An equatorial launch complex offers the opportunity to decrease the amount of fuel the rockets need to reach geosynchronous orbits — often the preferred location for satellites — by as much as 20 percent or more, lowering the cost of each launch. Boeing, Lockheed Martin and Vector are interested in the cost savings Alcantara may offer to launch satellites.
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Rocket fuel is cheap compared to the cost of the rocket, much less than 20%. And then there is the cost and time to transport the rocket to Brazil.
The issue is not the cost of the fuel, the issue is that you can put a bigger payload up with the same rocket if you launch from the equator. Transporting the rocket to Brazil is cheap when the alternative is using a bigger rocket.