Tiantong-1 Mobile Communications Satellite placed in Orbit by Chinese Long March 3B Rocket

A Long March 3B Rocket lifted off from China’s Xichang Satellite Launch Center at 16:22 UTC on Friday, carrying the Tiantong-1 01 mobile communications satellite into orbit.

Although launch success was confirmed within one hour of liftoff by Chinese State Media, no information other than the satellite’s name came forward which would suggest a military nature of the mission.

The satellite had been identified as an S-Band mobile communications satellite developed by the Chinese Academy of Space Technology for operation by ChinaSatcom, a division of CASC. It had been suspected that Tiantong-1 finds its roots in the China Mobile Multimedia Broadcasting (CMMB) project using S-Band and UHF frequencies at 2635-2660 and 470-860 MHz to deliver mobile data and multimedia distribution services.

After Friday’s launch, media articles described the satellite as ‘China’s first mobile telecommunications satellite.’ The satellite will take up a position in Geostationary Orbit to deliver services to a broad region centered around China, spanning from East Africa to the Pacific region. According to reports, the satellite will carry voice, video and data for 24/7, all-weather connectivity.

Long March 3B/E weighs approximately 456,000 Kilograms and stands 56.33 meters tall with a core diameter of 3.35 meters. The four boosters, first and second stage use storable propellants, Unsymmetrical Dimethylhydrazine and Nitrogen Tetroxide while the third stage uses cryogenic propellants, Liquid Hydrogen and Liquid Oxygen.

Liftoff was preceded by an eight-hour countdown operation during which the Long March 3B rocket was powered up and underwent final testing before heading into propellant loading on the cryogenic third stage around seven hours prior to T-0, filling the stage with 18,200 Kilograms of Liquid Oxygen and Liquid Hydrogen that were kept topped up until late in the countdown.

The boosters and two lower stages of the rocket received their propellant load before the countdown along with the attitude control system of the third stage since all these systems use storable propellants. Overall, the launcher was filled with 400 metric tons of Unsymmetrical Dimethylhydrazine and Nitrogen Tetroxide to be used by the boosters, the core stage and second stage in the first minutes of flight.

At 00:22:00 a.m. local time Saturday, Long March 3B/E ignited its boosters and core stage that soared to a collective liftoff thrust of 604 metric-ton-force. Thundering off four seconds later, the rocket rose from its pad, lighting up the night skies over the Xichang launch base in the Sichuan province in south-western China. After a vertical ascent of a few seconds, the rocket began to pitch and roll onto its planned ascent path, taking it south-east across China before passing over the Pacific Ocean.

With all engines firing at full throttle, Long March 3B/E burned 2,350 Kilograms of propellant per second as it started racing uphill and making its way downrange, passing Mach 1 and encountering Maximum Aerodynamic Pressure. Each of the four boosters delivered 75,500 Kilogram-force of additional thrust to the vehicle using a single DaFY-5-1 engine. The boosters consumed their propellant load of 41,200kg, each, over the course of a burn of 140 seconds after which they dropped away from the three-stage rocket.

With the boosters gone, the Core Stage continued powering the vehicle using a DaFY-6-1 cluster of four engines delivering 302 metric tons of thrust. Overall, the 24.8-meter tall first stage launched with a propellant load of 186,200 Kilograms that was expended in two minutes and 38 seconds. Immediately after engine cutoff of the first stage, the second stage commanded its four-chamber vernier engine of the second stage to ignite as part of the hot-staging sequence employed by the Long March 3B.

A series of 14 pyrotechnic bolts were fired to disconnect the first and second stage, allowing the second stage’s vernier engine to move the stack away from the empty core stage. Moments after staging, the second stage ignited its DaFY-20-1 main engine, soaring up to a full thrust of 75,660 Kilogram-force to continue powered ascent. The second stage was controlled by using the four-chamber vernier engine that added another five metric tons of thrust. Overall, the second stage launched with a propellant load of 49,400 Kilograms measuring 12.92 meters in length and 3.35 meters in diameter.

While the second stage was firing, Long March 3B departed the dense atmosphere, making it safe to jettison the protective payload fairing and expose the satellite for the rest of its ride uphill.

The second stage performed a nominal burn of 178 seconds with the vernier engine burning about six seconds longer than the main engine. Second stage cutoff occurred after the mission passed T+5.5 minutes. Immediately after shutdown, the pyrotechnic stage separation system was initiated and solid-fueled retrorockets moved the second stage away.

One second after staging, the third stage ignited its two cryogenic YF-75 engines. The 12.38-meter long third stage delivered a total thrust of 16,000 Kilogram-force as part of its initial burn to accelerate the stack to orbital velocity in order to enter a Low Earth Parking Orbit.

The Low Earth Parking orbit, around 190 Kilometers in altitude, was reached after a third stage burn of around four minutes and 45 seconds, marking the start of a coast phase. The coast phase, nearly 11 minutes in duration, was set up to allow the stack to fly to a position where the second burn could be performed around the equator passage so that the high-point of the orbit would be placed over the equator.

This second burn lasted for approximately three minutes and 15 seconds and was followed by a variable velocity adjustment that involved the vernier engines of the third stage which continued to fire until the navigation platform sensed that the targeted injection velocity was achieved, thus optimizing the accuracy of the orbital insertion.

Separation of the Tiantong-1 01 satellite occurred right at the T+26-minute mark and launch was declared a success by officials.