Japan developing wooden satellites to cut down on space junk | Hacker News Reader

Japan developing wooden satellites to cut down on space junk

bbc.com

215 pointsmmhsieh121 comments

So, this does nothing to actually combat space junk in the sense of debris in orbit. The actual goal is:

> We are very concerned with the fact that all the satellites which re-enter the Earth's atmosphere burn and create tiny alumina particles which will float in the upper atmosphere for many years

Right. The author is clearly conflating orbital debris with re-entry pollution.

It is baffling to me that the BBC, a fairly respectable organization, allows this sort of terrible journalism. The author clearly does not understand the subject matter at all, which is not surprising since he's a business reporter regurgitating (presumably) a press release from a university and/or a forestry company.

>> The author is clearly conflating orbital debris with re-entry pollution

To be fair to the journalist, so does wikipedia, the National history museum and the FAA.

On balance, the journalist (and perhaps the editor) appears to be correct here.

I don’t know enough to say if you’re mistaken or not but i can’t find a good definition for your term “re-entry pollution”. Do you have any handy links for that term?

Wiki & the NHM re-define “space junk” as “space debris”. Google does this too but is just relying on these sources.

The wikipedia for space debris includes material that falls back to earth. It even lists some notable incidents. Wikipedia doesn’t appear to recognise the term “re-entry pollution”.

The FAA deals with debris here: https://www.ecfr.gov/cgi-bin/text-idx?SID=685669905c05d232fc... - it treats orbital and re-entry debris under the same provisions and doesn’t seek to further distinguish them.

>> clearly does not understand the subject matter at all

What sentences in the article lead you to this conclusion?

The term "re-entry pollution" is not standard; I made it up. I did not say the author conflated these terms, I said he conflated the things themselves (i.e., the concepts). Krisoft's reply to your comment explains well what's wrong with the article.

That Wikipedia and the FAA do not have special terms for these distinct concepts does not mean they conflate them. Indeed, basically nobody cares about re-entry pollution because it's just an utterly trivial type of pollution (and it's the only thing this proposed tech addresses).

"What sentences in the article lead you to this conclusion?"

Each sentence in the article in itself is good. The sentences together reveal that the author had no understanding of the topic. (or decided to wilfully write a confusing mess)

Let me illustrate:

" Space junk travels at an incredibly fast speed of more than 22,300 mph, so can have cause considerable damage to any objects it hits.

In 2006 a tiny piece of space junk collided with the International Space Station, taking a chip out of the heavily reinforced window. " This is true! Objects on orbit have very high energies. When two of these objects collide they generate tiny shards which can collide into new objects, shattering them too. This can lead to a cascading problem where many satellites on a given orbit turn into mush at the same time. And not only that you loose these satellites, but their shards remain on the orbit posing risks for future satellites. You might heard of this effect as the Kessler syndrome.

You might be wondering, how does making the sat from wood would help with this? The answer is it wouldn't. But you wouldn't know that from the article. It has zero connective structure to illuminate this.

So why are these people working on a wooden satelite? To quote again from the article: "We are very concerned with the fact that all the satellites which re-enter the Earth's atmosphere burn and create tiny alumina particles which will float in the upper atmosphere for many years,"

Ah. So these people are not worried about the Kessler syndrome. They are worried that re-entering space craft break up, and particles from it can remain in the upper atmosphere. That's an interesting problem. Maybe worth addressing. But if that's the problem why is the article waxing about speed of objects in orbit and chips colliding with the international space station?

You say you can't find a good definiton of the term "re-entry pollution". And you are right. It's not a widely used term. But clearly an apt description of what the company is talking about. Is this a serious concern? Has there been studies about this effect? Is there a more commonly used term for this kind of pollution? Who knows. I don't know. You don't know. The article should be answering these questions for us. Instead all we have is a single sentence ""Eventually it will affect the environment of the Earth."" Nice. Not very well researched. And probably even the journalist felt this is not enough so they wrote multiple paragraphs about what he could find of the dangers of space junk. But sadly he found a totally irrelevant other kind of problem. If they realised this and wrote the article still as presented then they are wilfully confusing people. If they are just dazzled by all the terminology then so bad, I would still expect more from professionals.

"On balance, the journalist (and perhaps the editor) appears to be correct here." What do you mean by that? If someone writes a word salad they are correct just because others have wrote similar word salads before?

"Wikipedia doesn’t appear to recognise the term “re-entry pollution”." So bad for the company and the journalist. It sounds like they have to do more work to explain their problem then!

And your ecfr.gov link. It talks about making sure that your satelite does not explode on orbit. (To mitigate the problem of the Kessler syndrome.) It also talks about post-mission disposal in paragraph (4). It contemplates two scenairos. One where you put your sat to a lesser used orbit, or one where you deorbit your satellite. In case you choose to deorbit you have to show that you are not too likely to plonk anyone in the head. From the perspective of this second scenario the whole sat burning up into aluminium mist in the upper atmosphere is a success. The company disagrees and says that we should worry about other unspecified effects too. Are they right? Maybe! But the article sure didn't do a good job to explain the distinction, and thus failed to ask the pointy questions it should have asked.

What's the definition of debris?

The article mentions tracking/estimation of debris greater than 1cm. This seems reasonable to me. I doubt particulate matter counts as debris. We can see this in other parts of life. For example, if you are doing a FOD walk, you don't care about dust and "invisible" particulate matter.

I wish people (even physicists) would stop saying that the heat of reentry is from air friction. It isn't. It's from compression. The air cannot get out of the way fast enough, and it compresses, and compressing a gas raises its temperature.

That's why the leading edge, where the air is moving the slowest, is the hottest.

When you saying the heating is "from compression" do you mean (1) there's a process in which compression occurs, and that's where the heating is, or (2) the heating is that which necessarily occurs when a gas is compressed from pressure P1 to a higher pressure P2?

Because (2) is wrong. Compression occurs at a shock, as does heating, but that doesn't mean the heating is due (entirely) to compression.

Compressed air is hot, but the reason it makes a craft hot is that the air is touching the craft in a certain way.

Is the difference that hearing due to compression is a normal head-on collision, and heating via friction is a parallel "scratching" collision?

If you dropped a cube from space, the heat would be on the front face due do battery from air particles, not on the sides?

But isn't that what friction is?

No. You'll get the same temperature rise from an ideal frictionless gas.

(This was one of the exercises in fluid mechanics class in college.)

The bit about the air cannot get out of the way fast enough comes from its inertia, not friction.

You'll find the same temperature rise in high speed aircraft like the SST. The max temperature rise is at the stagnation point where the air velocity is zero.

(Compress any gas and it warms up, this is how refrigerators work.)

What makes the air too slow to get out of the way? I would have naively thought friction, and that if everything was frictionless the air would seamlessly move to replace the vacuum behind the aircraft, and thus no compression would occur.

To put it bluntly, air molecules aren't psychic. The only way they know what happens to neighboring air molecules is by running into them. At every-day velocities, this happens fast enough that we can treat it as though it is instantaneous. That the "vacuum" is a thing that sucks air in.

At high velocities, this intuition breaks down. The communication time between molecules is limited to the speed of sound, the speed at which air molecules travel and bump into each other. If you are traveling faster than the speed of sound, (or several times faster, as is the case for re-entry), the air molecules don't have any information that an object is coming to them, because there hasn't been enough time for molecules hitting the object to then hit them.

In an ideal frictionless gas (zero viscosity), the flow after the object has passed through will be identical to the flow before the object, so in that sense the air moves "seamlessly" around the object. But during this process, the pressure of the gas still changes. You can think of this as just newton's second law: in order to change the velocity of an air packet, you must apply a force to it, and pressure is just force per area. So any time a gas flows in anything other than a straight line, you know that there was a pressure gradient involved and the pressure was not constant.

It's a common example in fluid mechanics textbooks to derive the flow of a zero-viscosity gas around a cylinder, you can get an exact solution e.g. here: http://brennen.caltech.edu/fluidbook/basicfluiddynamics/pote... . Note that in this example there is no drag, but there are two zones of high pressure in front of and behind the cylinder. Those zones would have higher-than-ambient temperature.

I think this relates to the concept of viscosity for a gas.

Inertia.

Heating via compression is not the same as heating by friction.

When you squeeze a gas into a smaller volume it heats up because the heat energy of the gas which was spread out over the larger volume is now packed into a smaller one.

See Boyle's Law: https://en.wikipedia.org/wiki/Boyle%27s_law

Boyle's Law describes a behavior without positing the mechanism.

What does it mean for a gas to heat up? Is the quantity of heat energy increasing, or the temperature?

A thermometer generally measures the temperature of molecules adjacent to the thermometer, which is a function of the amplitude of those molecules' vibration. More molecules within a given space increases the heat capacity, and the total heat energy represented by a temperature of the total quantity of molecules, but the temperature is a function of the average heat energy per individual molecule.

The temperature increase described by Boyle's law is a consequence of the work required to compress a gas—somewhere there has to be a compressor imparting kinetic energy to individual atoms.

Think of it this way, you have two containers of heat energy represented by 1L of an ideal gas at 1 atmosphere and 20°C. If you magically transported the contents of both containers into a single 1L container, and they continued to express a temperature of 20°C, you would have twice as much stuff, and contain twice as much heat energy in 1L. If on the other hand you had twice as much stuff and a higher temperature, then you would have increased the total amount of energy present in the universe.

The temperature comes from the extra energy put into the system to compress the gas rather than expressly from the density of the heat energy.

And heating in a shock is not the same as heating by isentropic compression.

In physics the heating described by Boyle's law is a consequence of work, typically the kinetic energy imparted to molecules by a compressor.

A temperature increase resulting from compression is a temperature increase resulting from friction. In other words, it's friction all the way down (until it's electromagnetism and other fundamental forces).

No. Isentropic compression is reversible; friction generates entropy and is not.

The "compression" in front of a de-orbiting satellite does generate irreversible entropy, and the physicists are correct to say that air friction causes the heat during reentry.

Right. The argument that the heating is by compression is at best misleading, and at worst completely wrong. The dissipative process in the shock is more akin to friction.

Hmm, that is what I was getting at in this thread.

The other user claimed that physicists are making a mistake when they explain with friction rather than compression.

Looking back, I think your first comment was meant for the other user.

Also, what heating described by Boyle's Law? That law is the ideal gas law at constant temperature.

You're right, Charles's Law was the gas law about temperature and pressure.

That makes sense. Seems academic though as that heat could be avoided by making reentry more aerodynamic, but retardation is what we want. So technically maybe not friction but still a desired reduction of speed which is close enough in lay terms.

The retardation comes from the pressure at the leading edge being greater than the pressure at the trailing edge.

This is the result of agenda driven reporting. They are literally accepting anything which promotes their current focus which is on the environment.

Focusing on the environment is a good thing but we risk burning people out or worse having them assume everything they read if more scare and fiction that true issue.

we live in a world where the virtue signaling has gotten so loud people are deaf and just tune it out. those who cared will still care but we are losing an entire segment simply because we check ourselves

There was another instance with that happening recently https://news.ycombinator.com/item?id=25520481

BBC has been dropping the ball lately, there have been entirely too many articles that miss the thrust of whatever their source was.

It's baffling, but not surprising to me. I worked in mission operations on some NASA satellites. A reporter once asked our team "so how do you get up there every day to fly them?"

Surely he was taking the piss. Not even a journalist could be that stupid.

How much of a problem is actual orbital debris?

Going by the maxim of “Space is always more empty than one could possibly imagine.”.

>inb4 “if the moon were a pixel”.

It's a modest and pretty easily manageable problem now, but it will become pretty non-trivial in the future if not properly handled. However, all signs point to it being properly handled (it's in everyone's interest), so my advice to laymen is to not worry about it.

It's true that even near-Earth space is crazy, crazy big so that the amount of volume occupied by debris is extremely tiny, but what's also true is that debris is moving fantastically fast so that the volume "effectively occupied" by debris is only small rather than extremely tiny. This cashes out in the empirical facts (which fit perfectly with our models) that there have been four unintended collisions between satellites and debris:

https://en.wikipedia.org/wiki/Satellite_collision

These have all taken place in the past 25 year (despite > 50 years of spaceflight) because the density is increasing. If the density keeps increasing without the forthcoming mitigation efforts, the rate of unintentional collisions would keep rising to bad levels.

Imagine how wrong they can be about all other matters which shape reader’s worldview.

It's not a conflation anymore than me calling my recycling bin "trash". It's just a slightly more general term used when the distinction is not important because the meaning is completely obvious in context.

People who think space junk cannot polite the atmosphere are the confused ones, not the author.

Gell-Mann Amnesia, as described by Michael Crichton:

“Briefly stated, the Gell-Mann Amnesia effect is as follows. You open the newspaper to an article on some subject you know well. In Murray's case, physics. In mine, show business. You read the article and see the journalist has absolutely no understanding of either the facts or the issues. Often, the article is so wrong it actually presents the story backward—reversing cause and effect. I call these the "wet streets cause rain" stories. Paper's full of them. In any case, you read with exasperation or amusement the multiple errors in a story, and then turn the page to national or international affairs, and read as if the rest of the newspaper was somehow more accurate about Palestine than the baloney you just read. You turn the page, and forget what you know.”

Upvoted your comment because for whatever reason people don’t like to see this phenomenon invoked, but that’s exactly what’s going on here.

I didn't downvote but I think people do because it's almost a stock comment that a bot could automatically apply.

It's guaranteed to appear in about 5% of the comments every time an inaccurate article is being discussed.

Yes, that is why I downvoted. It is a stock comment which adds nothing worthwhile to the discussion.

It's a useful reminder for the many of us who, like me, tend to forget this.

> It is baffling to me that the BBC, a fairly respectable organization, allows this sort of terrible journalism

Unfortunately, the BBC is not what it used to be. In fact, it has probably never been as unpopular.

> tiny alumina particles which will float in the upper atmosphere for many years

Large quantities of such particles have actually been seriously proposed to help combat global warming. What are the downsides of them? When these particles finally migrate into the troposphere they quickly fall to Earth at relatively low velocity due to the very high drag.

I'm all against polluting the earth, but non-reactive aluminum particles in the quantities that we are talking about are such a non-issue in comparison to anything else.

Umm... I don't get it.

There is much more natural matter entering our atmosphere by way of dust and meteorites. This one says about 40 thousand tonnes each year:

https://skyandtelescope.org/astronomy-resources/astronomy-qu...

Granted, not all of this is aluminium but I can imagine there is more metal raining down than all man made satellites combined.

As to space junk which is matter floating on specific orbits around Earth, it does not matter much what it is composed of. If they hit each other at multiple kilometers per second it doesn't matter if it is made of wood, paper or steel. The result is from kinetic energy being released, not the composition of the bodies.

I think the goal should be to make less satellites, smaller ones and maybe also built in a way that would make them less prone shattering into multiple small parts if hit.

Less satellites -- satellites should be shared. We shouldn't be in a position where every company that decides to send thousands of satellites can do so at will. I think the number of satellites at various orbits should be limited and controlled the same way the electromagnetic spectrum is being controlled for common good. For this reason we should think how we can make as many possible uses with small amount of satellites and this I think should include some sharing schemes (the same way we share EM spectrum).

Smaller == less cross section for collisions, less matter spread in case it collides.

Less prone to shattering == further prevents or slows down any chain reactions from part of one satellites hitting another satellites.

One of the 'atmospheric' descriptions in The Expanse that I have loved is the use of antispalling coatings on the interiors of ships.

Micrometeoroids are a fact of space travel, and in this universe, so are kinetic weapons. so the authors imagined/researched a material meant to resist the tendency of the ship's materials to become secondary projectiles ricocheting through the ship turning everyone and everything into swiss cheese.

I think they may be defunct now, but there was a company called Tethers, Inc who had in their toolbox making 'cables' that look more like fishing nets. The idea being to reduce the likelihood of a single strike damaging multiple structural members at once.

I don't know what or if we can do for satellites that is in this direction. You can make the satellites tiny but you still need solar collectors.

Maybe inspired by some of the techniques used to defeat HESH[1] in WWII and beyond?

1: https://youtu.be/Uhz3w8-PSl8

Tethers isn't defunct. But they have pivoted to space robotics.

My brow raised when you said the share word. I just don’t see it happening because people are greedy. And then the minute some small country decides it wants to enter the space will they be allowed? How will space be allocated to players late in the game is what I am asking?

Space is limited and we share it whether we like it or not.

In case of physical landmass we have borders.

But in case of seas we have international treaties that describe sphere of influence of each country and what they are and are not allowed to do depending on some very arbitrary rules.

If you think about it, most of Earth surface is actually shared between countries, ie. there is not single country having exclusive access over it.

In case of electromagnetic spectrum we have other international treaties where countries agreed on how to share it so that they don't step on each other.

I don't understand why you don't like the word "share" since we are already sharing so much.

Space is limited :D

Actually, yes. Space in which we can put Earth satellites is limited and you can even calculate its volume.

https://en.wikipedia.org/wiki/Hill_sphere

Is this a pun?

The collision of space (the universe) and space (room to put things)? I think?

And what about countries such as Iran? Somehow I prefer a world with lots of space junk over a world in which the US effectively controls who gets access to space.

I honestly can't imagine an international organization that is fair in the least in allocation of space trajectories. See the UN, WTO, WHO, the Worldbank... No thanks.

It is a shame that geopolitically insightful comments are downvoted. Politics and technology are deeply intertwined. Perhaps China and Russia passively protect Iran's space interests.

Sharing of satellites does happen in some senses already. These tend to be large satellites with significant power/data resources that can afford to host an extra payload.

Some examples:

1. TCTE is a NASA instrument capturing solar radiance data hosted on an Air Force satellite: https://lasp.colorado.edu/home/missions-projects/quick-facts...

2. The US military uses bandwidth of commercial communications satellites. Note, the article is actually about how they can't do it very well and want to get better so I will admit this is a bit contradictory to my point. https://spacenews.com/to-predict-the-future-of-military-sate...

I just don’t see it happening because people are greedy.

People aren't uniformly greedy though. Some are 'I win when you lose' (maybe 30%), some are 'win win' entrepreneur types (15-20%), a similar proportion are 'insurance buyers', and some are natural volunteers. Perhaps the solution is to develop strategies that yield modest but reliable reward for the largest number, while frustrating the greedy.

Given the rich and intricate technical history of Japanese carpentry, it's not surprising that they're the ones pushing this forward. If you search for "Japanse joinery", you'll be in for a mesmerizing treat of intricacy.

Chinese carpentry is just as if not more intricate. As someone who does small carpentry projects, watching a bunch of guys build a house with wood and not a single nail is like watching pornography for the first time. The dedication to craft and tool is truly mesmerizing.

AFAIK the Japanese benefited from significant joinery knowledge from China circa the Nara period (~700CE). In Japan they rebuild temples regularly using these techniques and have thus kept them alive, and also have old standing examples. However, China lost most examples in the cultural revolution. I have visited what was at the time allegedly the oldest dated example in southern China, a temple north of Ningbo, and while impressive it is nothing on what's in Japan.

That said, this is more about material science than joinery.

With the Sony Clie PDA came a software disc, and it was in a slim ‘jewel’-case box that had the cd tray slide out from the side—and not slide out entirely but hold at the last inch or so. The box was made entirely from cardboard, except for the standard plastic piece that held the disc by the center hole. That's when I knew the Japanese take their origami seriously.

Wood is a very good heat shield and was used by China at the start of their space program when composite material was beyond their manufacture abilities. What they will likely achieve is to preserve what is inside the wooden box during re-entry and rise the chances of hitting something and cause damage.

Sumitomo Forestry released a press release in Japanese [1], and Google Translate works pretty well on it.

Additionally, there's an English version of the Japanese news coverage [3].

The main points I've seen when looking through these resources are:

- Wood is a renewable resource, unlike all these metals we keep burning in the atmosphere

- Electromagnetic waves are not blocked by wood. Because of this, if the proof of concept works out, astronauts will be able to keep all their communication equipment, like antennas, on the inside of the ship.

- When wood burns it decomposes into gases you would already expect to find in the atmosphere.

- The goal is to find something to increase the price of wood. Basically, this is a fishing expedition.

- Even if this doesn't work out, the research might lead to some new applications for wood.

- The project name is LignoStella and the satellite will be called LignoSat.

[1] https://sfc.jp/information/news/2020/2020-12-23.html

[2] https://univ-journal.jp/74704/?show_more=1

[3] https://asia.nikkei.com/Business/Science/World-s-first-woode...

Arstechnica article: [BBC] Coverage of “wooden satellites” misses the point

https://arstechnica.com/science/2020/12/wooden-satellites-an...

Edited to add [BBC] in title, to indicate that the Ars piece is a reaction to, and critique of, the Beeb's article.

Considering these are full of electronics, power sources and other metal 'things' - do they really reduce the amount of particles reduced into the atmosphere by much?

And how much of an issue is aluminium particles from burnt out satelites in the atmosphere anyway?

I normally agree with this kind of skepticism but doesn't it obviously reduce the number of metal particles by exactly the amount of material that you converted to be made of wood?

I don't really understand why wooden junking floating around space is any better than plastic. Microbes won't be able to break it down like they would on earth.

The article mentioned that small aluminum particles are left in the upper atmosphere after burning up. The wood would presumably not have this problem.

how does that solve anything?

getting hit by a chunk of wood at orbital speeds is pretty much the same as getting hit by same mass of ice or rock ..

That's not the goal...

"We are very concerned with the fact that all the satellites which re-enter the Earth's atmosphere burn and create tiny alumina particles which will float in the upper atmosphere for many years,"

It isn't the same. The density matters. A less dense object will spread the force of the impact over a larger area. It may be enough to result in deformation rather than puncture.

The reason knives cut is they concentrate the force over a very small area.

At a 10 km/s orbital encounter even a dry sponge will have no problem penetrating the metal hull of a spacecraft, both will turn to plasma. This is what a collision with a 7 gram object does[1], a sponge is about 100 grams and it's softness won't matter when it's traveling at hypervelocity.

[1]https://en.wikipedia.org/wiki/International_Space_Station#/m...

Tornadoes have been known to embed bits of straw or dried grass into trees. And tornado speeds are a gentle walk in the park compared to orbital speeds.

Wooden missiles are a thing too, or at least partially wooden. The WW2 German Rheintochter [0] surface to air missile had beautiful wooden control surfaces.

https://en.wikipedia.org/wiki/Rheintochter

Similarly, the Japanese Type 91 aerial torpedo was sometimes equipped with wooden aerodynamic stabilizers (which broke off when they hit the water.)

Russian Scientists Announce Six-Month Delay In Carving New Space Station: https://www.theonion.com/russian-scientists-announce-six-mon...

A large inverted cone could deflect space debris and junk off the orbit and towards earth. I don’t know how this feat could be executed though, maybe in the future when it will get cheaper to bring stuff into the obit a few cones like this could begin a cleanup stage.

I don't think the physics are on your side on this one.

This might be a good time to watch the movie made by the ESA about responsible satellite disposal.

https://www.youtube.com/watch?v=zT7typHkpVg

Wouldn't carbon fiber be a good candidate for replacing aluminium? It would burn up and result as carbon in the atmosphere similar to the wood, but should be more environment insensitive and probably lighter weight.

I don't know satellites at all, so bear with me if I'm being too naive.

Would it be feasible to put a self-destructive program in each satellite, such that when it retires, it moves off the orbit away from the earth, and spirals away?

Escaping earth's orbit is expensive. Much cheaper in mass/payload/$$$ to simply deorbit and burn up for a lot of low earth orbit satellites. Or even "free" - a lot of these satellite megaconstellations will be brought down by atmospheric drag within a year of running out of fuel:

https://en.wikipedia.org/wiki/Graveyard_orbit#Disposal_orbit

This also provides some passive decluttering of low earth orbit in case of hardware failures and the like.

Such self destruct programs (or manual commands from a ground station) are common for farther out orbits like geostationary, although they typically just enter a slightly different orbit where they're out of the way and not taking up valuable real estate in particularly useful orbits, instead of escaping earth's gravity or deorbiting completely.

No, it takes a lot of energy to get out of orbit. But unless the satellite is in a few very special locations in Earth's orbit, its orbit will naturally decay over time and eventually fall back to Earth, usually burning up in the atmosphere. (Above low-earth orbit this could take a very long time, but now satellites are required to be designed with deorbiting in mind)

Often some parts of the sat still make it to the ground, but SpaceX's Starlink sats for example are designed to fully burn up in-atmosphere within a year of deorbiting.

> No, it takes a lot of energy to get out of orbit

Does it? It takes ~10000 m/s of delta-v to reach low Earth orbit, but afaik only about extra ~30 m/s to deorbit, with aerobraking taking care of the rest of the velocity. Or is there any extra intricacy in the details?

I'm pretty sure parent meant "escape Earth's orbit", not "deorbit"

They were talking about escaping orbit (reaching escape velocity which is ~41% higher than the orbital velocity and requires getting more fuel into orbit), not degrading the orbit so that the satellite burns up in the atmosphere. As the article discusses, the latter has the flaw of putting alumina particles in the upper atmosphere which remain there for many years.

Orbital decay depends on a satellite's particular orbital height to a huge extent. A satellite orbiting 250 km up might come down in a week. The same one at 500 km might take centuries.

Graveyard orbits for GEO, and forced atmospheric drag for LEO.

Now, what happens if the propulsion is broken? Or out of fuel. Or the drag mechanism failed to deploy? How does any sophisticated deal with the physical reality of it not being able to move itself? Self retirement assumes the happy path that everything goes according to plan without breaking in a radiation rich environment moving at thousands of km per second.

The space debris section will have to pick it up manually: https://en.m.wikipedia.org/wiki/Planetes

One of my top three favorite shows ever. Still the standard I hold hard sci-fi to for doing the space environment right. Even if it's a bit dated on it's Japanese work place love interest plot.

Assuming you don't mean to literally blow up the satellite, unless you have enough fuel to boost the satellite to earth escape velocity (expensive), it's not going to "spiral away" but get boosted to an elliptical orbit where the highest point ("apogee") is going to be at a higher altitude, but the lowest point ("perigee") is still going to be the same low altitude it started from. You could do a second burn at apogee to circularize the orbit and thus keep the satellite at that altitude all the time, but that's more fuel again.

IIRC per a video by Scott Manley they do this for geostationary satellites and maybe at medium orbits, but for low-earth orbits (the majority of satellites) the extra fuel requirement goes against the cost advantage of LEO.

It’s a lot easier to go down than to go up - all you need is a spool of copper wire. When it’s time to deorbit, you just reel it out, and let the Earth’s magnetic field do the work.

+1 - delta v is what matters, and a regular explosive would not throw a satellite off orbit significantly.

But this makes me wonder - what is the minimum possible size for a nuke? I wonder if say 1-2kg nuke would be enough to throw all the debris out of orbit...

No matter how you explode it, turning one piece of debris into many pieces at even higher velocities is only making things worse.

To add to this, given what we're learn about nuclear weapons in school/media, you'd think a small fission device would convert the entire mass of the satellite into a ball of mixed plasma and vapour. A lot of the non-metallic mass of the satellite would probably vaporize, but any surviving bits would have a bunch of added kinetic energy.

Especially for things that reflect both infrared and soft x-rays, with pretty high melting points and pretty high thermal masses, nuclear explosions do less damage than you'd think.

There was a nuclear test where they put a steel sphere about the size of a bowling ball pretty close to a device similar to Gadget / Fat Man. Spoiler alert: it survived barely scratched.[0]

You could probably design a satellite with thin enough pieces of metal and add carbon black / carbon fiber to any polymers too transparent to IR/soft x-rays. You could probably also use a thermonuclear device, but the particle steams caught in the earth's magnetic field would damage satellites, and there's also the EMP to worry about.

[0] https://www.youtube.com/watch?v=by1xpy8ob8E

If the added velocities of the debris were unidirectional (along the debris's orbital velocity) then increasing their velocity enough would result in them breaking free of orbit. But I doubt that you would be able to do either in reality (not to mention detonating nuclear bombs in space seems like a bad idea regardless of any other factors).

>>" I wonder if say 1-2kg nuke would be enough to throw all the debris out of orbit..."

I don't get it. Can you blow something only in one direction?

Aproximately you can, if you detonate the bomb behind the object. But the depris of the bomb would still go in all directions.

Three problems with that idea:

[1] The smallest (publicly known) nuclear device ever built weighed about 23 kg.

[2] Detonating a nuke in orbit would cause a potentially devastating EMP.

[3] The Outer Space Treaty explicitly prohibits putting WMDs in space.

[1] https://en.wikipedia.org/wiki/W54

[2] https://en.wikipedia.org/wiki/High-altitude_nuclear_explosio...

[3] https://en.wikipedia.org/wiki/Outer_Space_Treaty

Probably better overall to vaporize your satellite by means of a ground based laser rather than an in-orbit nuke.

As usual, Scott Manley has an excellent video that discusses spacey things. This one is about Graveyard Orbits:

https://www.youtube.com/watch?v=ruf_mfjOt9k

Moving off the orbit is not as easy. You basically have to slow down in order to de-orbit, and that requires rockets. These end of life rockets adds to the weight of each satellite which adds to the cost of launching them.

Or do the opposite and use a hall effect thruster in order to maintain your altitude and velocity. Which is what Starlink has designed their LEO satellites to do, in order to have a natural failsafe in the event of a failure [1].

Though speculatively I've read that making sure the optics burn up in deorbit is a major problem to adding inter satellite laser links.

[1] https://spectrum.ieee.org/tech-talk/aerospace/satellites/spa...

"that requires rockets"

I'm curious about these absolute claims. Can a heavy mass object moving more slowly entangle a faster object to reduce velocity.

Can solar sails be used to reduce or change orbits?

Magnetic fields?

Physical characteristics and profile of sat vs orbit?

Put in a decaying orbit that is only maintained by a thrusters?

Very interesting to hear that the only way to slow something down is with rockets. Not atmo drag. No mag drag. No solar pressure etc.

You are right, the grand parent post was not absolutely correct. I also suspect that you already know the answers to your own questions. :) But in case someone don't:

"Can solar sails be used to reduce or change orbits?" Yes! It's a bit overkill, but yes that is something one can do.

"Magnetic fields?" There are very promising results in that direction too. A satellite can unfurl a long thin conductive tether. The magnetic field of the planet generates a current in the tether and a net drag on the sat.(To be 100% honest I don't understand this solution enough, but "Terminator Tether" is a term one can search for more info.)

"Physical characteristics and profile of sat vs orbit?" Maybe! On low orbits you can count on the very thin atmosphere to provide you some drag. It's a common practice for example with cube sats to not put them too high, so even if something goes wrong with their electronics they will deorbit on their own in a few months or years. You can also increase this drag by turning your sat to "face the wind" with the largest available cross-section. This trick doesn't really work on higher orbits though, and that's where "space junk" is generally a problem.

"Put in a decaying orbit that is only maintained by thrusters?" I'm not sure what you mean. Thrusters are rockets. But yes, that absolutely works. With the usual caveats. You have to budget enough fuel for the manoeuvre, and if your ageing sat craps out you might not be able to command it anymore.

The problem that wooden satellites would address is space junk falling to Earth and aluminum burning up on reentry, leaving particles in the atmosphere:

> We are very concerned with the fact that all the satellites which re-enter the Earth's atmosphere burn and create tiny alumina particles which will float in the upper atmosphere for many years

What about little drones that pushed them out of orbit?

https://www.hindawi.com/journals/jchem/2019/4753910/

There's some interesting work that's been done with using electromagnetic tethers to deorbit

This is interesting. Cant we automate this and have drones tether the debris? It could launch from the ISS by mechnical propulsion (throw that bad boy with a mechanical arm)

The ones I've seen are mostly intended to be installed on cubesats as a primary or backup method of deorbiting. However if it works well I suppose they could also be put onto little probes that latch onto problematic debris. Dunno if that's cost effective

Even if it were feasible... it seems like it would just defer the problem to a later time or place the burden on other intergalactic citizens.

Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.

it would be easier to have it spiral into the atmosphere and burn up

i mean thats what happens to most satellites anyway

So there is 3,600 piles of precious metals floating around up there. How long before someone builds a space drone to snare that bounty?

Once we start building things in space (beyond assembling pre-built modules) it might be worthwhile, although even then it might not be worth it, since it would take a lot of fuel to move from orbit to orbit catching dead satellites. In orbit fuel is approximately just as precious as metal, so any satellite-catching drone would have to be extremely fuel efficient.

What hurts more? Slamming into a 10 pound block of wood? Or a 10 pound block of metal?

> During this mission, he became the first person to throw a boomerang in space that had been specifically designed for use in microgravity.

Okay, you've won me over. This is awesome.

Doesn't smoke also float around in the atmosphere for years? Is it significantly different from alumina dust?

The year is 2132, and with the eradication of cancer, Japanese space splinters move into position of the leading cause of death in humans.

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