HST Orbital Ephemeris Files

Last updated: 2024-12-07 10:52:06

Files may be downloaded via the MAST HST Dataset Retrieval Tool

The purpose of this webpage is to provide information about how to download the suitable orbital ephemeris files to be used for correcting observation time events of STIS TIME-TAG data through the IRAF odelaytime task.

HST orbital ephemeris files are generated every 48 hours and provide the orbital locations of HST as a function of time for the past 48 hours in a FITS binary table format. These are required to correct for light delay from relativistic effects, displacement of the telescope from the center of the Earth, and displacement of the Earth from the solar system barycenter. The IRAF task odelaytime takes two main inputs: the TIME-TAG data (_tag.fits); and the ephemeris file (pXXXXXXXXr.fit). For further details regarding the odelaytime task and parameters, the reader is referred to STIS ISR 2000-02.

How to Download:

From the table below, keep notes of the name of the Dataset with Start Date preceding but closest to the observation time of the TIME-TAG data of interest. Then go to https:// archive.stsci.edu/cgi-bin/dataset_lookup and type (or paste in) the dataset name under the box titled "Enter a list of datasets", then hit the "Submit datasets for retrieval" button. You will be presented with a table that shows all the datasets chosen in the previous page. Make sure the Mark boxes are checked for the selected datasets and hit "Submit marked data for retrieval from STDADS". From the next HST Retrieval Options page, you can choose multiple options on how to retrieve the data. However, it is important that you uncheck the "Calibrated" box under File Options and manually select "fit" extension in the box on the right - otherwise the retrieval request will fail.

If you have questions, please submit them through https://hsthelp.stsci.edu