ORCAsat

Essentially ISS orbit, 420 km with inclination of 51.6 degrees.
Made heavens above account astrostubbs cat4heavens

Duty cycle of source:

Angular rate from ground at zenith: speed is roughly 2*pi*(6378+400)/90 min = 7.88 km/sec

At zenith height of 400 km the angular rate is 1.1 degrees/sec.

Angular extent of streak if sidereal tracking is 1.1 degrees/sec * 0.05 sec = 3.3 arcminutes and stars are PSFs.

Take 3 sec exposure to catch multiple pulses, set streak lengths equal. rate*3=(1.1-rate)*0.05. so 3*rate=1.1*0.05 - 0.05*rate, so 3.05*rate= 0.055 and rate=0.055/3.05 = 0.018 deg/sec = about 1 arcmin * (texp/3 sec)

Size of PSF in cross-track direction is D_telescope/Range, max is about 1.5/400e3 = 0.7 arcsec.
For Rubin the size would be around 4.5 arc at zenith

Trick is synchronizing pointing with ephemeris times.

Example ISS night-time pass over Pachon/Rubin:

Scintillation:

Goes as telescope diameter^0.66 so a 1m telescope has values 4.6 times smaller. That means a 50 msec source pulse vs. airmass would have

airmass. scint fraction

1.0000 0.0028
1.2000 0.0039
1.4000 0.0053
1.7000 0.0072
2.0000 0.0096
2.4000 0.0133
2.8000 0.0175
3.5000 0.0263

Conclusion- for a 1% measurement, scintillation is not a major factor for a 1m class telescope.

What about tracking the satellite? Angular rate would have to be around 1 degree/sec. Source is only on for 15 sec when at minimum zenith angle.

Nov 29 meeting with Justin Albert:

power and/or apparent magnitude? 14th or 15th

orientation knowledge? around a degree. That means rea

power to run over 5 minutes?

Knowledge of phase of on/off cycle? partial

stability of output vs. time as things warm up?

output duration is around 15 seconds per rev, but not entirely clear.

33 kbytes of downlink data per day.

Laser diodes =>

660 110 mW

840 nm 150 mW

dispersed stuttered imaging for background subtraction?

Does it have a GPS receiver on board for realtime TLEs?

Dec 1

link to information about Plaskett telescope:
https://webcache.googleusercontent.com/search?q=cache:fa5W7FLLqOoJ:https://ws-sf.canfar.net/transfer/bmVpZ2g9U0ZVJnNpZ2V4cD0yMDIyMTEyOTAwMTk1MyZhcmM9Vk9TcGFjJmlkPTIxODcxNDQ4MCZ1c2VyPWFub25Vc2VyJm5zPURBTyZtZXRoPWdldCZhdXRoQ29kZT0wJnJ1bklEPWl0OHRkYnNjaDlzYjdxZ3omdXJsPWh0dHAlM0ElMkYlMkZzdG9yLXNmLTAzLmNhbmZhci5uZXQlM0E4ODg4JTJGYXJjaGl2ZSUyRjA1ZWNmNTQ4JTJGMTE3MCUyRnZvc3BhYyUyRmRlZmF1bHQlMkZkZWZhdWx0JTI1NUYwMzYyJTJGMDAlMkYwNyUyRjM3JTJGMjE4NzE0NDgwJTI1M0IlMjUzQjIxNjkwNzUyMw%3D%3D-ZmlkPWRhbzcyLmh0bWwmY2xuPTMyNTkzJmNtZD1kZDI5ODI0MDI4M2YzYTVhZWUwNDNlZjI0ZWVhZmRkNSZsbWQ9MTQxNjg2MzA1MTc1Mw%3D%3D-ee62249fbb72002b99d209d6b7290daf/dao72.html&cd=1&hl=en&ct=clnk&gl=ca&client=safari

filters are 75mm x 75..

TLE to RA DEC:

https://www.satellite-calculations.com/TLETracker/SatTracker.htm

also https://evdc.esa.int/orbit/

LSST coordinates are -70:44:57..876 long and lat -30:14:40.6608

Analysis:

We get about 25 flash sequences in each pass (600 msec period, on for 15 sec).
No chance to get atmospheric extinction from zenith dependence. We get a monochromatic magnitude at two wavelengths, with partial overlap.
Aux Tel dispersed imager is an interesting option. Take dispersed images through longpass filter to avoid order contamination from stars.
We can indirectly tie GAIA spectrophotometric zero point to ORCA fluxes, using spectra from AuxTel and GAIA, I think.