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  1. #1

    How do The delta Series rockets Fly streight without fins?

    Does anyone know what means of stabilization is used for the Delta series, and other rockets that don't have fins? I have honestly never thought about it; but, i saw a model of the Delta rocket at an aviation museum today, and it made me wonder just how it works.

    Jeremy

  2. #2
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    Their nozzles swivel in response to commands from an active trajectory control system.
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  3. #3
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    Active guidance using gimbaled motor nozzles to vector the thrust.
    Mark S. Kulka NAR 86134 L1, ASTRE 471, Adirondack Mtns., NY
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  4. #4
    That's cool, sounds like a very complicated guidance system. It seems like that would require hundreds, if not thousands of minute adjustments per minute.

    Jeremy

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    Yes - it's quite complicated, but it's needed anyways for those rockets so they can adjust to the correct trajectory for orbital flight (besides, fins don't work in a vacuum, so fins would be pretty useless after the first minute or so of flight).
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    Quote Originally Posted by Jclark View Post
    That's cool, sounds like a very complicated guidance system. It seems like that would require hundreds, if not thousands of minute adjustments per minute.

    Jeremy
    The classic analogy involves imagining that you are balancing a pencil (vertically) on the tip of your finger. Yes, it has to make hundreds or thousands of adjustments during it's flight. All of the Titans, the Atlas 5, the Soyuz and Proton rockets, the Ariane series of rockets and many others also employ this method of stabilization. All of the Saturns did too, even though they had small fins. The wing and tail surfaces of the Space Shuttle Orbiter play no role in stabilizing it during boost, just as they don't on Dr. Zooch's kit of the Shuttle. The SRBs and the SSMEs all have gimballed mounts which provide active guidance for the Shuttle during boost. Fins on space launch vehicles add weight and drag and are unnecessary, because they spend most of their flights up where there is too little air for fins to be effective anyway.

    Military SAMs, air to air missiles, etc., and sounding rockets use fins for stabilization because they operate entirely or mostly within the atmosphere (and because fins are less expensive).
    Mark S. Kulka NAR 86134 L1, ASTRE 471, Adirondack Mtns., NY
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  7. #7
    That's very interesting. The Saturn V is my favorite space vehicle, and i knew that it employed a thrust vectoring system, but with such a crude guidance computer, i imagine the fins helped out a little.

    Jeremy

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    Quote Originally Posted by Jclark View Post
    That's very interesting. The Saturn V is my favorite space vehicle, and i knew that it employed a thrust vectoring system, but with such a crude guidance computer, i imagine the fins helped out a little.

    Jeremy
    They did. Although it was reported that if the Saturn had been continued well past Apollo 20 or so, it would've lost the fins, mainly because they had enough data to know how to fine tune the guidance such that the gimballing would be sufficient.
    Roy Green
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    Quote Originally Posted by MarkII View Post
    Military SAMs, air to air missiles, etc., and sounding rockets use fins for stabilization because they operate entirely or mostly within the atmosphere (and because fins are less expensive).
    This is true for sounding rockets, but SAMs and AAMs tend to be marginally stable or even completely unstable, and they use active guidance as well. They just tend to steer with the fins rather than with thrust vectoring, since they do operate entirely within the atmosphere.
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    Quote Originally Posted by cjl View Post
    This is true for sounding rockets, but SAMs and AAMs tend to be marginally stable or even completely unstable, and they use active guidance as well. They just tend to steer with the fins rather than with thrust vectoring, since they do operate entirely within the atmosphere.
    In their case, the instability is deliberate. It gives them the ability to change their trajectory quickly, and often radically. The fixed position fins on a passively-stabilized rocket also essentially steer the rocket, too.
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  11. #11
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    There have been HPR rockets with active guidance using gimbaled motor mounts. Some of the photos show a "lot" of deflection from the motor to straighten the flight out.
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  12. #12
    Quote Originally Posted by Jclark View Post
    That's cool, sounds like a very complicated guidance system. It seems like that would require hundreds, if not thousands of minute adjustments per minute.
    I took an advanced control theory class years ago. The professor cited the X-29, which had forward swept wings, and, for all intents and purposes, was a fighter plane mockup. It was inherently unstable and was kept stable by the flight computer. As I recall, he stated the sampling rate was 20Hz. So that'd be 1200 adjustments per minute.

    For a large rocket like the Delta, with all that mass, I suspect a lower sampling rate would suffice, but I'd swag 20-30 Hz there, too.

    Doug

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    Yes our liquid fueled and some of the solid motors have a Thrust Vectoring System (TVC). It is a hydraulic system (first stage) and the onboard guidance computer (RIFCA in the Delta world) has a preset flight plan and compensates with minute movements of the nozzles to keep it on that path.

    There are no uplinks from the ground, once it lifts off its on its own. Except for Range Safety who can terminate the flight if it goes too far off course.
    Last edited by Delta-IV; 20th November 2010 at 01:39 PM.
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    Quote Originally Posted by dave carver View Post
    There have been HPR rockets with active guidance using gimbaled motor mounts. Some of the photos show a "lot" of deflection from the motor to straighten the flight out.

    Not just HPR... John Pursley has flown several "large mod-rocs" at NARAM's, including the finless Vanguard, a scale finned Redstone, and (IIRC) a Saturn V all with active guidance from model airplane autopilot devices (for the 'brains' of the system, using it's horizon sensors feeding into the device which sends control signals to a pair of servos in the gimballed engine mount for thrust vector control (TVC in NASA parlance), all of which were powered by "G" size motors, utilizing super-lightweight construction, which kept them in the "model rocket" category, not HPR territory...

    Just sayin'.... It IS possible to do on large model rockets and stay under the HPR limits...

    Later! OL JR

    PS. There is also ANOTHER form of TVC that was used on the Titan III/IV rockets and all the US solid fuelled submarine launched ballistic missiles, or SLBM's. This system uses a 'steering fluid' which is injected into the rocket nozzle to divert the rocket exhaust coming out of the nozzle to create steering forces. The system uses an arrangement of a series of injectors and valves arranged in a ring around the nozzle, and a tank of "steering fluid" (hydrazine IIRC) in the base of the rocket. The guidance system of the rocket senses the rocket's orientation and flight direction and any deviations from the desired flight path, and near-instantly determines the corrective actions needed, and activates the proper valve(s) on the rocket nozzle to inject the steering fluid into the nozzle on the side opposite the direction the exhaust needs to be diverted, which then causes the rocket exhaust to point 'away' from the injector, steering the rocket back on course. This system was developed for the Polaris missile, because it was MUCH more compact than a standard gimbal-nozzle TVC system used on other solid fuelled land based ICBM's like Minuteman, and space was the ABSOLUTE confining factor inside a submarine! The follow on missiles after Polaris, Poseidon and Trident, have used the same system IIRC.

    Titan III/IV used the same system in it's SRB's, coupled with a non-swivelling nozzle, to achieve TVC control during the SRB burn, often coupled with the Titan's core liquid fuelled engines being airlit near SRB burnout. Kinda cool!

    OL JR
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    Robert H. Goddard's L-16 rocket, or "Movable Casing Rocket," launched in 1937 was the first rocket to use a gimballed engine mount receiving signals from an on-board gyroscope to steer a rocket via thrust vectoring. A brief discussion of the process and an animated GIF of the process can be found here:

    http://en.wikipedia.org/wiki/Thrust_vectoring

    One of the Apollo astronauts mentioned that during the boost aboard the Saturn V, he and his fellow crew members could feel things moving laterally behind (beneath) them, like the bottom of the rocket was doing a little dance.

    Last edited by MarkII; 20th November 2010 at 05:08 PM.
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  16. #16
    Something like that could be useful for high altitude, and two stage High power flights. High altitude winds, and other factors can greatly alter the trajectory of fin stabilized rockets.

    Jeremy

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    FWIW, some may want to check out my Sunguidance web page. Most of the flights were done with aerodynamic control surfaces. Notably with moving nose fins like a Sidewinder missile.

    http://homepage.mac.com/georgegassaw...unguidance.htm

    The bottom of the page also covers a little bit of a follow-up R&D (1989) involving gimbaled engines, using Sunguidance. The project was badly affected by over-control issues and the fact that Sunguidance had the engine mount deflected at liftoff when ideally a gimbaled rocket should have the engine STRAIGHT for liftoff. But as far as I know, that was the first model rocket to use a gimbaled engine successfully.

    Back to the Aerodynamic based controls, here is a link to a video showing a lot of the 1988 R&D flights, plus a few more recent ones (some as onboard footage). And one of the few good successful 5-stage flights you will ever see documented (D12-0/D12-0/D12-3/D12-0/E9-6), flown on an overcast day when the "sun" guidance worked to steer vertically.

    http://homepage.mac.com/georgegassaw...idance_Web.mov

    Finally, a bit larger version of my animated avatar, which includes more frames so it runs smoother. That flight was on a "hard ride" set-up. Note the chrome convex mirror (plastic) facing forward to show the sun reflected. That flight is in the above video link.

    - George Gassaway
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    Last edited by georgegassaway; 21st November 2010 at 12:52 AM.
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