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In today's Soyuz TMA-13M launch, the vehicle seemed to take a while to lift off after the boosters fired up. Here is the video. A huge flame and cloud of exhaust build up around the Soyuz, and it seems dangerous.

Was this an abnormal amount of time for the launch tower arms to hold onto the launch vehicle after booster ignition? If so, what went wrong?

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2 Answers 2

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It seems to be normal. The Soyus (like Falcon 9 and Saturn V) use a hold-down, or hold before launch, feature. Engines are fired up while the rocket is physically held down. This is a safety measure, if the engines don't fire to full thrust without any detected anomaly, the launch is automatically canceled (page 8) by shutting down the engines.

The firing time on ground seems to fit with this description of the Soyus launch sequence.

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I think you should find a source for your claim that "if the engines don't fire perfectly, the launch is canceled." My understanding is that the rocket is held down until the engines reach full thrust, since launching before full thrust is what resulted in some of the early, rather spectacular, failures of the early space programs. I'm not sure what happens if the rockets don't reach full thrust however, it's possible the emergency escape system on the Soyuz will activate. Not exactly the same thing as cancelling the launch... –  Nickolai May 29 at 17:26
    
I've edited it slightly now. Still, the little info I find about how it works is about Falcon 9. Soyus have some similar system, but I don't know how they differ. I would think that it is much more dangerous and expensive to fire off the crew with the launch abort rocket tower, than to shut down the engines. For Soyuz anyway, SpaceX plans to have their Dragon for their crew, which will have built in reusable launch abort and landing capability. Anyway, that detail is not very relevant for the flames while on the pad. –  LocalFluff May 29 at 18:39
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Nothing went wrong and the TMA-13M crew (Alexander Gerst (ESA), Maxim Suraev (Roscosmos) and Reid Wiseman (NASA)) are by now onboard the ISS. The way it looked to me (watched it live) was that the camera's aperture ratio wasn't adjusted fast enough with the fast changing incident light, so the frames were overexposed as the Soyuz-FG rocket engines were ignited.

A combination of rocket's own exhaust, reflected light from the deflected exhaust plume (Soyuz rockets launched from Baikonur Cosmodrome are placed over a quarry-like "hole in the ground", for lack of a better word) additionally illuminating the site, and camera's F-Stop in the same or similar position as prior to the engine ignition with dark night's background and the whole site only illuminated by a set of reflector lights, meant that the live transmission camera produced an overexposed image during liftoff. I could swear that the camera's position was also slightly more towards the "quarry" this time, more in the way of the deflected exhaust plume, but I can't confirm it.

So I'd have to say it just appeared that there was more flame than it should have been, and as @LocalFluff mentioned in his answer, no anomalies were reported.

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That "Hole in the ground" can be seen clearly in this image curtesy of the CIA en.wikipedia.org/wiki/File:Baikonur_CIA_U-2.gif –  David Wilkins May 29 at 13:45
    
@DavidWilkins That's an old image (1957), but yes, it's a quarry-like exhaust plume deflection "hole in the ground" that the Soyuz is suspended over by a gantry mechanism (with a platform at ground level). Here's a few newer photos: commons.wikimedia.org/wiki/… and commons.wikimedia.org/wiki/… With 17 seconds between ignition and liftoff, it would fill with exhaust plumes and they'd shoot up, apparently in the way of the cam. –  TildalWave May 29 at 13:48
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