How fast are the CubeSats travelling?

These miniature Satellites are currently whizzing around our planet in different Low-Earth orbits (orbiting between 200km and 2000km above the surface of the earth). But how fast are they truly going? This worksheet in conjunction with the spreadsheet will help to calculate the velocities, and then understand what’s going on.

What is CubeSat saying?

Open up the Excel spreadsheet and you will be faced with the numbers 1-35 on the top (for the 35 measurements you are about to take), followed by some other headings which are explained below:

Longitude: When you look at a globe there are lines going up and down them. These are called lines of longitude. They measure how far EAST and WEST you are of the Greenwich meridian (an imaginary line marking 0 degrees), which runs through Greenwich in London,these lines are measured in degrees and not meters and has to do with the Earth being this rounded shape. Thetricky bit to understand is that the lines cross at the poles, so if you are near the poles the lines are closer together. Technically this means if you are on the North Pole you can run around in a circle and run across all lines of longitude, and technically run round the whole world.

Still a bit confused? Here is a diagram to help; it even has lines of LATITUDE on there too, which is explained below.

Figure 1: Up and down lines? Longitude. Lines that go all the way around? Latitude.

Latitude: The Equator, the tropics, all horizontal lines that go ‘across’ the Earth. This value will only be recorded to show you whether the satellite is in the Northern Hemisphere, or the Southern Hemisphere.Just for a bit more angles, these lines are measured as 90˚ North and South, or can be negative and positive numbers.

Difference in Longitude: This is the difference between the 2 points of the satellite that you have measured, in degrees, in longitude.

Difference in Latitude: This is the difference between 2 points of latitude, also measured in degrees.

Angle between 2 points (rad): Due to the 3D objects we are using (like the Earth) which have 3 different types of co-ordinates (think not only x and y, but add z pointing out the page) the computer will calculate the angle between the points. The ‘rad’ part doesn’t just mean it’s awesome, but that’s the units, it’s like degrees but different.[

Physical Distance: Since the satellites are going in one massive circle, we can’t use the maths we have to use for straight line travelling, as this is the curved paththey travel. Similar to the straight line distance from your house to school is shorter than the one you have to walk. The distance the satellite has to ‘travel’ is further than the distance between the two measuring points.

Orbital Velocity: This is the number we will be looking at. This is how fast our satellite is travelling from one place to the other; an average of all your readings should give a pretty good idea of how fast it travels around the Earth.All this is in km/s. That’s how many 1000meters per second it travels. Pretty quick!

Time Stamp: You need to record the hour, minute and second that your measurement took place to ensure the greatest level of accuracy.

Time between measurements: This is the time between measurements in seconds; this allows the Orbital velocity to be calculated in km/s.

You have to enter the altitude of the satellite and the radius of the Earth ADDED TOGETHER, (don’t forget to look at units!)you will need to find out what the radius of the Earth is.

Now that’s all explained, follow these instructions to get started:

  • Go to:
  • You’ll be presented with a web page which looks like this:
  • Below the image is an ever changing sequence of numbers. To get an accurate value, make sure the spreadsheet is open, and press ‘printscreen’ on your keyboard and paste the image into paint.
  • Look at this image and write down the Longitude, Latitude, and the Time Stamp values.
  • Then go back to the webpage and repeat.
  • Take measurements every minute or so, and have a look at the variation of speeds.

Just an important mathematical side note, only put the first number out of the 3 for Longitude…. Or science breaks, and that’s just not fun to fix. Eg, 211˚34’17”W – use just 211.

So, Onto the Questions.

  1. What is your average orbital velocity? (HINT: There are 2 ways of working this out, one with the graph, one without…)

Answers: between 7km/s and 8km/s is normal.

  1. Knowing the Earth takes 24 ¼ hours to rotate, and using your researched radius of the Earth, how fast does the Earth rotate?

(HINT: Calculate the circumference of the Earth and remember there are 3600 seconds in an hour.)

Answers: Circumference = 2xπxr = 2xπx6500 = 40840.7km

Speed = distance/time = 40840.7/(3600x24.25) = 0.47km/s

Accept 0.5km/s

  1. With this number in mind, how many times will the satellite orbit the Earth in one Earth orbit (1 day)?

Answers: in one day satellite travels for 86400seconds with a speed between 7 and 8km/s.

Distance = speed x time = (604800km<distance<691200km)

Distance/Earth Circumference gives number of times orbited in a day = (14.8<number<16.9)

  1. How many times would this be in a year?

Answers: (5408<number<6172)

Group Discussion:

  • Did you notice the graphs under your table? They were plotting the data as you were entering it.
  • How does the path of the satellite changes?
  • Plot these changes on a World map to track the path of your satellite.
  • Which countries has it passed over whilst you were tracking it?
  • Has somebody else got different values for Orbital Velocity? Why might this be?
  • Put all of your data together to get the most accurate path. How does this change the Orbital Velocity?