The SpaceX Starhopper seems like the fastest development of a prototype rocket outside of a wartime rocket program. The purpose of the inexpensive testing is to have the first flight tests of the new Raptor engine. Three of the engines have been placed in a row and the tests will allow control software to be tested and the throttling of the engines to be tested.
The Starhopper rocket should be stacked and welded into one piece within a few days or weeks. The Texas launch pad is still being built and is still piled dirt.
The work on the rocket and the launch pad will come together over the next 60 days and then the rocket will be moved to the launch pad for a first flight in March or April 2019.
SpaceX is getting the regulatory license to fly to about 5000 meters and to go faster than the speed of sound.
SpaceX wants to build and fly to orbit with the full orbital version of the Super Heavy Starship in 2020. This would be with seven raptor engines for the new top stage of a full two vehicle.
The first orbital version may not have the full windows and cockpit of the completed rocket. It would likely also be a more complete prototype.
The Raptor engines are using a dual-bell design. There was a 2014 paper – Conceptual Design for a Dual-Bell Rocket Nozzle System Using a NASA F-15 Airplane as the Flight Testbed
The dual-bell will allow for one system to be used with good vacuum performance and good launch performance.
The dual-bell rocket nozzle was first proposed in 1949, offering a potential improvement in rocket nozzle performance over the conventional-bell nozzle. Despite the performance advantages that have been predicted, both analytically and through static test data, the dual-bell nozzle has still not been adequately tested in a relevant flight environment. In 2013 a proposal was constructed that offered a National Aeronautics and Space Administration (NASA) F-15 airplane as the flight testbed, with the plan to operate a dual-bell rocket nozzle during captive-carried flight.
Star ship hopper might be a bit bigger than we thought and with the crane placements over the nose end of the vehicle. This could suggest, @SpaceX are planning to move the segment elsewhere perhaps to the welding stand? We will have to wait and see. (Austin Barnard📸) #2019🚀 pic.twitter.com/kn8hhUPWCU
— Austin Barnard (@austinbarnard45) January 1, 2019
— Roger Holt (@RogerLewisHolt) January 1, 2019
— Cowboy Dan (@CowboyDanPaasch) January 2, 2019
Vacuum optimization will come with later iterations on BFR, at least according to his Sept. 2018 presentation. For now, Raptor SL or a medium-expansion compromise will do double duty on the booster and upper stage(s). Makes development dramatically simpler.
— Eric Ralph (@13ericralph31) December 27, 2018