**Flight Incorporated has just recently posted these advertisements:**

> 
> Buying Fuel for High Prices!
> ----------------------------
> 
> 
> Buying fuel for our spaceships  
> 
>  Fuel in possession/fuel needed in gallons: $\Delta = 1000/\infty$  
> 
>  Current Bank Balance: $100,000,000,000.00  
> 
> 
> 
> Required Balance = $\infty$ as fuel required is infinite  
> 
>  We will pay 1 gram of AN:92 per gallon of fuel.
> 
> 
> 

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> 
> Oxygen needed!
> --------------
> 
> 
> We need compressors... and oxygen tanks! You will be paid in brass-plated troughs with your name on a plate. Under the plating is a layer of plastic. Engraved on the bottom is our company name and logo.
> 
> 
> 

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The following was posted on Flight Inc.'s website.

> 
> Pilot's Guide
> -------------
> 
> 
> Remember to strap in your seat belts! Mass and speed increase simultaneously. Time is dilated. Communications will be offline, as no form of communication travels fast enough. Prepare for a breathtaking tunnel view.  
> 
>  Time to destination is: $cyears=year$  
> 
>  $C$ is the undisputable speed limit, proposed by the maker of $e=mc^2$
>  What we're doing is impossible, but that's never stopped us!
> 
> 
> 

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> 
> Technical Guide
> ---------------
> 
> 
> Classical engine runs off of hydrogen. Liquid fueled rocket needs two tanks for propellant and oxidizer. System cannot be distorted by mass increase.
> 
> 
> 

What do they need the fuel for and what are they being paid in?

Note: No knowledge of science fiction is required to solve this.
Tear every line apart :)

> 
> Trouble deciphering our ads?
> ----------------------------
> 
> 
> AN is an abbreviation for something related to materials. (Atomic Number)
>  Basic science knowledge is required. We don't buy from people who don't know science. We love the periodic table... Who cares about speed limits, even those universe-wide?
> 
> 
> 

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> 
> Hints
> -----
> 
> 
> AN is an abbreviation for Atomic Number.
>  This puzzle is related to Einstein, relativity, and classical physics.
>  The speed that they are trying to go to (or near it) does weird things to a spacecraft.
> 
> 
> 

Huge Spoiler:
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> 
> They are trying to travel at the speed of light. The oxygen is related to combustion and the hydrogen is the fuel.
> 
> 
>