These plots show the time history of ASCA's orbital parameters throughout the mission. These values are taken from the "orbit file" used to generate the filter (mkf) files. The X-axis labels are taken from that file's column names and have the following meanings:
| Name | Units | Description |
|---|---|---|
| A | km | Semi-major axis length |
| T | minutes | Orbital period |
| E | - | Eccentricity |
| I | degrees | Inclination |
| AN.DOT | degrees/day | Time derivative of ascending node |
| AP.DOT | degrees/day | Time derivative of argument of perigee |
The monthly oscillation of the parameters is due to lunar perturbations. The steepening of the orbital decay around 1998 is due to the approaching solar maximum, which expands the Earth's outer atmosphere (c.f. NOAO's sunspot count rates). For reference, the equatorial radius of the Earth is 6,378 kilometers.
Recent (1998 December) estimates predict reentry in 2000 February, if the upcoming solar maximum is similar to the last one. Reentry could be as early as 1999 November or as late as 2000 August, if the upcoming maximum is stronger or weaker than the last, respectively.
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