UmbralRaptor changed the topic of #kspacademia to: https://gist.github.com/pdn4kd/164b9b85435d87afbec0c3a7e69d3e6d | Dogs are cats. Spiders are cat interferometers. | Космизм сегодня! | Document well, for tomorrow you may get mauled by a ネコバス. | <UmbralRaptor> egg|nomz|egg: generally if your eyes are dewing over, that's not the weather. | <ferram4> I shall beat my problems to death with an engineer. | We can haz pdf
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<egg|laptop|egg>
raptop: hm, given that KSP can’t really model attitude concerns wrt imaging pointing, how much does FoV matter
<egg|laptop|egg>
I feel like it should, somehow, but I have trouble figuring out how
<egg|laptop|egg>
it clearly does for pushbroom width so there’s that
<egg|laptop|egg>
I guess you have to force planetary surface imagers to point to the nadir?
<raptop>
egg|laptop|egg: more in a "we assume that pointing is handled correctly, but some missions have defactor or actual FoV requirements"
<raptop>
eg: if you want full frame images of a planet, there's a minimum distance
<egg|laptop|egg>
yeah
<raptop>
Also smol FoV for a survey means it takes longer
<egg|laptop|egg>
raptop: but if pointing is abstracted away too much, you can take full-frame images of Earth with an HST-like in LEO, by spinning it to scan,
<raptop>
This is also a way to backdoor in how really large FoVs often require doing weird things to the optics, so you might get low effective aperture, or high costs
<egg|laptop|egg>
s/LEO/GEO/ the horizon is a thing
<galois>
egg|laptop|egg meant to say: raptop: but if pointing is abstracted away too much, you can take full-frame images of Earth with an HST-like in GEO, by spinning it to scan,
<raptop>
Ah, guess the options require more abstracting than I thought?
<egg|laptop|egg>
basically, a narrow FoV is a wide FoV if you allow for truly arbitrary shenanigans with attitude
<egg|laptop|egg>
see SEVIRI, which does full-disk GEO by literally being on a spinning sat
<raptop>
attitude and time!
<egg|laptop|egg>
true
<raptop>
Also see WFSE, which did all-sky surveys by spinning and waiting for Earth to move about its orbit
<raptop>
*WISE
<raptop>
IITC
<raptop>
*IIRC
* raptop
stabs fingers
<egg|laptop|egg>
right, but I think scanning by orbital motion and scanning by actually moving the spacecraft or bits thereof should be seen differently
<egg|laptop|egg>
I would imagine the correct abstraction for a SEVIRI-like instrument is that it has a wide FoV, since the spin-scannability is baked into its design
<egg|laptop|egg>
and then you would actually forbid doing that with an HST probably
<egg|laptop|egg>
which means, since you cannot model attitude, that everything that images a surface points towards the body centre?
<egg|laptop|egg>
and then if you point HST towards Earth your swath is minuscule unless you are very very far
<raptop>
The todo totally gives you an eggscuse to use Janskys
<raptop>
And yeah, if we care about UV vs visible vs IR, we need the different quantities
<raptop>
...oh, irradiance as in reflected sunlight
<raptop>
oh no
<raptop>
This means we need to consider geometric and/or bond albedo
<raptop>
I'll need some clarification on the irradiance, because I'm unclear on that πd²/4
<raptop>
Resolution stuff seems good
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<egg|laptop|egg>
raptop: the πd²/4 is just the area of the telescope aperture
<egg|laptop|egg>
(the assumption being that all the energy that gets into the telescope reaches the detector
<egg|laptop|egg>
)
<raptop>
Ah
<egg|laptop|egg>
raptop: but mostly the questions are: what is the energy that the CCD needs to detect a thing?
<raptop>
That varies weirdly with the type of instrument from "eh, close enough" to "laughably wrong"
<egg|laptop|egg>
hah
<raptop>
Uh, depends somewhat on the CCD, but in some cases it's "one photon"
<egg|laptop|egg>
right, to detect
<egg|laptop|egg>
but well, here to meaningfully observe
<raptop>
Like, directly imaging on a system with few optical elements is close enough. But polarimetry or high resolution spectroscopy (especially EPRV shenanigans)...
<egg|laptop|egg>
e.g. say you have a sky survey that goes to nth magnitude, what energy do you get from an nth magnitude star on the surveying instrument
<egg|laptop|egg>
also, re. resolution, how does that work when not diffraction limited
<egg|laptop|egg>
limited by sensor resolution I suppose? what is a sane value for that?
<raptop>
Yeah, and I'd have to run some numbers/double check, respectively
<raptop>
(re resolution)
<raptop>
For what counts as a detection, typically some SNR. I, er, would want to skim a few data release documents (SDSS, 2MASS, IRAS, WISE, whatever) for typical values
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<kmath>
<bsgaudi> ps. I've been told that we shouldn't use acronyms. It's the Roman Space Telescope or just Roman for short. You know, kinda like Madonna.
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<_whitenotifier-d13c>
[Principia] pleroy closed issue #2583: The flight plan should surface unexpected statuses - https://git.io/Jfz8L
<_whitenotifier-d13c>
[Principia] pleroy pushed 12 commits to master [+6/-6/±45] https://git.io/Jfaq2
<_whitenotifier-d13c>
[Principia] pleroy e1f3731 - Generated files before the change.
<_whitenotifier-d13c>
[Principia] pleroy 847787a - Journal and C# changes.
<_whitenotifier-d13c>
[Principia] pleroy 7957b14 - Const the returned pointers.
<_whitenotifier-d13c>
[Principia] ... and 9 more commits.
<_whitenotifier-d13c>
[Principia] pleroy opened pull request #2589: Use the Status message in the exceptions returned from the external interface - https://git.io/Jfaq5
<raptop>
uh, this makes some unrelated speggtrograph, CCD well depth, and fudge factor assumptions
<raptop>
We probably don't need to consider how read noise makes co-adds less effective than they should be?
<raptop>
Ah, more generally signal / sqrt(sum of various noise sources)
<raptop>
poisson noise means that signal shows up under the square root (so even with a perfect detector, SNR is signal/sqrt(signal) or just sqrt(signal))
<raptop>
the noise sources (I have read and dark current) get added in quadrature
<raptop>
I'm missing sky noise there because it's assuming vaguely bright stars
<raptop>
This is not safe for sufficiently faint point sources, eggstended objects, and areas with lots of sky glow (which may mean zodical light)
<raptop>
hrm
* raptop
opens several teggstbook pdfs to check
<raptop>
Incidentally, I'll be amused if this ends up including the Planck function somewhere for getting detection requirements in various wavelength ranges for self-luminous bodies
<egg|laptop|egg>
raptop: hm
<egg|laptop|egg>
so, a lot of those things we ought likely make constant (any CCD properties, we don’t want to model that)
<egg|laptop|egg>
the one variable that I can think of is temperature which we might be able to model somewhat ?
<egg|laptop|egg>
(and which determines mission constraints)
<raptop>
rabbit hole suggestion: vaguely model those properties, with lower noise and higher resolution options available at later dates
<raptop>
But it's entirely possible that we'd want to skip that, and do sqrt(photons)
<raptop>
So detector temperature would just be "you must be this cool to observe that wavelength"?
<raptop>
Also, I like how you did bolometric magnitudes to avoid having to choose between AB, Vega, and more exotic systems
<egg|laptop|egg>
should temperature really work as a hard threshold, or should a warmer instrument work at a degraded sensitivity
<egg|laptop|egg>
raptop: yes I started looking at magnitudes, screamed, and then used the IAU resolution
<egg|laptop|egg>
the IAU resolution will be with you, always
<raptop>
Depends on how much we're simulating eg: cooling
<raptop>
note to self: borrow チルノ so you don't need to mess around with helium tanks or hydrogen ice
<SnoopJeDi>
raptop, TIL 「ドストライク」
<SnoopJeDi>
neat little idiom
<raptop>
SnoopJeDi: oh?
<SnoopJeDi>
I saw it in a tweet where I think it was used in the "this is exactly my kind of thing" sense
<SnoopJeDi>
it was ドストライクな there
<SnoopJeDi>
vocab of the rest of it was ofc a bit beyond me but I happened to check out the katakana
<SnoopJeDi>
MS translate does predictably poorly with it and turned it into "dstrike"
<kmath>
<DACIWEI1991> love citing "unpublished manuscripts" and "private communications" despite being very aware of plenty of publicatio… https://t.co/nYkKvLnO37
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<WeylandsWings>
UmbralRaptop: that can be a good way of getting peoples name into the doc without giving them authorship