Ever since Nasa’s final manned mission to the Moon 40 years ago, our hopes of further human space exploration have somewhat dwindled.
But a recent recruitment drive for colonists of Mars – launched by maverick Dutch space experts – has rekindled the debate about how far we might dare to go.
Here, are five planned missions that aim to 'boldly go' beyond the confines of our Earth - some sooner than you might think. But which is most likely to succeed? Our (unscientific) ratings are below.
MARS ONE COLONY
Mars One, a Netherlands-based organisation, is planning to send humans to Mars by 2023 in order to build a colony there.
They have already started to recruit 40 astronauts – of whom only half will settle on the planet 140million miles away.
Organisers hope to provide most of the funding through a global reality TV show.
However, aside from the unrealistically low £3.7billion they need to put the first four astronauts on Mars, they also face problems making the nine-month journey.
Mars One is relying on a relatively untested private California firm, SpaceX.
A lot rests on the first test of the launch vessel, Heavy Falcon, which is due to take place later this year.
Living on frozen Mars is likely to prove an even greater headache.
Likelihood of success: 4/10
SPACE STATION ON THE MOON
Nasa chiefs are considering returning men to the moon by 2025. It would be the first time since the Apollo 17 mission of 1972.
Last month’s announcement comes after the agency’s success with the Mars Curiosity Rover and President Barack Obama’s 2010 commitment to manned space exploration.
On the plus side, Nasa have a proven track record with making the three-day, 240,000-mile journey to the Moon.
Trips to the International Space Station also demonstrate humans can live beyond Earth’s orbit.
The key factor on whether the mission takes place or not will be cost.
Will debt-burdened America and its polarised politicians be willing to spend an estimated £25billion? Not unless a different Congress is elected.
Likelihood of success: 6/10
Nasa have long planned to send a manned space shuttle on a 23million-mile journey and let astronauts fly by the planet Venus.
It cancelled a proposed 13-month mission to begin in October 1973 after the Apollo 13 disaster in 1970.
Since then the plans have stayed on ice.
But there still remains an interest by many Nasa experts in orbiting the hottest planet in our solar system.
Unfortunately, despite the opportunity for an epic human achievement, it would have relatively little scientific merit.
Sending a robotic probe would probably glean more information and, for £1billion, cost around a quarter of the price.
Likelihood of success: 3/10
Last year Nasa began training astronauts – including Britain’s Major Tim Peake - to land on an asteroid.
The biggest-yet manned mission, which echoes the movie Armageddon, would require travelling up to 3milllion miles to a space rock by the end of the 2020s.
Once there, astronauts could take samples and carry out tests that would help scientists better understand the risk they pose to Earth.
Although the £2billion cost of the year-long journey is somewhat prohibitive during the current climate, it is one of the cheapest projects being considered.
It also mixes a useful scientific enterprise with an awe-inspiring human endeavour that has been strongly supported by American politicians.
Likelihood of success: 8/10
COLONISING ALPHA CENTAURI
The most ambitious manned space journey envisaged by scientists would be to Alpha Centauri, a star system 4.3 light years away from our solar system, that may be able to sustain life.
Geoff Marcy of the University of California, Berkeley, suggested that it might be possible to begin the journey by 2100. It won't be a short trip, though - at 25.6 trillion miles, it would take current manned craft more than 100,000 years to get there.
The plan would require a purpose-built ‘Generation Ship’ - because several generations would die during the trip.
It's also not clear how the journey would be fuelled.
Also, there would be few people willing to take the risk travelling to a destination that, despite having the right energy levels, may not be hospitable.
Likelihood of success: 1/10