SPACE flight is difficult. It is also dangerous. Eighteen astronauts and cosmonauts have died in flights organised by the American and Soviet space programmes—and three others were killed in a fire during a rehearsal on the ground. Numerous unmanned rockets have gone wrong as well. Last week the lesson was hammered home again, on two separate occasions.

On October 28th an uncrewed Antares rocket operated by Orbital Sciences, a company contracted by NASA to fly supplies to the International Space Station (ISS), blew itself up shortly after launching from a pad in Virginia. The explosion rattled windows in a town 11km (7 miles) away, but, fortunately, there were no casualties.

Three days later VSS Enterprise, a spaceplane owned by Virgin Galactic, a firm that hopes to provide wealthy thrill-seekers with flights to the edge of space, crashed during a test flight over the Mojave desert (see picture). This time, the toll was higher: one pilot was killed; the other survived but was badly hurt.

Crashes and explosions are not uncommon, especially with new rockets. The accidents were unrelated. That both happened in the same week is nothing more than an unfortunate coincidence. But it is, nevertheless, an unwelcome blow for enthusiasts of the “New Space” industry, which aims to use private companies and the discipline of fixed-price contracts to cut the cost of getting into space.

With investigators still sifting through the wreckage and analysing flight logs, it is too early to say what caused either crash. But Orbital Sciences has indicated that the fault may lie with the engines on its Antares rockets. They are half a century old, having been built in the Soviet Union in the 1960s for use with the N1, an enormous rocket that itself suffered four failures, including one launch-pad explosion, before being abandoned. After the end of the cold war, a cache of the engines was discovered sitting in a warehouse. Two such engines, after refurbishment in America, are bolted to the bottom of every one of Orbital Science’s Antares rockets. The firm had been planning to fit more modern Russian engines to future versions. It is now likely to make the switch sooner.

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As for Virgin Galactic, armchair crash investigators had, to the annoyance of Sir Richard Branson, the firm’s billionaire owner, also talked up the possibility of an engine failure, especially since the firm had recently altered the fuel mix burned by the spaceplane’s rocket. But officials from America’s National Transportation Safety Board (NTSB), which is investigating the crash, announced on November 2nd that they had found the fuel containers and the rocket intact.

The leading theory now is that the spaceplane broke apart under aerodynamic stress. Virgin’s craft can fly in two configurations: a low-drag arrangement when climbing into space, and a high-drag one used to lose speed while descending. According to the NTSB, the high-drag mode seems to have been engaged while the engine was still firing. If that is correct, then the resulting forces could have caused the craft to break up.

Orbital Sciences’s accident is embarrassing, but unlikely to harm it too much. The firm, which was founded in 1982, has only a toe in the New Space industry. Besides the Antares, it makes small satellites, launches a variety of other rockets, and has contracts with the American armed forces.

If anything, the accident is more embarrassing for NASA, which relies on the private sector for launches more heavily than it did in its glory days—often in the face of complaints in Congress. It has a $1.9 billion contract with Orbital to provide eight resupply trips to the ISS (the failed launch was to have been the third). But any congressional complaints are likely to be minimal. Partly, that is because, as a big, established firm, Orbital has friends on Capitol Hill. And partly it is because the accident will not seriously inconvenience the astronauts aboard the station.

Even if the investigation unearths a fundamental problem with Antares’s design, NASA has a similar contract with SpaceX, an upstart rocketry firm founded by Elon Musk, an internet tycoon. SpaceX has already completed four missions out of a planned 12. The next is scheduled to launch in December. Ironically, Orbital’s accident may put extra pressure on SpaceX. If its flight should fail too, Congress may reasonably start complaining.

It is for Virgin Galactic that things look trickiest. The firm has no government contracts. It is entirely reliant on investors and ticket sales for cash. Those tickets cost $250,000 each and around 700 people have put down deposits. The firm cannot collect the balance of the money, though, until commercial flights begin. Its programme is already behind schedule. Such flights were once due to start in 2008. Following the change of rocket fuel, Virgin had hoped to begin flying paying passengers next year. That now looks impossible. And the crash must make many ticket holders wonder whether they really want to go. One who has made his views known publicly, Wilson da Silva, an Australian science journalist, still intends to fly. But around 20 others, the firm says, have asked for refunds.

Although Virgin is aiming only to take passengers to the edge of space (defined, somewhat arbitrarily, as beginning at 100km above the Earth’s surface), and not into full-blown orbit, its technology is, in many ways, trickier than the stuff operated by Orbital Sciences. Compared with spaceplanes, conventional rockets are reasonably well understood.

As George Whitesides, Virgin Galactic’s chief executive, pointed out in an interview that took place before the crash, there have been around 100 space-launch vehicles in history, but only a handful of rocketplanes, of which only two (the Space Shuttle and the X-15) have flown in space with anyone on board. New technology is always tricky to master; new rocket technology can be some of the trickiest of all.