Zero gravity flights: the closest you can get to being an astronaut without going to space

Fifty years ago this week mankind first stepped foot on the moon. Today, the human fascination with space travel has never been greater. 

Perhaps it is down to a spell of remarkably likeable characters - notably Major Tim Peake (Britain’s first official astronaut) and Commander Chris Hadfield (the first Canadian astronaut to walk in space) - or maybe it’s growing anticipation of space tourism, but there is certainly an appetite for all things out of this world.

As the wait goes on for Virgin Galactic et al to whisk us into orbit (for a hefty sum), one way to feel like an astronaut is to indulge in a trip on a “zero gravity aircraft”. But what does it mean to experience complete weightlessness and how is it possible? 

Here we unpack the history and mysteries of the “vomit comet”.

What is zero gravity?

Zero gravity is a condition of weightlessness referring to the absence of a gravitational force (g-force or Gs) - a measurement of the acceleration due to gravity that causes weight.

A body in a “zero gravity” (or “microgravity” - a state of near weightlessness) environment is acted upon only by gravity, with no reactionary forces exerted by its surrounding matter; the person therefore enters a state of freefall where all objects in that given space are falling at the same rate.

Passengers on a zero gravity flight (and astronauts on a spacecraft) appear to be floating around inside the plane but they are in fact falling at the same rate as the aircraft.

What is a zero gravity flight?

A zero gravity flight follows what is called a parabolic flight path, which involves three stages. The first part of the trajectory sees the plane - which is specially customised to cope with the demands of flight, and boasts a padded interior to help passengers avoid injury - reach an altitude of 24,000 feet, at which point the nose of the plane is lifted upward to an angle of about 45 degrees, until the plane reaches around 32,000 feet. Commercial aircraft typically cruise at about 35,000 feet. 

At this point, the nose of the plane is lowered to a level position, during which time passengers experience a sense of weightlessness for 20 to 30 seconds. After these few moments, the nose of the plane is tilted back downward 45 degrees to complete the third and final stage, before it levels off to a normal altitude.

Passengers experience a pull of nearly twice that of gravity (1.8 Gs) during the downward trajectory, at the bottom of the path, as well as the upward climb of the flight, which takes around 65 seconds to complete.

As well as the experience of floating, passengers will experience nausea due to motion sickness during the journey - which affords such flights the nickname of the “vomit comet”. During an outing for Nasa’s Reduced Gravity Programme (cancelled in 2014), one third of the participants were said to have become “violently ill, the next third moderately ill, and the final third not at all," according to John Yaniec, the former director of the programme.  

The main cause of the air sickness is anxiety, according to Yaniec, who said being in a state of zero gravity “is out of the ordinary” and [that] “it’s a bit of the fear of the unknown, too”.

How long have zero gravity flights been around?

The first zero gravity flights were proposed in 1949 by German physicist Heinz Haber and his brother Fritz Haber, a German aerospace engineer - both of whom had been brought to work for the US government as part of the Cold War-driven Operation Paperclip after the Second World War. They proposed that the flights could be used in experiments to simulate weightlessness.

Afterwards, for the best part of 60 years, Nasa operated zero gravity flights on different aircraft, including one of its last zero gravity aircraft - KC-135A - for many years from around 1959, when it began its Reduced Gravity Research Programme to train astronauts.

In Europe, the European Space Agency and France’s Centre National d'Etudes Spatiales have operated reduced-gravity flight missions on different aircraft since 1984 (including on a Nasa aircraft, an Airbus 300 and Airbus 310) from Bordeaux-Mérignac airport in France and Dübendorf Air Base in Switzerland. The first zero gravity flight for paying passengers in France took place in March 2015 on an Airbus A330 and cost €6,000 (£4,785) per person.

The first such flights in the US took place in 2004, courtesy of the Zero Gravity Corporation, and were operated on a Boeing 727. Since closing its own programme in 2015, NASA has been using the company's G-Force One plane - a modified Boeing 727-200 aircraft - for training and research purposes.

In America, Nasa continues work at the Zero Gravity Research Facility in Brook Park, Ohio, which has been running since 1966. It is the country’s main base for microgravity research and the world’s largest facility of its kind. The centre is used to develop and test equipment designed for flights on board the Space Shuttle and International Space Station (ISS).

How can I fly zero gravity?

Zero gravity aircraft are still used for astronaut training, expensive leisure pursuits and weightlessness experiments by Nasa but have also been used in the entertainment industry to shoot scenes requiring weightlessness, such as in the film Apollo 13. American rock band OK Go also shot a music video for their song 'Upside Down & Inside Out' in a zero gravity environment on board the Il-76 MDK jet as part of a campaign for Russia’s S7 Airlines.

While most zero gravity research is conducted on humans, there have also been some experiments looking at the effects of weightlessness on animals including cats and pigeons.

Increasingly, members of the public are also keen to experience weightlessness.  

The Zero Gravity Corporation (gozerog.com) offers such flights on its G-Force One plane from the Orlando Sanford International Airport and Fort Lauderdale International Airport in Florida, as well as from McCarran International Airport in Las Vegas and the Oakland International Airport in Oakland, California.

Flights are also offered in New York and Los Angeles, as well as in Austin and Houston in Texas. Each flight (priced from $5,400 - £4,350 ) consists of 15 parabolic paths, and therefore is said to offer relatively low levels of motion sickness, while those used in astronaut training typically entail 40-60 parabolic manoeuvres.

The G-Force One aircraft can also offer the experience of lunar gravity (the gravitational force of the Moon where you’ll weigh around a sixth of your weight on Earth) or Martian gravity (the level of gravity on Mars where your weight is around a third of that on Earth) by flying a larger arc at the top of the parabolic path.

Chartered zero gravity flights can also be arranged with the Zero Gravity Corporation so long as the location requested can accommodate a Boeing 727-200 aircraft. Prices from $165,000 (£133,000), plus tax.

In Europe, thrillseekers can turn to Air Zero G (airzerog.com), the only operator on the continent. The company operates an Airbus A310 Zero G out of Bordeaux Merignac, France.

Since starting, it has taken more than 10,000 passengers on weightlessness flights, each enjoying 15 parabolas over the course of an hour (12 gravity-free, one Martian and two Lunar), with prices starting from €6,000 (£5,420), with discounts for second and third flights. 

The Guinness World Record for the youngest human to fly on a microgravity flight was set in 2008 on a plane operated by the Ecuadorian Air Force and Ecuadorian Civilian Space Agency carrying a seven-year-old boy. It was also the first zero gravity flight to launch in Latin America.