Is it possible to use mechanical pencil instead of space pen and pencil in International Space Station ?
The primary consideration for pencils is the risk of breaking, and the need for sharpening producing waste products that can be hazards. But let's examine the major factors: Materials, mechanisms, and failure modes.
- nib: the small tube at the working end, past the mechanism. Not all forms have one. The nib is usually a friction fit that aids the mechanism's function.
- mechanism: the part of the pencil which advances the lead
- lead: the material which rubs onto the surface and is abraded away, leaving a mark.
- shaft: the structure into which the mechanism fits, and to which is often affixed the nib.
Lead is a holdover term from the early pencils, many of which used actual lead. Currently, the metal is only used by reenactors and forgers.
- Graphite — a shaft of pure graphite. Fragile, non-toxic, electroconductor.
- Graphite and binder — powdered graphite glued together into a shaft. Not overly fragile, usually non-toxic, can be electro-conductive.
- Wax & China Clay, with pigments — typical composition for colored pencils. depending upon which wax is used and what the pigment is, can be toxic or non-toxic. Non-conductor, usually. Tends to be fragile. Can write on many surfaces too smooth for other lead types.
- polymer and pigment — used for some small sized (0.3, 0.5, 0.7mm) colored leads. Specific polymer used can affect both fragility, and suitability for writing on various surfaces.
- soft metals - not common in modern uses. Gold, silver, copper and lead have all been used. Of these, only lead is soft enough for writing on modern papers reliably. Lead (Pb) is toxic, electro-conductive, and leaves a light line. It is highly ductile, and not fragile at room temperatures.
There are 3 common types of mechanical pencil mechanism, and several less common ones.
- twist action: the lead is affixed to a carrier which rides in a spiral slot and a straight slot; by twisting one or the other, the carrier is advanced. Skillcraft, Paper*Mate, and Cross have all used this for larger sizes; with graphite. This type is gravity-independent. Typically used for 0.9mm and 1.1mm leads; 0.7mm leads are a bit fragile, but are available.
- Leadholders, commonly called Drafting Pencils, have a friction mouth that holds a fairly thick lead (often 2mm). The mouth is simple: a ring sporting 3 to 5 jaws as a single piece, thicker towards the ends of the jaws, pulled back into a tube by a spring. The lead is advanced by pushing the jaws forward with a button, and letting the lead fall forward. This is gravity dependent. Note that this type usually has no nib.
- jaw-pushed lead. A set of jaws is held, much like the leadholder above, but is configured so that the jaws don't open until past a significant part of the stroke by a floating collet, but past a certain point, the collet is blocked, and the jaws then open from their own springiness. On retraction the collet moves back with the jaws, but again, is more limited in range of motion, and the jaws retract back into the collet. This is the most common mecahnism. Typically, additional leads are in a magazine, which gravity feeds a new lead when the first is advanced far enough; this makes it gravity dependent, as the typical lead is short - 3 to 5 cm.
- friction and wheel — a friction nib holds the lead in place; a small wheel in the pencil body advances the lead. Not suitable for smaller leads, the lack of jaws often allows the lead to slip, and advancing the lead can be a problem. Very rare. Gravity-independent.
- Friction manual advance - a sliding component retracts alongside the lead, and when pushed down and forward, pushes the lead forward as well. Some versions have one-way teeth. A friction nib is typical. Prone to lead slippage. Gravity independent. Requires larger leads (1.5 to 2.5mm)
- magazine of nibs with non-advancing lead — the shaft is also the magazine, holding 15 to 30 short (1cm) nibs with 5-6mm of lead. When the lead nib is worn down sufficiently, it is pulled out and fed through the back of the shaft, advancing the other nibs forward. Gravity-independent. Fairly durable (1.5 to 2mm leads are used), but failure mode results in 20 to 40 small items loose.
And, for comparison:
- lead bonded in shaft. The lead is bonded to the shaft at manufacture, and is revealed by removing material from the shaft. Shaft construction is typically wood, but can also be rolled and glued paper, or polymer. Sharpening results in both lead material and shaft material being generated in small pieces.
- wrapped lead — the lead is wide enough to be its own shaft. Messy if not wrapped; if wrapped, sharpening of some kind becomes needed; "china markers" are a wax lead wrapped in coiled perforated paper; the paper is removed in sequential spirals, each revealing about 5-7mm of the wax lead.
Mechanical pencils have several means of failing.
The mildest and most common is a lead break ahead of the advancement mechanism, and behind the nib. In single lead systems, especially screw advanced, this can render chunks of lead unusable, and chunks up to 1cm may need to be disposed of immediately.
A second form is vibration damage breaking lead inside the pencil, either within the advancement mechanism, or in the magazine. Breaks at certain points can render the jaw-pushed lead mechanism impotent; a break behind the retracted jaw but ahead of the magazine can render the pencil non-functional. Vibration damage can break leads in the magazine into chunks too small to feed from the jaw to the nib.
A third common failure mode is foreign debris in the mechanism. This can prevent jaw movement or prevent jaw closure.
A fourth common failure is a damaged nib. This requires the user to adjust the writing angles and pressure, or in cases where it bends, prevent function. Plastic nibs can be removed with a sharp knife; metal nibs often can be removed with pliers or even teeth.
Broken bits of lead can float in the environment. They are often small enough to not be visible, and large enough to be painful or even damaging if inhaled.
Electro-conductive leads can cause shorts in circuitry.
Wax and polymer leads can melt and then adhere to warmer components; this can result in potential for overheat of wiring.
Multiple failure modes can result in being deprived of writing implements. The space pen, by comparison, has fewer failure modes, and is vibration resistant. Vibration is a major issue during launch.
Gravity fed mechanisms, for example the magazine on typical 0.5 and 0.7mm lead jaw-advanced mechanisms, or the leadholder systems, do not operate in microgravity. Leadholders can be worked around.
Non-mechanical pencils (Traditional wood, or modern plastic or paper ones alike) produce shavings which are themselves hazards. Wood and paper shavings are fire hazards, as well as potentially painful to breath.
Any loose material, including the fairly common small flakes of the lead material generated when writing (that dust one normally blows off) is an inhalation issue, as well as potentially clogging the filters in the air recirculation system. When electro-conductive, it's also a risk of a short circuit.
With the right polymers, the right construction, and appropriate vibration reduction, certain types of mechanical pencils could be used safely; the space pen is already functional, flight ready, and vibration resistant, and can be made erasable if desired by the various space agencies.
There is thus little need for pencils' most noted utility, erasability, and the hazards outweigh the benefits.
Yes, it is possible. In fact, it's a better solution except for graphite getting into expensive things that don't like graphite.
If we think about how a mechanical pencil works, it doesn't involve gravity at all.
As you can kind of tell from the diagram, the only force that need be involved is that of the top button being depressed. The pencil is built in such a way that a clamp-like thing holds the lead in place when the pencil is in use.
When the button is depressed, the clamp releases the lead, and the lead is pushed down by another mechanism. After this, the clamp grabs the lead again.
Therefore, gravity is not needed to operate a mechanical pencil, and a standard pencil from Stap-o-les or Wally-Mart would work just fine.
However, there are concerns about the fine column of lead inside the pencil. If you've ever used a mechanical pencil (or a normal pencil, for that matter), you know that it's fairly easy to break the lead off the tip of the pencil. When this happens, the lead seems to fly at supersonic speeds, and hurts like crazy if it hits you.
This is a huge problem in space - since there is no downward force to pull the lead to the floor, it will just keep bouncing around the station until it finds a home. Unfortunately, this home would more often than not be in a piece of rare and expensive equipment.
So yes, it's certainly mechanically possible, but there are risks regarding the lead shooting off into something important.
Not only is it possible, it was so done. Mechanical pencils were used earlier. They were phased out because of the danger they posed.
NASA programs previously used pencils (for example a 1965 order of mechanical pencils) but because of the substantial dangers that broken-off pencil tips and graphite dust pose in zero gravity to electronics and the flammable nature of the wood present in pencils,a better solution was needed.