Slings, elevators, and many other orbital structures must be made
of materials having high specific strength (strength-to-mass ratio).
The specific strength of composites is only half of the specific
strength of the reinforcing fibers. High-strength plastics, e.g., PBO,
become brittle when exposed to thermal fatigue and space radiation.
Atomic oxygen erosion, space junk, and meteoroids also damage
orbital contraptions and towers. Contraptions protected by
the atmosphere or a pile of rubble, can be made of plastic.
- For details on atomic oxygen erosion see:
- -John N. Stevens, "Method for Estimating Atomic Oxygen Surface
Erosion in Space Environments," Journal of Spacecraft and
Rockets, Vol. 27, No. 1, 1990, pp. 93-95.
- -G. E. Caledonia and R. H. Krech, "Studies of the Interaction of
8 km/s Oxygen Atoms," in Materials Degradation in Low Earth
Orbit (LEO), edited by V. Srinivasan and B. A. Banks, Minerals,
Metals, and Materials Society, Warendale, PA, 1990, pp. 145-153.
- -R. C. Tennyson, "Atomic Oxygen and Its Effects on Materials,"
in The Behavior of Systems in the Space Environment, edited
by R. N. DeWitt, Kluwer Academic, Amsterdam, 1993, pp. 233-357.
- For details on space junk and meteoroids see:
- -William. A. Bacarat and C. L. Butner,
Tethers in Space Handbook, NASA, 1986, page 4-32.
- -Nicholas L. Johnson and D. S. McKnight, Artificial Space Debris,
Orbit Books, 1991.
Interagency Report on Orbital Debris, Office of Science and
Technology Policy, National Science Technology Council, November
- -Nicholas L. Johnson, "Monitoring and Controlling Debris in Space,"
Vol. 279, No. 2, August 1998, pp. 42-47.
- Glass ribbons are cheap and resistant to oxygen erosion but
fragile. For details see:
- John V. Milewski (ed.), Handbook of Reinforcements for
Plastics, Van Nostrand, New York, 1987, pp. 76-97.
- Polycrystalline diamond has a tensile strength of about 700
megapascals. A small device using plasma chemical vapor deposition
technique can deposit 25 micrometers of polycrystalline diamond per
hour. The same device can deposit graphite at the rate of several
millimeters per hour. A protective coating is needed to prevent
erosion of carbon by atomic oxygen. Details:
- J. J. Beulens, A. J. M. Buuron, and D. C. Schram, "Carbon
Deposition Using an Expanding Cascaded Arc D.C. Plasma," Surface &
Coatings Technology, Vol. 47, No. 1-3, 1991, pp. 401-417.
- A carbon matrix produced by a chemical vapor deposition technique
and reinforced with carbon fibers has a tensile strength of at least
1.5 GPa. Details:
- John V. Milewski (ed.), Handbook of Reinforcements
for Plastics," Van Nostrand, New York, 1987, p. 376.
- A glass matrix reinforced with carbon fibers is fairly strong and
resistant to oxygen erosion. Details:
- -Brian C. Hoskins and Alan A. Baker, (eds.) Composite
Materials for Aircraft Structures, AIAA, 1986, ISBN 0-930403-11-8.
- -William K. Tredway and Karl M. Prewo, "Fiber Reinforced Glass
Matrix Composites for Space Structures," in 23rd International
SAMPE Technical Conference, Vol. 23, ed. Robert L. Carri, 1991,
- Piano wire is cheap and has a tensile strength of about 3 GPa,
while the strongest commercial steel wire attains 5 GPa. Details:
- H. K. D. H. Bhadeshia and H. Harada, "High-strength (5 GPa) steel
wire: an atom-probe study" Applied Surface Science, Vol. 67, 1993,
- Buckytubes are microscopic carbon tubes. They are also known as
carbon nanotubes. Their specific strength is 2 orders of magnitude
greater than that of steel! Buckytubes are still too expensive to be
used as a structural material, but fabrication techniques have been
improving rapidly. Cheap buckytubes would make
Professor Richard E.
Smalley of Rice University is the leading buckytube expert.
(Richard Smalley, Robert Curl and Harold Kroto received 1996 Nobel
prize for chemistry for the discovery of a similar carbon structure
called buckyball.) You can learn more about buckytubes from:
-David Tomanek's Nanotube Site.
- -Web article:
"From Fullerenes to Nanotubes".
-Associated Press article: "Carbon material could be used for
- -Smalley speech:
"From Balls to Tubes to Ropes: New Materials from Carbon".
longitudinal speed of sound =
- Y is the Young's modulus
- R is the density of the solid
speed of sound
in thin rods
|Kevlar 49 (aramid fiber)
|Spectra fiber (gel-spun polyethylene)
|PBO (poly-paraphenylene benzobisthiazole, plastic fiber)
|buckytube cable (theoretical data)
- Table data compiled from:
- -Dominic V. Rosato, Rosato's Plastics Encyclopedia and
Dictionary, Hanser Publishers, Munich, 1993, p. 638.
- -Alan S. Brown, "Spreading Spectrum of Reinforcing Fibers"
Aerospace America, January 1989, pp. 14-18.
- -CRC Handbook of Chemistry and Physics, 66th edition, page E-43.
- -Theoretical buckytube cable data provided by
Boris I. Yakobson
(North Carolina State University, Department of Physics).