Can TOF 08PPs be shipped mounted to the Tracker?

[rocco8773]

In order to safe setup time at NTS for TVAC, can we ship the 08PPs mounted to the Tracker frame?

Background

• G-Loads experienced during flight
• Info on Tracker Crate Used to Ship form Bates to SSL
• NASA Handbook on Transporation
• Additional Shock and Vibration Literature

My Conclusions

• During Launch and Float the payload with typically experience g-loads <1G, but could see MAX g-loads of 2Gs.
• Jerry's FEA ran simulations up to 8G Vertical, but this is only experienced during descent (shoot shock and landing). However, it's my take to not load the panels beyond the launch load to mitigate any risk of damage before flight.
• NASA recommends using a 6G vertical limit for truck transportation, but this is for a traditional leaf sprung vehicle.
• Data collected in D. R. Ahlbeck's (1971) report shows shock loads of up to 1.5G for trucks using air-ride suspensions. However, traversed road conditions are not specified for the collected data. The author also specifically states that the presented air-ride data is limited and the plotted values are to be considered as conservative.
• The crate built by Crates and Freighters will dampen higher frequency (>33 Hz for 1psi static load) vibrations, but shocks will be coupled directly into the structure. So, the crate will not significantly help against shocks generate from going over curbs, potholes, etc. It's these events the will see the largest g-loads, and is what I'm most concerned with.

Expected transport g-loads are on par with the upper limit of launch g-loads. However, transport g-loads can still exceed the 2G limit depending on road conditions and driving style. The rate of these high g-load occurrences also depends on the two previously mentioned factors. Since these numbers are marginal and the Tracker crate will not isolate shocks (only vibrations from my interpretation from the provided material), my risk adverse nature is to choose to transport the panels separately from the tracker.

[rocco8773]

G-Loads Experienced During Launch and Float

This information was taken from an old Structural Requirements Document (OM-220-10-H-A) which has been replaced by 820-PG-8700.0.1. However, the new document does not list typical g-load and just outlines the FEA scenarios to apply to our Gondola. Thus, I'm just using the g-load numbers as a rough guide to compare to expected shipping g-loads.

Timeline	G-Load	Notes
Staging Area	N/A
Flight Line	Typ. .25G / MAX 2G	typical due to transporting payload, max is rarely seen
Launch	Typ. .5G / MAX 2G	g-load is from the jolt of release
Ascent	Typ. .5G	Due to shear force of the wind
Float	Not Specified	least stressful portion of flight
Termination & Descent	2-5G	caused by shoot shock
Landing	10G vert / 5G @ 45 deg
Recovery	N/A

[rocco8773]

Info from Tracker Shipment from Bates to SSL

• Tracker create design
• Vibration dampening chart for 2" 1.7LB PE used in crate
• Comment from Crates and Freighters

Here is an explanation of the floating base foam calculations and load rating:

Based on the floater size of 96” x 95”, the estimated weight of the plywood/lumber on top of the floater is 330 lb.

With an estimated item weight of 1,000 lb., the combined load is 1,330.

The optimum static loading for 1.7# PE is 0.75 psi.

I would use QTY X6 strips of 2” 1.7# foam @ 95” x 3.125” for the floater. This gives an area of 1,781.25 sq. in.

1,330 lb./1,781.25 sq. in. = 0.75 psi load

Looking at the vibration transmissibility chart below for 2 in. 1.7# PE, we can compare frequency and static load. We can see where trucks often travel between 40-60 Hz. At a 0.75 psi static load, the amplitude of the vibration force is reduced. This is the attenuation zone, which is the safest for the product. This is where the input vibration force is reduced by the packaging material.

According to the NASA Space Vehicle Design Criteria report, titled Transportation and Handling Loads, cargo transported by trucks can experience vertical load factors up to 6.0 g. Cargo transported by air can experience vertical load factors up to 3.0 g.

At 6.0 g, it is estimated that the floater foam will have a compression rate of 16 percent. The compressed foam thickness at 16 percent compression would be so 1.68”. As a result, there is not a concern with “bottoming out” the foam on the floating base.

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Adjusting for increased static load

The original shipping load (Bates to SSL) was 1330 lbs. At SSL the top layers of the Tracker were assembled adding around 200 lbs to the load. Each 08PP weighs roughly 55lbs. Assuming 2x panels, mounts, and keeping cables attached, then I'd estimate the combined weight at 150lbs. This brings the static load to ~1700lbs, or .96 psi. This appears to still be in the valid range for the 2" 1.7lb PE foam.

Questions to ask Crates and Freighters:

• Does the 2" thick 1.7lb PE foam need to be replaced after each shipment? How often does it need to be replaced?
• Do we need to need to increase the foam thickness for the increased static load?

[rocco8773]

NASA's Handbook on Transport Handling and Loads

• Transport and handling loads
• This document was referenced by Crates and Freighters

• NASA's handbook has a chart listing the design criteria for various transport methods. For Trucks the max vertical load is 6G. However, this does not specified if the truck is using air-ride or not.

  

[rocco8773]

Additional Shock and Vibration Literature

• D. R. Ahlbeck, "Study to Define the Shock and Vibration Environment During Truck Transport of Shipping Containers", Battelle Columbus Laboratories (1971)
• S. J. Maheras, et. al., "Transportation Shock Vibration Literature Review", PNNL (2013)

Ahlbeck (1971) is the most exhaustive literature I've found comparing trucks with transitional leaf springs vs. air-suspension. Air-suspension does significantly reduce the expected peak G-loads, <2G vs. <4G.

Note: This figure does not specify the type of road conditions that were traversed to collect the data. Shock limits will be higher for road conditions that bad and riddled with potholes.

[rocco8773]

I (@rocco8773) determined it was unsafe to both the Tracker Frame and panels to ship panels attached.