WHEN the Space Shuttle made its final flight in 2011, America was left without the ability to fly people into space. American astronauts wanting to go to the International Space Station have to hitch a ride with the Russians, at a cost of $71m a seat. That is rather humiliating for the world's premier space-faring nation. But exactly what to do about it is the subject of a bitter, drawn-out battle. On one side are a group of NASA traditionalists in Congress with a fondness for the glory days of the Apollo programme. On the other is a gaggle of enthusiasts for the private sector, led by Barack Obama's White House, who argue that the private sector can do human spaceflight better and more cheaply than NASA ever could.

According to Congress, the plan is clear: NASA is building the Space Launch System, a colossal rocket that will be even bigger than the Saturn Vs that flew the Apollo astronauts to the Moon. The eventual plan is to use it to send a crewed mission to Mars by the late 2030s. The price tag is colossal, too: America's General Accounting Office says that the official figure of $22 billion by 2021 is an underestimate, since it does not include the landers and payloads that the rocket would have to carry. Lori Garver, a former NASA deputy administrator, says that the SLS—which is in turn based on the Constellation programme pushed by George Bush junior—is not "financially sustainable" and should be scrapped.

All that money buys plenty of high-quality pork, though. Led by senators from Alabama, Texas, Utah and Florida—all states with space-related manufacturing jobs—Congress over-rode the president’s plan in 2010. Mr Obama's White House, by contrast, has pushed for NASA to contract with commercial space firms such as SpaceX, Orbital Sciences, Blue Origin and the Sierra Nevada Corporation to develop rockets and spacecraft capable of flying astronauts at least as far as the ISS by 2017 or 2018. That would leave NASA free to conduct robotic, science-focused missions elsewhere in the solar system.

Of course, commercial firms have long built spacecraft for NASA. The innovation is to use fixed-price contracts, in which any over-runs are borne by the contractors, instead of old-style cost-plus contracts, under which the firm simply hands the government a final bill with a percentage tacked on as profit. Critics of cost-plus, such as SpaceX’s founder Elon Musk, say that it gives firms no incentive to work quickly or cheaply, since any cost over-runs can simply be handed on to taxpayers with no effect on the firm's bottom line. Traditionalists counter that they at least grant NASA ownership of the intellectual property associated with the spacecraft in question.

The result was a compromise: Congress got about $3 billion a year to pay for the SLS (called the Senate Launch System by critics) and a spacecraft left over from the Bush era plan called Orion. The White House, meanwhile, got about $400m a year to help the private sector develop spacecraft of their own to fly NASA astronauts to the ISS. As with all compromises, neither side is really happy. The SLS and the commercial space program have been set off against each other in bitter budget and political battles. The late Neil Armstrong supported the big rocket and criticised the commercialisation of space exploration; his moonwalking mate, Buzz Aldrin, has favoured the other side.

For now, though, that compromise has allowed both efforts to co-exist. But events may run ahead of the SLS. SpaceX, the most successful of the private firms, is planning to build a super-heavy Falcon rocket of its own that would be even beefier than the SLS. If all goes to plan, the so-called Falcon XX could reach lunar orbit in the early 2020s and go on to Mars later in the decade, ten years ahead of the SLS. SpaceX already has the lowest launch costs in the industry. It is working on making its rockets reusable, which would cut prices even further. Some (admittedly speculative) estimates say that NASA could cut its costs by a factor of 25 or 50 by going with the Falcon XX rocket instead of the (non-reusable) SLS.

But this is not just an argument about money and jobs. The charitable interpretation of Congress's plan is that it takes its inspiration from the greatness of the government-run Apollo programme. But Mr Musk is equally forceful when he says that “NASA’s most valuable role is to fund advanced science projects such as the Hubble space telescope or the Curiosity Mars rover—things that are valuable for humanity as a whole [and] where there’s not an obvious commercial transaction." The rest, in other words, including colonising Mars, Mr Musk's ultimate aspiration, should be left to entrepreneurs.

(Photo credit: HANDOUT / NASA / AFP)