On July 21 2005, there was an attempt to paralyze London’s transport system and kill a large number of people. Mercifully, four bombs planted at three Tube stations and on a bus failed to explode, but the memory of the fatal London 7/7 bombings two weeks before was fresh and security forces were jumpy. With the help of CCTV pictures, the Metropolitan Police mounted a massive manhunt for the would-be bombers.

Intelligence had quickly linked a block of flats in South London with one of the suspects, and it was under surveillance the following morning when 27-year-old Jean Charles de Menezes emerged from the communal entrance and was identified as a possible suspect by the watching ‘Frank’. The undercover soldier thought the Brazilian national resembled one of the suspects caught on CCTV. But Frank was relieving himself and couldn’t video Jean Charles, so no picture was transmitted to Gold Command at police HQ.

The consequences of this ill-timed call of nature would soon prove fatal. Plainclothes policemen followed Jean Charles to Stockwell station, where the young electrician picked up a newspaper and boarded a waiting train. Meanwhile, Gold Command ordered that the presumed bomber should be prevented from entering the Underground system. Three surveillance officers followed him onto the train, swiftly followed by a specialist firearms team.

A volley of shots rang out, eight hitting Jean Charles de Menezes who was killed instantly. The tragedy revealed the existence of a ‘shoot to kill’ policy where an imminent terrorist threat existed, though the Metropolitan Police initially tried to justify the killing by falsely claiming that a warning had been shouted, then further muddied the waters before admitting their mistake the following day. They then issued an apology, but that was scant consolation to the innocent victim’s distraught family.

When: July 22 2005

Where: London, UK

Death toll: One

You should know: Although the Stockwell shooting revealed serious organizational failings within the Metropolitan Police, no individual was ever punished for their part in the unjustifiable killing of Jean Charles de Menezes, though the Met itself was fined under Health and Safety legislation. Thoughtful commentators described Jean Charles as another victim of terrorism, because he died as a result of official over-reaction to the terrorist threat that at times bordered on hysteria.

The National Aeronautics and Space Administration’s rather dull designation of its first space worthy shuttle was OV-102 (for Orbiter Vehicle). But to the wider world it would always be Columbia, pioneer of an entirely new sort of space flight from the USA. NASA launched Columbia for the first time in 1981 and it would go on to fly 27 successful missions.

Tragically, the 28th proved to be its last. After spending 300 days in space, completing over 4,800 orbits of the earth and flying around 200 million kilometers (125 million miles) in a long and honorable career, Columbia would self-destruct. The cause seemed innocent enough – a piece of insulating foam that detached from the external fuel tank during launch and hit the left wing – but the consequences of this near-routine happening proved disastrous for NASA’s unlucky 113th shuttle mission.

Engineers suspected damage to Columbia’s thermal tile cladding, but NASA vetoed a space walk to check on the basis that nothing could be done anyway. It is debatable whether a close- inspection of the damage would have allowed the astronauts or NASA to somehow save the day, but at least it might have given the doomed crew a chance. As it was, re-entry proved to be catastrophic. The holed wing was incapable of withstanding intense temperature as superheated gases entered and destroyed the wing structure, causing the rest of the shuttle to break apart. Horrified observers on the ground saw a fiery smoke trail high in the sky, even as mission control realized that Columbia had been tragically lost.

The second fatal destruction of a shuttle effectively ended the orbiter program. Though a number of further flights were planned and executed, NASA decided that the way forward would be Orion, developed from the successful multiple-stage Apollo spacecraft of an earlier era.

When: February 1 2003

Where: Above Texas, USA

Death toll: All seven crew members

You should know: There was already a peak in Colorado’s Sangre de Cristo Mountains – Challenger Point – named in memory of the previous lost shuttle. It would soon be joined by its immediate neighbor, which became Columbia Point to commemorate the second disaster. The crew were also honored by the naming of the Columbia Hills on Mars, which may one day be visited by their successors in space.

When an EA-6B Prowler aircraft left the Aviano Air Base in northeastern Italy on February 3 1998, it was a routine assignment for pilot Captain Richard Ashby, his navigator Captain Joseph Schweitzer and two crew members. The Prowler – call sign ‘Easy 01’ – was a twin-engine jet used for electronic warfare belonging to the US Marine Corps. It should have been a mission that passed without incident but constraints imposed by military regulations were ignored, either by accident or design, with disastrous consequences.

Easy 01 was flying considerably faster – at 805 kph (500 mph) – and much lower at 110 m (360 ft) than it should have been. As the Prowler scorched through the valley near Cavalese in the Italian Dolomites it hit and severed cables supporting a moving cable car, sending the gondola crashing to the ground and killing all 19 passengers plus the operator. The plane had wing and tail damage but returned safely to base.

Military personnel all too often escape the consequences of reckless or illegal actions, and so it proved. A US court martial accused Ashby and Schweizer of negligent homicide and involuntary manslaughter, but they claimed on-board maps did not show the cables, they were unaware of speed restrictions and the plane’s altimeter wasn’t working. Even though the pilot admitted to flying at 300 m (1,000 ft) when the official minimum was 610 m (2,000 ft), both were dubiously acquitted.

This outraged public opinion in Italy, where the disaster was christened Strage de Cermis (Massacre of Cermis), after the adjacent mountain. There was a surge of anti-American feeling, hardly appeased when the two men were subsequently convicted on lesser charges of obstructing justice and conduct unbecoming of a gentleman for destroying the in-flight videotape. They were dismissed from the service, with Ashby getting a six-month prison sentence.

When: February 3 1998

Where: Near Cavalese, Trento, Italy

Death toll: 20 dead (all adults, from six different countries).

You should know: Cavalese wasn’t the safest of places to ride a cable car. In a previous incident in 1976 a steel cable broke, sending a cabin plunging down the mountainside. The heavy overhead assembly then crashed down on top. One 14-year-old girl survived the world’s worst cable-car accident, 42 died.

By the mid-1980s, the Soviet Union was creaking. The Communist Party’s absolute control from Moscow had failed to deliver for assorted nations that had been forcibly combined to create the Russianized superstate.

The economy was stagnant, poverty was endemic and the tightly controlled peoples of this disparate empire were getting restive.

Cometh the moment, cometh the man. In 1985, a visionary new leader rose to power. Mikhail Gorbachev set about implementing a two-track reform plan. On one hand, glasnost (freedom of speech) would provide a safety valve for the frustrated people. On the other, perestroika (rebuilding) would address economic woes. But the long-suppressed ability to speak freely led to a wave of unrest, both in Russia itself and in satellite countries, especially as perestroika failed to deliver improved living standards.

By 1991, hardliners who once enjoyed absolute power became restive as they saw communist control start to slip. In a desperate move to regain control, they kidnapped Mikhail Gorbachev and mounted a coup. On August 19 they announced that Gorbachev was ‘indisposed’ and unable to govern. But this dramatic move proved to be a serious miscalculation with disastrous consequences for their cause.

The plotters were horrified by the subsequent uproar, with protests erupting in major cities throughout the Soviet Union. In desperation, they turned to the traditional totalitarian solution and sent in the army to restore order. When soldiers refused to fire on their fellow countrymen – as dramatically symbolized by pictures of future leader Boris Yeltsin addressing a Moscow crowd from the top of a tank – the coup was over. This failure proved terminal for the nationalists. Instead of restoring the Soviet Union to its former centralized strength, the fiasco ensured that the entire Union finally fell apart, along with Russian control over Eastern Bloc states like East Germany.

When: August 19 to August 21 1991

Where: Moscow, Russia, Soviet Union

Toll: The thwarted aspirations of the old guard to restore the Communist Party’s totalitarian control of the Soviet Union.

You should know: There is no evidence that Mikhail Gorbachev originally envisaged an end to the Soviet Union, but the failed coup was the last nail in the Union’s coffin and it almost immediately disintegrated into 15 separate countries… while Gorbachev himself had already won a Nobel Peace Prize for creating the conditions that allowed it to happen.

The Hajj is the world’s largest pilgrimage, drawing a vast crowd to Mecca every year. It is the fifth pillar of Islam and demonstrates the solidarity of Muslims everywhere. Attending the Hajj at least once in a lifetime is an obligation for every able-bodied Muslim who can afford the trip – an edict that has seen attendance rising sharply as a result of global prosperity and easy air travel.

The month of Hajj now attracts up to four million visitors annually, posing huge logistical difficulties for the Saudi Arabian authorities. They have not always succeeded in dealing with the vast crowds and the sheer weight of numbers can have disastrous consequences. There have been many serious crowd incidents over recent years, cumulatively costing many lives. The worst accident occurred on July 2 1990, when 50,000 worshippers were allowed to converge simultaneously on the 500 m (1,640 ft) al-Mu’aysam tunnel connecting Mecca to the huge tented encampment of Mina, below Mount Arafat, during the Eid al-Adha (Feast of the Sacrifices) at the end of the Hajj. The tunnel collapsed and 1,426 died, mostly pilgrims from Turkey and Indonesia.

In May 1994 there was a stampede at Mina during a ceremony where pilgrims stone three pillars representing the devil. This time 270 died, mainly Africans. A catastrophic fire destroyed 70,000 tents on the Plain of Mina in 1997, probably started by an exploding gas cylinder. After the fire, 217 bodies were recovered and 1,300 were treated in hospital. The following year 118 died during another stampede after police opened a walkway on the Jamraat Bridge, causing a fatal surge.

Sadly, it won’t be the last tragedy at Mecca. For as long as devout pilgrims gather in their millions each year, the Hajj will sometimes be a time of mourning as well as celebration.

When: 1990, 1994, 1997 and 1998

Where: At and around Mecca, Saudi Arabia

Death toll: 1,426 (1990); 270 (1994); 217 (1997); 118(1998)

You should know: Although the casualty figures for disasters at Mecca seem bad enough, some commentators have suggested that the Saudi authorities deliberately understate the totals in order to mitigate criticism of their stewardship of the Hajj – which, in fairness, is the world’s most demanding crowd-control challenge.

Spend billions of dollars, utilize the cutting-edge design and engineering capabilities of the world’s most technologically advanced nation and what have you got? For NASA (the USAS National Aeronautics and Space Administration) the answer was a snappy acronym – STS.

The Space Transportation System has at its heart the iconic space shuttles – reusable craft used for orbital flight that became operational in the early 1980s. Things had gone quiet for NASA after America won the race to the moon back in 1969, and the STS program revived public interest and showed arch-rival Russia that old-fashioned rocketry wasn’t the only route to the stars.

The STS consists of three main elements. The shuttle is the reusable orbiter vehicle (OV), propelled into space with the help of an external fuel tank (ET) and two reusable solid rocket boosters (SRBs). This incredibly sophisticated system has many thousands of components. Among the least expensive are 0-ring seals on the SRBs. Engineers had warned that these might fail if the external temperature was too low, but each launch was a major event that had to take place within a relatively short time window.

There were several delays to the launch caused by problems like unsuitable weather conditions or minor equipment failures. It was unusually cold on the morning of January 28 and ice had formed on Challengers gantry, but NASA was desperate to get the mission away and decided to go ahead. It took just 73 seconds from launch to dramatically demonstrate how disastrous the decision to ignore chill conditions had been. The weakened O-ring on the right-hand rocket booster failed. A plume of flame scorched outwards, setting in motion a train of events that swiftly destroyed Challenger and took the lives of the seven crew, including ‘people’s astronaut’ Christa McAuliffe.

When: January 28 1986

Where: Above the Atlantic off Cape Canaveral, Florida

Death toll: Seven

You should know: A stroke of bad luck contributed to the Challenger disaster. One feasible launch in warmer weather, on January 26, was postponed because Vice President George Bush wanted to stop off at the Kennedy Space Center and watch the launch on the following day, en route to Honduras. Ironically that launch, too, was postponed.