From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.lang.hm (unknown [66.167.227.145]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id DFC2C3CB37 for ; Mon, 24 Apr 2023 15:16:44 -0400 (EDT) Received: from dlang-mobile (unknown [10.2.2.69]) by mail.lang.hm (Postfix) with ESMTP id CE39F188E93; Mon, 24 Apr 2023 12:16:43 -0700 (PDT) Date: Mon, 24 Apr 2023 12:16:43 -0700 (PDT) From: David Lang To: Dave Taht cc: Dave Taht via Starlink In-Reply-To: Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Subject: Re: [Starlink] some post Starship launch thoughts X-BeenThere: starlink@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: "Starlink has bufferbloat. Bad." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 24 Apr 2023 19:16:45 -0000 On Mon, 24 Apr 2023, Dave Taht via Starlink wrote: > Everyone wants a water deluge system and flame diverter and a flame trench... about 3 months ago they started building water-cooled steel plates to go under the launch pad, but it wasn't ready yet and the testing they didn (static fire at 50% thrust and firing raptors into blocks of concrete at McGregor) made them think that the concrete would be badly eroded by a full power launch, but did not predict nearly the level of damage they saw this is the probem you run into extrapolating from known data, you can't predict inflection points where the behavior changes significantly a common answer I've been giving re: flame trench Both Florida and Texas launch pads started with the ground just a few feet above sea level, so neither one can dig down (unless they want to create a permanent pool under the rocket, which would have all sorts of problems) In Florida, NASA trucked in a huge amount of dirt and built up a hill, leaving a flame trench that they then lined with concrete and bricks, later adding a ramp to divert the exhaust (and had a lot of problem finding a material that would not wear away too fast). They also had problems with some shuttle launches tearing up the walls of the flame trench. In Texas, SpaceX instead built stilts and put the rocket on top of that. As I understand it, the distance from the nozzles to the ground is higher in Texas than in Florida and the exhaust can get out in 6 direction, not just two. So if they had put the Starship stack on NASAs mobile launch platform and launched it in Florida, it would have done significantly more damage there, probagly tearing up large chunks of ground around the pad as well (imaging the ground where the crawler goes disappearing) The raptor engines have a significantly higher ISP than the F-1 that the Saturn 5 had, so it's exhaust is moving about 25% faster, and with double the thrust it's also moving about 60% more mass. These are conditions that have not existed anywhere on earth before this launch (I will note that the shuttle had even higher exhaust velocity from it's main engines, but less overall thrust) David Lang