China launches X-ray telescope via Long March 4B

by Rui C. Barbosa

Initially scheduled for launch back in 2010, China has finally launched the long-awaited Hard X-ray Modulation Telescope (HXMT) using a Long March-4B (Chang Zheng-4) launch vehicle from the Jiuquan Satellite Launch Center. Launch took place at 03:00 UTC from the 603 Launch Pad of the LC43 Launch Complex. The new orbiting telescope will be used to monitor pulsars and other objects that could help unravel the mystery of their energy sources.

Scanning the hard x-rays:

Compared with previous X-ray astronomical satellites, HXMT has a larger detection area, broader energy range and wider field of view. These gives it advantages in observing black holes and neutron stars emitting bright X-rays, and it can more efficiently scan the galaxy.

The Hard X-ray Modulation Telescope was initially proposed by IHEP (Institute of High Energy Physics of the Chinese Academy of Sciences) scientists Li Tibei and Wu Mei based on their innovative direct demodulation image reconstruction method.

The main scientific objectives of HXMT are to scan the galactic plane to find new transient sources, to monitor the known variable sources, and to observe X-ray binaries to study the dynamics and emission mechanism in strong gravitational or magnetic fields.

There are three main payloads onboard HXMT, the high energy X-ray telescope (20-250 keV, 5100 cm2), the medium energy X-ray telescope (5-30 keV, 952 cm2), and the low energy X-ray telescope (1-15 keV, 384 cm2). All these three telescopes are collimated instruments.

Using the direct demodulation method and scanning observations, HXMT can obtain X-ray images with high spatial resolution, while the large detection areas of these telescopes also allow pointed observations with high statistics and high signal to noise ratio.

It is expected that HXMT will discover a large number of new transient X-ray sources and will study the temporal and spectral properties of accreting black hole and neutron star systems in more details than the previous X-ray missions.

The payload module of the HXMT was developed by IHEP and Tsinghua University, while the satellite bus was developed by the Chinese Academy of Space Technology (CAST) based on the Ziyuan-2 / Phoenix-Eye-2 satellite bus.

Launch mass of HXMT is 2,800 kg and its dimensions are 2.0 by 2.0 by 2.8 meters.

The Zhuhai-1 and ÑuSat-3 satellites:

With a launch mass of 50 kg each, the Zhuhai-1 earth observation satellites are the video component of the Chinese Orbita Earth observation system. Two OVS-1 (OVS-1a and OVS-1b) satellites constitute the prototype OVS-1 video component. The operational Orbita constellation is to consist of video satellites (OVS-2), hyperspectral satellites (OHS-2) and small personal satellites (OPS 2).

The additional payload on this launch is composed by the Argentinian ÑuSat-3 “Milanesat” satellite that is the third satellite in the Aleph-1 constellation developed and operated by Satellogic S.A.. The Aleph-1 constellation will consist of up to 25 satellites.

The satellite has mass of 37 kg, with dimensions 450mm x 450mm x 800mm. The primary objective of the mission is to commercially provide Earth observation images to the general public, in the visible and infrared parts of the spectrum.

The satellite is equipped with cameras operating in visible light and infrared, and will operate in 500 km SSO orbit with inclination at 97.5°.

ÑuSat-4 and ÑuSat-5 will be launched in August 2017.

The Long March-4B launch vehicle:

The feasibility study of the Chang Zheng-4 began in 1982 based on the FB-1 Feng Bao-1 launch vehicle. Engineering development was initiated in the following year. Initially, the Chang Zheng-4 served as a back-up launch vehicle for Chang Zheng-3 to launch China’s communications satellites.

After the successful launch of China’s first DFH-2 communications satellites by Chang Zheng-3, the main mission of the Chang Zheng-4 was shifted to launch sun-synchronous orbit meteorological satellites. On other hand, the Chang Zheng-4B launch vehicle was first introduced in May 1999 and also developed by the Shanghai Academy of Space Flight Technology (SAST), based on the Chang Zheng-4.

The rocket is capable of launching a 2,800 kg satellite into low Earth orbit, developing 2,971 kN at launch. With a mass of 248,470 kg, the CZ-4B is 45.58 meters long and has a diameter of 3.35 meters.

SAST began to develop the Chang Zheng-4B in February 1989. Originally, it was scheduled to be commissioned in 1997, but the first launch didn’t take place until late 1999. The modifications introduced on the Chang Zheng-4B included a larger satellite fairing and the replacement of the original mechanical-electrical control on the Chang Zheng-4 with an electronic control.

Other modifications were an improved telemetry, tracking, control, and self-destruction systems with smaller size and lighter weight; a revised nozzle design in the second stage for better high-altitude performance; a propellant management system for the second stage to reduce the spare propellant amount, thus increasing the vehicle’s payload capability and a propellant jettison system on the third-stage.

The first stage has a 24.65 meter length with a 3.35 meter diameter, consuming 183,340 kg of N2O4/UDMH (gross mass of first stage is 193.330 kg). The vehicle is equipped with a YF-21B engine capable of a ground thrust of 2,971 kN and a ground specific impulse of 2,550 Ns/kg. The second stage has a 10.40 meter length with a 3.35 meter diameter and 38,326 kg, consuming 35,374 kg of N2O4/UDMH.

The vehicle is equipped with a YF-22B main engine capable of a vacuum thrust of 742 kN and four YF-23B vernier engines with a vacuum thrust of 47.1 kN (specific impulses of 2,922 Ns/kg and 2,834 Ns/kg, respectively).

The third stage has a 4.93 meter length with a 2.9 meter diameter, consuming 12,814 kg of N2O4/UDMH. Having a gross mass of 14,560 kg, it is equipped with a YF-40 engine capable of a vacuum thrust of 100.8 kN and a specific impulse in vacuum of 2,971 Ns/kg.

Launch Site:

The Jiuquan Satellite Launch Center, in Ejin-Banner – a county in Alashan League of the Inner Mongolia Autonomous Region – was the first Chinese satellite launch center and is also known as the Shuang Cheng Tze launch center.

The site includes a Technical Centre, two Launch Complexes, Mission Command and Control Centre, Launch Control Centre, propellant fuelling systems, tracking and communication systems, gas supply systems, weather forecast systems, and logistic support systems.

Jiuquan was originally used to launch scientific and recoverable satellites into medium or low earth orbits at high inclinations. It is also the place from where all the Chinese manned missions are launched.

The LC-43 launch complex, also known by South Launch Site (SLS) is equipped with two launch pads: 921 and 603. Launch pad 921 is used for the manned program for the launch of the Chang Zheng-2F launch vehicle (Shenzhou and Tiangong). The 603 launch pad is used for unmanned orbital launches by the Chang Zheng-2C, Chang Zheng-2D and Chang Zheng-4C launch vehicles.

Other launch zones at the launch site are used for launching the Kuaizhou and the CZ-11 Chang Zheng-11 solid propellant launch vehicles.

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