SpaceX says that the test has a 30% to 40% probability of success, so it could all go pear-shaped. But the engineers there hope that the data collected during the attempt at a controlled descent will help them to refine their approach to building a more efficient launch vehicle. As we’ve written before, making a rocket reusable is something of a holy grail for Musk and SpaceX: While the rockets cost $54 million, their fuel costs only $200,000, so making most of the rocket reusable would save tens of millions of dollars and allow the fledgling rocket company—which already seeks to undercut its competitors on price—to dominate the putting-things-in-space business.

The 2.3 tons  (2.1 tonnes) of cargo in today’s launch consists mostly of scientific payloads to the station, including sensors and cameras for the station as well as VEGGIE, an experiment designed to allow astronauts to produce “salad-type vegetables in space.” But it will also contain food, additional spacesuits, and equipment needed to support a space walk on April 22 that will attempt to fix the malfunctioning computer.

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