Written by Andrea I. Jara 1º Bachillerato 2 IES Julio Caro Baroja Fuenlabrada Madrid Spain

3. If fitted with surveillance equipment, it can keep an eye on war or disaster zones, or it can carry communications technology to link people cut off from the world by, say, a catastrophe that takes out a bunch of cell-phone towers. Eel-shaped for a reason, the STS-111 works through an interchange of gases. In the head, there's a pouch of helium in an envelope of regular air. A pouch in the three back sections contains ethane for power. As the eel rises, the air surrounding the pouches is vented so the helium and ethane can expand. This means the vehicle should be able to ascend and descend without bursting. BACK

4. A ride like this one doesn't come cheap: the estimated price is $2 million to $3 million.