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Launches and Orbital Operations


Tyneside, UK
2021 May 11
Tuesday, Day 131

Maintained by:






Mission Events 2021:














Mission Events 2020:



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Timelines:




Shiyan 9 Unusual Behaviour


track map


Launch

Shiyan 9 was launched from Wenchang 2021 March 11 at 17:51 UTC using the second CZ 7A launch vehicle (the first had been lost twelve months earlier when the second stage failed to fire properly). It was described as being "...for space environment studies and related technology experiments".

It was placed in Geosynchronous Transfer Orbit (GTO) from where a Chinese satellite would normally move itself into a drift orbit less than 24 hours after lift off. It then remained in GTO although it did make a small orbit adjustment, raising the question of whether it suffered a failure.


Expected Behaviour

Launch to Geosynchronous orbit from Wenchang usually entails a short coasting period in LEO at 20° inclination followed by a launch vehicle re-start as it approaches the equator to produce the transfer orbit with perigee near the original height and apogee around 36000 kilometres. First apogee accurs above South America and on the equator. One Earth circuit later, the satellite is back at apogee but around 130° - 140° east longitude, well in view of China and close to its final location.

A thruster firing then simultaneously raises perigee and reduces the inclination to near-zero. The orbital period at that point is slightly above or below the 1436.1 minutes needed for it to become truly geosynchronous with the result that the satellite drifts along the Geosynchronous orbit arc. When it reaches its destined location, a small thruster firing matches its orbital period to the Earth's rotation, putting the satellite 'on station'.


Shiyan 9 Behaviour

Shiyan 9 followed all of the rules as far as second apogee, near 134° east, on March 12 at about 10:25 UTC. However the anticipated orbit correction did not occur and a continuing flow of orbit data from Space-Track over the next few days showed it still in a transfer orbit.

It did make one small change at that point with a very short thruster firing that raised perigee by just over 200 kilometres..


Conclusion

There are several scenarios that fit with Shiyan 9's behaviour, including:

It may have been intended to go into geosynchronous orbit but some problem prevented the onboard thruster from firing as intended. Fourteen days later the satellite was still in transfer orbit, indicating that the problem cannot be fixed.

Alternatively, given the 2020 failure of the earlier CZ 7A's second stage, programme managers might have deemed the fix for the 2020 failure as too risky for the rocket to carry a major payload. Shiyan 9 may be a cluster of instruments to monitor performance during launch hence the 'technology experiments' tag in its launch announcement. The shortened apogee engine firing could have been in order to prove the satellite had reached orbit undamaged.


Page date: 2021 Mar 26
updated: 2021 Mar 31

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