NSSDC Helps Ulysses Team Visualize Trajectory

Volume 10, Number 2, September 1994
by Sardi Parthasarathy
Almost four years from its October 1990 launch and 2.5 years since its February 1992 Jovian encounter, the Ulysses spacecraft attained its extreme southerly heliocentric latitude of -80.17 deg on September 13, 1994. This ESA spacecraft carries 11 ESA and NASA instruments for the in situ measurements of solar wind fields and plasmas, plus cosmic rays and other energetic particles. Already, Ulysses has yielded significant new insights into the solar wind and cosmic ray phenomenology of the never-before-visited high heliolatitude regions. Extreme northerly solar latitude of 80.17 deg will be attained on July 30, 1995. Prior to Ulysses, the extreme latitude reached by an Earth emissary (Voyager 1) was 33 deg N.

NSSDC has been actively supporting the Ulysses mission from the start by providing up-to-date trajectory-related data and graphics to the investigator community and the cognizant NASA Headquarters personnel. Soon after the launch, NSSDC generated (and later updated after Jupiter encounter) and loaded online for public access a list file of daily coordinates for Ulysses, along with software to manipulate these Cartesian coordinates into other sets, notably the heliographic latitude/longitude/radial distance. Similar online files of all other heliospheric spacecraft enable computations of their relative locations. The NSSDC Report 91-08, "Trajectories of Inner and Outer Heliospheric Spacecraft," has been requested often. (Higher resolution data may be obtained by executing the online code in DECnet: RUN NSSDCA::ANON_DIR:[ACTIVE.HELIO]HELICOOR.

More recently, due to the active initiative of NASA HQ for a coordinated IACG effort in data acquisition and analysis, NSSDC has supplied specially tailored plots and list files to the participants at the January '94 Interagency Consultative Group meeting in Easton, MD. The Space Physics Data Facility, a sister organization of NSSDC, was responsible for the hardware, software, and networking at the meeting. One of the plots included was a radial projection of Ulysses on the daily visible (and invisible) solar surface for the years 1992-96, to locate the coordinates on the sun from which wind speeds of different magnitudes emanate (see figure).

Image Showing Ulysses Projection on Solar Disk 1992-1996

This figure maps Ulysses' trajectory projection onto the solar disk. Note that the dashed lines and filled circles correspond to times when the Ulysses subsolar point is on the Sun's invisible hemisphere.

The next step was to invoke the finite travel time of the wind, typically several days, and compute the heliographic latitude and longitude from which each hourly wind measured by IMP 8, PVO, and Ulysses "precisely" originated on the solar surface. The plots of source regions' Heliographic longitude versus the observed wind speed at each hour clearly corroborated the persistence high wind speed coronal "holes", that IMP 8 and other near ecliptic plane spacecraft had been finding. This was done for all the Carrington rotation numbers 1850 through 1864, of 1992. IMP 8 will continue to provide "bench mark" speeds for the winds from the equatorial belt, as Ulysses monitors the higher latitude wind. A major player at the Easton conference was the concurrent set of X-ray pictures obtained by the ISAS spacecraft Yohkoh and ground-based measurements of magnetic field, both on the solar surface; these enabled a higher order scrutiny of the source regions.

NSSDC will be archiving and disseminating Ulysses sensor data shortly, in addition to its management and dissemination of trajectory data. Dr. John Cooper (JCOOPER@NSSDCA. GSFC.NASA.GOV) is NSSDC's primary acquisition scientist with responsibility for interactions with data-providing scientists.

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Author:Miranda Beall
Curators: Erin Gardner and Miranda Beall
Responsible Official: Dr. Joseph H. King, Code 633
Last Revised: 21 Nov 1996 [EDG]