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Experiment/Payload Overview

Brief Summary

Department of Defense Synchronized Position, Hold, Engage, Reorient, Experimental Satellites ? Chip Scale Atomic Clock (DoD SPHERES ? CSAC)demonstrates the performance of an atomic clock in the sustained microgravity environment of ISS. Atomic clocks are the most accurate time keepers in the world. An atomic clock is a precision clock that depends for its operation on an electrical oscillation regulated by the natural vibration frequencies of an atomic system.

Principal Investigator

Andrei Shkel, , Defense Advanced Research Projects Agency, Washington, D.C. (District of Columbia), United States

Matt Moye, , Department of Defense Space Test Program, Houston, TX, United States

Co-Investigator(s)/Collaborator(s)

Information Pending

Payload Developer

Aurora Flight Sciences Corporation, Cambridge, MA, United States

Sponsoring Space Agency

National Aeronautics and Space Administration (NASA)

Sponsoring Organization:

Information Pending

ISS Expedition Duration:

September 2011 - September 2012

Expeditions Assigned

29/30, 31/32

Previous ISS Missions

Information Pending

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Experiment/Payload Description

Research Summary

• Department of Defense Synchronized Position, Hold, Engage, Reorient, Experimental Satellites-Chip Scale Atomic Clock (DoD SPHERES-CSAC) is an ultra-miniatured, low-power, atomic time and frequency reference unit which is designed to achieve over two orders of magnitude decrease in size and power consumption, while maintaining comparable performance over current approaches. The objective is to demonstrate the performance of the DoD SPHERES-CSAC atomic clock in a sustained microgravity environment.

Description

Department of Defense Synchronized Position, Hold, Engage, Reorient, Experimental Satellites ? Chip Scale Atomic Clock (DoD SPHERES-CSAC)test sessions allow DoD SPHERES-CSAC to synchronize the timing between two clocks with a high precision off-board module, then measure drift over each test session and between test sessions. The differences in relative motion between the two clocks may provide useful data relating to movement-induced clock drift. Motion-induced drift is not easily observable while the DoD SPHERES-CSAC units are strapped down. Some mechanisms for drift may be device dependent, but some are due to relative motion between devices.

For this experiment, the SPHERES platform on ISS is used to demonstrate synchronized timing between multiple free-flying bodies using the Chip Scale Atomic Clock. This allows DoD SPHERES-CSAC to leverage the existing SPHERES hardware, software, and processes to facilitate safety reviews, crew training, data interfaces, and operations. It provides a limited space qualification of the component, allowing DoD SPHERES-CSAC to claim flight heritage. Part of the DoD SPHERES-CSAC effort will also develop a universal interface for future experimenters, as an upgrade to the existing SPHERES expansion port. These interfaces could be left on the SPHERES satellites, for future use by other experimenters.

Each of the three 9 in. diameter SPHERES microsatellites on ISS has twelve cold gas (CO2) thrusters, three rate gyros, three accelerometers, and a pseudo-GPS sensing system that permits state estimation relative to the frame of the US Laboratory on ISS to 2 mm and 2 degree accuracy. A typical test session starts with the uplink of algorithms one week before the test session, loading of the algorithms onto the SPHERES through the communication system, cross-link of real-time data to the ISS laptop, and downlink of the data. This data is analyzed, algorithms are revised, and the next test session is scheduled.

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Applications

Space Applications

The development of Chip-Scale Atomic Clock enables ultra-miniaturized (wristwatch in size) and ultra low power time and frequency references for high-security UHF communication and jam-resistant GPS receivers. The use of these ultra-miniature time reference units can greatly improve the mobility and robustness of any systems and platforms with sophisticated UHF communication and/or navigation requirements. DoD SPHERES ? CSAC also helps in the development of small-scale inertial navigation systems (INS) for use on small satellites (mass 1-10 kg). An INS is a navigation aid that uses a computer, motion sensor, and rotation sensors to continuously calculate via dead reckoning the position, orientation and velocity of a moving object without the need for external references. An INS can be used on vehicles such as ships, aircraft, submarines, and spacecraft.

Earth Applications

Information Pending

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Operations

Operational Requirements

DoD SPHERES is allocated five test sessions per Increment. This allocation of test sessions is shared between DoD SPHERES ? CSAC, InSPIRE-VBN, and InSPIRE-EMFF; as the facility lead, NASA Ames determines specific test session scheduling based on ongoing planning and research results for the three DoD SPHERES experiments.

Operational Protocols

A typical DoD SPHERES-CSAC test session will consist of:

• Uplink of algorithms one week before the test session.



• Loading of the algorithms onto the SPHERES through the communication system.



• Cross-link of real-time data to the ISS laptop.



• Downlink of the data for post-session assessment.

Once the data is analyzed, algorithms are revised, and the next test session is scheduled.

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Results/More Information

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Related Web Sites

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Publications

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Ground Based Results Publications

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ISS Patent Publications

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Related Publications

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Images

SPHERES Facility Single Unit.

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