Fancy a trip to the stars? A growing pool of private spaceflight operators will soon be blasting wealthy individuals out into space, and their founders say the journey will become far cheaper within the decade i.
Space tourism has to date been confined to the ultra-rich. Only eight privately funded travellers have visited the International Space Station since 2001 ii , and no wonder - it currently costs about US$52 million for a ten-day trip via commercial spaceflight operator Space Adventures iii.
Billionaire entrepreneurs Jeff Bezos and Richard Branson are betting on a more flexible definition of space tourism to bring costs down.
By flying to heights of only 110km iv, instead of the 400km needed to reach the ISS v, for example, Branson's Virgin Galactic will give tourists a few minutes of weightlessness for US$250,000 vi.
According to the United States' Federal Aviation Administration (FAA), space tourism will be a billion-dollar market within the decade vii. Surveys have found more than half of the general public wanting to visit space, predominantly for the opportunity to experience weightlessness and to see our magnificent planet from afar viii.
Quoting Goldman Sachs research, Forbes has described private spaceflight as a "space race" that could "turn into an investment opportunity of cosmic proportions" ix.
Here are the trips most likely to become commercially available in the coming years.
Blue Origin's New Shepard
Amazon founder Jeff Bezos' Blue Origin is building both sub-orbital and orbital spacecraft that will take humans into space.
Its New Shepard spacecraft seats six with enough room for passengers to "float freely and turn weightless somersaults" x. New Shepard successfully reached a sub-orbital altitude of 100.5km in a test flight last month. It landed safely, and could take paying passengers in two years' time xi.
Ticket prices have not yet been disclosed. Space tourists are expected to experience a few minutes of weightlessness.
XCOR Aerospace's Lynx
Spaceflight start-up XCOR Aerospace's two-seater Lynx is slated to take commercial passengers to suborbital altitudes above 100km by 2017 xii.
Tickets initially cost US$95,000 each, for which tourists would receive medical screenings, seminars, g-force training xiii, and five minutes of weightlessness.
XCOR has sold more than 300 tickets to date; ticket prices will increase to US$150,000 as of 2016, due to market demand xiv.
SpaceX was founded in 2002 by Tesla Motors' Elon Musk with the lofty aim of enabling humans to colonise other planets xv. Its Dragon spacecraft currently carries cargo to the International Space Station, but was designed to ultimately transport humans xvi.
The capsule was built with NASA's support and could ferry seven passengers plus cargo to the ISS at a cost of US$20 million a seat by 2017 xvii - far cheaper than the Russian Soyuz spacecraft that currently serves NASA as well as Space Adventures.
Virgin Galactic's SpaceShipTwo
Richard Branson's Virgin Galactic is slated to take groups of six passengers plus two pilots into space on board its SpaceShipTwo from 2017. The spacecraft targets sub-orbital altitudes of about 110km, from where Virgin says passengers will experience the "best possible view of Earth and the blackness of space" xviii.
Some 700 people from more than 50 countries around the world have already paid in full for their tickets, which cover the cost of three days of training at New Mexico's Spaceport America, custom flight suits, the flight into space, and video footage xix.
KosmoKurs' five minutes in zero-gravity
Russia's answer to Virgin Galactic expects to offer passengers five minutes of weightlessness at sub-orbital altitudes from 2020. Tickets cost US$200,000 to US$250,000, and include training, the spaceflight, video footage, and potentially a spacesuit xx.
CEO Pavel Pushkin is targeting Chinese space tourists and hopes to send 7,000 tourists to space - half the world's space tourism market - in its first decade of operations. The company is working exclusively with partners and suppliers in Russia.
Space Adventures' Moonflight
Space Adventures is currently the only company to have sent tourists into space xxi. To date, it has transported eight individuals 400km up to the ISS.
By 2018, Space Adventures plans to send tourists on a slingshot ride around the moon, which is about 382,500km away from Earth . The journey will take 16 to 17 days, including a ten-day stopover aboard the ISS. Tickets cost US$150 million iii.