At 20:45 Beijing time on December 27,2019,a LM-5,China’s largest carrier rocket,lifted off from the Wenchang Space Launch Center,launching the Shijian 20 satellite,which is China’s heaviest satellite as well as the first to test the adaptability of the DFH-5 satellite platform,into its preset orbit.This was the 323rd flight of the LM series launch vehicle,marking the perfect completion of China’s 2019 space missions.

The carrier rocket and the satellite were developed by the China Academy of Launch Vehicle Technology (CALT)and the China Academy of Space Technology (CAST)respectively.

The LM-5,with a height of about 57 m,take-off weight of 870 t and take-off thrust of 1078 t,is capable of launching 25-ton spacecraft into LEO and 14-ton spacecraft to GTO,making it comparable to the Delta 4 Heavy launcher.

The LM-5 made its maiden flight on November 3,2016.The launch marked the first flight of LM-5 carrier rocket since the launcher’s second mission in July 2017 which ended in failure,prompting a two-and-a-half-year grounding and redesign effort.

Shijian 20,weighing about 8 t,is China’s heaviest and most advanced communications satellite in geosynchronous orbit.It will carry out orbit experiments for a series of key technologies.

It will demonstrate in orbit its heat transfer technology based on cryogenic loop heat pipes,an efficient thermal control device for space applications,to lay the foundation for the development of highly sensitive space probes.

The satellite will test the controllable deformation of shape memory polymers,a type of smart material that can switch between temporary shapes,to pave the way for the development of large variable space structures.

It will also carry out satellite-ground communication tests using Q/V bands,which lie between 33 -75 GHz,within the extremely high frequency (EHF)area of the radio spectrum.These frequencies are used mainly for satellite communications.

Shijian 20 has the largest solar wings among all China’s satellites,with a total wingspan 10 m wider than that of a Boeing 737 aircraft.The solar wings will unfold twice,the first time after the satellite enters its orbit and the second after it flies around the orbit for about a week.The increase of the solar wing area will supply the satellite with abundant power.

A LM-5 flying to space from the Wenchang Space Launch CenterPhoto:SU Dong

The satellite adopts a hybrid propulsion system.Chemical propulsion is powerful but inefficient,and is used in rapid orbit change or satellite attitude adjustment to send it to its planned orbit as soon as possible.Electric propulsion is more precise and efficient but less powerful,hence suitable for long-term delicate adjustments in orbit.Electric propulsion is also a preferred technology for future deep space exploration.Missions to explore Mars,Jupiter and asteroids are all too far away from Earth to be fulfilled by chemical propulsion alone,as it is impossible to bring the amount of fuel needed for the mission.

Shijian 20 will also test the adaptability of the DFH-5 satellite platform,which may serve the needs of high-capacity satellites for high orbit communications,microwave remote sensing,optical remote sensing,space scientific exploration,in-orbit service and other purposes in the next 20 years.

So far,there are more than 20 communications satellites based on the DFH-4 platform running stably in orbit.

According to the design,the takeoff weight of a satellite based on the DFH-5 platform can reach 8 -9 t,and its payload capacity 1,500 kg to 1,800 kg.The power for the whole satellite is more than 28 kilowatts,while the power for its payload above 18 kilowatts.

The successful return-to-flight of the LM-5 paves the way for China to move forward with plans for lunar sample return,space station construction and Mars rover mission.