China launches Chang Zheng 3B for seventh TJSW mission

by Leo Bruce

At 15:41 UTC on August 24, a Chang Zheng 3B (internationally known as Long March 3B) successfully lifted off from LC-3 at the Xichang Satellite Launch Center in China.

It is believed the launch vehicle carried the seventh Tongxin Jishu Shiyan Weixing (TJSW-7) satellite to Geosynchronous Transfer Orbit.

The nature of TJSW satellites is not fully confirmed; however, official Chinese media outlines their purpose as “satellite communications, radio and television, data transmission and other services, and … related technical test verification.”

More specifically, it is thought the TJSW series are used for Chinese military purposes, with this seventh spacecraft of the series publicly referred to by China as a “communication technology test satellite.”

TJSW-7 was manufactured by the Shanghai Academy of Spaceflight Technology (SAST). While officially for “communication testing,” based on SAST and their TJSW history, it is likely the TJSW-7 spacecraft is of the Huoyan-1 series — military satellites that are thought to be part of an early-warning missile detection system for China, in similar nature to the United States’ Space-Based Infrared System (SBIRS).

Three SAST-built Huoyan-1 satellites are thought to have already been launched in the second, fifth, and sixth TJSW missions. SAST was also believed to have built the third mission’s pair of satellites, though likely not of the Huoyan-1 type.

Thus, the remaining first and fourth missions of the series are believed to be of the Qianshao-3 series, military satellites made by the China Academy of Spaceflight Technology (CAST) for signals intelligence purposes that demonstrate multi-band, high-speed communication techniques.

Since the first TJSW mission in September 2015, all flights have been secretive.


The Chang Zheng 3B (CZ-3B) for Tuesday’s mission was publicly spotted on August 15 by a witness at the Xichang launch facility.

Notices to Airmen (NOTAM) were released days after this sighting, confirming a launch from the Xichang Satellite Launch Center on August 24.

The launch occurred at 23:41 local time (15:41 UTC) with the launcher’s four boosters and first stage igniting their collective eight engines to propel the vehicle into the night sky for what was declared a successful mission.

The CZ-3B is a liquid-fuelled, medium-lift launch vehicle manufactured by the China Academy of Launch Vehicle Technology. It is heavily based on the successful Chang Zheng 3A (CZ-3A), with adaptations in the form of a 3B variant (four boosters) and a 3C variant (two boosters) to accommodate a wide range of payload capability.

The CZ-3B, which TJSW-7 used, features three stages (and an optional fourth stage), including four boosters on the first stage, with the launcher being able to lift up to 11,200 kg to Low Earth Orbit and 5,100 kg to Geostationary Transfer Orbit.

Enhanced versions of the 3B and 3C variants include lengthened boosters and first stage cores, designating the vehicle as CZ-3B/E and CZ-3C/E, respectively. This allows for a greater payload capacity over the base variant of the vehicles, and in the case of Tuesday’s CZ-3B/E, being able to loft an increased 5,500 kg to Geosynchronous Transfer Orbit – the orbit this vehicle specializes in.

The vehicle launched predominantly eastwards from Xichang as shown via a Google Maps trajectory.

The mission’s launch trajectory and stage drop zones. (Credit: GoogleEarth)

The four boosters each use the YF-25 engine, running off the hypergolic propellants of unsymmetrical dimethylhydrazine (UDMH) and nitrogen tetroxide (N2O4). Using the standard flight timeline of the CZ-3B, these are jettisoned from the first stage at approximately T+2 minutes 08 seconds.

Meanwhile, the first stage and its four YF-21 engines, utilizing the same hypergolic propellants as the boosters, burn until 2 minutes 25 seconds before separating from the second stage.

Both the boosters and first stage are lengthened by 0.8 meters and 1.5 meters, respectively, over the base CZ-3B, amounting to longer-duration burn times resulting in the aforementioned increased payload performance of the enhanced CZ-3B/E variant.

After first stage separation, the second stage ignites its single YF-22E main engine to burn until T+5 minutes 26 seconds with the stage’s YF-23 vernier engine shutting down 15 seconds later. The stage uses hypergolic propellants.

Fairing separation occurs during second stage flight at approximately 3 minutes 30 seconds after liftoff.

A Chang Zheng 3B in flight – via Chinese media.

After second stage shutdown and separation, the third stage ignites its two YF-75 engines, running off liquid hydrogen and liquid oxygen — the only cryogenic stage of the vehicle. This stage burns for approximately 4 minutes 44 seconds to reach near-orbital parameters.

A second burn to raise the perigee is conducted around T+21 minutes following a coast phase. As well as performing an orbital insertion, this 179-second burn then significantly raises the apogee to the parameters needed for a geosynchronous transfer.

Spacecraft separation from the third stage occurs at approximately T+25 minutes.

Tuesday’s mission marked the ninth launch from the Xichang Satellite Launch Center this year. Situated in southwestern China, the launch facility has been operational since 1984 with three launch complexes — one of which never came to fruition.

Specializing in geosynchronous and geostationary-bound missions, the complex handles a variety of civil and military payloads, utilizing the Cheng Zheng 2 and Cheng Zheng 3 series of vehicles.

Lead image: A CZ-3B rocket launches the TJSW-6 mission.

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