Russian Rocket Failure

Just as the story of the failure was breaking I saw video that showed a capsule, under parachute, touching down somewhere. A fraction of a second before contact there was an explosion that appeared to originate from the bottom of the capsule. At the time i thought, “How did they have a camera at the right location in order to capture the landing?” I’m now guessing that they didn’t but rather this was film of a prior landing or a test. In any case, does the Russian system include explosives to slow the capsule just prior to impact? If that’s not it, what was the explosion? I can’t find the video now but I watched it a few times so I know what I saw.

Yes, there are deceleration rockets on the Soyuz descent module that fire shortly before touchdown to reduce the impact velocity.

I should clarify that what you saw wasn’t really an explosion, at least not in the sense of a high-order detonation. These are solid-fuel rocket motors designed to give high thrust for a short period of time, very much like the motor on a fighter jet’s “zero-zero” ejection seat (that is, a seat that is capable of safely ejecting a pilot from an aircraft that is at zero speed and zero altitude). The solid fuel burns at a specifically designed (rapid-but-not-explosive) rate, and the gases are directed through a rocket nozzle for efficient generation of directed thrust.

Now that the question has been nicely answered, let me add that the deceleration rockets also come in handy when you need to get from one impact and fire destroyed space station to another. Especially if you’ve exhausted your maneuvering propellants trying to unsnag your prematurely deployed parachute.

Other options include lowering your capsule’s O2 levels, George Clooney, and vodka apparently. Consult ground control experts for the feasibility of that kind of orbital rendezvous before attempting.

Now I’m curious, how does Soyuz do on-orbit maneuvers?

I can’t read Russian but I think the Russian Wiki (via Google Translate) says the Soyuz orbital manoeuvering and deorbit engine is in the service module and uses nitrogen tetroxide/UDMH propellant.

Failure? I beg to differ. It was critically acclaimed, and peaked at number 49 on the Billboard 200.

There you have it - ignorance fought. The timing must be impeccable or perhaps the flames aren’t visible until the capsule is near the ground? In the video I saw the orange flame was visible for less than one second immediately before touchdown.

Nasa’s youtube has a number of different but similar landings of soyuz lander module in Kyzakistan. I just found landings from 2011, 2015… which feature commentary explaining the soft landing explosions …

The descent module uses a gamma ray altimeter to measure the altitude and determine the precise moment to fire the soft landing engines.

Soft landing on “Kaktus”article.

Stackexchange article, video link in the answer section.

H[sub]2[/sub]O[sub]2[/sub].

You send the H[sub]2[/sub]O[sub]2[/sub] over a heated catalyst, and it rather energetically breaks down, giving enough thrust to perform maneuvers.

Unfortunately, H[sub]2[/sub]O[sub]2[/sub] breaks down slowly over time no matter what you do, so that is why the Soyuz that is currently docked to the station has a “shelf life” of only 200 days.

Just to avoid confusion, the descent module uses hydrogen peroxide for attitude control, while the service module uses N2O4/UDMH for orbital maneuvers. The on-orbit Soyuz consist of three distinct modules.

Impeccable timing:

FWIW, the Mars Polar Lander had a similar strategy, i.e. fire retrorockets a moment before touchdown based on the movement of the landing legs, but that system didn’t work so well. NASA lost communications with it, and their leading theory is that spurious signals from the leg sensors triggered the retrorockets during the initial unfolding of the legs, which took place miles above the surface prior to atmospheric entry.

According to one of those links, the rockets fire only 70 cm above the ground. The seats have shock absorbers but one cosmonaut described the “soft landing” as the equivalent of a head-on collision between a truck and a small car with him being in the car.

A short burn makes the best use of available fuel; a longer, gentler burn would require more fuel, which would mean either a larger launch vehicle or a reduced payload.

The Falcon 9 lands using its famous “hover-slam” maneuver for the same reason: it minimizes fuel requirements. I expect they’d drop from altitude even faster if they could, but when it comes to the final last-second decel burn, they’re limited to the maximum thrust available from their ascent engines, which have a whole separate set of design/performance requirements. So they burn the engines just enough during the main descent phase to keep the descent velocity within the limits of what the engines can scrub off during the final few seconds before touchdown.

You’ve actually got it backwards with regards to the Falcon 9 and available thrust for landing. Because the spent booster has so little mass relative to when it’s full, a single Merlin engine has too much thrust to hover even at minimum throttle - the core would start going back upwards. They’ve got lots enough thrust to do the landing burn even later to save more fuel just by lighting more engines, which is exactly what they do for heavier GTO payloads where the fuel budget is tighter. The descent velocity is dictated by a couple things - first, their re-entry burn slows the booster enough to prevent damage from heating during re-entry. As the booster re-enters, it slows down a lot purely from atmospheric drag - you can see this happening in launch videos where they show 1st stage telemetry during this portion of the flight (often they have 2nd stage telemetry onscreen during this segment, but not always). On the re-entry burn, to save fuel you want to burn just enough to avoid re-entry damage because slowing any more is wasted cuz aero-braking is free. Then how late to leave the landing burn is just a tradeoff between leaving it later and burning with 3 engines to save fuel and starting sooner on a single engine to improve controlability.