So-called 'space pens' use ingenious refill technology to enable them to write in adverse conditions - particularly in zero gravity, but also in a range of earthbound conditions that cause problems for ordinary pens. Take a look at our range of pressurised 'space pens' below, or read on...
The story of pressurised pens starts with Paul Fisher, who invented a pen refill that was able to write in zero gravity and who then persuaded NASA to buy the Fisher Space Pen for space missions. The urban myth that NASA spent millions developing the space pen, while the Russians simply used a pencil is sadly not true.
So what was the problem that needed solving? Simply, pen refills rely on gravity for the ink to flow. Zero-gravity = no ink flow. While pencils don't need gravity to work, you don't want pencils shavings or lead fragments floating around in your spacecraft!
Pressurised refills are fully sealed and contain a small amount of inert gas under pressure at the opposite end to the writing tip. This gas constantly pushes the ink towards the tip, maintaining a positive flow of ink when required. The ink isn't forced out from the tip until the pen is actually writing. This is because the ball is very precisely machined to fit a very precise socket, and the thixotropic ink is so viscous that it doesn't flow unless some friction (from the rotating ball) causes it to liquify a little and spread around the ball. This is how all ballpoint pens work, but pressurised refills require more precision and more viscous ink.
However, unless you're an astronaut you're not in the habit of regular travel to outer space - so what's in it for the rest of us? Well, the technology that ensures that these pens can write in zero-G also enables them to:
Write upside-down - very handy if you're on your back, taking notes or doing the crossword. Ordinary ballpoints usually lose the will to write even when held horizontally.
Write in very low temperatures - obviously useful in very cold weather conditions but also useful in commercial cold-storage. Ordinary pen ink will solidify, but a pressurised refill will keep going at minus 20 degrees celsius.
Write in very high temperatures - perhaps less useful. The Schmidt refills claim to write in up to 200 degrees C. If you find yourself in that temperature, you probably have more pressing issues than whether your pen is working or not.
Write on greasy or wet paper, or even underwater - where ordinary ballpoints start skipping because the ball won't rotate properly or grease or water stops conventional ink sticking to the ball, a pressurised refill just keeps on working. Take notes in the rain on your damp notebook, or write your postcards at the bottom of the swimming pool...
Since the Fisher Space Pen was developed, several other writing equipment manufacturers have also perfected the technology.
Spacetec - a Diplomat brand - have been involved with the Fisher Space Pen company for many years and have a similar range of pens. The Spacetec Pocket Pen is virtually identical to the classic Fisher Space Bullet Pen, while the Spacetec 0 Gravity is the discontinued Fisher Zero Gravity Space Pen.
Tombow of Japan has a couple of interesting entrants in this category. The Tombow XPA is a rugged outdoor pen - a solid metal design, which telescopes for compactness and features a lanyard loop to keep it with you. Combined with the properties of the pressurised refill this is one of the most practical pens around. The refill for the XPA is the Tombow BR-VMP - another standard pattern refill, this time in multipen 'D1' format. This refill fits a huge range of multifunction and mini pens.
Uni of Japan have created one of the most interesting pressurised pens. The Uni PowerTank pen costs less than a Fisher refill, but features the same pressurised ink technology in a practical rubber-grip retractable pen design. A brilliant pen, available with black, blue or red ink, and it's even refillable with Uni SNP-10 refills.
The last word however goes to Tombow. A little lateral thinking on their part has come up with a novel take on the problem. Instead of a complex and expensive refill, the Tombow Airpress simply applies a little air pressure to the top of a conventional open-ended ballpoint refill when you click the push-button to open the pen. Simple, ingenious and perfectly effective.
We don't currently stock the Fisher brand, but we do stock all these great pressurised pens and refills - have a browse...