Ever since SpaceX tweeted a photo on September 13th, 2018. A lot of people fear the BFR is slowly turning into the Space Shuttle. Quoting ever growing wings and a giant heat shield covering the belly of the ship. So how is this any different than the space shuttle. So first up to compare the two, let's look at them side-by-side.
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When the Space Shuttle reentered had a 40-degree angle of attack that's quite a bit different from the BFS which is going to have about a 90-degree angle of attack. The reason the BFS will be able to do this is because of those wings. Now really these aren't wings and we shouldn't call them that. We need to think of these more as air brakes. As they are not there to provide lift, they're only there to provide more or less drag.
Now they do this by changing their angle just like an air brake and by adjusting the amount of drag at the top or the bottom of the BFS, they can change the pitch. So you might think isn't this kind of similar to a Virgin Galactic control spaceship twos reentry which has that giant tail that flips up that allows it to re-enter safely or perhaps you're a history buff and you're familiar with the Soviet Union's MIG 105 spiral or later the Bor-4 which have a variable dihedral wing which changes their angle of attack during descent.
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Although these vehicles do have variable surfaces to change their orientation. They aren't really dynamic, they move only to provide different configurations. Either a more stable reentry profile or then they change to provide more lift and control for the landing phase. They don't actively go back and forth to continually adjust the vehicle's orientation.
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By deploying what's essentially an air brake on one wing or the other the drag will actually steer and orient the vehicle. This is honestly about the closest example to a vehicle that changes drag to modify its orientation in this manner. When you factor in that belly-first reentry this dynamic drag control is one of the reasons why the BFS is more like a skydiver than an airplane. A skydiver controls their orientation by shifting the amount of drag each limb generates.
Besides those Finn wingy things and some massive control thrusters another key piece that will allow the BFS to do a full-blown belly flop through the atmosphere is the heat shield. The Space Shuttle used over 24,000 individual and unique silica tiles to cover the belly of the shuttle. The size of the wings and the amount of lift the shuttle needed to achieve in the upper atmosphere was largely due to making sure the shuttle didn't overheat the silica tiles. Overwhelming them would transfer the heat from the tiles to the fuselage of the orbiter.
The BFS, on the other hand, will use something very similar to what SpaceX uses on their dragon capsules. This is an ablative material known as PICA-X or if you don't like acronyms and prefer cool sounding words phenolic impregnated carbon ablator.
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SpaceX continues to advance their PICA-X and they hope to get to the point where it can be used a hundred times before needing to be replaced. PICA-X can handle much higher temperatures than the shuttle tiles which is necessary when trying to re-enter from Mars or the moon.
Not to mention with a really steep reentry profile one that tries to slow down as quickly as possible the heat shield will be pushed to the limits. So if the BFS will have an ablative heat shield that needs to be replaced isn't that an even worse refurbishment process than the Space Shuttle which had thousands and thousands of hours of checks to ensure that their tiles were okay for every single reef light.
When it comes to mounting the heat shield to the BFS according to Elon, " the heat shield place will be mounted directly to the primary tank wall that's the most mass-efficient way to go don't want to build a box in a box."
Just like how making hundreds of Merlin engines is cheaper than building dozens of rocket engines from a manufacturing standpoint having a common heat shield plate. That's easily mountable and replaceable, should help alleviate some of the headaches the Space Shuttle experienced in its refurbishment process.
Not to mention the Space Shuttle tiles were extremely fragile they could follow if you just looked at them wrong and it was very important to make sure that every single one was literally perfect before each flight. A more traditional heat shield is a lot more resilient in the sense.
Beyond the fact that it does look like the BFS is beginning to evolve more and more into the space shuttle the way, it performs reentry is completely different using different techniques, different technologies, different materials and an entirely different reentry profile.
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