Why is Orion conical?

[dronkit]

Just that. Why is the Orion capsule conical and not, say, cylindrical like the Mk2 Lander Can (lol). In space, you don't need aerodynamics. In takeoff, it's covered with a fairing. In reentry, it comes butt-down. If it was cylindrical they would gain useful habitable space. So why?

[Bill Phil]

Primarily for limited reentry control, a la Apollo. Plus it's easier to make an escape system.

[Red Iron Crown]

A cone is also a structurally stronger shape than a cylinder.

[rodion]

i imagine that it mostly has to do with the fact that the flat cone form is a great shape for a re-entry vehicle. it gives the capsule a nice low centre of gravity for stability and keeps the maximum amount of the capsule's upper skin out of the direct line of the plasma that will be streaming past it, whereas a cylinder would have much more of its surface exposed to the air and therefore need more, and heavier, thermal protection on its sides. the flat cone also gives keeps the amount of lift generated during descent to a reasonable level whereas the edge of a cylinder, depending on how long it was, would start to generate extra lift as it entered the atmosphere and might cause the craft to skip off the atmosphere. there are probably many more rationales for the design that i haven't even thought of but those are just a few i came up with just now.

[sal_vager]

It really has to be that cone shape, it allows for a wide and flat base which provides a lot of drag, essential when slowing down from orbital speeds, and that base actually helps prevent overheating as some of the air acts like a buffer.

The tapering cone shape is also necessary to prevent overheating of the much more vulnerable walls of he capsule, as the hot gas is deflected out far enough that it can't get back in to the pods angled walls, straight walls would be hit by the superheated air and require a lot of thermal shielding to protect.

Having that cone saves a lot of mass on heat tiles.

[Red Iron Crown]

Conical is not the only feasible shape. Soyuz's reentry module is more of a bell shape than a cone, which would give more volume for the same surface area, not sure if the side walls require much more heat shielding than on a conical capsule.

[magnemoe]

Conical is not the only feasible shape. Soyuz's reentry module is more of a bell shape than a cone, which would give more volume for the same surface area, not sure if the side walls require much more heat shielding than on a conical capsule.

Yes, dragon1 and 2 is an cone but far more cylindrical, even apollo is more cylindrical. However the width and weight restrictions also kick in. Unlike dragon orion has an service module.

[Tommygun]

I've always heard that the cone shape was chosen for all of the US capsules as it is self righting if it tumbles over during reentry.

[worir4]

So you can pick your nose with it .... XD

[sgt_flyer]

Well, they use lifting body techniques with the cone shape, which would be disturbed by other shapes. (Basically, they still have their numbers from apollo, no need to remake the wheel )

The apollo capsule had an offset gravity center, so the heat shield was not perpendicular to the reentry vector.

This offset during reentry allowed the capsule to steer it's course during reentry, simply by making the air 'bouncing' off the shield at an angle. (Which allows for a much wider reentry corridor, if you come in too steep, turn the capsule to deflect air downwards - in return the capsule goes upwards. On the other end, if you came in too flat and risks bouncing out of atmo, turn the capsule so the heat shield deflects the air upwards. This also allows to fine tune the final landing spot.)

The specific cone shape allows for a bigger 'range' of deflection than a soyuz bell shape would be able to. (However, keep in mind that soyuz is primarily made for leo operations, with much slower reentry speeds (and easier to predict reentry angles), whereas apollo / orion is meant for moon / interplanetary returns (so this extra amount of body lift could be useful - without having to expose anything else than the heat shield)

[Kryten]

I've always heard that the cone shape was chosen for all of the US capsules as it is self righting if it tumbles over during reentry.

Soyuz is also self righting, as demonstrated by Soyuz 5.

[Tommygun]

But isn't that partly made possible by having a large ballast weight at the bottom.

I think the cone shape needs less ballast.

[Kryten]

But isn't that partly made possible by having a large ballast weight at the bottom.

I think the cone shape needs less ballast.

You need uneven weight distribution yes, but not necessarily ballast. AFAIK it's just equipment.

[dronkit]

Wow thanks for all the thorough responses!