The purpose of cubesats in general, or this Ardusat in particular? Particular: to have 16 sketches that can be uploaded by random people running in space, all attempting to crash the hypervisor. That, or access the sensors and do fun stuff with it. Purpose of cubesats in general is easy: cubesats are cool!
Is that like the free software thing?
How do you make a profit on free software? Volume!
Seriously, I don't see what "experiments" can be carried out on a cubesat that a) haven't been done yet, b) couldn't be just as easily done from earth or c) the results worked out with some easy theory.
The main and very big advantage of cubesat's is that they are cheap! Very cheap even compared to the more mature big brothers.
Right now a lot of companies and universities are looking into them to use them for programs which would not be able to generate money or simply couldnt be accieved if they needed a 'big' satelite for it.
I for example worked for Stellenbosch University in South Africa, with there cubesat's there will be able to do agricultural measurements from space that potentially could help some of the more underdevelopted countries in Africa with there agriculture.
Also, in my own country (Netherlands) there is a company that is developing a coastal tracking system for ships, something that would not have been possible without cubesat's (
http://www.isispace.nl/cms/index.php/projects/triton-missions)
Also, they are a great way for students to learn about navigation, flightcomputers, reliablilety design etc.
Ans above all, ther plain fun
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