Symptoms of Age-Related Macular Degeneration (AMD) An early symptom of wet AMD is that straight lines appear wavy. An Amsler Grid chart can help spot this early distortion of vision. You may also notice a small blind spot, resulting in a loss of central vision.
Traveling at approximately 29,000 km/h (18,000 mph) the shuttle orbits Earth every 90 minutes. By using current technology and a spacecraft powered by chemical rocket engines, a trip to Mars could take between six to nine months.
The space shuttle has never gone more than 400 miles from the Earth. Except for Apollo astronauts, no humans even claim to have gone beyond low-earth orbit. When the space shuttle astronauts did get to an altitude of 400 miles, the radiation of the Van Allen belts forced them to a lower altitude.