I’m now going to fundamentally disagree with Elon Musk on a technical detail. Granted, this one is literally not rocket science. Nevertheless, it matters a great deal for people planning to put cargo on the surface.

In his 2017 IAC presentation, Musk said he’d been asked by many how SpaceX intended to get equipment from the cargo hold, high up on a BFR, down to the surface. He pointed at the artist’s conception of a BFR unloading on the Moon, and casually shrugged, “It’s a crane.”

Yes, it was. A very 1920’s style crane. The kind that relies on longshoremen and stevedores with years of experience bringing cargo off a ship. Experience needed to ensure the vessel doesn’t list and the cargo doesn’t unbalance the crane. The kind requiring manual labor to load and unload the crane itself.

Possibly fine once we have crew on Mars, this design is entirely unsuitable for robotically unloading cargo from Constellation and Finity’s End. We need something a lot more like today’s intermodal cranes. They’ll be much smaller and lighter, of course, more like air freight; but the idea is that the crane’s spreader and trolley can connect to our cargo in the hold, move it outside the ship, lower it to the surface, and disconnect, all autonomously. To accommodate this, our cargo will need intermodal-style corner castings on top corner posts which the crane’s twistlocks can lock into without human intervention.

For securing the cargo to the deck, we should look to the air cargo industry’s Unit Load Devices (ULD). These are lightweight containers or pallets (pallets secure their cargo with nets), but they’re loaded and unloaded by rolling them across scissor trucks. Fine for loading on Earth; that obviously isn’t going to work for unloading on Mars, hence the intermodal hybrid. One particular industry innovation we’ll want to implement, though, is the ability to automatically lock the ULD in place on the deck.

Without spending too much time designing at this early stage, we can still sketch out how this would work autonomously. The first thing down needs to be a rover/tractor with a robot arm. That gives us mobility on the surface and the ability to do work. To be autonomous, it will need lots of cameras; that will also be essential when it’s necessary to intervene from Earth. Adding corner posts with corner castings seems reasonably straightforward, as is ensuring the center of gravity is close to the geometric middle of the vehicle.

The second item down is a trailer, preloaded with equipment to set up the solar power field. Without knowing SpaceX’s design for the field, we can only speculate on whether this will be solar panels with integrated power cables, whether the cables will be run separately, and which gets positioned first. Regardless, the tractor connects to the trailer, heads out to the predetermined spot, and starts laying out solar panels and cabling. After the first load is deployed, the tractor trailer returns and spots itself under the crane to receive the next package. Here, the cargo again uses corner castings to connect to the crane and ULD auto-locks to secure to the trailer. Presumably, we have a stack of several solar panels, so we’ll need customized interconnectors to hold the stack together, analogous to “interbox” connectors used for intermodal containers. These are normally placed by stevedores, and we just have a robot arm, so the design will need to be creative. The solar panel stack will also, by necessity, be slightly smaller than the trailer, so our crane’s spreader will need to be adjustable. An advantage of adjustability is that we have more flexibility with center of gravity. The obvious disadvantage is more design complexity. But, there’s a whole industry that does this.

Goal #1 is providing enough power to keep the ships healthy. (We’ll talk about Goals 2+ in future posts.) The primary risk for this design appears to be whether everything we build will work the same in one-third gee as it does on Earth. As we did earlier with landing algorithms, checking this out in one-sixth gee seems both practical and prudent.

My sense is that SpaceX is well aware it will need to do this—design, build, and test the whole system we’ve just described until there’s virtually no doubt it will work reliably. That’s a lot of work—but not compared to designing, building, and testing BFR itself. SpaceX is likely waiting until BFR is demonstrably farther along before it starts serious work for a Mars solar power field, so it’s also reasonable they’ve put “crane” on a list of placeholders they’ll come back to later. Still, the cargo offload system is also the first component they could partially offload to others. That would bring in more people to work on the problem without diluting SpaceX’s core expertise. Tesla doesn’t build tractors, but John Deere, Caterpillar, and Mahindra do. They can also probably figure out how to make their products lighter and run on batteries a lot quicker than anyone else. SpaceX could probably also team with intermodal companies to figure out the best designs for unloading.

Certainly, there’s a giggle factor asking outsiders to start seriously considering how to build equipment for Mars. That’s a valid reason to wait until BFR is farther along. But, if we go back to that initial list we made, we see that there are a LOT of things people need to get started on. People like us. After all, that’s the whole point of this website.