In Space, No One Can Hear Your Nitrocellulose Explode

Copenhagen Suborbitals has been working toward the goal of suborbital spaceflight for almost 2,000 days now and we have learned and tried so much. The project is working a classical trial-and-error process in most areas, and technologies or solutions found in one place justify or kill others.

This past week we had to finally kill an idea that has actually been flagged as “GO” since the very beginning and has been installed and used numerous times (however, not in its correct environment).

Nitrocellulose

This very cute-looking explosive cotton widely used for all sorts of mines, grenades and New Year’s party-tricks was chosen by us to create instant over-pressure in dedicated chambers for opening lids and deploy parachutes. I was actually shocked to see that our specific use for this is actually mentioned on Wikipedia – especially now when we know it doesn’t work – in vacuum.

I tested the use of nitrocellulose with our certified pyro-technicians Niels Johansen and Claus Nørregaard already back in 2009 and it was since installed in all my spacecrafts and also used in the latest Sapphire rocket launched this summer.

The video below shows previous tests using nitrocellulose.

Nitrocellulose contains its own oxidizer and burns so rapidly that we have never observed any damage to its surroundings while creating large amounts of gas doing the trick we were looking for. This simple solution simply overruled any complex mechanical idea and even deleted the need for gas-containers, valves and inlets systems.

Nitrocellulose was beautiful!

One of the things that did not work during the Sapphire mission was the deployment of the nose-cone in altitude 8 km and speculations began if nitrocellulose actually worked in a low-pressure environment where deployment of capsule ballutes are required for a successful mission and basic survival.

Some of the more brainy people at Copenhagen Suborbitals did vouch for nitrocellulose would likely not work but the debate continued and damnit if suddenly the idea would be labeled useless – especially since I have based the deployment designs on this and we actually did fly it before.

To finally end all discussions Jonas from CS – working at the Danish Technical University, Space Department – created a test of nitrocellulose in vacuum documented in the video below. It pretty much speaks for itself and I had to take the humiliating beating and finally kill one of my darlings, permanently.

What basically happens is that the intermediate chemical reactions and energy used to continue the process it rapidly dispersed to its surrounding in vacuum and the reaction in the cotton slows down or stops.

So, not only may this be the reason why the nosecone of the Sapphire was not correctly jettisoned – even though we did measure some kind of reaction but this means that I have to come up with a new way to create over-pressure in my parachute chambers for parachute deployment – for both the full scale capsule and the scaled capsule for the HEAT2X-mission next summer.

The down-scaled 2X-capsule with little room for complex systems deploying chutes. Claus Nørregaard “exporting” airbag devices in the background. Image: Kristian von Bengtson

For the full scale capsule I intent to go with a solutions widely used by the pros. The solutions is simply using a gas container providing the pressure such as the once I use for the uprighting bags and in my kitchen for making club sodas.

There is not room for such solutions in the scaled capsule (image on the right) so we debated different stand-alone solution replacing the cotton and finally Claus Nørregaard presented the idea of using the device expanding air-bags.

There are many reason why I like this idea very much. First of all, these are “almost” off the shelf components made with the highest standards of the automobile industry and second it requires only 12 volts (like our igniters in cotton) turning the interior solid propellant into gas – very rapidly.

Airbag solid propellant device. Nitrogen gas in rapidly dispersed through side port holes. Image: Kristian von Bengtson

We obviously need to test such a device in a vacuum chamber to see if  it does not become damaged manically in vacuum – but also to see if the chemical reaction works. The chemistry involved in this process is highly toxic so we need to handle all this with care and respect.

For the scaled down 2X-capsule the air-bag device will be stored inside the parachute-chamber and ignited by the internal electronics when needed. No added gas-containers, no inlet-pipes or mechanical complexity. If it works it is really a perfect substitute for nitrocellulose.

Since it contains a solid propellant I doubt that a few minutes in vacuum will create out-gassing problems and the fast chemical reaction will work.

But hey – Apparently I have been very certain about other technologies before – and like most politicians I will revoke my statement later if it turn out not to make any sense.

Ad Astra
Kristian von Bengtson