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TOKYO (CNN) -- Starry-eyed poets are sending in their lines by the thousands to Discovery space shuttle astronaut Chiaki Mukai.

Mukai, who became Japan's first woman in orbit four years ago and is the first Japanese to fly in space twice, began writing a poem during her latest mission.

During a television broadcast November 5 while in orbit, the Japanese astronaut invited viewers to finish her tanka, a traditional Japanese poetic form. It begins:

"Turn space somersaults,
As many as you like,
That is weightlessness."

To complete the poem, contestants are asked to submit two lines of seven syllables each.

More than 15,000 entries have been received by postcard, and about 6,000 by the Internet, Yasuyuki Fukumuro, a spokesman for the National Space Development Agency, said Wednesday.

He declined to give examples to avoid compromising the contest, which ends December 1.

INTERACTIVE:

Finish Chiaki Mukai's poem.

Discovery took off October 29 from Kennedy Space Center in Cape Canaveral, Florida, and touched down November 7.