Many people don't know that you can actually see some of these satellites in the sky as they pass overhead, without a telescope or anything. I made a site to help catch them, which has been on HN before: https://james.darpinian.com/satellites/
Twice in my life I have seen what I believed to be a satellite make a sudden and abrupt (near instantaneous) 90-degree turn. I realize this is impossible [probably?], which is why I ask. Once was in 1992 - and I spent nearly 30 years telling myself I mis-remembered. And the second time was in 2018 while backpacking with my wife - she was a second witness and confirmed that we saw the same thing. Both times the turn occurred when directly over-head.
When casually stargazing, I don't spot the satellites when they first pop up on the horizon. I usually spot them around 30-45 degrees above the horizon. One way to differentiate between an aircraft and a satellite is the blinking, but that's not always reliable - so a more reliable way is to note how quickly the "perceived" speed changes as it moves from 30-degrees towards the azimuth. The larger the change in perceived speed, the lower the altitude, while constant speed indicates orbit.
In both cases, I was casually looking at the sky - I had no measurement or recording tools. In both cases I took mental note of the speed when I first spotted it and how it changed (or didn't) as it moved. I mentally noted that that both appeared to be a satellite. Obviously, a 90 degree turn is impossible (?), which leads me to guess that I may have seen an extremely high altitude, high speed, aircraft make a near 90 degree turn while reflecting sunlight shortly after sunset. This also seems to be a stretch.
I hate to ask such far-fetched "I saw..." questions here, but it's been driving me nuts since 1992. All attempts at research have been fruitless. I thought maybe someone here could help?
[2] March 2018, at approximately 8:30-9pm. Again, I don't recall the exact date or time, (I should have written it down immediately), but we were outside Borrego Springs, California approximately 100 miles east of San Diego. San Diego is also very close to a lot of Military bases.
So one moves into the shadow of the earth, the other moves out - at a 90° angle.
Edit: Did both objects change direction, or just 1 of the 2?
I would hazard a guess that you saw two objects that appeared to cross paths at the time one was disappearing and the other was appearing. Could be planes or satellites. Both can abruptly appear or disappear as they enter or exit shadow, or as they turn and reflect light in a different direction.
A bright white spot moving over the blue sky and suddenly doing a 90 degree turn. It really scared me at the time.
I now believe we saw a high-altitude balloon that got into a layer of different winds at that moment.
How about a smooth change in direction? This might be weird enough to be interesting in its own right. In that case picture a satellite in a highly elliptical orbit, where you catch it near apogee, and assuming conditions are such that you can see it (big enough shiny surface/close enough to earth for human eyes, sunlit) then the earth could “outrun” it for a bit while the sat. is at its slowest, and the craft might trace a loop out in the sky, or (presumably) some other curve depending out your relative line of sight, etc.
Edit: trying to remember if there was a more official name for this orbit. Perhaps a Molniya orbit could give the ground based observer a loop?
https://www.google.com/amp/s/www.researchgate.net/figure/A-3...
Any abrupt change in heading is indeed pretty much impossible. A 90 degree plane change would require a staggering amount of delta-v.
The typical pop-culture UFO shape, a saucer or a sphere, would be pretty good at distributing these forces across the "fuselage" I would guess, but internal systems are still affected. Anything with wings or solar panels would be toast, no?
If the satellite passed into the shadow of the earth and dissappeared, your eyes could move to track another one without you seeing any perceptual gap at all.
The easiest explanation is two satellites with 90 degree between their inclination and lucky situation with the shadow that hides one at the approximate time second satellite shows up. It's not common but it someone will see it with enough time.
Just like with enough time and observation you can see a meteor that is heading straight toward you (it looks like a bright dot that dissappears).
That object could appear to turn "90 degrees" in _two dimensions_ when actually it changes course by a smaller angle in 3D space.
Imagine a satellite is heading straight for you. It would appear to not be moving at all. Now imagine it is moving toward but slightly below you. It will now appear to be moving slowly "straight down" from your perspective, but actually, it could be moving towards you at high speed.
Now imagine there is a small impact with the satellite that causes it to bump up and right slightly from its current trajectory. It might now suddenly look like it's moving entirely rightwards, from your perspective, but it is still moving towards you.
This is hard to explain without visualisation, but completely explains all of these anecdotes about sudden direction changes.
[1] https://aviation.stackexchange.com/questions/12762/what-airc...
[2] https://en.wikipedia.org/wiki/Perspective_(graphical)#Foresh...
I take my two-year-old out satellite hunting a few times a week. He’s a big fan of Pluto but understands we can’t see it like we can some satellites, plus Venus, Saturn, Sirius, etc. Of course he’d still rather see a truck!
ps i didn't see a way to manually set a location, maybe just my old android tablet...