Why are the rockets tethered before take-off?

[Sixx]

What are those "hoses" that you see in all the rocket launch videos? The ones that let go of the rocket as soon as the rocket takes off? Example:

http://www.youtube.com/watch?v=Nv35OPKzCQw (50 seconds in)

[slang]

(The video, 50 seconds or so in, shows the hoses being pulled back during a Saturn V launch)

Some are for continually topping off the fuel. The type of fuel that's used tends to boil off, since it's extremely cold stuff. Others are for removing the fuel in case the launch is cancelled. They're not used to tether the rocket to the tower, there are other clamps and bolts for that. I'm not sure why they're only detached after lift off, I imagine that it's because only at that point it's absolutely sure that the hoses won't be needed anymore.

[AlexInOklahoma]

Those 'hoses' are typically called umbilicals. They do not hold the rocket whatsoever, but hold the hoses and cables that give the power and fuel(s) to rocket as said above Google the term umbilical for better info if you like. They are not attached until *after* liftoff (iirr) but are released very soon before - just slow to fall away. If held until rocket is moving they would likely give a tug, which is bad, of course. Lots of things happen in the (milli)seconds prior to liftoff, and is why a system goes into 'automode' (forget actual term at the moment) and not done manually. At least for the 'big rockets' anyways.

The bolts that generally hold a rocket down are at the base, and are probably much smaller than you would expect. The bolts are severed explosively (usually) after its certain that the the liquid engines are running within spec. Rockets that are solid-only first-stage do not light-up/test prior to release, fwiw (STS uses both, of course)

Alex

[nauthiz]

Here's a page with descriptions of what each of the Saturn V's service arms was for:

http://www.apollosaturn.com/srvcarms/armmain.htm

[Sixx]

Three informative answers in no time at all. This forum is great!

[Jens]

They are not attached until *after* liftoff (iirr) but are released very soon before - just slow to fall away.

I hope that's a typo and you meant that they are not detached until after liftoff. Attaching them after liftoff would require a fair amount of courage on the part of the engineer!

[Metricyard]

Kind of off top but on topic, had there ever been an incident where one of the umbilicals / service arms didn't detach or retract properly? I would assume that the umbilicals would be made to just "snap off" in the event of a release failure, but that probably wouldn't work for the service arms.

I guess this question would be more geared to the Apollo/shuttle, but I guess this would apply to just about any rocket launch.

[violentquaker]

Kind of off top but on topic, had there ever been an incident where one of the umbilicals / service arms didn't detach or retract properly? I would assume that the umbilicals would be made to just "snap off" in the event of a release failure, but that probably wouldn't work for the service arms.

I guess this question would be more geared to the Apollo/shuttle, but I guess this would apply to just about any rocket launch.

I would guess that the service arms move out of the way well before liftoff, so if they failed attached to the rocket it would be a scrubbed launch.

There was a near disaster during a launch attempt of Gemini VI-A on December 12, 1965 where an umbilical detached an instant too soon and caused the rocket engine to shut down.

I have no idea if a stuck umbilical could damage the lauch vehicle... anyone heard of that happening?

[AlexInOklahoma]

A stuck umbilical can/will make a BIG problem. Purely from memory, I think a Delta or similar rocket drug an umbilical uphill quite some distance before exploding (range safety??)... again, just a vague memory, and will see if I can find more.

An Atlas Agena B definitely 'failed to launch' (exploded on pad moments after liftoff) after automatic engine shutdown when umbilical did not detach. It was Samos 3 on 9-9-61. Went about a meter off pad, then fell back down and BOOM - oops

Pretty sure there have been others as well. If The_Jim sees this thread, he probably could list every failure-to-detach that has ever happened, LOL.

Alex

[violentquaker]

...An Atlas Agena B definitely 'failed to launch' (exploded on pad moments after liftoff) after automatic engine shutdown when umbilical did not detach. It was Samos 3 on 9-9-61. Went about a meter off pad, then fell back down and BOOM - oops
Alex

Yikes, that sounds scarily similar to the Gemini failure. Glad the manned one didn't go boom!

[JohnD]

Does happen in F1!
Car sets off before refuelling rig is detached.
Here's the latest incident (incendent?)
http://www.youtube.com/watch?v=v4eJcjwf4c8

Don't know if the refuelling hose is designed to break away, but surely the rocket hoses should be too?
John

[NEOWatcher]

Don't know if the refuelling hose is designed to break away, but surely the rocket hoses should be too?
John

I don't know either, but I would think the problem would be the location. It would need to be at the connection point. Can you imagine a rocket hauling a hose like that hanging from the side of it? I'm sure it could cause some serious issues.
Also; what kind of pressures are we talking about? That's going to make it much more difficult to design a breakaway.

[publiusr]

I think some LVs have a lanyard attached that, should the rocket body bend too much, the range safety destruct is initiated. I wonder if that could snag somehow.

[slang]

I think some LVs have a lanyard attached that, should the rocket body bend too much, the range safety destruct is initiated. I wonder if that could snag somehow.

Imagine a bat perching down on it... or an owl... :gasp: (<-- if this smiley doesn't work...it should!! )

[The Jim]

I think some LVs have a lanyard attached that, should the rocket body bend too much, the range safety destruct is initiated. I wonder if that could snag somehow.

They are internal and are there in case the vehicle breaks up.

[astromark]

In that sequence of events that are almost completely automated because you just can not trust people to do the right thing on time every time. In those milliseconds prier to 'Main engine start' and the ignition of the solid boosters those umbilicals are released. There has not been a fail to release on the shuttle or Saturn systems. Not one.
On the shuttle its a GO, NO GO, issue. If the umbilicals do not detach the boosters do not ignite. and the light in the fridge is GOooo...

.

[JohnD]

All,
I'm reading Mailer's "Of a fire on the Moon" about Apollo 11.
Never read it before.
I find Mailer's prose frustrating - pages and pages of vague philosophy, followed by pages of acutely observed hard reporting. He describes in some detail the umblicals and hold-downs on the Atlas, including as a final restraint a number of bolts that are pulled through dies mounted on the rocket. This, he says, is to gently release the rocket, and inhibit surges in the fuel tank.
Certainly, his description gave me a far greater insight into the process of the final launch than I ever had before, and I recommend it. Just skip the rubbish between the reports!

John

[The Jim]

A stuck umbilical can/will make a BIG problem. Purely from memory, I think a Delta or similar rocket drug an umbilical uphill quite some distance before exploding (range safety??)... again, just a vague memory, and will see if I can find more.

An Atlas Agena B definitely 'failed to launch' (exploded on pad moments after liftoff) after automatic engine shutdown when umbilical did not detach. It was Samos 3 on 9-9-61. Went about a meter off pad, then fell back down and BOOM - oops

Pretty sure there have been others as well. If The_Jim sees this thread, he probably could list every failure-to-detach that has ever happened, LOL.

Alex

First Titan II silo launch. Atlas D where the rocket is swaying has it leaves the pad. There was another Atlas Agena B Samos that ripped out the Agena GN2 disconnect and depleted the attitude control gas.

[The Jim]

In that sequence of events that are almost completely automated because you just can not trust people to do the right thing on time every time. In those milliseconds prier to 'Main engine start' and the ignition of the solid boosters those umbilicals are released. There has not been a fail to release on the shuttle or Saturn systems. Not one.
On the shuttle its a GO, NO GO, issue. If the umbilicals do not detach the boosters do not ignite. and the light in the fridge is GOooo...

.

Not true. The umbilicals come off at liftoff, which is after SRB ignition.