NASA is considering launching its Orion crew capsule on a commercial rocket rather than the Space Launch System, the agency's own megarocket that is currently under development.

The Space Launch System (SLS) is a super-heavy-lift launch vehicle touted as what will be the most powerful rocket in existence. It will be capable of carrying astronauts beyond low Earth orbit, as NASA aims to do with the Orion Multi-Purpose Crew Vehicle .

However, delays and cost overruns with SLS seem to indicate that the new rocket won't be ready on time for Orion's first test flight around the moon — Exploration Mission-1 (EM-1) — which is currently scheduled to launch in June 2020.

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"We're now understanding better how difficult this project is and that it's going to require some additional time," NASA Administrator Jim Bridenstine told the Senate Committee on Commerce, Science and Transportation at a hearing in Washington today (March 13). Bridenstine assured the committee that he and NASA are committed to keeping EM-1 on schedule, even if that means the agency will have to buy a commercial rocket.

Bridenstine did not name any specific launch providers at the hearing, but considering how powerful the rocket will have to be, NASA has two options: SpaceX's Falcon Heavy rocket or a Delta IV Heavy rocket built by the United Launch Alliance. Exactly how much it will cost NASA to hire a commercial launch provider is not clear at this point, but Bridenstine said the agency "might require some help from Congress" to fund it.

For now, SLS is not yet officially off the table for EM-1; NASA will make a decision "in a couple of weeks," Bridenstine said. Even if the agency does opt for a privately built rocket for EM-1, it still plans to use SLS for future Orion missions, Bridenstine said.

However, the White House's budget proposal for 2020 has also deferred plans to build an upgraded version of the SLS , known as the Block 1B, which the agency planned to use to launch components of the Lunar Orbital Platform-Gateway , a new lunar space station that astronauts could visit by the mid-2020s. Instead, the proposed budget calls for NASA to consider using commercial launch vehicles to build the gateway, too.