freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/intermediate-algorithm-scripting/map-the-debris.english.md

id	title	challengeType
af4afb223120f7348cdfc9fd	Map the Debris	5

Description

Return a new array that transforms the elements' average altitude into their orbital periods (in seconds). The array will contain objects in the format {name: 'name', avgAlt: avgAlt}. You can read about orbital periods on Wikipedia. The values should be rounded to the nearest whole number. The body being orbited is Earth. The radius of the earth is 6367.4447 kilometers, and the GM value of earth is 398600.4418 km³s^-2. Remember to use Read-Search-Ask if you get stuck. Try to pair program. Write your own code.

Instructions

Tests

tests:
  - text: '<code>orbitalPeriod([{name : "sputnik", avgAlt : 35873.5553}])</code> should return <code>[{name: "sputnik", orbitalPeriod: 86400}]</code>.'
    testString: 'assert.deepEqual(orbitalPeriod([{name : "sputnik", avgAlt : 35873.5553}]), [{name: "sputnik", orbitalPeriod: 86400}], ''<code>orbitalPeriod([{name : "sputnik", avgAlt : 35873.5553}])</code> should return <code>[{name: "sputnik", orbitalPeriod: 86400}]</code>.'');'
  - text: '<code>orbitalPeriod([{name: "iss", avgAlt: 413.6}, {name: "hubble", avgAlt: 556.7}, {name: "moon", avgAlt: 378632.553}])</code> should return <code>[{name : "iss", orbitalPeriod: 5557}, {name: "hubble", orbitalPeriod: 5734}, {name: "moon", orbitalPeriod: 2377399}]</code>.'
    testString: 'assert.deepEqual(orbitalPeriod([{name: "iss", avgAlt: 413.6}, {name: "hubble", avgAlt: 556.7}, {name: "moon", avgAlt: 378632.553}]), [{name : "iss", orbitalPeriod: 5557}, {name: "hubble", orbitalPeriod: 5734}, {name: "moon", orbitalPeriod: 2377399}], ''<code>orbitalPeriod([{name: "iss", avgAlt: 413.6}, {name: "hubble", avgAlt: 556.7}, {name: "moon", avgAlt: 378632.553}])</code> should return <code>[{name : "iss", orbitalPeriod: 5557}, {name: "hubble", orbitalPeriod: 5734}, {name: "moon", orbitalPeriod: 2377399}]</code>.'');'

Challenge Seed

function orbitalPeriod(arr) {
  var GM = 398600.4418;
  var earthRadius = 6367.4447;
  return arr;
}

orbitalPeriod([{name : "sputnik", avgAlt : 35873.5553}]);

Solution

function orbitalPeriod(arr) {
  var GM = 398600.4418;
  var earthRadius = 6367.4447;
  var TAU = 2 * Math.PI;
  return arr.map(function(obj) {
    return {
      name: obj.name,
      orbitalPeriod: Math.round(TAU * Math.sqrt(Math.pow(obj.avgAlt+earthRadius, 3)/GM))
    };
  });
}

orbitalPeriod([{name : "sputkin", avgAlt : 35873.5553}]);