Yaogan 31

During 2021, China completed its constellation of Yaogan 31 satellites, having set-up four groups of them in separated orbit planes.

The oldest group, from 2018, was probably a pathfinder with the later three sets forming a fully operational system.


Yaogan 34-01

2021 April 30 saw the first Yaogan 34 appear. Its orbit parameters were similar to the Yaogan 31s but the Right Ascension of the Asending Node was 3° to the east of that of the second Yaogan 31 Group. Yaogan 34 then moved to a position 36° of orbit arc behind the Yaogan 31s. It was allowed to drift but when the gap had a reduced to 32°, an orbit 'nudge' sent it drifting in the opposite direction. It then settled into a routine where regular orbit adjustments kept it between 32° and 36° behind Yaogan 31. From its position, Yaogan 34-01 has the other satellites in view all of the time.

A combination of the 3° spacing in RAAN and the on-orbit spacing between Yaogan 34-01 and its Yaogan 31 companions ensures that it passes along a near-identical ground track but ten minutes behind them. The RAAN difference takes account of the Earth's rotation over that ten minute period.


What Are They Doing?

The Yaogan 31s probably have an electronic intelligence gathering (ELINT) task, particularly over the world's oceans away from dry land. They orbit in a triangular formation about 120 kilometres from each other. Differences in Doppler shift of transmissions detected from the Earth's surface would allow the location to be pinpointed. They may also be able to perform as a long baseline interferometer.

Yaogan 31s are probably tasked with characterising the radio and radar transmissions that they detect. The job of Yaogan 34 may be to take a more forensic look at specific 'interesting' transmissions detected by its companion Yaogan 31 Group.


Yaogan 34-02

The second Yaogan 34 was launched 2022 Mar 17. It had been expected as a result of air navigation warnings that pointed to its launch time, orbital inclination and RAAN.

Its RAAN behaviour mirrored that of its predecessor but related to Yaogan 31 Group 3.

The launch time and target orbit were selected very carefully and it was injected into a near identical orbit to Yaogan 31 Group 3 and precisely 34° behind it. The operational relationship was set up from the moment of arrival on orbit.




NOTE - 'wiggles' in the plotted lines are due to the way that the separation distance is calculated.



Summary of the Launches Involved

These are the four launches and eight satellites now incorporated into the joint Yaogan 31 and Yaogan 34 constellation.

2018-034 CZ 4C Jiuquan Space Centre						2018 Apr 10, 04:25
Yaogan 31-01 Leader 2018-034A 43275						in space
Remote sensing satellite described as used for electromagnetic environment surveys and other related technology tests. Orbiting in close formation with the other two satellites from the launch, Its purpose may be signals or electronic intelligence gathering over the world's oceans, a similar task to the US NOSS triplet formations that orbited at a similar altitude and inclination.
epoch (UTC)	s-m axis ( km )	eccentricity	perigee ( km )	apogee ( km )	period ( min )	incl  ( ° )	ω   ( ° )
2018 Apr 11, 11:58	7471	0.0009	1086	1100	107.11	63.41	38
2018 Jun 15, 00:53	7468	0.0013	1080	1100	107.05	63.41	8
2021 Jan 29, 03:47	7468	0.0099	1016	1164	107.05	63.40	3
2023 Feb 13, 12:52	7468	0.0166	966	1214	107.04	63.40	4
2025 Feb 24, 10:42	7467	0.0233	915	1263	107.03	63.40	6
Yaogan 31-01 Follower 2018-034B 43276						in space
One of two further payloads forming the Yaogan 31-01 mission, and flying in formation with it. May be similar to the US NOSS triplet formations that orbited at a similar altitude and inclination.
epoch (UTC)	s-m axis ( km )	eccentricity	perigee ( km )	apogee ( km )	period ( min )	incl  ( ° )	ω   ( ° )
2018 Apr 11, 10:11	7472	0.0007	1089	1099	107.13	63.41	37
2018 Jun 15, 20:30	7468	0.0013	1080	1100	107.05	63.41	7
2021 Jan 29, 03:47	7468	0.0099	1016	1164	107.05	63.40	3
2023 Feb 13, 12:53	7468	0.0166	966	1214	107.04	63.41	4
2025 Feb 24, 12:29	7467	0.0233	915	1263	107.03	63.40	6
Yaogan 31-01 Outlier 2018-034C 43277						in space
One of two further payloads forming the Yaogan 31-01 mission, and flying in formation with it. May be similar to the US NOSS triplet formations that orbited at a similar altitude and inclination.
epoch (UTC)	s-m axis ( km )	eccentricity	perigee ( km )	apogee ( km )	period ( min )	incl  ( ° )	ω   ( ° )
2018 Apr 10, 19:54	7472	0.0008	1088	1100	107.13	63.41	46
2018 Apr 13, 13:49	7449	0.0010	1063	1078	106.64	63.41	338
2018 Apr 14, 08:14	7442	0.0019	1050	1077	106.48	63.41	3
2018 Apr 15, 01:19	7439	0.0015	1050	1073	106.43	63.41	7
2018 May 4, 18:56	7440	0.0018	1048	1075	106.43	63.41	4
2018 May 5, 00:27	7446	0.0014	1058	1078	106.57	63.41	30
2018 May 7, 05:36	7459	0.0015	1069	1092	106.84	63.40	32
2018 May 8, 01:16	7465	0.0013	1077	1096	106.98	63.41	353
2018 May 11, 04:07	7468	0.0011	1082	1098	107.05	63.41	8
2021 Jan 29, 03:47	7468	0.0099	1016	1164	107.05	63.41	3
2023 Feb 13, 12:53	7468	0.0166	966	1214	107.04	63.41	4
2025 Feb 24, 12:29	7467	0.0233	915	1263	107.03	63.40	6
Weina 1B 2018-034E 43279						in space
Small satellite - mission unknown.
epoch (UTC)	s-m axis ( km )	eccentricity	perigee ( km )	apogee ( km )	period ( min )	incl  ( ° )	ω   ( ° )
2018 Apr 16, 00:51	7470	0.0010	1085	1100	107.10	63.41	36

2021-007 CZ 4C Jiuquan Space Centre						2021 Jan 29, 04:47
Yaogan 31-02 Outlier 2021-007A 47532						in space
One of two further payloads forming the Yaogan 31-02 mission, and flying in formation with it. May be similar to the US NOSS triplet formations that orbited at a similar altitude and inclination.
epoch (UTC)	s-m axis ( km )	eccentricity	perigee ( km )	apogee ( km )	period ( min )	incl  ( ° )	ω   ( ° )
2021 Jan 29, 22:04	7472	0.0004	1091	1097	107.13	63.41	274
2021 Feb 2, 10:48	7493	0.0010	1108	1123	107.59	63.41	261
2021 Feb 21, 02:51	7486	0.0008	1102	1114	107.43	63.40	261
2021 Feb 22, 07:04	7477	0.0003	1096	1101	107.23	63.41	39
2021 Feb 25, 10:02	7468	0.0009	1083	1097	107.05	63.41	282
2021 Mar 3, 08:46	7468	0.0009	1083	1097	107.05	63.41	284
2023 Feb 13, 12:20	7468	0.0067	1040	1140	107.04	63.41	353
2025 Feb 24, 10:12	7467	0.0134	990	1189	107.03	63.40	359
Yaogan 31-02 Folower 2021-007B 47533						in space
One of two further payloads forming the Yaogan 31-02 mission, and flying in formation with it. May be similar to the US NOSS triplet formations that orbited at a similar altitude and inclination.
epoch (UTC)	s-m axis ( km )	eccentricity	perigee ( km )	apogee ( km )	period ( min )	incl  ( ° )	ω   ( ° )
2021 Jan 30, 01:39	7472	0.0005	1091	1098	107.14	63.41	276
2021 Feb 2, 10:31	7458	0.0012	1071	1088	106.83	63.41	348
2021 Feb 23, 04:31	7468	0.0009	1083	1096	107.04	63.41	283
2021 Feb 28, 16:32	7468	0.0009	1083	1097	107.05	63.41	284
2023 Feb 13, 12:20	7468	0.0067	1040	1140	107.04	63.41	353
2025 Feb 24, 10:12	7467	0.0134	989	1189	107.03	63.40	359
Yaogan 31-02 Leader 2021-007E 47536						in space
Remote sensing satellite described as used for electromagnetic environment surveys and other related technology tests. Orbiting in close formation with the other two satellites from the launch, its purpose may be signals or electronic intelligence gathering over the world's oceans, a similar task to the US NOSS triplet formations that orbited at a similar altitude and inclination. Formation was set up Feb 24 after one month of phasing manoeuvres.
epoch (UTC)	s-m axis ( km )	eccentricity	perigee ( km )	apogee ( km )	period ( min )	incl  ( ° )	ω   ( ° )
2021 Jan 29, 09:34	7471	0.0002	1092	1095	107.12	63.40	258
2021 Feb 1, 10:40	7458	0.0012	1071	1088	106.82	63.41	265
2021 Feb 19, 11:18	7467	0.0010	1081	1096	107.02	63.41	295
2021 Mar 3, 14:07	7468	0.0009	1083	1097	107.05	63.41	283
2023 Feb 13, 12:20	7468	0.0067	1040	1140	107.04	63.41	353
2025 Feb 24, 10:12	7467	0.0134	989	1189	107.03	63.40	359

2021-014 CZ 4C Jiuquan Space Centre						2021 Feb 24, 02:22
Yaogan 31-03 Follower 2021-014A 47691						in space
One of two further payloads forming the Yaogan 31-03 mission, and flying in formation with it. May be similar to the US NOSS triplet formations that orbited at a similar altitude and inclination.
epoch (UTC)	s-m axis ( km )	eccentricity	perigee ( km )	apogee ( km )	period ( min )	incl  ( ° )	ω   ( ° )
2021 Feb 24, 12:30	7472	0.0006	1090	1099	107.14	63.41	271
2021 Feb 27, 08:44	7464	0.0013	1077	1096	106.97	63.41	219
2021 Mar 26, 07:23	7468	0.0010	1082	1098	107.05	63.41	304
2023 Feb 13, 13:28	7468	0.0068	1039	1140	107.04	63.41	354
2025 Feb 24, 13:07	7467	0.0135	989	1190	107.03	63.41	359
Yaogan 31-03 Outlier 2021-014C 47693						in space
One of two further payloads forming the Yaogan 31-03 mission, and flying in formation with it. May be similar to the US NOSS triplet formations that orbited at a similar altitude and inclination.
epoch (UTC)	s-m axis ( km )	eccentricity	perigee ( km )	apogee ( km )	period ( min )	incl  ( ° )	ω   ( ° )
2021 Feb 24, 14:17	7472	0.0006	1090	1098	107.13	63.41	267
2021 Feb 27, 03:04	7491	0.0014	1102	1123	107.54	63.41	257
2021 Mar 25, 12:15	7472	0.0011	1085	1101	107.12	63.41	285
2023 Feb 13, 13:28	7468	0.0068	1039	1140	107.04	63.41	354
2025 Feb 24, 13:07	7467	0.0135	988	1190	107.03	63.41	359
Yaogan 31-03 Leader 2021-014E 47695						in space
Remote sensing satellite described as used for electromagnetic environment surveys and other related technology tests. Orbiting in close formation with the other two satellites from the launch, its purpose may be signals or electronic intelligence gathering over the world's oceans, a similar task to the US NOSS triplet formations that orbited at a similar altitude and inclination.
epoch (UTC)	s-m axis ( km )	eccentricity	perigee ( km )	apogee ( km )	period ( min )	incl  ( ° )	ω   ( ° )
2021 Feb 24, 12:30	7471	0.0005	1089	1097	107.12	63.41	278
2021 Feb 25, 04:34	7469	0.0007	1086	1096	107.07	63.41	280
2021 Feb 26, 07:19	7463	0.0008	1079	1092	106.95	63.41	257
2021 Mar 26, 07:23	7468	0.0010	1082	1098	107.05	63.41	303
2023 Feb 13, 13:27	7468	0.0068	1039	1140	107.04	63.41	354
2025 Feb 24, 13:07	7467	0.0135	989	1190	107.03	63.41	359

2021-020 CZ 4C Jiuquan Space Centre						2021 Mar 13, 02:19
Yaogan 31-04 Leader 2021-020A 47854						in space
Remote sensing satellite described as used for electromagnetic environment surveys and other related technology tests. Orbiting in close formation with the other two satellites from the launch, its purpose may be signals or electronic intelligence gathering over the world's oceans, a similar task to the US NOSS triplet formations that orbited at a similar altitude and inclination. Until 2021 Apr 8, this satellite was catalogued as 2021-020B/47855 - that ID now belongs to an item of debris.
epoch (UTC)	s-m axis ( km )	eccentricity	perigee ( km )	apogee ( km )	period ( min )	incl  ( ° )	ω   ( ° )
2021 Mar 13, 14:14	7471	0.0003	1090	1096	107.11	63.41	297
2021 Mar 18, 06:40	7467	0.0009	1082	1095	107.02	63.41	286
2021 Apr 8, 14:35	7468	0.0009	1083	1097	107.05	63.41	300
2023 Feb 13, 13:19	7468	0.0066	1041	1139	107.04	63.41	354
2025 Feb 24, 11:10	7467	0.0133	990	1188	107.03	63.41	359
Yaogan 31-04 Outlier 2021-020C 47856						in space
One of two further payloads forming the Yaogan 31-04 mission, and flying in formation with it. May be similar to the US NOSS triplet formations that orbited at a similar altitude and inclination.
epoch (UTC)	s-m axis ( km )	eccentricity	perigee ( km )	apogee ( km )	period ( min )	incl  ( ° )	ω   ( ° )
2021 Mar 13, 17:48	7472	0.0004	1091	1097	107.13	63.41	282
2021 Mar 18, 05:34	7496	0.0010	1111	1126	107.65	63.41	344
2021 Apr 8, 13:20	7489	0.0006	1106	1116	107.50	63.41	296
2023 Feb 13, 04:24	7468	0.0065	1041	1139	107.04	63.41	354
2025 Feb 24, 12:58	7467	0.0132	990	1188	107.03	63.41	359
Yaogan 31-04 Follower 2021-020D 47857						in space
One of two further payloads forming the Yaogan 31-04 mission, and flying in formation with it. May be similar to the US NOSS triplet formations that orbited at a similar altitude and inclination.
epoch (UTC)	s-m axis ( km )	eccentricity	perigee ( km )	apogee ( km )	period ( min )	incl  ( ° )	ω   ( ° )
2021 Mar 14, 11:40	7472	0.0004	1091	1097	107.13	63.41	279
2021 Mar 19, 07:42	7466	0.0009	1081	1095	107.00	63.41	286
2021 Apr 10, 04:03	7468	0.0010	1083	1097	107.05	63.41	302
2023 Feb 13, 13:19	7468	0.0065	1041	1139	107.04	63.41	354
2025 Feb 24, 11:11	7467	0.0132	990	1188	107.03	63.41	359

2021-037 CZ 4C Jiuquan Space Centre						2021 Apr 30, 07:27
Yaogan 34-01 2021-037A 48340						in space
Imaging satellite - orbit is similar to the Yaogan 31 electronic surveillance satellites,and the Initial orbit plane has RAAN about three degrees to the east of that of the second Yaogan 31 triplet (launch no 2021-007). 2021 May 8, Yaogan settled into formation with Yaogan 31 Group 2, sitting 34° of orbit arc behind and following a near-identical ground track.
epoch (UTC)	s-m axis ( km )	eccentricity	perigee ( km )	apogee ( km )	period ( min )	incl  ( ° )	ω   ( ° )
2021 Apr 30, 12:15	7472	0.0002	1093	1096	107.14	63.41	305
2021 May 1, 06:06	7467	0.0007	1084	1095	107.03	63.41	239
2021 May 1, 09:40	7463	0.0013	1076	1095	106.94	63.41	264
2021 May 1, 13:14	7463	0.0010	1077	1092	106.93	63.40	278
2021 May 7, 06:27	7468	0.0009	1083	1097	107.04	63.40	327
2023 Feb 13, 05:23	7468	0.0065	1041	1138	107.04	63.41	356

2022-027 CZ 4C Jiuquan Space Centre						2022 Mar 17, 07:09
Yaogan 34-02 2022-027A 52084						in space
Imaging satellite - orbit is similar to the Yaogan 31 electronic surveillance satellites,and the Initial orbit plane has RAAN about three degrees to the east of that of the third Yaogan 31 triplet (launch no 2021-014). Settled into formation with Yaogan 31 Group 3, sitting 34° of orbit arc behind it and following a near-identical ground track.
epoch (UTC)	s-m axis ( km )	eccentricity	perigee ( km )	apogee ( km )	period ( min )	incl  ( ° )	ω   ( ° )
2022 Mar 17, 12:23	7472	0.0003	1092	1096	107.14	63.40	262
2022 Mar 18, 11:28	7462	0.0014	1074	1094	106.92	63.39	263
2023 Feb 13, 08:16	7468	0.0026	1070	1109	107.04	63.40	345

2022-154 CZ 4C Xichang Space Centre						2022 Nov 15, 01:38
Yaogan 34-03 2022-154A 54249						in space
Imaging satellite - orbit is similar to the Yaogan 31 electronic surveillance satellites, and the Initial orbit plane has RAAN about three degrees to the east of that of the fourth Yaogan 31 triplet (launch no 2021-020). Expected to move into formation with the Yaogan 31 group.
epoch (UTC)	s-m axis ( km )	eccentricity	perigee ( km )	apogee ( km )	period ( min )	incl  ( ° )	ω   ( ° )
2022 Nov 15, 14:26	7473	0.0003	1092	1097	107.14	63.41	272
2022 Nov 17, 20:51	7462	0.0009	1077	1091	106.92	63.41	251

2023-048 CZ 4C Jiuquan Space Centre						2023 Mar 31, 06:27
Yaogan 34-04 2023-048A 56157						in space
Imaging satellite - orbit is similar to the Yaogan 31 electronic surveillance satellites, and the Initial orbit plane has RAAN about three degrees to the east of that of the first Yaogan 31 triplet (launch no 2018-034). Expected to move into formation with the Yaogan 31 group.
epoch (UTC)	s-m axis ( km )	eccentricity	perigee ( km )	apogee ( km )	period ( min )	incl  ( ° )	ω   ( ° )
2023 Mar 31, 10:05	7472	0.0003	1092	1096	107.14	63.40	257
2023 Apr 1, 09:07	7473	0.0002	1094	1097	107.16	63.40	277
2023 Apr 15, 14:15	7470	0.0007	1087	1097	107.09	63.40	307

Page Date - 2022 Mar 17
Updated 2022 - Mar 18