asssuber t1_j9v5wdd wrote on February 24, 2023 at 8:02 PM

Reply to comment by DBDude in After Vulcan comes online, ULA plans to dramatically increase launch cadence by OutlandishnessOk2452

Raptor isn't doing that fine. You had many failing during starship's fights (not always the engine fault, but still) and 2 failing in the latest static fire. IIRC it also started development before the BE-4 (well before if you count when it was still supposed to burn hydrogen, but not much development was happening then). And let's not talk about deadlines, we all know that in the space industry they are just optimistic targets.

The RD-180 is a Russian engine, they have experience with oxygen-rich stage combustion, not the USA. AFAIK BE-4 will be the first oxygen-rich staged combustion engine made in USA to be flown (if we ignore that a full flow staged combustion engine also has an oxygen-rich side).

DBDude t1_j9vjhn5 wrote on February 24, 2023 at 9:29 PM

They lit 31 engines, a world record. The last time someone tried 30 they blew up four rockets in a row, the second one destroying the launch facility.

>IIRC it also started development before the BE-4

They were kind of playing around with ideas before BE-4, but real design didn't start until around the same time.

>if we ignore that a full flow staged combustion engine also has an oxygen-rich side

We'd have to. It's amazing to me that a modern company absolutely flush with cash is having serious issues designing roughly a methane variant of what's just a dual-chamber version of what was at the time a 25+ year-old engine. Something's been very wrong at BO. I'm just hoping now that Bezos is actively involved they can clean up their act.

asssuber t1_j9wgqvt wrote on February 25, 2023 at 1:26 AM

> They lit 31 engines, a world record.

They lit 32 engines, one shut down during the (short) static fire.

> The last time someone tried 30 they blew up four rockets in a row, the second one destroying the launch facility.

N1 is a very low standard to compare against. It's engines could not even be test fired prior to being mounted in the rocket, much less had a chance to do a full static fire like SH. Those were also the first staged combustion engines ever made, oxygen-rich on top. And the failures had more to do with the rocket than the engines themselves.

On the other end a very high standard of reliability is given by SpaceX itself. SpaceX flew Falcon Heavy five times, each firing 27 engines (plus the upper stage one) and it was 100% successful with no Merlin having a problem in any of the flights. 27 is almost the same as 30, the phantasm of N1 was slayed by SpaceX itself already.

Raptor is clearly immature and problematic if you compare it with Merlin, RD-180, Vulcan-2, etc. We have seen it's engine-rich exhaust several times and they are still tweaking the film-cooling for optimal performance, and might have other problems they haven't spoken.

Given ULA's more stringent standards (they aren't expecting to lose/scrap several test vehicles, going through dozens of engines like Spacex. They don't have engine-out capability to shrug off a few bad engines like SH), I do not see BE-4 as being less fine than Raptor.