Precision Space Systems Laboratory

In the Precision Space Systems Lab we develop instruments and measurement techniques for gravitational science missions and future satellite navigation systems. On the technological side, our primary focus is on drag-free platforms, precision accelerometers and gyroscopes, and precision timing instruments for spacecraft. These technologies will improve our understanding of mass transport on the surface and in the interior of the Earth due to seasonal and secular effects, open up a new window to our universe through the first ever observation of low-frequency gravitational waves, test the limits of general relativity, and benefit future satellite navigation systems. In the area of space mission design, our goal is to reduce cost and increase robustness through the use of small satellites and disaggregated architectures.

Drag-free technology

A drag-free satellite is designed to follow a pure geodesic in spacetime. At the heart of this technology is a gravitational reference sensor, which contains and shields a free-floating test mass from all non-gravitational forces and precisely measures the position of the test mass inside the sensor. A feedback control system then commands thrusters to fly the “tender” spacecraft in formation with the test mass. Thus, both test mass and spacecraft follow a purely gravitational orbit. Precisely tracking a low Earth orbiting drag-free satellite allows us to determine the detailed shape of geodesics and through analysis, the higher order harmonics of the Earth’s geopotential. With a pair drag-free satellites, a more accurate differential measurement between geodesics can be made, for example using laser interferometry. In addition to geodesic information, the commanded thrust, test mass position and GPS tracking data can be combined to estimate atmospheric drag forces, which are caused by a combination of atmospheric density and wind. With three drag-free satellites flown in deep space a gigantic Michelson interferometer can be formed to measure fluctuations in the spacetime metric caused by the passage of gravitational waves.

At the University of Florida we are developing two drag-free platforms. The first is a fempto-g system for the future gravitational wave observatory eLISA. The primary effort here is in the development of a laboratory testbed involving a torsion pendulum for testing and performance evaluation of the eLISA gravitational reference sensor. The second class is a pico-g level, small scale drag-free system primarily for Earth geodesy and aeronomy, and for autonomous navigation. We are designing a three-axis drag-free control system that utilizes a single thruster and reaction wheels for attitude control, which will be integrated with a small satellite bus for an eventual flight demonstration.

Future Navigation Systems

A disaggregated space system is one in which the essential functions of a large space asset are separated into smaller platforms, each with a single capability that is shared with the others. In future satellite navigation and communications systems one of these critical functions is precise time-keeping. A low Earth orbiting precision timing satellite could, for example, provide timing information to the GPS constellation, alleviating the need to host and maintain atomic clocks in each one. To this end the precision space systems lab is designing a compact sub-nanosecond time transfer system from Earth to low Earth orbit. The system will use modulated short laser pulses emitted from a satellite laser ranging facility to simultaneously compare and update atomic clocks in orbit with respect to terrestrial time standards. Demonstration of this technique with a 3U CubeSat equipped with a small scale atomic clock, optical components and precision timing electronics is planned for 2017.

The Laser Interferometer Space Antenna

Gravitational wave detection is one of the most compelling problems in astrophysics today. It represents an entirely new way of observing our universe and therefore provides enormous potential for scientific discovery. Gravitational waves are fundamentally different from electromagnetic waves. The acceleration of electric charges creates electromagnetic waves, which propagate in the framework of space and time. Gravitational waves, however, are created by the acceleration of massive objects, such as black holes, and propagate in spacetime itself. Low frequency gravitational waves in the 0.1 mHz to 1 Hz band, which can only be observed from space, provide the richest science and the greatest opportunity for discovery. Space observatories complement observatories on the ground such as the Laser Interferometer Gravitational-wave Observatory LIGO, which are only sensitive above 1 Hz. A space-based observatory will improve our understanding of the formation and growth of massive black holes in the distant universe and create a census of compact binary systems within the Milky Way. It will observe black holes as they collide with one another at the speed of light, and test general relativity in the ultra-relativistic limit by tracing out the paths of compact objects traversing curved space-time around supermassive black holes. Observation of low frequency gravitational waves will also probe new physics and cosmology by exploring the universe closer to the Big Bang than is possible with electromagnetic observations.

The Laser Interferometer Space Antenna (LISA) is the most mature concept for detecting gravitational waves from space. The LISA design has been studied for more than 20 years as a joint effort between NASA and the European Space Agency (ESA). LISA consists of three Sun-orbiting spacecraft that form an equilateral triangle, with each side measuring 1-5 million kilometers in length. Each spacecraft houses two free-floating test masses (TM), which are protected from all disturbing forces so that they follow pure geodesics in spacetime. A single test mass together with its protective housing and associated components is referred to as a gravitational reference sensor (GRS). A “drag-free” control system is supplied with measurements of the TM position from the two LISA GRSs and commands external micronewton thrusters to force the spacecraft to fly in formation with the test masses. Laser interferometry is used to measure the minute variations in the distance, or light travel time, between these purely free-falling TMs, caused by gravitational waves.

At the University of Florida, we are constructing a new torsion pendulum for measuring fN-level forces and for testing the LISA gravitational reference sensor. This experimental facility consists of a vacuum enclosed torsion pendulum that suspends mock-ups of the LISA test masses, surrounded by their electrode housings. With the aid of this facility, we are developing (a) a novel test mass charge control scheme based on ultraviolet LEDs, (b) simplified capacitive readout electronics, and (c) a six degree-of-freedom, all-optical TM sensor.

Official eLISA site

The University of Florida will host the 10th International LISA Symposium in May of 2014. The official symposium website is here.

Gravity Probe B

Gravity Probe B is a NASA space-borne physics experiment designed to test two predictions of General Relativity. Launched in 2004, the probe uses four of the world's most precise gyroscopes to measure the subtle curvature of spacetime around the Earth. Since 2009 I have been leading the data analysis, which involves the modeling and optimal estimation of gyroscope dynamics in the presence of small electrostatic disturbances and other systematic effects. The final results were published in a 2011 Physical Review Letters paper, and a complete volume of Classical and Quantum with roughly 20 scientific and engineering papers detailing the entire experiment will be published in 2014.

Official Gravity Probe B website

 

Drag-free Small Satellite Technologies

Supported by KACST of Saudi Arabia, the NASA Ames Research Center, and the Florida Space Institute, this work focuses on the design of a complete drag-free small satellite platform for future Earth geodesy and aeronomy applications. The performance goal of is 10E–11 m/sec^2/Hz^1/2 over 10 mHz to 1 Hz (the current state of the art) on a 10 kg, 10 W space vehicle. We are working toward a flight demonstration before 2020, with two pre-curser missions in various stages of development: (a) The UV LED Small Satellite to be launched in March of 2014, and (b) the DOSS CubeSat to be launched in 2015-2016. Contributions primarily focus on drag-free and attitude control design and simulation, satellite bus development, and optimization of satellite constellation configuration for the determination of Earth’s geopotential and upper atmospheric winds and density.

 

Compact Precision Time-transfer Systems for Spacecraft

Sponsored by the Air Force Research Laboratory, this project will demonstrate sub-nanosecond time transfer from ground to an orbiting 3U CubeSat using modulated laser pulses. The CubeSat hosts a time transfer instrument, which consists of Cs and Rb atomic clocks, optical equipment for fast photodetection and retroreflection, and precision timing electronics. Initially this technique will be proven in the laboratory using picosecond laser pulses, modulated with the timing information. These pulses will be detected by the time transfer instrument and used to simultaneously determine and update the instrument's atomic clock offset. This laboratory demonstration will be used to assess the instrument's performance and its sensitivities to the temperature, magnetic field, and attitude variations expected on-orbit.

The CubeSat demonstration mission itself, CHOMPTT (CubeSat Handling of Multi-Satellite Precision Time Transfer), is a competitor in the Air Force’s 8th University Nano-satellite Program. The CHOMPTT team at UF consists of roughly 20 graduate and undergraduate students who are developing and testing both the time transfer instrument, as well as the CubeSat bus.

 

Dr. John W. Conklin, PI

Assistant Professor
Department of Mechanical & Aerospace Engineering
University of Florida
322 MAE-A Building
Gainesville, FL 32611

phone: 1-352-392-9129
email: jwconklin at ufl dot edu

CV


Stanford University
Cornell University
Cornell University

PhD
MEng
BS

2009
1998
1997

John Conklin joined the UF Mechanical and Aerospace Engineering faculty in August of 2012 after working for three years at the W.W. Hansen Experimental Physics Laboratory at Stanford University as a research associate. He received his BS and MEng degrees from Cornell University and PhD from Stanford. In 2011, John was the Fulbright Junior Lecturer at the University of Trento in Italy. He has been awarded the NASA Early Career Faculty award (2014), the Zeldovich Medal (2010) by COSPAR & the Russian Academy of Sciences for contributions to fundamental physics in space, the Balhaus Prize (2009) for best PhD thesis in Aeronautics and Astronautics at Stanford, and the NASA Group Achievement Award (2005) as a member of the Gravity Probe B science team. John’s research is in the development of precision PNT (position, navigation, and Time) instruments, spacecraft dynamics & control, and the design and analysis of space missions that depend heavily on these technologies.

 

Precision Space Systems Lab, 10 October 2013 (from left to right: Nguyen Vu, Anh Nguyen, Seong Hyeon Hong, Paul Serra, Nathan Barnwell, Taiwo Olatunde, Paul Buchman, Ryan Shelley, Dr. John Conklin)

Graduate Students

Anh Nguyen

Seong Hyeon Hong

Taiwo Olatunde

Nathan Barnwell

Paul Serra

Undergraduate Students

Seth Nydam

Maria Carrasquilla

Leopoldo Caro

Paul Buchman

PSSL Alumni

Ryan Shelley (MS)

Dr. Conklin's Google Scholar page

Selected publications by research topic

LISA: The Laser Interferometer Space Antenna

  1. P. Amaro Seoane, S. Aoudia, H. Audley, G. Auger, S. Babak, J. Baker, E. Barausse, S. Barke, M. Bassan, V. Beckmann, M. Benacquista, P. L. Bender, E. Berti, P. Binétruy, J. Bogenstahl, C. Bonvin, D. Bortoluzzi, N. C. Brause, J. Brossard, S. Buchman, I. Bykov, J. Camp, C. Caprini, A. Cavalleri, M. Cerdonio, G. Ciani, M. Colpi, G. Congedo, J. W. Conklin, et al, “The Gravitational Universe”, arXiv eprint 1305.5720, (2013).

  2. D. Bortoluzzi, C. Zanoni, J. W. Conklin, “Prediction of the LISA-Pathfinder release mechanism in-flight performance”, Advances in Space Research, Vol. 51, No. 7, pp. 1145-1156, (2013).

  3. D. Bortoluzzi, M. Benedetti, J. W. Conklin, “Indirect measurement of metallic adhesion force-to-elongation function under dynamic conditions”, Mechanical Systems and Signal Processing, Vol. 38, No. 2, pp. 384-398, (2013).

Gravity Probe B

  1. C. W. F. Everitt, D. B. DeBra, B. W. Parkinson, J. P.  Turneaure, J. W. Conklin, M. I. Heifetz, G. M. Keiser, A. S. Silbergleit, T. Holmes, J. Kolodziejczak, M. Al-Meshari, J. C. Mester, B. Muhlfelder, V. G. Solomonik, K. Stahl, P. W. Worden Jr., W. Bencze, S. Buchman, B. Clarke, A. Al-Jadaan, H. Al-Jibreen, J. Li, J. A. Lipa, J. M. Lockhart, B. Al-Suwaidan, M. Taber, S. Wang, “Gravity Probe B: Final Results of a Space Experiment to Test General Relativity”, Physical Review Letters, Vol. 106, No 22, p. 221101, (2011).

  2. M. Salomon, J. Berberian, J. W. Conklin, G. M. Keiser, J. Kozaczuk, D. I. Santiago, A. Silbergleit, P. Worden, “Nanohertz Frequency Determination for the Gravity Probe B High Frequency Superconducting Quantum Interference Device Signal”, Review of Scientific Instruments, Vol. 82, No. 12, pp. 125110-125110-9, (2011).

  3. A. Silbergleit, J. W. Conklin, D. B. DeBra, M. Dolphin, G. M. Keiser, J. Kozaczuk, D. Santiago, M. Salomon, P. Worden, “Polhode Motion, Trapped Flux, and the GP-B Science Data Analysis”, Proceedings of Nature of Gravity: Confronting Theory and Experiment in Space, Space Science Reviews, Vol. 148, Nos. 1-4, pp. 397–409, (2009).

  4. J. W. Conklin, “The Gravity Probe B Experiment and Early Results”, Proceedings of the 6th International Conference on Gravitation and Cosmology, Pune, INDIA, Journal of Physics: Conference Series, Vol. 140, No. 1, (2008).

Drag-free technology

  1. D. B. DeBra, J. W. Conklin, “Measurement of Drag and its Cancellation”, Proceedings of the 8th International LISA Symposium, Classical and Quantum Gravity, Vol. 28, No. 9, (2011).

  2. J. W. Conklin, A. Swank, K-X. Sun, D. B. DeBra, “Mass properties measurement for drag-free test masses”, Proceedings of the 7th International LISA Symposium, Journal of Physics: Conference Series, Vol. 154, No. 1, (2009).

  3. J. W. Conklin, G. Allen, K-X. Sun, D. B. DeBra, “Determination of Spherical Test Mass Kinematics with a Modular Gravitational Reference Sensor”, AIAA Journal of Guidance, Control, and Dynamics, Vol. 31, No. 6, pp. 1700–1707, (2008).

  4. J. W. Conklin, K-X. Sun, D. B. DeBra, “Mass Center Determination by Optical Sensing of Velocity Modulation,” Laser Interferometer Space Antenna: 6th International LISA Symposium, Greenbelt, MD, American Institute of Physics Conference Series, Vol. 873, pp. 566–570, (2006).

 

 

 

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