[nicktelford]

It always irks me that discussion of space debris invariably talks about their high velocity relative to the ground, which is completely meaningless.

What really matters is their velocity relative to each other, which of course will vary, especially for objects on different orbits that happen to intersect.

The closing velocities involved can still be very high, and the "bullet" metaphor still applies in most cases, but it's misleading to label them as travelling at "17,500 mph (28,160 kph)".

The other thing that always bothers me is the graphical depictions that show a "point cloud" of debris in orbit around Earth. These always underplay the size of the earth and overplay the size of the orbital objects.

When discussing space debris, it's always worth remembering that there's approximately 10,000 planes in the air at a given time, and yet if you look up, how many can you see in the sky above you?

Since orbits are much higher, they're consequently much larger, providing even more available space than there is to commercial aviation. Not only that, but there's a far greater altitude range available for satellites than for planes, making the available space out there even more massive.

I don't doubt that space debris is an (emerging) problem, but the current severity of it often seems overplayed by the mainstream media.

[pacbard]

> It always irks me that discussion of space debris invariably talks about their high velocity relative to the ground, which is completely meaningless.

It's obviously an issue with point of view, but considering only relative velocity isn't also a solution.

If two spacecrafts are on a close approach trajectory, one of them might need to course correct to fix that. Changing the relative direction might allow them to avoid the collision, but will also change their orbit, leading to other problems down the road (e.g., out of wack apo/periapsis). Fixing the orbit after the close approach will also cost more fuel and/or angular momentum, which is in short supply on most spacecrafts.

I like to think about it like two nascar cars. Sure, if you are driving one, the other cars seem to be almost not moving from your seat, but the spectators see something completely different. Any small change (from the driver's view) in steering can have big effects overall.

[bagels]

The vast majority of encounters are thousands of meters per second relative velocity. There is enough energy in this to smash a satellite pretty good, even if it encounters one of the thousands of pieces of relatively small debris.

If two objects have a close approach once today, this means they will likely have another in the future due to the nature of orbits.

The visualizations are done this way because there is no way to draw everything to scale and have them be visible.

Planes move slower and still have midair commissions.

Maybe the amount of press it gets is too high for you, but it is a real concern for satellite operators. The amount of media attention given to celebrities is the real problem.

[wkat4242]

At those kinds of speeds, the orbital paths have to be really improbably similar to not have "bullet" like destructive effects. The relative velocity will almost aways be in the same order of magnitude as the ground speed and definitely more than bullet speed which is super slow compared to the ground speed.

And calculating the collision speed is pretty complex while the ground speed is static so I can imagine the press just take that.

After all pretty much any speed will be destructive to a satellite that's not designed to be bumped around.

[HPsquared]

Orbital inclination is the big one. A polar orbit intersecting an equatorial orbit would have a very high relative velocity.

On the other hand two orbits in the same inclination, with one being slightly eccentric, their relative velocity is much lower.

[wkat4242]

It doesn't matter though. Even if they hit at 0.01% of their orbital velocities, that's still 100km/hr. So it's like a full highway speed car crash. No way two sats colliding will survive that.

And remember the collision speed can range from 0 to 200% of their ground velocities. Getting that close to zero is extremely unlikely.

[bagels]

Two objects at the same inclination can still have very high relative velocity if on different planes.

[HPsquared]

Ah, so like the "phase" of the inclination? orbital plane being a vector quantity (angle between the Earth's rotational axis and the normal vector of the satellite's orbital plane)

[bagels]

Yes. Find a visualization of starlink orbital shells. They are all in one of just a couple inclinations, lots of crossings

[euroderf]

Thinking about this, and about the big launchers that the three-letter agencies use...

I wonder if US satellites (a) use a lot of Kevlar (or similar), and (b) can see nearby explosions (like, the triggering of a fragmentation weapon) and quickly close semi-armored shutters over their vital bits.

One would defeat this by creating - out of detection range - a fragment cloud that is on an intercept course. But that might be too complex and time-consuming if a war is starting. So what is the threshold for plausible deniability ?

And of course there's also railguns, à la The Expanse.

[wkat4242]

No. Satellites don't use armouring at all. It makes the launch way too expensive. And there's always exposed bits that can't be armoured like solar panels and antennas.

What they do use is... foil! There's a thin layer of foil a bit away of the main body. If a small piece of dust hits it at crazy speed, the impact with the foil will make it (and a bit of the foil) vapourise, and then it won't cause much damage to the main body because it's all vapour.

It's not really like the expanse because a railgun fires tungsen rounds that are meant to penetrate. Most random space crap is just flecks of paint, drops of oil etc.

[euroderf]

I get your point about the utility and appropriateness of foil.

But then what about warfighting ? I'll betcha the US has a railgun up there somewhere.

[throwbadubadu]

> but it's misleading to label them as travelling at "17,500 mph (28,160 kph)"

Really is? Ground speed is still what I expect and want to read, relative speed to each other at time of rendezvous would also be nice sure.. still, I mean depending on vectors, it may be over- or underestimating almost the same.. and I claim ground speed is what most people would expect. As someone said, the chance that their rendezvous speed is magnitudes off is slim.

[konstantinua00]

I'd prefer sattelite speed in km/s, as these numbers in a thousands don't parse in my mind... I don't know anything to relate it to that is expressed in km/h - transition point is in ~1000km/h =~= 300 m/s

[orbital-decay]

Eh, with these particular orbits (~600km, 74.1 and 82.5 deg) it's somewhat fair - high inclination LEO is always crowded and risky. With sun-synchronous orbits it's often even worse than "17,500mph" because the hit can come from almost any direction.

Compare this with the GEO, where everything is in one slow plane, the orbit is well-kept and dead stuff drifts away.

[nullindividual]

Orbital mechanics are difficult to understand unless you're a Ksp pro or some NASA dude that has played Ksp as a pro. The concept of "falling" while traveling at 28k kph is difficult for the public to understand as there is no frame of reference in everyday life. But everyone can understand that 28k kph is "really really fast!".

It is writing for the lowest common denominator which outside of scientific articles, is probably for the best. Imagine if every article had to re-state some even minor point about orbital mechanics. You'd lose too many people in the weeds.

tl;dr: People are ignorant/stupid/dumb/don't care. The author needs to write for that audience.

[creer]

That's still progress. My now automatic reaction in US reporting is "how much is that in football fields? Or perhaps libraries of congress?" /s?