[mixmax]

A few reasons:

- They only make liveburns a few times a year.

- They experiment with different cheap fuels. One rocket ran on rubber and actually worked quite well.

- They're quite known around Denmark, so they get unbelievable prices on fuel from companies that want to be associated with the project.

[jigg4joe]

It would be interesting to see what could be accomplished with alternative fuels. Although, the exhaust from something like rubber is probably not so good for the environment? Best of luck to them, thanks for the response.

[bigiain]

Do you really think the shuttles solid fuel booster's chemical composition was chosen for it's environmental friendliness?

[electromagnetic]

Depends on the type and the additives. If natural, then it's probably not all that bad if it burns cleanly. Although I'm guessing it's more likely to be synthetic, which puts you into problems. But then even that has to be taken with a grain of salt. Sulphur Dioxide emissions from vulcanized rubber might actually be beneficial to the environment if it's released in the stratosphere.

[ars]

That is utter nonsense!

There is not the slightest difference between natural and synthetic fuels. Either one can be toxic or not.

And good luck even defining "natural". Crude oil is natural - so I guess it gets a free pass? Uranium is natural too.