Using JSON Schema to Define a Systems Modeling Vocabulary: The Tradespace Analysis Tool for Constellations (TAT-C)

Abstract

With the emergence of large-scale constellations and commercial services to supplement government programs, space systems engineering must draw on new approaches to improve standardized information exchange across organization boundaries. This chapter models distributed space systems in the Tradespace Analysis Tool for Constellations (TAT-C) using JavaScript Object Notation (JSON) Schema to improve interoperability among disparate systems engineering analysis tools. JSON Schema is a standardized vocabulary to define object schemas using the JavaScript Object Notation (JSON) encoding. TAT-C object schemas define four types of orbits, observing instruments, standalone satellites, and two constellation configurations (train and Walker). The proposed schema has been implemented in TAT-C to structure inputs and outputs to analysis functions using a web-based Representational State Transfer (REST) Hypertext Transfer Protocol (HTTP) interface specified by OpenAPI. An example JSON request document demonstrates how the object schema encodes and formats inputs to analyze coverage statistics over the United States for a proposed space mission with five satellites.

Appendix A: JSON Schema Listings

The following code listings document TAT-C objects in JSON Schema specification.

Listing 2

Two-line elements object

TwoLineElements: { type: "object", required: [ "tle" ], properties: { type: { type: "string", enum: [ "tle" ], default: "tle" }, tle: { type: "array", minItems: 2, maxItems: 2, items: { type: "string" } } } }

Listing 3

Circular orbit object

CircularOrbit: { type: "object", required: [ "altitude" ], properties: { type: { type: "string", enum: [ "circular" ], default: "circular" }, altitude: { type: "number" }, trueAnomaly: { type: "number", minimum: 0, exclusiveMaximum: 360, default: 0 }, epoch: { type: "string", format: "date-time" }, inclination: { type: "number", minimum: 0, exclusiveMaximum: 180, default: 0 }, rightAscensionAscendingNode: { type: "number", minimum: 0, exclusiveMaximum: 360, default: 0 } } }

Listing 4

Keplerian orbit object

KeplerianOrbit: { type: "object", required: [ "altitude" ], properties: { type: { type: "string", enum: [ "circular" ], default: "circular" }, altitude: { type: "number" }, trueAnomaly: { type: "number", minimum: 0, exclusiveMaximum: 360, default: 0 }, epoch: { type: "string", format: "date-time" }, inclination: { type: "number", minimum: 0, exclusiveMaximum: 180, default: 0 }, rightAscensionAscendingNode: { type: "number", minimum: 0, exclusiveMaximum: 360, default: 0 }, eccentricity: { type: "number", minimum: 0, default: 0 }, perigeeArgument: { type: "number", minimum: 0, exclusiveMaximum: 360, default: 0 } } }

Listing 5

Sun-synchronous orbit object

SunSynchronousOrbit: { type: "object", required: [ "altitude", "equatorCrossingTime" ], properties: { type: { type: "string", enum: [ "sso" ], default: "sso" }, altitude: { type: "number" }, trueAnomaly: { type: "number", minimum: 0, exclusiveMaximum: 360, default: 0 }, epoch: { type: "string", format: "date-time" }, equatorCrossingTime: { type: "string", format: "time" }, equatorCrossingAscending: { type: "boolean", default: true } } }

Listing 6

Instrument object

Instrument: { type: "object", required: [ "name" ], properties: { name: { type: "string" }, fieldOfRegard: { type: "number", exclusiveMinimum: 0, maximum: 360, default: 180 }, minAccessTime: { type: "number", format: "time-delta", default: 0 }, reqSelfSunlit: { type: "boolean" }, reqTargetSunlit: { type: "boolean" } } }

Listing 7

Satellite object

Satellite: { type: "object", required: [ "name", "orbit" ], properties: { type: { type: "string", enum: [ "satellite" ], default: "satellite" }, name: { type: "string" }, orbit: { anyOf: [ {$ref: "#/TwoLineElements"}, {$ref: "#/CircularOrbit"}, {$ref: "#/SunSynchronousOrbit"}, {$ref: "#/KeplerianOrbit"} ] }, instruments: { type: "array", items: {$ref: "#/Instrument"}, default: [] } } }

Listing 8

Train constellation object

TrainConstellation: { type: "object", required: [ "name", "interval", "orbit" ], properties: { type: { type: "string", enum: [ "train" ], default: "train" }, name: { type: "string" }, orbit: { anyOf: [ {$ref: "#/TwoLineElements"}, {$ref: "#/CircularOrbit"}, {$ref: "#/SunSynchronousOrbit"}, {$ref: "#/KeplerianOrbit"} ] }, instruments: { type: "array", items: {$ref: "#/Instrument"}, default: [] }, numberSatellites: { type: "integer", minimum: 1, default: 1 }, interval: { type: "number", format: "time-delta" } } }

Listing 9

Walker constellation object in JSON Schema

WalkerConstellation: { type: "object", required: [ "name", "orbit" ], properties: { type: { type: "string", enum: [ "walker" ], default: "walker" }, name: { type: "string" }, orbit: { anyOf: [ {$ref: "#/TwoLineElements"}, {$ref: "#/CircularOrbit"}, {$ref: "#/SunSynchronousOrbit"}, {$ref: "#/KeplerianOrbit"} ] }, instruments: { type: "array", items: {$ref: "#/Instrument"}, default: [] }, configuration: { type: "string", enum: [ "delta", "star" ], default: "delta" }, numberSatellites: { type: "integer", minimum: 1, default: 1 }, numberPlanes: { type: "integer", minimum: 1, default: 1 }, relativeSpacing: { type: "integer", minimum: 0, default: 0 } } }

Listing 10

Point object

Point: { type: "object", required: [ "id", "latitude", "longitude" ], properties: { id: { type: "integer", minimum: 0 }, latitude: { type: "number", minimum: -90, maximum: 90 }, longitude: { type: "number", minimum: -180, maximum: 180 } } }

Listing 11

Point generator object

PointGenerator: { type: "object", properties: { method: { type: "string", enum: [ "cubed_square", "fibonacci_lattice" ], default: "cubed_square" }, distance: { type: "number", default: 1000000 }, region: { anyOf: [ {$ref: #/Polygon"}, { type: "string", minLength: 3, maxLength: 3 } ] } } }

Listing 12

Coverage analysis request object

CoverageAnalysisRequest: { type: "object", required: [ "satellites", "start", "end", "points" ], properties: { satellites: { type: "array", items: { anyOf: [ "#/Satellite", "#/TrainConstellation", "#/WalkerConstellation", ] } }, start: { type: "string", format: "date-time" }, end: { type: "string", format: "date-time" }, points: { anyOf: [ { type: "array", items: {$ref: "#/Point"} }, {$ref: #/PointGenerator"} ] } } }

Listing 13

Coverage analysis response object

CoverageAnalysisResponse: { type: "object", required: [ "points" ], properties: { points: { allOf: [ {$ref: #/FeatureCollection"} ] } } }