It looked like one of the attached cold gas thruster pods that where reused from old Falcons. Or a COPV tank. Here is the official SpaceX video:
It sure looks like something that is a cross between a Rocket engine and a water tower I'm amazed at the fine control they demonstrated today. Way to go SpaceX's Starhopper team
Awesome! Mach diamonds, cold gas thrusters, Raptor vectoring and fine control all made me happy. The best thing I've seen today. Why does the Raptor exhaust change colour all the way back up to the rocket when the tail-end of the exhaust first touches the ground just before landing? It goes bright orange instead of blue-and-yellow. And the Mach diamonds disappear... Forgot to add: and it looks like me and my sons knocked it up in our backyard. Looks almost deliberately ramshackle. And reminds me of an early Lost in Space episode!
All four COPVs are still there. So what was it? Jack Beyer on Twitter Here is the unknown flying pressure vessel (UFPV) Trevor Mahlmann on Twitter
Some say that it's due throttling and uneven combustion. But it's visible with other vehicles and during lift off too, so the orange color is probable end result of flame reacting with dust cloud.
My guess is that the reflected pressure wave disturbs the exhaust flow. Turbulence prevents the Mach diamond formation and orange is CH4 that cooled from hitting the ground and then combusted in a less oxygen rich environment. You can see a potentially similar phenomenon if you get a nice small laminar flow from a faucet and then put your finger in the stream and move it toward the spout.
Last night on Twitter Scott Manley (With an MS in physics, just one his many exceptional credits) attributed the Raptor exhaust plume color change to "black body radiation from the dust". Google can help to understand, others here might be able to simplify the concept. Scott will likely go into more detail during his next YouTube video.
To quote someone on reddit that paraphrased Douglas Adams: "The hopper hung in the sky in much the same way that bricks don't."
In some order: Starships Mk 1 and Mk 2 with 3 engines doing sub orbital tests Super Heavy tests Starship (6 engine) + SH orbital tests Uncrewed Moon flyby trip Dear Moon trip Crewed? moon landing Crewed moon landing Uncrewed Mars Crewed Mars Europa Infinity Beyond
I'd have to say they have all changed their resumes (or created one if they didn't have one previously). Saying you built the first flying prototype of a Full-flow staged combustion powered spaceship is a pretty big line item on a resume. Especially considering it's never happened before in the entire know history of the world as we know it. I'd have to imagine they got a bonus for a milestone achievement. Probably have another bonus coming up for the starship when it first flies.
Elon is already hinting at an even bigger Super Heavy Starship with a diameter of 18 meters. That would be twice the width of the current super heavy starship!!! SpaceX CEO Elon Musk says Starship could be followed by a dramatically larger rocket
Sad to hear (from Scott Manley) that this beautiful water tower will probably become some type of test stand. But hey, we won’t care much once the Orbital Water Prototypes start flying!