This page (revision-7) was last changed on 07-Dec-2016 14:14 by David R Williams

This page was created on 16-May-2007 13:04 by David R Williams

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6 11-May-2010 12:39 3 KB David R Williams to previous | to last
5 16-Mar-2010 15:38 3 KB PeterYoung to previous | to last
4 19-May-2009 11:31 2 KB David R Williams to previous | to last
3 16-May-2007 13:14 2 KB David R Williams to previous | to last
2 16-May-2007 13:12 2 KB David R Williams to previous | to last
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At line 1 changed one line
When Hinode goes into eclipse, the pointing mode changes from gyros-plus-UltraFineSunSensors to gyro only (because it can't see the Sun any more!). In this case, there was prediceted to be a drift in the pointing. This gets corrected some time after Hinode comes out of night.
!!!Eclipse Effects
At line 3 changed one line
In the one case i've looked at where a mode change occurs (from gyro to gyro+ufss), the repoint takes of order 15 seconds. This was taken from the shift seen in 20070509_074627, a HH---N03 raster, with nominal 5 second cadence (more like 6-and-a-bit). This repoint happened between 07:53:27.275 (expo start time, admittedly) and 07:53:47.117 (expo start time). The corresponding NGT_EXIT happened at 07:45:30, so there is just over 8 minutes until the repoint due to mode switch. Since the few datasets I've looked at so far (all from the same date, from the merged telemetry) indicate that EIS twilight isn't over until about 10 minutes after NGT_EXIT, this repoint delay is not such a worry for us. The bigger worry is the length of night, including twilight, which cannot easily be calibrated out.
!!What happens when Hinode goes into and comes out of night
At line 5 added 11 lines
!1. There is ''Hinode night'' and ''Hinode twilight''!
The Earth appears bigger to EIS than to the other two instruments on ''Hinode'' because of the EUV attenuation of the Earth's atmosphere (be thankful for it). So we see longer "night times" than the Orbital Event file (obev...) indicates. In fact, we have to factor in about ten minutes before the official NGT_ENTRY and the same after the NGT_EXIT in those files to take account of the period when EIS suffers the effects of the Earth's atmosphere. ''Night proper'' typically lasts about 17 minutes, but factor in the ingress and egress ("twilight" times), and the whole thing last for about 24 mins each orbit (''i.e.'', quarter of the orbit). And that's based on the first couple of days for which NGT events were predicted. These figures may evolve.
!2. Pointing mode
When ''Hinode'' goes into "eclipse", the pointing mode changes from gyros-plus-UltraFineSunSensors to gyro only (because it can't see the Sun any more!). In this case, there was prediceted to be a drift in the pointing. This gets corrected some time after Hinode comes out of night.
In the __one__ case I've looked at where a mode change occurs (from gyro to gyro+ufss), the repoint takes of order 15 seconds. This was taken from the shift seen in eis_l0_20070509_074627.fits, a HH---N03 raster, with nominal 5-second cadence (more like 6-and-a-bit). This repoint happened between 07:53:27.275 (expo start time, admittedly) and 07:53:47.117 (expo start time). The corresponding NGT_EXIT happened at 07:45:30, so there is just over 8 minutes until the repoint due to mode switch.
Since the few datasets I've looked at so far (all from the same date, from the merged telemetry) indicate that EIS twilight isn't over until about 10 minutes after NGT_EXIT, this repoint delay is not such a worry for us. The bigger worry is the length of night, including twilight, which cannot easily be calibrated out.
This page (revision-7) was last changed on 07-Dec-2016 14:14 by David R WilliamsTop