Times of Orbital Events for Oct. 1, 2017 to Apr. 2, 2019

Radiation zone passages occur between the end of one orbit and the beginning of the next. During radiation zone passages, no Chandra observations are possible due to the high particle background and the need to protect ACIS. For observations which must be tightly constrained, observers may wish to check projected estimates of usable orbit intervals (and their unusable complement during the radiation zone).

The begin and end orbit times listed below are conservative guesses as to the actual radiation zone entry and exit times. They are found from the perigee times given in a predictive ephemeris in the following manner:

• 1) end orbit times are perigee time - 10 hours (i.e. end radzone times are perigee time + 10 hours)
• 2) begin orbit times are perigee time + 10 hours (i.e. begin radzone times are perigee time - 10 hours)

Actual useful segments of orbits are likely to be somewhat longer, but should not be shorter than the times listed here. However, the perigee times will be less accurate as time increases from the creation date. At one year after the creation date, the perigee times are expected to be about 20 minutes off from the actual perigee time.

The date/times are provided here in Calendar (UTC) format. To convert to other date formats, please see the Date Conversion Tool page.

Earlier orbital event times can be accessed on our archived orbits pages.