Thesis Proposal Modular Gravitational Reference Sensor

  • Uncategorized

Modular Gravitational Reference Sensor 12

ThesisProposal:ModularGravitational Reference Sensor


DifferentialOptical Shadow Sensor (DOSS) validation in vacuum environment, fordrag-free satellites

Potentialadvisor(s) (all relevant fields):

CoursesI have had which support my thesis proposal:

  • Introduction to Control (Engr. 105)

  • Complex analysis (ME 308)


Inthe review of the progress to develop a medullar gravitationalreference sensor, it was first proposed as a simple core sensor forspace gravitational wave detection. Within the medullargravitational reference sensor, a laser beam from a remote sensorilluminates the proof mass directly. Also, the housing of the proofmass is separated from external interferometry.

Moreover,in the recent progress, an optical sensing design provideshigh-precision interferometry measure and a perfect optical shadowsensing scheme. Therefore, the optical measure of the mass midpointposition of a spherical mass is of high precision without the effecton dynamic range.

Also,the visibility of fabricating a localized grating pattern unto thedielectric and gold materials is demonstrated. Currently, the UV LEDthat is used for AC charge management is being experimented. This issupposed to make the modular gravitational reference sensor to be anin-time and cost-effective for advanced laser interferometryantennae.

Keywords: Medulla Gravitational Reference Sensor, UV LED, Laser beam,Drag Free Satellites, Differential Optical Shadow Sensor, MagneticLevitation System and Power Dissipation.

Thedrag-free satellites were first used in 1972. The drag-free satelliteworks under the basic idea that shields a free-floating test massfrom all the other forces apart from gravity. This puts the test massinto a geodesic orbit. A control system is then set-up to ensure thatthe satellite closely follows the test mass and this puts the wholesatellite into a geodesic orbit. The drag-free satellites have beenput into different missions since then, and these include navigation,geodesy and fundamental physics (Lu,2012).There are also plans to use drag-free technology especially inapplications of basic physics and geodesy. Because of these plans,there has been the new development of gravitational reference devicesensor, the Modular Gravitational Sensor (MGRS).

Theoptical shadow device sensor is an essential component of the ModularGravitational Reference Centre. It`s a sensor that measuresfree-floating displacement of the test mass inside the satellite. Theoptical shadow of the differential sensor is experimented both in thevacuum and in the thermal research.

Statementof the Problem

Theoptical sensor system has to be enhanced to obtain accuratemeasurements and hence valid results before being subjected to space.This then requires the space environment be stimulated. It now meansthen means that then experiments have to be conducted in a vacuum.The differential optical shadow sensor system will have to beenhanced by replacing the air bearing magnetic gravitation.

Theheat power dissipation from this system is an issue due to theabsence of cooling in a vacuum environment. Hence, the coil is usedto levitate the test mass that needs a cooling system. One of theways to be used for cooling is cooler water to conduct the heat. Thiscooler water system should be carefully designed to avoid leakage tothe vacuum. The two techniques to be used are discussed later in thisproposal.

Thesystem works to stimulate the zero-g operation and provides themeasure of the differential optical shadow sensor system in a vacuum(Markowitz &amp International LISA Symposium, 2013). Furthermore,the differential optical shadow sensor has a factor that obscures theeffect on the measurement and has to be studied. The study of theeffects improves the instruments since the thermal disturbances inspace causes significant temperature variations.

Purposeof the Study

Themain aim of the survey is to design and build an instrument using thegravitational reference sensor mechanism to measure the displacementfor satellites and also for fundamental physics emissions. Specificobjectives of the research can make measurements at low frequenciesto the extent of less than 100 MHz

Theresearch also aims to provide a tool to measure the temperaturedependence of the differential optical sensor system in more detailsand also stimulate temperature profile of a satellite in orbit.


Thisresearch project entails two main aspects under investigation: theseare the magnetic levitation and the Modular Gravitational ReferenceSensor.

Figure1: Magnetic Levitation in a Vacuum environment

Themagnetic levitation system will be built to be able to levitate andbe able to hold and spin in the vacuum to simulate the zero-goperation. This, therefore, serves as the ground test system thatstimulates space the way the environment is needed. It then improvesthe testing of the drag-free mass system (Markowitz &ampInternational LISA Symposium, 2013). As indicated in the figure 2below, the system is attached to the top is a simple optical shadowsensor which has an infrared emitter and a pair of phototransistors.

Ananalog control system will be built in the system and debugged toachieve a reliable operation as shown in figure 3. The nextelectronics board will be built and assembled to convert the analogsignal to digital. Its layout is as shown in figure 4. This boardwill have a switch to serve the current direction through the coil incase the fuel becomes magnetized and sticks to the coil in thevacuum. A digital control code will be designed to provide a stablefeedback control system to drive the coil and hold the ball in astably levitated position. This board will be able to be adjusteddigitally.

Thissystem will be designed to restore the ball to the levitated positionwhenever it drops out of the lock and also performs initiallevitation while it is running within the vacuum. The ball can alsobe spun using the four calls that are driven by digitally generatedsine and cosine to produce a rotating magnetic field around theequator of the sphere. The operation can achieve a 10 Hz. The systemmeasurements while running are as indicated in figure 5. The forcethat is produced by the coil will be calculated using COMSOL.

Figure2: The Vacuum top Lid and System Structure (Lu,2012)

Figure3: Experiments running in air before being moved to vacuum

Figure4: Magnetic Levitation Board layout

Figure5: The Signals when the coil catches the sphere

Figure6: Electromagnetic force VS distance from coil using COMSOL.

Thethermal model will consist of two conductive shield materials and avacuum separation together with the supportive spacers that willregister in between low thermal conductivity. The external layer iscomposed of a 10-millimeter aluminum wall that will connect to theplate interface through the adaptor ring low thermal conductivity.The thermal diffusivity is represented by the division of thermalconductivity by density at specific heat (Lu,2012).It determines the capacity of a thermal material to conduct heatenergy in relation to its ability to store the very energy. Forinstance, a titanium alloy having a diffusivity of 2*10-6m2/swill be chosen for the adaptor ring. The ring spacer will be designedto minimize the heat while also supporting launch loads as on figure8. The spacer, rectangular in shape, that will attach the externalhousing to the internal housing is shown in the figure 9 and iscomposed of the same alloy.

Figure8: The Ring Spacer

Figure9: The Rectangular Spacer

Thetemperature control system that is active consist of temperaturesensors the walls of the internal and external housing of the plate,with the heaters residing on the external part of each of the layersand the adapter plate. Every stage will possess four heaters withevery heater on the side of the outer and inner housing. The firstheater will give approximately 660 m-W at 5 volts, while the secondheaters will provide an approximate of 780 m-W at 5 volts. More so, acontrol algorithm will need to be developed in order to meet reachthe requisite requirements and then vary them with regards to thethermal enclosure laboratory model. The Vishay resistors will be putin use for stability as reference resistors. Also, a Model 55016thermistors for the purposes of controlling the temperature. Theexcitation voltage for the bridges will be a 2-volt peak wave, andthis is a trade-off that exists between the signal-to-noise wave andthe thermometer’s self-heating.

Theexcitation frequency will record approximately 10H. This is the veryminimum operating frequency of the amplifier in use. The lowfrequencies will in turn minimize the effects of reduced parasiticcomponents. Then the lock-in time must be set constant at 10 secondsto minimize the noise. The output will be logged by a converter runusing a primary visual program. With the use of this set-up, the risein Hertz temperature will record1micro-K. The control of thetemperature is then got by the use of a digital PID controller thatretains in visual basic. Both the A/D and A/D boards will be put inuse both output and input and conversion.

Thesystem also will have the capacity to undertake real-time control ofa bandwidth of 100 H ch will be adequate for control of thetemperatures thermal. Omega and Minco heaters provide excellentheating transfer when in use (Lu,2012).Also, the control system and thermal isolation systems must maintainthe thermal environment and the housing from less than 1Mk and thensubsequently degrade to 10Mk at 1H.

Methodsand Procedures

Thecooling system will be designed to use the cooled water as a coolerso that the heat generated by the coil in the vacuum does not affectthe system. The coil will be attached to the vacuum led from insideand the cool water will be filled to the coil from top.


Theimprovement on the Modular Gravitational Reference Sensor (MGRS)enables the minimization of disturbance forces and noise as thedesign uses optical sensing. It is incorporated with the use of TMforcing beam which does not require position and orientation forcing.The absence of position force and the use of optical sensing willreduce the path effect of the sensing beam. More so, this researchaims at allowing the application of a high intensity beam and modularengineering through separating the main interferometer and the localTM measurement beams.


Lu,P. P. (2012).&nbspDiffractiongratings for optical sensing.

Markowitz,S. M., &amp International LISA Symposium. (2013). Laserinterferometer space antenna: 6th International LISA Symposium,Greenbelt, Maryland, 19 – 23 June 2006. Melville, NY: American Inst.of Physics.