29

Before the engines started but after the Auxiliary Power Units (which provide hydraulic power) were started, the engines were gimbaled to ensure that the thrust vector control system was working properly. At T minus 4 minutes, the fuel system purge begins. It is followed at T minus 3 minutes 25 seconds by the beginning of the engine gimbal tests, ...


26

The first stage of the Soviet N-1 moon rocket (Block A) used this type of differential thrust system. It had 30 engines in 2 rings. The outer ring of 24 engines used differential thrust control to control pitch and yaw, and was set up to shut off opposing engines in case of a single engine failure. Four launches were attempted and all failed in the first ...


14

First of all, it's worth to mention that engine gimbaling is not the only way to control a rocket. You can use differential thrust, or vernier thrusters, or even aerodynamic flight control surfaces. But you are right on that, that all of these systems require some sort of control. The gimbaling angles can't be pre-programed, because they have to dynamically ...


13

Differential thrust of a set of axially aligned engines can't provide roll control by itself; either dedicated roll-control thrusters or at least one off-center and movable engine is needed. Rocket development literature frequently mentions differential throttle as a possibility, but it seems like it hasn't been used in practice very often. The Surveyor ...


12

Some solid rocket motors provide thrust vector control by injecting fluid into ports around the nozzle. In this system, neither the nozzle nor engine is gimbaled. Vehicles that utilize(d) this system include later Titans and the PSLV. My answer to this question includes a description of the Titan system with schematics: What was the purpose of the small red ...


11

Rockets generally use an inertial navigation system (INS). This system uses the input from accelerometers and gyroscopes to calculate the rocket's position (relative to the launch pad) and attitude. This is a form of dead reckoning ("I have traveled x km at n degrees, so my position must be y"). The INS takes care of both navigation and error correction (...


10

Let's take the second image for the F1 engine - the situation is similar for SSME, though everything is 'upside-down' in its pictures. The 'seat', 'body' and 'block' are three parts that turn against each other. The block can turn around the shaft in X axis. The body can turn around the block in the Y axis. The Z axis remains fixed, as the block can't ...


10

As Jörg W Mittag says, we don't know. But since they can gimbal all of the engines, I'd be surprised if they didn't. Gimbaling all of the engines a little, as opposed to gimbaling just a few of them a lot, has (at least) the following advantages: It generally maximizes the clearance between adjacent engine bells, since you're turning all the engines by the ...


9

We don't know. What we do know is that the Falcon 9 has engine-out capability which means you cannot pick a fixed setup beforehand, you have to be able to adapt to the loss of any one of the 9 engines. Other than that, everything is possible. We also know that SpaceX is constantly improving and changing, so what is true today is not necessarily true tomorrow ...


8

I haven’t seen very many detailed mass breakdowns of engines that call out the mass of the gimbal system. For the Apollo Service Propulsion system, the gimbal actuators alone contributed about 20kg to the 300kg engine according to the original spec; that’s a lower bound since it doesn’t include the gimbal mounting & bearing itself, but suggests that ...


7

The RD-180 can gimbal each thrust chamber independently, allowing for roll control. Each Chamber assembly is gimballed in two planes for thrust vector control. This feature is implemented through the innovative construction of the gimballing unit on each hot oxygen gasline. Strains developed by the actuator for ...


6

How common or uncommon is that solution? Can one, for example, just plausibly assume a rocket with 4 radially placed engines (central, 5th engine disabled for certain reasons) can continue flying straight on three engines with one of the side engines switched off (without knowing much more about the rocket)? It's very common. I'd hesitate to say you can "...


6

Gimbaling the engines off the line intersecting the center of mass produces torque, which yields a rotation rate; if the vehicle is stable then a very small deflection should eventually bring you to the desired pitch angle. The basic logic is an automatic control loop using something like a PID controller, usually with several additional constraints -- like ...


5

The Mars Reconnaissance Orbiter and the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft have six non-gimbaled main engines, relying on smaller attitude control thrusters to counter any torques.


5

Here are some shuttle ascent guidance basics so you can interpret my answer. During first stage, the shuttle flew a predesigned (therefore open-loop) pitch-yaw-roll profile based, among other things, on the measured winds of the day. (Note that only the attitude targets were open-loop. The shuttle used a closed-loop control system to fly to those targets.) ...


5

SSME & Merlin use hydraulic actuators. For instance, The engine is gimballed through two planes by hydraulic actuators for vehicle pitch, yaw, and roll control. - Space Transportation System, Space Shuttle Main Engine Orientation, pg 4 (PDF) and Engine failure modes are minimized by eliminating separate subsystems where appropriate. For ...


4

According to the Blue Origin publicity web site https://www.blueorigin.com/new-shepard/ , the aft fin hydraulics are effective up to mach 4 (altitude isn't specified, but actual max is [remember it's sub-orbital] mach 3), and those fins are also used as steering canards during descent. If you are interested in re-entry control, then you should also check ...


4

The gimbal angle is some function of the error angle; this is a typical application of control theory. One common approach is the PID controller. This algorithm starts with a gimbal angle proportional to the steering error (the P part). It then adds additional correction based on the integral of the error (effectively, a measure of how long the rocket has ...


4

Astra is currently developing a small sat rocket with differential thrust, and they even "launched" it. Though it's not clear how far the launch procedure has gotten. Check out The part about differential throttling starts at about 5:00, but I recommend watching the whole thing. I know this question is about past ...


4

How does my spacecraft know if the thrust is actually pointing in the right direction? The stars are very far away and there are no handy planets or asteroids nearby. That the stars are very far away is a huge advantage. Parallax will not be an issue for a star tracker that looks for distant bright stars, at least not within the solar system. The inherent ...


4

This image has a better view of the top of the engine: The quadrapod structure is attached rigidly to the rocket. At the bottom of the quadrapod there's a gimbal joint. The exact structure of this joint is hard to see in photos, but it looks like the joint sits on top of the thrust chamber. The Merlin 1D structure is more compact, but uses the same ...


3

For deep space craft, another alternative to a gimbaled main engine is to use differential thrust with multiple engines; four small thrusters in square or diamond layout gives straightforward two-axis steering by firing them in different duty cycles (or throttle levels). If no large-delta-v maneuvers are needed (e.g. the spacecraft is performing flyby rather ...


3

The Merlin Engine is a gas generator cycle engine which uses liquid Oxygen(LOX) and refined Kerosene(RP1) as its propellants. The SuperDraco engine is a pressure fed cycle engine which uses mono-methyl hydrazine (MMH) and dinitrogen tetroxide (N2O4) as their propellants. The key differences of the engine are the size of the engine, the way the propellants ...


3

It's worth noting this is rather unique as its requried to be aerodynamically stable when going forwards and backwards. This is tricky as the centre-of-lift/pressure has to be 'behind' the centre of mass in both directions. The anular-fin being covered when the capsule is on, and open after release (which correlates to going 'up' and 'down'), helps with ...


3

This is not an exhaustive list, feel free to add to it. RS-25 - (SLS, Shuttle) ±12.5° Merlin - Falcon 9 5-10°? Shuttle SRBs 8° RS-68 - SLS, Delta IV 6° F1 - Saturn V 5.15° HM7-B - Ariane 5 upper stage 3° NERVA - concept 3° Long March yes Soyuz 0° (although the RD-00110R Vernier thrusters have 45°)


3

The gimbal performs the following functions: Allows the engine to gimbal around a single point under thrust when driven by the thrust vector control actuators. It is desirable to minimize friction to minimize actuator force/size required. Prevents rotation of the engine around its thrust axis and prevents other components from taking that torsional load. ...


3

I don't know of any source that would give a comprehensive survey to this kind of question, so answers are probably going to come from people who remember specific examples. If they remember which ones to look up and verify. I've seen some but can't remember which ones, so I haven't said anything. But I just read about the Japanese Mu-3 family of rockets, ...


2

Supplemental to Organic Marble's answer: Additional questions include: 1) Is the RL10B-2 used as a testbed for the CECE? Are the CECE, physical dimension the same as the as the RL10B-2? The RL10B-2 uses an 2-piece extensible sliding nozzle to get an extremely high nozzle expansion ratio of 280:1 and consequent specific impulse of 465 seconds. The CECE ...


2

Upper stage engines used or planned for human cargo: RL10 / Atlas 5 & ICPS & EUS / Good performance (Isp > 400) RD-110 / Soyuz / OK performance (Isp > 300) Merlin / Falcon / OK performance (Isp > 300) YF-25 / Long March / Poor performance (Isp > 200) (I probably forgot something) (Source Wikipedia various) The CECE testbed seems to have been ...


2

At a very high level, it works like this: 1) The onboard computer is constantly calculating the attitude (roll, pitch, yaw) the vehicle should be in at the current time (target attitude). 2) The onboard computer is also constantly calculating the actual attitude the vehicle is in at the current time (actual attitude) using data from the vehicle's sensors (...


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