Vis-viva orbital speed API

Returns the orbital speed at radius r on an elliptical orbit of semi-major axis a via the vis-viva equation v=sqrt(mu*(2/r-1/a)), validating that r is reachable. Answers 'Speed at perigee/apogee?', 'How fast on this transfer ellipse?'.

Price$0.04per request

MethodPOST

Route/v1/space/vis-viva-velocity

StatusLive

MIME typeapplication/json

Rate limit120/minute

Cache0s public

spaceastronomyvis-vivaorbital-velocityorbital-mechanicsellipseastrodynamicsperigee

API URLhttps://x402.hexl.dev/v1/space/vis-viva-velocity

Integration docs

Example request

{
  "body": "earth",
  "radiusM": 6771000,
  "semiMajorAxisM": 24371000
}

Example response

{
  "body": "earth",
  "mu": 398600441800000,
  "radiusM": 6771000,
  "semiMajorAxisM": 24371000,
  "velocityMs": 10068.8638,
  "velocityKms": 10.06886,
  "interpretation": "Speed at r=6771 km on an a=24371 km orbit is 10.069 km/s."
}

Input schema

{
  "type": "object",
  "required": [
    "radiusM",
    "semiMajorAxisM"
  ],
  "properties": {
    "body": {
      "type": "string",
      "examples": [
        "earth"
      ]
    },
    "mu": {
      "type": "number"
    },
    "centralMassKg": {
      "type": "number"
    },
    "radiusM": {
      "type": "number",
      "examples": [
        6771000
      ]
    },
    "semiMajorAxisM": {
      "type": "number",
      "examples": [
        24371000
      ]
    }
  }
}

Output schema

{
  "type": "object",
  "additionalProperties": true
}