A ship moving at .90c is moving at 90% of the speed of light. This is an incredibly high speed, and would result in a significant amount of time dilation and length contraction according to Einstein's theory of special relativity.
The ship is 100ft long. This is a relatively small length compared to the speed at which it is traveling. At .90c, the ship would appear to be shorter than 100ft to an outside observer due to length contraction.
The high speed of the ship would create a distortion in the fabric of space-time, creating a wake of gravitational waves. These waves would be more intense the faster the ship is moving, and would eventually dissipate as the ship slows down.
If the ship collided with a planet, the impact would be catastrophic due to the high speed and mass of the ship. The planet would experience a massive explosion and the ship would likely be destroyed as well.
A ship moving at .90c represents a significant advancement in technology and understanding of physics. It also raises important questions about the implications of traveling at such high speeds, such as time travel and the possibility of exploring distant parts of the universe.