A closer view of the Discovery II upper shuttle cradle complete with shuttle. I wondered when I saw this ship what I would call it if I owned one, and came up with the name you see on the ship and image title. Big, bulky and very capable, the shuttle is powered by a gravity manipulation engine — more popularly known as an M-Grav. This means it can't operate except in the vicinity of a decent sized astronomical body like a planet or a moon, because otherwise the M-Grav can't produce any significant effect. That's the disadvantage of the M-Grav; the huge advantage is that it requires very little power to run so the shuttles can transport 100 metric tonnes of cargo or, depending how it is fitted out, over 200 people, and do it on nothing but a rechargeable battery weighing less than half a tonne. The propulsion battery can still power the drive for more than eight days of continuous operation on one charge. As Discovery II has two powerful fusion reactors recharges can be performed in less than an hour.