---
id: af4afb223120f7348cdfc9fd
title: Map the Debris
challengeType: 5
---

## Description
<section id='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 <code>{name: 'name', avgAlt: avgAlt}</code>.
You can read about orbital periods <a href="http://en.wikipedia.org/wiki/Orbital_period" target='_blank'>on Wikipedia</a>.
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 km<sup>3</sup>s<sup>-2</sup>.
Remember to use <a href='http://forum.freecodecamp.org/t/how-to-get-help-when-you-are-stuck/19514' target='_blank'>Read-Search-Ask</a> if you get stuck. Try to pair program. Write your own code.
</section>

## Instructions
<section id='instructions'>

</section>

## Tests
<section id='tests'>

```yml
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>.'');'

```

</section>

## Challenge Seed
<section id='challengeSeed'>

<div id='js-seed'>

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

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

</div>



</section>

## Solution
<section id='solution'>


```js
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}]);

```

</section>
