Look Out Below! China’s Heavy-Lift Rocket Due For Uncontrolled Reentry Within Days

On April 28th, China successfully put the core module of their Tianhe space station into orbit with the latest version of the Long March 5B heavy-lift booster. This rocket, designed for launching large objects into low Earth orbit, is unique in that the 33.16 m (108.8 ft) first stage carries the payload all the way to orbit rather than separating at a lower altitude. Unfortunately, despite an international effort to limit unnecessary space debris, the first stage of the Long March 5B booster is now tumbling through space and is expected to make an uncontrolled reentry sometime in the next few days.

The massive booster has been given the COSPAR ID 2021-035-B, and ground tracking stations are currently watching it closely to try and determine when and where it will reenter the Earth’s atmosphere. As of this writing it’s in a relatively low orbit of 169 x 363 km, which should decay rapidly given the object’s large surface area. Due to the variables involved it’s impossible to pinpoint where the booster will reenter this far out, but the concern is that should it happen over a populated area, debris from the 21 metric ton (46,000 pound) booster could hit the ground.

The Tianhe core module.

This is the second launch for the Long March 5B, the first taking place on May 5th of 2020. That booster was also left in a low orbit, and made an uncontrolled reentry six days later. During a meeting of the NASA Advisory Council’s Regulatory and Policy Committee, Administrator Jim Bridenstine claimed that had the rocket reentered just 30 minutes prior, debris could have come down over the continental United States. Objects which were suspected of being remnants of the Long March 5B were discovered in Africa, though no injuries were reported.

China’s first space station, Tiangong-1, made an uncontrolled reentry of its own back in 2018. It’s believed that most of the 8,500 kg (18,700 lb) burned up as it streaked through the atmosphere, and anything that was left fell harmlessly into the South Pacific Ocean. While small satellites are increasingly designed to safely disintegrate upon reentry, large objects such as these pose a more complex problem as we expand our presence in low Earth orbit.

57 thoughts on “Look Out Below! China’s Heavy-Lift Rocket Due For Uncontrolled Reentry Within Days

  1. You would think once the track is established that if it posed a direct danger to a large city or populated area they could intercept with a air-to-air missile. Yes, I get it will be likely going 17,000+ kph, but you only need to be at the point of intersection, not catch up to it. At least that way you could bring it down sooner or modify it’s trajectory assuming there was a safer, shorter debris landing spot that could be picked. A shame they couldn’t hit it right before hitting the atmosphere burn zone, reducing the larger mass to a smaller pieces more likely to burn up. I mean the cost of a missile might be 20+ mil for such a task, but the damage would be a lot bigger presumably.

    On the other hand I would rather a single larger piece come down, easier to track, and doesn’t leave a lot of dangerous smaller pieces in orbit.

    Or not.

    1. Then you risk disintegrating it into many many small pieces, some of which will have been pushed to a much higher orbit. Not exactly a great thing either. If it’s DEFINITELY a danger then is possible to chance it, but intercepting it has large unknown and unpredictable results

    2. Air-to-air missiles work at low altitudes and in, well, air. Once the booster has reached that point it’s already gone through reentry, broken up, and the pieces are spread over a huge area and falling vertically downwards at terminal velocity. Even hitting it _above_ the atmosphere would merely cause it to break into a few large pieces there and not really help the situation much. Anything fragile will vapourise during reentry anyway; the problem are the dense, tough parts like the smaller fuel tanks or pieces of engine, and missiles won’t help there.

      1. OK, as apparent by my first paragraph – I know nothing or orbital mechanics and falling objects. All good to know, thanks. I would have thought that breaking the thing into smaller pieces would increase the likelihood of them burning up, and yes – I understand it would have required something special to hit it above 6 miles.

        1. I’m guessing that if we do have the capability to efficiently and completely destroy this thing before or after interface, we wouldn’t reveal that fact for this amount of danger.

          1. You must not have heard of MDA? Even so, we don’t have a weapon that could vaporize something that size completely, especially without worse implications (nuclear). Not until massive terrawatt lasers are a thing.

        2. Usually the problem is the parts of the debris that are inherently heat resistant. Breaking something up before re-entry helps in that a large enough piece of anything is heat resistant, but something like a single stage to orbit heavy lift rocket is naturally going to have lots of big, heat resistant parts like portions of the engines, big steel plates, etc. They’re the type of thing that probably won’t break up too much even after a missile strike.

          Orbital mechanics are weird, but at least when you accelerate, you raise the opposite end of your orbit. If you accelerate debris at a low altitude, you may put debris into a bunch of weird orbits, but it’s either going to escape the Earth’s gravity well and never come back, or it will eventually orbit back around to that low altitude again. As long as it’s low enough, there will be enough air drag to decelerate the debris each pass until it de-orbits eventually.

          The opening scene of “First Man” irritated me, when Armstrong’s jet was skipping off the atmosphere. That actually happened, but the concern was that he travelled farther than intended and couldn’t make it back to the airstrip, and so he had to land the experimental aircraft in the flats. In the movie, they made it sound like he was going to get stuck in orbit! Without thrust, any sort of atmospheric drag at all removes momentum, and you’ll eventually fall back down. It would be like skipping a rock on a lake and having it fly away.

      2. So given I don’t know squat about the subject – as pointed out by a few People above, could they use a shock wave from a detonation – not a direct hit, but something that would change the trajectory of the debris by 1 or 2 degrees to steer it away from populated areas?

          1. In general I agree that it’s probably not a good idea and it would be a hard engineering problem to make work. I don’t really follow what you mean about the missile mass, though. 100Kg is a lot of reaction mass when you have a crazy amount of energy to release. I’m not completely sure this is right, but just looking up the equation, impulse equals mass times change in velocity:

            F • t = mass • Delta v

            For every force there’s an equal and opposite force. What that means is, the faster the 100kg projectile is moving relative to the object you’re trying to move, the more you’ll change its velocity by colliding into it. Explosives are a pretty good way to accelerate mass to a very high speed. 100Kg can definitely alter the velocity of a several ton mass, simply by running into it fast enough.

            Said another way, the chemical/nuclear energy of the warhead is converted into kinetic energy, which is then ideally transferred into the object you’re trying to move. That’s where the engineering gets difficult. You need to figure out a way to maximize that energy transfer by directing it into the object. Otherwise, most of the explosion will be wasted sending particles off in useless directions.

            In general when it comes to space ships, the more velocity the better. Ion engines get significantly more delta-V for the amount of reaction mass than chemical rockets, aka “specific impulse”. They work by accelerating charged particles to velocities significantly faster than can be achieved chemically, and so you literally get more impulse for the same mass. Ion engines are limited by their electrical power source, though, and so they provide low thrust (force) over a long period of time. An explosive is an incredibly huge power source, and so you can get an insane amount of thrust for a very short period of time.

        1. To push it without making it break up anyway you would have to push it in the right places, and not too hard – it might be really bloody heavy but that doesn’t equate to really strong in every direction – its still a space craft where saving every gram you can counts, so its only particularly strong in the directions it needs to be to survive launch.

          Now aiding in the breaking it up once its in the upper atmosphere should help safeguard the population below somewhat, but its still going to drop bits with enough inertia to be dangerous, its turning something more like elephant rifle bullet (though it will still be bitty and broken up – its flying a relatively tight formation) into something more like a shotgun round of serious size. Neither really works for soft squishy people unfortunate enough to be in the way..

          About the only things you can do for this sort of thing is make it re-enter where its safe or nuke it, as while a nuke isn’t exactly safe for a population below, or the world as a whole it will vapourise enough of the darn thing even with a near miss that its the radiation you have to worry about…

        2. There’s a good chance the US Navy will still take a shot at it. Just about every Aegis class ship has some form of missile capable of orbital interception. Like the others have said, you don’t want to hit it in a deeper orbit because you’ll spread debris. But if you hit it during an established reentry you can assist in breaking it up. This could be another opportunity to demonstrate to China what technology the US is wielding. Years ago the US Navy made an interception ‘Burnt Frost’ and successfully handed Russia and China proof of the US reach. Clearly, they don’t want to be handed a role of space sweeper. But if they want to demonstrate some intimidation while at the same time illustrating that China is a polluter with no conscience they might just send one up.

          1. I don’t really understand the claim made by the article that China polluted space. The whole point is their stage’s orbit decayed relatively quickly.

            Maybe the point is that they’re polluting Earth by letting the stage (most likely) sink into the ocean. I’m pretty sure that’s what most countries and launch companies do, though. At worst, it seems like they are doing it in a less controlled manner than typical, and so i guess the location of the pollution is less controlled.

            One time use launch vehicles in general seem like they’re pretty wasteful, and a lot of the negative impact is externalized. On the other hand, it seems like there’s still plenty of positive impact from these sorts of projects. I have no idea what China hopes to achieve by launching their space station, but it’s a drop in a bucket in the grand scheme of things. The really exciting developments seem to be in reusability, and the subsequent decrease in cost to reach orbit. I think reusability based cost reduction naturally reduces the externalized waste. A lot of manufacturing processes are energy intensive or chemically toxic, and so building something once and reusing it until it’s worn out is way better than using it once and throwing it away. You could claim that one time use pieces are built more flimsy and that makes a difference, but launch vehicles by their nature need to be so heavily optimized that the difference is marginal.

    3. Once it’s tumbling in the atmosphere, forget about predicting course of all the big pieces with any accuracy. The best solution would be mass evacuation of millions of people days in advance (maybe to another planet) or better yet play the numbers game and hope the odds are low any debris will be landing on grandma’s house. I think that’s what the Chinese are doing, betting on the odds, it’s a cheap solution. Funny but gambling is now against the law in China. I don’t know if that law applies to their space agency. If there are consequences of debris damaging property or killing people (let’s hope not), then China will say Oops my bad and settle in a civil court.

    1. The appropriate response is to send up a mission to forcefully deorbit the core module into the south pacific, to make it clear that they cannot benefit in any way if they disregard their responsibilities and that there is no technical reason for them to do so either. i.e. The punishment should also serve as a demonstration of why they should be punished.

      1. That we know of – in the more isolated parts of the world it could have happened and nobody ever finds out. Probably true though.

        But that is largely because all the really big dangerous debris from even pretty early launches was planned for safe re-entry and the other large dangerous debris is in high enough orbits it isn’t coming down any time soon without help – those massive early but now failed satellites are just stuck out there as dead junk for a considerable time… We haven’t made a habit of throwing massive heavy objects into LEO that will comedown uncontrolled who knows where, those massive and dangerous boosters/objects with quick return schedules have almost all been planned to crash down in the middle of nowhere away from people in the past.

  2. Well, unlike the US and Arianespace facilities on the coasts, the Chinese launch sites are pretty far inland, so the Chinese launchers regularly drop boosters on “rural but not all that empty” areas inside China itself.

    So… maybe having big rocket chunks fall out of the sky doesn’t seem all that weird to the people who plan these things…?

  3. Fire a ‘conventional’ ICBM ahead of it, with a remote detonator, and detonate it so that it produces enough thrust to slow it down, and de-orbit it where we want it, instead of guessing. Use it as a training exercise.

  4. You know, if you got your booster making it to orbit, then it sounds like a perfect opportunity to make it do a once-around and land. That seems like it would be more efficient than trying to do a F9-style boost-back burn.

    1. No. That’s not how it works at all. Vast majority of F9 flights do not do any boostback and land on ships. But all do reentry burn to shed speed before hitting denser atmosphere otherwise they would burn up.
      And an on orbit vehicle has more than 2 times F9 booster’s speed. And reentry heating goes up with cube of speed. No orbital vehicle ever has ever had any practical fuel margin to do F9 style reentry burn but from orbital speeds. Not even Starship is going to have such margin.

    2. There is a huge difference in momentum between a suborbital trajectory and an orbital one, even if the apoapsis of the suborbital trajectory is much higher.

      In most cases, it’s not that hard to use small retro-burn solid motors to help scrub some energy from the booster at separation, but when payload weight and booster technology forces you into an extremely efficient gravity turn profile launch, the booster’s periapsis isn’t low enough for this to really help.

      And it’s not just limited to the Chinese. The US and Russians both experienced similar issues with Skylab and Mir. And the US dropped bits of the 70 ton Skylab all over Australia when solar activity resulted it reentering a couple of years earlier than planned.

      Either way, it’s actually helpful in a counter-intuitive fashion if it breaks up early. The intact booster will decelerate much harder than the individual heavy components would, but would still have a fairly high terminal velocity.

      After a breakup, most of the debris will have very high surface area to density and thus will easily lose velocity. The heavy bits will retain most of their velocity, thus will experience much greater shock heating once they finally get deep enough into the atmosphere. Any such bits that survive will have relatively low terminal velocities, and will usually impact at less than 200 mph, sometimes *much* less. The main bodies of the engines, turbopumps, and a few reinforced pressure vessels tend to survive better, but their greater density causes much greater heating and vaporization. Those surviving masses can impact somewhat faster, as much as 350-400 mph.

      People tend to assume that anything that survives will hit like an icbm reentry vehicle… but those are carefully engineered to minimize their terminal drag (maximize terminal velocity) so as to make them less affected by atmospheric conditions. Close may count in horseshoes, hand grenades, and nuclear weapons… but even a few hundred yards will result in failing to destroy military (as opposed to civilian) targets.

      A sad consequence of the Columbia disaster is that there is a thoroughly documented public body of modern knowledge on how debris behaves during reentry, and what happens at ground level.

      As far as reasonable risk assessment goes, it’s more likely to win the lottery every day of your life than it is to get killed by reentry debris.

      Despite this, for plenty of reasons, it appears that the Chinese are actively working to develop technology to ensure that subsequent boosters at least degrade out of orbit much faster. If nothing else, it’s a convenient step on the way toward their stated goal of competing with SpaceX in pure technical capability.

  5. If you watch Scott Manley’s video on this launch, at 1:28 the mission control center screen shows the station’s orbit clearly passes directly overhead Sydney.
    Given that diplomatic relations between Australia and China are at a very low point (over Huawei, COVID origins investigation, south china sea, human rights, trade) I wonder if there might be some ulterior aspect to this station and its orbit rather than just pure science.
    Almost two years ago Chinese warships sailed unannounced into Sydney Harbor (and not even the state government knew anything about it!) so it would seem this orbit would make it very easy for them to keep a watch on what strategic movements occur in the south pacific for years to come.

    1. Other than geosynchronous orbits, once in space your no longer influenced by earth’s rotation. As in the planet is rotating below you so every orbit shifts by so many degrees. Roughly 22.5.

  6. > despite an international effort to limit unnecessary space debris

    It is in such a low orbit that there is absolutely no risk of it being a space debris hazard in the traditional sense. It’s not going to run into anything and even if it did everything would just come down in weeks. It is completely following the spirit of the international efforts to limit space debris.

    There’s no need to hassle China about this when there’s so many things they actually do inconsiderately.

  7. Relax, it’s just the Chinese trying to demonstrate parity with SpaceX’s orbital strike capabilities. And since it’s not an NRO bird, the Navy it not likely to to do an encore performance.

    1. That was an accident. They even did an emergency fuel dump (not to cause a bigger spread in a case of an explosion during reentry). By design Falcon’s 2nd stage do a controlled deorbit from all but very special trajectories/orbits.

  8. If a little bit of it could hit my car, sufficient for a write-off but no collateral damage, that would be great (it’s rubbish). Unfortunately the odds appear to be 10 trillion to 1. Now, there’s a grumpy bloke down the road, and while I’d never wish anything on him, he has 2 cars, so double the odds :)

    1. That doesn’t make much sense. I got the feeling that it’s more or less in free fall and tumbling. Unless they are planning on purposefully bringing it down at some point. Otherwise they have the same math and limitations of predictions as anyone else. They might just not care as long as it doesn’t land in China.

  9. As a former Pratt &. Whitney and NASA Engineer, I can honesty say, that with all of the Scientific calculations, we are still unsure of the precise results of or exact landing coordinates of falling space material.
    That said, a plus or minus debris field is calculated, which is commonly known as
    a best guess scenario, rendering Chicken Little’s screams to be somewhat relevant.
    As the “sky is falling” … luck plays a significant roll in the outcome as to whether there is human carnage or not.
    All the warnings about falling debris in your area will fail to alert or concern anyone.
    That’s the way we are, “ it couldn’t possibly hit me.”
    So, we sit back and watch the news, totally unprepared for the outcome, butt vitally interested in it… with our Lawyers phone number at hand…

  10. Amazing how when China does it they’re bad and awful but when everyone else does it there’s just a collective shrug.

    Also “just 30 minutes prior” is scare mongering bullshit. Seriously, at its speed lots of bad shit could happen, but most is not likely to happen.

    I could have won the lottery…

  11. The reason it’s unlikely to cause damage, is simply because most of the surface is water, and most of what isn’t is uninhabited. While it’s likely unintended, and there was some system that should have deorbited it, the lack of comment from China makes it clear it’s just not a priority. They are 2 for 2 on deorbit failures for this rocket now. If they don’t fix it, and keep using the same system, eventually one will come down in a city.
    Maybe the best deterrent for China allowing this would be if large, useful to analyze chunks come down in an empty area of a country with no interest in giving them back. Give the US or Australia or someone a chance to go over it with a fine toothed comb and “learn some secrets”

  12. I just find it…. interesting, that China already had an entire spacestation fall out of orbit. Given thier track record we probably don’t have long before thier latest station falls too.

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.