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/
This is bit of an off-topic question, and I realize that it might sound a bit "out there", but I'm compelled to ask and I'll take the down-votes that I deserve:
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?
An object moving through the sky at a far distance from you is moving through 3D space. It appears to you to move in 2D space because of the fact that the image is being projected onto the back of your eyes, and our eyes aren't far enough apart to discern depth beyond a certain distance.
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.
This is exactly what I thought about when reading about the UFO sightings of the Roswell era. Less than 30 years after the biplane era, there were secret jet engine aircraft projects screaming around the Southwest desert at near Mach speeds and aircraft in production well over 500 mph. See one of those flying low almost directly toward you at night would look appear as if it is floating or barely drifting across the sky. If it then had a moderate course change left or right, it would appear to you to go from floating to extreme speeds with almost instant acceleration.
Right. I try to apply Occam's Razor in these scenarios. Either aliens fly around in the sky regularly enough that I've witnessed it multiple times, or there's something about perspective that I just don't fully understand (not meaning to throw shade on OP here).
Just to add to this, when a satellite goes into the Earth's shadow it disappears like turning off a light, and vice versa for a satellite going in the other direction coming out of the Earth's shadow.
I suspect this is it - you can't "see" where the shadow is but satellites go in all sorts of directions - and your eyes see a light moving and then another moving another direction and assume they're the same thing.
That was my first thought as well. It's not unusual to see several satellites overhead at the same time, and they can appear and disappear suddenly as they cross the earth's shadow boundary. Also they're quite faint and a brief discontinuity in their visibility is hard to spot reliably, or distinguish between blinking, glancing away for a moment, etc.
Have you ever noticed how sometimes when you look at your watch, the second hand seems to linger for slightly more than a second? This is due to saccadic masking. When your eyes move quickly, your brain cannot process the visual data. So it just backtracks and fills it in backwards with whatever it ends up seeing.
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.
Even if somehow that delta-v can be reached without burning so much fuel/energy that it makes any mid- to longterm mission fail, the forces on the satellite equipment which need to be withstood are insane. At orbital speeds it would just break the satellite/the craft unless there are some very special designs out there (?).
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?
Next time remember the exact date, time and location. You can look up satellites overhead.
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).
This is a fairly common phenomenon in aviation. After seeing planes do the same thing you're describing I looked into it and this post covers what's happening accurately [1]. The phenomenon is called Foreshortening [2].
I have also seen something similar at Surfside Beach, SC. I was in a hot tub, star gazing, and watched what I thought to be a satellite actually intersect another object and make a sharp 90 degree turn before disappearing. Still no idea what it was to this day!
Is it possible that you witnessed a collision? I don't recall having seen what appeared to be an intersection. But if it was a satellite, then it's possible that there was a second one up there that wasn't angled correctly to reflect light and be seen from the ground - maybe I witnessed a collision, in which only 1 of the 2 objects was angled/big-enough to be visible? Do others on HN know how often collisions occur?
Edit: Did both objects change direction, or just 1 of the 2?
An orbital collision would not cause an object to change direction 90 degrees. Satellites are not billiard balls. They are traveling at ten thousand miles per hour plus. Collisions at that speed result in two debris clouds that are largely traveling in approximately the same direction as before.
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.
If it was fast, it might be a meteor fracturing, and the fractured parts slowing down very quickly. It's hard to judge directions and speeds accurately against an empty blue sky, so a sudden change in velocity could easily be misinterpreted.
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?
Same experience in the early 90s, Midwest summer evening starwatching with my mom. We were pretty well in the habit of discerning satellite from plane, and saw a satellite stop for a few seconds, go a different direction for a short bit, stop again for a second, then a different direction until the horizon.
[1] 1992. I was extremely young, so I can't recall anything other than the location. In my adulthood, I can lookup the exact GPS coordinates. For privacy reasons, I'll say "Downeast Maine". It was about 1.5 hrs after sunset and I wasn't in bed, but it was dark, so I'd like to guess either the spring or fall - neither winter nor summer. I was old enough to know that you should note the change in perceived speed. It's note-worthy that Downeast Maine was not terribly far from Loring Airforce Base, which was still operating in those days.
[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.
If it was just AFTER sunset you get a situation where the sun is set for you but it is NOT set for the satellite tens of miles above, as long as they're in the right part of the sky.
So one moves into the shadow of the earth, the other moves out - at a 90° angle.
Great site. The easiest/laziest (in a good way! - I need a one or two click interface right now) method of finding the next star-link pass that I know of. Thank you!
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!
I like this a lot because it shows the distance between me and the satellite on the same scale as the distance between me and other ground locations. Otherwise it's hard to know how close/far satellites are.
Thank you. I've been wanting to spot some Starlink satellites for awhile, but I haven't been able to using sites that tell azimuth & elevation with a date. I like that your site shows the satellites superimposed on google street view so I know exactly where to look. I'm going to try to spot a starlink train tonight.
Cool! Many years back I made a little program that scraped HeavensAbove data and local weather, and made my phone buzz when there was about to be a bright Iridium flare overhead (just the good ones - every week or two).
I remember being able to see them fly over slowly when hunting in northern russia as a kid. Maybe my eyesight is not so good anymore but I doubt it’s doable within few hundred miles of any major population center today.
ISS is much brighter now than any satellite you would have seen then. Sometimes it can even be seen before sunset. Other satellites sometimes get bright enough to be seen in large cities too.
They're working on four additional radar installations for tracking space debris. Their current installations can track objects down to about a 10 cm diameter, but with their new installations they'll theoretically be able to track objects as small as 2 cm. In general, current radar systems tend to be limited on the lower end to objects in the 5-10 cm range. Systems like LeoLabs’ and the US Air Force’s upcoming Marshall Islands-based Space Fence will improve coverage, but still won’t see the 128 million objects from 1 mm to 1 cm. For perspective, a collision with a 10 cm object will likely completely destroy a satellite, a 1 cm object will likely disable it, and a 1 mm object may disable a subsystem. At closing velocities around 10 km/s, the kinetic energy of even an untrackable chip of paint is greater than the destructive power of an equivalent mass of stationary TNT. Whipple shields around the ISS’s crewed areas are built to absorb impacts with objects of up to around 1 cm. For anything bigger, an avoidance maneuver is used (if we see it coming).
Wow 2cm is still huge if it rams into the ISS at 10km/s. It's like a 20mm bullet with at least 5 times the speed of a gun round (not sure how fast guns are actually :) What are those 'whipple shields'? Are those the foil sheets that basically vaporise the object (and part of the shield) so it won't penetrate the inner hull?
I assume they have better tracking than 2cm for the orbit the ISS is in? Does the ISS have its own radar warning? Though I guess if it sees it coming it's already too late for avoidance.
> Are those the foil sheets that basically vaporise the object (and part of the shield) so it won't penetrate the inner hull?
Yes. Orbital hypervelocity impacts basically vaporize immediately on hitting anything, so you can offset a thin material in front of what you want to protect and cause any incoming object to turn into a cone of many much smaller objects which are less likely to penetrate the main hull.
This is so amazingly cool. Wow. You can even see 3D models (probably from a list of standard ones) and how they tumble (I wonder how accurate that is?)
Thanks vortex_ape. I love the way random cool stuff pops up on HN like this.
PS: It does look a lot more crowded in space in this view than it actually is, because the objects are shown at like a million times their actual size :) And it doesn't show vertical separation graphically.
I wonder is there a way to "make it scale" in the sense where the planet stays the same size but the satellites become like a pixel... so you can more accurately see how far apart things are... seems like "omg Kessler syndrome" whenever I see these things.
I don't follow the space industry as closely as I used to so I don't know how true this is, but some folks have accused Leolabs of being a bit alarmist with their conjunction alerts. They have sent out alerts for collisions that the DoD said had essentially 0 chance of happening (and they didn't).
If you were cynical, you might say that those sorts of false alarms are a marketing/PR stunt. If that's the case, it's in their best interest to not offer to-scale visualizations, making LEO look as crowded as possible.
I've been meaning to implement SGP4 from scratch as a learning exercise. What I found really interesting is how the USAF/NORAD tracks and reports objects in LEO: they publish Two-line Element Sets (TLEs), which are a fixed-width ASCII format derived from punch cards.[1] The format is pretty easy to parse.[2]
Just want to give props to the skyfield python library. I have no idea what any of the numbers in the TLE mean but just by following some examples have been able to plot the location of Starlink satellites vs time very easily.
Pretty incredible. I would like to see the assets to scale though, otherwise it seems crowded up there when it clearly isn't. It reminds me of all those graphics a year ago of the Australian bushfires where the fires were represented by huge graphics that were completely out of scale to the actual fire and folk actually believed that Australia was just charcoal!
This just made me realize, if cars are to satellites, we don't really have a bus to xyz equivalent. Cars are great and all, it gave a generation flexibility to go where they like but they don't scale. There are denser forms of transport for urban areas like rail or bus. And as the sky gets more debris filled it's going to be like the urban area analogy where we need a public transport for space where we co-locate payloads on one object at scale. Some places host a 3rd party payload on one satellite, but nobody hosts 50 on one structure.
One of the harder parts about that is setting up the attitude of the SV so that each payload gets time pointed at the earth (if that's what it cares about). A while back I worked on https://en.wikipedia.org/wiki/CASSIOPE, which had multiple payloads, and giving each of them appropriate earth-facing time at specific parts of the orbit was... a delicate scheduling problem.
Thank you. What is the difference between the two read areas showing pulsating beams and appear as blades growing upward and outward from the ground vs. the 6 pointed shape appearing to float over Alaska?
The pointed shape ones are 2D phased array radar. The radar is a grid of 4096 elements. It can observe things anywhere in the sky above it, however there are practical limits to how far off boresight it can operate. These limits are related to the arrangement of the elements, and result in the 6 pointed shape.
The others are 1D phased array radar. They consist of a line of elements rather than a grid. They use a parabolic reflector along the length of the array to focus the radar's observable area to a single line to make up for that missing 2nd dimension. So the reflector limits the radar to only observing across a single line, and the array allows the radar to control where across the line to radiate or listen.
Filter for starlink in the top left and set the speed at 200 or so.
Very interesting and entertaining. I’ve not been excited for a piece of tech in years but starlink has me on the edge of my seat. I can’t wait to get my equipment.
Feel that initially when you load this page, it looks crowded. Which for visualization sake makes sense, but it definitely doesn’t do space justice. It’s just so vast, and there’s so much more space that all these satellites would practically be invisible.
The way they're laid out on the map looks like there should be thousands of collisions every second. True size of each object is not perceptible on this and the distance between each object. Is there a log of collisions in real time?
I'd also like to know if there are non-artificial objects orbiting earth what their ratio is compared to man-made objects. Are there an equal amount or perhaps more comet/astroid-type objects that we simply don't track?
Is it fair game if a space company developed a craft that gathered and collected the non-working objects or somehow brought them back to earth and mined their precious metals or otherwise take their technology etc?
Works well on my wee i5 laptop, and certainly a LOT better than ye olde NASA World Wind with all the satellite plugins added on, which regularly crashed my machine when I used to play with it back in 2005 or so!
The Kiwi Space Radar (KSR), located in the Central Otago region of New Zealand, is the third radar in LeoLabs’ global radar network. KSR is an advanced radar based off LeoLabs’ proprietary S-band technology and consists of multiple one-dimensional phased array radar systems. KSR is the first of LeoLabs’ systems in the Southern Hemisphere, and the first of its systems that is sensitive to small, currently untracked space debris.
I'm getting a little more relaxed about Kessler Syndrome the more I look into it, at least in the short term. Each of those icons is about 10km across and the satellites are at different orbital altitudes. Also objects in LEO eventually drop into the atmosphere due to drag. As you move out of LEO the average distances between satellites balloons. For satellites in geosynchronous orbit each one is allocated a 'box' around 70km across although they can drift especially when they lose power and there are some in rogue orbits.
For comparison it's estimated that approximately 100 tons of pebbles and dust fall into the atmosphere every day, and plenty more just drifts past Earth continuously. We do need to come up with better mitigating controls and accidents will happen, but I think it's achievable.
Hopefully if it happens it is a short term LEO event and we are able to learn from it. There has already been one satellite-satellite collision, one is not a lot of data points to extrapolate from, but that event raises my wariness a lot:
