In physics and materials science, a drop tower or drop tube is a structure used to produce a controlled period of weightlessness for an object under study. Air bags, polystyrene pellets, and magnetic or mechanical brakes are sometimes used to arrest the fall of the experimental

payload Payload is the object or the entity which is being carried by an aircraft or launch vehicle. Sometimes payload also refers to the carrying capacity of an aircraft or launch vehicle, usually measured in terms of weight. Depending on the nature of ...

. In other cases, high-speed impact with a substrate at the bottom of the tower is an intentional part of the experimental protocol. Not all such facilities are towers: NASA Glenn's

Zero Gravity Research Facility The Zero Gravity Research Facility at the NASA Glenn Research Center in Cleveland, Ohio is a unique facility designed to perform tests in a reduced gravity environment. It has successfully supported research for the United States crewed spacecraft ...

is based on a vertical shaft, extending to below ground level.

Typical operation

For a typical materials science experiment, a sample of the material under study is loaded into the top of the drop tube, which is filled with inert gas or evacuated to create a low-pressure environment. Following any desired preprocessing (e.g. induction heating to melt a metal alloy), the sample is released to fall to the bottom of the tube. During its flight or upon impact the sample can be characterized with instruments such as cameras and pyrometers. Drop towers are also commonly used in combustion research. For this work, oxygen must be present and the payload may be enclosed in a drag shield to isolate it from high-speed "wind" as the apparatus accelerates toward the bottom of the tower. See a video of a microgravity combustion experiment in the NASA Glenn Five Second Drop Facility a

Fluid In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...

physics experiments and development and testing of space-based hardware can also be conducted using a drop tower. Sometimes, the ground-based research performed with a drop tower serves as a prelude to more ambitious, in-flight investigation; much longer periods of weightlessness can be achieved with parabolic-flight-path aircraft or with space-based laboratories aboard the Space Shuttle or the International Space Station. The duration of free-fall produced in a drop tube depends on the length of the tube and its degree of internal evacuation. The 105-mete
drop tube
at

Marshall Space Flight Center The George C. Marshall Space Flight Center (MSFC), located in Redstone Arsenal, Alabama (Huntsville postal address), is the U.S. government's civilian rocketry and spacecraft propulsion research center. As the largest NASA center, MSFC's first ...

produces 4.6 seconds of weightlessness when it is fully evacuated. In the drop facility Fallturm Bremen at University of Bremen a

catapult A catapult is a ballistic device used to launch a projectile a great distance without the aid of gunpowder or other propellants – particularly various types of ancient and medieval siege engines. A catapult uses the sudden release of stored p ...

can be used to throw the experiment upwards to prolong the weightlessness from 4.74 to nearly 9.3 seconds. Negating the physical space needed for the initial acceleration, this technique doubles the effective period of weightlessness. The NASA Glenn Research Center has a 5 second drop tower (The Zero Gravity Facility) and a 2.2 second drop tower (The 2.2 Second Drop Tower). Much of the operating cost of a drop tower is due to the need for

evacuation Evacuation or Evacuate may refer to: * Casualty evacuation (CASEVAC), patient evacuation in combat situations * Casualty movement, the procedure for moving a casualty from its initial location to an ambulance * Emergency evacuation, removal of per ...

of the drop tube, to eliminate the effect of aerodynamic drag. Alternatively the experiment is placed inside an outer box (the drag shield) for which, due to its weight, during its fall the reduction of acceleration due to air drag is less.

Historical uses

Though the story may be apocryphal,

Galileo Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He was ...

is popularly thought to have used the Leaning Tower of Pisa as a drop tower to demonstrate that falling bodies accelerate at the same constant rate regardless of their mass. Drop towers called shot towers were once useful for making lead shot. A short period of weightlessness allows molten lead to solidify into a quasi-perfect sphere by the time it reaches the floor of the tower.

List of drop towers

The vacuum-dynamic stand in Academician V.P.Makeyev State Rocket Centre NASA Glenn Research Center 2.2 Second Drop TowerNASA Glenn Research Center Zero-G Research Facility
*Micro-Gravity Laboratory of Japan (MGLAB) (Closed June 2010) * HASTIC 50m Drop Tower, Sapporo * Fallturm Bremen
Applied Dynamics Laboratories drop tower for spinning spacecraft
*Experimental drop tube of the metallurgy department of Grenoble

* ttps://www.pdx.edu/dryden-drop-tower/ Dryden Drop Tower, Portland State University, Maseeh College of Engineering and Computer Science*National Microgravity Laboratory (China) * The pagoda at the Royal Botanic Gardens, Kew was used during the Second World War as a drop tower for testing bomb designs. * Queensland University of Technology drop tower, Brisbane (Closed 2014)

References

{{Reflist Laboratory equipment Towers Weightlessness

Typical operation

Historical uses

List of drop towers

See also

References