RHESSI's Re-entry
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Figure 1 shows the predicted altitude via estimates made on Friday, April 15. | Figure 1 shows the predicted altitude via estimates made on Friday, April 15. | ||
| - | The actual time for this | + | The actual re-entry forecast time for this epoch was 20 April (Thursday) 00:05 +- 30 hours, |
but this number will improve as we get closer to the end. | but this number will improve as we get closer to the end. | ||
| - | The final stages of re-entry are uncertain because of unpredictable | + | The final stages of re-entry are uncertain in detail because of unpredictable |
fluctuations in the drag force from Earth's upper atmosphere. | fluctuations in the drag force from Earth's upper atmosphere. | ||
Revision as of 15:58, 15 April 2023
| Nugget | |
|---|---|
| Number: | 447 |
| 1st Author: | Pascal SAINT-HILAIRE, |
| 2nd Author: | Hugh HUDSON |
| Published: | April 17, 2023 |
| Next Nugget: | |
| Previous Nugget: | A Glasgow geomagnetic observation of a solar flare |
| List all | |
Introduction
Our inspiration for these Nuggets, the RHESSI went into orbit February 5, 2002, and observed the Sun successfully for many years. Finally the fate of any spacecraft in low Earth orbit has arrived: re-entry into the Earth's atmosphere.
Orbit predictions
Figure 1 shows the predicted altitude via estimates made on Friday, April 15. The actual re-entry forecast time for this epoch was 20 April (Thursday) 00:05 +- 30 hours, but this number will improve as we get closer to the end. The final stages of re-entry are uncertain in detail because of unpredictable fluctuations in the drag force from Earth's upper atmosphere.
Observability
The re-entry will suddenly interrupt RHESSI's final orbit. The imprecision of the exact time means that it could happen anywhere along the predicted orbital path, and the conservation of momentum means that the resulting fireball will trace out that path. Figure 2 shows some of the orbits, spaced approximately at 90-minute intervals and therefore about 23-degree spacings in longitude as the Earth rotates. One can see the that RHESSI's orbit was inclined to match the latitude of its ground station (at the [Space Sciences Lab] in Berkeley, California.
As with any re-entry, we expect that visual observations of the fireball will be possible for a very lucky observer. Ideally one would have clear skies, a dark night, and the great luck of having the just the right moment along the orbital track. Figure 3 shows the local area around Berkeley, where some RHESSI-lovers may be watching.
What will the observer see? Most elements have distinctive flame spectra colors, and germanium is light blue. As a speculation a lucky observer might see the last moments of the RHESSI detectors this way. This is very speculative, of course, as is the speculation that the tungsten grids (green), being massive, dense, and highly refractive, may even survive re-entry
| RHESSI Nugget Date | 17 April 2023 + |
| RHESSI Nugget First Author | Pascal SAINT-HILAIRE, + |
| RHESSI Nugget Index | 447 + |
| RHESSI Nugget Second Author | Hugh HUDSON + |
