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Name of Group

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Chairperson

Chairperson E-Mail Address

Chairperson Agency

Deputy Chairperson

Deputy Chairperson E-Mail Address

Deputy Chairperson Agency

Mailing List

Scope of Activity

Rationale for Activity

Goals

Survey of Similar Standards Efforts Undertaken in Other Bodies and elsewhere in CCSDS

Patent Licensing Applicability for Future Standards

Technical Risk Mitigation Strategy

Management Risk Mitigation Strategy

Description of Change

Peter Shames (5/6/2019 7:22 PM): This is a new Working Group chartered to reply to the IOAG request for a set of Time Management standards.

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Name of Group

1.07 Time Management Working Group

Area

Systems Engineering Area (SEA)

Chairperson

Jon Hamkins

Chairperson E-Mail Address

jon.hamkins@jpl.nasa.gov

Chairperson Agency

NASA-JPL

Deputy Chairperson

Sinda Mejri

Deputy Chairperson E-Mail Address

Sinda.Mejri@esa.int

Deputy Chairperson Agency

ESA

Mailing List

sea-time@mailman.ccsds.org

Scope of Activity

The Time Management Working Group will concentrate on creating and maintaining standards relating to time transfer, time correlation, and time synchronization in space operations contexts.  The activities will be coordinated under the Systems Engineering Area (SEA).

Rationale for Activity

Space agencies need to manage time on their spacecraft for the effective execution of maneuvers, coordination of scientific observations, docking or other robotic collaboration, and for scheduling of communications links or other activities. CCSDS member agencies see value in standardizing parameters and protocols for accomplishing time correlation and synchronization, so that agencies can offer cross support for their timing needs. The biggest motivation for doing this work in CCSDS is to enable a move from mission or agency approaches to internationally interoperable standardized approaches.

Goals

Standards shall be developed to promote common understanding of time correlation and synchronization approaches and to facilitate cross support of time management operations among space operations assets. The Working Group has the following goals: 1) Collect and analyze the technical literature, and codify it into specific time correlation and synchronization methods that can be analyzed and compared, in preparation for developing CCSDS Green, Blue, and Magenta Books. As part of this, the requirements for time correlation and synchronization for emerging mission domains/enterprises will be determined and reviewed with other CCSDS stakeholders. 2) Produce a Green Book describing suitable operational domains, applications, and methods used for time correlation and synchronization. The Green Book will identify requirements for interoperable time correlation and time synchronization services. Applications that may make use of time correlation and/or synchronization include maneuvers, coordination of scientific observations, one-way ranging, docking or other robotic collaboration, and scheduling of communications links or other activities. The book will describe methods for time correlation and synchronization, including those for near Earth, cislunar, and deep space regimes. The book will separately address application domains in which a Global Navigation Satellite Service (GNSS) is or is not available. A multitude of time transferand synchronization methods will be described, using correlation techniques such as existing CCSDS ranging methods, one way data delay coupled with trajectory data, two-way range signaling similar to that used by the Tracking and Data Relay Satellite System (TDRSS)), the use of local aera time zones (e.g., rovers and orbiters around Mars), and methods using or not using explicit time code format representations in the signaling. The Green Book will also discuss the roles of clocks, frequency standards, and topics such as X-Ray Pulsars as frequency sources for timekeeping. Error sources will be identified, including limitations in orbit knowledge, calibration, and time tags. 3) Produce one or more Blue Book describing protocols for time correlation and for time synchronization. The Blue Book(s) will define the signaling of time correlation data (signaling containing time code formats) or use of other suitable signals such as telemetry/PN/GMSK+PN ranging needed to accomplish time correlation. They will define protocols for time synchronization that are suitable for use in traditional single space link deployments as well as in Solar System Internet (SSI) deployments using DTN or IP protocols. 4) Produce a Magenta Book that defines recommended procedures for using these normative approaches, in space and on the ground, to produce the desired outcomes for cross supported mission and multi-mission time management.

Survey of Similar Standards Efforts Undertaken in
Other Bodies and elsewhere in CCSDS

CCSDS has developed standards for Time Code Formats (CCSDS 301.0-B-4), Pseudo-Noise (PN) Ranging Systems (CCSDS 414.1-B-2), GMSK+PN Ranging, and is in the process of developing a standard for telemetry ranging (to be included in CCSDS 401.0-B-30), PN ranging using CDMA from a Relay Satellite (CCSDS 415.1-B-1), Earth Receive Time (ERT) time stamps delivered by Space Link Extension (SLE) return frame services (CCSDS 911.1-B-4, CCSDS 911.2-B-3). Each of these standards relates to the representation of or exchange of time, or the measurement of elapsed time useful in determining the range between a reference point on the ground and a reference point on a spacecraft. A series of IETF RFCs (RFCs 778, 781, 956, 958, 1059, 1305, 5905, 7822) describes the Network Time Protocol (NTP) and its extensions, for time synchronization over the Internet. NTP is one of the oldest Internet protocols in current use. There is not yet a corresponding set of time synchronization standards for the Delay Tolerant Network (DTN) suite. There are time and position services from GPS/GNSS that are in wide use for near Earth and that have a usable service volume that may extend to cis-Lunar distances. There is an European Cooperation for Space Standardization (ECSS) clock correlation standard that is used in Europe, and there are other agency and mission clock correrlation approaches, some of which are well documented. This is not intended to be a comprehensive list, but NIST maintains an atomic clock standard, and has established standard definitions for much of the terminology involved. BIPM also maintains an atomic clock standard and uses the same standard definitions. There are a few terrestrial deployments of synchronized clocks that may be used for timekeeping on Earth, but, aside from GNSS systems, no such “fabric” is deployed in space. These various standards and standard definitions will be utilized where they are suitable in formulating a time transfer and time correlation protocol, and time synchronization standards. In formulating this approach we will study and utilize, as possible, standards efforts and related reports from other international and national organizations.

Patent Licensing Applicability for Future Standards

The current WG participants know of no limitations at this stage on usage of the planned technologies as far as patent restrictions or licensing requirements are concerned. Certain GPS localization technologies may be patented and require a license. 

Technical Risk Mitigation Strategy

No technical risks have been identified by the BOF at this stage. There are several systems that already support parts of the desired features in specific environments. The Space Network (SN) has deployed transponders that successfully use PN ranging since 1985. GPS and other GNSS systems, for Earth surface and near Earth uses, provide highly accurate time and position information that is globally used. The following is one example of recent activities that provide some technical risk mitigation. JPL has been testing telemetry ranging and PN ranging and the next generation transponder has accepted the requirement to time tag their clock in association with a specified bit in the PN. The WG will review and evaluate existing approaches to determine where, and if, they are applicable in the space operations domain. The WG will define a consistent set of terms that align with best current practices, see annex for definitions of the terms used in this Charter.

Management Risk Mitigation Strategy

Schedule relies upon the support of multiple CCSDS Agencies and on the allocation of adequate Agency resources to the WG. This work involves coordination between the Systems Engineering Area (SEA) and the Space Link Services (SLS) and Space Internetworking Services (SIS) areas which develop specific link and internetworking protcols used in time exchange. This will be particularly important for IP and DTN “wide area” deployment in the Solar System Internet. Coordination will also be required between this WG and the Mission Operations and Information Management (MOIMS) SM&C & Nav WGs for requirements and as stakeholders when they work on MO Time Services and Nav data exchange standards. Coordination will also be required between this WG and the Spacecraft Onboard Information Services (SOIS) App WG when they work on electronic data sheets for onboard clocks to provide time access services for MO Time Services and for other applications. Security topics, if there are any, will be reviewed with the SEA Sec WG when and as required. A risk management approach will be used to formulate a risk management plan and identify risks other than schedule and resources.
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Time Management Green BookGreenBehind ScheduleProject ApprovedBrian Oliver