Hypersonic aircraft shock layer color

[Xforce]

TL;DR

Do you ever wonder the Mach wave, shock layer or whatever you call it... of a hypersonic aircraft or a spacecraft at re-entry are always red, and yellow or white at hotter regions? What happens if they gets faster and hotter?

As a lot of people know, when things go hypersonic or even orbital velocities in the atmosphere, it’s going to get hot, scorching hot. The air emits black body radiation that are at the red spectrum (around 2000 to 3000 kelvins) sometimes goes yellow (5000-8000 kelvins maybe?) at re-entry spacecraft s. But according to black body radiation, there is more to go.
When a aircraft (I call anything that fly in the atmosphere “aircraft”) goes sufficiently fast, and without melting, can the shock layer becomes so hot that it actually glows green, or even a brilliant blue? I mean the light by black body radiation, not by ionisation. Furthermore, does this got something to do with the atmosphere composition (aka spectrum of oxygen and nitrogen atoms)

 

[trurle]

The color of very hot (reentry) shocks may be white, blue or even violet (although violet is possible to view only on panchromatic photos, not visually, because human eye is not very sensitive to violet). Green is possible due ablative carbon flourescence in hydrogen/helium atmospheres only (this is largely speculative - nobody yet got a good photos of gas giant reentries).
Photo below is the Hayabusa spacecraft reentry on Earth at 12 km/s.

 

[Xforce]

I also seen pictures and videos of similar things... like in the fairings of a falcon 9 rocket but they are seemingly to be caused by the ionization of air.
And... is that spacecraft undergoing a rapid unscheduled disassembly?
What is the estimated temperature of the blue shock?

 

[trurle]

I also seen pictures and videos of similar things... like in the fairings of a falcon 9 rocket but they are seemingly to be caused by the ionization of air.
And... is that spacecraft undergoing a rapid unscheduled disassembly?
What is the estimated temperature of the blue shock?

It was a rapid scheduled disasembly. Spacecraft have just jettisoned reentry capsule and was burning the rest of chassis. Hottest temperatures on that photo (for violet-halo) was at least ~12,000 K, and about ~8,000 K for blue halo, assuming panchromatic camera. May be even more if camera is color-corrected.

 

[Xforce]

It was a rapid scheduled disasembly. Spacecraft have just jettisoned reentry capsule and was burning the rest of chassis. Hottest temperatures on that photo (for violet-halo) was at least ~12,000 K, and about ~8,000 K for blue halo, assuming panchromatic camera. May be even more if camera is color-corrected.

So, for a re-entry capsule, in order to survive the re-entry, usually go at lower speeds? I heard a lot of astronauts saying they saw things glowing white and yellow outside the window, not blue and purple.
And,I think this phenomenon also occur at low altitudes as well, if you manage to achieve this by a hypersonic aircraft that flies at low altitudes, or launch a hyper-velocity projectile with a coilgun?

Green is possible due ablative carbon flourescence in hydrogen/helium atmospheres only (this is largely speculative - nobody yet got a good photos of gas giant reentries).

Probably the Cassini–Huygens spacecraft did this to Saturn. And as you said, this got something to do with the spectrum of air

 

[trurle]

So, for a re-entry capsule, in order to survive the re-entry, usually go at lower speeds? I heard a lot of astronauts saying they saw things glowing white and yellow outside the window, not blue and purple.
And,I think this phenomenon also occur at low altitudes as well, if you manage to achieve this by a hypersonic aircraft that flies at low altitudes, or launch a hyper-velocity projectile with a coilgun?

Probably the Cassini–Huygens spacecraft did this to Saturn. And as you said, this got something to do with the spectrum of air

Hayabusa reentry at 12 km/s was a bit of extreme speed (ISS return is at 8 km/s and Moon return is at 11 km/s). Therefore, more bluish reentry colors on photo i inserted. Also, windows of manned spacecraft are always pointed diagonally rearward, wherefore you cannot see hottest part of reentry glow from spacecraft (actually if you will see 8000K blackbody glow from inside of spacecraft , the occupants will fry in seconds even if window will not fail).

Regarding ET guns, coilguns and railguns, these are mostly limited to 4 km/s with current technology. Light-gas guns had up to 8.5km/s in tests.