What does the shuttle rest on?
Leslie Bonser
on?
The reason I ask is that I'm getting into model rocketry; when you put your
model on the launch rod, you typically put an empty motor casing down for
the end of the body tube to rest on. This keeps the model up enough that the
ignitor clips don't short out on the blast shield.
Just got me to wondering...I realize the shuttle is a bit different, but it
has to be resting on something. It weighs quite a bit...
Can't be resting on the actual engines, we see those moving around just
prior to ignition. Are there structural components ("legs"?) that the
shuttle rests on? Or is it actually bolted (explosive bolts, no doubt) to
the launch pad?
Thanks in advance.
Christopher M. Jones
IIRC it rests on the outside of each of the SRBs. One of the
things I love about watching a launch is when the SSME's light
up you can see the whole Shuttle stack *flex* away from them
as it sort of rocks on its base. Then, it springs back and the
SRBs light and off it goes. Personally I like the events right
up before launch more than right after. After the launch it's
pretty much just a big flame pushing the stack into space
(which is cool, don't get me wrong). Before launch the
anticipation is at its highest and everytime I hear those
turbopumps whir up I get all tingly. Gotta love it.
(Looks like the ol' random sig generator is on a roll today!
Maybe it has become self aware. I'll have to keep an eye on
it. If the world ends in a large scale global thermonuclear
exchange followed by the robotic extermination of mankind in
the next few days, you'll know why. And, in that event, I'd
just like to say ahead of time "sorry, my bad".)
--
I'm like the man who singlehandedly built a rocket and went to the moon.
What was his name? Apollo Creed?
Brian Thorn
<lbo...@worldnet.att.net> wrote:
>When the shuttle is staged to the launch pad, what is it actually resting
>on?
>Can't be resting on the actual engines, we see those moving around just
>prior to ignition. Are there structural components ("legs"?) that the
>shuttle rests on? Or is it actually bolted (explosive bolts, no doubt) to
>the launch pad?
The Shuttle is secured to the Mobile Launch Platform by four hold-down
posts/bolts at the base ("aft skirt") of each SRB. The External Tank
is suspended between the two SRBs, and the Orbiter hangs off the ET
without touching the launch platform.
The eight bolts securing the SRBs to the hold-down posts are
pyrotechnically severed by the same signal that ignites the SRBs. But
even if the bolts don't separate, the Shuttle will fly anyway, it'll
just cause some damage to the launch platform and the aft skirt.
Brian
Jorge R. Frank
news:B7770C6E.45377%lbo...@worldnet.att.net:
> When the shuttle is staged to the launch pad, what is it actually
> resting on?
The entire weight of the shuttle stack (orbiter/ET/SRBs) is supported by
eight bolts at the base of the SRBs, four on each one. The bolts have
frangible nuts with pyro charges that are fired at the time of SRB
ignition.
--
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Henry Spencer
Leslie Bonser <lbo...@worldnet.att.net> wrote:
>When the shuttle is staged to the launch pad, what is it actually resting
>on?
The bases of the SRBs are bolted to the pad, and the rest of the stack all
rests on them. The ET is hanging on the SRBs, and the orbiter is hanging
on the ET.
(There are a couple of rectangular lumps flanking the orbiter's aft end
which might be mistaken for supports, but they house umbilical connections
only -- there is no support structure there.)
The same signal that ignites the SRBs also blows explosive nuts within the
SRB bases, releasing the shuttle to rise off the bolts.
--
When failure is not an option, success | Henry Spencer he...@spsystems.net
can get expensive. -- Peter Stibrany | (aka he...@zoo.toronto.edu)
Graham Nelson
> The Shuttle is secured to the Mobile Launch Platform by four hold-down
> posts/bolts at the base ("aft skirt") of each SRB. The External Tank
> is suspended between the two SRBs, and the Orbiter hangs off the ET
> without touching the launch platform.
This is probably a naive thing to say, but the tank must be
extraordinarily strong to bear the whole weight of the Orbiter
(and with no matching weight on the other side of it)... I was
under the impression it was as flimsy as could reasonably be,
in the interests of keeping dead weight to a minimum.
--
Graham Nelson Oxford, UK
Christopher M. Jones
Yes, both. The ET is incredibly flimsily-strong. Keep in
mind that the Orbiter only weighs about 13% of the full
weight of the ET, the ET doesn't have to be too much more
flimsily-strong to support it.
--
The earth is made of dirt and wood
And I'd be water if I could
Live in a dream
In your stream
Live in a dream
Paul F. Dietz
> This is probably a naive thing to say, but the tank must be
> extraordinarily strong to bear the whole weight of the Orbiter
> (and with no matching weight on the other side of it)... I was
> under the impression it was as flimsy as could reasonably be,
> in the interests of keeping dead weight to a minimum.
Support the weight of the orbiter? What about supporting
the weight (at > 1 gee) of the remaining liquid propellant after
the SRBs drop away? All the thrust accelerating that mass
is being transmitted from the orbiter to the tank.
Paul
Graham Nelson
> Yes, both. The ET is incredibly flimsily-strong. Keep in
> mind that the Orbiter only weighs about 13% of the full
> weight of the ET, the ET doesn't have to be too much more
> flimsily-strong to support it.
But surely the ET isn't filled until the stack is already out
on the pad, because otherwise the fuel would simply boil off in
the days and days before launch?
Ripley69
There are two supports which provide stability as the stack sits on the pad.
The weight of several of the payloads necessitates that something support the
back spine of the orbiter as it is moved around.
I could be wrong, but it doesn't seem logical that the tank truss system would
contain extra weight to support the orbitrer on it's own.
H. McDaniel
Ripley69 wrote:
Well in photos I have seen a rectangular frame about the size of the cargo bay
that is attached to the exterior of the shuttle and connects along the sides of
the craft above the wings. This rig is used to lift the shuttle into mating
position with the ET.
As long as the stack doesn't get the anular momentum to tip over, I don't see why
one should be surprised that the weight of the *SRBS* is enough to keep the
shuttle upright while the ET is empty.
---
-McDaniel
surucan on Netscape-AOL Instant Messenger
Chris Bennetts
"Graham Nelson" <gra...@gnelson.demon.co.uk> wrote in message
news:3B52043D...@gnelson.demon.co.uk...
> But surely the ET isn't filled until the stack is already out
> on the pad, because otherwise the fuel would simply boil off in
> the days and days before launch?
Entirely right. The ET is loaded (through the tail service masts and through
the orbiter's plumbing, and out into the tank) only about 6 hours or so
before launch, IIRC. But it still has to be able to support the lot for
those few hours (and the launch loads), so carrying the orbiter while empty
isn't too much of an ask. Kim Keller's site
(http://www.geocities.com/kimekeller/) has some good shots of the struts and
other hardware that joins the ET and orbiter.
--
--Chris
jcmbenn AT austarmetro DOT com DOT au
Jim Mantle
bearing. There is some sort of a big box thing that sits beside the tail
and provides various interconnects with ground support systems -
electrical power, ET fill, SRB cold-soaking systems and so on...
Also note that the support struts between the ET and the SRBs are not a
long distance away from the interconnects between the ET and the shuttle
- so you don't have a long "lever" motion to worry about.
And I'm not going to go look at Kim Keller's web page right now (time
contraint), but there are some fab pictures there of the struts
themselves.
And in case, I would bet that the static weight (sitting ont he pad)
isn't the load factor that was used to determine strength of the system
- the dynamic forces during launch are probably much more of an issue.
Jim
Chris Bennetts
"Ripley69" <ripl...@aol.com> wrote in message
news:20010715174137...@ng-bj1.aol.com...
No, the orbiter is completely supported only by the ET, and both of those
are mounted solely on the SRBs. The tail service masts contain *only*
umbilicals. It may seem illogical at first, but that's the way it is.
Christopher M. Jones
Nope, wrong, the tank holds up everything.
Why does it seem illogical that the ET would need to support
the weight of the Orbiter? The Orbiter has the engines and
of necessity there must be some sort of interface between
those engines and the ET that allows them to stay attached
while the SSME's are thrusting. It makes perfect sense to
me that a structure designed to hold the weight of a nearly
full ET while at 1-3 gee forces and transfer that weight to
the Orbiter and the SSME's would also have the strength to
keep the ET and the Orbiter together at only 1g.
--
Ooo eee,ooo ah ah ting tang Walla walla, bing bang Ooo eee ooo ah ah ting
tang Walla walla bing bang...
Mike Miller
The tank truss system holds the orbiter and SRBs together when
the stack is accelerating at 3Gs. Holding the inert shuttle on
the pad at 1G should be easier.
Mike Miller, Materials Engineer
GCGassaway
skirt has 4 flanges to support the weight of the fully loaded stack. Eight
explosive bolts secure those aft skirts to the pad until the SRB’s are ignited.
Going upwards on the SRB’s, there are aft attach fittings between the SRB’s and
the rear portion of the ET. Those transmit no thrust loads at all. They keep
the SRB and ET aligned in yaw and pitch, so essentially anti-sway struts.
Going further upwards on an SRB, to the “forward skirt”, which is a short
cylindrical section that is atop the SRB’s actual motor (SRM). The Forward
Skirt has a special thrust fitting built into it on one side, which engages a
crossbeam in the ET intertank.
This crossbeam carries all the thrust loads of the SRB’s (or looking from a
different point of view before launch, this crossbeam carries the gravity loads
of the ET mass and orbiter to the SRB’s which are acting as pillars). The
crossbeam itself transmits structural loads to the “intertank” which is the
corrugated-looking structure that supports the Lox tank (ET nose) above it and
loads to/from the Liquid Hydrogen tank below it.
As already mentioned, the aft attach fittings between the ET and SRB only
carries sway loads in pitch and yaw, no thrust loads.
Now for the orbiter. The THRUST loads and on-pad gravity loads (no thrust) are
carried by the aft attach struts between the ET and orbiter. Those struts
include a diagonal strut and a strut perpendicular to the ET. There is also a
horizontal crossbeam that connects the junctions of left and right aft strut
assemblies, as well as a small diagonal brace/strut that helps provide
stability against yaw sway forces.
The “bipod”, or inverted V-Shaped strut assembly near the orbiter nose, carries
no thrust loads at all. It only carries loads about the pitch and yaw axes, to
keep the orbiter from pitching up (or down) in pitch or swaying sideways in
yaw.
Interestingly, the orbiter's’s bipod pivots at the base, where it is attached
to the ET. The ET shrinks due to the extreme cold when fueled, it shrinks about
5.5” along the distance between the aft strut attach points and the bipod. This
is actually visible, in photos on the pad before fueling you might notice a
slight backward slant of the bipod, but in photos before launch or during
flight the bipod looks to be perpendicular.
For similar reasons the SRB to ET aft attach struts also are designed to allow
for ET shrinkage, but it is not as easily noticed in photographs as the Bipod
is.
So, essentially the orbiter travels its first 5.5” of a mission a few hours
before liftoff.... :-).
The ET is very light but it does have hard points to help carry the structural
loads. There is some lengthwise reinforcement along the area where the
orbiter/ET aft struts are mounted to the ET, you can see foam ramps covering
some of that. As well, internally, there are stiffeners that are beefed up
as-needed to help transfer the loads to the ET. I’m almost tempted to say
attached to internal bulkheads but there are no internal bulkheads (other than
the actual domed ends), but the internal stiffeners serve a somewhat similar
effect. The SRB aft struts are attached to the same internal stiffener as the
rearmost parts of the ET/Orbiter struts use.
As for the mass of the orbiter seeming to be an awful lot for the ET to have
hanging off of it, consider this. An orbiter with payload weighs around 250,000
or so (give or take a few 10k). While the thrust of the SSME’s is over a
million pounds, or over 4 times as much.
Now true, one is a tension force and one is a compression force, but you can
imagine that if it’s designed strong enough to be able to handle that much
thrust, plus a healthy safety factor, that unless some really basic design flaw
was ignored that it would not be that hard to make it strong enough for the
orbiter to hang off of the ET just sitting on the pad.
One last little bit of shuttle stack on the pad trivia. When the orbiter’s
SSME’s come up to thrust, that million pounds of thrust coming from the side
tries to topple the stack over. The SRB’s are still bolted on to the pad of
course, but the thrust does produce enough force to bend the SRB’s a bit. The
ET nose sways about 30”, stops, then sways back the other way (it’s called
“Twang”). The SSME ignition start time in the countdown is set with that in
mind, so that by the time the ET nose has swayed (or twanged) back the other
way, to vertical, it is T-0 and the SRB’s are ignited. This is easily noticed
in a close-up side view of the full stack at launch, if they cut away from the
SSME ignition close-up to show that side view in time.
- George Gassaway
Peter Harding
> [...] The
> ET nose sways about 30”, stops, then sways back the other way (it’s called
> “Twang”).
They have a rather light breakfast before launch, don't they?
--
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ICQ 40628243 Tel 07092057581 Fax 08707345230
Ron Beecroft
Answered several questions of mine at the same time.
--
Ron Beecroft
GCGassaway wrote in message
<20010717051440...@ng-bh1.aol.com>...
>The shuttle is attached to the pad by the aft skirts of the SRB’s. Each
SRB aft
<snip>>- George Gassaway
>
Andrew Boyd
I had a look at the actual bolts used to connect the ET to the shuttle
recently at KSC - from memory there are only two of them, and they *do not
look thick enough*. Obviously they are though!
GCGassaway
>>> I had a look at the actual bolts used to connect the ET to the shuttle
recently at KSC - from memory there are only two of them, and they *do not look
thick enough*. Obviously they are though!<<<
The orbiter attaches to the ET at 3 points.
A single point at the nose, atop the Bipod strut.
Two points on the aft strut assembly, left and right.
Now when I mentioned the aft struts before, I didn't meant to imply that all of
those struts individually attached to the orbiter. They are connected into one
assembly, including an external beam that runs across horizontally. This beam
has two umbilical connection plates, one left and one right, that interface
with the orbiter. The interface plates include electrical cable connections and
pipe connections that carry the Liquid 0xygen and Liquid Hydrogen. Also just
next to each of those plates is a hardpoint post (at 90 degrees to the
ET/Orbiter) that carries the structural shear (thrust) loads between the
orbiter and ET.
Now, those are not explosive bolts which carry those forces. The explosive
bolts are what connect the orbiter to those hardpoint posts, at 90 degrees to
the direction of thrust (or gravity when sitting on the pad). The explosive
bolts only carry the tension forces that keep the orbiter from moving away from
the ET in a perpendicular direction.
As for the explosive bolt on the Bipod near the orbiter nose, the bolt is what
keeps a ball assembly attached to the bipod (as mentioned before, the bipod
strut has to pivot due to cryogenic shrinkage of the ET, so there is something
akin to a ball and socket assembly connecting the top of the bipod to the
orbiter). IIRC , the explosive bolt fires to separate the ball from the rest of
the bipod., so the ball stays with the orbiter.
- George Gassaway
GCGassaway
actually an explosive "frangible nut".
- George Gassaway
Dan Hartung
gcgas...@aol.com says...
> BTW - in many cases where I mention an explosive "bolt" being used, it is
> actually an explosive "frangible nut".
Mmmmm. Frangible nuts.
Didn't those used to be made by Marshall Field's?
--
Dan Hartung * dan [at] dhartung [dot] com
Lake Effect weblog: http://www.lakefx.nu/
CHICAGOSTORIES: post yours @ chicagostories.org
JF Mezei
>
> BTW - in many cases where I mention an explosive "bolt" being used, it is
> actually an explosive "frangible nut".
OUCH !
I think I prefer the term "bolt" :-) :-) :-)