Re: Possibility of JWST flares and antiflares?

From: Marshall Eubanks via Seesat-l <>
Date: Thu, 06 Jan 2022 17:28:30 -0500
Here is a movie from the University of Hertfordshire Observatory

and a plot of magnitude changes.

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.


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
Received on Thu Jan 06 2022 - 16:30:44 UTC

This archive was generated by hypermail 2.4.0 : Thu Jan 06 2022 - 22:30:44 UTC