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Strange observations - only one person noted its trajectory across the sky (south/north through named constellations) and only one the time. Quoting same as you or whatever doesn't count. Some timed pics please eg just basic stuff otherwise it remains hearsay:-)

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What a fun mystery. Good luck! Be sure to use only a handheld phone with camera to record and digitally zoom in and out multiple times and cause your autofocus to go wacky for half the video.

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what speed does the x-37 do in low orbit? if that is even known?

there will be no records for its activitys available.

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what speed does the x-37 do in low orbit? if that is even known?

there will be no records for its activitys available.

Speed in orbit will be determined by height and mass.

Wikipedia gives its orbital speed as 28,000Km/h

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Read Mike's excellent post, then read it again. Most stuff is in LEO and what isn't is moving much slower (or apparently not at all) relative to our vista. I see such events sometimes here. It's the Army playing in their Apaches.

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How intriguing I saw a similar thing about 10pm (ish) tonight, i just assumed it was an incredibly fast satellite. Only had the binos out and by the time I'd got it in focus it had gone behind the neighbours.

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I observed the ISS 2 nights in a row this week. I have to say that in yesterday's observation, the ISS 'seemed' to go much slower (3x time) than the nigth before. Knowing that the speed does not change, it has to be that the relative speed is not the same depending on the trajectory.

As it was flying by on thursday, from my point of view it was going very fast, and then it seemed to slow down when it's position changed. Yesterday, as it appeared and flew by on a different path, it looked as if it was going much slower. Surely more savvy people can explain this effect better than me but have you consider this in your observation ?

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You observe its true speed when it flies directly overhead. As the angle changes its speed appears to slow down but its apparent size begins to change instead. Its actual velocity remains constant.

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ISS is a great one to watch for this effect. Take last nights high pass, potentially visible from horizon to horizon.

When it first appears in the west it seems almost stationary. Most of it's movement is towards you (radial). As it gets closer more of it's motion is across your line of sight (angular). When overhead or "abeam" (ISS never goes overhead up here) all its motion is angular. You see the full effect of it's 17000 miles per hour orbital velocity.

As it recedes everything is in reverse. Until eventually it's almost stationary as it fades on your easterly horizon. 

The change in apparent speed is smooth and steady. Nothing to do with flight dynamics or anything. It's entirely a visual perspective effect.

Should an object change its apparent speed abruptly or change it's path in any way it is almost certainly within the atmosphere under powered flight. 

The only orbital parameter that the space shuttle could change significantly whilst in orbit was it's altitude (and thus its orbital period). To rendezvous with ISS the shuttle had to be launched in a fairly narrow window  as ISS's orbital plane passed overhead. The shuttle was then effectively fired at it like a bullet. All the directional adjustments to ensure correct orbital insertion were done with the engines while in the atmosphere. Once in orbit all the shuttle had to do, and could do, was  play catch up and dock. Then to come home, it would turn blunt end forwards and fire its thrusters in the direction of travel to "de-orbit" . Again, no significant directional control was possible until back in the atmosphere when aerodynamics came into play and the wings did all the work.

These limitations (on any orbiting craft) are why the crew of Space Shuttle Columbia could not take refuge on ISS even if they had been aware of the damaged wing on that fateful mission. That flight was not in ISS's orbital plane and there was no way of getting there.   :(

Edited by Paul M
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ISS is a great one to watch for this effect. Take last nights high pass, potentially visible from horizon to horizon.

When it first appears in the west it seems almost stationary. Most of it's movement is towards you (radial). As it gets closer more of it's motion is across your line of sight (angular). When overhead or "abeam" (ISS never goes overhead up here) all its motion is angular. You see the full effect of it's 17000 miles per hour orbital velocity.

As it recedes everything is in reverse. Until eventually it's almost stationary as it fades on your easterly horizon. 

The change in apparent speed is smooth and steady. Nothing to do with flight dynamics or anything. It's entirely a visual perspective effect.

Should an object change its apparent speed abruptly or change it's path in any way it is almost certainly within the atmosphere under powered flight. 

The only orbital parameter that the space shuttle could change significantly whilst in orbit was it's altitude (and thus its orbital period). To rendezvous with ISS the shuttle had to be launched in a fairly narrow window  as ISS's orbital plane passed overhead. The shuttle was then effectively fired at it like a bullet. All the directional adjustments to ensure correct orbital insertion were done with the engines while in the atmosphere. Once in orbit all the shuttle had to do, and could do, was  play catch up and dock. Then to come home, it would turn blunt end forwards and fire its thrusters in the direction of travel to "de-orbit" . Again, no significant directional control was possible until back in the atmosphere when aerodynamics came into play and the wings did all the work.

These limitations (on any orbiting craft) are why the crew of Space Shuttle Columbia could not take refuge on ISS even if they had been aware of the damaged wing on that fateful mission. That flight was not in ISS's orbital plane and there was no way of getting there.   :(

Space flight sure "aint like dustin crops"

Yet.....

Edited by Earl
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As it recedes everything is in reverse. Until eventually it's almost stationary as it fades on your easterly horizon. 

As it happens, I stuck my head outside just in time to see the ISS last night. As it disappeared towards the horizon, I thought...

How far away is that then? 

It disappeared at an elevation of around 15 degrees (into the trees). How far away is it: in line of sight to the ISS and; what part of the world would it be over at that point?

Richard

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As it happens, I stuck my head outside just in time to see the ISS last night. As it disappeared towards the horizon, I thought...

How far away is that then? 

It disappeared at an elevation of around 15 degrees (into the trees). How far away is it: in line of sight to the ISS and; what part of the world would it be over at that point?

Richard

This tracker here might help: http://www.isstracker.com/

The circle round the ISS icon represents the horizon of visibility. So in theory, ignoring the observers local limitations, anyone on the ground within that circle should have ISS above their horizon.

I just had a look at tonight's late evening pass with SkySafari and it tells me that when ISS is about 15 deg above my west horizon its' just under 1200km distant yet at 5 deg elevation it's 1800km distant! Which puts it way off over the Atlantic.

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This tracker here might help: http://www.isstracker.com/

The circle round the ISS icon represents the horizon of visibility. So in theory, ignoring the observers local limitations, anyone on the ground within that circle should have ISS above their horizon.

I just had a look at tonight's late evening pass with SkySafari and it tells me that when ISS is about 15 deg above my west horizon its' just under 1200km distant yet at 5 deg elevation it's 1800km distant! Which puts it way off over the Atlantic.

Thank you for that - I was expecting to have to do some hard sums

Richard

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ISS is a great one to watch for this effect. Take last nights high pass, potentially visible from horizon to horizon.

When it first appears in the west it seems almost stationary. Most of it's movement is towards you (radial). As it gets closer more of it's motion is across your line of sight (angular). When overhead or "abeam" (ISS never goes overhead up here) all its motion is angular. You see the full effect of it's 17000 miles per hour orbital velocity.

As it recedes everything is in reverse. Until eventually it's almost stationary as it fades on your easterly horizon. 

The change in apparent speed is smooth and steady. Nothing to do with flight dynamics or anything. It's entirely a visual perspective effect.

Should an object change its apparent speed abruptly or change it's path in any way it is almost certainly within the atmosphere under powered flight. 

The only orbital parameter that the space shuttle could change significantly whilst in orbit was it's altitude (and thus its orbital period). To rendezvous with ISS the shuttle had to be launched in a fairly narrow window  as ISS's orbital plane passed overhead. The shuttle was then effectively fired at it like a bullet. All the directional adjustments to ensure correct orbital insertion were done with the engines while in the atmosphere. Once in orbit all the shuttle had to do, and could do, was  play catch up and dock. Then to come home, it would turn blunt end forwards and fire its thrusters in the direction of travel to "de-orbit" . Again, no significant directional control was possible until back in the atmosphere when aerodynamics came into play and the wings did all the work.

These limitations (on any orbiting craft) are why the crew of Space Shuttle Columbia could not take refuge on ISS even if they had been aware of the damaged wing on that fateful mission. That flight was not in ISS's orbital plane and there was no way of getting there.   :(

Great post Paul (and a good explanation of why the film Gravity is based on pure fiction). Orbital movements are very counter-intuitive and to change an orbit requires huge amounts of fuel, certainly to make a significant change. Changing an orbit to the extent that it would be visible to an observer on the ground would probably be impossible.

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"Gravity" pure fiction ... ! ... next thing you'll be telling us is that "Interstellar" wasn't a documentary ...  :grin:

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"Gravity" pure fiction ... ! ... next thing you'll be telling us is that "Interstellar" wasn't a documentary ...  :grin:

:grin: :grin:

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I enjoyed both films because I like escapism.

At least now, if called upon, I think I could manage to get home in a Soyuz lifeboat :D

"Gravity" did absolutely flout the laws of physics.

Whereas with "Interstellar", well, you just don't know what you don't know.

It would be a physical impossibility for me to fly off through some black hole and return to find my daughter is 50 years older than me. But only because I don't have a daughter! 

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The fastest speed for a LEO satellite at the lowest possible Earth orbit, 150Km, is approx 7.8Km/sec.

ISS is at approx 330Km and moving at 7.7Km/sec.

So no satellite will appear to move 4 times faster than ISS.

If the ISS sits at 330km and  moves @7.7km/sec that would that not mean an object at 150km moving 7.8km/sec would aprear to move much faster as it is less than half the distance away?

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I just spent an  hour or so watching "Apollo 18" on YT ... quite enjoyable in a predictable kinda way ...  :p

Edited by Steve Ward

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I saw a super fast one last night. Looked small but it was screaming fast compared to other satellites I've ever seen.

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If the ISS sits at 330km and  moves @7.7km/sec that would that not mean an object at 150km moving 7.8km/sec would aprear to move much faster as it is less than half the distance away?

Yes............by 0.1km/sec.

Lets face it we won't find much if anything orbiting at 150kms.

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I saw a super fast one last night. Looked small but it was screaming fast compared to other satellites I've ever seen.

If it's a lot faster than something like ISS it's not a satellite.

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If the ISS sits at 330km and  moves @7.7km/sec that would that not mean an object at 150km moving 7.8km/sec would aprear to move much faster as it is less than half the distance away?

Yes, something in orbit at half the height of the ISS would cross the sky in half the time i.e. it would appear to be twice as fast as the ISS to an observer on the ground.

Mark

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Wxsatuser, do you have any idea of the orbit of the X37B? I haven't looked into it,but I've heard others have worked together to track it's orbit. I'm sure it's probably a lot lower than the ISS. I don't know much about satellites. Definitely cool to see though, and always I interested in learning more!

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