Mars has us tied in knots.

There are a thousand technical challenges to overcome when you want to launch and run a rover on Mars.  Some of these challenges are fascinating.

One that took my interest was the fact that you can’t use duct tape to hold things together in space.

What? Every home-MacGyver knows duct tape is the solution for every problem! And yet, it doesn’t work in space! This unfathomable problem has the knock on effect of NASA having created a special standard for knots that will hold!

 

If you look closely at some of the photos of Perserverence, you can see some of the knots in action.

So why doesn’t duct tape work in space?

Duct tape is a ‘pressure-sensitive adhesive’ which, according to a few experts, relies on pressure to maintain the ‘stick.’  The ‘glue’ is simply a fluid that removes air from between the tape and the surface, and air-pressure basically keeps the tape in place.

A great experiment you can do at home is to open up a ‘dead’ hard drive and remove the platters – be careful NOT to get your fingerprints on surfaces (you will understand shortly).

Stack the platters on top of each other and push them together as hard as possible (you can get fingerprints on the outer platter surfaces).  This will squeeze the air out from between the platters.  If you have time, leave them for a few days to make sure all the air is out.

Now, try to pull them apart.

It will be VERY difficult – unless you got fingerprints on the surface which prevents you getting all the air out.

On Mars it will be very easy!  Because Mars has about 0.6% of the atmosphere as Earth.

A 3.5” hard drive platter is approximately 10cm across.  That’s 3.141*(0.10/2)*(0.10/2) = 0.00785m2.  On Earth, one atmosphere of pressure = 101325N/m.  So, if you have two hard drive platters, squashed together with no air between them, it will take ~0.00785*101325N of force to separate them ~795N.  On Earth, with gravity 9.8m/s2,  you would be able to hang 795/9.8 = 81kg’s from the bottom platter and not be able to separate them.  

BUT on Mars, where one atmosphere is only 681N/m,  you only need 0.00785*681 = 5.3N of force to separate them.  Acceleration due to gravity on Mars is only 3.68m/s2 (it is a smaller planet), so you could hang 5.3/3.68=1.4kg’s from the platter.

This means, your duct tape is 0.017 as effective on Mars as it is on Earth.  Which isn’t very useful at all.

Hence, why NASA scientists tie or bolt everything together. Ties and bolts rely on the friction between the components, which is directly proportional to how hard you tighten a bolt or pull the the string.

Oh yeah –  they also use special string or cable ties, which have a very rough surface, to get the friction up when it is pulled tight!

As I said, fascinating! These are the fun facts that occupy my brain at night! But I love to untie the knots.

 

By Stuart Midgley

Stuart Midgley is DUG's CIO and self-confessed "mad scientist". He holds a PhD in theoretical physics and is a world expert in high-performance computing. Stuart designed and developed the DUG Cool system of immersive cooling technology and was instrumental in the construction of DUG's world-class greenest data centres on earth. He's just as handy behind a BBQ. After all, he owns 17 of them.

DUG