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Old Russian Proton rocket engine explodes in orbit, creating more space junk

According to tracking data from the Space Force, an old Russian Proton upper stage engine, originally launched in 2007, broke up on April 15, 2022, creating a small cloud of new space junk in a highly elliptical orbit.

These Proton upper-stage ullage motors are known as SOZ motors, and there are currently 64 of them in Earth orbit, McDowell tweeted. The acronym is short for “Sistema Obespecheniya Zapuska,” which translates roughly as “Launch Assurance System,” he said.

The SOZ motors don’t use up all their propellant when they fire. And they have an unfortunate tendency to go bang years or decades later, leaving a bunch of debris in highly elliptical orbit. At least 54 SOZ motors have now exploded,” McDowell tweeted.

The SOZ motor that just blew up had been racing around Earth in a highly elliptical path, getting as close as 241 miles (388 kilometers) and as far away as 11,852 miles (19,074 km), McDowell said in another tweet, noting that “the debris will take quite a while to reenter.”

“So — this debris event was predictable and is well understood; still very unfortunate,” he wrote. [emphasis mine]

The highlighted words suggest a certain irresponsibility on the Russian’s part. If these upper stage engines are abandoned with fuel still on board, why doesn’t Russia use that fuel to fire the engines to de-orbit them safely, especially as the engines have a tendency to eventually blow up and cause space junk? There might be complex technical reasons, but I suspect the real reason is pure laziness on Roscosmos’ part. No one ever bothered to think about it.

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7 comments

  • Gealon

    My understanding of ullage motors, is that they are used to settle the fuel in the bottom of a rocket stage’s tanks prior to engine start. If they are solid rockets, they burn until their fuel is exhausted and then they are done. On the S4B stage of the Saturn 5 though, the ullage motors did run on liquid fuel. This was done so that the propellant be settled and so that orientation of the stack to be controlled with just those two little engines running, at least until Trans Lunar Injection, when the J2 main engine would assume control. The stage remained stable even after CSM separation because the SIVB also carried the stack’s guidance computer which had control over these motors.

    It could be that the Russians are using liquid fueled motors and that, unlike the SIVB, once the payload is released, they no longer have the ability to fire the ullage motors and use up the propellant. But then I have to ask, why shut them down in the first place? Just run the ullage motors during the main engine burn and let them run until their fuel is exhausted. If this is a known issue after a minimum of 64 launches, then it sounds more like negligence than anything else. Or include a function to dump the remaining propellant after the main engine burn is complete. If on the other hand, there is still a functioning computer on the stage after payload separation and they choose not to burn that remaining propellant, that is definitely negligence. Miiiiight be where China got the idea to leave control of the core stages of some of their rockets completely off from.

  • David Eastman

    The SOZ motors are solids, with one ignition. In theory they should use up all their propellant when they burn to perform their one-time duty, but they’re not very well manufactured, and there are tiny bits left over, presumably not as one mass, but as little bits here and there in the chamber, otherwise it would have burned with the rest. The only reasonable ways of disposing of that would be to bring the whole stage back into the atmosphere, or use a better solid fuel mixture/manufacturing process that results in all the fuel being consumed, and any tiny residuals not decaying into an unstable state that might ignite on it’s own. I don’t think a modern graphite epoxy motor would have this problem, but the Russians never pushed their solid fuel tech very far.

    It appears that this was a Block D/M stage, which is capable of multiple restarts, but each one required the use of the ullage motors that are the concern here. I believe the RCS thrusters on that stage only handle pitch and roll, not any form of translation, so to do a burn to bring it into a decaying orbit would require an additional set of ullage motors and another ignition of the main motor, or a complete re-design of the RCS. Proton probably had the margins to add another 10kg or so for that purpose, but back when Proton was being designed, nobody thought in terms of “lets make the rocket less capable so as not to leave debris in space.”

  • David Eastman: The Proton was designed in the 1960s. Space junk has been an issue since the 1970s. In fact, the Soviets punished one cosmonaut who during a space walk released a nut to watch it tumble as it drifted away. They knew, and for more than fifty years did nothing to address this, even when they were making lots of money launching Protons.

  • Col Beausabre

    I’m shocked! Shocked!

  • Jeff Wright

    The Briz upper stages are good confettii producers…

  • Star Bird

    Mad Magazine Joke & Dagger Spy vs Spy Black Spy steals the White Spies defective Rocket and BOOM

  • Edward

    For some time, the FAA has been making an effort to avoid space debris. A couple of decades ago, a Pegasus rocket was delayed a launch license because a software update had not been installed to dump the liquid propellants after the end of launch and payload release. If liquid propellants are left in a rocket, they can evaporate and increase the internal pressure until the tank(s) bursts, causing a debris hazard.

    Some jetsam and flotsam in the oceans can be a hazard to shipping safety and has been avoided for decades, if not centuries, but virtually all jetsam and flotsam in space is a hazard to satellite safety.

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