CALT develops new CZ-3B variant for SSO missions

A significant development in China’s space programme, CALT is developing a new variant of its CZ-3B launcher that could be used for SSO missions

China Academy of Launch Vehicle Technology (CALT) revealed that it had completed the concept evaluation of a new variant of its Chang Zheng-3B (CZ-3B, or Long March 3B) launch vehicle, paving the way for the next phase of the development programme.

First introduced in 1996, the CZ-3B has been typically used for the launch of geostationary telecommunications satellites and lunar probe from the Xichang Satellite Launch Centre (XSLC) in Sichuan Province. According to CALT, a total of four variants of the launcher have been introduced so far. The basic variant CZ-3B is no longer in production and has been replaced by the improved CZ-3B/G1. The enhanced CZ-3B/E series, which was first introduced in 2007, includes three variants: CZ-3B/G2, CZ-3B/G3, and CZ-3B/YZ-1.

The latest fifth variant, designated CZ-3B/G5, is said to have been derived from the CZ-3B/YZ-1, which made its debut in July 2015 to place a pair of Beidou-III experimental navigation satellites into a 21,500 km Medium Earth Orbit (MEO). The launch vehicle consists of a three-stage core vehicle, four strap-on boosters, and a Yuan Zheng-1 (YZ-1) upper stage, all burning the hypergolic UDMH/N2O4 bi-propellant.

The main improvement on the CZ-3B/G5 over its predecessor is its payload fairing, which has been stretched by 0.9 m to accommodate larger payload. CALT also highlighted the improved flexibility of the CZ-3B/G5, which is said to be capable of supporting not only GEO and Translunar Orbit launch missions, but also Sun-Synchronous Orbit (SSO) missions from Xichang.

CZ-3B GF-4 Xichang

The revelation of the CZ-3B/G5’s SSO launch capability is a significant development in China’s space programme. So far the CZ-3 family and the Xichang launch centre have been used exclusively for GEO and lunar launch missions, while all launch missions to SSO are conducted from the other two inland space launch centres: Taiyuan and Jiuquan, using the CZ-2C, CZ-2D, and CZ-4B/C series launchers.

The two-stage CZ-2C is capable of placing around 1,400 kg (or 1,900 kg if added with a solid motor upper stage) payload to a 600 km SSO, and CZ-2D is capable of placing around 1,300 kg. The three-stage CZ-4B/C is capable of placing 2,200—2,800 kg to this altitude. Although never been used for such a mission, according to its official user manual the basic variant CZ-3B is capable of lofting an impressive 6,500 kg payload to a 600 km SSO, or 6,000 kg to an 800 km SSO. This payload capacity can be further increased when the launcher is added with the YZ-1 upper stage.

CZ-3B SSO payload capacity

CZ-3B SSO payload capacity (Source: CALT/CGWIC)

Once operational, the CZ-3B/G5 will represent a significant boost to China’s orbital launch capabilities to SSO, typically used by the various Earth-observation satellites for military reconnaissance, maritime surveillance, meteorology, and environment monitoring roles. The Chinese space industry currently has a number of active Earth-observation satellite programmes for both commercial and military users, ranging from high-definition electro-optical imaging, mapping and surveying, to radar imaging. The payload capacities of existing SSO launchers in the Chang Zheng family may soon be exceeded by the weight of those satellites currently in development, and a more powerful launcher is therefore required to loft these heavier satellites.

For almost exactly two decades, the CZ-3B remained the heaviest launch vehicle in the Chang Zheng family, capable of delivering 5,100 kg (or 5,500 kg on later variant) payload to the Geostationary Transfer Orbit (GTO), or 11,200 kg to a 200 km Low Earth orbit (LEO). This record was only broken last month, with the introduction of the more powerful CZ-7 launcher (13,500 kg to LEO). In a few months’ time this record will be broken again with the debut flight of the heavy-lift CZ-5 (14,000 kg to GTO and 25,000 kg to LEO). However, the continued effort to further enhance the CZ-3B’s capabilities indicates a cautious approach in rolling out the new-generation launchers. Before the technologies of the new-generation CZ-5 and CZ-7 launchers mature, China will continue relying on the existing Chang Zheng launchers to fulfil most of its orbital launch requirements.

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