Rocket science is always a risky business, which is why crewed capsules and the rockets that launch them carry a variety of systems built in to ensure the safety of those aboard, as the world remembered today.

One of the longest-serving and most renowned rockets suffered a serious launch failure shortly after liftoff during what was supposed to be a routine crew trip to the International Space Station today (Oct. 11) carrying NASA astronaut Nick Hague and Russian cosmonaut Alexey Ovchinin. The astronauts landed safely and an investigation is already underway as to what went wrong.

It will take awhile for the full details of the incident to be pieced together, but so far, NASA has blamed it on a problem that occurred during booster separation of the Soyuz rocket powering the launch. That triggered a warning light to turn on inside the crew capsule, NASA astronaut Reid Wiseman said during a news conference held today. [In Photos: Space Station Crew Aborts Mission After Soyuz Launch Failure]

At that point, the crew capsule automatically fired engines that carried it and the astronauts away from the troubled booster and its giant stash of extremely flammable rocket fuel. After a few moments of free fall, the capsule's parachutes deployed. The duo took a little more than half an hour to land and were immediately met by a Russian search-and-rescue team that had been deployed as part of the standard procedure for launches.

Hague and Ovchinin left their capsule, were examined by the search-and-rescue team, and began the journey back to Baikonur Cosmodrome in Kazakhstan to reunite with family members and NASA and Roscosmos officials. Soon after, they will head back to Star City in Moscow, where astronauts live while they prepare for launch.

While whatever caused the anomaly is of course of deep concern, NASA officials were clear to stress their confidence in Russian spaceflight and their relief that everything — aside from that anomaly — performed perfectly.

The rocket, Russia's Soyuz system, is one of several flavors of the same basic rocket the country has been launching since the late 1960s, for crewed and uncrewed missions alike. Today's vehicle type, a Soyuz-FG rocket, is the only design currently certified to carry humans. It has been launching since 2001 and has long been slated to be replaced by a newer model, although it has not previously failed, Asif Siddiqi, a space historian at Fordham University, told Space.com.

Even over the full history of Soyuz rockets, failures have not resulted in any fatalities during launch, he added. The two other serious launch incidents occurred in 1975 and 1983, respectively.

The 1975 failure "was probably the most dangerous one," Siddiqi said, "because they had to endure a lot of Gs coming back in and they landed way off course." During that re-entry, Soviet cosmonauts experienced over 21 G's of gravity, or more than seven times that experienced by Hague and Ovchinin today.

The first Russian Soyuz capsule to carry a crew of astronauts to the International Space Station was the Soyuz TM-31, which launched in 2000. (Image credit: NASA)

During the 1983 launch, the Soyuz hadn't quite launched when crewmembers had to quickly command the capsule's escape tower to activate after the booster rocket caught fire. Had the escape mechanism taken even just a couple seconds longer, the cosmonauts likely would have died, later analyses suggested.

Nevertheless, after more than 100 crewed launches by Soyuz rockets, today's incident remains just the third serious launch failure, and all astronauts have survived those incidents. (A few Soyuz missions have ended with deaths upon re-entry, long after the rocket itself had done its job.)

That safety record is thanks to a well-engineered set of recovery options for the crew, Siddiqi added. Those protection measures include, of course, the separation and ballistic re-entry sequences that were automatically initiated today as the safest escape technique for the situation. [See the Breathtaking View from a Russian Soyuz Rocket As It Launches into Space]

"They've had a lot of close shaves, many of them in fact, but they've managed by the skin of their teeth to save their crew," Siddiqi said. "They have a pretty good safety system in place during launch phase to recover the crew — and it worked, the crew is fine."

But while crewed missions have in general been proceeding according to plan, the Russians have struggled recently with cargo missions and with the infamous small air leak aboard the space station in August. That context makes this additional incident more concerning than it would be on its own, Siddiqi said.

"There's a cumulative sense that the Russian space program is degrading," he said. "In isolation it's serious, but it's not a catastrophe."

But in light of other issues? "I'm not surprised that this happened, because they're dealing with a lot of problems," he said. Fortunately, the safety systems weren't among them.

Email Meghan Bartels at mbartels@space.com or follow her @meghanbartels. Follow us @Spacedotcom and Facebook. Original article on Space.com.