In article ,
says...

On 2019-08-03 12:58, Jeff Findley wrote:

They are essentially a completely new design. Different size (5
segments instead of 4), different propellant mixture, different
insulation, zero recovery hardware, and etc. In the first full scale
ground test of the 5 segment SRB, the nozzle literally blew to huge
pieces


Thanks for the reality check. I had been aware only of vibration issues
dating bac from Ares.

Wouldn't having 3 o4 4 smaller SRBs have yielded fewer challenges in
terms of scaling them up while keeping roughly same thrust?

Doubtful. They wanted to stay with, roughly, the same structural layout
for connecting the SRBs to the tank. One big beam through the intertank
area (at the top of the SRBs) to transfer the thrust and help with
vibrations.

Are the SRBs what is currently holding back SLS? what other problems are
causing delays?

Not at all. The SRBs are lagging, but not as much as the rest of the
thing.

The long pole in the tent has always been the core stage being built by
Boeing. The Exploration Upper Stage, also being designed by Boeing, has
been placed on hold and rumor has it that NASA may try to cancel the
failing EUS contract and open it up for a competitive bid. The EUS is
needed for Block 1B and Block 2.

The interim upper stage of Block 1A is a slightly modified Delta IV
upper stage. It's undersized for SLS (hence the lower payload of Block
1A), but it's obviously "ready to fly" since it works just fine on Delta
IV.

Jeff
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