Drop tower
Encyclopedia
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
. 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 is based on a vertical shaft, extending to 510 feet (155 m) below ground level.
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 camera
s and pyrometer
s.
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 at http://www.youtube.com/watch?v=SZTl7oi05dQ.
Fluid
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-meter drop tube at Marshall Space Flight Center
produces 4.6 seconds of weightlessness when it is fully evacuated. In the drop facility Fallturm Bremen
at University of Bremen
a catapult
can be used to throw the experiment upwards to prolong the weightlessness from 4.74 to nearly 9.3 seconds. Neglecting 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
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.
as a drop tower to demonstrate that falling bodies accelerate at the same constant rate regardless of their mass.
Drop towers called shot tower
s 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.
Drop tubes are used for Handloading
Black Powder; the drop allows the powder to settle into a case, improving the compression of powder charges.
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
and materials science
Materials science
Materials science is an interdisciplinary field applying the properties of matter to various areas of science and engineering. This scientific field investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It incorporates...
, a drop tower or drop tube is a structure used to produce a controlled period of weightlessness
Weightlessness
Weightlessness is the condition that exists for an object or person when they experience little or no acceleration except the acceleration that defines their inertial trajectory, or the trajectory of pure free-fall...
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
Cargo
Cargo is goods or produce transported, generally for commercial gain, by ship, aircraft, train, van or truck. In modern times, containers are used in most intermodal long-haul cargo transport.-Marine:...
. 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 is based on a vertical shaft, extending to 510 feet (155 m) 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 backfilled with inert gasInert gas
An inert gas is a non-reactive gas used during chemical synthesis, chemical analysis, or preservation of reactive materials. Inert gases are selected for specific settings for which they are functionally inert since the cost of the gas and the cost of purifying the gas are usually a consideration...
or evacuated to create a low-pressure environment. Following any desired preprocessing (e.g. induction heating
Induction heating
Induction heating is the process of heating an electrically conducting object by electromagnetic induction, where eddy currents are generated within the metal and resistance leads to Joule heating of the metal...
to melt a metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
), 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 camera
Camera
A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...
s and pyrometer
Pyrometer
A pyrometer is a non-contacting device that intercepts and measures thermal radiation, a process known as pyrometry.This device can be used to determine the temperature of an object's surface....
s.
Drop towers are also commonly used in combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...
research. For this work, oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
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 at http://www.youtube.com/watch?v=SZTl7oi05dQ.
Fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....
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
Parabola
In mathematics, the parabola is a conic section, the intersection of a right circular conical surface and a plane parallel to a generating straight line of that surface...
-flight-path aircraft
Vomit Comet
A Reduced Gravity Aircraft is a type of fixed-wing aircraft that briefly provides a nearly weightless environment in which to train astronauts, conduct research and film motion pictures....
or with space-based laboratories aboard the Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
or the International Space Station
International Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...
.
The duration of free-fall
Free-fall
Free fall is any motion of a body where gravity is the only force acting upon it, at least initially. These conditions produce an inertial trajectory so long as gravity remains the only force. Since this definition does not specify velocity, it also applies to objects initially moving upward...
produced in a drop tube depends on the length of the tube and its degree of internal evacuation. The 105-meter drop tube at Marshall Space Flight Center
Marshall Space Flight Center
The George C. Marshall Space Flight Center is the U.S. government's civilian rocketry and spacecraft propulsion research center. The largest center of NASA, MSFC's first mission was developing the Saturn launch vehicles for the Apollo moon program...
produces 4.6 seconds of weightlessness when it is fully evacuated. In the drop facility Fallturm Bremen
Fallturm Bremen
Fallturm Bremen is a drop tower at the Center of Applied Space Technology and Microgravity at the University of Bremen in Bremen. It has a 123-metre-high drop tube , in which for 4.74 seconds , or for over 9 seconds weightlessness can be produced...
at University of Bremen
University of Bremen
The University of Bremen is a university of approximately 23,500 people from 126 countries that are studying, teaching, researching, and working in Bremen, Germany...
a catapult
Catapult
A catapult is a device used to throw or hurl a projectile a great distance without the aid of explosive devices—particularly various types of ancient and medieval siege engines. Although the catapult has been used since ancient times, it has proven to be one of the most effective mechanisms during...
can be used to throw the experiment upwards to prolong the weightlessness from 4.74 to nearly 9.3 seconds. Neglecting 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
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
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 is popularly thought to have used the Leaning Tower of PisaLeaning Tower of Pisa
The Leaning Tower of Pisa or simply the Tower of Pisa is the campanile, or freestanding bell tower, of the cathedral of the Italian city 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 tower
Shot tower
thumb|The Shot Tower, Bristol, EnglandA shot tower is a tower designed for the production of shot balls by freefall of molten lead, which is then caught in a water basin. The shot is used for projectiles in firearms.-Process:...
s were once useful for making lead shot
Lead shot
Lead shot is a collective term for small balls of lead. These were the original projectiles for muskets and early rifles, but today lead shot is fired primarily from shotguns. It is also used for a variety of other purposes...
. A short period of weightlessness allows molten
Mölten
Mölten is a comune in South Tyrol in the Italian region Trentino-Alto Adige/Südtirol, located about 60 km north of Trento and about 12 km northwest of Bolzano .-Geography:...
lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
to solidify into a quasi-perfect sphere by the time it reaches the floor of the tower.
Drop tubes are used for Handloading
Handloading
Handloading or reloading is the process of loading firearm cartridges or shotgun shells by assembling the individual components , rather than purchasing completely assembled, factory-loaded cartridges...
Black Powder; the drop allows the powder to settle into a case, improving the compression of powder charges.
List of drop towers
- The Queensland University of Technology Drop Tower Facility, Phenomena in Microgravity Laboratory
- NASA Glenn Research Center 2.2 Second Drop Tower
- NASA Glenn Research Center Zero-G Research Facility
- Micro-Gravity Laboratory of Japan (MGLAB) (Closed June 2010)
- Fallturm BremenFallturm BremenFallturm Bremen is a drop tower at the Center of Applied Space Technology and Microgravity at the University of Bremen in Bremen. It has a 123-metre-high drop tube , in which for 4.74 seconds , or for over 9 seconds weightlessness can be produced...
- Applied Dynamics Laboratories drop tower for spinning spacecraft
- Experimental drop tube of the metallurgy department of Grenoble
- NASA Marshall Space Flight Center Drop Tube Facility is currently mothballed
- Portland State University Dryden Drop Tower
- National Microgravity Laboratory (China)
See also
- Glenn Research CenterGlenn Research CenterNASA John H. Glenn Research Center at Lewis Field is a NASA center, located within the cities of Brook Park, Cleveland and Fairview Park, Ohio between Cleveland Hopkins International Airport and the Cleveland Metroparks's Rocky River Reservation, and has other subsidiary facilities in Ohio...
- Marshall Space Flight CenterMarshall Space Flight CenterThe George C. Marshall Space Flight Center is the U.S. government's civilian rocketry and spacecraft propulsion research center. The largest center of NASA, MSFC's first mission was developing the Saturn launch vehicles for the Apollo moon program...
- Magnetic levitationMagnetic levitationMagnetic levitation, maglev, or magnetic suspension is a method by which an object is suspended with no support other than magnetic fields...
- Shot towerShot towerthumb|The Shot Tower, Bristol, EnglandA shot tower is a tower designed for the production of shot balls by freefall of molten lead, which is then caught in a water basin. The shot is used for projectiles in firearms.-Process:...
- WeightlessnessWeightlessnessWeightlessness is the condition that exists for an object or person when they experience little or no acceleration except the acceleration that defines their inertial trajectory, or the trajectory of pure free-fall...