[HN Gopher] Space junk removal is not going smoothly
___________________________________________________________________
Space junk removal is not going smoothly
Author : awb
Score : 156 points
Date : 2021-04-14 14:18 UTC (8 hours ago)
(HTM) web link (www.scientificamerican.com)
(TXT) w3m dump (www.scientificamerican.com)
| coldtea wrote:
| Who would have thought...
| hinkley wrote:
| 'Catching' a piece of space debris is really a 7-dimensional
| problem, isn't it?
|
| You have to be in the right place at the right time (4), but if
| you have the wrong velocity (+3) you just end up causing the very
| problem you're trying to prevent.
| andrewflnr wrote:
| I think there has to be a way around this, at least for the
| small stuff. You ought to be able to catch flecks of paint and
| the like with a Whipple shield backed by a plate of steel. Or
| maybe the same kind of aerogel setup they use for collecting
| comet tails.
| hinkley wrote:
| I think we have done some experiments with that already but I
| can't recall what the outcomes were.
| ryandrake wrote:
| All I had to do is play a little Kerbal Space Program to
| understand how difficult it would be to clean up space junk in
| orbit. Orbit isn't like some 3D grid where you stick a roomba up
| there, and have it go back and forth until you get everything.
| Even if you have the technology that lets you grab anything you
| encounter, you first have to reach something. And then burn some
| fuel to match its orbit. And then burn some fuel to get to the
| next thing. And then burn some fuel to match that thing's orbit
| (more than before because you are now carrying more mass around).
|
| It might be better to keep everything up there. Assuming the junk
| is re-usable in some way: If one day, we do manage to build some
| kind of industry in orbit, it will need to consume raw materials,
| and having all this scrap in orbit already means you saved most
| of the energy cost it would have taken to get all that mass up
| there.
| phreeza wrote:
| I think the much more likely method would be a laser that heats
| one side of an object, causing a net propulsive effect leading
| to eventual deorbit.
|
| https://en.wikipedia.org/wiki/Laser_broom
| jcims wrote:
| Directed energy approaches are the only thing that will scale
| IMHO.
|
| The heating approach is one way, but I believe something that
| could use the kinetic energy of ablative laser pulses would
| work for smaller objects. To get the correct retrograde
| velocity, however, I believe you would need an orbital
| platform and some ridiculous laser technology (which, when
| combined, tend to create political drag)
|
| I also wonder about sending focused packets of ionized gas to
| collide with an object and reduce its kinetic energy. If you
| were operating in an opposite orbit you'd have a ~35km/sec
| closing velocity. Then spit out small targeted puffs of
| krypton/xenon at 50km/s, it wouldn't take a lot to knock real
| energy off of the target. (Stubby pencil work says 80
| femtojoules per molecule or roughly 30 micrograms of gas to
| reduce the velocity of a 20g bolt by 1000m/s. I think.)
| sand500 wrote:
| How would you prevent the puff of gas from diffusing into
| nothing? Where did you get ~35km/sec? ISS orbital speed is
| 7.66 km/s and it only gets slower the higher you go up.
|
| I was thinking something similar but instead launching
| equivalent mass of water in the exact same orbit in the
| opposite direction. Right before the collision, release the
| water. The water would spread enough that the entire
| spacecraft would basically slam into a wall. The net
| momentum post collision should be 0. Most spacecraft debris
| would fall straight down to earth.
| jcims wrote:
| Quick caveat, I'm extremely shallow in my knowledge of
| any of this:
|
| >How would you prevent the puff of gas from diffusing
| into nothing?
|
| My thinking about this is that at low concentrations the
| gas would maintain a largely ballistic trajectory and not
| be subject to typical diffusion properties. Would require
| a purpose-built accelerator to condition for 'beam'
| coherency. Not sure how well that scales.
|
| > Where did you get ~35km/sec? ISS orbital speed is 7.66
| km/s and it only gets slower the higher you go up.
|
| Major brain-o.
|
| Ultimately I think we're on the same page of 'kinetic
| deorbit', just a function of what is actually feasible.
| phreeza wrote:
| I assume you are proposing to launch these packets from
| some other sattelite? Then by conservation of momentum, you
| will be boosting your own orbit by the same amount you are
| diminishing the target, right? Not sure this would be a
| very sustainable model.
| jcims wrote:
| Yes it would require equal/opposite correction and lots
| of mass on board to send.
| hinkley wrote:
| I believe I saw a Scott Manley video recently where he
| mentioned that he does consulting work for people, and one of
| his customers apparently doesn't know about KSP because he
| built their simulation in something like a day and they were
| astonished that he was done already.
|
| Most of the SpaceX commentators use it too.
|
| It's always cool to me when something meant as a toy gets used
| for real. Like city planners practicing in SimCity or more
| recently CitySkylines.
| jniedrauer wrote:
| It should be noted that Kerbal Space Program's orbital
| mechanics are not all that realistic, especially when you
| introduce the three-body problem. The world of KSP is also
| scaled down to about 1/10 of real life unless you use mods. A
| game like Orbiter really reinforces how much harder the
| problems are at real-life scale.
| Dylan16807 wrote:
| It always struck me as weird that you have to mod KSP just
| to make gravity assists work accurately or Lagrange points
| work at all.
| wtallis wrote:
| The default physics model in KSP was chosen for its
| computational simplicity, which allows for the extensive
| maneuver planning tools without requiring high-end
| hardware to continually re-run n-body simulations at
| several orders of magnitude faster than realtime.
| uomo wrote:
| For those that haven't seen the video, he consulted on the
| Netflix film 'Stowaway' (that comes out later this month). He
| whipped up a design for the proposed spacecraft in a few
| minutes to help the directors visualize it better.
|
| Video: https://www.youtube.com/watch?v=WCwXJMVVdck
| dylan604 wrote:
| There's another game that I think really goes to show orbital
| mechanics in how a little for longer is better (in
| controlibility) than faster for shorter. It's one of those low
| action games, so if you're into FPS, probably not your cup of
| tea. There are a couple of levels specifically for the
| oribiting examples.
|
| https://apps.apple.com/us/app/osmos-for-ipad/id379323382
| rtkwe wrote:
| In theory you could do it without completely matching orbits to
| save a lot of fuel. Just getting a close slow encounter,
| grabbing it and letting your orbit just be whatever the new
| average of your velocities is. It'd require a stronger capture
| system perhaps depending on the mass of your capture vehicle,
| but it would save a lot of fuel.
|
| Recycling what's up there might eventually be viable but for
| the start we'll be shipping up raw stocks. Recycling is
| probably about as difficult as refining from metal rich
| asteroids once you consider all the coatings and paints that
| are added to things and having to sort all the different
| metals, plastics, and what have you out.
| fatiherikli wrote:
| This is amazing too
| chr wrote:
| Netflix has the South Korean SF flick "Space Sweeper". Do read
| the serious article first. The film is for entertainment.
| Crossing Belter and cyberpunk aesthetics, mixing up human
| languages as you'd expect from the future, it's fun.
|
| Warning, link autoplays with sound:
| https://www.imdb.com/video/vi1534902553?playlistId=tt1283876...
| Diederich wrote:
| The following is based on the assumption that more and more stuff
| is going into earth orbit over time.
|
| As others have noted, putting satellites in lower orbits, below
| 500km or so, definitely helps with keeping things tidy.
|
| Beyond that, robust regulation about ensuring that very little or
| no additional non-useful stuff is placed into orbit is also good.
| That is, require everything that isn't useful to deorbit right
| away or relatively quickly, and have the ability to deorbit at
| EOL.
|
| What's beyond all that is the set of all things in orbits that
| aren't useful and that will naturally stay up there for a long
| time, in addition to any NEW stuff that's added, either by error
| or by accident. For example, a satellite in a 1000km orbit that
| has everything it needs to deorbit at the ends of its life, but
| fails to do so for whatever reason.
|
| As others have noted, matching orbits is a lot harder than most
| people realize. Specifically, it's quite energy intensive.
|
| At this point, basic physics tells us what we must do. In order
| to get long-lived, useless stuff out of orbit, we need to be able
| to send up specifically designed stuff, and a lot of it.
|
| In summary: the most fundamental solution to this problem is to
| vastly decrease the price per kg to orbit. Regulation helps, but
| does nothing to clean up what's already there, and to resolve the
| unintended addition of new junk.
|
| Summary to the summary: the newest crop of launch providers are
| aggressively working on this problem by aggressively pursuing
| reusability.
| tester89 wrote:
| This is the premise of _Planetes_ if anyone is an anime fan here.
| aeroheim wrote:
| I was just thinking this!
| albalus wrote:
| Same!
| masklinn wrote:
| > if anyone is an anime fan here.
|
| Or manga, it's originally a manga series before the 26-episode
| anime adaptation.
|
| The anime actually diverges from the manga in the latter
| section, because it was started before the series had ended
| (the manga finished serialisation in January 2004, the anime
| finished airing in February of the same year... and it was a
| 26ep full-season thing), so viewing both can be interesting in
| more ways than the usual watching of filler and interest in
| cross-media adaptation:
|
| > While the manga deals more with existential themes, and
| humanity's relationship with space, the anime further expands
| the political elements of the story.
| somedude895 wrote:
| Man I love Planetes, such a good series! They put some effort
| into keeping it realistic too:
| https://en.wikipedia.org/wiki/Planetes#Realism
| sand500 wrote:
| Love Planetes, I always tell my friends its Gravity done right.
| joshstrange wrote:
| It might be silly that it wasn't until watching this anime (and
| the whole premise for WHY space junk removal was/is so
| dangerous as shown by the show) that I fully "understood" the
| problem with space junk. It was good show on it's own as well
| but it really made the "space junk" click for me.
| busterarm wrote:
| bomb ass opening theme song, for real.
| readingnews wrote:
| And after all those warnings.
| https://www.youtube.com/watch?v=1REkejAMnNo
| visviva wrote:
| "Not going smoothly" is weird phrasing - it's not "going" at all.
| It's still in the technology development phase, and meanwhile
| there is still insufficient consensus that more dramatic action
| needs to be taken.
|
| I know the article touches on these points, I am mostly just
| commenting on the strange headline.
| mesofile wrote:
| My hope is that the space junk problem becomes so severe that it
| forces all humans to realize there's no point to pursuing schemes
| of colonizing other planets, or even our own planet's orbital
| reaches, until we learn to better manage the industrial processes
| that take us there. Like a safety mechanism that ensures species
| who pollute excessively remain trapped on their own spheres and
| don't go spewing their shit all over the cosmos.
| tjs8rj wrote:
| Why not do both in parallel? A few decades of pausing space
| progress now could have a much bigger impact than later, and
| it's not like space travel is so easy that we'll suddenly wake
| up colonizers of the entire solar system. Did you fully mature
| before you went out into the world? Sometimes making relatively
| small mistakes is the fastest way to learn. "Move fast and
| break things", but on the species scale.
| [deleted]
| adwn wrote:
| > _and don 't go spewing their shit all over the cosmos_
|
| Why? What's the downside to littering on some random asteroid?
| There's no ecosystem that would care - not even bacteria -
| nothing and nobody would mind if you drop a plastic bag on 423
| Diotima. Take a step back and think about why pollution on
| Earth is bad, and you'll realize that "polluting" an asteroid
| isn't ethically wrong.
|
| Of course, that only applies as long as those asteroids are
| utterly devoid of life. Once there's an ecosystem, polluting
| becomes ethically wrong again.
| 5e20ad3b-cdda wrote:
| >Take a step back and think about why pollution on Earth is
| bad, and you'll realize that "polluting" an asteroid isn't
| ethically wrong.
|
| Of course, that only applies as long as those asteroids are
| utterly devoid of life. Once there's an ecosystem, polluting
| becomes ethically wrong again.
|
| Why? There is no ecosystem on top of Everest yet people will
| get upset when they see what it looks like.
|
| This is an aesthetic decision, not a moral one.
| wongarsu wrote:
| I think in the vast majority of cases it is an ethical
| concern, but I agree that even in the absence of ethics
| there is an aesthetic dimension. Usually we rephrase it
| under the umbrella of "preserving it for future
| generations"
| aero-glide2 wrote:
| Heh, reminds me of that Jeff Bezos incident : At one meeting,
| Bezos was regaling attendees with visions of hollowing out
| asteroids and transforming them into space arks when a woman
| leapt to her feet. "How dare you rape the universe!" she
| said, and stormed out. "There was a pause, and Jeff didn't
| make a public comment," says Kevin Polk, another member of
| the club. "But after things broke up, Jeff said, 'Did she
| really defend the inalienable rights of barren rocks?' "
| aardvarkr wrote:
| Ha that's a pretty funny anecdote, thanks for sharing
| dalbasal wrote:
| Before we get so excited about those high tech huts everyone is
| sleeping in these days, we should work on the problems we have
| right here in our caves.
|
| Will huts help us share our mammoth meat more peacefully? Will
| huts make Atkinson Clan stop beating up Montanas? Will huts
| make Montanas any less annoying?
|
| Mark my words, sisters and brothers. These problems will go
| with us wherever we build huts. Until we learn to make Montanas
| less annoying and Atkinsons less murderous, I say we stay in
| these caves.
| yifanl wrote:
| Kicking the can down the road is a sustainable policy, making
| the can bigger each time we kick it is not.
| dalbasal wrote:
| That's true. Shortly after we moved out of the caves
| Atkinsons and Montanas invented warfare. We should have
| stayed in the cave. I'm sorry, my grandchild. Never leave
| earth.
| yifanl wrote:
| Sure, we can sustain ourselves off "one step forwards,
| one step back still moves us somewhere else", but the
| average person doesn't see how many steps back we take to
| make those steps forward and will come to an overly
| optimistic plan to move.
| barbazoo wrote:
| Except that the cavemen were able to live sustainably in the
| cave in the first place.
| adwn wrote:
| That's highly misleading. Pre-agricultural humans weren't
| some kind of noble savages, living in perfect harmony and
| balance with nature. They lived "sustainably" only in the
| sense that their environment killed them off at the same
| rate as they procreated, not of their own volition.
| dalbasal wrote:
| Between (and in defiance of) those two positions are some
| interesting ideas about sustainability.
|
| On one end, "cavemen" are sustainable humans with implied
| cultural virtues. On the other, the pre agricultural
| equilibria is mostly about high human mortality and low
| population size.
|
| At any given time though, people often had cultural
| understandings of natural ecosystems. We started being
| humans by living as part of such ecosystems, and
| undoubtedly both caused and witnessed all sorts of sudden
| changes and disasters... some linked to human activity.
|
| If you live in an areas, and rely on plants, game and
| such... your culture is more likely to be "literate" in
| these things. Game can be hunted out, plants
| overharvested. A population surge in one species may
| deplete another. "Balance" can be restored, sometimes in
| a more or less beneficial way than before. These are all
| observable, and of great interest to people (those left)
| who make their living this way. The occasional and
| unpredictable flush of rabbits one autumn, is relevant to
| the life of someone who eats them.
| wizzwizz4 wrote:
| https://en.wikipedia.org/wiki/Mammoth#Extinction
| barbazoo wrote:
| Interesting, thanks for the link. My comment however was
| in response to the comparison cave/hut, not caveman
| lifestyle in general. But I get what you're saying. Maybe
| we're just fundamentally unable to live sustainably, by
| design so to speak.
| dalbasal wrote:
| _" And the problem is now poised to get much worse because of the
| rise of satellite "mega constellations" requiring thousands of
| spacecraft, such as SpaceX's Starlink..
|
| ..It takes an Iridium-Cosmos-type collision to get everyone's
| attention. That's what it boils down to.... And we're overdue for
| something like that to happen._"
|
| Perhaps the former is gentler, more statistical an alternative to
| the latter. Everybody be so cataclysmic these days.
| xoa wrote:
| While I know Scientific American is a fairly mainstream targeted
| and softer science publication, this
|
| > _And the problem is now poised to get much worse because of the
| rise of satellite "mega constellations" requiring thousands of
| spacecraft, such as SpaceX's Starlink, a broadband Internet
| network._
|
| really could have used a LOT more qualification particularly
| since it's become a major recent talking point. There is one
| ultimate sure-fire way to reduce space junk: _launch stuff to
| very low orbits_. There is still some atmosphere (varying with
| heating and other factors) up a long ways in "space", and it's
| only above 600km or so that orbital drag becomes negligible
| enough that lifetimes really stretch out. The ISS for example
| requires regular reboosts or it would decay back into the
| atmosphere.
|
| SpaceX focusing on economics has made it feasible to start
| planning constellations of comm sats that are low and very low
| earth orbit, with the understanding that inherently their
| lifetimes will be measured in single digit years. But that's ok
| since they can be replaced so cheaply. This is much better, not
| worse. Even if they go offline or got hit, the debris would have
| a very restricted lifetime. The media should do a better job of
| conveying how cheaper $/kg to LEO opens up a lot of new
| possibilities in what regulations are feasible and how we think
| about the basics of satellite design. A simple "Mega
| constellation bad!" is all wrong, and that's not necessarily
| going to be intuitive to everyone.
| sandworm101 wrote:
| >> launch stuff to very low orbits. >>Even if they go offline
| or got hit, the debris would have a very restricted lifetime.
|
| That approach can help, but the problem persists. Lower orbits
| are much smaller than higher orbits. Focusing
| megaconstellations into a narrow 100-110km band is asking for
| trouble. The kessler syndrome could occur in a very narrow
| band, quickly rendering even short-lived satellites
| uneconomical. The narrower the band of orbits, the more likely
| and more aggressive kessler becomes. It is one thing to loose a
| few sats every year, very much another to have your entire
| constellation wiped out _every_ year.
| Tuna-Fish wrote:
| If you are low enough, Kessler is simply not possible because
| square-cube scaling means that the fragments deorbit in less
| than a single orbit.
| SavantIdiot wrote:
| > inherently their lifetimes will be measured in single digit
| years. But that's ok since they can be replaced so cheaply
|
| Oh cool, let's shoot even more soon-to-obsolete pollution into
| the atmosphere. That's working so well on Earth. /s
| javagram wrote:
| 1000s of satellites are irrelevant to atmospheric pollution.
| The numbers are so small compared to the vast size of the
| atmosphere it isn't really a concern to worry about.
|
| Atmospheric pollution from earth based sources is different
| because it's something that is being done in the scale of
| billions of people, not 1000s, and CO2 doesn't naturally
| disappear from the atmosphere over time and is growing decade
| after decade.
| SavantIdiot wrote:
| You're so confident. How adorably naive.
| mminer237 wrote:
| Aren't their lifetimes so short because they will fall out of
| orbit? That's not really polluting orbit.
| phreeza wrote:
| Wait, how does launching stuff to low orbits reduce space junk?
|
| Edit: I think I now understand your comment. I mean sure it
| maybe adds less space junk than launching things into higher
| orbits, but it doesn't really reduce it, right?
| aftbit wrote:
| There's atmosphere up there, so it creates drag which slows
| the stuff down and causes it to re-enter and burn up or crash
| onto the planet in only a few years. Compare that to higher
| orbit, where there's much less drag and space junk could last
| centuries or more before it deorbits.
| ericbarrett wrote:
| Low Earth orbit satellites drag in the fringes of the upper
| atmosphere a lot more, so their lifetime in space, unboosted,
| is typically only a few years. If your satellite dies, it's
| "self-cleaning."
|
| That said, an impact at this level can still spew debris into
| higher orbits, as the chaos of the collision can impart
| enough energy to some collision ejecta to change their orbit
| significantly. So you still don't want things bumping into
| each other.
| [deleted]
| gumby wrote:
| It's subject to drag from the whispy atmosphere and
| relatively quickly de orbits and burns up (thus no junk is
| left behind)
| jkilpatr wrote:
| It's not a matter of 'more' or 'less' rather than 'easier to
| deal with'.
|
| LEO sats will probably produce more space junk by mass but
| junk in LEO will be gone in a few years, no matter how much
| or little of it their is.
|
| On the other hand Geostationary satellites produce much less
| junk in terms of mass, but once it's up there it's not coming
| down for centuries.
| ortusdux wrote:
| Atmospheric drag causes a relatively speedy deorbit if not
| actively resisted. The starlink satellites use Hall effect
| thrusters to maintain their orbit. If a unit fails, it should
| deorbit in under 5 years. If the thrusters work, they could
| also force it to deorbit much faster. The risk comes from
| debris from a possible collision being ejected into a higher
| orbit.
|
| https://en.wikipedia.org/wiki/Orbital_decay#Atmospheric_drag
|
| https://en.wikipedia.org/wiki/Starlink#Space_debris
| gregmac wrote:
| > The risk comes from debris from a possible collision
| being ejected into a higher orbit.
|
| Is that a thing that can happen?
|
| My intuition is it would be possible if a rocket currently
| boosting to a higher orbit were to collide with something
| on its way there, but two objects in the same orbit
| colliding couldn't get enough delta-v to actually get to a
| higher orbit. They could maybe get "higher", but not at
| orbital speeds and so would rapidly decay.
|
| I know next to nothing about orbital mechanics, so maybe
| someone who does can provide some better insight here.
| pilom wrote:
| Set a baseball on top of a basket ball and drop them both
| from waist high, the baseball will shoot really high into
| the air by stealing energy from the basketball. The same
| principle can occur when you start breaking pieces off of
| spacecraft with collisions. Also the two colliding
| objects might not be in "the same orbit" one could be in
| a polar orbit and one could be in a more equitorial
| orbit. One could be circular and the other highly
| eliptical, etc. This could boost parts of one of them
| into a higher orbit (though honestly it would be just as
| likely to slow things down).
| SideburnsOfDoom wrote:
| > Ejected into a higher orbit. Is that a thing that can
| happen?
|
| Apparently not as such. See sibling comment
| here:https://news.ycombinator.com/item?id=26809297
| Dylan16807 wrote:
| The way to think about orbits is not one height but two:
| apoapsis and periapsis.
|
| Debris from an explosion/collision can have an unlimited
| apoapsis, but the periapsis is _at most_ the altitude of
| the incident.
|
| So if it started in low orbit, it will still drop down
| regularly, and drag will still remove it over time.
| IlliOnato wrote:
| I am no expert either, but a paper-napkin calculation
| tells me yes, this can happen.
|
| Basically, just based on impulse and energy conservation,
| and some assumptions on the size and number of fragments,
| a head-on collision of two satellites going opposite
| directions at the same orbit should send some pieces of
| debris into much higher orbit.
|
| How likely this is to happen in reality, and thus how big
| a problem this could be is a subject of modeling and much
| more complex calculations.
| bdamm wrote:
| It turns out that intuitive reasoning for orbital
| mechanics is not easy. Two satellites having a head on
| collision become space junk because now you have many
| fragments that themselves can't control their altitude or
| deorbit. Fragments that are ejected from the collision
| cannot have more than energy than they had originally,
| nor can they change direction very much. If pieces are
| ejected vertically, they are always going to have less
| lateral velocity than they had going into the collision,
| therefore will end up in an elliptic orbit with a high
| probability of colliding with the atmosphere at perigree.
|
| See "can you throw a baseball from the ISS and hit the
| earth" (No, you can't.)
| jholman wrote:
| I think you're claiming that it is impossible for two
| colliding objects to release fragments that have more
| energy than either of the original objects. That's wrong.
|
| If it helps, start by imagining two satellite-like
| machines colliding in interstellar space (i.e. not in
| orbit), where they were initially moving at 1m/s in
| opposite directions. Even ignoring the possibility of an
| explosion (unspent fuel, pressurized areas, I dunno),
| it's still very easy for interactions to violently fling
| individual parts outward at speeds higher than 1m/s.
|
| Of course, my guess is that the possible amounts of
| additional delta-v are pretty low, like 100 m/s, and as
| such the resulting orbit would not be _much_ higher than
| the original orbit. But that 's just wild conjecture.
| lutorm wrote:
| If you were to collide two LEO satellites and turn them
| into fragments, even if you give those fragments much
| higher velocity than the initial satellites, you _cannot_
| launch them into a higher orbit.
|
| Fragments that are launched down obviously hit the Earth.
| But an orbit is a closed ellipse, so the fragments that
| are launched up will _also_ hit the Earth -- they'll just
| go up steeply, turn around, and come down. The only
| fragments that won't initially hit the Earth are the ones
| that are ejected tangentially, parallel to the Earth's
| surface. Those will go into an elliptical orbit with a
| high apogee and perigee at the altitude of the collision.
| Which means they will _still _come down to that altitude
| and gradually lose energy.
| phreeza wrote:
| The key insight there doesn't have that much to do with
| orbital mechanics, it's more that in a collision, small
| fragments can come out with vastly more momentum than
| they went in with, which in orbits translates to a higher
| apogee. If you have ever bounced a small ball off a large
| one, you know the effect. See this video for an intuitive
| example https://youtu.be/2UHS883_P60
| lutorm wrote:
| Yes, it translates into a higher apogee, but not a higher
| perigee. So they will still come down to the altitudes
| with higher drag.
| myself248 wrote:
| It's like building a structure in the middle of the plains
| where it'll sit untouched for decades, versus building a
| structure on the beach where the incessant waves will grind
| it to bits in short order.
|
| Objects in low orbit don't stay there. They're slowed down by
| the atmosphere, and re-enter in a few months or a few years.
| Only if they're healthy enough to orient themselves, and have
| the fuel to do it, can they perform the re-boost maneuvers
| necessary to overcome atmospheric drag and stay up for
| longer.
|
| So, a satellite which loses control, or gets smashed into
| bits which can't individually control themselves, just
| becomes fodder for the drag. It gets swept out of orbit by
| the wisps of atmosphere out there. Low orbit is very "clean"
| in terms of junk, because junk simply can't linger there.
| Just like there aren't a lot of ancient ruins on the beach.
|
| The exact degree of drag is unpredictable because the
| exosphere is subject to a lot of variables, hence the "months
| to years" ambiguity. But they don't stay out there for
| decades or millennia, like junk in higher orbits.
| cptskippy wrote:
| > It's like building a structure in the middle of the
| plains where it'll sit untouched for decades, versus
| building a structure on the beach where the incessant waves
| will grind it to bits in short order.
|
| That is a fantastic analogy.
| bombcar wrote:
| If the cost to LEO is a fraction of the cost to HEO or
| geostationary, it becomes economical to send cheap satellites
| to LEO and let them burn up in a few years than to send
| expensive satellites to HEO or geostationary and let them
| become multi-decade space junk.
|
| Eg if it is $10m to LEO and $15m to HEO you will pay the
| extra to get to HEO and put a satellite designed for long
| life - but if it is $1m to LEO you can build a cheaper
| satellite and launch it 5 times over the following decades.
| jakear wrote:
| But they aren't building 1 satellite and launching it 5
| times over the next decade. They're maintaining a constant
| fleet of 42000 satellites, which means putting up new junk
| to replace the old junk while its still flying junk and not
| de-orbited junk.
|
| I like the idea of having internet on my sailboat as much
| as the next guy, but it takes some serious cognitive
| dissonance to convince oneself that 42,000 pieces of nearby
| junk is better than a handful of pieces of far away junk.
| xoa wrote:
| > _They're maintaining a constant fleet of 42000
| satellites, which means putting up new junk to replace
| the old junk while its still flying junk and not de-
| orbited junk._
|
| No. First, The whole reason they need to _maintain_ a
| fleet, rather then just having it sit there for decades,
| is that they 're so low. The vast majority of planned
| Starlink satellites from that number are from Phase 2,
| and are V-band VLEO sats with orbits around 340 km, which
| is _really_ low. At that altitude, natural decay time is
| measured in weeks at best. To work they 'll need both
| active thrusters providing regular boost and aerodynamic
| low drag design (and maintaining orientation for that
| will itself require fuel). Should they actually lose all
| control through malfunction or a collision, they and
| resulting debris will deorbit very rapidly (they'll both
| have no boost and be less aerodynamic).
|
| And second, "through _malfunction or collision_ ",
| because it's not as if SpaceX (and other LEO satellite
| operators) doesn't have, and indeed are required to have,
| plans for controlled deorbit at EOL. Most of the
| satellites can be expected to get deorbited in a
| controlled way as planned. Making sure everything burns
| up has been one of the things slowing Starlink
| development, it took some work to ensure the optical
| links would properly go for example.
|
| SpaceX is not interested in leaving them up there. I
| mean, FFS people, who would be hurt _more_ than SpaceX by
| Kessler Syndrome!?
|
| > _I like the idea of having internet on my sailboat as
| much as the next guy, but it takes some serious cognitive
| dissonance to convince oneself that 42,000 pieces of
| nearby junk is better than a handful of pieces of far
| away junk._
|
| Your dismissiveness towards hundreds of millions of
| underserved people and challenging use cases and
| ignorance of orbital dynamics does you no favors here.
| vagrantJin wrote:
| > Your dismissiveness towards hundreds of millions of
| underserved people and challenging use cases
|
| This is pompous and elitist nonsense of the highest
| order. People have other more pressing concerns than fast
| internet. You know...like water, food and cheap power.
| SonicScrub wrote:
| Communications infrastructure is essential for any
| developing/developed nation. It's easy to take for
| granted while living in an urban center of a 1st world
| nation just how game-changing communications is. A truly
| global, easily accessible network has the potential to
| lift millions out of poverty through facilitating
| economic growth of remote, unconnected areas. Dismissing
| satellite constellation networks as merely "faster
| internet" misses the bigger picture.
|
| Also it's worth noting that communications networks is
| but one application for LEO satellite constellation
| technology.
| matmatmatmat wrote:
| > Your dismissiveness towards hundreds of millions of
| underserved people and challenging use cases and
| ignorance of orbital dynamics does you no favors here.
|
| Imagine thinking that a product that costs $500 up-front
| and $99/mo thereafter and uses ~100 W constantly is
| designed for "hundreds of millions of underserved
| people".
| xyzzyz wrote:
| > and maintaining orientation for that will itself
| require fuel
|
| With some gyroscopes, I think they only need electricity
| for it, not actual reaction mass.
| ravi-delia wrote:
| It's not less so much as zero. Space junk isn't really a
| problem to worry about below a certain point.
| dahfizz wrote:
| > I mean sure it maybe adds less space junk than launching
| things into higher orbits, but it doesn't really reduce it,
| right?
|
| Sure, but that's not really the point. Using biodegradable
| plastic is much better than traditional plastic that stays in
| landfills forever. "Just don't generate trash" isn't an
| option.
| ouid wrote:
| There is literally no problem with plastics that stay in
| landfills forever. Landfills are underground, like the oil
| that the plastic is derived from.
| simonh wrote:
| Landfills are generally very close to the surface,
| filling holes created by activities like strip mining, so
| they do occupy surface area. Unless you're wiling to dig
| down under existing landfill to dig out voids to pack
| with more landfill.
| ouid wrote:
| Landfills are covered when they are full, effectively
| isolating them from surface ecosystems.
| simonh wrote:
| The point is you can't use that area for getting rid of
| landfill anymore. From that perspective that area is
| 'used up'.
| boringg wrote:
| Also, take out SpaceX from the name and add all the competitors
| (potentially lower quality) that are starting or about to get
| into the space and you can understand the concern.
|
| edit: my concern is the long chain of the curve of low-orbit
| satellite companies as price continues to have downward
| pressure.
| samstave wrote:
| Why not incentivize these companies with grant such that they
| will get the grant if their TO orbit launches _include_ the
| retrieval of space junk as well on the RETURN back to earth.
|
| In order to go up, you have to bring something back.
| simonh wrote:
| Rendezvousing with, capturing and then manoeuvring with a
| captured object is an extremely hard and as yet unsolved
| problem, although there are some experiment. Also it is
| only feasible to rendezvous with a target on an almost
| identical orbit, otherwise the fuel and thrust requirements
| to reach it very quickly balloon to hugely prohibitive
| proportions.
| ChickeNES wrote:
| > Rendezvoing with, capturing and then manoeuvring with
| another object is an extremely hard and as yet unsolved
| problem, although there are some experiment
|
| Umm...this is utterly wrong, and has been since Gemini 10
| in 1966, not to mention Skylab, Mir, ISS
| nordsieck wrote:
| > Umm...this is utterly wrong, and has been since Gemini
| 10 in 1966, not to mention Skylab, Mir, ISS
|
| There's a big difference between docking with a
| spacecraft that is designed to be docked with and
| capturing a satellite that was not designed to be
| captured.
|
| People are making good progress on this - Northrup
| Grumman just had a successful life extension satellite
| mission very recently. But it's far from a mature
| technology.
| TeMPOraL wrote:
| Makes no sense. Satellite retrieval is something that you
| definitely want to run a _separate_ mission for - you don
| 't want to bolt a visit to a completely separate orbit (and
| then transfer back to reentry) on top of a regular mission.
| The amount of fuel you need to launch something grows
| exponentially with the amount of fuel you need at the final
| stage.
|
| Not to mention, if you're thinking of making LEO launches
| do this, then they'd either have to capture other LEO junk
| (makes little sense, most of it will deorbit itself), or
| you'd have to bolt on additional stage, which may very well
| introduce _more_ junk itself (are people still using
| explosive bolts for upper stage separation?).
| xoa wrote:
| > _edit: my concern is the long chain of the curve of low-
| orbit satellite companies as price continues to have downward
| pressure._
|
| While this isn't entirely unreasonable, consider a few
| things. First, this is one case where even natural incentives
| line up pretty well. For the foreseeable future, no one is
| going to have more economic incentive to prevent the loss of
| usable LEO than companies that build themselves around usage
| of LEO. There are also virtuous spirals in the very
| technology that makes low cost possible, ie., the only way to
| reach SpaceX's targeted launch costs with Starship are to
| have a full reusability, and that itself cuts a ton of
| orbital debris (spent stages).
|
| Second, much cheaper mass and higher cadence changes
| everything in space engineering, and that includes giving
| regulators significantly more leeway in what they can
| reasonably require. Things like more redundant controlled
| deorbit systems, requirements for lower orbits by default
| with higher orbits reserved, requirements for materials, and
| so on all ultimately boil down to how much it costs to get a
| kg to orbit and how regularly it can be done. More leeway
| there makes a lot of things easier without destroying
| utility, which in turn raises the chances we can make solid
| systematic changes.
|
| Not saying there isn't plenty of room for error overall, or
| that regulators shouldn't be thinking about it too. But I do
| think the "mega constellation commercial" focus is mostly
| misguided. If anything the biggest risks seem to be from
| government actors, in terms of things like a-sat weapons and
| Old Space big companies not feeling the need to care.
| arrosenberg wrote:
| > For the foreseeable future, no one is going to have more
| economic incentive to prevent the loss of usable LEO than
| companies that build themselves around usage of LEO.
|
| This line of reasoning never seems to work out the way you
| are suggesting. It's more likely to wind up in a giant
| Mexican standoff once there a multiple entities who all
| have the individual ability to ruin it for everyone.
| boringg wrote:
| Full reusability makes sense and limits space junk - though
| the counter to that is they are launching more satellites
| into space - so probably negate each other to a certain
| point.
|
| I guess my concern would be who actually has regulatory
| authority over space and how can they ensure all actors
| play fairly. I would have to imagine this is a situation
| that is similar to the tragedy of the commons type
| scenario.
|
| To be clear - I really don't fall into one side of the camp
| or the other but I can see how a lot of the waste
| management side of things can fall by the wayside given our
| track record on waste cleanup (mines, municipal solid
| waste, nuclear)
| nordsieck wrote:
| > and that itself cuts a ton of orbital debris (spent
| stages).
|
| Almost all upper stages for LEO missions get deorbited (or
| at least they're meant to be deorbited). It's typically
| only the high energy missions like GEO/GTO where upper
| stages get left in a "graveyard orbit".
| [deleted]
| vict7 wrote:
| You seem to know a lot about this subject! Years ago, an
| acquaintance of mine told me of their idea to use railguns to
| remove space junk. Is this a remotely feasible solution?
| TeMPOraL wrote:
| From space, maybe. A railgun on the surface of Earth that was
| trying to slow down a piece of space junk would, by
| necessity, be aimed at a low angle. Getting a projectile a
| couple hundred kilometers up while launching at such angle
| would make this railgun be something between a window-
| shattering nuisance and a weapon of mass destruction,
| depending on muzzle velocity and the size of the projectile.
|
| The problem is, of course, the atmosphere. That thick soup of
| gas that's at its densest near the surface, and has the
| annoying tendency of engulfing hypersonic projectiles in a
| thick ball of screaming-hot plasma.
| nabla9 wrote:
| Altitude Lifetime 200 km 1 day 300 km 1
| month 400 km 1 year 500 km 10 years 700
| km 100 years 900 km 1000 years
| tim333 wrote:
| Ha - and the altitude of the space station is 408 km so most
| of the junk should clear out in a year? That sounds too easy.
| pilom wrote:
| The space station has to add energy almost weekly to
| overcome drag. If it didn't it would likely come down
| within a couple years. When they want to throw trash away,
| they literally just drop it off the side and it burns up
| eventually: https://gizmodo.com/iss-ditches-2-9-ton-pallet-
| of-batteries-...
| spookthesunset wrote:
| Would that stuff cause a huge fireball in the night sky?
| 2.9 tons is a hell of a lot of mass... amazing to think
| it will just burn up in the atmosphere.
| SonicScrub wrote:
| Because it is really that easy. Space-junk in low-earth
| orbit is not really a concern, and alarmist articles about
| space-junk in connection with projects like Starlink are
| just click-bait that rely on the general public's ignorance
| of orbital mechanics and space.
|
| Medium and high orbits are a different story. Space junk is
| absolutely a real concern here.
| IlliOnato wrote:
| This is important correction. But a high-speed collision at a
| very low orbit can trow debris to not-so-low orbit.
|
| How big of a problem this can be is something to model and
| calculate, it's not something one figures out just from the
| general principles.
| fooker wrote:
| > But a high-speed collision at a very low orbit can trow
| debris to not-so-low orbit.
|
| This seems wrong, from what I understand of orbital
| mechanics.
| bdamm wrote:
| Yeah, the terminology is wrong. It's not a high orbit, it's
| a high ballistic trajectory, which then is terminated on
| the low side. But if that object improbably happens to
| collide with a high-orbit object then you could get a
| spreading of the consequences to higher orbit.
| nharada wrote:
| Curious how big of an issue this actually ends up being since
| they can't be put in a _stable_ higher orbit without a second
| burn /collision to circularize. Without a change to the orbit
| perigee it would still decay, just more slowly?
| [deleted]
| arjunnarayan wrote:
| A high speed collision in low orbit can change a circular low
| orbit into an elliptical eccentric orbit that _intersects_ a
| higher circular orbit, but unless there is an additional
| accelerating event at that higher altitude, it cannot
| recircularize its orbit at that higher altitude.
|
| There are thus two takeaways:
|
| 1. By definition, this means that part of the orbit will
| always be at low altitude, regardless of the collision
| dynamics. So this means that it will continue to decay over
| time, albeit perhaps at a slower rate (decay being
| proportional to the time spent at lower altitude).
|
| 2. While that eccentric orbit will intersect with a higher
| circular orbital plane, it does so in a predictable fashion
| that can be routed around. The higher orbits are also much
| sparser, so the chance of this intersecting with a satellite
| that is already present is very, very small.
| IlliOnato wrote:
| Thank you, others pointed this out too. Proves that
| "celestial mechanics" is trickier than I thought.
|
| I guess if a collision is messy enough, there would be
| secondary collisions between debris pieces, and it sounds
| like these in principle can push some junk into higher
| orbits. But I think the probability is really low; this
| should not be a concern.
| cogman10 wrote:
| I don't see how that's a major issue, It'd take a pretty odd
| angle for a high speed collision to push something into a
| higher orbit. That seems like a pretty rare event.
| bodhiandphysics wrote:
| Not really. High speed collisions are high entropy events,
| so debris fills state space, and you get SOME debris at
| high altitudes (usually in highly eccentric orbits). That
| being said, low altitude is much safer since you don't get
| as many long lived dead satellites
| jerf wrote:
| From super-low Earth orbits, more of the orbits that go
| really high also impact Earth or its atmosphere on the
| other side, so they only are up there once, rather than
| over and over and over.
| bodhiandphysics wrote:
| Yep!
| hypertele-Xii wrote:
| > a high-speed collision at a very low orbit can trow debris
| to not-so-low orbit
|
| How so? According to my understanding of orbital mechanics,
| if an object begins its orbit at a certain altitude, it will
| return to that altitude exactly one orbit later. While a
| collision can change the shape of the object's orbit, it
| can't change the spot of collision - which it will return to
| every cycle of its orbit.
| simonh wrote:
| Some of the debris will be thrown into eccentric orbits
| reaching significantly higher altitudes as part of the
| orbit. If these fragments hit objects in these higher
| orbits, that will create further debris clouds in more
| stable high orbits, etc, etc. That way you can get a
| runaway chain reaction that could escalate to arbitrarily
| high orbits and debris cloud lifetimes.
| azinman2 wrote:
| When these satellites burn up in the atmosphere, what happens
| to all the particles? Do we have lots of likely toxic material
| just constantly being burned and circulating around?
| sbierwagen wrote:
| If you are concerned about metal oxide dust, then you would
| want to shut down every blast furnace in the world, and also
| pave over the Sahara, since it throws millions of tons of
| iron oxide dust into the air every year:
| https://en.wikipedia.org/wiki/Saharan_dust
| doikor wrote:
| > Also pave over the Sahara, since it throws millions of
| tons of iron oxide dust into the air every year
|
| And at the same time fuck up our planet in a major way.
| There is a lot of life dependent on the plant on that dust.
| Everything from micro organisms in the sea, the Amazon gets
| its phosphorus from it, etc (it is a long list of things).
| AnimalMuppet wrote:
| No, we have _very small amounts_ of likely toxic material
| circulating around.
|
| Earth's atmosphere is around 5 x 10^18 kg. All the satellites
| put together are not going to increase the amount of toxic
| material enough to matter whatsoever.
| simonh wrote:
| We estimate that the amount of dust and meteorites entering
| earth's atmosphere is about 100 metric tons per day. Combine
| that with emissions from volcanoes, many of which are highly
| toxic, and vaporised satellites are really insignificant.
| kitsunesoba wrote:
| The proportions remind me of another somewhat common space-
| related misconception, which is that rocket launches are
| big polluters.
|
| With each launch emitting roughly as much as a single
| commercial flight and typically around 100 launches
| happening globally per year, even a tiny change in the
| _tens of millions_ of commercial flights per year has a far
| larger impact on emissions than launches will for the
| foreseeable future.
| TeMPOraL wrote:
| > _With each launch emitting roughly as much as a single
| commercial flight_
|
| It's one of those "connective" facts that puts so many
| distinct things into perspective. When I first learned it
| a few years ago, I became simultaneously very relieved
| that a rocket launch doesn't really have that big of a
| carbon footprint, and horrified by how much emissions a
| single passenger plane can make. It's a lesson about how
| visuals can be misleading: a plane looks tiny and doesn't
| really seem to be doing anything, while a rocket is big
| and rises to heavens on a pillar of flame, propelled by
| the anger of hell itself - and yet it turns out they're
| roughly the same, emissions-wise.
| [deleted]
| WhompingWindows wrote:
| Can you give a rough estimate of what fraction of space waste
| is due to differing orbits of satelites? Like very low vs low
| vs geostationary? I don't know the gradations between those
| either.
| orbital-decay wrote:
| The actual amount/distribution of stuff can be misleading.
| What really matters is the risk of collision, which is the
| highest for Sun-synchronous orbits. The fact that lower SSOs
| are also the most convenient for remote sensing work doesn't
| help.
|
| GEO is more or less safe because it's unstable (dead stuff
| drifts outwards), well kept (slots are limited by the
| resolution of customers' terminals) and typically doesn't
| have high relative velocities.
| Ottolay wrote:
| Wikipedia to the rescue (note the log-log scale)
| https://en.wikipedia.org/wiki/File:Spacedebris_small.png
|
| The biggest issue is by far the 600km to 2000km altitude
| band. It is popular for both LEO and SunSync sats and is high
| enough above the atmosphere that minimal propellant is needed
| for orbit boosting.
| Gwypaas wrote:
| Here's an awesome diagram of all tracked space debris from 1959
| to 2021 showing the constant cleaning by drag happening at
| lower orbits. It's the higher ones we really need to care
| about.
|
| https://www.reddit.com/r/space/comments/ld4vlq/gabbard_diagr...
| lend000 wrote:
| That's an amazing visual. Really helps to inform the debate.
| (Watch on full screen).
| hn_throwaway_99 wrote:
| Was waiting for that time in the '00s when China conducted an
| anti-satellite missile test. Did not disappoint.
|
| Let's not do that again.
| misterkrabs wrote:
| Thank you for showing me the coolest graph I have ever seen.
| jacquesm wrote:
| Can someone explain the reason for the mirror across the
| diagonal? Is there some altitude/velocity ratio that causes
| debris to spiral outward vs inward?
| Hypocritelefty wrote:
| It is weird how these clowns turn up to defend space karen
| yread wrote:
| SpaceX is planning to launch up to 42 000 satellites (there are
| about 3000 now). Cheaper $/kg leads to more space junk and
| higher risk of Kessler syndrome, that doesn't need any
| qualifications, I think. If something goes wrong the fact that
| the cloud of debris will be there for 10 years and not 100
| years is not a huge consolation
| whimsicalism wrote:
| > If something goes wrong the fact that the cloud of debris
| will be there for 10 years and not 100 years is not a huge
| consolation
|
| Seems like a pretty big consolation to me, no?
| aardvarkr wrote:
| No kidding. Order of magnitude
| Strilanc wrote:
| How does the cloud of debris stick around? For context, I've
| played Kerbal so I know a bit about orbits but not much.
|
| My intuition is that the velocities involved in being in
| orbit in the first place are so big (7 kilometers per second
| according to a quick search) that the orbit of the debris
| won't be substantially different, so it will still decay.
| Even if you give enormous kicks to the debris, most of it
| will end up with orbits intersecting the earth. The ones that
| don't will still intersect the original collision location,
| and so still experience decay during that part of their
| orbit.
|
| Basically, to change your orbit you need to boost once to
| push the other side of the orbit out and then again at the
| other side to push the original side out. A collision can
| only give one of the boosts, and so is sort of inherently bad
| at moving the orbit.
| paulmd wrote:
| And this is exactly the sort of comment that grandparent
| addressed with their post.
|
| More stuff in orbit doesn't _necessarily_ lead to higher risk
| of a catastrophic kessler syndrome event, if it 's low-earth
| orbit. The risk is not the same as geosynchronous where it
| can stay there forever. The satellites themselves (and even
| the debris if there is a collision) will decay on a very
| short-term basis (single-digit number of years).
|
| By making launch cost-per-kg cheaper, it is now plausible to
| put things in LEO instead of geo or other orbits. And doing
| that probably actually _reduces_ the risk of a catastrophic
| event, even if there is more stuff.
|
| Possibly higher risk of a smaller event, sure, but that is
| true of anything that puts more stuff in space. That's a
| generic argument that we shouldn't be doing anything in space
| at all, which I think is not compelling.
| LeifCarrotson wrote:
| Timing is absolutely a huge qualification to Kessler
| syndrome.
|
| If the cloud of debris is gone in 5 years, that's a hurdle to
| some careers and a (hopefully) temporary shutdown for some
| businesses. Covid has taught us that the modern economy has
| traded a lot of robustness for profit and efficiency, and
| those would certainly be significant losses of billions or
| trillions of dollars, but it would be a small fraction of
| GDP, we would hopefully learn from the mistake, and we would
| still be a spacefaring species.
|
| If Kessler syndrome occurred among geostationary satellites,
| that could potentially be a problem for _millions of years._
| That 's six orders of magnitude different and definitely
| needs qualification.
| yread wrote:
| But there is a lot more space in geostationary orbits and
| lot less stuff so the risk of chain of collisions is lower
| duskwuff wrote:
| There is far _less_ space in geostationary orbit, because
| the locus of GEO is a one-dimensional ring above the
| equator.
| fogof wrote:
| It's true that there is less GEO real estate in this
| sense. But to kick off Kessler syndrome, you need two
| objects in different orbital planes so that they collide
| at very high speed. It wouldn't be possible for two
| defunct GEO satellites to collide, because two nearby GEO
| satellites are moving in the same direction at the same
| speed.
| yread wrote:
| but aren't the satellites in GEO stationary relative to
| one another? And if by chance they all get destroyed in
| collision the debris would mostly also stay in that ring
| so we could still launch rockets and have satellites in
| other orbits that don't cross it.
| SideburnsOfDoom wrote:
| > There is one ultimate sure-fire way to reduce space junk:
| launch stuff to very low orbits
|
| Really? If there's a collision in LEO, doesn't debris spray in
| all directions, including some in the direction of higher, more
| stable orbits?
| enchiridion wrote:
| Not a physicist, but I doubt the debris would have the energy
| to reach geostationary orbits.
| SideburnsOfDoom wrote:
| Not relevant? There are many orbits that are below
| geostationary and are also high enough to avoid atmospheric
| drag for a long time.
| hinkley wrote:
| I thought the debris that gets lifted upward tends to go into
| elliptical orbits. Apogee would still create a significant
| amount of drag, wouldn't it?
| SideburnsOfDoom wrote:
| Yes, I'm aware that orbital mechanics is not that simple,
| that's why I specifically didn't talk about "upward" as a
| higher orbit isn't necessarily caused by a push in that
| direction.
|
| Sibling comment (
| https://news.ycombinator.com/item?id=26809297 ) is better
| at outlining that I was wrong: apparently a single impact
| cannot produce an entirely higher orbit, for debris sent in
| _any_ initial direction. At best, it produces elliptical
| orbits with a higher apogee, and the same drag at perigee.
| wizzwizz4 wrote:
| In the direction, yes, but it would still cross the original
| orbit. You need a second collision to actually get stuff
| _into_ higher orbits.
| ravedave5 wrote:
| With my limited knowledge of orbital mechanics I believe this
| wouldn't be a problem. It takes a lot of energy to move to a
| higher orbit. I would think the probability of enough energy
| to fling something to a higher orbit where it would be stable
| for a noticeably longer time would be very low.
|
| Think of exploding something 2 miles up the side of a
| mountain, what are the chances a piece goes another mile up
| the mountain. Like that but even harder.
| xoa wrote:
| Just to add to sibling comments who already answered this,
| that isn't how orbital mechanics work (or else a lot of
| things would be much easier!). A good place to start reading
| is on Hohmann transfer orbits [1, 2]. They're commonly
| covered in the context of interplanetary travel, but the
| exact same principle applies to changing orbits around a
| single gravity well. The key take home as applied to here is
| that a single instantaneous addition of energy (delta-v) to
| an object in stable circular orbit just changes it to an
| elliptical orbit where the high point is determined by the
| added delta-v but the low point is the same as where it
| started. It takes a properly timed second instantaneous
| application of energy to stabilize at a different orbit.
|
| So any ejecta from a single collision will still orbit
| through whatever altitude they started at, and in turn will
| be affected by atmospheric drag at that point regardless of
| how much farther out they get at the high point. In principle
| it's of course not impossible that they could collide with
| something else already in a higher stable orbit, but the odds
| of that get very, _very_ low particularly in the short time
| frame they have before decay assuming they 're starting in
| VLEO.
|
| ----
|
| 1: https://ocw.mit.edu/courses/aeronautics-and-
| astronautics/16-...
|
| 2: https://solarsystem.nasa.gov/basics/chapter4-1/
| IlliOnato wrote:
| Thank you, this is really informative.
| tgb wrote:
| > high point is determined by the added delta-v but the low
| point is the same as where it started
|
| Is it the low point that is that same? I would have thought
| it was the _current_ point (at time of delta-v addition),
| wherever that is, that must be part of the new orbit. Not
| that this is relevant for the topic at hand, just trying to
| check my understanding.
| omegaham wrote:
| This is correct. The simplification being made is that
| the original orbit was circular, so if you increase the
| debris' velocity, the current point is now the low point
| of the new orbit.
| tgb wrote:
| Even for circular orbits, is that the case? The new low
| point would be lower if impulse is not parallel to the
| velocity.
| xyzzyz wrote:
| Yes, if you start from roughly circular orbit, and the
| impulse is in the opposite direction to the direction of
| travel, it will slow you down and then the location of
| impulse is now the new _highest_ point on orbit, and the
| lowest point after the impulse is even lower than before
| it.
| sand500 wrote:
| Correct, so basically the lowest point(periapsis) of the
| new orbit cannot be any higher than the point where the
| collision happened.
| TeMPOraL wrote:
| Another way to think about it is, an orbit around a
| single body is entirely defined[0] by your current
| position and your instantaneous velocity. Six numbers.
| Where you are, which direction you're going, and how
| fast. Such orbits are closed, which means wherever you
| are right now, you'll return to that exact point later.
|
| So if you're at point P in your orbit and suddenly
| kinetic energy was added, your velocity changes in some
| arbitrary way. While you aren't sure where you'll go and
| when you'll get there, as long as the new (position,
| velocity) pair still defines a closed orbit around the
| body, you can be damn sure you'll return to the exact
| point where you are now.
|
| From this follows that the lowest point of your new orbit
| cannot be higher than where you are now, and the highest
| point of your orbit cannot be lower.
|
| --
|
| [0] - Ignoring gravitational effects of other bodies,
| residual drag, magnetic fields, solar pressure, etc. None
| of these matter on the scale of days to months.
| SideburnsOfDoom wrote:
| That's a comprehensive answer, thank you. TIL.
| mediaman wrote:
| This would just create an oblong orbit, which would still
| cause re-entry into thicker atmosphere for a portion of the
| orbit.
| bilekas wrote:
| http://stuffin.space/
|
| For some context of the amount of 'stuff' in space..
|
| This does include debris also. It's a serious amount.
|
| There is an incredible amount of Iridium from the mentioned
| collision :
|
| http://stuffin.space/?search=1999-037
| amelius wrote:
| That first picture: wouldn't that sphere deform as well?
| danuker wrote:
| I would guess so (like a bullet). I suspect they placed a
| second ball for illustration.
| VBprogrammer wrote:
| I think you are correct. The original ball is what appears
| like a paint splatter inside the deformed area.
| bombcar wrote:
| I assume they put another sphere in the hole for the purposes
| of the picture.
| wavefunction wrote:
| It's probably not the aluminum sphere that was used in the
| impact but included for reference to allow readers to visualize
| the effect of impact versus the size of the debris.
| [deleted]
| [deleted]
| marcinzm wrote:
| As other have said it's likely a second sphere there for
| illustration purposes. Also, I wonder if the original sphere
| would outright vaporize or melt into the block.
| verytrivial wrote:
| As other comments point out, the sphere would have immediately
| vaporized. Similar reason behind most impact craters being
| circular. Scott Manley has a nice explainer:
| https://www.youtube.com/watch?v=BCGWGJOUjHY
| toss1 wrote:
| I want to know the collective mass of this 'space junk'.
|
| It is indeed unusable now, but it is a lot of highly refined
| matter that is already high in the earth's gravity well.
|
| The question is whether whether enough of it exists that it could
| become useful, or even profitable, to reuse/recycle it.
|
| Once you've gotten a herding satellite to rendezvous and
| dock/grab the junk, how much extra energy is needed to park it in
| a useful common orbital location for later reuse/recycling, vs
| making it new on the ground and lifting it out of the gravity
| well again?
|
| Seems it could be a profitably exploitable resource, if the scale
| is right?
| qayxc wrote:
| It's not much and it's definitely not profitable.
|
| The vast majority of space junk (by number) is small pieces of
| metal, bolts, specks of paint, that sort of thing.
|
| The few bigger things are rocket stages, decommissioned
| satellites, and larger collision fragments.
|
| The problem is that the most dangerous debris (e.g. debris that
| doesn't deorbit on its own anytime soon) orbits between 2000km
| and GEO at varying inclinations.
|
| These orbits are difficult to get to and the debris is worth
| nothing compared to the energy you'd have to spend to catch it.
|
| The value of the debris itself is comparable to the value of
| junk here on Earth.
|
| Unless space faring nations are paying for removal, I cannot
| see any scenario in which the ~8,000 metric tons of space
| debris [0] can be collected and recycled at a profit. It's just
| too difficult and costly to do.
|
| [0] https://trumpwhitehouse.archives.gov/wp-
| content/uploads/2021...
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