Two days ago, SpaceX was running a series of static fire tests of their Crew Dragon spacecraft, designed to carry astronauts back to the ISS. This was the same Dragon that launched back in March and visited the International Space Station for a few days before returning to Earth. SpaceX had planned on reusing this spacecraft on the In Flight Abort test, where it would test its abort system during launch to ensure safety in the event of an anamoly.
During these static fire tests of the abort system, there was an anamoly just prior to igniting the engines that caused and explosion and loss of the vehicle. A leaked video showed Crew Dragon on the test stand counting down to ignition and an explosion occured about 8 seconds before firing in the center of the spacecraft. The cause of the anamoly is unknown and is being investigated. This suggests seeing astronauts launching from american soil being delayed into 2020 for SpaceX.
While this is not good for progress and puts some worry into
the reliability of the Crew Dragon spacecraft, this is a big learning opportunity. It is better for an issue to be uncovered during testing than for it to be found accidentally during a crewed flight and killing astronauts. It's always beneficial to find flaws in a design before putting them to human use and risking people's lives. It does delay the human flights, but at least SpaceX's Crew Dragon spacecraft will become a safer and more reliable vehicle in the end.
As of now, SpaceX's Cargo Dragon spacecraft is still on track to launch to the ISS on its CRS-17 mission early next week. CRS-17 is currently targeting 4:22am EDT on Tuesday, April 30th.