China launches Yaogan 15 via Long March 4C at short notice

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A Chinese Long March 4C has launched with a military passenger – understood to be the Yaogan 15 military satellite – from the Taiyuan Satellite Launch Center. Launch was recorded at 07:31 UTC, catching out most observers, with the only news of the launch on Tuesday leaking out on the internet, prior to official media reports of a successful ride to orbit.

Chinese Surprise:

This mission was on the schedule, yet it was not expected to launch as soon as the early hours of Tuesday. Normally, despite a lack of Chinese media coverage of military campaigns, warning notices of no fly zones and drop zones for the stages of the rocket are published, providing the required clues to a launch a few days in advance.

With Chinese bloggers posting references to an imminent launch on the internet, confirmation of the lift-off was released by State media shortly after the mission was deemed to be a success.

The satellites in this range are officially intended for “scientific experiments, land survey, crop yield assessment, and disaster monitoring” purposes. However, after analyzing the other previous launches in this series, it’s believed there are two versions of this spacecraft; a synthetic aperture radar imaging series and an electro-optical observation series.

The first YaoGan Weixing satellite (29092 2006-015A) was launched by a Long March 4C (Chang Zheng-4C) from the Taiyuan Satellite Launch Center on April 27, 2006. At the time the details about this satellite were closely guarded by the Chinese, before being revealed as the first Jian Bing-5 satellite – equipped with the first space-based synthetic aperture radar (SAR).

Several other launches followed in the series, prior to the Yaogan Weixing-6, launched by a Long March 2X (Chang Zheng-2C-III) from Taiyuan on April 22, 2009, this time based on a second-generation SAR satellite developed by SAST, having a spatial resolution of 1.5m.

Other second-generation SAR satellites were the Yaogan Weixing-8, launched on December 15, 2009, Yaogan Weixing-10, launched on August 9, 2010, Yaogan Weixing-13, launched on November 29, 2011.

The YaoGan Weixing-9 mission, launched March, 2010 from Jiuquan, had a different architecture from the previous missions on the series. Launched by Long March 4C, the mission placed a triplet of satellites in Earth orbit. Flying in formation these three satellites appeared to be like a type of NOSS system.

Based on the orbital placement and launch vehicle campaign, the Yaogan 15 is a Yaogan-8 class payload.

The launch was confirmed to have used a Long March 4C (Chang Zheng-4C) launch vehicle, an optimized version of the Long March 4B (Chang Zheng-4B), using an upper stae with restart capability and a new interstage adapter between the first and second stages. This vehicle also used a 3.35m diameter fairing for the Yaogan 15 ride uphill.

With its main commonality with the Long March 4B, 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.

This was the 164th successful Chinese orbital launch, and the ninth successful orbital launch for China in 2012.

Situated in the Kelan County on the northwest part of the Shanxi Province, the Taiyuan Satellite Launch Center (TSLC) is also known by the Wuzhai designation. It is used mainly for polar launches (meteorological, Earth resources and scientific satellites).

The center is at an altitude of 1400-1900m above sea level, and is surrounded by mountains to the east, south and north, with the Yellow River to its west. The annual average temperature is 4-10 degrees C, with maximum of 28 degrees C in summer and minimum of -39 degrees C in winter.

TSLC is suitable for launching a range of satellites, especially for low earth and sun-synchronous orbit missions. The center has state-of-the-art facilities for launch vehicle and spacecraft testing, preparation, launch and in-flight tracking and safety control, as well as for orbit predictions.

(Images via ChinaNews).

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