Media playback is unsupported on your device Media caption Challenger's ill-fated 10th flight

Twenty five years ago the Challenger space shuttle broke apart over a minute after its launch, killing all seven on board. It was both a tragedy and profoundly shocking event, the consequences of which are still being felt today.

Seventy three seconds was all it took.

Millions of people around the world watched as coverage of Nasa's space shuttle launch on 28 January 1986 was played out.

But as the commentary fell silent, and the exhaust trail snaked across the sky, it became clear that something had gone horribly wrong with Challenger's mission.

The shuttle rapidly disintegrated, with the loss of all seven crew.

The flight had been delayed for several days due to freezing weather. An investigation concluded that the seal on the rocket booster had failed because of faulty design unable to cope with the cold weather and other factors.

It was the first time the US had lost astronauts in flight, and it was a profound loss for the country.

National grief

The US had prided itself on being able to send manned shuttles into orbit, and from 1981 until 1986 had successfully launched Space Transportation Systems (STS) more than 20 times from its centre at Cape Canaveral.

It was from there that the fateful Challenger journey began. Around the world, people watched the shocking events unfold.

Brian Ballard, 16 at the time, witnessed events first-hand from the viewing deck.

"At first I thought that it detached at the normal time, but then I heard echoes of a large explosion," he recalls.

"Everyone was confused about what had happened. I was in a daze. I was still an optimist and I thought maybe there's some sort of a back-up plan."

Image caption Onlookers watch in horror as the Challenger shuttle broke into pieces in the sky above them.

"It took me a little while to realise that they weren't going to be coming back," he says. Ballard had been in Florida covering the shuttle launch for his school newspaper, The Crimson.

He was sent there because one of the teachers at his school, Christa McAuliffe, was on board Challenger, hoping to become the first teacher to go into space.

Mrs McAullife, who taught at Concord High School, New Hampshire, had been selected as the winner of Nasa's Teacher-in-Space programme. The aim of the scheme, which had been announced by President Reagan in 1986, was to encourage an interest in space and science education and to conduct some lessons from the shuttle.

"We were excited at the prospect of engaging our students in space activities and getting lessons from space, and truly thought that once one teacher had gone - who knows who will be the next," says Dan Barstow who taught at a school in Hertford, Connecticut in 1986.

Space education

It was for this reason so many schools took an interest in following Challenger. Footage of its launch was beamed into hundreds of classrooms so children could see it.

"The whole school was watching events in the auditorium," remembers Barstow, "we all stopped and paid attention to it."

For Barstow, plans to celebrate space travel quickly turned very sombre, many of his students left in stunned silence after what they had seen.

The shuttle launches were a beacon to many worldwide for optimism in science, so Challenger's loss was both national disaster and a blow to the space programme.

This wasn't America's first space tragedy - all three crew members on board Apollo 1 died when the command module caught fire in 1967.

But what made the Challenger accident so different was that it was played out on television for all to see.

Landmark moment

"People felt like they had actually witnessed it in person," says Valerie Neal, a curator at the Smithsonian National Air and Space Museum.

One former US pupil recalls I was six at the time. We knew there was a teacher going into space and we thought it was very cool. It was a very exciting idea for me. When the disaster happened I remember feeling that the country needed solace. I felt we were all together, united in grief. I saw it as part of the heroic history of space exploration - it didn't deter people from wanting to explore and push the bounds of human experience. BBC's 1986 news report on shuttle tragedy Q&A: Challenger shuttle disaster

"Americans in particular had become so accustomed to success in space, with the landing on the moon and the return of Apollo 13 - we had never had a visible failure in our space programme."

That sense of failure was compounded by the fact that an "ordinary" American who had been selected to teach from space was never able to realise her dream.

The grief felt for the seven astronauts was combined with a sense of sadness about the blow to space education, says Dan Barstow.

To ensure this legacy was not completely lost, the families of those who lost their lives created the Challenger Centre for Space Science Education - which Mr Barstow heads up - and which continues to encourage and promote an interest in space travel.

For many children who witnessed events, the Challenger disaster was a landmark moment.

Marc Adelman was seven years old at the time.

"I remember going into the classroom and everybody was yelling - 'the space shuttle has exploded, the space shuttle has exploded'."

There was added resonance at his school because one of the teachers had applied to the Teacher In Space project.

"For a lot of kids this was the first time something relatable to them had an impact on their lives. It struck me how it could've been our teacher from our school," he recalls.

Mr Adelman looks back on it as a moment where Americans "pulled together", likening it to other big tragedies such as 9/11 in its unifying effect.

That sense of national mourning was summed up by President Reagan, who cancelled his planned State of the Union message that evening to address the nation, and even made a special mention to the many children who were affected.

"We know we share this pain with all of the people of our country. This truly is a national loss," he said staring straight into the camera.

"It's all part of the process of exploration and discovery. It's all part of taking a chance and expanding man's horizons. The future doesn't belong to the fainthearted; it belongs to the brave."

Too complacent?

The president touched upon previous explorers such as Francis Drake, who he said had also paid the ultimate price for their bravery. It was a message many commentators said summed up the national sense of disbelief that space travel could be fallible.

"As a country I think we'd become a bit blase about space travel and a little too complacent. The accident shocked us into the recognition that there are still risks and dangers," says Neal.

One of the biggest outcomes from the tragedy was the recommendation that NASA needed a stronger safety organisation, she says.

In September 1988, NASA resumed shuttle missions with the launch of Discovery. But in 2003 tragedy struck once again when the Columbia shuttle disintegrated over Texas, leaving all seven crew members dead.

Two years later President Bush announced that he would be cancelling the space shuttle progamme. The fleet is expected to retire this year.

"Our role in space is very much part of the American identity, and that we have been pioneers in space affirms that," believes Neal.

The Challenger disaster will be remembered as a moment where that element of the national identity suffered a setback.