why are the noses of rocket, shuttles, planes, missile(…) half spheres instead of spikes?
In: 5557
On a rocket a shape of the nose is irrelevant, because it’s gonna leave thick layers of the atmosphere shortly after start. It’s the shape that allows more payload and some aerodynamics. A blunt cone is enough.
For the shuttle the main reason for blunt shape is the thermal barrier. It’s the one coming after super-sonic barrier and is experienced at hyper-speeds. The shuttle have to slow down from orbital speed of 8 kilometers per second to a speed of a plane in order to land.
Sharp pointy shape have heat energy acting on the surface exceeding the limits modern materials can take. If you look at the heat diagram for a sharp cone, the side surfaces close to the tip and the tip itself take enormous amount of heating. Blunt shape for comparison can reduce the stress something like 6 times. That’s the only reason as far as I know. Sorry, I don’t have the exact numbers.
EDIT: expanded a bit.
The “angle of attack” is not always directly ahead, so a needle-bow won’t always be pointed directly into the flow.
If you’re in a ship, trying to cruise due north at 30mph, and you have a 10mph current flowing from west to east, the bow of your ship isn’t going to be pointing north. It’s going to be pointed about 30 degrees west if north. If you trail a kite behind the ship, the kite is going to be directly south of you; you’re going to be headed directly north. The water is going to be hitting the right side of your bow, not straight on the point of the “needle”. The needle won’t be cutting through the water efficiently; it will be pushed through the water sideways.
Aircraft have the same issue. You can see it most clearly during a [crosswind landing](https://www.youtube.com/watch?v=w4EQuM_t8Fo). The aircraft is “crabbing” into the wind, cutting across it sideways rather than head-on. It happens at cruising altitude, too, when the winds aren’t parallel with the direction of travel.
A rounded, bulbous bow is *almost* as efficient as a needle bow when traveling directly forward, but it doesn’t lose that efficiency as the wind is coming in sideways.
Some aircraft do indeed use a needle-like nose. Aircraft designed for sustained supersonic flight have a needle-like nose. ELI5, these planes fly so much faster than the wind can blow that the apparent wind is always nearly directly ahead. (They also manage the supersonic shockwave, but that’s well beyond the scope of your original question.)
Great question. Long story short it’s thermal control. Blunt nose designs are only appropriate for really really high-speed, or hypersonic stuff. Pointy noses are great until heating becomes an issue. A blunt nose is pushing back the boundary layer flow and to keep the shockwave stood off from the surface or ‘stagnation point’.
Heat concentrates at the tip on a spike, because of basically friction. Blunt noses make the shock wave form in front of the body, and also more surface area to disperse heat.
Source: Former rocket scientist turned AI enthusiast.
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For an e-like-I-work-for-nasa explanation nasa has a [free book](https://www.nasa.gov/connect/ebooks/coming_home_detail.html) published that details how they landed at the rounded shape, plus lots of material engineering challenges for figuring out how to make a spacecraft capable of surviving many reentries
“it is too round at the top it needs to be pointy!”
“Round is not scary, pointy is scary!”
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