Comments by "The Esseboy" (@TheEsseboy) on "Thunderf00t"
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@AWAVAVA I would be surprised if they reach 100 tons in reusable mode, realistically I think they will have to settle for 60-80 tons if they can't get their current heat shield layout to work, might even be as low as 50 tons to LEO. They clearly have severely underestimated the insulation and tiles needed for re-entry, the upper stage is HUGE, we are talking several tons just to insulate the parts that have zero insulation (like the spaceshuttle had, the white insulation on top of the craft), then many more tons of tiles as they probably need to be thicker and or cover more area.
Then we have reusability, as it stands it seems like the engines run way too hot being crowded like that under the booster, so more insulation might be needed to have a higher rate of reuse.
All in all, it looks like they will have to enlarge it to reach their design goal of 200 tons to orbit in reusable mode, 100 tons might be achievable IF they are fortunate enough to only need to redesign the insulation and not add much much more of it....which I doubt as so much of it got glowing hot.
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@AWAVAVA SLS is human rated, and it's componenets are proven to be reliable. Launch cost is 2.6 billion, mostly due to them NOT being allowed to develop new systems and where FORCED to use old systems, engines and boosters...
As you increase the weight of anything that is NOT fuel, you have to bring about 50 to 100 times that weight in fuel to bring it to space...meaning, if you add 1 ton of tiles to the upper stage, you need 50-100 tons of fuel to compensate! If we compare it to the most similar rocket and adjust it because it uses solid rockets in combination with hydrogen oxygen engines (Space shuttle), we are looking at a 1.5-1.8 % launch efficiency (Cargo mass to orbit of total launch weight), Hence, if you increase the mass of the upper stage by 1 ton, you need 55-66 tons of fuel to compensate, and in my mind they need AT LEAST 2 tons more heat tiles and 3-5 tons of insulation else where on the upper stage, meaning they will need 275-462 tons more fuel to reach orbit. The add 60 tons of cargo and we are looking at 3,300 to 4,000 tons more fuel for the cargo, 100 tons is 5,500 to 6,600 tons...200 tons is 11,000 to 13,200 tons!
This is why you don't make a reusable second stage UNLESS you need to bring satellites down from orbit...which is why they made the space shuttle, that and the curiosity about it. For a heavy launch rocket it is utterly dumb, unless you wanna increase launch costs by 30-50% (if not more as you need larger launch pads, infrastructure etc.)
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@AWAVAVA I was refering to the inherent problems of making a fully reusable rocket, it leads to a lower payload to orbit in comparison to launch mass...meaning you need much heavier rocket for the given payload to space...you cannot get around this unless you find a much lighter way of heat shielding the last stage of the rocket, as it needs to survive full re-entry speeds!
No, I am not giving you a trust me bro source, there is ample amounts of articles, books and lectures on this topic you can look up yourself, it is not a novel issue, this is why most of the rocket industry have settled on partially or single use rockets, the benefits of reusability doesn't outweigh the fact you need a 30-50% larger rocket...and going from a 5,000 ton rocket to a 6,500 - 7,500 ton rocket is not small, it requires totaally different launch pad infrastructure!
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