCE and GWE) making use of the spacecraft's radio communication link in specific periods. Each experiment team is led by a Principal Investigator (PI), and involves Co-Investigators (Co-I's) from European and American institutes (Table 1). In total, more than 120 scientists are directly associated with one or more of the investigations.
Table 1. The Ulysses scientific investigations
Investigation Acronym Principal Investigator Measurement
---------------------------------------------------------------------------------------------------------------------------
Magnetic field VHM/FGM A. Balogh, Imperial College, London (UK) Spatial and temporal variations of the
heliospheric magnetic field: 0.01 to 44000 nT
Solar wind SWOOPS J.L. Phillips, Los Alamos National Lab. (USA) Solar-wind ions: 260 eV/q to 35 KeV/q;
Solar-wind electrons: 0.8 to 860 eV
Solar-wind ion SWICS J. Geiss, Univ. of Bern (CH) Elemental and ionic-charge composition
composition G. Gloeckler, Univ. of Maryland (USA) temperature and mean speed of solar-wind ions:
145 km/s (H + ) to 1350 km/s (Fe +8 )
Radio and plasma
waves URAP R.J. MacDowall, NASA/GSFC (USA) Plasma waves, solar radio bursts, electron density,
electric field
Plasma waves: 0-60 kHz; radio: 1-940 kHz;
magnetic: 10-500 Hz
Energetic particles
and interstellar
neutral gas EPAC/GAS E.Keppler, MPAe, Lindau (D) Energetic ion composition: 80 keV-15 MeV/n
Neutral helium atoms
Low-energy ions
and electrons HI-SCALE L.J. Lanzerotti, AT&T Bell Labs., Energetic ions: 50 KeV-5 MeV
New Jersy (USA) Energetic electrons: 30-300 keV
Cosmic rays and
solar particles COSPIN J.A Simpson, Univ. of Chicago (USA) Cosmic rays and energetic particles
Ions: 0.3-600 MeV/n
Electrons: 4-2000 MeV
Solar X-rays and
cosmic gamma-ray
bursts GRB K. Hurley, UC Berkeley (USA) Solar-flare X-rays and cosmic gamma-ray
M. Sommer, MPE, Garching (D) bursts: 15-150 KeV
Cosmic dust DUST E. Grün, MPK, Heidelberg (D) Dust particles: 10(exp -16) to 10(exp -7) g
Coronal sounding SCE M.K. Bird, Univ. of Bonn (D) Density, velocity and turbulence spectra in the solar
corona and solar wind
Gravitational waves GWE B. Bertotti, Univ. of Pavia (I) Doppler shifts in spacecraft radio signal due to
gravitational waves
The data sets used for the archive have been generated by the PI teams, thereby guaranteeing the use of the best data-reduction algorithms available. The selected time resolution of the data sets is not necessarily the highest resolution of the experiment. Instead, a compromise is often necessary in order to ensure the statistical validity of the measurement without restricting the scientific potential of the data. Furthermore, the physical parameters included in the data files do not always represent an exhaustive list of measured quantities. This may apply to measurements contaminated by noise, or may simply be to limit the size of the data files.
The organisation and formatting of the files is kept as uniform as possible, the general case being one ASCII file per day for each experiment (or subsystem of an experiment). However, there exist a few exceptions to this guideline, most notably the GRB data set, which because of its high time resolution is stored in binary format and then further compressed in order to conserve both disk space and data transmission times.
Table 2 summarises the current data sets available on-line from the ESA archive, providing information about the time resolution of the data and the physical parameters included in each file. From the typical size of each file, estimates are provided of the total disk storage required for each experiment for the prime mission. As higher resolution data become available to the archive, these figures will increase, necessitating the use of alternative storage media such as CD-ROMs.
Table 2. The data set currently available from the ESA archive for Ulysses data
Instrument Measured Parameters Data Available Time Resolution Estimated Volume
of Prime Mission
Data (MByte)
------------------------------------------------------------------------------------------------------------
VHM/FGM Magnetic field (Total field and components) 298/90-273/93 1 hour 3
SWOOPS/IONS/
ELECTRONS Ion velocity, temperature and density 322/90-365/94 4 minutes and 1 hour 45
Electron velocity, temperature and density 322/90-366/92 4 minutes 40
SWICS Velocity, temperature and density for 341/90-365/93 3.5 hours 2
selected ion species
URAP Peak and average electromagnetic wave 307/90-365/94 10 minutes 400
intensities
EPAC Ion and electron fluxes 274/90-365/94 1 hour 140
HI-SCALE Ion and electron fluxes 318/90-365/94 1 hour 30
COSPIN/AT Ion fluxes 001/91-365/93 10 minutes 50
COSPIN/LET Ion and electron fluxes 296/90-365/94 10 minutes 80
COSPIN/HET Ion and electron fluxes 296/90-365/94 10 minutes 40
COSPIN/HFT Ion and electron fluxes 296/90-243/94 10 minutes 40
COSPIN/KET Ion and electron fluxes 296/90-365/94 10 minutes 70
GRB Detector count rates 302/90-365/94 0.25-2 seconds 3000
DUST Dust impact speed, launch-end 199 N/A N/A
mass and arrival direction
Access to the ESA archive for
Ulysses data can be gained through the WWW. Using a browser, such
as Mosaic or Netscape, it is necessary to open a Universal
Resource Locator (URL) pointing to
to reach the top-level page of the archive directory. Figure 3 shows the layout of this home page, as seen with the Mosaic browser.
Figure 3. The archive's WWW home page, as viewed using the Mosaic
browser
Figure 4. The data-set description for the GRB experiment
Figure 5. The Ulysses/ESA home page, as viewed with Mosaic
Detailed information about how to contact the PI and the investigation representative responsible for generating the data sets is provided for each experiment. Indeed, any user wishing to use Ulysses data for scientific analysis is requested to contact the relevant PI to inform him of their intention, and is recommended to collaborate with the experiment team where appropriate.
Also available is a short description of the data products supported by the archive, which include previously generated 27- day (approximately corresponding to the synodic rotation period of the Sun) PostScript plots for browsing periods of interest, data files (compressed and grouped into yearly files), and documentation material (including format descriptors to read the data files, detailed information about the instrument, caveats and data reduction techniques used, and a list of relevant references). As an example, Figure 4 shows the data-set description for the GRB instrument. More general information about the Ulysses mission itself, including regular status reports and the current spacecraft position, can be found on the accompanying Ulysses/ESA page using the URL
This page also provides links to the Web sites maintained by the Ulysses institutes, the NASA Ulysses page at Jet Propulsion Laboratory (JPL), and the US archive sites at NSSDC and PDS.
The layout of this page is shown in Figure 5, again using the WWW browser Mosaic.
Measurements made by the solar-wind plasma instrument (SWOOPS) and the Low-Energy Telescope of the COSPIN particle instrument, from launch until the end of 1994, are shown in Figures 6 and 7, respectively, as examples of the quality of data available from the public archive.
Figure 6. Solar-wind velocity measured by the SWOOPS instrument
from launch until the end of 1994 (Courtesy of J.L. Phillips, Los
Alamos National Laboratory)
Figure 7. Proton intensities in the L2 (1.2-3.0 MeV) channel of
the Low-Energy Telescope of the COSPIN instrument
The archive data and data products are stored on an anonymous FTP server, which is a dedicated computing facility belonging to the ESA Space Science Department at ESTEC for staging information and data for public access. It is therefore possible to obtain Ulysses archive products directly by using anonymous FTP to the server helio.estec.esa.nl (or using the IP number 131.176.17.136) and logging in with ANONYMOUS as the user name and providing the user e-mail address as the password. The Ulysses data products are located in the 'ulysses' directory and are arranged in sub- directories named according to the experiment and the type of product. Figure 8 summarises the FTP access procedures and portrays the directory structure.
Figure 8. Summary of FTP access procedures and the Ulysses data
archive directory structure
Ulysses trajectory information is also available through the Ulysses archive. Daily values for the spacecraft's position in heliocentric and geocentric coordinates are provided for the prime mission and for the second solar orbit. This information was supplied by the Ulysses project office at JPL.
The software used to generate the 27-day plots will shortly be interfaced to the archive home page, to allow users to make 'on- the-fly' plots of selected parameters and time intervals.
A useful application offered by the Ulysses/ ESA home page is a facility allowing a dynamic search of a database (maintained by the Ulysses science team at ESTEC) containing references to papers published in scientific journals using Ulysses data. This search uses the standard SQL interface to query a relational database (RDB) in real time, and is interfaced to the WWW page using HTML forms. The search capability allows multiple selection of authors, character strings contained within the article title, journal and year of publication. An example of the result of such a search is shown in Figure 9. In the future, this facility will be extended to provide the user with the text of the article's abstract.
Figure 9. Results of a real-time query to the Ulysses
publications database
The ESA archive for Ulysses data will continue to add new data as they come into the public domain. The data sets will also be updated if a more complete selection of parameters becomes available, or if more refined data-reduction algorithms are employed to generate them. It is planned to make higher resolution data available when submitted to the archive by the experiment teams. Such voluminous data sets will most likely be stored off-line, and will need to be requested by interested users and distributed on high-density media such as DATs or exabyte tapes and CD-ROMs. Available non-electronic data products, such as microfiche plots (as supplied by the investigator teams) and data books, will be announced and mailed upon request.
In summary, the ESA data archive will allow today's space scientists easy access to the measurements made during the Ulysses mission, but will also ensure the data's availability for future generations.
ESA Bulletin Nr. 86.