Global Transmission Services 2 (GTS-2) - 11.22.16

Overview | Description | Applications | Operations | Results | Publications | Imagery

ISS Science for Everyone

Science Objectives for Everyone
Global Transmission Services 2 (GTS-2) is a technology experiment for the test, validation and demonstration of radio transmission techniques for the synchronization of earth-based clocks and watches from the ISS. In addition the GTS data services, based on a unique coding scheme, could ultimately lead to commercial services, such as blocking of stolen cars or lost credit cards, directly from space.
Science Results for Everyone
Let us synchronize our watches. This experiment tested synchronization of clocks on Earth and watches on the station using radio transmissions. An Ultra-Stable quartz clock with an accuracy of within one trillionth of a second provides unprecedented precision on station when synchronized with an atomic clock on Earth. Testing showed lower-than-expected signal strength, traced to interference from the hull of the module and blocking by the docking of the Soyuz spacecraft. Corrective measures for the signal strength were successful and ground hardware improvements allowed signal reception on every station pass.  Second-generation testing ran from 2007 to 2009 and reactivation is expected in 2014.

The following content was provided by Felix Huber, Ph.D., and is maintained in a database by the ISS Program Science Office.
Information provided courtesy of the Erasmus Experiment Archive.
Experiment Details


Principal Investigator(s)
Felix Huber, Ph.D., Steinbeis Transferzentrum Raumfahrt, Gaufelden, Germany

Information Pending

German Aerospace Center (DLR), Cologne, Germany

Sponsoring Space Agency
European Space Agency (ESA)

Sponsoring Organization
Information Pending

Research Benefits
Information Pending

ISS Expedition Duration
April 2007 - October 2009

Expeditions Assigned

Previous Missions
Information Pending

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Experiment Description

Research Overview

  • The Global Transmission Services 2 (GTS-2) is designed to investigate the possibilities of transmitting a time signal from the International Space Station (ISS) to synchronize clocks on the ground.

  • Time signal stations on Earth usually broadcast their information at long wavelengths. Watches and clocks synchronize themselves with these signals by activating their receivers typically once per day or after turn-on.

GTS is transmitting a UTC time signal from the Station via an external antenna with a broad antenna pattern. The Station's orbit means that this signal covers almost the whole globe every day. It can be received at any location several times daily, for 5-12 min at a time, strong enough for even small wrist watches. GTS also broadcasts the Station's current orbital position, so clocks know their local time zone.

GTS-2 will verify the performance and accuracy of a time signal broadcast to Earth from low orbit under real space operational conditions. GTS-2 will also measure the signal quality and data rates on the ground and measure disturbing effects such as Doppler shifts, multi-path reflections, shadowing and elevation effects.

GTS-2 is a continuation of the Global Transmission Services (GTS) experiment, which will be possible when a new electronic unit is launched on Progress flight 22P to the ISS. On 5 December 2005, the current GTS was re-activated, after a long time of theoretical investigations and practical tests to find out the reasons and successfully introduce corrective measures for the weaker than expected transmitted signal strength experienced by GTS receivers on the ground.

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Space Applications
Information Pending

Earth Applications
Information Pending

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Operational Requirements and Protocols
Information Pending

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Decadal Survey Recommendations

Information Pending

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Results/More Information

Following launch of the principal elements in 2000 and 2001 the system underwent testing. The Electronics Unit inside the Zvezda Module has an Ultra Stable quartz Oscillator which has an accuracy of 10-13 s. This unit provides unprecedented accuracy for the Station’s applications if synchronized with an atomic clock on ground. Testing showed a lower than expected signal strength traced to interference from the hull of the Russian Service Module on which the GTS antenna was launched to the ISS, as well as additional field of view blockage from the Pirs Docking Module and its attached Soyuz spacecraft (not originally scheduled to be at the ISS during the GTS testing). The initial two-year operational test phase started in June 2003 and improvements were made to ground hardware in order to receive signals on every ISS pass. Signals are generated over the UHF band (which will later be used for commercial services) and L-band for better understanding of signal propagation and multi-path effects. On 5 December 2005, GTS was re-activated, after a long time of theoretical investigations and practical tests to find out the reasons for the weaker than expected transmitted signal strength experienced by GTS receivers on the ground and successfully introduce corrective measures. Following launch of a new Electronics Unit on progress 22P in June 2006, the second generation GTS operational test phase started in the summer of 2007 under the title of GTS-2. The Global Transmission Service was deactivated on 31 May 2009. All though following negotiations with Russian representatives regarding upgrades of Russian computer systems on ISS, the instrument will be again fully re-activated in 2014 as a cooperative European-Russian experiment on the ISS.

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Related Websites
The information provided is courtesy of the ESA Astrolab Mission web page.

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image NASA Image: ISS003E5477 - Cosmonaut Vladimir Dezhurov of Rosaviakosmos, Expedition Three flight engineer, holds a Global Time System (GTS) electronics unit in the Zvezda Service Module.
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