That's not really it. "Speeding up" and "slowing down" are equally easy (or hard). They're both acceleration, just in a different direction. The reason it's go

That's not really it. "Speeding up" and "slowing down" are equally easy (or hard). They're both acceleration, just in a different direction. The reason it's going faster is because it's lower. The lower an orbit, the faster the thing is moving. In order to slow down, you have to accelerate twice (I'm using the term "accelerate" here to refer to "going faster in the direction you're already going"). The first acceleration raises the far side of your orbit. You then have to "climb" up to that new higher orbit. Once there, you accelerate again to raise the low side of the orbit (otherwise you'd pick up all that speed again then "falling" back down to the lower altitude). At the end, you're in a new, higher, orbit, going slower than when you started.