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The ISS reaches out and touches Mars, transit on September 14, 2020

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#26 dcaponeii

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Posted 16 September 2020 - 09:42 AM

This is without doubt one of the most spectacular achievements I've ever seen by an amateur astronomer anywhere and anytime.  Very impressive.



#27 Adaptive_Optics

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Posted 16 September 2020 - 01:29 PM

Very cool, there is an earlier video of a Saturn "occultation" by the ISS:

 

 

https://www.youtube....h?v=tB76_hubraI



#28 Tom Glenn

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Posted 16 September 2020 - 01:40 PM

Thanks for all the responses so far everyone!  I'm definitely excited to share the result, because it was quite challenging to obtain this sequence, and I think represents a fairly rare and unique image.

 

 

That is very cool!  If you haven't already, forward it to over to the ISS folks.  I'm sure the astronauts and cosmonauts would love it.

It would be cool to have the folks on the ISS see it, although I don't actually know how to make that happen, other than submitting to APOD (which I did).

 

 

 

Very cool, there is an earlier video of a Saturn "occultation" by the ISS:

 

 

https://www.youtube....h?v=tB76_hubraI

Yes, I am familiar with Szabolcs's work, which is fantastic (definitely check out his website if you haven't).  



#29 Tom Glenn

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Posted 16 September 2020 - 02:29 PM

...........

I think one of the most interesting parts is you trying to figure out where to set up.  I imagine you poured over Google with Satellite view to try and find a reasonable location to image from that was not trespassing, in the middle of a road, and that you wouldn't likely get shot at 3:30 or 4 a.m. setting up.

...........

How did you pick your spot to set up and did you have anyone asking you what you were doing?

This was one of the greatest challenges.  The predicted ground path constantly changes by small amounts.  Even for a solar or lunar transit, these changes can alter your plans.  For a target like Mars, which is smaller in angular diameter than the ISS, the problem essentially becomes perfectly positioning the ISS itself, with almost no margin for error.  By studying the movement of a few other transit lines over time, I had noticed that the path appears to be more unstable shortly after a station keeping rocket burn, which is performed every so often to maintain altitude (although this is just anecdotal, I don't have any measurements to confirm this).  Fortunately, the last rocket burn had been performed several days prior, with no additional burns scheduled before the Mars transit (at least according to Calsky...I was at their mercy here!).  Nevertheless, the path did move.  In the three days leading up to the event, I had to scout several locations.  It is difficult to accommodate a 100m wide corridor, in the middle of the night/early morning, without trespassing.  I first scouted a YMCA parking lot, which would have been good, but then the transit line moved away from that.  Next up there was a series of two small parks that the line skirted, neither of which looked ideal (because of parking availability), but I was prepared to make it happen.  But the line moved again.  About 24 hours out, the line went through a high school parking lot.  Looked good.  But then it moved again, and I would have had to carry my gear into regions of the high school where I would have been trespassing.  Then, with 16 hours to go, the line passed through another park, that had convenient parking, a large field, and claimed to be open 24 hours per day (according to Google, although this is questionable!).  This looked perfect, so I scouted it out at about 6pm Sunday evening before sunset.  It looked really excellent.  Over the next 12 hours, I watched the line, and it moved from one side of the park to the other, about 200-300m.

 

I set my alarm for 3am, but I didn't sleep.  I had already packed the car earlier in the evening, so I was ready to go.  I had no idea what the conditions would be, or even which telescope or camera to use, so I brought everything.  If conditions looks really bad, I was going to use my 6" f/6 Newtonian, which would have much lower resolution, but would be faster, and could accommodate poor seeing or heavy smoke in the sky better.  I was hoping to use the C9.25 Edge though.  I also brought both the ASI224mc and the ASI183mm, not sure which to use until I saw the conditions.  I parked on the side of the road at the park (map below), and rechecked the transit line at 3:50am (using Calsky on my phone).  I setup in the baseball field directly on the transit line.  Note that the line depicted in the image changed after the fact, and so I wasn't exactly on this line (but rather on the "X").  Although neither was correct.  I placed a dotted line near where I think the true line would be, based on my image (this is just a guess though).  

 

Calsky_map_091420_TG.jpg

 

Starting at 3:50am until the transit at 5:15:47, there were a series of heart stopping events.  When I first showed up, the sprinkler system was on in the field!  Fortunately, the region I wanted to setup in looked like it had already been watered.  I hoped they weren't going to water again!  What a nightmare that would be!  So I set up my C9.25 Edge, because the sky was somewhat smoke free, and I decided to go big.  Transparency was poor, however, from the CA fires.  Mars was clearly visible, as were a few bright stars, but otherwise visibility was poor.  I couldn't see Polaris, for example.  

 

The next problem I encountered was that I was having trouble getting Mars on the ASI183mm sensor.  My finder scope had been knocked in the car and was useless.  With the clock ticking, this was exactly the sort of thing I didn't need!  Thankfully, my good friend the crescent Moon was just rising, and so I used this to find my focus and adjust the finder, and then I got Mars centered.  I decided at that point there was no way I was using my ASI224mc.  I needed the larger sensor for a margin of error.  As it turned out the ASI224mc would have worked and with a higher frame rate, but with lower resolution at f/10, and worthless color at 0.35ms.  I also wanted the sensitivity of the monochrome sensor, on which I did not use any filters.  Seeing looked "OK", but I wasn't worried about that.  I needed speed and sensitivity.  I wanted to limit motion blur to 1".  Given the radial velocity of the pass at about 2766"/s, I decided to use a shutter speed of 0.35ms.  Setting the gain was questionable.  I knew the ISS would be brighter than Mars (-4 versus -2 magnitude), but the specifics here of exposure are murky because of their difference sizes and the fact that the ISS has a few very bright spots.  I decided to expose Mars at 25% filled histogram (meaning the brightest pixels on Mars only register 25%).  This already required a gain of 66% available, at which point there would have been no benefit to going higher anyway (versus increasing in post).  This was pure guess work, but the exposure was perfect, given the limitations imposed by the shutter speed.  Shown below is the raw frame with the closest separation between the ISS and Mars.  This is downsized (original is 5496x1500), but is unprocessed.  Using information from the Firecapture log file and frame number and FPS, I can pinpoint the time stamp of the image to 05:15:46.788.  You will see from the Calsky map that the predicted time was 05:15:47.40 (PDT), so only 0.6s discrepancy.  

 

raw_frame_1186.jpg

 

I knew how to align the camera because the spacecraft trajectory is known, and I used a Mars simulated image so that I knew exactly what it would look like and its orientation at the time.  I then used Mars's terminator and Syrtis Major to align the camera so the ISS would pass from right to left through the long axis of the sensor.  Then it was just a waiting game, although I had to constantly adjust the hand controller for the CGEM mount to keep Mars centered, because I wasn't polar aligned (there had been no time for that, other than crude work with a compass).  I had a dreaded Firecapture "failure" error with 5 minutes to go that required a reboot.  This was heart attack inducing, but I got things reopened, setup, and rechecked focus and centered Mars with about 1 minute to go.  According to my log file, I started recording at 29s before the predicted transit.  At this point I glanced up, noticed the ISS flickering, just coming out of shadow.  It was much dimmer than I thought it would be, because of the smoke and the fact that it takes a bit of time to achieve full brightness.  Fortunately, as it quickly soared towards Mars it gained brightness, surpassing the brightness of Mars just before "impact".  I looked by naked eye until the two objects were very close, and then looked at the monitor, and saw it flash by!  It was awesome.  

 

And no, I didn't interact with anyone, or have the police called on me, or anything like that.  When I was taking down my equipment I did start to see some people running and walking in the park before dawn.  And a really big owl (probably great horned) flew right over me, totally silent.  Quite memorable.  


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#30 PhotonJohn

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Posted 16 September 2020 - 02:40 PM

THE BEE'S KNEE'S! Killer shot of all time. Tougher than hitting a missile with a sling shot. I'm not worthy! 



#31 descott12

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Posted 16 September 2020 - 03:17 PM

Quite the story! Murphy's law never fails to rear it's ugly head!



#32 santafe retiree

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Posted 16 September 2020 - 04:25 PM

DUDE!!!!!  Eff---ing AMAZING!!!!  The absolute coolest shot I have seen in my decades of this hobby.  The research, the planning, the choice of gear, the setup, the in the field drama and adrenaline pump -- and you kept your cool and GOT THE SHOT!!!!  Kudos, hats off, top marks, DANG!!!!    


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#33 Tulloch

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Posted 16 September 2020 - 04:35 PM

This was one of the greatest challenges.  The predicted ground path constantly changes by small amounts. 

Well, knowing the back story of how this image was created just enhances the quality for me - I had no idea it would be such an effort to position yourself so accurately to create the shot of the year, not just the shot of the day. Congratulations, just awesome bow.gif



#34 Tom Glenn

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Posted 16 September 2020 - 05:31 PM

Thanks for the additional comments and "likes" everyone.  I appreciate it.

 

 

I had no idea it would be such an effort to position yourself so accurately to create the shot

 

Yes.  In theory, if the orbit was defined with as much precision as that of the Earth, Moon, etc., then this would simply amount to being in the right place at the right time.  The only real obstacles that you would not be able to control would be the weather, and any unforeseen technical mishap with the equipment.  The element of timing is largely taken care of by high speed cameras recording video (minus the aforementioned technical mishaps that can happen).  But the orbit is not as well defined, because low-Earth orbits are unstable due to slight atmospheric drag.  If no station keeping rocket burns were performed, the ISS would gradually lower its altitude until it incinerated in Earth's atmosphere.  So the real wild card here is that you never really know how accurate the ground path will be, and it will sometimes make an unexpected jump of several hundred meters right at the last minute.  In which case you're out of luck.

 

So, I did have several elements of luck here.  Although I believe it was Louis Pasteur who said "Dans les champs de l'observation le hasard ne favorise que les esprits préparés."  In the fields of observation, chance favors only prepared minds.


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#35 jerobe

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Posted 16 September 2020 - 06:20 PM

Time for a figure of speech based on where you were positioned for the shot.  Even though you were out in left field, you knew exactly what you were doing.



#36 Jkaiser3000

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Posted 16 September 2020 - 06:36 PM

To keep with the figurative speech, you knocked it out of the park.

Seriously though, next time plan on the ISS to actually occult mars in the video, some shoddy planning if you ask me lol.gif

 

just kidding of course, Beautiful shot and beautifully executed bow.gif



#37 Tom Glenn

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Posted 16 September 2020 - 06:48 PM

To keep with the figurative speech, you knocked it out of the park.

Seriously though, next time plan on the ISS to actually occult mars in the video, some shoddy planning if you ask me lol.gif

 

just kidding of course, Beautiful shot and beautifully executed bow.gif

Haha!  Thanks!  I know you're kidding, but I do like that Mars isn't obscured in the image, and it creates a unique aesthetic result IMO.  At least part of the solar array is touching the planetary disk, so I consider that a success.  The error in path predictions is normally assumed to be at least one full diameter of the ISS, meaning that the chances of getting the central points of both objects aligned is basically zero.  Also at play is the frame rate.  Even if I had been on the true path, my frame rate of 41fps would have been sufficiently slow that it would be possible for Mars to be exactly in between two ISS images and not touch.  This is why I had initially considered using my ASI224mc, which can do 150fps, in which case images of the ISS would actually partially overlap.  However, as I mentioned in the earlier response, I had a number of reasons for choosing the ASI183mm instead.  


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#38 R Botero

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Posted 17 September 2020 - 03:04 AM

Tom

Your write up on the preparations and implementation to get the image only make it better! :bow: again. This will help others trying to emulate your achievement do their homework properly.

Roberto

#39 astrovienna

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Posted 17 September 2020 - 03:45 AM

Tom, thanks so much for undertaking the huge effort for this shot.  It never even would have occurred to me to try something like this.  I really appreciate your discussion of the preparations necessary to make this succeed.  It would make for a nice article for some publication, I'd say.

 

Kevin


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#40 KillGit

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Posted 17 September 2020 - 04:28 AM

fantastic!



#41 Tom Glenn

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Posted 17 September 2020 - 06:30 PM

Thanks for the additional comments folks.  I'm glad if even a few people liked the descriptions of the methods.  The real excitement of this type of imaging is the planning and preparation.  Of course, it's easy to say that when it works out, but I have had a few epic failures with ISS transits that don't get posted!



#42 moonwatching ferret

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Posted 17 September 2020 - 11:40 PM

very rare photo op that ones going in the gold file lol iwish i got that with my 16 incher at 21



#43 RedLionNJ

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Posted 18 September 2020 - 03:03 PM

Great story and superlative final images - surely a shoo-in for another APOD?

 

Wonderful, just wonderful.  A capture par excellence, Tom.



#44 dhammy

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Posted 18 September 2020 - 04:56 PM

Excellent Tom! I’m late to the party as on holiday but dropped in to see your fantastic image! Great write up showing how you put it all together too. Not easy and about a hundred things that could go wrong! Get that one framed :)



#45 Kokatha man

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Posted 18 September 2020 - 09:05 PM

What a feat! - congratulations for your amazing accomplishment here Tom..!!!  waytogo.gif waytogo.gif waytogo.gif waytogo.gif waytogo.gif



#46 Tom Glenn

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Posted 19 September 2020 - 06:09 AM

Joe, Grant, David, and Darryl, thanks for the additional kind words!  I truly appreciate it.  This was an epic case in which dozens of variables, any one of which could have easily doomed the mission, all converged towards success.  So I'll be riding high for a while.  Despite the small inaccuracies in ISS ground path predictions, I'm always amazed at how accurate these orbital projections are.  There was something magical about looking up at the sky, and seeing the spacecraft appear out of the darkness, going from nothing to magnitude -4 in 20s, exactly on cue, and streaming like a missile towards Mars.  

 

 

surely a shoo-in for another APOD?

 

As much as I'd like the honor, I don't think anything is guaranteed in those realms.  All I can say is that I feel that my image offers something very unique, and that is not easily replicated.  



#47 Tom Glenn

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Posted 22 September 2020 - 11:08 PM

Just an update, my ISS Mars transit image is today's APOD, September 23, 2020. 

 

https://apod.nasa.go...d/ap200923.html


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#48 Tulloch

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Posted 22 September 2020 - 11:13 PM

Just an update, my ISS Mars transit image is today's APOD, September 23, 2020. 

 

https://apod.nasa.go...d/ap200923.html

applause.gif applause.gif applause.gif applause.gif applause.gif applause.gif applause.gif



#49 santafe retiree

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Posted 22 September 2020 - 11:23 PM

Just an update, my ISS Mars transit image is today's APOD, September 23, 2020. 

 

https://apod.nasa.go...d/ap200923.html

bow.gifbow.gifbow.gifbow.gifbow.gifbow.gifbow.gifbow.gif



#50 astrovienna

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Posted 22 September 2020 - 11:48 PM

Congratulations Tom!  Well deserved.

 

Kevin




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