Soyuz landing profile
In contrast to the two-day journey to the ISS, a Soyuz undocking and landing only takes approximately 3.5 hours. Only the Descent Module (SA, СА) makes it to Earth as the other two modules are discarded enroute – the Orbital Module (BO, БО) is released about three hours after undocking, and the Instrumentation/Propulsion Module (PAO, ПАО) is discarded at the same time, after it has performed the deorbit burn. The SA has a secondary guidance, navigation and control system that enables the crew to retain maneuverability. The usual landing zone for a nominal landing is in central Kazakhstan, near the town of Arkhalyk.
|Undocking −00:00 minutes; landing −03:23:00 hours||Separation command to begin opening hooks and latches, which hold the Soyuz spacecraft to a docking port on the Space Station|
|Undocking +03:00; landing −03:20:00||Hooks opened. Soyuz begins physical separation from the Pirs docking compartment at 0.1 meters per second|
|Undocking +06:00; landing −03:17:00||A 15-second separation burn when the Soyuz is about 20 meters from the Station|
|Undocking +02:29; landing −00:54:00||When the Soyuz is at a distance of about 19 km from the ISS, the engines fire for a 4-minute, 21-second deorbit burn|
|Undocking +02:57; landing −00:26||The unoccupied Orbital Module separates from the Descent Module and burns up upon re-entry into the atmosphere|
|Undocking +03:00; landing −00:23||The Soyuz reaches Entry Interface – 121,920 meters in altitude – 31 minutes after the deorbit burn|
|Undocking +03:08; landing −00:15||Parachutes are commanded to deploy. Two Pilot Parachutes are deployed, the second of which extracts the Drogue Chute. The Drogue slows the spacecraft’s descent from a rate of 230 meters per second to 80 meters per second.
The Main Parachute is then released. It slows the Soyuz to a descent rate of 7.2 meters per second. First, its harnesses allow the Soyuz to descend at an angle of 30 degrees to expel heat, then it shifts the Soyuz to a straight vertical descent.
|Landing −00:02||Six Soft Landing Engines fire to slow the vehicle’s descent rate to 1.5 meters per second just 0.8 meters above the ground|
|Undocking +03:23||Soyuz lands|
Below are descriptions of Soyuz landings, from various sources.
What will the Soyuz TMA-2/6S crew (Expedition 7 + Pedro Duque) encounter during reentry/descent?
On descent day (10/27)
Special attention will be paid to the need for careful donning of the medical belt with sensors and securing tight contact between sensors and body.
During preparation for descent, before atmosphere reentry, the crew should settle down comfortably in the seat, fasten the belts, securing tight contact between body and the seat liner in the couch.
Dust particles starting to sink in the Descent Module cabin is the first indication of atmosphere reentry and beginning of G-load effect. From that time on, special attention is required as the loads increase rapidly.
Under G-load effect during atmosphere reentry the crew can expect the following sensations:
Sensation of G-load pressure on the body, “burden in the body,” labored breathing and speech. These are normal sensations, and the advice is to “take them coolly”. In case of the feeling of a “lump in the throat,” this is no cause to “be nervous”. This is frequent and should not be fought. Best is to “try not to swallow and talk at this moment”. Crew should check vision and, if any disturbances occur, create additional tension of abdominal pressure and leg muscles (strain abdomen by pulling in), in addition to the “Kentavr” anti-G suit.
During deployment of drogue and prime parachutes the impact accelerations will be perceived as a “strong snatch”. No reason to become concerned about this but one should be prepared that during the parachutes deployment and change of prime parachute to symmetrical suspension swinging and spinning motion of the Descent Module occurs, which involves vestibular (middle ear) irritations.
It is important to tighten restrain system to fasten pelvis and pectoral arch. Vestibular irritation can occur in the form of different referred sensations such as vertigo, hyperhidrosis, postural illusions, general discomfort and nausea. To prevent vestibular irritation the crew should “limit head movement and eyes movement,” as well as fix their sight on motionless objects.
Just before the landing (softened by six small rocket engines behind the heat shield): Crew should be prepared for the vehicle impact with the ground, with their bodies fixed along the surface of the seat liner in advance. “Special attention should be paid to arm fixation to avoid the elbow and hand squat”.
Crew should not get up quickly from their seats to leave the Descent Module. They are advised to stay in the couch for several minutes and only then stand up. In doing that, they should limit head and eyes movement and avoid excessive motions, proceeding slowly. They and their body should not take up Earth gravity in the upright position too quickly.
– Source: 17 October 2003 On-Orbit Status Report.
At the ISS, hatches were closed at 1:45 p.m. EDT and tunnel leak checks performed at 2:05 p.m. With that, the return to Earth of Soyuz TMA-3/7S with Michael Foale, Alexander Kaleri & André Kuipers is ready to proceed along the following event sequence (all times EDT):
- ISS free drift & DC1 port hooks open – 3:15 p.m. (ISS returns to attitude control);
- ISS maneuvers to 7S undocking attitude – 4:19 p.m.;
- ISS in free drift – 4:48 p.m.;
- Hooks Open command – 4:49 p.m.;
- Separation springs action (delta-V ~0.12 m/sec) – 4:52 p.m.;
- Separation burn (15 sec, ~0.55 m/sec) – 4:55 p.m.;
- ISS maneuvers to LVLH/MinProp attitude – 4:57 p.m.;
- ISS maneuvers to Burn Observation (“Relaksatsiya,” Релаксация) attitude – 6:45 p.m.;
- Deorbit Burn (4 min 17 s; delta-V 115.2 m/sec) – 7:20 p.m.;
- ISS maneuvers to Soyuz comm attitude – 7:25 p.m.;
- Tri-Module separation – 7:45 p.m.;
- Atmospheric entry – 7:48 p.m.;
- ISS maneuvers to LVLH/TEA – 7:56 p.m. (remaining thru 5/5);
- Parachute deploy command – 7:57 p.m.;
- 7S Landing (nominally) – 8:11 p.m.;
- ISS attitude control handed back to US – 8:20 p.m.
– Source: 29 April 2004 On-Orbit Status Report.
If undocking from the nadir port of Pirs, the ISS is maneuvered to the Y-axis in the Velocity Vector position (Zvezda pointing downwards; the Truss parallel with the Earth) – see Motion control & navigation.
There are 3 different types of descent profiles for the Soyuz. The normal type of landing is a controlled descent, where the automation software constantly orients the descent vehicle by its flat lower part to the Earth, ensuring lift due to the incidental airflow, and also inflicting minimum overloads on the crew up to 4 gravities. If for whatever reason the automation fails (as has happened in the TMA series to date with Soyuz TMA-1, TMA-10 and TMA-11) a backup program prompts the capsule to enter on a shorter and more severe ballistic trajectory. The capsule is rotated around its axis to mimimize the g-forces on the crew (it would otherwise fall like a stone and possibly kill them), though they still experience up to 8.5 g’s.
The descriptions below have been taken from the SoyCOM Manual.
Автоматический Управляемый Спуск
The AUS (Avtomaticheskii Upravlyaemyi Spusk) mode is the nominal and preferred descent mode, where the spacecraft lands in a preselected landing area. The crew input the trajectory before descent, and the onboard computer takes care of the actual descent.
The spacecraft/station undocking occurs 1.5 revolutions prior to the engine fire. The spacecraft undocks and the spring pushers accelerating the spacecraft up to the velocity of 0.12-0.15 m/s. When the separation range reaches the value of ρ=20-25 m the ДПО-Б, DPO-B thrusters are fired for 8 s accelerating the separation range rate up to 0.5 m/s. In 1.5 revolutions the spacecraft is above and behind the ISS.
Soyuz TMA-8 nominal descent g-profile (September 29, 2006) – the gravitational forces the crew experience on the way down (via NASASpaceflight.com forum):
|Beginning of deorbit burn (00:23:53 UTC, 353.5 km, 7.397 km/sec)||0g;|
|Ending of deorbit burn (00:28:12 UTC, 341.9 km, 7.298 km/sec)||0.05g;|
|Separation of modules (00:47:31 UTC, 140.1 km, 7.545 km/sec)||0g;|
|Entry into atmosphere (00:50:25 UTC, 102.3 km, 7.591 km/sec)||0g;|
|Beginning of computer control (00:52:10 UTC, 80.3 km, 7.594 km/sec)||0.09g;|
|Maximum g-load (00:57:01 UTC, 33.2 km, 1.964 km/sec)||3.96g;|
|Command of parachute deploying (00:58:54 UTC, 10.8 km, 213 m/sec)||1.17g;|
|Landing (01:13:21 UTC, 0 m, 0 m/sec)||1g|
Ручное Управление Спуском
The crew can transfer to the RUS (Ruchnoe Upravlenie Spuskom) mode from the AUS mode anytime during the autonomous flight of the SA, Descent Module. Transfer to the RUS mode is irreversible. In manually-controlled descent the cosmonaut using the RUS Handle buttons issues commands for the basic roll angle decrements of 15 degrees each, the maximal possible decrement being 45 degrees. In case of the attitude control equipment sensor failure the RUS mode is impossible.
The BS (Ballisticheskii Spusk) is the descent with the average-integral zero lift. The BS is a backup descent mode used in case of the RUS mode failure or “nominally” is most emergency descent modes. However this mode, just like the AUS mode, can be selected in advance or can be transferred to from the controlled descent procedure in case off-nominal deviation occurs in the SA or its system operation. The latter case is called the “fall into БС”.
The ballistic descent can be executed in case of the descent control system failures resulting in loss of the spacecraft or the SA attitude control, failures in the descent reaction control system (the SA attitude control thrusters) etc. In all such cases the SA is driven into rotation about its velocity axis Oxv with the rate of ω.x=12.5 degr./s. The BS trajectory mainly features the atmosphere part range decrease by approximately 400 km with respect to the controlled descent and also the axial acceleration increase up to n.x=8.5 g.
In case of a failure in the primary equipment set used in the ballistic descent, transfer to the backup ballistic mode (BSP – Баллистический Спуск Резервный, Ballisticheskii Spusk Rezervnyi) is executed.
Unconditional compulsory selection of the ballistic descent is provided for the urgent descent from orbit in case of off-nominal situations jeopardizing the crew safety (depressurization, fire etc.). The ballistic (trajectory) support for such situations is envisaged: once a day (if no dynamic operations are accomplished) form №23-14 is uplinked to the crew onboard the ISS, that form containing data on the engine ignition and the retrofire impulse value for each revolution. The ignition time is selected so as to ensure landing in areas which are called backup landing areas and which are selected in advance taking into account the arbitrary position of the orbital path with respect to the Earth’s surface.
Because cosmonauts could land anywhere in the USSR (or elsewhere) a rescue team, initially comprised of parachutists, was formed in 1960 before Yurii Gagarin’s flight. On 10 October 1966 the paratroop rescue team was integrated into a special Rescue and Research organization in the Air Force. Later on a specialist organization was formed: the Federal Management of Research and Aerospace Rescues, ФПСУ, FPSU.
It is made up of one hundred men, equipped with Mi-8 helicopters, An-12 aircraft and a specially-designed all-terrain rescue vehicle. The FPSU are on standby during Soyuz launches and before and during landings. A helicopter lands near where the Soyuz capsule has come down and extract the cosmonauts (there is a special platform that is brought along and used if the capsule lands upright), taking them to a temporary field hospital set up nearby, then transporting them to the nearby town (usually Arkhalyk in the Northern Kazakhstan landing zone).
After the off-course landing of Soyuz TMA-1 (440 km off-course), the FPSU changed the deployment plan of its planes and helicopters.
In 2006 the FPSU was reorganized and merged with the civilian Russian Federal Aeronavigation Service (Росаэронавигации, Rosaeronavigatsii). The civilian and military services had previously conducted Soyuz retrievals as separate bodies; they now both were under the command of Rosaeronavigatsii (though not completely merged as both had specific tasks). The first mission they worked to retrieve was the landing of Soyuz TMA-8 in September 2006.
Diagrams from the MARS Center.
Soyuz TMA undocking sequence (all diagrams about 24 KB):
- Step 1: crew enters Soyuz
- Step 2: hatches close
- Step 3: cosmonauts don suits
- Step 4: undocking (after 3 hours)
Soyuz TMA re-entry profile:
- Kosmonavtika: La Direction Fédérale des Recherches et Sauvetages aérospatiaux (F.P.S.U.) (in French)
- NASA: Soyuz Undocking/Landing Timeline illustrations
- Spaceref: How the Expedition 6 Crew Will Return to Earth