According to North Korean defector Kim Kil Sŏn, the No. Seven factory is under the control of the Second Natural Science Institute, which manages all weapons research and development in North Korea. This factory produces prototypes of missiles and conducts performance tests before the missiles begin mass production at the Man'gyŏngdae Electric Machinery Factory. Kim Kil Sŏn believes the No.7 Factory is probably the same facility that some analysts have called the "San'ŭm-dong" or "San'ŏp-dong" Research and Development Center. [Note: Historically, and for a variety of technical reasons, prototype production is usually done at, or very near, the missile design facility. Therefore, it is very plausible that the No. Seven Factory is a missile design center. Kim's comments about this facility are supported by the historical precedent of other cases].

Sources:
[1] Kim Kil Sŏn interview with Daniel A. Pinkston, senior research associate, Center for Nonproliferation Studies, 10 April 2001, Seoul;
[2] Kim Kil Sŏn interview with Daniel A. Pinkston, senior research associate, Center for Nonproliferation Studies, 23 August 2001, Seoul;
[3] Lee Jŏng Hun, "Pukhan Missile Shilche Irŭmŭn 'Hwasŏng'," Chugan Donga, No. 212, 9 December 1999, pp. 30-31;
[4] "Taepodong 2 Ho'nŭn Ŏpta," Joongang Ilbo, 12 January 2000, www.joins.com;
[5] Federation of American Scientists, "North Korea Special Weapons Guide," www.fas.org;
[6] Chŏng Ki Hae, "Kyŏngjenan'ŭi Bburi/Min'gan'gyŏngje Kalg'amŏngnŭn Kunsusan'ŏp (A! Bungnyŏk'dongp'o: 23)," Joongang Ilbo, 30 March 1995, p. 8, in KINDS, www.kinds.or.kr.