On 28 September, 2019, Elon Musk gave an update on “Starship,” formerly BFR, in what has become something of an annual tradition. After n hour-long delay due to high winds, the outdoor presentation took place in front of the best possible backdrop--an assembled Starship Mk 1 suborbital test vehicle. A thousand miles away, a second suborbital Starship was taking shape at Cape Canaveral. Following a major design change in October 2018, the vehicles now sport 301 stainless steel construction. As Musk pointed out, SpaceX found that stainless steel has a number of advantages. Cost is one--$2,500 per ton, vs. $130,000 for the previously planned carbon fiber—making the raw material for the ship (minus engines) about $275,000 vs. $14,300,000, just using the “about 200 tons” figure. Obviously, both versions will include wasted material, and this figure doesn’t include the Super Heavy booster. Ease of fabrication is another advantage—traditional welding techniques can be used, reducing labor costs and letting the assembly team experiment with manufacturing techniques. Musk pointed out two additional advantages—because stainless steel melts at 1500C, the heat shield requirement is considerably reduced, again reducing material and labor cost. And, because stainless steel is strong (end even stronger at cryogenic temperatures), very little is required, counterintuitively making it a very lightweight solution. The new design is expected to tip the scales at 110 tons, once prototyping is done and a variety of small design improvements are implemented. Musk hinted at a stretch goal of 99 tons.
For our design, the change from fins as landing legs means we need a new place to connect ground power, but this seems fairly trivial. More landing legs (six) frankly seems like a good choice, particularly since Mars landing sites aren’t going to be perfectly level.
Much more important, though, is that we might suddenly be able to build and send far more ships than originally planned. When the ITS/MCT version of the ship was expected to cost perhaps a billion dollars, we could consider one—maybe two—per launch window. The suborbital prototypes are taking about four months to assemble. Just making the math simple assume teams of 10 working 20 hours a day (3 shifts, but including some slack) for 120 days, making $100 per hour. That’s $2.4M. The design work is the high cost investment, and the Raptor engines are going to expensive. But the hulls, not considering heat shields or pricey actuators, are low-cost in terms of material and labor. So low, in fact, that there’s a significant advantage to amortizing the design cost over lots of hulls. If you’re only hauling cargo to Mars in a bare-bones freighter, about the only part of the vehicle you’d like to get back are the six Raptors. You can leave the hull there to be scrapped and recycled into the million things you can build with steel.
At this point, it’s too soon to rework our entire mission reference architecture, but we can see the shape of an incredibly more ambitious plan—imagine ten bulk cargo ships per launch window, in addition to a crewed MCCS and a high-end MFR. The MFR’s primary job on the return might be hauling Raptor engines back to Earth.
What else might we do? For starters, we might put a thermal jacket on one of those freighters and send a load of LH2. Or a load of drill pipe. More on that later.