How to Destroy the Universe (8 page)

Newton's theory predicted that the minimum speed needed for a rocket to achieve a circular orbit around Earth is around 7,800 m/s (25,500 ft/s)—quite quick. In fact, the speed of the orbit itself is just part of the equation. After adding in air resistance, the energy spent climbing out of Earth's gravitational field and other losses, the speed needed to get to orbit is actually more like 9,400 m/s (30,800 ft/s).

Imparting this much speed to a rocket is no mean feat. But Konstantin Tsiolkovsky came up with a neat trick to make life easier for the engineers—multi-staging. His idea was for the rocket to shed weight as it flew by jettisoning sections of itself that had served their purpose, such as empty fuel tanks. For example, his equations showed that for a rocket of fixed body mass and fuel load, and carrying a payload that makes up 0.1 percent of the total launch mass, splitting the rocket into three stages (each weighing 10 percent as much as the stage below it) would leave the payload ultimately traveling 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
would
only 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.

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 well
these 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.

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. At an altitude of 16 km (10 miles), the rocket is released—rather like an air-launched missile—and then fires its engine to take it into space.

The low speeds mean there's negligible heating when the spacecraft re-enters the atmosphere. No heat shield is needed and the G-forces are far less traumatic. Like the shuttle,
SpaceShipTwo
has wings to enable it to glide down to a controlled landing on a runway. Branson has stated that the ticket price is expected to fall dramatically after the first few years of operation and may ultimately drop as low as the cost of a luxury holiday on Earth. If that happens then we may well get to spend a few minutes in outer space.

• Deadly discharge

• Electric current

• Electrical resistance

• What is lightning?

• Where to shelter

• Out in the open

• What are the odds?

It is said that lightning never strikes in the same place twice. Tell that to Pennsylvania man Don Frick who in 2007 proved the pundits wrong when he was struck by lightning 27 years to the day after first being hit by this awesome force from the heavens. Amazingly, he survived again—quite an achievement when you're tangling with up to a billion volts of electricity and temperatures nearly six times hotter than the surface of the Sun.

Lightning strikes Earth 50 times every single second. In the US alone, lightning strikes cause damage estimated at $4–5 billion and kill 90 people annually. Each
strike produces electrical currents measuring tens of thousands of amps, and a peak power of a terawatt: 1,000 billion watts, or about twice the rate of electricity consumption of the entire United States. The temperature around each strike reaches 30,000°C (54,000°F), causing the air to expand at supersonic speed to generate the ominous thunderclap that warns of the oncoming storm.

Lightning is the sudden discharge of electricity from a storm cloud down to the ground—or to another storm cloud of opposite electric charge. Charge is the fundamental property of electricity and is measured in coulombs, C, after the pioneering French physicist Charles-Augustin de Coulomb. Electric charges create electric fields, which enable the charges to interact with one another over distance. The charges can be either positive (+) or negative (-) and the electric fields they set up cause the charge carriers to either repel one another, as is the case for two “like” charges (++ or--), or to attract, which happens when the charges are opposite (+-).

The most common charge carrier is a subatomic particle called the electron. It is normally found in the atoms from which all materials are made, where large numbers of electrons orbit around each atom's nucleus and
determine, among other things, the atom's chemical properties—how it reacts with other atoms. Each electron carries a tiny negative charge equal to −1.6 × 10
^−19
C. That is, −1.6 divided by a 1 with 19 zeroes after it. In some materials, however, electrons leak from the atoms and slosh around between them to form a “sea” of electric charge carriers. Materials in which this happens are known as conductors, of which metals are a prime example. The surplus of electrons inside a conductor means that electric charge is free to move around inside it. And this can set up what's called an electric current. Current is a measure of the amount of electricity flowing through a conductor, and is measured in amps, after the French mathematician Andre-Marie Ampère. An amp is defined as the amount of electric charge (measured in coulombs) flowing per second past a given point in a conductor. Because the charge on the electron is so tiny a current of 1 amp corresponds to a flow of 6.2 × 10
¹⁸
(6.2 billion billion) electrons per second.

Current doesn't flow of its own volition but moves to or from concentrations of electric charge. This happens because of the way charges attract or repel one another. So a negatively charged electron will tend to drift away from a concentration of negative electric charge (because like charges repel) and move toward an area
of positive charge (because opposite charges attract). This is referred to as an “electromotive force,” or emf. Sometimes also known as a “potential difference,” it is measured in volts—after the Italian physicist Alessandro Volta. Batteries are a source of emf.

How much current flows through a particular conductor, say a piece of wire, when it is connected up to a battery is given by another property known as electrical resistance. This is the opposition that a current experiences as it tries to flow through the conductor, as the electrons jostle and squeeze between the lattice of atoms from which it is made—rather like commuters at a busy railway station. Resistance is particular to different materials and is measured in ohms, after the 19th-century German physicist Georg Simon Ohm. He also came up with a mathematical relationship, now known as Ohm's law, revealing that resistance is simply given by dividing the voltage applied to a conductor by the current that this voltage produces.

Resistance is also the reason lightbulbs work. The resistance of the filament inside the bulb causes it to get hot—as the electrons all trying to squeeze through it rub against one another and against the atoms in the material. The rate at which heat and light are generated is measured in watts (after Scottish engineer James Watt) and is just given by the current times the resistance of the filament squared. Light-bulb filaments
generally have a high resistance to maximize the amount of energy they give off.

Lightning happens when the undersides of clouds acquire a large quantity of negative charge, building an emf of hundreds of millions, and in some cases even billions of volts between the underside of the cloud and the ground. The reason this happens is thought to be all down to ice crystals. These tend to gather positive charge, and are then carried to the top of the cloud by swirling currents within it. At the same time, heavier pieces of ice and water sink to the bottom of the cloud, carrying with them negative charges. This process of separation induces a massive negative electrical charge on the underside of a storm cloud. As this charge grows, it attracts positive charges, causing an equal but opposite charge to gather on the ground below. The high electrical resistance of the intervening air stops the charges from coming together and canceling out—until, that is, the accumulated charge gets so great that it overcomes the resistance in one almighty discharge.

The air's resistance breaks down because of a phenomenon called ionization, where the huge electrical forces literally rip electrons from their parent atoms, gradually turning the air into a conductor. The process begins gradually. Tendrils of negatively ionized air called
“leaders” begin to snake their way down from the bottom of the thundercloud toward the ground. At the same time, on the ground, the storm bashes electrons from atoms to make positively charged ions, which also begin wending their way upward from high points such as trees, telegraph poles—and people. When a leader from the cloud and one from the ground finally meet, current can flow and lightning strikes.

The first thing you might know about a storm on the way is the distant rumble of thunder. Sometimes you can see flashes of lightning, too. Light travels much faster than sound in air (300,000,000 m/s compared with 343 m/s), and counting the number of seconds between seeing the flash and hearing the rumble is a good measure of the distance between you and the storm—about a kilometer for every three seconds. Normally you can start to hear thunder when the storm is about 16 km (10 miles) away—the bad news is this means you're already within range of the lightning. If you're able to, the safest course of action is to get indoors. Don't think you're safe under shelters and canopies. Get inside a building, where a lightning strike should be conducted safely down to the ground. But being inside doesn't make you totally safe. Lightning can still be transmitted into your home via the electricity supply. So do not use any electrical equipment
during a storm—most indoor injuries from lightning are sustained by people talking on the phone. If you're away from buildings during a storm, a different strategy is needed. If your car is near then get inside and shut the door. The rubber in your tires will do little to stop an electric current that's powerful enough to make it down through hundreds of meters of thin air. But the metal bodywork, so long as you're careful not to touch it while you're in there, should protect you—acting like a “Faraday cage.” British physicist Michael Faraday showed in 1836 that the electric charges within an enclosure made of conducting material will always cancel out—and if there are no charges there can be no dangerous currents. It's the same mechanism that protects you if you're in a plane that gets struck by lightning. The average commercial jet aircraft gets struck about once per year—just as well its aluminum skin is designed to withstand currents of up to 200,000 amps.