## A Photon Propulsion System for Astronauts

Update: January 1999: Don't laugh - scientists think that the 85 watts of heat radiated by the Pioneer spacecraft might be contributing to a variation in the spacecraft's trajectory. See Scientific American and this scientific paper

This page describes a compact photon propulsion system for use by astronauts during "space walks". It can be fabricated using current technology.

The principle of the device is that stored energy is converted to photons which are projected in a narrow beam in the opposite direction to the desired direction of motion. In accordance with Newton's 3rd law the astronaut will be propelled by the photon propulsion system.

Three simple, fundamental scientific equations describe the operation of the system:

1. Energy released by the system in the form of photons (light) is equal to the power of the system multiplied by the duration of the "burn".

Energy (joules) = Power (watts) x Time (secs)

2. The photons have an equivalent mass according to Einstein's famous equation:

Energy is equal to mass times the speed of light squared

Therefore equivalent mass m (grams) = E (Joules) / (C x C )

3. For conservation of momentum the mass of the astronaut times her velocity equals the equivalent mass the the photons times their velocity:

M (astronaut, grams) x V (astronaut, metres per second) = m (photons, grams) x C (metres per second)

So V = m x C / M but m=E/(C x C) therefore

V = E / (M x C)

The following picture shows a prototype photon propulsion system being tested. The reader is invited to substitute appropriate values in the above equations to derive a typical speed at which the astronaut will be propelled by the device. Some typical values might be::

• Power of photon propulsion system: 10 watts
• Duration of "burn": 60 seconds
• Mass of astronaut: 100,000 grams
• Speed of light: 3 x 10 to the power of 8 metres per second (300,000,000 m/s).
• The estimated development costs for the Photon Propulsion System (PPS) are US\$250 million and each unit would cost about US\$10 million. Alternatively a cheap version of the PPS can be purchased from a supermarket for about US\$5!

Acknowledgement (apologies) to "Maglite"!!

This web page prepared by Michael Paine, First posted 31 August 1997.
More science ideas!