NASA to Install “Shock Absorbers” to Mitigate Thrust Oscillation


NASA will add a system engineers equated to shock absorbers to Ares 1 rockets to reduce significant vibrations that could shake the Orion spacecraft and astronaut crews during early stages of the flight. Earlier, engineers had determined that at about 115 seconds into the flight, the Ares rocket would vibrate for about 5 seconds, enough to potentially make it difficult for crews to read console displays. To mitigate what’s called thrust oscillation, engineers have proposed an active tuned mass absorber that would detect the frequency and amplitude of the thrust oscillation with accelerometers and internal pressure sensors, and use battery-powered motors to move spring mounted weights up and down to damp the vibration out. A spring-and-damper ring will separate the first and second stages of the rocket, and 16 actuators that act like shock absorbers will be added to the bell-shaped aft skirt at the bottom of the rocket.

Engineers are also looking to use a passive “compliance structure” which is a spring-loaded ring that would detune the stack by softening the interface between the first and upper stages while preserving lateral stability in the Ares 1 design concept.

This concept is expected to reduce the G-forces on the astronauts from about 5 G’s to .25 G’s.
Computer modeling and early design analyses showed the Ares 1 rocket would shake near 105-115 seconds into the flight after liftoff, subjecting the Orion spacecraft and astronauts onboard to high G forces for only about 5 seconds. But NASA engineers were concerned that astronauts could be injured or critical systems could be damaged during that time of the flight.

The thrust oscillation occurs as solid fuel in the first stage depletes, leaving a long, empty shell that takes on the characteristics of an organ pipe, resonating, at frequencies between 12 and 14 hertz. The second stage of the rocket and the Orion spacecraft atop it will naturally dampen the resulting pressure pulses, which essentially would jackhammer the astronauts and make it difficult for them to read console displays and respond.

Source: NASA news conference.

14 Replies to “NASA to Install “Shock Absorbers” to Mitigate Thrust Oscillation”

  1. This was actually experienced during the 2nd launch of the Saturn V rocket test back in the 60s. Something which didn’t occur during the initial launch. Luckily it occured before we added astronauts to the top of it. It was solved by adding “shock” dampeners on the first stage.

  2. More time, more money, more risk.

    Why not add em!

    Throw in a hot tub while you are at it to let passengers relax their pogo injured bodies after.

  3. Ares 1 with Orion looks like a Kebab, it looks awful, the old adage, ‘if it looks right, it is right’ is so true.

    The 2nd Saturn V problem was a pogo effect caused by the propellents and oxident, this thins a solid and is a different thing. They are using something that was not designed to fly like this.

  4. Why add actuators and all kinds of things that could work imperfectly, 5 seconds of vibration? I’d rather deal with that. Although I guess with the level of tech in this new “kebab” might as well make the whole ride plush

  5. They are using something that was not designed to fly like this.

    Agreed, and when I noted the continuing adjustments over at the Bad Astronomer I got an interesting tale in reply that the history goes back to IIRC the Romans (standardized road for military reasons (?), standardized wagon wheel base, standardized [sort of, I suspect] train base, standardized bridge clearance, and, finally) deciding the transport width of the SRBs.

    My reaction was, and still is, that it is choosing economics over safety. But if they can handle it despite the bad feelings the iterations and kludges leave an interested bystander with, it’s nothing for me to nitpick on.

    Btw, if it was an actual organ pipe there would be easier methods to change its resonance behavior. But I suspect more drastic measures here would detract even more as regards safety and development time.

  6. Why not damp the vibrations in the capsule. It just seems a whole lot simpler to give the rocket passengers (aka astronauts) waterbeds and dampen the dashboard mountings then try to muck about with mission critical systems.

    This seems like the curse of engineers the world over coming into play: “If it works, it doesn’t have enough features.”

  7. Sounds awefully heavy.

    Wouldn’t it be better (for some value of “better”) to design the solid booster shells in such a way that they resonance frequencies either aren’t reached or are less bothersome? Make sure sure they’re ‘out of tune’ so to speak.

  8. Reading the commentary, is somewhat
    dishartening. Changing or altering an osilation frequency is no laughing matter.
    It requires an understanding of the materials
    and the dynamics of the structure. In order
    to reduce weight, the booster is not rigid enough to counter the schock waves. My
    suggestion would be to simply add open ended pipes along side the booster for reenforgement and airo dynamics. True, it will
    increase the weight only minimal but none
    the less. The advantage of this suggestion,
    when dampers are added on the bottom of
    each pipe, they will function in 3 way’s.Altered frequency, reduction of vibration and they also function as a limited steering mechanism. At leased 6 or more pipes are
    required, aero dynamics testing will determine the actual number. My preliminairy
    calculations said 6 as a minimum. There is
    a drawback to this, it will increase noise! But
    this is only during the time from takeoff to
    stratosphere, which is only 6 minutes.
    Even leaniary half pipes can do, but then the number of 6 will increase. Maybe NASA will look in to this alternative? Reducing the “G” forces is a whole different ball game, and
    as an ex fighter jog, I know what it feels like!
    But I will not offer a suggestion to that it is
    still classified.

  9. Sili-
    The weight of the actuators is about 1,400 lbs, but the engineers and managers have been holding about 8,000 lbs of performance margin in reserve to handle unexpected problems that might come up.

    They thought about just putting special springs on the seats to take care of it, but decided to damp out the entire rocket so it wouldn’t affect performance
    or cause some other unknown problem.

  10. This reminds me of a software bug in the old DBase 3+. After writing a program for awhile, a bug would pop up that that the company could not ftix, so there was an added “feature” that one had to employ to keep the program from deteriorating into pablum. They tried to pawn it off as a feature, but really it was just extra dead weight.

  11. The problem is in trying to retro-fit a new component (orion) onto an old one (the boosters) to save money. The eveidence of our eyes alone tell us that this design is unstable – the boosters are not wide enough to handle the resonances that will be caused by the wider Orion capsule, which will wobble like the top of a cat-tail. Just like a building, the base must be wider than the top to be truly stable – but NASA seems to be ignoring common-sense physics. I look for an early flight to have the Orion simply snap off on launch. I feel sorry for the astronauts being suckered into flying in this contraption. Interestingly, this design perfectly reflects the fragile American ecnonomy – increasingly unsound at its foundation, with ambitions of vainglory far bigger than we can any longer support..

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