NASA MCP Server

Instructions

Implementation Reference

• src/handlers/jpl/horizons.ts:12-80 (handler)

  Core handler function `horizonsHandler` that executes the JPL Horizons API request using axios, customizes resource metadata based on parameters like COMMAND and EPHEM_TYPE, adds the JSON response as a jpl://horizons resource, and returns formatted content or error.

  export async function horizonsHandler(args: Record<string, any>) {
    try {
      // Base URL for the Horizons API
      const baseUrl = 'https://ssd.jpl.nasa.gov/api/horizons.api';
      
      // Make the API request
      const response = await axios.get(baseUrl, { params: args });
      const data = response.data;
      
      // Create a resource URI that represents this query
      let resourceUri = 'jpl://horizons';
      let resourceName = 'JPL Horizons ephemeris data';
      
      // Customize resource name based on the request type
      if (args.COMMAND) {
        // Add the object identifier to the resource URI
        resourceUri += `/object/${encodeURIComponent(args.COMMAND)}`;
        
        // Update resource name based on EPHEM_TYPE
        if (args.EPHEM_TYPE === 'OBSERVER') {
          resourceName = `${args.COMMAND} observer ephemeris data`;
        } else if (args.EPHEM_TYPE === 'VECTORS') {
          resourceName = `${args.COMMAND} vector ephemeris data`;
        } else if (args.EPHEM_TYPE === 'ELEMENTS') {
          resourceName = `${args.COMMAND} orbital elements data`;
        } else {
          resourceName = `${args.COMMAND} ephemeris data`;
        }
        
        // Add time range info if available
        if (args.START_TIME && args.STOP_TIME) {
          resourceName += ` (${args.START_TIME} to ${args.STOP_TIME})`;
        }
      }
      
      // Add query parameters to the URI
      const queryParams = Object.entries(args)
        .filter(([key]) => key !== 'COMMAND' && key !== 'format')
        .map(([key, value]) => `${key}=${encodeURIComponent(String(value))}`)
        .join('&');
      
      if (queryParams) {
        resourceUri += `?${queryParams}`;
      }
      
      // Add response to resources
      addResource(resourceUri, {
        name: resourceName,
        mimeType: "application/json",
        text: JSON.stringify(data, null, 2)
      });
      
      // Format the response
      return {
        content: [{
          type: "text",
          text: JSON.stringify(data, null, 2)
        }]
      };
    } catch (error: any) {
      return {
        content: [{
          type: "text",
          text: `Error accessing JPL Horizons API: ${error.message}`
        }],
        isError: true
      };
    }
  }

• src/index.ts:1231-1287 (registration)

  Registration of the 'jpl_horizons' tool in the tools/list handler response, including full name, description, and detailed inputSchema for parameter validation (e.g., COMMAND required, EPHEM_TYPE enum).

  name: "jpl_horizons",
  description: "JPL Horizons - Solar system objects ephemeris data",
  inputSchema: {
    type: "object",
    properties: {
      format: {
        type: "string",
        description: "Response format (json, text)",
        enum: ["json", "text"]
      },
      COMMAND: {
        type: "string",
        description: "Target object identifier (e.g., '499' for Mars, '1' for Ceres, 'C/2020 F3' for Comet NEOWISE)"
      },
      OBJ_DATA: {
        type: "string",
        description: "Include object data",
        enum: ["YES", "NO"]
      },
      MAKE_EPHEM: {
        type: "string",
        description: "Generate ephemeris",
        enum: ["YES", "NO"]
      },
      EPHEM_TYPE: {
        type: "string",
        description: "Type of ephemeris (OBSERVER, VECTORS, ELEMENTS)",
        enum: ["OBSERVER", "VECTORS", "ELEMENTS"]
      },
      CENTER: {
        type: "string",
        description: "Coordinate center (e.g., '500@399' for Earth)"
      },
      START_TIME: {
        type: "string",
        description: "Start time for ephemeris (e.g., '2023-01-01')"
      },
      STOP_TIME: {
        type: "string",
        description: "Stop time for ephemeris (e.g., '2023-01-02')"
      },
      STEP_SIZE: {
        type: "string",
        description: "Step size for ephemeris points (e.g., '1d' for daily, '1h' for hourly)"
      },
      QUANTITIES: {
        type: "string",
        description: "Observable quantities to include (e.g., 'A' for all, or '1,2,20,23' for specific ones)"
      },
      OUT_UNITS: {
        type: "string",
        description: "Output units for vector tables",
        enum: ["KM-S", "AU-D", "KM-D"]
      }
    },
    required: ["COMMAND"]
  }

• src/index.ts:533-536 (registration)

  Brief registration of 'jpl_horizons' tool in the tools/manifest API response with id 'jpl/horizons'.

    name: "jpl_horizons",
    id: "jpl/horizons",
    description: "JPL Horizons - Solar system objects ephemeris data"
  },

• src/index.ts:1897-1932 (helper)

  Dynamic import and dispatch logic in handleToolCall for JPL tools: imports `./handlers/jpl/horizons.js` (endpoint='horizons') and executes its default export handler function with the provided arguments.

    // Extract the JPL API endpoint name
    const endpoint = internalToolId.split("/")[1];
    serverInstance?.sendLoggingMessage({
      level: "info",
      data: `JPL Endpoint: ${endpoint}`,
    });
    
    try {
      // Dynamic import for JPL handlers using the original slash format path
      serverInstance?.sendLoggingMessage({
        level: "info",
        data: `Importing handler module: ./handlers/jpl/${endpoint}.js`,
      });
      const handlerModule = await import(`./handlers/jpl/${endpoint}.js`);
      
      // Try to find the handler function in various export formats
      const handlerFunction = handlerModule.default || 
                             handlerModule[`jpl${endpoint.charAt(0).toUpperCase() + endpoint.slice(1)}Handler`] ||
                             handlerModule[`${endpoint}Handler`];
      
      if (typeof handlerFunction === 'function') {
        return await handlerFunction(args);
      } else {
        throw new Error(`Handler for ${endpoint} not found in module`);
      }
    } catch (error: unknown) {
      const errorMessage = error instanceof Error ? error.message : String(error);
      return {
        content: [{
          type: "text",
          text: `Error executing JPL tool '${toolName}': ${errorMessage}`
        }],
        isError: true
      };
    }
  }

• src/index.ts:2142-2148 (registration)

  Global MCP tool registration for 'mcp__jplhorizons' that delegates to handleToolCall('jpl/horizons', args).

  registerGlobalTool('mcp__jplhorizons', async (args: Record<string, any>) => {
    serverInstance?.sendLoggingMessage({
      level: "info",
      data: `MCP JPL Horizons called with args: ${JSON.stringify(args)}`,
    });
    return await handleToolCall('jpl/horizons', args);
  });