Why does no one ever remember momentum?

If you accelerate a space craft to 100,000 m/s in space, it will forever continue to move at that speed forever unless something slows or stops it.

So, with this reasonable and very provable inference, if a space craft is already going 100,000 m/s, then it’s speed can be counted as zero and be considered then at rest.

Then you give it some gas and accelerate it to 100,000 m/s relative to its beginning speed of zero, and alacazam, the space craft will be moving at 200,000 m/s relative to actual zero.

When you evaluate momentum in relation to general relativity, general relativity becomes the most idiotic crap ever thought up by man. But general relativity sounds good don’t it? Lol