Just so we're clear, SpaceX built a Mars rocket out of rolls of steel, in tents, in South Texas, in weeks. And the first time they flew it, it made a smooth launch, a controlled flight, and safely landed. This is truly remarkable.
Wednesday, August 5, 2020
The Flying Grain Silo Flies
In the last hour of daylight in South Texas, after a much earlier attempt that resulted in Yet Another Abort, Starship Prototype Serial Number 5 (SN5) took a powered flight up about 500 feet, translated sideways a little way, and soft landed. We've been talking about this milestone since early May and the actual minute of flight was, to quote Twitter, “... simultaneously cool as hell and fucking ridiculous.”
Another view of the launch is in this video from LabPadre. It's a bit longer than necessary, but I put the start just before ignition.
A comment I saw somewhere was that Starhopper did this almost exactly a year ago, so what's the big deal? That comes down to the purpose of the vehicles. Starhopper was a test bed for the controllable Raptor engines. It was built heavy - I've read mostly half inch steel plate, so far too heavy to make orbit and carry a payload. SN5, in contrast, was built as a pathfinder for testing the assembly concepts of the Starship itself. It's built of thin stainless steel sheets, 4mm or about 5/32" thick, and part of pathfinding was learning how to weld the ship so that it stays together. That hasn't been a sure thing. (example 1, example 2, example 3).
In time, they will almost certainly invest in sophisticated robots to improve weld quality and speed, but instead of doing that first, they hired expert welders to develop the process and do it manually.
Why does the flight look so awkward? Starship is designed for three Raptor engines laid out in a triangle on the base. Because SN5 is so light compared to an orbital class Starship, they used one engine but that meant the line of action of the thrust is off the centerline, which both pushes the vehicle sideways and acts to tip it over. Even with going down to one engine, one is still too powerful for this load, so they had to put a huge mass on the top of the vehicle. Back on SN4, that was lost in a Ground Support Equipment methane explosion, the so-called mass simulator weighed over 50,000 pounds. I have no reason to think this one was any smaller. With the 50,000 pounds on top and one Raptor engine, the thrust to weight ratio was better.
So what's next? I don't know. I know the plans are to launch one of these Starship prototypes to quite a bit more than 150m/500 feet approved for this one and eventually to 20 kilometers (65,000 feet) but I don't know if they'll use prototypes SN6 or 8, already built and standing by, or if they'll do more with SN5. Considering that a few attempts to fly were aborted by a valve in the Raptor engine, that will have to be looked at, too. The booster for Starship, Super Heavy, will have over 30 Raptor engines and if they have trouble getting one to start reliably a Super Heavy will never fly. In the long run, there will be suborbital flights of Starship and orbital tests. Those will require Super Heavy. I've heard that we might see a Super Heavy by the first of the year. It's helpful to remember the first of the year is five months away.
The Super Heavy vertical assembly building is being built, and as recently as June, Hans Koenigsmann, SpaceX's VP of Build and Flight Reliability, was saying we might be able to see an orbital Starship mission by the end of the year. Seems ambitious to me, but it's worth keeping an eye on them for progress.