* Nikkei up 0.15 pct, on track for weekly gain of 2.9 pct
* N.Korea missile launch not entirely unexpected, reaction calm
TOKYO, Sept 15 (Reuters) - Japan's Nikkei share average inched up on Friday with the market apparently unruffled by North Korea's ballistic missile launch, wih the dollar remaining relatively stable against the yen despite Pyongyang's latest challenge.
Prior to the Tokyo financial markets' open on Friday, North Korea fired a missile that flew over Japan's northern island of Hokkaido far out into the Pacific Ocean, South Korean and Japanese officials said.
The Nikkei initially dipped in a knee-jerk reaction soon after the open but pared the losses and last stood at 19,835.43, up 0.15 percent on the day.
The index was poised to end 2.9 higher on the week, helped by Wall Street's surge to record highs and a weaker yen.
On Thursday the Nikkei had risen to 19,918.39, its highest level since Aug. 9, rebounding from a four-month low of 19,239.52 set a week ago on North Korea and Hurricane Irma concerns.
Pyongyang's missile launch on Friday capped Japan's equity markets but was unable to trigger the sort of risk aversion seen last week.
"The Nikkei is holding up as currencies have reacted relatively calmly to the missile launch, with dollar/yen back above the 110.00 yen threshold," said Masahiro Ichikawa, senior strategist at Sumitomo Mitsui Asset Management.
"Also, the missile launch did not catch the market entirely off guard, as North Korea was expected to react after the latest U.N. Security Council sanctions."
The dollar fell to as low as 109.550 yen after North Korea launched the missile but last stood at 110.200, unchanged from late U.S. trade on Thursday.
Oil producer Inpex Corp added 1.6 percent after it extended a production sharing agreement with Azerbaijan's state oil company. The duration of Inpex's production-sharing agreement on oil fields in Azerbaijan's Caspian Sea sector has been extended by 25 years until 2049.
Astellas Pharma Inc advanced 3.3 percent after the company and Pfizer Inc said on Thursday their blockbuster prostate cancer drug met the main goal of a key study that tested it for treating the disease in its early stages.
Shares related to bitcoin fell after the cryptocurrency remained volatile after it was reported that China plans to close all bitcoin exchanges by the end of September.
Financial information service provider Fisco Ltd, which operates a cryptocurrency exchange, fell 3.4 percent. Remixpoint Inc, which is also engaged in virtual currency trading services, lost 4.9 percent. Caica Inc, a systems company involved in blockchain technology research, dropped 1.5 percent.
The broader Topix was 0.15 percent higher at 1,634.63 after setting a two-year high of 1,642.56 on Thursday.