42

Ok, I asked so I could use these awesome photos in an answer... I confess. The material has changed from Aluminium with an ablative paint to bare titanium. The specific shape, size, and mount points have changed as well. Let's start with a nice shot of the Mod 3 design on a Falcon 1.1 Full Thrust. You can see the size, shape, and design differences in ...


20

The Apollo capsule was allowed to tumble after being pulled away by the LAS. This tumbling would continue until the first drogue parachute was deployed, which would stabilize the capsule. The LAS and command module shroud have to be separated from the CM. There's a second set of rockets on the LAS that takes care of that. This can be done even if the ...


18

According to Elon Musk (during the post-flight press conference): New design coming for Grid Fin. Will be largest titanium forging in the world. Current Grid Fin is aluminum and gets so hot it lights on fire... which isn't good for reuse. After the reentry burn, the stage still flies at high speed (I don't have an exact figure, but it's at least ...


15

tl;dr - Better aerodynamics at high speeds. There is a paper that compares the plain grid fins with locally swept "toothed" grid fins: Novel High-Performance Grid Fins for Missile Control at High Speeds (PDF). To quote a part of its conclusion (emphasis mine): The results show an essential reduction of the drag for the locally swept configurations. ...


14

From Spaceflight101: For Shenzhou Missions, a stretched version of the typical Long March fairing is used ... Four aerodynamic stabilizers are attached to the upper part of the fairing that is part of the Launch Escape System in a escape scenario, those would deploy to stabilize the vehicle while flying under the Launch Abort Engines. The Fairing’s ‘wings’...


14

Getting rid of the nose cones would make things worse, not better. The reason the nose cones allow less control than the typical F9 (or FH center core) is because the cylinder of the rocket usually continues well above the grid fins. The interstage (which extends above the grid fins, and does not separate from the first stage at any point) is the same width ...


13

They needed to upgrade the grid fins anyway, this is one of the modifications intended for Block 5. So the new grid fins were available. This meant the choice is between: switching to more expensive (but reusable) grid fins, or throwing away the nose cones, and adding another separation event, making sure the nose cone doesn't hit the stage after ...


11

As far as I know, the RCS uses nitrogen cold gas thrusters. The grid fins are covered in an ablative material, they are heated by atmospheric friction. The landing is badly filmed because this is a recording of the live webcast. The transmissions from the barge get disrupted by the rocket landing.


11

TLDR the main purpose of the grid fins is to steer the spent 1st stage away from populated areas when it's falling to the grond. CZ-4B targets SSO and is mostly launched from T-SLC (Taiyuan Satellite Launch Center). China currently operates 4 SLCs, T(Taiyuan), J(Jiuquan), X(Xichang) and W(Wenchang). While J-SLC launches into the desert and W-SLC into the ...


10

I know, I know, I am asking, so I can answer. But these are such great photos, and they are interesting questions... From Facebook a possible answer (Not authoritative, I get that) the following: It's the nose cones. They make it more unstable, so they need the increased control authority from the Ti gridfins. The center core's interstage acts like the ...


9

I can think of three principal issues raised by launching with fins deployed; I would guess that none of them would endanger a mission, but I don't have any inside information to support that. Increased drag from the deployed fins. This would hurt performance slightly, but there is some performance margin in the launcher, and the fins aren't designed to ...


9

If you have noticed, the fins deploy by opening upwards. This makes me wonder if they considered your case. When in normal use, the force vector upon them pushes upwards. In your case, the force vector would be forcing them down and closed. So first approximation they would be forced down to a minimum. They would add significant drag in a non-fully ...


8

It's pretty rare to see popular news articles get technical details right, and this is no exception. The grid fins referred to in earlier QAs here are, as Polygnome notes, not maneuverable; they just act as passive stabilizers during LES aborts for the shroud-enclosed Shenzhou spacecraft. (See also this QA regarding the Soyuz grid fins.) The new article ...


8

The issue seems to be the need for a single control surface (for simplicity) to work at hypersonic speeds, down to subsonic. Grid fins have been used high speed missles in this speed regime, so why reinvent the wheel. It works, it is well known, they traded off and decided on this design.


8

Musk tweeted an answer to a question. Musk Tweet in which he wrote: For now, we only use those on super hot reentry missions. Will go to all Ti with Falcon 9 V5, which is a few months away. So the Block 5 (v5/mod5/Falcon 9 1.3) that is due soon enough, designed for rapid reuse will be the full time target. Until then they are using the cheaper ones, ...


7

Yes, the grid fins can control the rotation of the stage -- and they're the primary mechanism for that during descent, since the cold-gas thrusters have little force and the engines are shut down for most of the time. To keep the stage stable, the fins are left horizontal, and adjusted by small amounts to correct for other sources of rotation. To spin the ...


6

On official spacex website I found dimensions: http://www.spacex.com/news/2015/08/31/grid-fins Falcon 9’s first stage is equipped with hypersonic grid fins which manipulate the direction of the stage’s lift during reentry. The fins are placed in an X-wing configuration and are stowed on ascent and deployed during reentry. While the fins are relatively ...


6

There are 3 regular geometric patterns you can use: triangle, rectangle and hexagon. All others have irregularities (e.g. very small cells next to larger cells) or space lost (circles). According to the 2004 study, 'Grid pattern effects on aerodynamic characteristics of grid fins': The results of the wind tunnel test indicate that the aerodynamic ...


6

Helium is a gas at any reasonable temperature, so a system using helium would be pneumatic. Pneumatic systems are less suited for exact position control than hydraulics: because gases are compressible, it's difficult to predict the piston position from a given input. In hydraulics there's an exact relationship so you have good position control, and ...


6

It was thought, initially that the grid fins used RP1 propellant as a hydraulic fluid, when it was using an open system (The fluid is ejected after use until you run out, which they did). After a landing failure, they changed to what they call a "Closed System" where the system reuses the hydraulic fluid, but I cannot find a reference to that actually being ...


5

As a general rule electric motors excel at high speed low loads while hydraulics work best at the low speed high torque end. Especially where the range of motion is small, the forces large and precise control is required there is a lot of knowledge and existing design around hydraulics. In particular with the grid fins there is the need to make rapid precise ...


5

The earliest use of the grid fins failed to land successfully because it ran out of hydraulic fluid. They use the RP1 from the main tank to run the hydraulics and they were initially open loop (the hydraulics). This meant they would use the fluid, and throw it away as they used it. Thus they ran out. They later switched to a closed loop system so they do ...


4

After the entry burn, the first stage is still going pretty fast - About 8200km/h, or Mach 6.6 or so. Still plenty fast enough for atmospheric friction and compression heating to take their toll. The entry burn reduces the booster's speed from 8200km/h down to ~5800km/h - from deadly to mostly-survivable. The landing burn only slows the booster down from ...


4

They are hydraulics which initially used an open loop, using kerosene as the working fluid. Some of the initial landing attempt failures were because they ran out of fluid. Closed loop would keep the fluid in the system, open loop dumps it after it is used. When they land, the hydraulics also retract the fins so you can see it is under active control. ...


4

If you look at the webcasts you'll see that they are extended while in free fall (before re-entry) and you can kind of see them bounce and lock into place with a jolt. I believe they are hydraulically actuated and do not rely on aerodynamic force to stay extended. I do not know about your second question however. See the OTV5 / X-37B launch from 2017 just ...


3

To answer the edited addition: The mechanics to do something like this would: Add considerable mass to the stage This would prevent the use of the stage for the non-recoverable (all fuel used) launches that I believe are required for geosyncronous orbit insertion Add complexity to the design More points of failure Fail to land safely having read a ...


3

A reference "length" can't be a surface area, the units are wrong. I suggest using the major dimension of the fin. Example: For an airfoil, it's the chord length. The introduction to the web page says " An optional temperature increment can be added or subtracted to model a hot or cold day. For example, enter "10" to see the effect of a 10° increase above ...


3

Part of it is that the shape of the side boosters requires larger fins for maintaining control authority. (The core interstages's cylindrical shape increases it by 30%, according to Musk.) The other part is that the side boosters have a much steeper reentry, thus most of the heating happens in thicker, slower air. Some of the heat can be carried away by it ...


3

The Falcon 9's grid fins exist to solve a particular problem: Control during engines-first descent. Aerodynamic stability during that phase comes from having the center of mass well below/ahead of the center of pressure due to heavy engines at the bottom. But a stable descent to the wrong place isn't the desired outcome. Further, Falcon 9 flies a specific ...


3

Fins are usually used for aerodynamically controlling the vehicle. Grid fins are a simpler and more storable form (as mentioned folding flat, especially during ascent) of fins as compared to the conventional ones. The New Glenn seems to follow on the legacy of fins developed, tested, and validated during the New Shepard flights, that have used conventional ...


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