Warp Drives are solutions of the Einstein Field Equations that allows superluminal travel within the framework of General Relativity. There are at the present moment two known solutions: The Alcubierre warp drive discovered in $1994$ and the Natario warp drive discovered in $2001$. The major drawback concerning warp drives is the huge amount of negative energy able to sustain the warp bubble.In order to perform an interstellar space travel to a "nearby" star at $20$ light-years away in a reasonable amount of time a ship must attain a speed of about $200$ times faster than light.However the negative energy density at such a speed is directly proportional to the factor $10^{48}$ which is $1.000.000.000.000.000.000.000.000$ times bigger in magnitude than the mass of the planet Earth!! Although the energy conditions of General Relativity forbids the existence of negative energy the Casimir Effect first predicted by Casimir in $1948$ and verified experimentally by Lamoreaux in $1997$ allows sub-microscopical amounts of it.We introduce in this work a shape function that will low the negative energy density requirements in the Natario warp drive from $10^{48} \frac{Joules}{Meter^{3}}$ to $10^{-7} \frac{Joules}{Meter^{3}}$ a low and affordable level. However reducing the negative energy density requirements of the warp drive to arbitrary low levels works only for empty bubbles not for bubbles with real spaceships inside because the positive mass of the spaceship exerts over the negative mass of the bubble a gravitational repulsive force and a spaceship with a large positive mass inside a bubble of small negative mass destroys the bubble.According to Lobo and Visser we can reduce the negative energy density of the warp bubble only to the limit when the negative energy becomes a reasonable fraction of the positive mass/energy of the spaceship.and no less otherwise the bubble is destroyed.The analysis of Lobo and Visser must be taken in account when considering bubbles with real spaceships inside otherwise the warp drive may not work.We reproduce in this work the analysis of Lobo and Visser for the Natario and Casimir warp drives.The work of Lobo and Visser is the third most important work in warp drive science immediately after the works of Alcubierre and Natario and the Lobo-Visser paper must also be considered a seminal paper like the ones of both Alcubierre and Natario.