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twice as fast as it would if the rocket were just a single stage.
    Tsiolkovsky was right on the money with his multistaging idea, which proved to be crucial for the mighty
Saturn V
rockets that carried the first human beings to the Moon in 1969. Without staging, the
Saturn V
wouldonly have been able to muster a delta-
v
of around 5,900 m/s (19,300 ft/s)—insufficient to get it to orbit, let alone the Moon. The
Saturn V
made use of so-called “serial staging,” where stages are burned and ejected one after the other. The other variant is “parallel staging,” where two or more of the stages are burned simultaneously and then jettisoned. The Space Shuttle’s solid rocket boosters are an example of parallel staging.
Atmospheric re-entry
    It’s not just getting into space that’s difficult. Getting back down again is no cakewalk either. The main problem is the heating effect caused as the spacecraft re-enters Earth’s atmosphere. A tragic demonstration of just how deadly this can be was the destruction of the US Space Shuttle
Columbia
on re-entering Earth’s atmosphere on February 1, 2003. Damage sustained to the shuttle during launch allowed hot gases to melt the structure supporting its left wing, causing the spacecraft to break apart killing all seven astronauts on board. Heating during re-entry is due to compression of the air in front of the spacecraft. It is the same effect that makes a bicycle pump get hot as the air inside is compressed. When the spacecraft comes in from orbit at a speed of over 7,000 m/s (23,000 ft/s) it literally squashes a layer of air in front of it, heating it to 1,600°C (3,000°F)—hot enough to melt iron. The Apollo spacecraft returning from the Moon were traveling even faster, heating their exteriors to 2,800°C (5,000°F). Just as wellthese spacecraft were expendable. They consisted of a conical capsule, the blunt wide base of which hit the atmosphere to spread the force of re-entry (the deceleration could reach up to 7G, making the astronauts feel seven times as heavy as they do at Earth’s surface). The base was coated with a heat shield to prevent the rest of the craft from melting. Apollo’s heat shield was an ablator—a material that isn’t totally impervious to heat but instead burns very slowly, charring until pieces break off, carrying heat away and exposing a fresh layer of shielding beneath. Parachutes then deliver the capsule to a soft landing. For Apollo an ablative heat shield was fine because the spacecraft were not re-usable. But the Space Shuttle was. So a new heatshield system was designed for it using heat-resistant foam tiles that cover its underside. Unlike Apollo’s tough shield, which was concealed during launch, the shuttle’s tiles are fragile and exposed—and this proved to be
Columbia
’s downfall.
Space tourism
    Until very recently, traveling into space was the preserve of a select few professional astronauts. But space tourism is about to become a reality. British entrepreneur Richard Branson’s Virgin Galactic company is offering to carry members of the public into space for a cool $200,000. Virgin Galactic’s spacecraft is called
Space-ShipTwo
. The prototype,
SpaceShipOne
, won the Ansari X Prize in 2004 for the first private manned space launch.
    Unlike Apollo and the Space Shuttle,
SpaceShipTwo
does not go all the way to orbit. Instead it flies on a so-called suborbital arc, crossing the boundary into space at an altitude of 100 km (62 miles) and peaking at 110 km (68 miles) above the planet’s surface before dropping back to Earth. The passengers on board enjoy about six minutes of weightlessness at the top of the trajectory. As this is not an orbital flight the speeds involved are much lower. Branson’s rocket delivers a delta-
v
of about 2,000 m/s (6,500 ft/s). It doesn’t take off from the ground, but instead climbs into the sky slung beneath a jet aircraft.