Regarding the story Mr Lin told us during DNT lesson to tackle the "root cause":

When NASA first started sending up astronauts, they discovered that ball-point pens would not work in zero gravity. To combat this problem, NASA scientists spent a decade and $12 million developing a pen that writes in zero gravity, upside down, underwater, on almost any surface including glass and at temperatures ranging from below freezing to over 300C.

When confronted with the same problem, the Russians used a pencil.

However, this has been proven to be a rumour:

Summary of the eRumor
The message says that the U.S. National Aeronautics and Space Administration spent ten years and $12 million developing a pen that writes in zero gravity for use by astronauts. The pen will write upside down, underwater, on almost any surface and is functional at extremely hot and cold temperatures. The Russians, however, filled the need for a space writing instrument by simply using pencils.

Fact:

For some people, it’s sport to point out government waste and bureaucratic stupidity, but this story about the space pen won’t provide ammunition for it. The government did not fund the development of the pen, it did not cost $12 million to perfect, and neither the Americans nor the Russians consider it desirable to use pencils in space. In fact, both Americans and Russians use the space pen for their flights.

The famous space pen, which is still a popular product today, was developed by Paul Fisher the founder of the Fisher pen company. An engineer who improved ball point technology, he created his "bullet pen" in the 1940’s, which became one of the best-selling pens of the Twentieth Century. Later, he perfected a pen that was sealed with pressure inside of the cartridge that made the ink to flow regardless of gravity. It also worked in high and low temperature extremes, underwater, and wrote on many kinds of surfaces. According to the Fisher Pen company, after extensive testing, NASA chose the pen in 1967 for use by Apollo astronauts and it’s been a part of space travel ever since. The company says it took Fisher about 2 years and $2 million to develop the space pen. Prior to 1967, there were no pens that worked in space so there were pencils used, but there were concerns about pencil dust floating around the space capsules as well as fears that if the tip of a pencil broke off and drifted into the electronics, there would be problems.

Source: http://www.truthorfiction.com/rumors/s/spacepen.htm

Buy one: http://www.spacepen.com/usa/catalog/1001/cat_1001.htm