# Upcoming DSLWP-B Moon occultations

In my previous post I showed that during the DSLWP-B observation on 2018-10-27 17:20 UTC, the orbit of DSLWP-B would take it behind the Moon. This doesn’t happen every orbit (read as every day, since the orbit period is around 22 hours). It depends on the angle from which the orbit is viewed from Earth, and hence on the lunar phase.

Knowing beforehand when DSLWP-B will hide behind the Moon allows to perform radio occultation studies. These consist in measuring the RF signal from DSLWP-B as it gets blocked by the lunar disc. Interesting phenomena such as diffraction can be observed.

I have calculated the occultations that will be visible from the Dwingeloo radiotelescope in the remaining part of this year.

To calculate the occultations I use the contact locator in GMAT. This tool generates a list of the periods when the spacecraft will be visible from a given groundstation, taking into account blocking by astronomical bodies such as the Moon. This doesn’t give the occultation periods explicitly. An observation window breaks into two segments as the spacecraft hides and reappears behind the Moon.

The idea is thus to process the output of the contact locator with Python and compare the ending time of an observation window with the beginning of the next one. If the time difference is short, then an occultation has happened. It if is long, then it is just because the Moon has set in Dwingeloo and we need to wait around 13 hours to see it again.

The GMAT script can be found in dslwp_occulations.script and the Jupyter script to process its output is here. The results are the following:

```2018-10-30 09:58:21.209 --- 2018-10-30 10:25:59.668
2018-10-31 07:22:01.275 --- 2018-10-31 07:45:38.106
2018-11-01 04:44:57.579 --- 2018-11-01 05:02:42.190
2018-11-02 02:11:21.047 --- 2018-11-02 02:12:59.662
2018-11-06 12:44:43.693 --- 2018-11-06 13:23:19.613
2018-11-07 10:05:22.057 --- 2018-11-07 11:28:49.040
2018-11-19 15:49:49.037 --- 2018-11-19 16:28:06.893
2018-11-23 04:54:04.355 --- 2018-11-23 05:30:16.488
2018-11-24 02:16:22.270 --- 2018-11-24 02:49:01.205
2018-11-24 23:39:53.318 --- 2018-11-25 00:09:42.339
2018-11-25 21:03:31.502 --- 2018-11-25 21:31:30.765
2018-11-29 10:21:47.946 --- 2018-11-29 10:52:16.227
2018-11-30 07:36:10.530 --- 2018-11-30 08:10:39.004
2018-12-01 04:49:17.434 --- 2018-12-01 05:30:35.754
2018-12-17 21:25:36.664 --- 2018-12-17 22:14:11.025
2018-12-18 18:44:18.173 --- 2018-12-18 19:26:16.703
2018-12-19 16:02:54.214 --- 2018-12-19 16:39:24.685
2018-12-23 05:26:21.937 --- 2018-12-23 05:53:34.464
2018-12-24 02:48:48.456 --- 2018-12-24 03:16:34.352
2018-12-25 00:09:56.572 --- 2018-12-25 00:39:35.818
2018-12-25 21:28:46.338 --- 2018-12-25 22:01:41.686
2018-12-30 07:39:06.592 --- 2018-12-30 08:32:19.181
2018-12-31 05:07:55.443 --- 2018-12-31 05:38:54.256
```

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