Enviromental impacts of satellite and debris re-entry

[DreamyPickle]

One of the objections raised to recent mega-constellation projects is that it will greatly increase the amount of material that re-enters the atmosphere. This is worth discussing in a patient manner.

For example this article makes several claims about possible harms caused by reentry: https://www.space.com/starlink-satellite-reentry-ozone-depletion-atmosphere

It seems to be based on this paper (very readable pdf): https://www.nature.com/articles/s41598-021-89909-7.pdf

One claim is that satellites that burn on re-entry deposit alumina in the upper atmosphere in larger amount that from meteorites. This can affect the albedo and slightly cool the planet, something that was proposed as deliberate geo-engineering and has uncertain impact.

Another claim is that "alumina impact the ozone layer" and it's based mostly on studies of the effects of solid rocket launches.

[jstrotha0975]

I'm more worried about a satellite somehow surviving reentry intact and spreading toxic fuel in an area on impact.

[DreamyPickle]

I'm more worried about a satellite somehow surviving reentry intact and spreading toxic fuel in an area on impact.

Both Starlink and OneWeb use electric propulsion so this can't apply. This comes with big mass advantages so it's likely other constellations will do the same.

Searching for cases of hydrazine tanks re-entering I found a bunch of controversy regarding USA-193: The US claims it destroyed the satellite because of the danger of hydrazine reaching the ground but critics claim that this was just an excuse to test an anti-satellite weapon.

Hydrazine is dangerous in ground handling and launch failures but those are mostly local problems.

[Jim]

I'm more worried about a satellite somehow surviving reentry intact and spreading toxic fuel in an area on impact.

not an issue

[Joseph Peterson]

Another claim is that "alumina impact the ozone layer" and it's based mostly on studies of the effects of solid rocket launches.

Ozone is a strong oxidizer so chemical reactions with anything that can easily be oxidized are to be expected.  Alumina is already an oxide.  Ozone depletion due to solid rockets is far better blamed on the chlorine in aluminum perchlorates.  As with the chlorine in CFCs, chlorine atoms in solid rocket fuel end up as Cl radicals that destroy thousands of ozone molecules.

The aluminum in satellites isn't oxidized though.  As a satellite burns up during reentry some of the 3 billion metric tonnes of ozone in the ozone layer will be lost.  The figure given in the Nature article is Starlink reentry's mass will reach 2 tonnes per day, or 730 tonnes per year.  Assuming all of this mass is aluminum, all of the aluminum reacts with ozone, and natural processes don't replace the losses we would be depleting the ozone layer at a rate of roughly 200 ppb(Parts Per Billion) per year.  200 PPB isn't nothing but it is a long way away from being something to lose sleep over.

[kevin-rf]

Searching for cases of hydrazine tanks re-entering I found a bunch of controversy regarding USA-193: The US claims it destroyed the satellite because of the danger of hydrazine reaching the ground but critics claim that this was just an excuse to test an anti-satellite weapon.

Or has been argued, they where more worried about various parts surviving reentry to be exploited by unfriendly nations. It was the first of a new generation of something that I'm sure they will classify in another 20 to 30 years.

But, still...

[DreamyPickle]

Assuming all of this mass is aluminum, all of the aluminum reacts with ozone

Ozone density peaks in the 30km range which is very low by spaceflight standards. Satellite on re-entry start burning much higher, isn't it possible that all that reaches the ozone layer is already-oxidized alumina? Also, isn't O2 far more abundant at all altitudes?

I also don't know why aluminium would behave differently from other metals more common in meteorites such as iron.

The research in this area seems to be specific to the launch of solid-fueled rockets which is a very different phenomenon.

[Joseph Peterson]

Assuming all of this mass is aluminum, all of the aluminum reacts with ozone

Ozone density peaks in the 30km range which is very low by spaceflight standards. Satellite on re-entry start burning much higher, isn't it possible that all that reaches the ozone layer is already-oxidized alumina? Also, isn't O2 far more abundant at all altitudes?

To answer your questions, yes and yes.  It is also true that the entire mass of a satellite is not aluminum.  Additionally natural processes will restore ozone, unlike my initial extreme assumption.  When I did my calculation that returned 200 ppb I was doing a sanity check to see if it was worth the time to do more homework to see instead of going to sleep.  200 ppb is already so low it isn't a concern so I elected to go to sleep rather than speed time refining the calculation.  Since I have a little time now I decided to check and the maximum ozone concentration is 20 ppm at ~30 km.  Merely accounting for ozone concentration reduces annual ozone depletion to single digit parts per trillion.  I could continue but I don't see the point.  It is obvious to me that ozone depletion from reentering aluminum is not something we need to worry about.

I also don't know why aluminium would behave differently from other metals more common in meteorites such as iron.

Aluminum is lighter than iron so each tonne of aluminum oxide more oxygen than a tonne of iron oxide but since we're talking about a non-issue the difference is insignificant.

The research in this area seems to be specific to the launch of solid-fueled rockets which is a very different phenomenon.

Agreed, although I wouldn't know that from most of the articles I read when I searched for alumina ozone depletion.  Far too often the journalists blame alumina/aluminum when the real problem is chlorine. 

[Vultur]

Far too often the journalists blame alumina/aluminum when the real problem is chlorine.

That's very odd, because chlorine is the "traditional" cause of ozone depletion - I believe the actual active species in CFC ozone depletion is chlorine radicals, not the CFCs themselves.

(IIRC originally CFCs were thought to be environmentally harmless because they are basically chemically inert under "usual" conditions, but the CFC - chlorine reaction in the upper atmosphere is a photochemical one driven by UV in the upper atmosphere.)

[JacobTheInvestigator]

Satellites are better to reenter than to remain in orbit. I also can't understand people. They complain about dead satellites orbiting our Earth and complain about satellites that deorbit and enter the atmosphere. What solution do you offer?

[eeergo]

Satellites are better to reenter than to remain in orbit. I also can't understand people. They complain about dead satellites orbiting our Earth and complain about satellites that deorbit and enter the atmosphere. What solution do you offer?

Too much of anything is generally bad.

[Vahe231991]

Satellites are better to reenter than to remain in orbit. I also can't understand people. They complain about dead satellites orbiting our Earth and complain about satellites that deorbit and enter the atmosphere. What solution do you offer?

Too much of anything is generally bad.

The 2009 collision between the Cosmos 2251 and Iridium 33 satellites along with the thousands of space debris generated by the destruction of the Chinese satellite Fengyun 1C in a Chinese ASAT test in 2007 are reminders by why the benefits of letting derelict satellites reenter the atmosphere outweigh the dangers. According to SatFlare, a Soviet rocket stage from a December 1973 launch will reenter the atmosphere this month (http://www.satflare.com/track.asp?q=7004&sid=2#TOP).

[Hobbes-22]

They complain about dead satellites orbiting our Earth and complain about satellites that deorbit and enter the atmosphere.

well, yes. Both scenarios cause problems. And instead of just complaining, the author of the Nature paper has done something constructive: he tried to quantify the harm done by deorbiting so a better-informed decision can be made.

The next step is to take these results and apply them to satellite design and operations, to see how we can mitigate the problem.

This is what progress looks like.

[DSarkar]

Aside from the surviving components and parts from satellite launches, space debris also poses a threat to the environment.
This is owing to the employment of radioactive materials in satellite activities.

[daedalus1]

Aside from the surviving components and parts from satellite launches, space debris also poses a threat to the environment.
This is owing to the employment of radioactive materials in satellite activities.

That's a sweeping statement, do you have any satellites in mind, and what they carry?

[Hobbes-22]

A small number of mainly US and Russian military satellites carry nuclear power sources (RTG, a few reactors).

[daedalus1]

A small number of mainly US and Russian military satellites carry nuclear power sources (RTG, a few reactors).

Do they still put nuclear power source satellites into low earth orbit after that Soviet one crashed into Canada in the 1970's? If so which do?

[Hobbes-22]

From that list, the last launch into any Earth orbit was in 1988. Since then, only interplanetary spacecraft have used RTGs.

[daedalus1]

From that list, the last launch into any Earth orbit was in 1988. Since then, only interplanetary spacecraft have used RTGs.

That's what I thought, so no issue there then.