How does the Saturn V Dynamic Test Stand work?

Question

This photo instantly provokes a ton of questions in me:

It shows the Dynamic Test Stand at Marshall SFC with the Enterprise, which was a Space Shuttle test vehicle, suspended for vibration testing. It was built to test the Saturn V in the same way. From the explanation below the image in an old NASA image of the day article, they were far from done getting things ready in this photo. They attached the external tank and the boosters too, and tested the whole thing.

Okay. The few articles I can find on this building are quite short and vague. Apparently it is the tallest building in Alabama, and is a national historic site (duh). But how did it work?

Was the rocket suspended for the test? If not, why would the rockets be placed in the building that way? How do you shake an entire rocket in a way that imitates vibration during launch? Do you have to put something in the fuel tanks to make it a proper test? How do you assess the results? Are all rockets tested this way?

Why are there only a few stub articles about the facility that don't answer anything about how it works in the first two pages of results on Google, after which the results get even vaguer? Okay, I don't expect an answer to that, and yet it sort of amazes me. My head is spinning with questions.

Answer 1

I can answer the Shuttle part.

The test in question was the Mated Vertical Ground Vibration Test (MVGVT). Here's how the stack looked in the test stand.

Five configurations were tested

1. Liftoff
2. First stage (SRBs attached)
3. early, mid, and late 2nd stage

For the launch testing, the SRBs stood on hydrodynamic supports which "provided the vertical support as shown in Figure 2 and six degrees of freedom for the supported vehicle" (this config is shown in the paper linked below, but it's a lot blurrier than the picture I chose). For the boost (ascent flight) testing the stack hung from a huge crane which attached at the forward SRB attach points (this was for 2nd stage flight).

Shakers were attached near the midbody, lateral restraints to the top and bottom of the SRBs. The shakers would vibrate the vehicle at various frequencies and sensors attached all over the stack took data on the response.

Water was used to simulate the liquid oxygen in the tank, air for the liquid hydrogen!

There's an enormous amount of detail in the paper the picture and quote came from, please check it out if interested.

The tests were extremely valuable in identifying deficiencies in the design. Both hardware and software changes resulted. The most important changes that resulted were:

• The left and right SRB forward mounted rate gyros exhibited abnormally high transfer functions which required a structural redesign.

• Test rate gyro values showed greater response variations than those used in the analytical studies in determining the Redundancy Management (RM) trip levels. For STS-1 flight, RM software trip levels and cycle counter levels were increased. The Fault Isolation Routine was modified to inhibit kicking out RGA's and accelerometers after first sensor failure. Changes to the control system for the other flights will be: evaluated after STS-1 flight.

You can also read about the tests and the resulting changes on the design in the Space Shuttle Technical Conference book, volume 1, page 325 " Shuttle Structural Dynamics Characteristics, the Analysis and Verification" (warning, huge pdf)

Answer 2

It is indeed difficult to find information on this building. As you can see in the photo below, it was part of a massive test facility at Marshall Space Flight Center:

(Overview of MSFC; Mike Jetzer/heroicrelics.org)

Some details of how the test stand worked can be found in the nomination form for the US National Register of Historic Places Inventory:

When in use the test vehicle rests on hydrodynamic supports which provide a maximum of 6 degrees of freedom of movement which is required when large space vehicles are dynamically tested. Vibration loads can be induced in the pitch, yaw, or longitudinal axis to obtain resonance frequencies and bending modes. Vertical mating procedures between stages can also be investigated and checked out.

It is also mentioned in "Stages to Saturn":

[...] the Dynamic Test Stand, 129 meters high, designed to accommodate the complete Saturn "stack" of all three booster stages, the instrument unit, and the Apollo spacecraft. Inside the Dynamic Test Stand, heavy duty equipment shook [70] and pounded the vehicle to determine its bending and vibration characteristics during flight.

The facility is referenced in "AN INVENTORY OF AERONAUTICAL GROUND RESEARCH FACILITIES Volume III - Structural and Environmental Facilities" (pdf; page 7-54), but I am unable to find the reference therein ("Technical Facilities and Equipment Digest"). I did find however a patent application for "SUPPORT APPARATUS FOR DYNAMIC TESTING", which has the following image:

I can't tell for certain if this is the Saturn V test stand, but I would assume the principle operation is the same. The patent proposes a solution to the limitations of suspending a test vehicle from cables (in particular the way those suspensions modify the vehicle's dynamic behaviour) by introducing a special hydrostatic bearing (oil-based, virtually frictionless). The actual tests are not described, but from the technical description we can infer the following:

1. The vehicle is supported by independent, self-adjusting hydraulic supports. Each support consists of a hydrostatic bearing and a vertically floating piston. The floating piston acts like a spring, while the bearings allows the vehicle to move in translational and rotational direction in a frictionless manner, simulating free floating conditions in 6 dimensions.

(The vehicle sits on plate #31)

2. In addition, some springs should be attached to the vehicle to prevent it from tipping over. These springs should be of low stiffness and attached to nodal points of the rocket so they do not affect the dynamics.
3. A "shaker" is attached to the bearing to apply the desired vibrations.

(The shaker is part #110)

So yes, they shook the entire rocket while it was free-standing (!) on those supports.

Answer 3

Just created a new account to comment here, but apparently I need more reputation to comment direction on a previous post... I just wanted to chime in that Ludo is correct, that patent, co-authored by my grandfather "George von Pragenau" is indeed what was used for the Saturn V dynamic test stand. He was the dynamic stability guru for NASA during the space race and designed this test stand along with redesigning the turbo machinery (specially the creation of new damping seal technology) all with the intent of providing dynamic flight stability. This allowed for him to predict and (mostly) solve the pogo oscillation issue which nearly doomed the entire project or at least put the timeline in severe jeopardy.

The dynamic test stand truly had 6 DOF as he personally had the pleasure of moving the entire Saturn V while on the stand just by pushing with his index finger. While he pasted away several years ago, he would have loved the interest in this topic and answered every question with more information than you probably wanted. One more fun note: As recently as the early 2010s, NASA employees from the Constallation program were contacting him to help understand how he even made this dynamic test stand and solved the oscillation issues as they were beginning to experience them again in their simulated testing of the Ares V.

Cheers!