Conventional rockets are great and have gotten us far, but they have their limitations. These rockets also work on the basis of thrust: The engine burns fuel, creating a high pressure gas that gets forced out of the rocket nozzle at high speed and the rocket gets propelled in the opposite direction [source: Brain]. Rocket fuel, however is very heavy and super-inefficient. It cannot provide enough power to get places fast. The rocket fuel is burned up in the effort to get off the earth and into orbit, and then the spaceship basically is forced to just coast [source: Verhovek].
A plasma rocket, on the other hand, uses a lot less fuel than these conventional engines – 100 million times less fuel, in fact [source: Science Alert]. It's so fuel-efficient that you can go from Earth's orbit to the moon's orbit with just about 30 gallons (113 liters) of gas [source: Charles]. Plasma rockets accelerate gradually and can reach a maximum speed of 34 miles (55 kilometers) per second over 23 days, which is four times faster than any chemical rocket [source: Verhovek]. Less time spent traveling means less risk of the ship experiencing mechanical failures and astronauts being exposed to solar radiation, bone loss and muscle atrophy. With VASIMR, propulsion will also theoretically be available throughout the entirety of the trip, meaning that changes in direction could be possible at any time.
To be realistic, at this point, travel to Mars in a short time is still a long way off. Reaching these types of extreme distances will require a lot of power. Most Hall thrusters and gridded ion engines run on about 5 kilowatts of power. To get to the levels of power you'd need to reach Mars in about 40 days, you'd need at least 200 times that amount [source: Walker]. The most viable source of energy to generate this amount of power while in outer space is nuclear power sources built into the engine. At this time, however, putting a nuclear power source on a rocket ship that we blast from earth into space poses too much threat of radiation exposure in the case of a crash.
So the power source to reach those distances remains a major challenge. Not to mention the uncertainty of how the human body would react to travelling 34 miles (54 kilometers) per second (as opposed to the 4.7 miles or 7.5 kilometers per second astronauts travel to get to lower earth orbit in conventional rockets) [sources: Verhovek, Northwestern University Qualitative Reasoning Group]. But in theory, given enough power, these engines have the capabilities of reaching Mars in about 40 days, a feat we wouldn't have dared dream possible just 50 years ago.