Theoretically, if we had enough energy, someone (in a properly designed vehicle) could reach speeds close to the speed of light. To be sure, micrometeoroids are not the only obstacle to future space missions, where higher human travel speeds are likely to come into play. However, shortening travel times would mitigate these problems, so taking a faster approach is highly desirable. The best argument for powering fast spaceships is antimatter, twice that of normal matter. These G-forces are mostly benign G from front to back, thanks to the intelligent practice of holding passengers to space in seats facing their direction of travel.
Speculative dangers could also arise if humans manage to travel faster than light, either by taking advantage of gaps in known physics or through paradigm-breaking discoveries. Therefore, to achieve significantly faster travel speeds for humans bound for Mars and beyond, scientists recognize that new approaches will be needed. Eric Davis, senior research physicist at the Austin Institute for Advanced Study and collaborator of NASA's Innovative Propulsion Physics Program, a six-year research project that ended in 2002, describes three of the most promising ways — assuming conventional physics — to bring humanity to reasonable speeds of interplanetary travel. In fact, it's the fastest thing that exists, and a law of the universe says that nothing can move faster than light. The Orion spacecraft is meant to take astronauts to a low Earth orbit, and it's a good bet for the vehicle that will break the 46-year record for being the fastest we've ever traveled.
Marc Millis, a propulsion physicist and former director of NASA's Innovative Propulsion Physics Program, warns that this possible speed limit for traveling with humans is still a distant concern. He and his father roughly estimated that, barring some kind of conjectural magnetic shielding to deflect the deadly hydrogen shower, starships could not go more than half the speed of light without killing their human occupants. In essence, the ship resides within a piece of space-time, a “warp bubble” that moves faster than the speed of light. However, assuming that we can overcome the considerable technological obstacles involved in building faster spaceships, our fragile masses, mostly of water, will have to face new and important dangers associated with such high-speed travel. The most obvious danger is micrometeoroids, tiny pieces of rock and dust that are constantly flying through space at high speeds. These particles are so small that they can't be seen with the naked eye but can cause serious damage if they hit something at high speed.
To protect against these particles, spacecraft must be equipped with shields made from materials such as titanium or Kevlar. Another danger is G-forces. When a spacecraft accelerates or decelerates quickly, it creates G-forces on its passengers. These forces can cause nausea and disorientation in humans if they are too strong.
To reduce these forces, spacecraft must be designed with special features such as shock absorbers or inertial dampers. Finally, there is the danger posed by relativistic effects. As an object approaches the speed of light, its mass increases and time slows down relative to an observer on Earth. This means that if a spacecraft were to travel close to the speed of light for an extended period of time, its passengers would age much more slowly than those on Earth. These dangers may seem daunting but they are not insurmountable. With careful planning and engineering, it is possible to design spacecraft capable of safely traveling at high speeds without endangering their passengers.
With enough research and development, humanity may one day be able to explore the stars at speeds far beyond what we can currently imagine.