Russia’s Angara A5 Booster has Serious Flaw

Angara A5 launch (Credit: Khrunichev)

If you are among the millions of space enthusiasts who have been losing sleep over why Russia’s new Angara rocket hasn’t flown in more than four years, be prepared to snooze soundly again.

Rueters reports that engineers have found a flaw in the engine of the Angara A5 booster that could cause it to explode in flight.

The issue with the Angara A5 was brought to attention by scientists at rocket engine manufacturer Energomash in a paper ahead of a space conference later this month.

The paper, reported by RIA news agency on Friday and published online, said the engines of the Angara A5 could produce low frequency oscillations that could ultimately destroy the rocket.

A special valve had been fitted to mitigate the issue, but in some cases the oscillations continued, it said. Energomash did not immediately reply to a request for comment.

The Angara A5 rocket is the most powerful of a family of boosters designed to replace the Proton and other launch vehicles currently in the Russian arsenal. The Angara series is based around a common first stage core with additional strap-on stages.

The Reuters story says that Russian President Vladimir Putin is eager to see the rocket start launching more frequently because it is vital to the nation’s national defense.

The Angara 1.2PP rocket made the maiden flight test of the series on July 9, 2014. The booster flew a suborbital mission carrying a mass simulator from the Plesetsk Cosmodrome in Northern Russia.

Angara A5 flew was launched from Plesetsk five months later on Dec. 23, 2014. Using a Briz-M upper stage, the booster placed a mass simulator into geosynchronous orbit.

The Wikipedia page for Angara lists two launches of the Angara A1.2 and one flight of Angara A5P for 2019. There is one Angara A1.2 flight listed for 2020. However, it is not clear whether this schedule is still valid; it came from a schedule compiled in late 2017.

  • Jeff2Space

    Sounds like this could be POGO, but it’s hard to tell since something might be getting lost in translation.

    The US had a lot of POGO problems with Saturn V (I believe both the first and second stages). These were eventually solved, but not before it was flying crew (yikes!). During the space shuttle program, the Saturn V experience with POGO prompted very careful design, analysis, and testing of the SSMEs and their associated plumbing during the space shuttle program. No POGO there.

    IMHO, this whole thing is a big “nothing burger” because the usual fix(es) for POGO are not all that hard. And since the problem has already been identified during a test flight with a mass simulator, I don’t see the engineering side of things being an issue here. I’d be more worried about the seemingly rampant quality control issues in the Russian space industry in general.

  • Robert G. Oler


  • Jeff Smith

    I believe Titan had the pogo problem first. And then SV had the pogo problem on A6 and had put the fix in and ground tested before A8 (first crew). If it has been a problem for so long (and a valve/accumulator/whatever hasn’t fixed it), it seems like it is more likely a combustion instability issue.

  • Pete Zaitcev

    As much as I understand, it can be classified as a kind of POGO, although it’s not in tanks or pipelines. In Russian nomenclature, parasitic oscillations are divided into two categories: “low frequency” (LF) and “high frequency” (HF). The LF has waves moving alongside the flow, and they are of course lower frequency. The HF has waves moving across the flows and is characterized by higher frequency. In order to combat LF, some sort of fluid dynamics solution is used: dampers, blow-off valves, that sort of thing. To deal with HF, they use curtains, fences, and other disruptors.

    In case of Angara, the root of the problem is the extremely low power setting for RD-191: 30% thrust. The rocket needs it because the lower modules have the same fuel capacity. They could give up on that throttling a little bit and that would resolve the HF cleanly, but that in turn drops the payload because of reduced staging effect. And A5 is already underperforming, so they can’t.

  • Bill Clawson

    IIRC, the F-1 engine, used on the first stage of the Saturn V, had resonance issues within the combustion chamber itself. The engineers ended up installing baffles across the injector face (top of the combustion chamber. Also, since the center core is running at just 30% for part of the flight, they might have a big underexpansion problem. If bad enough, underexpansion can result in laminar flow separation at random locations on the expansion nozzle. You could shake apart an engine with either of these problems.

  • Jeff2Space

    True, but I thought most of the combustion instability issues were already taken care of on the test stand.

    POGO was arguably an entirely different problem that could only be found during flight testing. It was literally a coupling between the compression mode of the entire launch vehicle and turbine inlet pressure (which was determined by the “weight” of the propellant above which was determined by the acceleration of the vehicle). Fluctuations in thrust (which could be very minor to start with) caused deflections of the compression mode which caused fluctuations in the inlet pressure which caused fluctuations in the thrust. The fluctuations could therefore build once they got started from the tiniest variation in thrust (e.g. see the Tacoma Narrows Bridge collapse for an example in the field of civil engineering).

  • Lee

    You’re the only one who said it was pogo. Neither the original article nor Pete’s clarification said pogo.

  • Jeff2Space

    O.k. Sorry for the idle speculation.

  • duheagle

    I doubt it. The Russkies have traditionally dealt with combustion instability issues by splitting the output of a common set of turbomachinery among two or four combustion chambers and expansion bells. The Angaras use the RD-191 which is basically a single-chamber version of the four-chamber RD-170 and the twin-chamber RD-180, famously used on ULA’s Atlas 5. The RD-191 is also nearly identical to the RD-181 which NGIS now uses in the first stage of the Antares. The chance of there being combustion instabilities seems pretty remote.

    Vibration issues based on resonances between the engines, especially in a cluster configuration like the Angara 5, and the rest of the rocket structure, though, are entirely possible and much more likely. Something of this general sort seems to be what bit the Boeing Starliner’s launch abort escape system recently. Even a veteran engine can yield problems when used in a new vehicle with its own idiosyncratic set of resonances.

  • duheagle

    Could be you’re right. The F-1 engineers essentially quartered the F-1’s injector plate with fences. You might say they did internally what the Russkies did externally with multiple combustion chambers and bells on the RD-170. Neither solution was what you’d call elegant, but I think the F-1 approach was better. The RD-170 made more total thrust than the F-1 but it also weighs 3,000 lbs. more and has a T/W ratio of 82:1 in contrast to the F-1’s 94:1.

  • Saturn1300

    Like the Protons that crashed? I guess that their super biggy will never get built or will have the same problem.