[Just thinking (OP)]

Space junk vs meteors how can we tell the difference as they burn crossing the sky. This can be very challenging to the average person. Most meteors and space junk can burn and disintegrate with a rainbow of colours as meteors contain many elements that a found in all types of metals whether iron steel or alloy so it's not that easy going by the colours that we might see. A good rule of thumb is that space junk whether that is a large spacecraft or a small piece of space junk is travelling with a velocity of the speed that maintained its orbit and that is the closer orbiting craft that is most likely to crash back to earth as there orbit decays. almost all of the space junk that re enters the atmosphere is travelling about 25 to 30 thousand kilometres per hour if the space junk is of appreciable size and consists of many components this debris will break up very early in its re entry and we will see many portions of this streaking across the sky. Now most meteors that enter the earth atmosphere are travelling considerably faster with speeds averaging out to 70 or 80 thousand kilometres per hour even faster than that this will be much more noticeable as a single streak at first so its not that easy to determine all of the time as there is many variables to consider and every re entry or entering space debris can be a different story. I hope this got you thinking.

[evan_au]

Current space launches are supposed to have plans for safe re-entry of the vehicle at end of life, so they don't contribute to a cascade of space junk (as portrayed in the movie Gravity).
- This means that many large pieces of de-orbited space junk will come down in the South Pacific (between New Zealand and Chile), where there is almost no-one to see them
- For boosters, they often come down in a known zone down-range of the launch pad. All shipping and airlines are warned to stay clear of the landing zone. (The extreme case is the reusable boosters, where they return to launch site, or to a barge in the open ocean...)
- Most meteors come in known meteor showers (debris from Near Earth comets), which can be predicted well in advance, and have a known source, or "radiant".

It is the sporadic meteors and the uncontrolled space junk that causes surprises.
- Fortunately, telescopes are getting better at detecting large rocks as they are approaching Earth (although often by just a day).
- That should improve dramatically when the Vera Rubin Observatory comes online around 2023. See: https://en.wikipedia.org/wiki/Vera_C._Rubin_Observatory

Here is the final path of a Chinese Long March rocket that did not have a workable reentry plan. Observers knew with reasonable accuracy the ground track of the booster, but they couldn't tell where it would land along that ground track.


Chinese_Long_March_Booster_Reentry_May-21.jpg (68.12 kB . 970x486 - viewed 5926 times)

[Just thinking (OP)]

It is the sporadic meteors and the uncontrolled space junk that causes surprises.

You make a number of very good points I should have mentioned that space junk is by far more rarer than meteorites.

[Europa]

Current space launches are supposed to have plans for safe re-entry of the vehicle at end of life, so they don't contribute to a cascade of space junk (as portrayed in the movie Gravity).
- This means that many large pieces of de-orbited space junk will come down in the South Pacific (between New Zealand and Chile), where there is almost no-one to see them
- For boosters, they often come down in a known zone down-range of the launch pad. All shipping and airlines are warned to stay clear of the landing zone. (The extreme case is the reusable boosters, where they return to launch site, or to a barge in the open ocean...)
- Most meteors come in known meteor showers (debris from Near Earth comets), which can be predicted well in advance, and have a known source, or "radiant".

It is the sporadic meteors and the uncontrolled space junk that causes surprises.
- Fortunately, telescopes are getting better at detecting large rocks as they are approaching Earth (although often by just a day).
- That should improve dramatically when the Vera Rubin Observatory comes online around 2023. See: https://en.wikipedia.org/wiki/Vera_C._Rubin_Observatory

Here is the final path of a Chinese Long March rocket that did not have a workable reentry plan. Observers knew with reasonable accuracy the ground track of the booster, but they couldn't tell where it would land along that ground track.


Chinese_Long_March_Booster_Reentry_May-21.jpg (68.12 kB . 970x486 - viewed 5926 times)

What would the plans be for a satellite without thrusters be for reentry after a decades long life?  Even if the satellite is new

[Bored chemist]

What would the plans be for a satellite without thrusters be for reentry after a decades long life? 

There would not be one.
And we know that

Current space launches are supposed to have plans for safe re-entry of the vehicle at end of life

So we deduce that satellites are supposed to have thrusters at the ends of their lives.

Do you find the inability to combine pieces of information and make deductions is a problem for you in your everyday life?

[Petrochemicals]

X rays. Get yourself  an xray gun and have a look being as metal will reflect the xray much better.

[Just thinking (OP)]

X rays. Get yourself  an xray gun and have a look being as metal will reflect the xray much better.

And a speed gun see how fast it's going.

[evan_au]

So we deduce that satellites are supposed to have thrusters at the ends of their lives.

Not necessarily. If the satellite is in a low orbit, it will naturally deorbit due to friction with the upper atmosphere.
- Guidelines recommend that satellites should be removed from orbit within 25 years of their end-of-life
- This is especially useful for cubesats. They have very little space for electronics, let alone thrusters.
- But depending on atmospheric friction can be unpredictable - an outburst from the Sun can suddenly expand the outer atmosphere, and result in premature termination of the satellite mission.

See: https://en.wikipedia.org/wiki/Space_debris#Dealing_with_debris

[Just thinking (OP)]

Not necessarily. If the satellite is in a low orbit, it will naturally deorbit due to friction with the upper atmosphere.
- Guidelines recommend that satellites should be removed from orbit within 25 years of their end-of-life
- This is especially useful for cubesats. They have very little space for electronics, let alone thrusters.
- But depending on atmospheric friction can be unpredictable - an outburst from the Sun can suddenly expand the outer atmosphere, and result in premature termination of the satellite mission.

I believe that satellites are designed to fragment to allow for a compleat burnup most probably the larger ones.

[Bored chemist]

X rays. Get yourself  an xray gun and have a look being as metal will reflect the xray much better.

You seem to have picked the wrong wavelengths.
Metals are shiny.
They typically reflect light well.
And they are conductive, so they typically reflect radio waves well.
But they aren't particularly opaque to. or reflective of, X-rays.
If they were then we could make X-ray telescopes using ordinary mirrors (rather than grazing angle ones).

So we deduce that satellites are supposed to have thrusters at the ends of their lives.

Not necessarily. If the satellite is in a low orbit, it will naturally deorbit due to friction with the upper atmosphere.
- Guidelines recommend that satellites should be removed from orbit within 25 years of their end-of-life
- This is especially useful for cubesats. They have very little space for electronics, let alone thrusters.
- But depending on atmospheric friction can be unpredictable - an outburst from the Sun can suddenly expand the outer atmosphere, and result in premature termination of the satellite mission.

See: https://en.wikipedia.org/wiki/Space_debris#Dealing_with_debris

True; but I'm not sure how it applies to a satellite with a "decades long life".

[Bored chemist]

I am guessing

You should stop; your guesses are so silly that you are embarrassing yourself.

What scale was your 173 IQ achieved on?

My guess is the Stanford–Binet scale
2nd or 3rd edition.

[TommyJ]

The Earth has always been vulnerable to outer space.
Occurrences like large asteroids are rare, but natural activities, such as solar storms, strike from space much more frequently. These have a direct effect on electronic systems, especially satellite-based technologies.
The burst of human-made satellites has created a space hazard of its own, as the loads of orbiting debris have the potential to destroy other satellites.
In the US both NASA and the U.S. Space Force tracks space debris, the National Oceanic and Atmospheric Administration monitor space weather, Planetary Defense Coordination Office coordinates the search for potentially hazardous asteroids and other near-Earth objects (NEOs).
The European Space Agency (ESA) has pulled all these activities together under the umbrella of its Space Situational Awareness program.
The key should be in collecting all the data together and handling it with the help of Data Science methods.

[Just thinking (OP)]

The key should be in collecting all the data together and handling it with the help of Data Science methods.

This is something to consider but not necessary for space junk and meteors.

[TommyJ]

Sporadic meteors as well as space junk collisions and entering atmosphere are not much reported, for my understanding.
2008 TC3 (ateroid though), exploding over Sudan.
https://en.wikipedia.org/wiki/2008_TC3
One of examples.
The asteroid was discovered by Richard A. Kowalski at the Catalina Sky Survey (CSS) 1.5-meter telescope at Mount Lemmon, north of Tucson, Arizona, US, on October 6, 06:39 UTC, 19 hours before the impact.

'as they burn crossing the sky' already might be a matter of a second to take note of time and place and try to find out later.

One of the largest junk piece is about double decker size. But the most dangerous on the orbit itself are ones from 1 to 10 cm, which can easily make working satellite into a junk waiting to make surprise in atmosphere.

[Just thinking (OP)]

One of the largest junk piece is about double decker size. But the most dangerous on the orbit itself are ones from 1 to 10 cm, which can easily make working satellite into a junk waiting to make surprise in atmosphere.

That is of big concern if a satellite is impacted by either a small meteor or a piece of space junk it will become a runaway problem. I think this has happened before and we have so far avoided moor. Just wait till space X is complete it could become a train reck.

[TommyJ]

ISS had to take several manoeuvres last year.
And one bright satellite collision that was in the news before.
For new launches, yes, avoided so far, but for what is there only owners might know.

[Just thinking (OP)]

ISS had to take several manoeuvres last year.

They must have to have plenty of notice if an object is on a posable collision course with ISS as ISS is very large and will take a bit of time to reposition.

[TommyJ]

ISS had to take several manoeuvres last year.

They must have to have plenty of notice if an object is on a posable collision course with ISS as ISS is very large and will take a bit of time to reposition.

Yes, and it is man driven and precisely observed.
Other 20k+ are either junk or not so sophisticated in this way, what I meant.

[Just thinking (OP)]

Yes, and it is man driven and precisely observed.
Other 20k+ are either junk or not so sophisticated in this way, what I meant.

I guess ISS is rather special as it is occupied and any collision will be of the greatest concern And ISS is one of the earth's greatest allies builder in space.

[TommyJ]

Yes, and it is man driven and precisely observed.
Other 20k+ are either junk or not so sophisticated in this way, what I meant.

I guess ISS is rather special as it is occupied and any collision will be of the greatest concern And ISS is one of the earth's greatest allies builder in space.

Fully agree, no argue would be possible.

I think of statistically it is one of 20k+ objects (even the big one). So a math model would show thousands collisions times for the whole.