Yes, you’re right, and there’s a really good reason for that. When we build houses, we hide the wiring and plumbing inside the walls to make it easier to maintain a hygenic and aesthetically pleasing environment. We don’t mind having to chop through drywall to fix a pipe, or open up the siding to replace a failed wire.
A vehicle hull, though, has to be immensely stronger and more structurally cohesive than a static structure. Cars and trains are made of metal, not drywall and vinyl siding. So your car is built with all the components accessible through hatches and panels, rather than forcing you to chop into the sheet metal to replace a fuel pump.
A spacecraft, in addition, needs to have as much of its infrastructure be both visible and accessible from the inside as possible. It won’t be possible to climb out onto the hull and bang on a stuck valve during re-entry, and even in orbit if you have to tape up a shorted wire inside a conduit you really want to do it without your space-suit gloves on.
So the passenger compartment of a good spacecraft is going to look more like what’s under the hood of your car, with all the attendant visual clutter, than it will look like your living room or a 1950s movie rocket ship. Every part of the vehicle that isn’t a deadly hazard (like T-Stoff tanks or ACM nozzles are, for example) should be entirely visible and accessible to the flight crew.
I think it’s a safe bet that those shiny geometric interior panels are decorative covers, and that if you pop one off the guts of the ship will be carefully arranged for maximum accessibility. I wouldn’t be at all surprised if they fly this bird with the covers off, either.
Well the geodesic appearance of the interior indicates to me, anyway that is the pressure vessel, not merely interior panels. And yes as a functional machine where weight matters, the interior is likely to be…unpretty. One of the things that made Gemini spacecraft an improvement over the Mercury was putting as much of the mechanics as possible in the service module behind the crewed part of the spacecraft…That made it much easier to work on on the ground and meant that you were carrying less mass down to the surface. If it wasn’t needed for reentry they don’t put it inside the reentry vehicle. The film certainly shows them separating from the service module before reentry.
If you’re right I’ll be very surprised. I used to be in the space business (it’s sort of the family trade) and I’ve never seen a crew compartment that wasn’t lined with access panels, or one that put the working guts on the outside of the pressurized volume.
Also, in my experience the preferred shape for a pressure hull is a sphere, and “edges” (such as the ridgelines geodesics have) should be avoided at all costs. On the other hand a geodesic pattern of access panels inside a sphere would let you use a single size panel everywhere, rather than having to keep track of multiple different curved panels.
Granted, though, we don’t know how “real” that crew compartment is. SpaceX is implying that’s the real ship, but I don’t really know how trustworthy they are.
@halloween_jack_, my father met von Braun a few times; Dad said the man was a Nazi and would always be a Nazi, so I’ve always enjoyed Lehrer’s song. Thanks for the video!
The electronics to control a spacecraft can fit in a handheld - the power switching components should be near the actuators, not at the end of a cable bundle, and bluetooth weighs less than wires. The outer hull shape is dictated by aerodynamics - for landing, smaller is not better, though small is good if you are packing a human on top of a repurposed ICBM launcher like Mercury, Gemini, and Soyuz. SpaceX starts fresh.
Why shiny, thin, and spacious? Just outside the skin is incandescent reentry plasma. The shell of Dragon 2 will get HOT. Shiny means low infrared emissivity. The inside wall of the shell could be 800C and not appear red hot, no heat radiating at the astronauts, presumably wearing IR reflective garments and getting cool breathing air. Lots of air convection in the capsule, sure, but that may be managed in some clever way, too. Use cleverness, not kilograms.
I would put heavy robust equipment under the seats, fragile equipment near the nose, so the center of gravity stays low, but with automatic control, who needs passive aerodynamic stability?. Servicing the vehicle on the ground, I would place temporary foam covered hard panels around outside and inside surfaces to avoid scratches, so featureless surfaces will again be a win.
Just keep in mind that this is a 21st century spacecraft, not a 20th century aircraft or warhead. Cable bundles are stupid. Automotive CANBUS is all you need. Dragon probably evolved from a Tesla Roadster, not an aircraft.
BTW, what do they pressurize the cabin with? 50/50 O₂/He at 20KPa would be lightweight and low heat capacity. The astronauts could breath pure O₂. SpaceX uses a lot of helium for propellant pressurization.
I wonder what we will use to pressurize our spacecraft and cool our MRI machines when all the Earth’s helium is used up? Perhaps we can mine it on the sun. It is hot there; we’ll go at night
Well, if you’re in an aircraft and you mistime a burn by three or four seconds you’re unlikely to plow into the ground at orbital velocity.
Spacecraft are not very much like aircraft or cars. Thinking of them in those terms is a bad paradigm that will lead you astray. A spacecraft is like a submarine, only more so, and with rockets on. The allowable margins of error are similar to those of a submarine at the bottom of the ocean, not really in the ballpark with planes or cars.
I don’t think that access panels would require that amount of reinforcing. After all, they only have to carry their own weight. (Of course in this case they’d be designed to hold up under something like 6-10 g s, rather more than their weight on Earth.) The reinforcing ribs are reminiscent of, but a different pattern from, the reinforcing on the outside of the pressure envelope of the ISS modules (which are usually hidden from view. I’m not sure why the decision was made to put the reinforcing ribs on the inside, but I’ll bet there was a reason. Yeah, spheres are volumetricly the most efficient shape, but they can be a bitch to fabricate and aren’t particularly aerodynamic. So the Mercury through Apollo spacecraft were primarily frustrums but with a spherical or elipsoidal rear.
You’re certainly right that space ships resemble subs more than aircraft in many ways… They’re sealed pressure envelopes with people inside.
It can be mined from the moon… (A bit closer than the sun) There are some relatively well-developed plans to mine Helium from the moon because it is a rich source of He32 (vs the “normal” He42 which is really good for clean fusion power. (I think that is what they were doing in the movie “Moon”)
Nitrogen in sea level air is heavy, 78.1% (by mass??) of 1.225 kg/m³, or about 0.96 kg/m³. Displacing the nitrogen with helium would mass 0.1785*0.781 or 0.14 kg/m³, saving 0.82 kg/m³. Estimating 10 m³ of cabin volume, that is 8.2 kg savings, and guesstimating $5000/kg for a man-rated launch (cargo will be cheaper), that is $41,000. Helium gas costs $2.73/m³, so 7.8 m³ of helium costs $21. There is probably much more cabin air stored in tanks - multiply accordingly.
SpaceX is using a LOT of helium for propellant pressurization. If you use the same helium tank for cabin pressurization, and use boiloff propellant oxygen for the same, you save a lot of complexity and launch mass. A minor savings is that He has a lower specific heat than N₂, so expanding it from high pressure doesn’t require quite as much heat. It also cuts down the convective heat flow from the hot cabin walls during reentry (and running at 6 psi 50/50 He/O₂ would cut it down more).
Yes, your astronauts will sound like Donald Duck. Fix that with a few pennies worth of computer sound processing on the ground.
Note added: If you can share between propulsion and breathing, then in an emergency you can use your propulsion oxygen and helium for breathing, and use the parachute and hard landing. Dented capsules are better than dead astronauts. If the propulsion system is using hypergolics(?), I wonder if a little oxygen would boost Isp, another reason to keep extra LOX around.
Offhand I can only think of two reasons to use bluetooth - to reduce weight of wiring and for PR purposes. Personally, I would never use it for vehicle control regardless; it’s too hard to diagnose and field-repair compared to equivalent wiring and I’m paranoid about hardware failures in hostile environments. If you took a 3mm hull puncture during reentry, so that you had pure electromagnetic hell streaming in through that hole, would bluetooth still work? I have no idea!
But for public relations, having some interfaces be wireless might be desirable for the same reason I have a huge whiteboard. Technically speaking, old-fashioned blackboards are much better, but since people mistakenly think whiteboards are “high tech” it helps me project a certain professional image when I am dealing with money-people and meme-driven meat puppets. SpaceX works hard on their image (for very good reasons) and most people think wirelessness is the bee’s knees.
I didn’t see any reinforcing; I’ll have to look at it again. I confess I looked harder at the printed engines than at the crew space interior when I was actually watching the video.
We probably shouldn’t base any theories about launch and reentry vehicles on ISS module design. The modules start life as cargo and end up as space station compartments, and everyone understands that they periodically get holes punched in them yet they still build 'em with up to 30% of the hull completely inaccessible from the interior, so that spacewalking is required for routine patching! Crew quarters that you can evacuate and repair at leisure will be very different from vehicle cockpits.
And personally I’ve probably dealt with more spherical volumes in spacecraft than all other shapes put together, because most of the STAR series of solid fuel rocket motors had spherical bodies. The Elkton plant’s junkyard at times looked like a mister bubble commercial. Maybe my view is skewed! I only ever expect to see cylindrical, spherical or conical volumes in a launch platform, and nothing with any leading edges to it.
I’ll be quite surprised (and fascinated) if the structure we’re talking about is any sort of pressure hull. But it’s a new design after all - you could still be right!
