STARSHIP — USA, 2023/2026?

Starship the spacecraft is just the upper part of SpaceX’s Starship rocket, in which the second stage tanks and engines are integrated permanently with the payload section so both are reusable. If they manage to build this ship in passenger configuration, it’ll have around 1000 cubic meters of pressurized space — the size of a big airliner, or the entire International Space Station. They envision a Mars vessel with forty little cabins holding up to 2.5 passengers each, and a big chunk of common space. (They do hope to send a hundred colonists per shipload, and they could probably do more if they want to put poor emigrants into steerage.) Traditional space capsules tend to have only two or three cubic meters per person, and that can be okay for flights of a week or two, but it will hardly suffice for a voyage to Mars. (The one earlier vessel that did have a lot more room per person was the Shuttle.) A ship this enormous probably could take a hundred people to Mars... if, that is, a colony were already well established there, so the ship did not have to be mostly filled with essential equipment they would need after arriving. It’s clear that early flights will have far fewer people on them.

Their mockups show large windows at the front; if I were a passenger I’d feel a bit nervous about having a big weak point like that. They have not mentioned anything like, say, making the cabins have airtight doors in case of a blowout, probably because they have a hard time imagining a scenario in which they could ever be rescued. One important bit they are planning to include will be a solar storm shelter; if there’s a flare or something, everybody will have to crowd together into a shielded bunker in the middle of the ship until it passes. (In today’s spacecraft, all you get is a protective vest.)

According to SpaceX, the big heat shield on the belly will be the most difficult part to make, as they want it to withstand reentry from interplanetary velocities. That reentry will try to lose as much velocity as possible at as high an altitude as possible: though the shape is streamlined for going up, they want the opposite of that when coming down, so it descends crosswise with its nose pointed steeply upward, like the Shuttle did. The ship has protruding fins at both ends which are not wings or control flaps, but adjustable air-brakes whose purpose is to increase drag. Even once it has lost its horizontal speed, they maintain this same crosswise approach and have it belly-flop straight down through the lower atmosphere, using the fins at both ends the way skydivers use their limbs, to balance the ship on a level plane. This would be a slower descent than in any normal capsule or spaceplane, though it’s still faster than the terminal velocity of a falling person. Then, in the final seconds, it lights the engines and goes vertical to land on its tail. This is tricky enough in Earth’s thick atmosphere, and they’re planning to try the same thing on Mars, which will be tougher since there’s so much less drag at lower speeds — they’ll probably have to light the engines while the descent is still supersonic.

Their original idea was to use a conventional ablative heat shield. Once they switched to making the ship’s skin out of steel, they dropped this and actually said they would just leave the metal exposed and polish it very brightly. This would reflect away most heat (which is radiated by glowing air in the shock front) and they would use liquid cooling to dissipate the rest — the liquid in question being unburned propellant, which means that if you don’t have tons to spare, you can’t come back down. (TMBG prophesied this when they sang “They run out of gas, the plane can never land.”) The fuel would not return to the tank, but boil out through pinholes in the shield surface. By their calculations this wastage would still come out lighter than an ablative shield over carbon fiber.

I soon realized that this approach would face tough challenges at edges and corners, and especially at protecting the hinges for the fins. And that even the flat areas would have a tough time keeping the evaporative cooling uniform and consistent, without hot spots. And unlike an ablative shield, any hot spot could rapidly start absorbing more heat in a vicious cycle, because once an object is warm enough to glow, even if just in the infrared, it also absorbs radiation in the same frequencies that it is emitting. It loses its reflectivity. A few clogged pores, or even a region of below average pressure in the coolant, could lead to a warm spot that just keeps heating until it melts through. In a conventional ablative heat shield, a divot or other weak spot can be somewhat sheltered by the good areas around it, but in this approach, any local imperfection in shedding heat just becomes a magnet that draws in even more heat. This inherent fragility substantially undermined my confidence in the success of the Starship idea, which sounded great and revolutionary back in 2017.

But then the SpaceX engineers sobered up, and they said they were moving away from the evaporative cooling idea, and realized that they needed a ceramic tile which would protect the steel. The challenge was to give it the right emissivity to minimize absorbtion and maximize dissipation of radiant heat. But since the steel behind the tile is still okay with being heated to a thousand degrees, the tile can be thinner and lighter than it would normally need to be. (They said they might still use a bit of evaporative cooling in a few critical spots, such as the flap hinges, but as far as I know nothing ever came of that.) The tile material ended up being pretty much a direct copy of what NASA came up with for the Shuttle, but much cheaper because the tiles ren’t very thick and can be mass-produced as identical hexagons. Only the hinges and the nose need custom curved shapes.

Fortunately, the first Starship version they’ve found some paid work for doesn’t need a heat shield, this being the lunar model which will be used to land astronauts near the moon’s south pole for Artemis III and IV. This would be set up inside for a small number of astronauts and a large amount of equipment, with a pair of airlocks and fold-out elevators to reach the surface. Instead of heat tiles, it would have solar panels and a thin layer of micrometeorite protection. This craft could make many visits to the surface of the moon, but never return to Earth. And it could be used as an impromptu space station, perhaps making the Lunar Orbital Platform-Gateway redundant for the earlier parts of the Artemis plan.

Early designs for the lunar ship showed solar panels wrapped around the upper body, and four stubby legs. Newer ones show solar panels on five articulated wings, which should make quite a bit more juice, and longer legs to handle uneven ground. The old plan had a ring of twelve midsized rocket motors that angle out the sides at the bottom of the crew cabin, high off the ground, to land and take off without blowing too much dust and gravel off the surface. In the new one, there are eighteen smaller thrusters which are mounted in protruding pods so they can point straight down.

If they get the heat shielding solution to a dependable state, the capability to refuel in orbit will make this a step beyond all other capsules and spaceplanes. It would be in every sense a true spaceship — humanity’s first — because with fully refilled tanks it can go to almost any planet or asteroid in the solar system. This would allow a large number of flights to get to Mars affordably... but not safely. The ship won’t have fuel to orbit Mars; it can only stop itself from whizzing right past the planet by plunging into the atmosphere, at which point it has no way to back out or abort, and little choice about where to land. It won’t even have fuel to come home with. This approach suits Elon’s dream of populating a large colony there, but is badly suited to initial exploration. There is probably some way to redesign an exploratory mission so it can use Starship, but as yet no such plan has come from SpaceX. Everything they’ve proposed is oriented toward colonization, and their only plan for returning to Earth is to manufacture tons of fuel out of the water and carbon dioxide they find there, which might take years.

They started building the factory for the Starship and its superheavy booster in the Port of Los Angeles, which they picked so the rockets could be transported by sea. They already started making some large pieces of carbon fiber cylinder before the building was built there... and then they tore down their preliminary construction, and scrapped at least one piece of expensive tooling which they had purchased to wrap carbon fiber around. They then said the manufacturing of the steel version would be done in Florida and Texas. At their existing Texas facility, they built a “hopper” to test taking off and landing in a fake Starship, shorter and lighter than the real thing but with the full nine meter diameter. They flew this just once (with a rough landing) before immediately moving on to two full sized prototypes. Then, as the first true flyable Starship was taking shape, they decided to reopen the Los Angeles facility. Then they apparently forgot about it again, concentrating all their efforts on expanding their test facility in Boca Chica (near the mouth of the Rio Grande) into a full shipyard. Before long they were making ship prototypes by the dozen. They eventually showed that the belly-flop landing could work, and then they started making boosters.

At this point they are struggling to get the thing up to orbit and back down again intact, and the clock is ticking on the promised lunar lander. And they can’t just build the one; they need a set of tanker Starships to fuel it. At this point I’ve hardly heard a peep about progress on making a passenger section able to support astronauts.

If they ever do get it ready to go to Mars, they say they’re going to rotate it so it has a hint of artificial gravity. It might be a barely noticeable amount, but they guess that even the tiniest bit of gravity is better than none. As far as medical effects go, I don’t think this has never been tested, but it’s possible they may be right. Two rotations a minute would produce about 0.02 G, which would hold you to the outer wall reasonably well and would probably make toilets easier to use. And if you want to be aggressive, less than six RPM would be enough to yield lunar gravity, and Mars gravity could be had with just under nine RPM. Maybe they could try that during an outbound trip for short-term practice sessions, with safety warnings ahead of time against dropping from the center axis.