SpaceX is in the middle of a very busy year. The company has launched five of its Falcon 9 rockets — which matches the amount sent into space in all of 2014 — and it’s getting closer and closer to landing the first reusable rocket stage ever. The next test of that system won’t come until June, but today the company has an important test of a different kind. SpaceX will test its "pad abort" system, the company’s back-up plan in case of a launchpad emergency when it attempts to send astronauts to the International Space Station in a few years.

The pad abort test will last just 107 seconds, and SpaceX will fire eight "SuperDraco" engines (which we saw the company test back in March) for just six of those seconds. NASA will provide live-streaming coverage of the test, which was originally scheduled to begin at 6:35AM ET but has now been pushed back to 9:00AM ET.

During the test, the SuperDracos will propel the Dragon spacecraft more than one-third of a mile away from the Falcon 9 in just five seconds. After reaching a peak altitude of nearly a mile, the spacecraft will rotate until the heat shield points down, and small "drogue" parachutes will stabilize the craft. Those will give way to three main parachutes, and less than two minutes after the SuperDracos fire, the capsule should splash down in the Atlantic Ocean 1.4 miles from the Cape Canaveral launch pad.

The abort system works much like a fighter pilot's ejector seat, except the entire craft is ejected instead of just the crew. And while today's test will focus only on a launchpad abort, the system allows for an abort to be executed all the way until the craft is in orbit. (An in-flight abort test is scheduled for later this year.)

The attempt is the most important milestone in the company's plan to send humans to space since it was awarded part of NASA’s Commercial Crew contract last fall. Back then, NASA chose designs from SpaceX and Boeing, and awarded the agency’s largest contracts ever — $2.6 billion and $4.2 billion, respectively — to have crewed capsules ready by 2017. For its entry, SpaceX decided to repurpose the design of its Dragon cargo capsule, which has already proven to be reliable after six successful missions to the space station. Boeing, on the other hand, is developing its spacecraft (called the CST-100) from the ground up.

NASA is in the middle of developing its own crew capsule called Orion, which made its first successful test flight late in 2014. But that won’t resume testing until at least 2017, and crewed testing of Orion isn't expected for another five years after that. In the meantime, NASA still relies on Roscosmos, the Russian space agency, to bring its astronauts into orbit. Political tensions and sheer cost — Roscosmos charges NASA about $70 million per astronaut per launch — are why NASA wants to use SpaceX and Boeing to bring astronauts to the ISS instead. To do that safely, however, the agency has laid out a roadmap that requires these private space companies to test certain aspects of their systems before crewed tests can be attempted.

If SpaceX is successful with today's milestone attempt, the company will unlock about $30 million of the money NASA has budgeted for the contract. A failure would mean the company faces a tighter schedule going forward.

Update May 6th, 7:20AM ET: Updated to include new timeframe for the launch.