American Institute of Aeronautics and Astronautics1

A Small Artificial Gravity Generator for ExperimentalMicrogravity Flights

Stephen Hirst1, Benjamin Corbin1, Jeffrey Cunningham1, Joe Coverston1, and Jeremy Lawrence1

University of Central Florida, Orlando, Florida, 32817

The University of Central Florida chapter of the Students for the Exploration andDevelopment of Space (SEDS-UCF) have designed and built an autonomous experimentalartificial gravity centrifuge that meets all of the requirements for the experiment to be flownas crew cargo onboard a ZERO-G Corporation microgravity research flight. The currentexperimental configuration is designed to qualitatively view the effects of artificial gravity onfluid boundary layer motion. However, the configuration can be changed for future flightcampaigns and multiple artificial gravity experiments.

Nomenclatureg = acceleration due to gravityac = centripetal accelerationFc = centripetal forcevt = tangential velocityr = radiusm = mass

I. IntroductionN April 26th, 2007, world-renowned physicist Stephen Hawking participated in a parabolic flight on the ZERO-Gravity Corporation’s G-Force One.1 Afterwards, a new program was started for students to conduct research

in microgravity using small, automated boxes taken onboard the plane as crew equipment. The University of CentralFlorida chapter of the Students for the Exploration and Development of Space (SEDS) has built one of the first fiveexperiments that will fly on the program’s maiden flight. The experiment contains a rotating platform with a largeprism that can hold mixtures of liquids, and the centripetal acceleration generated by the rotation is very close to theforce of gravity on Earth.

What follows is a brief Background of this microgravity program and the fundamental physics governing thebehavior of objects under rotational acceleration. The Experiment Design section details the many requirements thatthe final design must meet in order to be flown legally under FAA regulations and describes the technicalspecifications of the design. Finally, the Future Applications section discusses many of the alternative experimentsthat can be done using the exact same equipment apparatus and a modified version of the spinning system.

II. BackgroundMicrogravity flight research is the most inexpensive way to do reduced-gravity research for sustained periods of

time. The National Aeronautics and Space Administration (NASA) developed microgravity flight, and they haveused such research flights to train and assist manned and unmanned missions to space. With the national goal to firstcolonize the moon and then take on the endeavor of becoming a multi-plant species, microgravity research isessential to the advancement of these goals. This section is devoted to explaining what can be concluded aboutmicrogravity experiments based off of prior knowledge.

A. Program Introduction.This Project is a part of the pilot program for Stephen Hawking’s Microgravity Education and Research Center.

Since Stephen Hawking’s first microgravity experience in April of 2007, the Research Center has been in

1SEDS-UCF Member, Mechanical, Materials, and Aerospace Engineering, 4000 Central Florida Blvd, Orlando, FL32817, AIAA Student Member

O

American Institute of Aeronautics and Astronautics2

partnership with Space Florida and NASA. Onthese experimental flights, 15 parabolas will beflown, as is for research flights using G-ForceOne

B. Process of Microgravity Flight.A specially modified aircraft approved by

the FAA performs microgravity flights.2

Maneuvers are conducted in dedicated airspaceapproximately 1000 square miles (100 mileslength by 10 miles width). Since controlling anaircraft of that magnitude worthy of carryingmultiple research payloads is in itself difficult, specially trained pilots fly the aircraft in a series of parabolas tocreate microgravity conditions in the research-payload area for approximately 30 seconds at a time.

The first stage (the preparation stage) of Microgravity Flight is when the aircraft pitches its nose to an angle of45 degrees above the horizon. At this stage the experiment experiences increased amounts gravity due to an increasein altitude. This takes the aircraft approximately 20 seconds to complete its climb from approx. 24,000 feet to32,000 feet.

Stage 2 (the microgravity stage) consists of the pilots “pushing over” the aircraft at the “top” of the parabola tocreate the “weightlessness/microgravity effect” which is between 20 and 45 seconds from when the parabolaofficially begins. It is during Stage 2 that the experiments onboard will feel the effects of microgravity. It is crucialfor the accuracy of the experiment and for the safely of the crew that the pilots slowly conduct the plane to a levelaltitude so that maximum amount of “Microgravity Time” is allowed for experiment to get the best results.

Stage 3 (the recovery stage) consists of the crew “recovering” the airplane to a stable flying altitude on which itstarted (approximately 24,000 feet). This is so the aircraft can repeat the process until all required or desiredparabolas are achieved. Figure 1 shows these stages

C. The Physics of MicrogravityMicrogravity is the condition in which an object is in synchronization with the acceleration of an object of a

greater mass. Also called “Free Fall”, Microgravity is the state of an object “constantly” falling. In space,Microgravity is created either by being away from a bigger mass or by being in orbit (a state of constant free fallaround a reference object). Achieving microgravity on earth using aviation is simple. An airplane must change itsacceleration towards the earth at a rate equal to that of the acceleration of gravity. This is done on research aircraftthat fly parabolas to first increase altitude then rapidly change acceleration (equaling that of gravity) downward. Thetime of absolute microgravity is restricted to about 30 seconds due to airspace restrictions; however, the amount ofparabolas made is depended upon the fuel capacity of the aircraft.

There is a common misconception about the term “zero gravity.” Gravitation is the natural phenomenon bywhich all objects with mass attract each other. Any object that has mass has attractive force to another body of mass.This reveals that gravitation is a force and therefore must have mass and acceleration. Therefore, absolutely zerogravity is impossible when another body of mass is present anywhere in the universe. The term “microgravity”accounts for the ever-present miniscule amount of gravity (Approximately 1x10^-6 g) on a “weightless” system inour universe.

D. The Physics of Artificial GravityCurrently the most feasible way to achieve artificial gravity in a microgravity environment is use centrifugal

force. According to Newton’s mechanics, Eq. 1 can describe centrifugal force.

Fc m ac⋅ mv

2

r⋅

(1)

With the current configuration of our experiment, the fluid containment area is approximately 9 inches indiameter; therefore, the radius is 4.5m inches. There are several side effects to using rotational artificial gravity,including having a gravity gradient. A gravity gradient is in effect when there is a lesser gravitational force as youapproach the axis of rotation. We have designed the motor system to achieve and acceleration at its endpoints equal

Figure 1. Approximate flight path of a parabolic flight.2

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to that of gravity (approximately 9.8 m/s2). Therefore, the system has a gravitational gradient with approximately1x10-6 g at the axis of rotation and 1g at the endpoints. This would require the tangential velocity to be about 1.058meters per second.

III. Experiment Design

A. RequirementsThe ZERO-G Corporation battled the FAA for 10 years to gain permission to fly civilians on parabolic flight

campaigns. However, in order to stay in business, ZERO-G must still follow many of the rules set forth by the FAAfor airline companies. One FAA rule is that all airliners must have a luggage security manual in order for anypassengers to legally carry anything aboard the plane. Since ZERO-G does not have this manual, passengers cannotbring on any equipment. Therefore, all flight experiments under this campaign must be classified as crew equipmentand pass the same standards as commercial airliner crew equipment.

In order to be classified as crew equipment and fit on board the pre-designated slots on board G-Force One, allexperiments must follow many strict requirements. In order to fit in the crew cargo closet, the experiment must becontained in a 12x12x16 inch non-flammable box (There are spaces for 12x12x9 inch experiments underneath someof the few passenger seats on board the plane). In addition to the given dimensions, the experiment had to have bothan inner and outer containment mechanism for the liquid experiment inside to safeguard against the possibility ofleakage. The outer casing of the experiment box had to be constructed of non-flammable and durable materials. Theinner experiment also had to be constructed so that it would continue to operate when tilted at all angles and shakenon the ground. If the experiment contains Velcro, even that must be fireproof.

Because the experiment will be stored in an unreachable location during the flight, the entire experimentaloperation must be automated once the experiment is activated by a ZERO-G crewmember. Passengers andresearchers will not be able to turn on the experiment, so instructions for turning on the experiment must be clearlyplaces on the front of the apparatus.

B. Design SpecificationsThe box was constructed from 12 angle aluminum 1/16” x 3/4” x 48” from Crown Bolt, Inc., and was bolted

together using 3 bolts per corner with machine round head slotted bolt and nut #6-32 x 3/8”, zinc for a total of 8corners with 24 bolts. Holes were drilled into the 16” angle aluminum so that the Valley Roll AL EC 14” x 10’ sheetaluminum could be bolted using machine round head slotted bolts and nuts #6-32 x 3/8”. The top and bottomaluminum plates were made out of 5005 aluminum plating and were bolted to the angled aluminum in the samemanner as the sheet aluminum. The door was constructed from galvanized sheet metal and 2 flat aluminum pieces,

1/8” x 1” x 36” from Crown Bolt, Inc. were added to thealuminum angle frame on the outside to connect the door to theframe. Silicone sealant was placed in a ridge surrounding the dooron the aluminum angle and aluminum flat pieces in order for thedoor to form an airtight seal. Silicone sealant was also used on theinside of the box to seal the sheet aluminum and aluminum plateto fulfill the FAA requirement of double containment. For theinner rotating mechanism, 2 iron pipe flanges were weldedtogether and then bolted to the bottom aluminum plating of thebox. A Solidworks design of the experiment is shown in Fig. 2and a recent photo of the final design is shown in Fig. 3.

Although experiments similar to this one have been performedin previous microgravity campaigns under NASA’s MicrogravityUniversity and other ZERO-G research campaigns, thisexperiment is the first one to be fully automated. A Sony DSC-S700 camera carrying a 2-gigabyte memory card and freshbatteries is mounted to the upper platform. Four LED flashlightsmounted on the support rods provide enough illumination to viewthe movement of liquids within the prism. Once the experiment iscompleted, video data can be analyzed using a variety of videosoftware.

Figure 2. Solidworks model of experiment

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IV. Future Applications

A. Alternate Experiments in the Same Design ConfigurationsThe first flight will only contain water and oil to demonstrate

the durability of the experiment and the ability to handle moredangerous liquids that may not be allowed by the FAA. The FAAis already worried about the flammability of oil and is onlyallowing the experiment because it contains water. In the future,more scientifically relevant fluids will be studied.

In addition to the separation of fluids of varying densities, theapparatus can also accomplish the flash distillation of misciblefluids by separating the phases created during partial vaporization.Such a “phase separator” has a variety of alternative researchapplications, such as conducting experiments to improve theliquefaction of cryogenic fuels. Similar experiments can alsoimprove the thermodynamic efficiency of nuclear-electricpropulsion drives, of which a centrifugal phase separator is acritical component.3 The distilling process involved also aids inthe decontamination of water, which proves invaluable to studiesof in-situ resource utilization systems on manned deep spacemissions. Further experiments can also observe the effect of theabsence of gravity-induced buoyancy effects on alloy melting,diffusion, crystal growth, and more.

B. Experiments with a Modified ApparatusAlthough the current experimental configuration only supports liquid testing, applications of a small centrifuge

that can generate 1-g of acceleration at the endpoints are useful for studies in biology and animal behavior amongothers. By surrounding the circular platforms with a flexible wall panel and moving the flashlights to the other sidesof the rods, a cage for small animals can be made to study how animals react to changes in the direction of theacceleration vector. Whether or not these types of experiments will be allowed is still up for debate, however.Because this experiment is automated, it can be placed on any microgravity flight that has room for it, whether itflies with NASA or with ZERO-G.

V. ConclusionThe maiden voyage of this experiment will be conducted two days after this paper is submitted for publication.

SEDS hopes that this experiment will be used not only for this flight and this experiment but also for future studiesin fluid mechanics under artificial gravity. After the first flight of this pilot program, flights will be conducted moreoften, resulting in more experiments and more contributions to microgravity studies.

AcknowledgmentsThe authors would like to acknowledge the help of Al Ducharme, PhD. as a project advisor for the experiment.

They would like to recognize the assistance of Ryan Maticka, Jason Dunn, Roberto Cloretti, and Erich Dondyk onconstruction of the experiment. They would also like to thank Dr. Larry Chew, Matthew Reyes, the NationalAeronautics and Space Administration, Zero Gravity Corporation, and the University of Central Florida for all oftheir efforts in making sure the project was successfully completed.

References1Boyle, A., “Hawking goes zero-G: ‘Space, here I come’,” MSNBC. 26 April 2007. URL: http://www.msnbc.msn.com/id/

18334489/ [cited 20 February 2008].2Zero Gravity Corporation, "How Parabolic Flight Works." Zero Gravity Corporation. URL: http://www.gozerog.com/how-

it-works.htm [cited 16 Feb 2008].3Committee on Microgravity Research, Space Studies Board, National Research Council, Microgravity Research in Support

of Technologies for the Human Exploration and Development of Space and Planetary Bodies, National Academics Press, 2000.

Figure 3. Experiment ready for flight.