Whatever Happened to the Five-Hole Probe?

Remember that probeon the top of the rocket? It’s still being watched carefully today, and notjust because of its hard-to-remove cover.
As we noted yesterday, the five-hole probe is a very important set of sensorsfor collecting aerodynamic data during the flight. It remained covered whileAres I-X was rolled out to the launch pad and just prior to launch because theavionics team did not want water, bugs, bird messes, or other debris getting onor in the sensors. Inside the five holes is a diaphragm of flexible materialagainst which air vibrates to produce data. If water or foreign object debris(FOD) gets onto the diaphragm, there is a risk that the data from the sensorscould be harder to interpret after the flight. Once the Ground Operations teamremoved the cover, there is no way to put it back on short of rolling therocket back into the Vehicle Assembly Building. The I-X team knew this mighthappen, but now that the cover is off, what next? Just to add to the challenge,Cape Canaveral expected (and got) an inch and a half of rain on Tuesday night.
What NASA did was take a spare five-hole probe out to the pad, put it on thefixed service structre and gave it a similar exposure to rain as the flighthardware. The spare unit was tested before and after the rain to determine itseffects on the sensors’ behavior. In this way, NASA will be able to account forany changes in sensor measurements due to water on the sensor and use thatinformation to interpret the data after the flight. This is just one of manylessons the Ares team is learning as it continues testing on the Ares I-Xrocket.

5 thoughts on “Whatever Happened to the Five-Hole Probe?”

  1. When I read about this problem with the probe, I just think that maybe they should of implemented a way to house the sensors within the interior of the probe. Possiblly with small shutter doors to protect the membranes from exposure to the elements prior to launch. But maybe that would of been too easy. Just a thought!

  2. Who the heck designs a cover that can’t be put back on? Sheesh. How long have you people been doin’ this stuff?

    For that matter, some day you might really need to launch through rain. It would be good to have collected some test flight data in rain first.

  3. Actually, this points up the issue of the launch structure. When the time comes to put an astronaut in the bird, I can’t see them shinnying up the rocket. When is the tower structure going to be heightened to accomodate the taller rocket?

    As for the first commenter below: the five-hole sensor is a modified pitot tube that has to be the very top (or first) pointy thing in the airflow. There’s no good way to put a shutter on it that won’t invalidate the data.

    And for the second commenter: the Stationary Service Structure isn’t tall enough to reach the top of the rocket – which is a one-time design.

  4. I work in Boca Raton and watched the launch from my 4th floor window. We have seen shuttle flights from this far south relatively easily. I did see what I took to be the Ares but it’s flight path continued well beyond the 2 minute mark that the separation of the booster took place. I watched until approximately 11:39am and still saw the arc of a vapor trail heading east. Is it possible this was still the upper simulator stage?

  5. >> Who the heck designs a cover that can’t be put back on? Sheesh. How long have you people been doin’ this stuff?

    My firm (Aeroprobe Corporation) designed and built the five-hole probes under contract from LMCO. NASA made the cover themselves. It was meant to slip onto the probe like a sock. It was supposed to be removed by pulling it straight up and away from the probe.

    Since this turned out to be unfeasible, NASA tied a rope to the tip of the cover hoping that they could remove it from the ground. They expected the cover to just slide up and over the tip if they tugged on the rope. If you’ve ever tried to remove a sock by pulling it in any direction other than away from your toes, you’d surely recognize the difficulty of such an operation. We warned the NASA engineers that it likely would get stuck, but they had no other options and hoped that the nylon-mesh material would easily slide along the smooth probe body.

    Unfortunately, the sharp tip of the probe perforated the fabric and the rest of the cover simply tore around it. Since the cover was destroyed it could not be reused.

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