So how high can you go in a hot air balloon? Higher than you might expect. Certainly high enough that it's nice to be able to close the canopy and stay in a sealed, heated, pressurized space. In case of a loss of cabin pressure, oxygen masks will be released from the panel by your seat.

Suppose, however, that this is not just an ordinary balloon. Suppose that once you're as high as the balloon can take you, you turn a small brushed chrome switch. Through the plexiglass canopy top you see the balloon collapse in a compilcated feat of origami too fast for the eye to follow into a small package which is reeled in and stowed behind the cabin. Now you are falling.

There is a small mechanical sound as a set of pumps start feeding fuel to the SCRAMjets. The engines jerk and sputter at first; they don't like to operate at low speeds. Fortunately, you're falling fairly fast now. In a moment the engines start thrusting. You accelerate rapidly, first straight down, then through a high G turn and upwards again.

In a few minutes you're high enough that the jets become starved for air. This isn't a problem; a secons set of pumps starts injecting liquid oxygen. Now you're in a rocket, and shortly you've left the atmosphere behind entirely and are in orbit around Earth.

Can you go higher? Where can you go from here?

Once you're in orbit, it's not too dificult to rendezvous with anything else in low earth orbit. A satellite perhapse, or a space station. Maybe you would like to visit the ISS.

If you've packed supplies for a few days, you could head for the moon. If you're prepared for a longer journey, maybe even another planet. Mars? Saturn?

If it turns out that this is a really unusual hot air balloon, and has some even more exotic equipment on board, you might be able to go much farther.

Of course, you can also choose to enjoy the view for a while, and then come back down.