Reduced gravity flights have been used by NASA since 1959; however NASA is unsure as to when new flights will occur. The way the “Reduced Gravity” flights work is the planes climb and dip to fly in a way that simulates weightlessness in about 30 second intervals. This helps astronauts get introduced to being in zero gravity. However, because of the constant altering between climbing and diving, some people on the flight become very ill. This is why planes that fly reduced gravity flights have earned the nickname “Vomit Comet.” Although NASA is not operating any reduced gravity flights, another group is. The Zero G Corp. is still flying reduced gravity flights and even tourists can experience “Zero Gravity.” However, a trip on one of these flights costs $4,950 with an additional 5% tax.
Information from http://www.livescience.com/29182-what-is-the-vomit-comet.html