[skgough]

Could you elaborate on that? Why would the exhaust reflecting off the shock wave cause damage to the nozzle?

[echoangle]

I don't think it implies damage, but it implies that the exhaust pressure is lower than the outside air pressure (which you would not want for perfect efficiency). That's normal though because the first stage operates in a wide range of pressure, and you can only adjust it for one exhaust pressure. So mach diamonds on liftoff should be normal.

[adastra22]

Mach diamonds are absolutely normal and expected. Not sure what GP is talking about.

[cubefox]

Maybe he means the New Glenn should have had aerospike engines.