wkitty42 has it right. While I understood the orbit, I didn't fully understand the relationship between the bus and the telescope. So, any flare prediction will need to know where the -V3 axis is pointing. If it's within a degree of half the angle between -V3 and the barycenter of Earth, there's a good chance for flares. The orbit is shown in detail here, Figure 1: https://jwst-docs.stsci.edu/jwst-observatory-characteristics/jwst-orbit The bus axes are shown here, Figure 1: https://jwst-docs.stsci.edu/jwst-observatory-hardware/jwst-telescope How the vehicle will tilt while on orbit around L2 is shown here, specifically Figure 3: https://jwst-docs.stsci.edu/jwst-observatory-characteristics/jwst-observatory-coordinate-system-and-field-of-regard So, flare prediction will need to take into account the orbital position of the vehicle plus its angle to the sun, which is a lot easier than all of the physics which I first thought would be involved. Perhaps there's a way to get the project office to publish when -V3 will match those conditions: there's still a lot of time-sensitive data and motion planning which aren't readily accessible. John On 1/6/2022 16:28, Marshall Eubanks via Seesat-l wrote: > Here is a movie from the University of Hertfordshire Observatory > _at_BayfordburyObs > > https://twitter.com/BayfordburyObs/status/1479085057126158341 > > and a plot of magnitude changes. > > https://twitter.com/BayfordburyObs/status/1479091173234987011 > > Note around 23:30 there is a > 1 magnitude change up and down in about > 9 minutes. I'd guess that this is a spot (glint) moving under the > rotation of the spacecraft. > > Regards > Marshall > > > > On 2022-01-06 14:31, wkitty42--- via Seesat-l wrote: >> On 1/6/22 1:00 PM, John A. Dormer 2 via Seesat-l wrote: >>> I think it necessary to know the approximate total mass of JWST and >>> either the mass of the sunshield side, below the rotation points >>> used in a particular pointing, or the mass of the telescope above >>> the same rotation points. >>> >>> The ratio between the masses will affect how much the sunshield >>> moves when the telescope points. Only the moving mass will affect >>> the orientation of the sunshield. Think "conservation of angular >>> momentum." Lever moments will be important, too. High precision >>> would also contemplate the history of movements up to the time that >>> a new calculation is performed. >>> >>> The mass of the sunshield side will change with time as fuel is >>> used, and knowing the percentage of sunshield mass this makes up >>> will determine how important this is in any calculations. There is >>> also a great deal of importance to how the burns will be used to >>> correct the sunshield's orientation over time. >> >> it took some hunting and quite a few attempts to formulate search >> terms that would return what i was looking for... i was finally able >> to find the following... >> >> [quote] >> The telescope axis is fixed relative to the shield. However the shield >> is sufficiently big that the entire JWST can tilt forward 5º and back >> 45º, and 5º side to side before the angle to the sun is too close. It >> can of course rotate a full 360º around its z axis. Overall it can see >> about 35% of the sky at any one time, and over the course of the year >> the full extent. There are two tiny patches of sky it can see all year >> around without issue. >> [/quote] >> >> from this and other information, it seems to me that the sun shield >> will always be between the telescope and the sun/earth/moon... i've >> not found anything, in layman's terms, that says how much the shield's >> perpendicular angle may change with regard to the direct line from the >> sun to L2... it may change some but my understanding is that the >> alignment system (reaction control wheels?) will keep it within a few >> degrees of perpendicular and will move to return it to the optimum >> positioning for best protection of the scope and instruments... >> >> if we see flares, i expect they will be fairly steady for long periods >> of time and not like the fast brightening and dimming flares we see >> from ISS and other satellites... granted, it takes only a little bit >> of movement (fractional degrees at this range?) to redirect the "beam" >> of reflected light slightly off of the earth and those of us looking >> at the scope... i am but a layman, though... this topic is very >> interesting to me and i shall keep reading and learning with intrigue >> and much interest... > _______________________________________________ > Seesat-l mailing list > http://mailman.satobs.org/mailman/listinfo/seesat-l _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-lReceived on Thu Jan 06 2022 - 17:24:46 UTC
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