About Microgravity by Dr. Ir. V. Pletser

Gravity is omnipresent on Earth. It accompanies us in all our movements since birth and it is difficult to imagine our environment without it. How to conceive that, without it, the slightest step would propel us in the air or that liquids would take a spherical form?

Nevertheless, gravity can only exist if the gravitational attraction is thwarted by the presence of a solid surface that prevents the gravitational force of continuing its action of attraction. Although gravitation is omnipresent in the universe, gravity is the exception and its absence, weightlessness, the general rule.

Weightlessness is obtained in a free-falling vehicle. In other words, to not feel your weight anymore, you need to fall freely in a vehicle (airplane, spacecraft, …) that falls freely itself.

Free-fall is obtained in a vehicle subject to the only force of gravity, the sum of all other forces being null.

Attention: the force of gravity is never cancelled; and weightlessness is not due to the absence of atmosphere; nor to a great distance from the earth or from any other mass; nor to a high velocity.

Aircraft parabolic flights are used to perform short duration scientific and techno­logical experiments in re­duced gravity. Together with drop towers, sounding rockets, the International Space Station (ISS) and other manned and unmanned spacecraft, aircraft parabolic flights with the Airbus A310 ZERO-G completes the set of flight research opportunities for European scientists (see Figure 1).

Fig. 1: Reduced gravity platforms accessible to European scientists (Credit: DLR)

Aircraft parabolic flights are the only flight opportunity beside ISS and Chinese spacecraft where medical research on human test subjects can be performed in weightlessness.

The mi­cro­gravity environment is created in the Airbus A310 ZERO-G flying the following ma­noeuvres (see Figure 2):

from steady horizontal flight, the aircraft climbs at 50° (pull-up, see Figure 3) for about 20 s with accelerations between 1.8 and 2 g;
all aircraft engines thrust is then strongly re­duced for about 20 to 25 s, compen­sating the effect of air drag (parabolic free fall);
the aircraft dives at 42° (pull-out), accel­erat­ing at about 1.8 to 2 g for approxi­mately 20 s, to come back to a steady horizontal flight.

Fig. 2. The parabolic flight manoeuvre of the Airbus A310 (Credit: Novespace)

Alternatively, for partial g parabolas at Moon and Mars g-levels, the engine thrust is reduced sufficiently to a point where the remaining vertical acceleration in the cabin is approximately 0.16g (Moon gravity) for approximately 25 s or 0.38g (Mars gravity) for approximately 32 s with angles at injection of 42° and 38° respectively for Moon and Mars parabolas.

These manoeuvres are flown sepa­rated by inter­vals of several minutes. Duration of intervals between parabolas can be arranged prior to the flight. A typical flight duration is between two and half and three hours.

Take-offs and landings are made at the Bordeaux airport, although other airports have been used in the past. Parabolas are flown in dedicated air zones over the Gulf of Biscaye.

Fig. 3: The Airbus A310 in pull-up (Photo: Novespace – Eric Magnan / Airborne Films)