Author Topic: Soyuz landing constraints (Read 3867 times)

Phillip Clark · « **on:** 06/28/2017 04:30 pm »

I have been looking at the times of Soyuz landings compared with the local sunset and I have belatedly realised that the constraints which defined the nominal "landing window" have clearly changed.

For the original Soyuz and Soyuz-T missions the nominal landing time was normally within 2.5 hours of local sunset: OK there were a few successful missions which came down before sunrise and others which came down earlier in the day than 2.5 hours before sunet, but I am thinking of the general trend. And of course, flights which were recalled earlier than intended (eg, Soyuz 10, Soyuz 15) came down in darkness.

Starting with the Soyuz-TM series the landings now appear to take place at just about any time during local daylight.

Therefore, to me, it is clear that the rules which originally led to the nominal landing opportunities have changed, starting with the TM series. Does anyone have details please?

Many thanks.

fregate · « **Reply #1 on:** 07/04/2017 06:11 am »

Have a look here https://www.space.com/18537-soyuz-spacecraft-rare-night-landing.html - Soyuz could land in night too!

Phillip Clark · « **Reply #2 on:** 07/04/2017 06:49 am »

Quote from: fregate on 07/04/2017 06:11 am

Have a look here https://www.space.com/18537-soyuz-spacecraft-rare-night-landing.html - Soyuz could land in night too!

I have never claimed that a Soyuz could not land at local night time. In fact missions like Soyuz 15 which were curtailed early after a docking failure with a Salyut station had to come back in darkness. The point that I make is that while Soyuz and Soyuz-T were targeting after their planned flights to come down between 2.5 hours before sunset and sunset itself (see my article "Soyuz Missions to Salyut Stations" in BIS Spaceflight, June 1979) , starting with the Soyuz-TM series the landings would take place at *any* time during local daylight. And yes, there has been an occasional landing in darkness after the planned flight time. So clearly there was a change in the constraints which had previously restricted the descent times.

LtCmdr · « **Reply #3 on:** 03/03/2018 05:01 pm »

A more general question about Soyuz capsule landing...
After the reentry of a Soyuz capsule a sonic boom is heard, but I wonder if the capsule itself deploys smoke markers after Soyuz descent module reentry?
Before full parachute deployment, the Soyuz heat shield is jettisoned and maybe the smoke markers are related to this piece of hardware ?

LtCmdr · « **Reply #4 on:** 03/04/2018 03:43 pm »

Smoke trails possibly related to the separation pyro technics on the parachute lines ? $:-\$

asmi · « **Reply #5 on:** 03/04/2018 06:15 pm »

Quote from: LtCmdr on 03/04/2018 03:43 pm

Smoke trails possibly related to the separation pyro technics on the parachute lines ? $:-\$

No - this is hydrogen peroxide vented from capsule's RCS system to eliminate the risk of fire after landing.

LtCmdr · « **Reply #6 on:** 03/05/2018 03:38 pm »

Thanks... I know that once the main parachute is deployed, the smoke is the venting process but I was talking about the very first smoke trails recoveries crews on the ground spot so they get an idea of the location of the capsule... In fact smoke trails shortly after the sonic boom...

Phillip Clark · « **Reply #7 on:** 03/13/2018 04:26 pm »

Sorry to be boring, but ............ does anyone know the answer to my original question on this thread, please?

Basically, I am trying to find the rules which govern the lighting and times of Soyuz retrofires and landings these days, please. I have a couple of things from the ASTP era, but of course things have moved on since then.

Many thanks.

asmi · « **Reply #8 on:** 03/13/2018 05:44 pm »

Quote from: Phillip Clark on 03/13/2018 04:26 pm

Basically, I am trying to find the rules which govern the lighting and times of Soyuz retrofires and landings these days, please. I have a couple of things from the ASTP era, but of course things have moved on since then.

From what I've read, there are no constraints per se, current landing times are a matter of convenience (pre-dawn landings make spacecraft very visible since it's lit by the Sun while it's relatively dark).

The Soyuz is designed to land within 3.5 hrs in case of emergency (that time is an upper bound of time interval from decision to land to touchdown). To facilitate that, MCC-M daily uploads retro fire time windows so that it will land in more-or-less favorable locations (these includes zones outside Russia/Kazakhstan), there are also procedures in place for groups crews and MCCs when the spacecraft must land outside its' nominal landing zones. On top of that, there is a software mode that would allow crew to "aim" to any location (that is physically reachable of course given its' orbit), and onboard computer would calculate retro burn time and duration to land there.

To date there were no such emergency landings (there were two early mission terminations for medical reasons IIRC), but such last-resort plans existed even in pre-ISS times.