In fact, not only we had to face a fire, but for good measure our instructor Dima threw at us a leak in the nitrogen tanks, which contain high pressure gas that pressurizes our propellant lines. Simply put – no pressure in the nitrogen tanks, no engine burns!
I’ve talked several times about dealing with a fire in the Sokol, for example here.
Today I would like to talk to you about “separation”. As you might now, the Soyuz capsule is made of three components: the orbital module, which is the roughly spherical element on one end, the service module with (most of) the engines on the other end and the bell-shaped descent module in the middle. Only the descent module, as the name suggests, is meant to return to Earth: it has the proper shape and a heat shield to survive atmospheric reentry. Therefore, after the engine burn that slows us down and commits us to get back into Earth atmosphere, we need to separate: as we’re safely strapped in our seats in the descent module, the hatch to the orbital module closed, pyrotechnical charges blow the three elements apart. One of those unforgettable moments during the roller coaster ride that is a descent in the Soyuz, or so I am told. You can learn more about that ride in this great video by ESA:
But how is separation initiated?
Nominally, by the computer, according to an automatic sequence. After engine cut-off, the relief valve in the orbital module is opened and its atmosphere is vented to space. Also, a pitch maneuver is initiated to assume a safe attitude for separation: that’s to make sure that we and the “discarded” modules go our separate ways and don’t meet again any time soon. As unkind as it sounds, they’re bound for burn-up and we’re bound for home! Finally, at the predetermined time, the command to fire the pyrocharges is sent.
If the main computer fails, we can manually assume the proper orientation and give a series of commands to separate manually at the proper time.
What happens, though, if our main engine fails and we have to complete the burn on backup thrusters? Well, that burn takes longer, because the available thrust in that case is a lot smaller. If the main engine failed early on, we’ll probably NOT be done with the burn when the predetermined separation time comes. In that case, separation is tied to heating of thermal sensors located on the service module. As some point, as we get into thicker and thicker atmosphere (but we’re still above 100 km!) they will reach a certain temperature threshold and that is what will trigger separation.
After that, in most cases, the reentry will be ballistic. Just to provide some stabilization, during the ride the descent module will spin around its axis as 13 degrees per second. Other than that, no active control of the trajectory: in a way, we fall like a rock. Might not sound good, but ballistic reentries have occurred multiple times and the crews were safe and sound at arrival!
In the picture you can see Anton and me before the sim this morning: Terry will join us next week! (Credit: GCTC)
Futura mission website (Italian): Avamposto42
avamposto42.esa.int
(Trad IT) Traduzione in italiano a cura di +AstronautiNEWS qui:
https://www.astronautinews.it/tag/logbook/
(Trad FR) Traduction en français par +Anne Cpamoa ici:
https://spacetux.org/cpamoa/category/traductions/logbook-samantha/
(Trad ES – Currently not updated) Tradducción en español aquí:
https://www.intervidia.com/category/bitacora/
14/10/2014