Sudden compressive failure of large SAS module under stress?

[Dave Kerbin]

I'm designing a heavy lift rocket, and after getting a preliminary design worked out (one that didn't explode on the pad or wobble and then explode) I encountered a problem during testing. I took the booster stage straight up and things seemed to go well with a smooth if noisy trip. As the booster stage was almost out of fuel the whole thing suddenly exploded.

After rerunning the launch I found the cause: as the booster+orbiter reached about 950m/s the "Advanced S.A.S Module, Large" in the orbiter suddenly compressed or blew up, resulting in most of the orbiter 'falling' into the still accelerating booster stage and causing a massive explosion about half a second later. I reran the launch with the SAS removed and it didn't explode, though the orbiter was a whale to turn without it.

Are certain components more delicate then others when it comes to compressive forces?

Edited August 27, 2013 by Dave Kerbin

[Johnno]

Are certain components more delicate then others when it comes to compressive forces?

Yes.

I'd say move it higher on your craft + add struts to lessen the stress on it. Or just add more struts from your launch vehicle to your payload.

[aNewHope]

Somehow thin objects are way easier to crush than bigger ones (e.g. fuel tanks) even if they have a lot of impact resistance.

The only way to get out of this dilemma is to move the weak object up in the rocket, strengthen it by struts and try to lower your acceleration forces by better staging and throttle control.

This is the easiest accomplished by using the data readouts and/or control utilities like Kerbal Engineer or MechJeb.

[King Arthur]

The (A)SAS modules, reaction wheels, and in-line battery packs are all notoriously delicate and simply cannot take any physical stress whatsoever. For launching, the easiest way to address this is to strut the part to whatever's above and below using two sets of 4-symmetry struts.

[Dave Kerbin]

Yes.

I'd say move it higher on your craft + add struts to lessen the stress on it. Or just add more struts from your launch vehicle to your payload.

Somehow thin objects are way easier to crush than bigger ones (e.g. fuel tanks) even if they have a lot of impact resistance.

The only way to get out of this dilemma is to move the weak object up in the rocket, strengthen it by struts and try to lower your acceleration forces by better staging and throttle control.

This is the easiest accomplished by using the data readouts and/or control utilities like Kerbal Engineer or MechJeb.

The (A)SAS modules, reaction wheels, and in-line battery packs are all notoriously delicate and simply cannot take any physical stress whatsoever. For launching, the easiest way to address this is to strut the part to whatever's above and below using two sets of 4-symmetry struts.

Thanks. My battery was at the very top of the orbiters service module (just below the dummy payload) and didn't suffer any problems. I'll try moving the SAS up there. Then I'll try to fix the orbiter modules problem of not packing enough thrust to stabilize the orbit in time to prevent it from becoming a not orbit.

[SRV Ron]

SAS works best near the top of the rocket. Also, if your rocket is sluggish to turn when unpowered, consider adding a thruster pack to the upper stage.