Constant length

Is there some way that I can construct a curve like an elipse and maitain a constant length while deforming the curve to fit another object

You can scale a curve to give it a specific length. Or you can cut off the ends of a long curve to get to a specific length. If you wish to continually deform a curve while maintaining a constant length and have the result of each deformation serve as the input for the next, then I think your only good option is to set up a Kangaroo system with constraints.