Why is the Space Shuttle upside down during launch?

[cjp]

Why is the first part of a Space Shuttle launch in a 'heads-down'(*) orientation? If it were rolled to a heads-up orientation, wouldn't that allow the wings to help reduce a bit of the gravity drag?

(*) You know, with the heads of the astronauts closer to the center of the earth than their feet. I initially called this 'upside down' because of the unusual orientation for an aircraft-like vehicle like the Space Shuttle, and for the astronauts themselves. This caused some (deliberate?) confusion further down in the thread.

 

[insane_alien]

reduces stress on the frame during launch, this means you can build it lighter. the wings will not have much effect on anything as they are grossly undersized considering the mass of the whole assembly.

 

[Urwumpe]

First of all, because the ET blocks the antennas of the orbiter and prevents them from sending to the ground stations during launch.

Second because this is slightly more effective because the orbiter is then flying in the wake of the ET during the first 80 seconds of flight, which means that it gets less vibrations.

 

[Donamy]

Also allows the astonauts to better view of the horizon.

 

[Kevon Daye]

Another good reason is, when they launch they're pulling a good +3g's(or thereabouts), which is bearable.If they launch the same trajectory, only pushing over instead of pulling, the crew will be subjected to -3g's, which is uncomfortable, to say the least:

[ame="http://en.wikipedia.org/wiki/Redout"]Redout - Wikipedia, the free encyclopedia[/ame]

 

[Urwumpe]

Another good reason is, when they launch they're pulling a good +3g's(or thereabouts), which is bearable.If they launch the same trajectory, only pushing over instead of pulling, the crew will be subjected to -3g's, which is uncomfortable, to say the least:

Redout - Wikipedia, the free encyclopedia

Wrong. Not about the red and black out, but about the direction and magnitude of the acceleration vector.

 

[Bloodworth]

Actually, according to NASA, the shuttle is upside down during launch for purposes of balance. You note that the shuttles engines point almost straight at the ground as the entire stack pitches over, its like balancing a pencil on the tip of your finger. Otherwise the shuttle would pitch all the way over and slam into the ground due to the imbalance of the stack.

 

[Urwumpe]

Actually, according to NASA, the shuttle is upside down during launch for purposes of balance. You note that the shuttles engines point almost straight at the ground as the entire stack pitches over, its like balancing a pencil on the tip of your finger. Otherwise the shuttle would pitch all the way over and slam into the ground due to the imbalance of the stack.

Wouldn't matter, the angle between flight path and engines would have to be the same in ANY orientation around the flight path for zero torque. Gravity induced torques are low on the Shuttle stack.

 

[Bloodworth]

Wouldn't matter, the angle between flight path and engines would have to be the same in ANY orientation around the flight path for zero torque. Gravity induced torques are low on the Shuttle stack.

I'm just saying what NASA stated a little before that first launch of the Columbia.

 

[statickid]

i think it's a moot point. first of all it was designed that way so technically it's right side up. second of all, what is upside down and rightside up? and thirdly during the "first" part of the sequence, it's mostly kinda vertical, it's only really "upside down" towards the upper part of the sequence

---------- Post added at 07:33 PM ---------- Previous post was at 07:27 PM ----------

Gravity induced torques are low on the Shuttle stack.

i don't think it has anything to do with gravity torque, i think it has to do with the engine thrust balancing with the center of mass together with the drag profiles. turn on only one engine in your delta glider and watch it spin around its center of mass, nothing to do with gravity.

 

[clickypens]

it's not just the shuttle, seems like lots of things launch heads-down. I've always wondered why as well.

 

[Zatnikitelman]

Another question that possibly fits in this topic: aside from making easier modifications to the LCs from Apollo to Shuttle, why does the vehicle have to roll from the Orbiter facing land to the Orbiter facing water? Why didn't they design the pad so the vehicle only had to pitch down instead of having to roll then pitch down? Any guidance maneuver involving gimbaling the engines would reduce the thrust put into acceleration so you could launch less payload. Right?

 

[Bj]

Ahh you people, use Google :thumbup:

Upside down in space;

http://www.ksc.nasa.gov/nasadirect/archives/KSCDirect/archives/launch/sts110/shuttle-qa.htm

Charles from Oklahoma City
Why does the shuttle always orbit the earth upside down?

Ah – good question. The reason we go in upside down is the payload bay doors. The insides of those are a giant freon-filled radiator and there is a lot of heat being generated inside the crew module. There are hundreds of electronic boxes, and the astronauts – the human body – is generating heat all the time. And that heat must be dissipated, and so you have water that flows into the crew module and cools it. You have radiators in there, and fans blowing across and that cools everything and that water flows back out to the payload bay. Then there is freon out there, the freon cools the water. The freon has to get rid of the heat that it just picked up from the water. It does that by flowing through the radiators. Your best place to reject the heat is to point toward deep space all the time. But when you are on the Sun side of the Earth that is hard to do. So you just turn towards the Earth and that is cooler than facing towards the sun. And instead of using a whole bunch of fuel to keep the orbiter rotating everytime we go from sunlight into darkness, which is once every 45 minutes, we just stay oriented towards the Earth. There have been times when we really needed to cool the orbiter and while we were on dark side we’d point to deep space and reject more heat. But that’s why we do it.

Upside down in launch;

http://www.ksc.nasa.gov/facts/faq07.html

During the vertical rise phase, the launch pad attitude is commanded until an I-loaded V(rel) sufficient to assure launch tower clearance is achieved. Then, the tilt maneuver (roll program) orients the vehicle to a heads down attitude required to generate a negative q-alpha, which in turn alleviates structural loading. Other advantages with this attitude are performance gain, decreased abort maneuver complexity, improved S-band look angles, and crew view of the horizon. The tilt maneuver is also required to start gaining downrange velocity to achieve the main engine cutoff (MECO) target in second stage

 

[Hielor]

Another question that possibly fits in this topic: aside from making easier modifications to the LCs from Apollo to Shuttle, why does the vehicle have to roll from the Orbiter facing land to the Orbiter facing water? Why didn't they design the pad so the vehicle only had to pitch down instead of having to roll then pitch down? Any guidance maneuver involving gimbaling the engines would reduce the thrust put into acceleration so you could launch less payload. Right?

The shuttle doesn't always launch to the same azimuth, so it has to be able to roll to the right azimuth anyway.

 

[Urwumpe]

i don't think it has anything to do with gravity torque, i think it has to do with the engine thrust balancing with the center of mass together with the drag profiles. turn on only one engine in your delta glider and watch it spin around its center of mass, nothing to do with gravity.

Yes, but it will spin in the same plane, regardless how you rotate the plane by banking.

The thrust of the SSMEs is also just 6% at launch of the total thrust, the SSMEs are just gimballing for reducing the loads, but don't have any steering effect until the SRBs separate.

 

[Linguofreak]

i don't think it has anything to do with gravity torque, i think it has to do with the engine thrust balancing with the center of mass together with the drag profiles. turn on only one engine in your delta glider and watch it spin around its center of mass, nothing to do with gravity.

This still fails to apply to shuttle launches. Whether the shuttle launched heads-up or heads-down, the engines would still be in the same place with regards to each other and the rest of the stack, including the CG.

Another good reason is, when they launch they're pulling a good +3g's(or thereabouts), which is bearable.If they launch the same trajectory, only pushing over instead of pulling, the crew will be subjected to -3g's, which is uncomfortable, to say the least:

Redout - Wikipedia, the free encyclopedia

The problem with that theory is that the three G's the shuttle is under are in the forward direction, not the "top side of the orbiter" direction. The G-forces the astronauts are feeling are pushing them into the backs of their seats, and this wouldn't change whether or not the stack was "pushing over".

However, what you stated might be somewhat of a "historical", rather than technical reason, see below:

it's not just the shuttle, seems like lots of things launch heads-down. I've always wondered why as well.

It may be that, while it doesn't matter too much in the case of a space launch whether you launch heads up or heads down (or heads left or heads right, for rotationally symmetrical vehicles), that launching heads-down is simply a convention stemming from aerodynamicists working on launchers / the pilots of manned launchers, being used to aircraft making turns "heads in". At the pitch rates most launchers (and pretty much any manned launcher) would use, the reasons why airplanes turn heads-in wouldn't apply, but it may just be that the rule is so engrained in the heads of the people that spend alot of time around rockets that there's an unconcious or semi-concious mental bias to launching heads down, since launches involve a gradual downward turn, and "everyone" knows that you turn heads in.

I, for one, when hand-piloting launches in Orbiter, find it awkward to launch heads-up. Not that real launches are typically hand flown, but what seems "logical" to the designers and flight planners might have as much to do with it as anything.

 

[Andy44]

Also, as stated already, launching heads-down gives the crew a better view of the horizon. In the event of trouble, the crew has more attitude information available by glancing out the window. This is also the reason why Gemini and Apollo did heads-down re-entries; because the pilot had to be able to see the vehicle's pitch and roll angle in order to fly the re-entry manually if the autopilot failed.

 

[statickid]

This still fails to apply to shuttle launches. Whether the shuttle launched heads-up or heads-down, the engines would still be in the same place with regards to each other and the rest of the stack, including the CG.


I was talking about that other guys quote from nasa talking about balancing the shuttle on a pencil. although i can't really imagine the shuttles engines can be in their current configuration and not do the launch heads-down unless the crew seats were made to hang upside down while landing.

thrust torque does not fail to apply to the original design and thruster configuration considerations that were made when the vehicle was made. they seem to not apply because it is well designed.

the original question was not why it was "heads up or heads down", someone else brought that up later. it was why does the shuttle launch "upside down", and the answer to that is that it DOESN'T launch upside down!:rofl:

this question was most likely sparked by the fact that it looks like a plane. then all the while nobody even noticed the rockets launching upside down because a cylinder had no top and they couldn't see the windows from the ground.

 

[Urwumpe]

I was talking about that other guys quote from nasa talking about balancing the shuttle on a pencil. although i can't really imagine the shuttles engines can be in their current configuration and not do the launch heads-down unless the crew seats were made to hang upside down while landing.

No, sorry, but you still don't understand it. The balancing of a pencil on your fingertip analogy of a rocket launch comes from the fact that the center of gravity is in front of the engines, and the rocket is really kept balanced by gimballing the engines behind the CoG.

The SSMEs are mere 6% of the total thrust during lift-off and the first 50 seconds of flight. later they become more dominant, until they are producing a tiny bit more thrust than the nearly burned out SRBs.

The Shuttle does not rotate, if the engines produce no torque in their sum. The torque is just the cross product of the position of the engines relative to the CoG and the force vector. Notice something? There is absolutely no dependence on HOW you rotate the Shuttle in space or where up is.

The other torques acting on the shuttle are gravity gradient and aerodynamics. Gravity gradient depends on where the Shuttle is, but is a very weak force. Aerodynamics produce way more powerful torques, but depend only on the orientation of the shuttle relative to the air flow.

By pure mechanics, you can't explain the rotation heads down.

The things change if you for example look at the RTLS maneuver. After the Powered-Pitch-Around maneuver (PPA), the Shuttle would fly heads down and would require a turn around, if you would launch normally heads up. Pretty bad to do, since a RTLS is for example called for a engine failure early in flight. So, launching already heads down is better, since during these stressful moments, the orbiter will directly be in the right orientation for separating at low altitude from the ET. For a TAL or AOA, it doesn't matter if the ET is above the Shuttle, since you have all the air below you.

 

[statickid]

:thumbup: