André Kuipers during one of ESA's Parabolic Flight Campaigns

Practically speaking, the best way of achieving such a state would be to place an object in orbit, such as the International Space Station. This allows the time of the free fall to be extended almost infinitely.  
 
Since sending payloads to the ISS requires a large investment, scientists often prefer to use other means of achieving microgravity. These include sounding rockets, parabolic flights and drop towers. These solutions offer a limited duration of microgravity but higher flexibility and much lower cost.

Parabolic flights involve a specially equipped aircraft that repeatedly climbs with a high angle, before dramatically reducing its thrust. As a result, the plane falls freely along a parabolic trajectory, before returning to the horizontal. Each parabola includes phases with different gravity levels: 1g – 2g (while climbing), 0g (about 20 seconds per parabola), 2g (while going back to a horizontal trajectory); 1g (on a horizontal flight).
 
 
More information about parabolic flights can be found at the ESA Human Spaceflight website and the prime contractor's (Novespace) website.
 
 
Last update: 2 September 2009