the aerospike... where is it?

[jevry]

in my ksp playtroughs i have noticed something weird. i see all the youtubers every nwo and then using the aerospike engine which if you have yourelf never found it either... is a giant black spike with flames emitting from it.

where is it? is it not researchable in careermode? is it modded in? secret option? have i been stupid and simply missed it all this time?

i only need 1 answer on this topic so... i am a bit noob-ish with forums so if a proper answer has been given feel not obliged to reply.

thank you in advance

[Zeiss Ikon]

I can assure you, I have it in both of my sandbox games (1.2.2 and 1.3.0).  It's in the "hypersonic flight" node, about 1/3 of the way down from the top, at the next to last science cost level.  The icon looks like a top view of a Space Shuttle.

[Geonovast]

According to the wiki, it's under Hypersonic flight on level 8.

[qzgy]

The other two answers have been correct, though I'd like to chime in and say if you have it researched or are in sandbox, it should be in the engines section. As with other things.