Voyager Pointing Information

SPICE C kernels contain the pointing and orientation history of spacecrafts.

For more information about SPICE visit the home page of PDS’s Navigation and Ancillary Information Facility (NAIF).

SEDR Files

Traditionally, the pointing information for the Voyager instruments was distributed in the form of Supplemental Experiment Data Record (SEDR) files. These were generated shortly after each flyby and were distributed on 9-track tape. The format of the tapes was unique to each instrument but at minimum the tapes contained the direction in space that the instrument was pointed. Today, many of the SEDR tapes have been lost.

The one major exception is Voyager’s Imaging Science Subsystem (ISS), for which the SEDR files were later converted to Vax binary format and are still widely available. However, the ISS SEDR files only describe the camera direction and orientation at the time when images were taken, leaving large intervals during each flyby when the pointing is unknown.

The Ring-Moon Systems Node has recently obtained SEDR files for the Ultraviolet Spectrometer (UVS), which have the advantage that they provide nearly complete temporal coverage of each encounter. However, the accuracy is not as good as that of the ISS SEDR files.

These files will be posted on line shortly, along with complete descriptive information. Meanwhile, contact Mark Showalter if you would like any of these files.

C Kernels

Unfortunately, because the Voyager mission pre-dates the PDS and the SPICE toolkit, reliable C kernels were never generated for the scan platform, which carried the four remote sensing instruments: ISS, IRIS, PPS, and UVS. The Ring-Moon Systems Node has recently undertaken the project of generating reliable C kernels for all of the Voyager flybys.

To date, we have generated C kernels for the Voyager 1 flyby of Saturn. Other C kernels will follow shortly.

For completeness and to preserve historical information, the C kernels are being generated in five versions:

1. The ISS pointing information exactly as recorded by the ISS SEDR files. These C kernels are discontinuous; they only contain the pointing information at the times when images were taken.

2. The UVS pointing information exactly as recorded by the UVS SEDR files. These kernels have been interpolated to provide continuous and nearly-complete temporal coverage, although with less accuracy than the Version #1 ISS-based C kernels.

3. Merged C kernels, in which the UVS SEDR information has been used to interpolate between the times of the images. These kernels have the accuracy of the Version #1 C kernels but also the temporal coverage of the Version #2 kernels.

4. “C-smithed” C kernels for ISS, in which a subset of the images have been used to correct pointing errors in the original ISS SEDR files. These kernels should be significantly more accurate than the Version #1 kernels. However, they are discontinuous, containing pointing information only at the times of the Voyager images.

5. Finally, merged, “C-smithed” kernels, in which the UVS SEDR files have been used to interpolate between the times of the images. These should be as reliable as the Version #4 C-smithed kernels but also provide continuous, nearly-complete temporal coverage.

NOTE: These files have not yet been through peer review. We believe them to be accurate but further testing is probably appropriate. Please send any questions or problems to Mark Showalter.

Downloads

Follow the links below for more information and files to download. Check back later for additional C-smithed and merged C kernels. In the table below, “Type 1” refers to a kernel that only records pointing at discrete times (e.g., versions #1 and #4) whereas “Type 3” refers to a continuous kernel. Note that the latter are much larger, and so the Type-1 kernels are probably more appropriate for users only interested in the Voyager images.