Technologies tend to change all the time as improvements are made and new designs are implemented that produce more power or a higher efficiency. One of the few technologies that has not changed much over the years is propulsion technology for space shuttles and rockets. The earliest Space rockets were just larger, slightly more sophisticated versions of weapons used during World War 2. Solid fuels are still used for propelling rockets out of the Earth’s orbit, and will likely be used for many years to come, however alternative deep-space propulsion systems are being developed and tested with fairly promising results.
One of the technologies that has advanced furthest in its development is the solar sail. The solar sail works on the principle that any surface exposed to radiation experiences a small force known as radiation pressure.
The idea of using this force as a means of propulsion through space was first suggested by Johannes Kepler in 1610, when he discovered the force due to radiation and announced that if we could “provide ships or sails adapted to the heavenly breezes, there will be some who will brave even that void.”
The technology is already used to make course corrections and increase fuel efficiency in current space exploration. For example, NASA’s Mercury MESSENGER probe used solar radiation to steer itself on the way to the first planet.
And whilst still in its infancy as a technology, solar sails have been used as the primary propulsion system for Ikaros, a prototype space craft launched by the Japanese Aerospace Exploration Agency in May 2010. NASA also launched its orbital solar sail prototype Nanosail-D in November 2010, which successfully orbited the earth for 240 days. Ikaros continues its journey around the sun.
Ikaros uses a 27 square metre sail to take full effect of the radiation emitted from the sun, however that entire area still only provides about 0.00089 Newtons of force less than the average weight of a Goose feather. The acceleration created is incredibly small, however given a long period of time incredible speeds can be reached.
A very long period of time.
If we assume the average mass of a human to be around 70kg, then in order to accelerate him with 0.00089 Newtons of force to the average velocity of a space shuttle in orbit around the Earth, 28,000km/h, would take 1,138 years; and that is without even taking into account the mass of the space shuttle in which he would be sitting.
Obviously much larger sails will be used to propel larger ships capable of transporting people, but the acceleration will never be great.
Future tests will see the missions grow longer and longer, however the further from the sun that the solar sail travels, the lower the radiation pressure, and therefore the slower the acceleration.
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By. Charles Kennedy of Oilprice.com
