A SpaceX Mars rocket prototype exploded. It was still a success

SpaceX rocket explodes on attempted landing SpaceX Starship rocket exploded on landing during a test flight on Dec. 9. Elon Musk says the test was a success despite the incident.

A giant experimental rocket built by Elon Musk's SpaceX successfully soared 12 kilometres (eight miles) above the company's testing facilities in South Texas on Wednesday and came back down as planned, before crashing into the ground in an enormous plume of flames and smoke.

The hulking rocket didn't have anyone onboard. It was an early developmental model of Starship, a 48-metre-tall) (160 feet) spaceship proposed by Musk that he hopes will be used for hauling massive satellites into Earth's orbit, shuttling people between cities at breakneck speeds and — eventually — establishing a human settlement on Mars.

The test flight marked the highest test flight yet of the technology Musk hopes will one day ferry the first humans to go to Mars, and a fiery ending was not totally unexpected. Musk attempted to dampen expectations before the flight, saying in one tweet that he predicted the "SN8" vehicle, the name for the Starship prototype used Wednesday, had a one-in-three chance of landing safely back on Earth.

The SN8 did manage to maneuver back to its landing target, but Musk said via Twitter that an issue with the rocket's fuel system caused it to make a crash landing. Green and yellow flames engulfed the landing site, which lies just outsides the small coastal town of Boca Chica, Texas.

SpaceX and Musk are known to embrace mishaps during the early stages of new spacefaring technology development. The company's ethos is to move quickly and learn from errors, rather than taking the more NASA-esque approach of slowly conducting thorough research and ground tests before putting a rocket on a launch pad.

Several previous Starship prototypes were destroyed during pressure tests, which are designed to check whether a vehicle can withstand the enormous pressure it undergoes during fueling and in flight.

SpaceX did not reveal before flight exactly how the test was supposed to look, but shortly aftter liftoff, one of the Starship SN8's three engines shut off. That did not appear to drastically affect the spacecraft's maneuvering while in the air. When all three engines powered down, the vehicle was able to orient itself at an angle during decent — a move that Musk previewed during a September 2019 presentation, billing it as a spacecraft landing method that mimics a skydiver falling through the air. Musk said he hopes a fully operational Starship would tilt about 60 degrees, putting its belly down toward the Earth, as it plunged back through the atmosphere in order to make it less aerodynamic and reduce its speed. Then, just before landing, the vehicle would swing back into the upright position and land gently on a ground pad.

SpaceX had previously tried twice this week to launch the test flight, but both of the first attempts were halted with just moments left on the countdown clock.

It was not clear why SpaceX halted the launches, though last-minute scrubs are not uncommon even during routine rocket launches. Computers or flight controllers may have caught an abnormal reading about the rocket's health and stopped the engines from igniting.

The company is still a long way from building an operational Starship spacecraft. So far, it has constructed various prototypes that have been used to test how well their steel frames perform under pressure and to conduct suborbital "hop tests," which have tested how the rocket's gargantuan engines can steer the vehicle to soft, pinpoint landings after flight. Musk has said the technique is essential for recovering and reusing the vehicles as well as one day conducting a controlled landing on the Moon or Mars.

Previous test flights of Starship prototypes have traveled less than about 500 feet in the air and made use of only one engine. The vehicle that will be used on SpaceX's next Starship test flight, called SN8, will be the first to have three engines installed. And it will be by far the highest and riskiest Starship test flight yet.

Initially, Musk had said via Twitter that SpaceX would launch the SN8 prototype to 48,768 metres (60,000 feet) — about 17 kilometres (11 miles) — or higher. That would have taken the vehicle into the stratosphere, the second layer of Earth's atmosphere, where weather balloons are flown and supersonic airplane flights are conducted. But the company later decided to target 12,192 metres (40,000 feet), according to Reuters. It's not yet clear how high the Starship SN8 actually traveled on Wednesday.

It's not clear why the company decided to lower its target altitude of this test flight, though 12,192 and 48,768 metres are still well below the roughly 100 kilometre mark, which is widely considered to mark the edge of outer space.

The SN8 rocket wouldn't be able to reach Earth's orbit on its own anyway. The final Starship design will need six rocket engines, and even then the vehicle will require a separate, hulking rocket booster, dubbed the Super Heavy, to blast the spacecraft into orbit because that trip will require it to travel at speeds topping 27,358 kilometres per hour. It's not yet clear if the company has started development or testing of the Super Heavy booster.

For a journey to Mars, Starship will also eventually need to reach "escape velocity" — about 40,233 kilometres per hour — which is the speed required to rip a spacecraft away from Earth's gravitational pull, allowing it to travel into more distant regions of our solar system.

Musk founded SpaceX around his interplanetary travel ambitions, claiming he wanted to develop the technology to allow humans to settle the Red Planet.

SpaceX's plans for a Mars settlement bring up numerous technological, political and ethical questions. It's not clear for example, if Musk envisions working with Earthly governments to establish a space colony or if he intends to create a sovereign nation, which could violate existing international treaties that govern human behavior in outer space. One of the most challenging hurdles may also be financial: Not even Musk has ventured to guess an all-in cost estimate.

But Starship could have plenty of other practical purposes closer to home. The spacecraft could be capable of hauling massive satellites or research telescopes into Earth's orbit, resupplying the International Space Station, or, perhaps, shuttling people between cities at unprecedented speeds. In a September 2017 presentation, SpaceX said Starship could be "capable of taking people from any city to any other city on Earth in under one hour."