SNIP Concept

Sufficiently compatible data relay satellites and corresponding ground systems should be able to provide data coverage for a "foreign" user spacecraft.

The three agencies, NASA, ESA, and NASDA operate or plan to operate a Data Relay Satellite Systems for their own projects/missions consisting of:

• User Spacecraft in low earth orbit
• Data Relay Satellites in Geostationary Obit
• Earth Terminals

General Space Network Data Flow

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• Each agency’s space network must be capable of supporting:
  - Their users and the resultant loading in normal operations
  - All priority users during a DRS failure situation
• Other Space Networks
  - Provide emergency backup to DRS failures
  - Provide support to user emergencies
  - Support low priority user missions during peak periods
  - Provide extended coverage
• International data transfer is important

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The SNIP provides direction for the exploration of Interoperability options and concepts and based upon the options selected to be pursued, makes recommendations to their respective program management officials.

• Coordinate DRS activities between participating agencies
• Exchange information and review SN implementation and operational progress
• Define data relay Interoperability concepts and options
• Conduct studies and proof of Interoperability concept testing
• Prepare required technical specifications and international agreements

The current objectives of the SNIP are to determine the feasibility and extent of international Space Network Interoperability and to achieve NASA/NASDA/ESA decisions to either proceed with the implementation of Interoperability or to terminate Interoperability studies.

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Interoperability should provide the following capabilities when they can be shown to be of net benefit to the tripartite members:

1. Emergency Space Network support in case of maintenance, failure, catastrophe, or over commitment of a data relay or failure of a low earth orbiting (LEO) satellite
   
2. Zone of Exclusion (ZOE) coverage around the far side of the Earth where each data relay system has a different "blind" spot
   
3. Unmanned/manned cross support
   
4. Simplification of data interchange
   
5. Flexible support of interagency cooperative missions (i.e. TRMM, POPs, ISS)
   
6. Peak period SN service off-loading of selected missions

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The study is broken down into two parts:

• Phase 1 - S-band (2 Ghz) Interoperability
• Phase 2 - Ka-band (23/26 Ghz) Interoperability (In addition to S-band)

** S-Band **

• All DRSs will have full tunable S-Band user services
  -- Forward Link Frequency 2025 - 2110 Mhz
  -- Return Link Frequency 2200 - 2290 Mhz
• All DRSs will use 240/221 coherent frequency translation ratios
• All DRSs will provide coverage to spacecraft up to at least 1000 Km
• All DRSs will support LHC and RHC polarization
• All DRSs systems will provide data rates between
  -- Forward Link 100 b/sec - 300 Kb/sec
  -- Return Link 100 b/sec - 3 Mb/sec
• All DRSs will provide for Doppler compensation (implemented on the ground)

** Ka-Band **

• All DRSs will use the following frequencies
  -- Forward Link Frequency 23 GHz
  -- Return Link Frequency 26 GHz

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Interoperability is specifically defined as the use of one Agency’s data relay satellite to provide communications and/or tracking services for an orbiting spacecraft of another agency.

• The Host Agency is defined as the Agency whose data relay satellite provides the Interoperability service.
• The User Agency is defined as the Agency whose user spacecraft is provided with Interoperability service.
• Cross Support is defined as an interchange of Interoperability services between agencies under a specific agreement, typically without exchange of funds.
• An Interpretable User Spacecraft is capable either by virtue of its basic design or by virtue of specific modifications of operating over data relay satellites of more than one Agency.
• Zone of Exclusion (ZOE) Closure, to enable communications with a user spacecraft to continue through the period when it is invisible from its own Agency’s data relay satellite (User spacecraft which are not equipped with two interoperable space terminals, each with a complete set of transmitting and receiving equipment, will still experience loss of continuous communications. This occurs usually three times each orbit for periods typically of two minutes, each time that the spacecraft hands over from one data relay satellite to another.
• Hit-Less ZOE Closure, to enable a user spacecraft equipped with two interoperable user space terminals to obtain fully continuous communications services.
• Direct Data Return, to enable data to be sent directly to the Host Agency’s country without requiring inter-continental data links.
• Emergency Support, in case of failure of critical parts of the user Agency’s data relay satellite system.
• Contingency Load Sharing, in a case of an unexpected overload of a User Agency’s data relay satellite system, especially if the overload is caused by interoperable use of the User Agency’s own data relay satellite with the Host Agency and by a third party.

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