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Launches and Orbital Operations


Tyneside, UK
2021 Sep 28
Tuesday, Day 271

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CZ 5B Re-entry - 2021 May 9

2021-076 SMA


Background

2021 April 29 - China launched the core module of it's space station. The launch vehicle was a CZ 5B rocket that also put its own 18 tonne second stage into orbit, setting the scene for the May 9 re-entry of one of the most massive objects since the 40 tonne Salyut 7/Cosmos 1686 combination in 1991.


Space Track

Space-Track is the main source of orbital data as it publishes timely orbital data of unclassified space objects. One of its services is to provide estimates and, eventually, actual times of re-entry for objects brought down from orbit through air drag. There are other sources for re-entry estimates but they use mainly Space-Track published data and apply their own mathematical models to make a prediction.

Starting a few weeks before the event, the Space-Track feed provides an estimate of re-entry date which is updated weekly. For major objects, the Space-Track output switches to issuing 'TIP messages', giving a more precise estimate of date and time and an indication of the expected location on the Earth's surface. The derivation of the acronym 'TIP' is lost in the mists of the 1960s or 1970s. Space-Track has adopted "Tracking and Impact Prediction" but it could equally be something like 'Terminal Impact Point'.


Evolution of the Space-Track Estimate

Below are extracts from the TIP messages issued by Space-Track between May 5 and May 9 in descending order of date/time issued. Latitude and Longitude represent the location when the object is expected to be down to 10 km altitude. It is an arbitrary measurement with no real significance but serves to indicate the general area.


Estimated Date & Time
(UTC)
Window
± minutes
Latitude
(°)
Longitude
(° east)
TIP Message Issued
2021-05-09 02:14:00122.2502021-05-09 03:22:00
2021-05-09 02:11:006035.924.42021-05-08 23:42:00
2021-05-09 02:04:006041.6350.72021-05-08 20:00:00
2021-05-09 02:27:00180-3.979.42021-05-08 14:06:00
2021-05-09 02:52:00360-39.4180.52021-05-08 02:22:00
2021-05-08 23:13:0054038.162.52021-05-07 04:48:00
2021-05-09 04:25:00900-32.4179.32021-05-06 04:07:00
2021-05-08 22:11:001260-27.7176.72021-05-04 22:46:00


The steadily narrowing window as time goes by reflects increasing confidence in the prediction.

The final entry was issued after the event and the ±1 minute confidence is probably down to the infrared signature of the event being detected from orbit by one or more satellites tasked with monitoring rocket and missile launches.


China - Pre-event Notification

China's Xinhua News Agency published the following item that emanated from China's Manned Space Engineering Office (CMSO) shortly before the expected impact:

"BEIJING, May 9, 02:16 UTC -- China's Manned Space Engineering Office announced today on its official WeChat that at [11:24 UTC] on May 9, 2021, the last stage of the Long March 5B Y-2 carrier rocket had a perigee altitude of about 130 km, an apogee altitude of about 160 km and an inclination of 41.5 degrees. The re-entry time is expected to be [02:12 UTC] ±15 minutes on 9 May, with the re-entry centre at 28.38 degrees east longitude and 34.43 degrees north latitude."


China - Wrap Up

After the event, there was a further release from Xinhua:

"BEIJING, May 9, 03:02 UTC -- According to China's Manned Space Engineering Office, after monitoring and analysis, on May 9, 2021 at [02:24 UTC], the Long March 5B Y-2 carrier rocket last-stage debris re-entered the atmosphere, the landing area is located at longitude 72.47 degrees east, latitude 2.5 degrees north over the sea, the vast majority of debris was destroyed by the re-entry process of ablation.

"On April 29, China launched the space station's sky and core module into its intended orbit with the Long March 5 Y-2 carrier rocket at the Wenchang Space Launch Site. The success of the mission marks the full start of the in-orbit assembly and construction of the Chinese space station."


Debris Impact

Re-entry of the previous CZ 5B launch in 2020 reportedly resulted in debris impacting the ground over Africa so, by inference, some components of this rocket will also have got throught the atmosphere. Any such debris will have impacted the Indian Ocean between the Space-Track location and the location announced by China.

Page Date - 2021 May 9

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