|
The Parabolic Flight
A parabolic flight (or Vomit Comet as it's sometimes more commonly known!) is an airplane that provides a nearly weightless environment for a period of about 20-25 seconds.
This page will explain how the weightlessness environment is achieved and why we have chosen to fly our experiment on a parabolic flight.
Figure 1: Students from previous campaigns performing experiments in microgravity.(Photo from ESA)
What is Gravity?
Gravitational attraction is the force which tries to pull two objects together. It is a fundamental property of matter that exists throughout the known universe. It was over three centuries ago that Sir Isaac Newton produced a mathematical model known today as the Law of Universal Gravitation. According to this law the attractive force between any two objects is inversely proportional to the square of the distance separating the two objects and directly proportional to the product of the two masses being considered. This Law of Universal Gravitation was quantified later by Henry Cavendish who found the universal gravitational constant, G, with a value of 6.67 x 10^-11 Nm^2/kg^2
The Universal Law of Gravitation: F = G m1m2/r^2
What is Microgravity?
The acceleration on an object acted upon only by the Earth's gravity is approximately 9.8 m/s2. We commonly refer to this as one Earth gravity, or one g. Mass is the property of a body which describes how much it accelerates under a given force. Weight is the vertical force exerted on an object by the Earth's gravitational field.
It is possible to alter the environment of an object in such a way that it's apparent weight changes.
Imagine standing on a scale in a lift. If the lift begins to accelerate upwards a force additional to gravity comes into play. Your apparent weight is the force that the lift floor exerts on you. This is greater than if the lift was stationary and so you will be heavier than normal as the lift accelerates upwards. The opposite is true if the lift accelerates downwards; you will be lighter than normal.
Imagine now that you are in the lift at the top of the building and the cables supporting the lift snap causing you and the lift to fall towards the ground. Ignoring any effects of air friction then the lift, the scales and you are all accelerating downwards at the same rate, which is due to gravity alone. You would float if you lifted your feet off the lift floor. This is weightlessness.
A microgravity environment is one in which the apparent weight of a system is small compared to its actual weight due to gravity i.e. the weightlessness is not perfectly attained due to small residual forces.
Creating Microgravity
One way of creating a microgravity environment is using a specially equipped aircraft that repeatedly climbs with a high angle, before dramatically reducing it's thrust. The plane thus falls freely along a parabolic trajectory before returning to the horizontal. See Figure 1 below, taken from the NOVESPACE website.
Figure 1: Schematic diagram of a parabola during a parabolic flight
The Flight Sequence
The aircraft first becomes stabilised at an altitude of 20,000 feet (6km). The plane then climbs for 20 seconds until reaching an angle of +45 degrees at an altitude of 24,000 feet (7.5km). During this time the load experienced is 1.8g
At this point the pilot maneuvers into the injection parabola by canceling the lift exerted on the aircraft wings while the engineering crew reduces the engine thrust to balance the drag exerted on the aircraft.
At the end of this transition, which lasts for under 5 seconds the aircraft is subject only to the force of gravity and all of its occupants are in free fall for about 22 seconds. At the top of the parabola the plane reaches an altitude of 28,000 feet (8.5km).
When the aircraft is once again at an altitude of 24,000 feet in descent, the pilot recovers the aircraft to return to a situation of steady flight ready to begin another parabolic flight maneuver. The recovery phase lasts about 20 seconds and a load of 1.8g is felt during this time.
In total about 30 parabolic flight maneuvers are performed in each parabolic flight and the experimenters have 3 flights on which to perform their experiments thus giving a total of 90 parabolas.
Why a Parabolic Flight?
There are many different ways of creating a microgravity environment. The table below lists some of these methods with the associated advantages and disadvantages.
MICROGRAVITY ENVIRONMENT |
PROS |
CONS |
Parabolic Flight |
~20 secs of microgravity |
Not perfect microgravity environment i.e. ±0.05g |
Drop Towers |
"Cleaner" microgravity |
Short periods of microgravity (<5secs)
|
Sounding Rocket (not spin stabilised) |
Long periods of microgravity |
Can't repeat experiments as can only launch once |
Centrifuge |
Can create higher gravity (>2g) |
Cannot represent small asteroid surface gravity |
Others (e.g. neutral bouyancy, magnetic levitation) |
Possibly easier to perform experiments
Can conduct experiments for any length of time |
Individual grains still experience gravity |
-----> Parabolic flight microgravity is the best option.
- To go back to the home page click here.
- To go to the main science page click here.
- To read about the AstEx experiment click here.
|
