Last week, we were reminded how truly difficult space flight is, and how people continue to risk their lives, in order for us to get closer to the stars.

With two rocket failures over U.S soil, it might look like hard times ahead for private space exploration. But NASA officials and industry leaders alike say that they're determined to learn from both accidents, and make space travel safer, if not easier.

First, on Tuesday, October 27th, private space company Orbital Sciences lost one of its Antares Rockets after it failed to launch, destroying the rocket and its Cygnus spacecraft, which held over 4,000 kilograms of supplies and scientific experiments bound for the International Space Station. Fortunately no one was harmed in the incident.

It was the third mission for Orbital Sciences, which along with SpaceX, has contracted with NASA to make deliveries to the ISS. So although these weren't NASA vehicles, NASA did lose some precious and expensive cargo. As for why, we don't know yet and we probably won't know for a pretty long time.

At NASA's Wallop's Flight Facility in Virginia, countdown and liftoff went smoothly, but then about 15 seconds after liftoff, when the Antares was in its first stage of ascent, it just stopped working. Instead of propelling the payload up, it started falling back down. 

A fast acting safety official activated the rocket's self destruct mechanism, so that it would explode in the air, causing less damage on the ground. The explosion scattered debris for hundreds of meters, littering the area around the launchpad and damaging the pad itself, a much smaller footprint than the crash would have damaged if it hadn't self destructed.

NASA, Orbital Sciences, and the Federal Aviation Administration are now cleaning up the site and sizing up any environmental damage to the area. After that, the plan is to gather clues about what went wrong with Antares' first stage.

This stage of the rocket was powered by two AJ26 engines, extremely efficient kerosene burning engines, built in the 1970's for Russia's moon program. Orbital Sciences bought the engines from Russia in the 1990's, and while they had never flown a mission, they had been tested several times. Though old, these engines produce more power for their weight than any other liquid fueled engine of comparable size. So far, the age of the engines is the only speculated cause of the crash.

Then, on Friday, October 31st, Virgin Galactic's SpaceShipTwo crashed during its 55th test flight, near Mojave, California. Pilot Michael Alsbury was killed in the crash, while Pilot Peter Siebold was able to escape with a parachute, but was badly injured and remains in the hospital.

SpaceShipTwo was launched in flight after being carried to an altitude of just below 15,000 meters by its mother ship, White Knight Two. From there, it was supposed to ascend to an altitude of 100 kilometers before returning to Earth. But soon after its release, SpaceShipTwo's rotating tail booms, the two feather-like devices that regulate the vehicle's angle for re-entry, were activated. This was odd because the craft was still ascending, and soon after, the ship plummeted to the ground with no observed explosion.

Investigators don't yet know if the tail boom's early activation caused the crash. Another possible culprit may be the new type of fuel that Virgin was using for the first time, a cheaper fuel made from solid plastic instead of the liquid fuel it had been using.

With the debris field some 8 kilometers wide, it may be up to a year before Virgin and the National Transportation Safety Board are able to find the cause of the accident. But Virgin's official statements are similar to NASA's when it comes to addressing the general cause of these two crashes, and statements from both organization's officials simply point out that space flight is exceedingly hard, one of the most difficult and dangerous things that humanity has yet attempted. And history doesn't disagree.

Friday wasn't SpaceShipTwo's first fatal accident, for example. In 2007, an on-the-ground explosion of one of its fuel tanks killed 3 people. And there have been hundreds of fatalities associated with space flight around the world since the 1960's.

About 30 astronauts have died in accidents, about 20 of which happened on space flight missions. Then there are the 32 non-fatal rocket and spacecraft crashes, which seem to happen every couple of years. So it's true, space flight is hard, and we can't forget that. And we want to thank all the men and women who risked their lives in the name of space exploration and science.

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