The next half of the title literally says it's one of the largest and brightest globular clusters.

Half a million stars is incredibly large for a globular cluster. I guess context is hard.

Eh, there are other electric engine options that are better than ion engines, such as plasma engines or mass drivers. And if power isn't a limiting factor the ultimate in propellent efficiency is a photon rocket, aka a light bulb. No need to carry propellent, though you need 300 megawatts of photons to get a pathetic newton of thrust, so whatever reactor is powering it will need a shit ton of fuel. Though if you're using a laser array to push a mirrored sail that power plant can remain on the ground.

Yeah it was awesome, I hadn't known they had a shuttle it so was a wonderful surprise when the movie faded revealing the real craft on the other side of the glass.