Our goal is to test the sticking probability (aggregation and agglomeration properties) of ice and dust particles in microgravity. This sample is representative of the predominate material found around newborn stars and must be the building blocks for Earth-like planets.
Describing this "grain growth" from small aggregates (loosely bound collections of ice and dust) to large terrestrial planets requires both theoretical and experimental tests. And experiments like ours can only be done by eliminating the effects of the Earth's gravity, whose influence encourages different particle behaviour. For this reason, our student-initiated proposal was accepted to participate in the 45th Professional Parabolic Flight Campaign of the European Space Agency (ESA).
To read further about the Parabolic Flight Campaign, skip down to here.
To read the student's experiment proposal, see the Science link in the menu.
The Experiment Design
Many conditions must be met for our experiment to accurately simulate the environment in which planets form:
vacuum (10^-3 mbars),
cryogenic temperatures (50-150 K for this experiment),
and zero gravity (or microgravity).
In addition, our particles must collide at very low velocities (slower than 1 m/s), which are extremely difficult, and sometimes impossible, to investigate in Earth-based laboratories.
We have obtained a vacuum chamber on loan to the us from Nijmegen University. Our experiment will be contained within the vacuum chamber.
The 6 ports (4 side holes, 1 bottom and 1 top) will be covered with flanges to seal the chamber. Most of these will have special feedthroughs attached so that electrical wires and cooling liquid, for example, can pass into the chamber without affecting the vacuum seal.
One of these special feedthroughs will be used to connect the vacuum pumps so that they can pump the chamber. In total, two different pumps (a molecular and a mechanical turbopump) will be used in parallel to achieve the pressures listed above during the experiment.
The actual experiment consists of several large pieces, all made from copper, which will be completely contained inside the vacuum chamber.
Large, cylindrical Copper Cooling Block (a heat sink)
Coliseum device to store the particles
Radiation shield (cover)
Two Pistons (or firing devices)
Two Guiding Tubes to assure collision trajectories
Additional equipment includes: two cameras placed on top of the chamber to record the collisions inside the chamber, a computer to control the movements, several power supplies, a pressure sensor, temperature sensors, and more. Some drawings based on blueprints produced from a CAD program are shown below.
The picture at left is the whole experiment with the radiation shield on top and the cooling block at the bottom. Inside the radiation shield is the "coliseum" device, which houses and cools the ice and dust particles. At right the coliseum winds down into the copper block so that individual compartments in the coliseum are rotated into view of the pistons (the tubes extending at 180 degrees opposite one another) before each collision.
Prior to flight, the Copper Cooling Block is cooled to approximately 50 K using liquid nitrogen. This is expected to take at least one hour to reach the identified starting temperature. Copper was chosen because its combination of mass per cubic centimeter, conductivity, and ability to keep cold for the duration of the flight.
When the Copper Cooling Block is cold enough, the ice and dust samples will be loaded through the side ports into the Coliseum. This is a cylindrical device with separate compartments, each one 180 degrees opposite another. The holes are just large enough to hold millimeter- to centimeter-sized ice and dust aggregates.
The Coliseum provides cold housing for the particles through the Thread at the base of the coliseum. The Thread is also responsible for winding the coliseum up and down to reveal each Coliseum compartment once during the flight.
As each Coliseum compartment becomes aligned with the Pistons, the coliseum pauses, the Pistons push through the Coliseum compartments, accelarating two separate aggregates very slowly from opposite sides of the chamber through their respective Guiding Tubes and towards a collision at the center of the chamber.
Once the Pistons have completely retracted, the Coliseum resumes turning until the next compartment is aligned with the Pistons.
In the second half of the experiment, a Collision Screen will be used to measure collisional properties at varying angles of smaller particles with a large particle, in this case an ice- or dust-covered screen at the center of the chamber.
Collisions will be observed in real time through viewing ports in 2 of the side flanges, as well as they will be recorded by several cameras placed atop the chamber so that collisional velocities, impact angles, sticking or breaking probability, etc can be extracted later.
Variables in the experiments include collisional velocities, particle sizes, particle compositional interactions (ice-ice, dust-dust, and ice-dust collisions), impact angles, and temperature variations.
ESA's Professional Parabolic Flight Campaign
The Professional Parabolic Flight Campaign consists of specially reinforced Airbus A300 airplane. It provides a unique laboratory that simulates the absence of gravity by flying in a parabolic trajectory.
Novespace operates the flights out of Bordeaux, France. Professional research teams are granted 2 weeks time at the airport in Bordeaux. The first week is meant to prepare the experiment before the flight, as well as to go over safety procedures. The second week is the flight week.
Each team is granted 3 flight days. Each 3-hour flight consists of 31 parabolas, which are approximately 22 seconds of microgravity at a time. Our team has been approved to keep 3 team members on board the flight on each of our flight days in order to run our experiment and monitor its progress. On board the plane our experiment will consist of two racks, one for the experiment, another for the supporting equipment.