Transcript
Hello, it’s Scott Manley here. Today, a Chinese Long March 7A rocket suffered a spectacular failure about 80 seconds into the flight. The only footage we have is from amateurs on the ground, but we see some pretty spectacular fireballs emerging from this vehicle early on in the flight. And based on footage that we’ve seen, it looks like this is a failure near Max Q and very likely was a result of a structural failure in the rocket. In short, the front fell off.
So, the Long March 7A is one of China’s more modern rockets. It uses kerosene and liquid oxygen as a propellant, and the initial Long March 7 essentially had four boosters strapped around a core and a second stage. It was mainly used for launching the Tangio spacecraft to China’s space station, which is the cargo spacecraft. The Long March 7A is an evolution designed to carry payloads to geostationary orbit. It keeps the same basic first stage and boosters, shortens the second stage, and then adds a third stage which burns liquid oxygen and liquid hydrogen, giving it the capability of putting payloads up into geostationary orbit. Now, we don’t actually know what payload was being carried on this flight, but it’s believed that this was a military geostationary communication satellite of some sort.
Interestingly, a lot of the footage we have of the Long March 7A comes from amateur sources because they don’t release public video of a lot of the sources since it’s usually carrying sensitive payloads. Also, this particular piece of footage is a rare daytime launch. Almost all the Long March 7A launches I’ve seen actually happen at night. So, you know, you’re also dealing with lighting conditions which don’t really show the launch vehicle itself.
Now, this is not the first time a Long March 7A has had a failure. It actually failed on its very first flight due to a fuel pressure issue in one of the boosters. That meant that during stage separation, the spacecraft skewed around and apparently damaged the second stage, which was unable to reach orbit and ultimately failed as a result. The Long March 7, by comparison, seems to have been far more successful. This is a launch of a Tangio spacecraft to the Chinese space station. Again, notice this is a shorter version, but it maintains the same back end with the same four strap-on boosters. These are powered by YIF-100 kerosene oxygen stage combustion engines. They generate about 125 tons of thrust. Importantly, this engine design is used across the Chinese rocket fleet from Long March 5, 6, 7, 8, 10, and 12. It’s everywhere.
So, you know, when we saw this failure, we were wondering whether it was going to be an engine problem because an engine problem could have dramatic knock-on effects for the rest of the Chinese rocket fleet. But as we saw from that footage earlier, this was a structural failure in the rocket. That’s a very different kind of problem. It’s almost certainly just confined to that specific rocket. It’s probably only affecting the Long March 7A, not even the Long March 7.
Now, based on previous flights, we would expect the first stage and the boosters to operate for about 3 minutes, whereas this ended up failing around 82 seconds into the flight. What we don’t know is when we expect Max Q to happen. Max Q is basically the maximum aerodynamic pressure. As a rocket ascends and gets faster and faster, the aerodynamic drag increases on it. But at a certain point, the fact that it’s getting higher and higher means the air density is dropping. And so the dynamic pressure, or the drag, starts to drop. The point where this meets, where this curves over, is called Max Q, maximum aerodynamic pressure. Because this is the point of maximum stress on the launch vehicle, it’s quite common for rockets to throttle down their engines or shut off something or make some changes to the flight profile to reduce the impact on this and give them extra structural margins.
Consider that there’s something like 700 tons of thrust in this stage, and the acceleration visibly drops off as it goes through the sound barrier because of the amount of aerodynamic drag. That means there are hundreds of tons of aerodynamic drag acting on this thing. This will be designed to carry the forces through the structure. But if the forces perhaps aren’t applied correctly, then you’ve got hundreds of tons of thrust that can act to bend the rocket. We’ve seen this in Kerbal Space Program, right? The whole FL wobbly rockets thing is actually a legitimate thing that happens, right? While real rockets will flex and bend under the load, it’s rare to see them absolutely break in half like we saw in this case.
Once the structure starts to fail, it fails very rapidly. This is very clearly bending at the interstage between the second and the third stage. That stage very obviously disintegrates into a fireball right away. I think that the second stage immediately goes up as well. But while this looks pretty catastrophic, I think that the core and the boosters are still sort of held together and still flying at this point because a few seconds later, out of this massive conflagration, you can very clearly see the rocket booster emerging with fire still coming out of those nozzles for a few more seconds until it explodes.
I presume at that point that is the automatic flight termination system destroying it so that there is not any large debris coming back to Earth or at least coming back into the ocean because this launch did happen from Wang Chang, which launches out over the sea. I guess that’s good because it means there’s not anything downrange there or there’s very likely to be few things downrange that have people living in them. China’s first big rocket failure ended up killing a bunch of people nearby.
Now, I wanted to synchronize these two angles. Turns out that’s kind of hard because the footage from the TV is already slowed down. So, I have to sort of speed things back up to make it smooth. Totally had to guess what the frame rate was. But you can see that there are a series of events on both sides that sort of seem to line up. We’ve got the initial fireball caused by the upper stage rupturing as it falls off. Then we have a few seconds later the much larger explosion from the boost stage going up. The long-distance footage also shows this vapor trail showing up, which is pretty common as rockets go transonic around the sound barrier, which is very often close to where Max Q happens. This is very consistent with what we’d expect for a structural failure due to aerodynamics.
But look, we still have plenty of questions. Was the vehicle at normal attitudes when this occurred? Right? Because if you modify the angle of attack, that will increase the sideways forces, the lateral forces, which can increase the bending strain and therefore in turn cause the rocket to fail. If there was an attitude control issue, that could lead to this. If the rocket hit unexpected wind shear, that would change the airflow across the rocket, and it might be enough to push it over the edge. Now, there was no wind shear expected, but your predictions are sometimes wrong. Remember, the original 7A failure was because of engine control issues that resulted in poor attitude. Someone observed the engine fail a fraction of a second before the first fireball. It takes them a second to figure out what’s happening, but if they pan across, they see the rest of the giant fireball from the main event.
So, again, watching this in slow motion, watch the center engine here. It’s correctly exposed; good for the photographer. It shuts down, and then almost simultaneously we get that fireball forming in front, and that is, of course, from the third stage as it ruptures. These events are so close in time. The rocket was bending at the point where that center engine was shutting down. I’m thinking that might be a commanded engine shutdown. I don’t think this shutdown was caused by a loss of tank pressure in the core since the engine was seen to shut down before the fireball was actually seen. Look, we can take these two things and we can stick them side by side again. Again, we are just guessing at the timing for the screen on the right, but it seems to sort of line up. So again, the bend happens, it breaks, and then you get the fireball, and that engine in the center is shutting down already.
But then the question is, if they decided to shut down the center engine because things were going wrong, why didn’t they shut down the engines and the boosters at the same time? I don’t know. I would love to know more about what exactly happened, what the sequence of events is. Unfortunately, I think this is a Chinese launcher. It’s carrying a military payload. They’ve not been really communicating a great deal about this mission in particular. So, I fully expect that this will get investigated, cleaned up, and we will have almost no clue as to what actually happened. I am, however, happy that despite this being a spectacular conflagration seen by many people, it appears that nobody has actually been injured by this. That’s good.
A number of people on the ground appear to be, well, not so much cheering but clapping or whatever. They seem to be enjoying the show, despite it being something going wrong that they have nothing to do with. I don’t think this is going to slow down China’s space program at all. They have an amazing amount of diversity in their launch vehicles, and this is just one of many. They are just going to keep on flying rockets. I’m Scott Manley. Fly safe.
