Static Fire Tests: How is the rocket prevented from flying?

Question

In rockets like Starship, if 35 Raptors are firing at same time, then in a full-duration static fire test there would be enormous loads being exerted from 35 raptors, on the clamps holding the rocket. What type of clamps/holding technology is being used to prevent the rocket from flying up (or away)?

I understand the load on the clamps will be thrust minus rocket's mass, but in a full duration test the rocket's mass will keep on decreasing while thrust will not decrease in same proportion.

So, how does "holding-the-rocket" technology works?

In short: large concrete or steel "thrust blocks" that are far too heavy to be moved by the engines they are testing. Sometimes this means bolting directly to the foundation. Given enough mass, bolts, and maybe even welding to the rocket itself, you can make the rocket stick to your test stand.
There is some room for smart design in launch clamps; hopefully an answerer can give examples of the systems used for some different vehicles. — CourageousPotato, Mar 19 '21 at 07:54
Not Starship but answers contain related information: How does a simple construction keep a firing rocket on the ground? and What holds the Space Shuttle orbiter itself stable on the launch pad? and What holds SpaceX’s rocket in place in this launch? (there's a GIF!) and especially What is a launch vehicle resting on prior to launch? — uhoh, Mar 19 '21 at 07:55
Oh, this is the one I was looking for: Saturn V and STS holding to launch pad mechanism — uhoh, Mar 19 '21 at 07:57

score 3 · Answer 1 · answered Mar 19 '21 at 15:17

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The same way that they hold down Starship from T-1.3 seconds when the engine ignites to T-0. With the stongback clamps and the TE (Transporter Erecter). This information comes from Spacex's numerous Falcon 9 webcasts, so this is information is only correct if Falcon 9 and Starship use the same method.

answered Mar 19 '21 at 15:17

Saturn 5

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Oh boy. I want to know about the mechanism involved in smooth, simultaneous release millions of pounds of thrust. – Eric G Mar 20 '21 at 02:38
Holding a rocket before T-0 is bit different thing than holding it after T-0. The force requirements would be several folds higher. And also with passage of time, the required holding force will increase further as the total mass of rocket decreases. – Raj Arjit Mar 20 '21 at 10:16
@RajArjit You are wrong, thrust just before T-0 is equal to thrust just after T-0. – Uwe Mar 20 '21 at 22:46
@Uwe: I never said of "thrust". I said "holding force". Holding force = thrust minus weight of the rocket. The weight of rocket decreases with passage of time with ejection of propellant. – Raj Arjit Mar 22 '21 at 05:21

Static Fire Tests: How is the rocket prevented from flying?

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