What is the big deal with Isp?

One of the most important measuring factors of a rocket engine is the Isp (Specific Impulse). Isp is essentially how fast the exhaust is coming out of your propulsion system, which correlates to how hot that exhaust is (the faster it is expelled the higher the temperature). The hotter the exhaust of a rocket the better. Chemical rockets are in the range of the thousands of degrees (around 10,000 degrees), our engine, on the other hand, expels exhaust in the millions of degrees.

A chemical rocket’s Isp is really fixed by the chemical reaction it produces. Chemical reactions have limits on how hot they get and how long they burn. The VASIMR® engine is electric, and therefore those limitations do not apply. Our engine is limited only why whatever power source it is getting the electrical energy from (battery, solar arrays, nuclear electric, etc). Depending on where it is getting its power from, will determine, in some ways, what it can do. However, our engine is special in that our Isp is not fixed but variable (This is the ‘VASI’ in “VASIMR”- Variable Specific Impulse). We can achieve variable Isp because we can use multiple types of gases.

So, broken down: Because we can use multiple types of gases (i.e. Argon, Krypton, Hydrogen, Neon, Helium) we can achieve a variable Isp (depending on the gas we use)

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