The Sky Bow, or Tien Kung (Chinese: 天弓; pinyin: Tiān gōng), are a series of surface-to-air anti-ballistic missile and anti-aircraft defense systems developed by Taiwan's National Chung-Shan Institute of Science and Technology (NCSIST). Development of the TK-1 was completed in 1986 and this system is now retired. The TK-2 and TK-3 are in service with the Military of the Republic of China. TK-4 is in development.

Research into what became the Sky Bow project began after the United States ended bilateral relations with the Republic of China in 1979. Other names proposed by chief engineer Chen Chuan-hao for the project included Sky Horse (Pegasus) and Flying Horse. Upon formal approval of the project in October 1980, it became known as Sky Bow. Under the influence of aerospace engineer and rocket scientist Huang Hsiao-tsung the project expanded to include testing of ramjet motors. In 1981 the project received increased support from minister of defense Sung Chang-chih and was expanded into a general purpose air defense project benchmarked to the American Patriot and Soviet 2K12 Kub. Sung set a seven year deadline for the project. The first test flight in 1982 ended in failure as did other early test flights. Huang left the project in 1982 for an executive role at NCSIST.

In 1984 Taiwan gained the cooperation of Raytheon and was allowed to examine semi-obsolete missiles in detail. NCSIST experts traveled to the United States studied the technology, but they were not allowed to ask any questions and quickly came to the conclusion that many of the missiles they had been allowed to examine were old and had been damaged while in storage. Dedicated facilities needed to be constructed to support the development of the TK-1 including Taiwan's first hypersonic wind tunnel. In 1986 the 12th flight test ended in a successful intercept of a target aircraft, the system's first. The system was officially unveiled in 1986 at a large ceremony presided over by premier Yu Kuo-hua. Its designation it was given, Zhongzheng 100/Sky Bow 1, referred to its 100km range.

Missiles initially used a semi-active radar homing seeker. A passive infrared homing terminal seeker was also developed as a secondary seeker for the TK-1, this was successfully tested against a HAWK missile target but was never put into production. NCSIST also developed a large multifunction, phased-array radar known as Chang Bai (long white) for use with the Tien Kung (Sky Bow) series surface-to-air missile systems with 120 degree coverage and a maximum range of 450 km. Two versions of the phased array radar exist, a towed trailer radar and fixed "hardened" radar sites. The Chang Bai radar system is reported to be based on the Lockheed Martin's ADAR-HP (Air Defense Array Radar-High Power) design and operates in the 2–4 GHz range (S-band). At least seven systems were said to be in service in 2006. The system performance specifications remain classified, but its effective detection range against a 1m² target is reported to be around 400 km.

There was also a mobile version of the phased array radar developed in the late 1990s which could provide all-round radar cover with four separate faces but with a much decreased detection range. This version only appeared in public once but was never put into service. The development of Sky Bow 2 started around 1986, this added a tandem boost motor and an active radar homing terminal seeker. Proposals were reported to develop Sky Bow 2 into a surface-to-surface missile; unconfirmed reports suggest that this missile is known as Tien Chi. Modifications have been developed for Sky Bow 2, changing it into a single-stage rocket and to provide it with a limited capability against shorter-range ballistic missiles; the first test firing against a ballistic missile target was reported in September 2008. Seven batteries were in service in 2006. In 2010 TK-1/2 SAMs were in service and deployed throughout Taiwan, on the Pescadores, and Dong Ying island.

Chen claims that the Sky Bow I project was completed in less time and using less money than any comparable air defense system. The project was NCSIST's first ambitious weapons project and its success would have a large influence on the organization.

The Sky Bow I (TK-1) (天弓一, Tien Kung I) is a surface-to-air missile (SAM) system developed by the NCSIST in Taiwan. Originally based on the aerodynamics of the MIM-23 Hawk missile, the original missile design resembled a scaled-up Raytheon AIM-54 Phoenix. The TK-1 missile was subsequently redesigned and eventually became very similar in appearance to the US Patriot missile after the US government allowed Raytheon to transfer 85 percent of the MIM-104 Patriot missile technology. There is no track-via-missile (TVM) homing capability as this technology was not included in the technology package licensed to Taiwan; the TK-1 system operates in a similar manner to the US Standard SM2 missile, requiring an illuminating radar during the terminal phase.

The TK-1 is designed primarily to target low and medium altitude attacks. Each TK-1 battery has one Change Bai 1 (Long White 1) S-Band phased-array radar for search and target tracking and two CS/MPG-25 target illuminator radars that operates in the X-Band (18–32 GHz) range for the terminal phase, servicing three or four 4-round missile launchers. The combination of inertial/autopilot and mid-course command guidance with a terminal semi-active radar seeker allows the TK-1 missile to fly an energy-efficient flight path to the vicinity of the target where the seeker's semi-active radar would then receive target illumination for the final seconds of the engagement, giving the target minimum amount of time either to evade or commence electronic countermeasure (ECM).