Fastrac was indeed nearly twice the mass, at 910 kg compared to 470 kg, but nobody measures rocket engine size in mass. The Fastrac only had 284 kN of vacuum thrust, compared to 825 kN for the latest up-rated Merlin 1D...the Merlin is nearly 3 times larger. It would take 25 Fastrac engines to match the sea level thrust of a Falcon 9. The T/W ratio of the Merlin 1D is 180...Fastrac was 32. Yes, Fastrac had an utterly abysmal T/W ratio, while the Merlin sets records.icekatze wrote:hi hi
Actually, the Fastrac was heavier than the Merlins, but whatever. Tweaking the nozzle was cool and all, but it is still an iteration on past work. I look forward to seeing if they can succeed in making recovery cost effective, they've got one step out of the way, I'll be sure to follow them along the next few.
Fastrac had an ablatively-cooled combustion chamber and expendable carbon fiber nozzle, Merlin has a regeneratively cooled combustion chamber and a radiatively cooled niobium alloy expansion nozzle.
Fastrac was fixed thrust, set prior to launch, the avionics were limited to opening and closing valves and firing an expendable ignition cartridge. The Merlin 1D can throttle down to at least 70% (possibly more with the recent updates to the 1D), quickly and precisely enough to allow landing of the first stage. Merlin is also capable of relighting multiple times in a single flight.
Merlin has a vacuum variant with even higher thrust and far deeper throttling, down to 39%. There'd be little point in even trying to put a Fastrac on an upper stage.
SpaceX also makes heavy use of 3D printing to reduce complexity and manufacturing costs and improve performance, including parts of the Merlin engines...a technology that didn't even exist when Fastrac was canceled.
They didn't "tweak the nozzle", they developed a series of several new engines, and several launch vehicles using them. At best, they used the Fastrac design as a reference while designing the Merlin 1A...they immediately went well beyond it. The 1C and 1D aren't even entirely the same kind of engine, they both are regenerative cooling designs and each takes a very different approach to combustion chamber construction, while Fastrac used a thick layer of phenolic composite ablative material.
As for the notion that SpaceX could cobble together a few over-budget, behind-schedule, canceled NASA projects into a medium-heavy launch vehicle that operates with a small fraction of the launch costs of the competition...really? They're reducing costs by blindly copying designs from an organization that has consistently failed miserably at reducing costs? Do you honestly not see how absurd an idea that is?