DailyTech has covered advances in the field of rocket propulsion and spaceflight. From such theoretical technologies as a laser engine, to actualized devices like ion drives, there are many unique ideas in the field, despite the relatively tight budgets.
The key challenge facing rocket designers is basic physics. Propulsion is determined by two key factors -- how much stuff you throw out the back of the rocket (mass) and how fast that stuff is going (velocity). One of these factors can be relatively low if the other is high to compensate. Thus on one extreme you have the solid-fuel and liquid fuel rockets -- these exit burning chemicals at relatively low velocities (compared to alternative technologies), but they dump large quantities of mass and therefor produce sufficient thrust. On the other extreme you have technologies such as ion drives, which exit a minuscule amount of mass at much higher speeds, to eventually produce a sufficient impulse.
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An artist's rendition of three plasma engines burning in space, propelling a spacecraft, perhaps to Mars. (Source: Ad Astra Space Corporation)
The engine features a three cell design. The first cell creates plasma from hydrogen at 10,000 deg. C. The next cell heats the plasma with radio waves to approximately 100 million deg. C. The last cell is a nozzle which controls how fast this fuel is let out, protecting the spacecraft and allowing acceleration control. (Source: Ad Astra Space Corporation)