China has launched today Tianlian-1D, their latest, fourth from series of data relay satellites. Satellite was launched at 15:24 UTC on atop of Long March 3C/G2 from Launch Complex 2 at Xichang Satellite Launch Center.

It is fourth from series of data relay and communication satellites designed by China Academy of Space Technology (CAST). Until today, constellation was based only on three spacecrafts  Tianlian-1A, Tianlian-1B and Tianlian-1C. All three were launched from Xichang on atop of Long March 3C: first in 2008, second in 2011 and third in 2012. All three were based (and probably Tianlian-1D is also using same platform) on DFH-3 bus with 8 years of planned operational life and two solar arrays combined with onboard battery. Tianlian constellation operates on GEO orbit and serve as support for communication between satellites remaining on orbit and ground control stations to provide real time communication.

Dongfanghong-3 platform used for creating Tianlian satellite weighs was 2100 kg, what places this spacecraft in the class of medium sized spacecrafts. Similar situation refers to powering system which is able to provide 1.7 kW what makes impossible to install highly efficient communication equipment. DFH-3 offers 3 axis Attitude Control System and integrated with bus thermal control system; payload capacity is 220 kg.

Long March 3C is medium sized launch vehicle designed in 2000s with maiden flight in 2008.   Rocket is long for 54.8 m with diameter at 3.35 m and with total mass of 345000 kg. Payload capacity for GTO missions (just like during Tianlian-1D mission) is up to 3800 kg and could be extended to 3900 kg in C/E version. C/E is slightly larger comparing to C version; it has longer boosters and first stage with larger fuel tanks. Since maiden flight performed in 2010, larger version was used for 13 missions with success ratio at 100% – exact success ratio as regular version with three missions more.

Rocket is equipped with two boosters fueled with N2O4/UDMH and powered with single YF-25 engine each. Thrust of single booster is 740.4 kN and propellant mass is 41100 kg. Each booster is long for 15.33 m with diameter of 2.25 m.  First stage is powered by 4 YF-21C liquid fueled engines each burning 171800 kg of N2O4/UDMH. YF-21C engines are able to provide thrust at 2961.6 kN. Stage is long for 23.27 m with diameter at 3.35 m. Second stage is powered by combination of central YF-24E (742 kN) and four stabilizing YF-23C (47.1 kN) engines. They are fueled with 49400 kg of N2O4/UDMH. It has diameter at 3.35 m and length of 12.92 m.  Third stage is fueled with 18200 kg of LH2/LOX and its propulsion is based on single YF-75 engine generating thrust at 167.17 kN. Third stage diameter is slightly smaller and is exactly 3 m in diameter with 12.387 m of length.