Author Topic: ISS missed total eclipse shadow by only 15 seconds. Why no cubesat ejected?  (Read 4652 times)

Offline Holger Isenberg

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How bad luck is that? This was the closest the ISS ever came to a total solar eclipse and they missed it by 15 seconds! The totality would have been also only about 15-30 seconds for the crew as that's the time it takes for the station to cross the 200km wide totality band. But this raises a few questions: Why wasn't a small cubesat ejected from the station to observe from inside the shadow?

Eclipse ground track for Google Earth:
http://xjubier.free.fr/en/site_pages/solar_eclipses/TSE_2024_GoogleMapFull.html

ISS ground track:
https://www.heavens-above.com/gtrack.aspx?satid=25544&mjd=60408.8148698257&lat=46.1251&lng=-67.8408&loc=Houlton&alt=0&tz=Moroc

Eclipse and ISS track 3d interactive viewer:
https://eyes.nasa.gov/apps/solar-system/#/sc_iss?rate=0&time=2024-04-08T19:33:00.000+00:00

I waited with this posting after a few pictures from the ISS had been published to confirm the ground track. Photos from their on-board Nikon Z9 which have been brought to the station in February 2024 are available on
https://www.flickr.com/photos/nasa2explore/53643867905/in/album-72177720316098512
« Last Edit: 04/14/2024 08:11 pm by Holger Isenberg »

Offline mn

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How bad luck is that? This was the closest the ISS ever came to a total solar eclipse and they missed it by 15 seconds! The totality would have been also only about 15-30 seconds for the crew as that's the time it takes for the station to cross the 200km wide totality band. But this raises a few questions: Why wasn't a small cubesat ejected from the station to observe from inside the shadow?

Eclipse ground track for Google Earth:
http://xjubier.free.fr/en/site_pages/solar_eclipses/TSE_2024_GoogleMapFull.html

ISS ground track:
https://www.heavens-above.com/gtrack.aspx?satid=25544&mjd=60408.8148698257&lat=46.1251&lng=-67.8408&loc=Houlton&alt=0&tz=Moroc

Eclipse and ISS track 3d interactive viewer:
https://eyes.nasa.gov/apps/solar-system/#/sc_iss?rate=0&time=2024-04-08T19:33:00.000+00:00

I waited with this posting after a few pictures from the ISS had been published to confirm the ground track. Photos from their on-board Nikon Z9 which have been brought to the station in February 2024 are available on
https://www.flickr.com/photos/nasa2explore/53643867905/in/album-72177720316098512

It would possibly make for some cool pictures, but if you are seriously asking why NASA didn't do this you have to tell us what would have been the scientific value?

Edit: Additionally, deploying a cubesat would not make it magically stop in orbit so it could observe the eclipse, how much deltaV would you need to get from the ISS to a stable position inside the totality? Could a deployment mechanism supply sufficient force (and ensure it flies in an exact straight line to get to the right position)? Or would it need a cubesat with propulsion and navigation, starting to sound like not such a trivial matter.
« Last Edit: 04/14/2024 09:25 pm by mn »

Offline sdsds

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The trade-off to consider is whether an ISS-launched cubesat could provide anything more than a payload launched on a sounding rocket.
— 𝐬𝐝𝐒𝐝𝐬 —

Offline Holger Isenberg

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whether an ISS-launched cubesat could provide anything more than a payload launched on a sounding rocket.

It can, because soundings rockets don't reach 400 km altitude.

Offline Holger Isenberg

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It would possibly make for some cool pictures, but if you are seriously asking why NASA didn't do this you have to tell us what would have been the scientific value?

Edit: Additionally, deploying a cubesat would not make it magically stop in orbit so it could observe the eclipse, how much deltaV would you need to get from the ISS to a stable position inside the totality?

Why? The most important reason is that no good quality photo exists of the corona seen from space.

About required deployment deltaV from the ISS: Walking speed is completely sufficient when ejecting a few days before the eclipse :)
Which means just simple batteries would have been sufficient to power them for that short time.

https://humans-in-space.jaxa.jp/en/biz-lab/experiment/facility/ef/jssod/ lists the commercially available magical deltaVs available for common cubesat sizes: 0.77 - 1.7 m/s (walking speed) which easily covers the 200 km in 3 - 10 days. Also good to see how cubesats are currently always ejected rearwards, what would have been a perfect match as the ISS was 15 - 30 seconds ahead of the eclipse.

Offline mn

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It would possibly make for some cool pictures, but if you are seriously asking why NASA didn't do this you have to tell us what would have been the scientific value?

Edit: Additionally, deploying a cubesat would not make it magically stop in orbit so it could observe the eclipse, how much deltaV would you need to get from the ISS to a stable position inside the totality?

Why? The most important reason is that no good quality photo exists of the corona seen from space.

About required deployment deltaV from the ISS: Walking speed is completely sufficient when ejecting a few days before the eclipse :)
Which means just simple batteries would have been sufficient to power them for that short time.

https://humans-in-space.jaxa.jp/en/biz-lab/experiment/facility/ef/jssod/ lists the commercially available magical deltaVs available for common cubesat sizes: 0.77 - 1.7 m/s (walking speed) which easily covers the 200 km in 3 - 10 days. Also good to see how cubesats are currently always ejected rearwards, what would have been a perfect match as the ISS was 15 - 30 seconds ahead of the eclipse.

I don't know the math involved and perhaps this is as easy as you describe, but I have a hard time imagining deploying something with enough accuracy that it can free float for a few days and hit a target location with 15-30 second accuracy.

Perhaps it is actually easy and routine? I honestly have no idea.
« Last Edit: 04/15/2024 12:59 am by mn »

Offline Holger Isenberg

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I don't know the math involved and perhaps this is as easy as you describe, but I have a hard time imagining deploying something with enough accuracy that it can free float for a few days and hit a target location with 15-30 second accuracy.

It's relatively simple. And to increase the chance to be in the shadow, just launch a few more. It's even not that precise aiming necessary as the shadow area has 200km diameter.

Offline DaveS

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whether an ISS-launched cubesat could provide anything more than a payload launched on a sounding rocket.

It can, because soundings rockets don't reach 400 km altitude.
They can, here's one routinely that is lauched from Wallops. Maximum payload to a 550 km trajectory is 136 kg or 300 lbm: https://sites.wff.nasa.gov/mpl/w_blackbrantix.html

Black Brant X and XII can do about same to twice the altitude.
« Last Edit: 04/15/2024 04:35 am by DaveS »
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Offline Jim

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whether an ISS-launched cubesat could provide anything more than a payload launched on a sounding rocket.

It can, because soundings rockets don't reach 400 km altitude.

That would be wrong.

Offline Jim

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Why? The most important reason is that no good quality photo exists of the corona seen from space.


Sounding rockets can do that better and more often if there was need. 
Looks like cubesat is not worth the effort.

Offline Holger Isenberg

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Sounding rockets can do that better and more often if there was need. 

So we have a good quality photo of the corona taken in space already? Or was it taken with one of the 3 rockets launched during this eclipse?

Offline Holger Isenberg

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Black Brant X and XII can do about same to twice the altitude.
Nice! Looking forward to the pictures!

Offline Holger Isenberg

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For those in doubt about scientific value of observing from inside the eclipse shadow above the atmosphere, check out what effort NASA invested for a flight of the old timer WB-57 aircraft through the higher atmosphere, not even in or above the ionosphere: https://science.nasa.gov/solar-system/skywatching/scientists-pursue-the-total-solar-eclipse-with-nasa-jet-planes/

Offline mn

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For all the discussion I think it is worth linking to a photo of the corona (taken from earth) during an eclipse.

https://apod.nasa.gov/apod/ap240402.html

Online DanClemmensen

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There is no particular magic about the eclipse being viewed from space while it is happening on Earth.  There is a locus of points (the path of a point directly away from the Sun from the Moon and varying in distance around 384,000 km from the moon) Where the Moon is exactly occulting the Sun.  If you can figure out a way to put a spacecraft at that point, it will see an eclipse. This point hits the Earth every once in a while, so please do not bonk your spacecraft into the Earth.

Offline mn

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There is no particular magic about the eclipse being viewed from space while it is happening on Earth.  There is a locus of points (the path of a point directly away from the Sun from the Moon and varying in distance around 384,000 km from the moon) Where the Moon is exactly occulting the Sun.  If you can figure out a way to put a spacecraft at that point, it will see an eclipse. This point hits the Earth every once in a while, so please do not bonk your spacecraft into the Earth.

That is a good points, the moon passes in front of the sun every month, if we want to put a spacecraft in the right place we can have an eclipse whenever we want.
« Last Edit: 04/15/2024 10:25 pm by mn »

Offline Holger Isenberg

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With that, only the photo(s) taken by Jim Lovell and Buzz Aldrin from Gemini 12 in 1966 remain the only pictures of a total solar eclipse seen in space where the eclipse was created by the Moon: https://www.astronomy.com/space-exploration/57-years-ago-first-solar-eclipse-from-space

But with low quality as the Sun was close to their local visual horizon above Earth.

While during Apollo 12 a total eclipse was observed as well, it was created by Earth which produced a more fuzzy outline effect due to its atmosphere: http://www.collectspace.com/news/news-081617a-total-solar-eclipse-from-space-astronauts.html

Offline 1

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Even at the cubesat level, your resources are better spent on a mission that can function for weeks or months (or longer) rather than minutes or seconds.

Besides, the ESA's been working on PROBA-3 for years; and that'll likely do everything you want and more. Your attention is probably better spent elsewhere instead of worrying about eclipse-chasing cubesats.

Offline Holger Isenberg

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Besides, the ESA's been working on PROBA-3 for years; and that'll likely do everything you want and more.

https://en.wikipedia.org/wiki/PROBA-3
That looks like an interesting concept and would even provide more insights than photopgraphy from LEO with being able to simulate an eclipse in high orbit of 60000 km radius. Unfortunately they "forgot" the blue channel as the camera's spectral sensitivity begins at 540nm.

Offline Orbiter

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whether an ISS-launched cubesat could provide anything more than a payload launched on a sounding rocket.

It can, because soundings rockets don't reach 400 km altitude.

Why does a cubesat 400 km up have an obvious beneft over a sounding rocket going 100 km up for a 4-minute event?
« Last Edit: 04/15/2024 11:23 pm by Orbiter »
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