Thursday, 23 August 2007
The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) system encompasses three linked magnetic cells. The "Plasma Source" cell involves the main injection of neutral gas (typically hydrogen, or other light gases) to be turned into plasma and the ionization subsystem. The "RF Booster" cell acts as an amplifier to further energize the plasma to the desired temperature using electromagnetic waves. The "Magnetic Nozzle" cell converts the energy of the plasma into directed motion and ultimately useful thrust.
Coupled with nuclear power this new type of rocket technology could dramatically shorten human transit times between planets (less than 3 months to Mars) and propel robotic cargo missions with a very large payload mass fraction. Trip times and payload mass are major limitations of conventional and nuclear thermal rockets because of their inherently low specific impulse (less than 1000 seconds). Plasma rockets such as VASIMR enable a very high specific impulse (greater than 10,000 seconds.) For these missions VASIMR will operate with hydrogen or deuterium propellant, both are abundant throughout the known universe.
The VASIMR has two additional important features that distinguish it from other plasma propulsion systems:
1. Ability to vary the exhaust characteristics (thrust and specific impulse) in order to optimally match mission requirements. This results in the lowest trip time with the highest payload for a given fuel load.
2. VASIMR is driven by electromagnetic (RF) waves and has no physical material electrodes in contact with the hot plasma. This results in greater reliability and longer life and enables a much higher power density than competing designs.
4-th State of Matter
The first step to understanding how a plasma rocket operates is learning about plasma. A plasma state can be achieved when a substance in its gaseous state is heated to very high temperatures - tens of thousands to millions of degrees. At this temperatures, electrons are stripped, or lost, from the neutral atoms.
In the overheated gas, electrons, which hold a negative charge, and ionized atoms, which hold a positive charge, mixed together making an electrically neutral "soup" of charged particles that is a plasma. This is a very common occurrence in nature. In fact, 99 percent of the visible universe is in some form of a plasma state, including lightning, very hot flames, nebulas, the Sun and other stars. The plasmas at the extreme temperatures required of a plasma rocket cannot be contained by any known material. Fortunately, plasmas can be controlled by a magnetic field.