Space Pens
Published on Mar 27, 2008 at 1:11 pm.
9 Comments.
Filed under history, space exploration.
When I was in high school, someone gave me an “astronaut pen.” I was awfully proud of that pen. After all, how many people got a chance to use a pen that had been used in space, I thought? Eventually, though, I lost my prized astronaut pen. Later, I found that you could buy the pens not just in NASA gift shops, but anywhere that had a large selection of pens. They are made by Fisher Space Pen Company. Oh, so does that mean that they really are not astronaut pens? Well, as it turns out, these pens were, in fact, developed with astronaut use in mind.
It takes a special pen to be used in space. For one thing, most ballpoint pens and all fountain pens use gravity assist to pull the ink down. Anyone who has tried to hold something against the wall and write on it has quickly found that they don’t get more than a few words before the pen runs dry. Furthermore, in the vacuum of space, the ink would evaporate and dry out and quit flowing. If the ink gets too cold, then it will get too thick to flow. If it gets too hot, then it will dry out and not flow. So, for a variety of reasons, ordinary pens can’t be used in space. According to an urban legend, NASA spent millions of dollars designing pens to fly in space, while the Soviet Union simply equipped their cosmonauts with pencils. Like so many urban legends, though, this one is false. NASA did not spend any money at all developing the pens. They purchased 400 of the pens for about $6 apiece. That’s a bit much for a pen, perhaps, but they are quite good pens. Eventually, NASA bought even more. The pens were used on Apollo missions, Skylab, and the Space Shuttle. And, eventually the Soviet Union began purchasing Fisher space pens for its cosmonauts. They are still used in space today.
As it turns out, both NASA and the Soviet space agency realized that ordinary pens would never work in space. So, they gave the astronauts pencils. The problem, though, was that the pencil leads broke off and floated around in the space capsule. Such bits of pencil lead could drift into an astronaut’s eye, risking injury. The astronaut could inhale the pencil lead. And worst of all, the pencil lead could find its way into a sensitive switch, interfering with the operation of the spacecraft during a critical moment. No spacecraft was lost due to a pencil lead, but NASA didn’t want to take the chance. Also, ordinary pencils were made of wood, which was flammable in the pure oxygen atmosphere of the space capsule. Furthermore, astronauts had trouble holding the pencils and writing when wearing bulky space suit gloves. And, to make matters worse, the pencil with it’s sharp point floated around the capsule in the way, and also risking injury to the astronaut’s eyes. The Soviet Union gave its cosmonauts grease pencils with which to write in space. But, grease pencils can be messy, and the writing can smear and rub off. Instead of using grease pencils, NASA had special pencils created for the Gemini missions. The original Mercury missions were not designed for extravehicular activities (space walks) so the Mercury space suits were not as thick and bulky as the Gemini space suits, which were designed for exposure to the vacuum of space, since one of the goals of the Gemini project was to conduct extravehicular activities. This required special pencils that were large enough for the astronaut to handle with heavy gloves on, and these pencils needed special housings that could be attached to the walls of the capsule so that they wouldn’t float around. An ordinary clip wouldn’t do because the astronauts would not be able to manage its operation with the gloves on. Those special pencils were very expensive, and NASA got a lot of bad public press attention over them.
But, all that attention brought the whole issue of writing in space to the attention of Paul C. Fisher. He realized that there ought to be a way of making a pen write in space. The solution was simple. Don’t use gravity to move the ink. Instead, he used a sealed ink cartridge with a pressurized gas chamber at the end instead of it being open to the atmosphere. The chamber is filled with nitrogen gas at a nominal pressure of 35 pounds per square inch. The gas in the pressurized chamber pushed on a plug at one end that in turn pushed the ink towards the ball point. Reportedly, his company spent nearly a million dollars developing the pen. But, the ink refills were of a size that they would fit into many other pens, effectively making them into “space pens,” too. Once Fisher was assured that his space pen met NASA’s requirements, he submitted it to the space agency for further assessment. NASA engineers tested the pen, and it passed all tests and proved to be safe, so 400 pens were purchased from Fisher, at a price of about $6 per pen.
One of the more difficult things in terms of pen development, though, was the ink itself. It had to operate under all sorts of conditions that were not the normal environment for writing, not just with lack of gravity. Ordinary ink simply wouldn’t do. So, his company developed a type of thixotropic ink to fill the cartridge. This ink was practically a solid, more like a gel or a super viscous fluid than the normal liquid of most inks. A thixotropic fluid is one that has a variable viscosity, with the viscosity becoming less under shear stress. The rolling ball at the writing end of the pen provided the shear stress as it moves past the end of the ink. That means the the ink typically only flows if the ball is turning, as when the pen is used for writing. But, this property means that it takes less ink to make a visible line, so the same volume of ink can be used to write far longer than a normal pen. The other advantage is that the ink is not as affected by temperature as most inks, and it doesn’t dry out. The ink can even be deposited on oily surfaces. Since the ink is not water soluble, the pen can even be used to write underwater (though you’d need special paper for that!).
The pressurized gas chamber even allows the ink to flow against the pull of gravity. That means the the space pen can be used here on Earth in the horizontal position or even upside down. That makes this a very versatile pen. It is no wonder that the pens are so popular. They now come in all shapes, sizes, and colors, including very compact bullet pens
, as seen here. These things are really nice. They are only about three inches long with the cap on. The cap comes off and sticks on the other end, making it a full sized pen. The classic AG-7 astronaut pen is a retractable pen. Fisher now makes all sorts of specialized pens for firefighters, police, and even matte black pens for the military. In fact, they sell far more of the pens for use here on Earth than the do in space!
-Astroprof
Images courtesy of Fisher Space Pen Co.
Vossinakis Andreas on March 27, 2008 at 2:49 pm: 1
At last, the pen myth is busted. Great article, thanks
MissM on March 27, 2008 at 6:22 pm: 2
I have been using space pens (the bullet version fits in my pocket perfectly) for more than 15 years, I love them!
Nice article. I never knew about the special ink, I did know they were pressurized ink cartridges.
ThuVT on March 28, 2008 at 7:43 am: 3
Very interesting story and informative. Initially I believed in the joke and laughed at NASA
but now I have a whole new story to tell others. Thanks for sharing!
Dwayne Day on March 28, 2008 at 4:41 pm: 4
http://www.thespacereview.com/article/613/1
Astroprof on March 28, 2008 at 6:27 pm: 5
Oh, good link. Thanks.
Keith Cowing on March 29, 2008 at 1:39 pm: 6
I have several Fisher space pens given to me personally by Mr. Fisher at the STS-1 launch in 1981. They still write perfectly. THAT in and of itself is amazing.
Darnell Clayton on March 30, 2008 at 7:46 pm: 7
I guess I now can point to your site to dispel this urban space legend.
Thanks for the info!
propertyless on March 31, 2008 at 12:59 am: 8
nice story,its really worth visiting this site.now i’ve got a great joke on the nasa for sharing with others.
How does a pen work in space? « My Dark Sky on April 2, 2008 at 12:54 am: 9
[…] Head over to Astroprof for a very interesting and informative story on “space penâ€. […]