For nearly seven years and 20 launches, Space Exploration Technologies Corp., the upstart teenager among United States rocket-makers, has enjoyed an unbroken string of successes.

Now, the company is having to deal with a launch failure the likes of which it hasn't seen since the early days of its first rocket offering, the Falcon 1.

A Falcon 9 rocket bearing more than 2 tons of cargo bound for the International Space Station exploded Sunday morning 139 seconds after launch from the Cape Canaveral Air Force Station, adjacent to the Kennedy Space Center in Florida. The rocket was not manned.

Yet analysts suggest that while the mishap is a problem for SpaceX, it is an expected cost of pushing the envelope in space – in this case by trying to drive down the cost of launching payloads by moving toward a fully reusable rocket.

"It's definitely a setback," says Bill Ostrove, a market analyst at Forecast International, an aerospace- and defense-industry consulting firm based in Newtown, Conn.

But the Falcon 9 also has recorded 18 successful launches, following two consecutive successes with the Falcon 1. Sunday's failure gives the rocket a 94 percent success rate through its first 19 launch attempts, he adds.

Eighteen successes in 19 launches is pretty decent, compared with the success rates of the launch industry as a whole, where rates within the mid- to upper 90-percent range are common, he says.

NASA officials have repeatedly cautioned that launching rockets is not a cake walk and that the agency's space-station resupply plans account for launch failures.

"We've always assumed we would lose a vehicle every so often," noted Michael Suffredini, who heads NASA's space-station program, during a post-accident press briefing. "Getting to low-Earth orbit is extremely challenging."

Indeed, Sunday's loss of the Falcon 9 and its cargo-laden Dragon capsule marks the third space-station resupply failure since last fall, when Virginia-based Orbital Sciences Corporation's Antares booster exploded last Oct. 28, just seconds after launch.

In April, Russia launched a Progress resupply capsule to the station. The capsule reached orbit. But something caused the capsule to begin rolling uncontrollably. After 10 days in orbit, the capsule with 2.5 tons of cargo reentered the atmosphere and burned up.

Orbital Sciences is getting set to resume resupply missions in December by putting its Cygnus cargo capsule on an Atlas rocket, provided by United Launch Alliance, a nine-year-old joint venture between aerospace giants Lockheed Martin and the Boeing Company.

While the space station has sufficient supplies to keep the crew comfortable and enough experiments to keep the crew busy, "having three [failures] this close together is not what we'd hoped for," Mr. Suffredini said.

He and his team will be exploring options for tweaking the cargo lists for three upcoming resupply and crew-exchange missions, including Orbital Sciences' December mission, which he said might be moved up slightly.

Given this string of high-profile failures among different launch providers and different rockets, "there's a tendency to over-dramatize something that has been a staple of our industry for 40 or 50 years," says Marco Caceres, a senior analyst and director of space studies for the Teal Group, an aerospace consulting firm based in Fairfax, Va. He adds the crash of Virgin Galactic's Spaceship 2 last year to the list as well, in which one of the test flight's two crew members died.

"They are more high-profile because the industry is evolving" and people are questioning whether it's the right direction, Mr. Caceres says.

Where NASA and the US Air Force ordered up and operated their own rockets, "now you have private companies owning and operating their own rockets and selling their services to the government," he says. "The idea is to drive competition and therefore bring down launch costs to the US taxpayer."

Sunday's loss of the Falcon 9 and its cargo is a setback, but not a tragedy, he says.

The mission was unmanned, so the event left no fatalities or injuries to tally, he observes. And the company has enjoyed a string of 18 successes with the rocket.

"That's pretty darn good, particularly for a private company that's funded this effort pretty much on its own," Caceres says.

The success rate doesn't match the "stellar" record of United Launch Alliance's Delta and Atlas vehicles, he acknowledges, because they have a longer history.

But those are expensive rockets – costing upwards of $300 million a launch versus $60 million per launch for a Falcon 9, according to Forecast International's Mr. Ostrove.

Conceptually, the Falcon 9's basics are similar to rockets launched since the dawn of the Space Age. But the company is at the cutting edge of efforts to turn traditional rockets into vehicles that are fully reusable. Evidence of that comes from the legs and steering paddles the company has added to its latest versions of the Falcon 9's first stage. The technology is improving, although it has yet to bring the booster to a soft landing on a specially designed drone ship that is its current target.

To hold down costs in advance of full reusability, the company has taken a different path to building its rockets. From design to fabrication of components and construction, the rockets are designed and take shape in-house. Subcontractors are relatively few and far between. And the rockets are assembled horizontally, rather than vertically – an approach that allows for faster construction.

And since SpaceX is privately owned, it can make a profit without shareholders demanding that those profits be maximized.

"As long as they are making a profit and can pay their staff well, everybody's happy," Caceres says.

It also helps to have a founder, Elon Musk, who brought a substantial personal fortune to the table and who is the company's driving force, something that can lead to quick decisionmaking.

Indeed, the company has been so successful in marketing its services to the military, to other government agencies, and to commercial satellite firms and garnering launch contracts as a result that "their biggest enemy really is themselves," Caceres cautions. That packed schedule puts pressure on the company to maintain a steady launch cadence.

"It's just a matter of time before you have a failure. That's true for any company," he says. But SpaceX has been so successful at filling its rocketry dance card "that everybody is just waiting for that failure."

Indeed, from the standpoint of marketing and reliability, this could be SpaceX's next big test, Ostrove suggests. The pace at which the company can thoroughly troubleshoot Sunday's mishap – initially believed to be the result of an unusual increase in pressure in the second stage oxygen tank – and fix the problem could influence prospective future customers.

Customers with missions already on the company's manifest are likely to stick with SpaceX unless there is something truly time-sensitive about the payload they want to loft. Companies that have projects on the drawing boards and haven't yet selected a launch provider could be the toughest sells, should the investigation and needed changes take too long to complete.

It's unclear at the moment how long it will take SpaceX to return to flight.

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But "we're certainly in an extraordinary position to know what happened, to find what happened, to fix what happened, and to get back to flight," said Gwynne Shotwell, SpaceX's president and chief operating officer. "The majority of this launch vehicle and all its components are ours. We don't have to go through legal and contracts negotiations and discussions to get data on any components."

"I'm sure we'll find it rapidly and we'll get back to flight as soon as we safely and reliably can," she said.