Originally planned to be launched in 2016, NASA reported to Congress on Wednesday that its new heavy lift rocket, the Space Launch System (SLS), won't be ready for its rescheduled June 2020 launch.
It is likely that reliance will have to put upon SpaceX's Falcon Heavy to initially test fly an Orion capsule.
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https://phys.org/news/2019-03-nasa-c...ls-rocket.html