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Shenzhou 10


Tyneside, UK
2018 Oct 16
Tuesday, Day 289

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Shenzhou 10 - Return to Earth

2013 Jun 24 at 23:05 UTC, Shenzhou 10 undocked from the Tiangong 1 space laboratory carrying Nie Haisheng, Zhang Xiaoguang and Wang Yaping. At the time, Tiangong was above southern Africa, in view of the Swakopmund tracking station and heading towards the next staion along-track near Malindi, Kenya.

Hatches between the two craft had been closed a little earlier, at 21:07 UTC, when Tiangong 1 was above another Chinese tracking station near Santiago, Chile.

After undocking, Shenzhou 10 began a fly-round of Tiangong 1, passing below it and then taking station behind. The manoeuvre was probably conducted in automatic mode. At the same time, Tiangong rotated to keep its docking port pointing at Shenzhou. Eventually it was pointing backwards along the orbit. Shenzhou reportedly moved forward for a further, possibly simulated, docking with Tiangong. The docking may have involved contact between the two vehicles' docking rings without them latching firmly to pull the craft together and make a seal. Whatever the reality, China did not claim it as an actual docking.

Shenzhou 10 then backed off for one final time.


Retro-fire to Landing

Landing was set for June 26 at 00:07 UTC. The Chinese press said only that landing would be shortly after 8 o'clock local time but a simple calculation involving orbital dynamics and event timings from earlier Shenzhou missions pointed to the precise moment. All the major pre-landing events happened in the dying minutes of June 25 UTC.

Shenzhou 10 was set to land in the same area of Mongolia as its predecessors. The main NOTAM ws worded similarly to ones for the earlier missions:
A0790/13 - A TEMPORARY RESTRICTED AREA ESTABLISHED,ALL ACFT ARE PROHIBITED TO FLY INTO 
THE AREA. LATERAL LIMITS: IN CHINESE TERRITORY OF FOLLOW AREA: N4304E10241-
N4318E11403-N4209E11405-N4021E10259 BACK TO START. VERTICAL LIMITS: GND-UNL. GND - UNL, 
25 JUN 23:40 2013 UNTIL 26 JUN 00:21 2013. CREATED: 25 JUN 03:27 2013
A second NOTAM listed a number of air route closures over the area. Further NOTAMs were issued for times later in the day and after landing. They were to protect aircraft movements over the next few hours as they lifted out the Shenzhou crew, recovery teams and equipment.

The map shows the main events from retro-fire to landing. All times are estimates made at the time but they accord with reality.

Re-entry events

The three Tianlian 1 satellites at 17° east, 77° east and 177° east could see the whole of the Tiangong 1 orbit for all of the time. At re-entry, Tianlian 1A at 77° east was in a position to 'watch' every event starting with separation of the Orbital Module.

One thing the map illustrates is how carefully sites for China's overseas tracking stations were chosen to support Shenzhou missions. Every major Shenzhou 10 re-entry event was in sight of one of them. It suggests that China's space station plans are very firmly tied to the 42° inclination orbit currently used by Shenzhou and Tiangong.


Swakopmund

To support earlier Shenzhou missions, China had four active ships in the Yuan Wang fleet. Yuan Wang 4 was forcibly retired in 2007 as a result of collision damage leaving only Yuan Wang 3, Yuan Wang 5 and Yuan Wang 6 to support Shenzhou 7 and later missions.

Shenzhou 10 represented the first time on a Shenzhou mission when there was no ship off Namibia to monitor OM separation. For earlier flights presence of a Yuan Wang was probably nnede because OM separation occurs at Swakopmund's horizon and China may still have been building confidence in the whole system. Also, the Tianlian geosynchronous satellte-tracking satellites were not fully deployed on the previous occasions.


Emergency Scenarios on Land

Like Soyuz, Shenzhou follows a lifting re-entry to reduce g-loads on the crew. It results in a long track between the initial re-entry point into the atmosphere and the landing point. Also like Soyuz, Shenzhou can change to a ballistic re-entry but it results in a higher g-loads and a reduced-length incoming track. There was an area back along the track, to the south-west of the main landing zone for a possible ballistic landing.

Had a re-entry at the first opportunity not been possible, the restricted area for the main landing zone was shaped in such a way that a landing attempt one orbit later would put Shenzhou down in the same zone. With earlier missions, the restricted time period in the NOTAMs extended right through to the second landing opportunity. On this occasion, the restriction was to be lifted a few minutes after touch down but it is unlikley to to be indicating that the possibility of a second landing opprtunity was not in the planes. Maybe confidence was high or, as sometimes happens, there was an administrative error.

Re-entry events


Yuan Wang Involvement

Yuan Wang 3, Yuan Wang 5 and Yuan Wang 6 were to play no part in the planned return to Earth providing it went well. They were strung out on a great circle across the Pacific Ocean and Shenzhou did not rise above any of their horizons during the return to Earth. However, if re-entry had to be delayed because of a technical issue and a landing in China became problematic, there was the possibility of a splashdown - something that crews had practiced and trained for. There was reportedly a pick-up vessel stationed in the Pacific near Yuan Wang 6.

A little over three hours or two circuits of the Earth after the intended landing, if it had still been in space, Shenzhou 10's orbit would carry it overhead each of the ships in turn as it passed southwards across the Pacific. Retro-fire over western China could have been used to initiate a ballistic, rather than a lifting, re-entry and splash it down near Yuan Wang 6.

Re-entry events


This scenario is speculative because it has never been used in anger but it fits with the emphasis that China had placed on a possible maritime recovery, and the ships were perfectly located to support one. Otherwise, it is difficult to explain deployment of the ships.


Originally published in zarya.info Blog: 2013 Jun 25
Re-edited for web: 2016 Jan 10
Copyright © Robert Christy, all rights reserved
Reproduction in whole or in part without permission is prohibited