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# Structures in a Weightlessness Environment

## Structures in a Weightlessness Environment

(OP)
I am curious about the deformation that occurs when the structure I have designed is placed in a Weightlessness environment.

maybe static analysis is good. In that case, what kind of forces should be applied to the structure?

Would it be correct to apply a -1g gravity force in the xyz directions simultaneously?
or.. how should study the deformation in a zero-gravity environment?

I would appreciate your expert opinion.
Replies continue below

### RE: Structures in a Weightlessness Environment

Acceleration is a vector quantity, so in what direction, xyz, are your forces acting?

### RE: Structures in a Weightlessness Environment

#### Quote (test123)

I would appreciate your expert opinion.

I doubt that anyone here is expert about a weightless environment. You probably should make an educated guess about the acceleration due to gravity, then assume it could occur in any direction.

### RE: Structures in a Weightlessness Environment

"Would it be correct to apply a -1g gravity force in the xyz directions simultaneously?"

Weightlessness is a lack of reaction to gravity. You could put in 1000 Gs of "gravity force" and as long as there's no restraint against it the entire assembly will be weightless. This is how, near the surface of the Earth, an item in a vacuum in free fall experiences no weight.

In finite element analysis this used to be a common failure - no restraint applied and the solution fails to converge with the item going 10,000 miles per hour and accelerating. Easier to do in the punch card days.

What else is going on with the item? In low Earth orbit the biggest contributor to strain is thermal cycling due to entering and exiting Earth's shadow, which can cause low frequency vibrations.

### RE: Structures in a Weightlessness Environment

yeah, I'm with 3DD on this ... weightness is not opposite weight (like -ve g means). It is easier to ignore weight (as a load) or you could apply equal and opposite body forces ... in orbit I believe there is a lower value for "g" (ie not 32 ft/sec2) but whatever it is is is balanced by an opposite body force, due to the orbit. Maybe this is what you meant (when you say apply -1g gravity force) only you didn't say "in addition to applying +1g gravity force").

There will be inertia forces on the satellite, the rocket's thrust produces an acceleration.

Remember, your satellite is going to be built on earth, so it will need to resist 1g loads, and launch loads, and on-orbit thermal loads.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

### RE: Structures in a Weightlessness Environment

When a piece of equipment is in a zero g environment, gravity loads are zero, not '-1'.

There are two approaches to designing things for zero gravity, depending on exactly what you're doing.

Approach 1: design for mechanical robustness/stability against whatever your highest temporary loading condition is. For spaceflight hardware this is almost always going to be loads experienced during the launch. Loads experienced during orbital changes will almost always be quantitatively smaller than launch loads, but they may be off-axis from the launch load, in which case you need to account for that too. Then assume that if you're safe against 6+ g of launch load, you're safe with zero gravity load. This works most of the time.

Approach 2: design for mechanical robustness/stability against whatever your highest temporary loading condition is, BUT also determine what the exact response of the system will be to no gravity load at all. IE, if I have a frame holding widget x that weights 500kg under 1g, and under 1g widget x is 999mm from widget y, at 0 g that distance may become 1001 mm because of a lack of gravity induced deflection in the frame. This is necessary if you're designing VERY precise instruments- for example, the structures that hold the optics of orbital telescopes and downward looking cameras on satellites require very precise control of zero gravity dimensions.

In either approach you also need to make sure you understand and correctly account for thermal loads - they can be very large in orbit or transit between orbits.

### RE: Structures in a Weightlessness Environment

For optical structures, the lack of gravity load makes a good challenge for testing of optical performance, since it's difficult to simulate zero-g conditions on Earth.

TTFN (ta ta for now)
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