The tool below (Google Earth plugin required) may be used to display the ISS orbit history in addition to the predicted orbit. Please note that although HICO is no longer in operation, this page continues to be updated daily with current orbit information for the ISS. Note that orbit prediction accuracy decreases considerably with time. Please see below the figure for more information.
Tracks: Only those portions of the tracks during local daytime when the solar elevation was at least 15 degrees are shown. This is the time of day that HICO scenes could be collected. Tracks are shown in different colors for different days (GMT). The tracks vary in location and lighting each day - on some days, all tracks are descending (northwest to southeast), on other days they are all ascending (southwest to northeast), and the remaining days are a combination of both. The width of the track (in transparent grey) shows the area of the earth that was visible to HICO. Only targets within the grey area could be collected.
Dots: The yellow dots list the date and time that the ISS passes over that point on the earth.
Rectangles: If target areas are displayed, they are represented by rectangles. Targets can be seen in two different orientations, "ascending" (southwest to northeast) or "descending" (northwest to southeast). See the "HICO targets" section below for more information. The red rectangles designate targets that were in active use at the end of HICO operations (September 2014). Grey rectangles were inactive targets (no longer collected).
Available dates: Orbit prediction is limited here to six months in advance. Note that orbit prediction accuracy decreases considerably with time, and is only considered accurate for 2-3 days in the future. See the "ISS orbit details" section below for more information.
Orbital data: The orbits above are re-calculated daily using the most recent orbit information available. The orbital files used are TLE (two-line element) files. SpaceTrack provides accurate TLEs for the past and present (generated twice daily). NASA provides predicted TLEs for 14 days in the future (updated every two days). The orbits above are calculated using whichever TLE is closest in time to the day of interest. The accuracy of the orbit prediction decreases considerably with time. Although HICO is no longer in operation, the orbit information presented by this tool continues to be updated daily.
ISS orbit details
The International Space Station (ISS) orbital track travels from west to east. It takes approximately 90 minutes to complete each orbit, resulting in approximately 16 orbits per day. The location of the track for each orbit moves to the west as the earth rotates. It has an approximate orbital repeat of 3 days (and a 63-day lighting cycle). More information can be found in the NASA Space Station Orbit Tutorial.
The orbit has a 51.6o inclination - it only travels between 51.6 oN and 51.6 oS. Higher latitudes are not covered.
The altitude of the ISS varies over time, but is approximately 343 km above the earth's surface. Over time the ISS altitude drops due to atmospheric drag. Increased solar activity increases the drag. Reboosts are performed to adjust the orbit. More information on orbital decay can be found in the NASA Science News article "Solar S'Mores".
HICO has the ability to tilt to view targets on either side of the track. It can tilt 45 degrees to the left, and 30 degrees to the right. When the ISS is travelling in its standard forward orientation (+XVV), this means it can see 45 degrees to the north and 30 degrees to the south of the track. This view is represented by the transparent grey areas on the above figure. Occasionally the ISS travels in a backwards orientation (-XVV), in which case the view is offset from that shown above (it is instead 45 degrees to the south and 30 degrees to the north of the track).
Targets can be collected during ascending (SW to NE) and descending (NW to SE) orbits.
The location of the HICO targets can also be viewed from the "Targets" page.
HICO scene collection limitations
Because of downlink limitations on the ISS, only one HICO target scene could be collected per orbit.
Targets were only collected during local daytime when the solar elevation was at least 15 degrees. Targets were not collected at night.
Targets could not be collected during the HICO command window (19:00 - 21:30 UTC during daylight savings time, 18:00 - 20:30 UTC otherwise).
Page updated: March 20, 2015