Why is the Space Shuttle upside down during launch?

[statickid]

hahah yeah i get that, i was just pointing out that the pencil analogy is about the CoG and not about gravity, and that the shuttle is designed to launch in the direction that it does according to reasons this thread has pointed out to be many and varying, hence, just because the pilots heads are facing the ground does not mean the vehicle is upside down and the only reason it looks upside down is because it has wings.

 

[Urwumpe]

Or because it drops a half-full external tank during an RTLS abort maneuver.

 

[markl316]

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.

To clarify, I assume you mean that each individual SSME is 6%, and the total thrust of the 3 SSMEs is 18%.

 

[cjp]

[LOLcatz image]

I know, I know, I should have said 'heads down', and not 'upside down'. Do you always make images like that to make your point clear?

I'll edit the initial post of the thread to fix this.

 

[Urwumpe]

To clarify, I assume you mean that each individual SSME is 6%, and the total thrust of the 3 SSMEs is 18%.

No, really 6% - 94% of the liftoff thrust (including atmospheric pressure effects) is by the SRBs.

 

[statickid]

To clarify, I assume you mean that each individual SSME is 6%, and the total thrust of the 3 SSMEs is 18%.

Solid Rocket Boosters
Two Solid Rocket Boosters (SRBs) each provide 2.8 million lbs of thrust at liftoff, which is 83 percent of the total thrust needed for liftoff. They are jettisoned two minutes after launch at a height of about 150,000 feet (45.7 km), then deploy parachutes and land in the ocean to be recovered. The SRB cases are made of steel about ½ inch (1.27 cm) thick.

http://www.newworldencyclopedia.org/entry/Space_Shuttle

hmm looks like markl316 might be right... I got curious and found this number in several places but here is one example

---------- Post added at 11:32 AM ---------- Previous post was at 11:28 AM ----------

hmm but that is written really confusing. "each provide 2.8 million lbs of thrust, which is 83% of total thrust needed" does that mean 2.8 million lbs of thrust is 83% of thrust needed? or does it mean 5.6 million lbs of thrust is needed? or does it mean that they provide 2.8 million together or each by itself? rrrrgh :blink:

 

[Urwumpe]

I think it means that they produce 83% of the thrust needed for just countering the gravity force.

http://www.astronautix.com/lvs/shuttle.htm

One SSME has 3,167.400 kN at sealevel.
One SRB is 10,149.400 kN at sealevel

Makes the SRBs producing only 68% of the total lift-off thrust. Still not the 94% that I heard in comparison of Shuttle stack and Energia.

 

[statickid]

got it:

srbs:2.8mil X 2 = 5.6mil
ssmes: .3938mil X 3 = 1.1814mil

5.6+1.18=6.78

which matches this other thing:

Total liftoff thrust: 30.16 MN (6,780,000 lbf)

REF:

Solid Rocket Booster specifications

Length: 45.46 m (149 ft)[34]
Diameter: 3.71 m (12.2 ft)[34]
Empty weight (per booster): 68,000 kg (150,000 lb)[34]
Gross liftoff weight (per booster): 571,000 kg (1,260,000 lb)[35]
Thrust (at liftoff, sea level): 12.5 MN (2,800,000 lbf)[19]

System Stack specifications

Height: 56 m (180 ft)
Gross liftoff weight: 2,000,000 kg (4,400,000 lb)
Total liftoff thrust: 30.16 MN (6,780,000 lbf)

 

[Urwumpe]

ah damn, took the plug-nozzle SSME data, not the sealevel thrust of the flown SSME....

3 x 1,817.400 kN + 2 * 10,149 kN = 25.75 MN.


78 % of the total liftoff thrust.

 

[David413]

Or because it drops a half-full external tank during an RTLS abort maneuver.

Better check again; the ET is almost empty when attempting a RTLS, not half-full.

 

[Urwumpe]

Better check again; the ET is almost empty when attempting a RTLS, not half-full.

As far as I remember, it is still at the top limit for safe separation, which is why the alpha recovery is needed, which counts as half-full for me (as in "pretty much fuel inside")

 

[David413]

As far as I remember, it is still at the top limit for safe separation, which is why the alpha recovery is needed, which counts as half-full for me (as in "pretty much fuel inside")

No, I'm afraid not...

After RTLS is selected, the vehicle continues downrange to dissipate excess main propulsion system propellant. The goal is to leave only enough main propulsion system propellant to be able to turn the vehicle around, fly back towards the Kennedy Space Center and achieve the proper main engine cutoff conditions so the vehicle can glide to the Kennedy Space Center after external tank separation. During the downrange phase, a pitch-around maneuver is initiated (the time depends in part on the time of a space shuttle main engine failure) to orient the orbiter/external tank configuration to a heads up attitude, pointing toward the launch site. At this time, the vehicle is still moving away from the launch site, but the space shuttle main engines are now thrusting to null the downrange velocity. In addition, excess orbital maneuvering system and reaction control system propellants are dumped by continuous orbital maneuvering system and reaction control system engine thrustings to improve the orbiter weight and center of gravity for the glide phase and landing.
The vehicle will reach the desired main engine cutoff point with less than 2 percent excess propellant remaining in the external tank. At main engine cutoff minus 20 seconds, a pitch-down maneuver (called powered pitch-down) takes the mated vehicle to the required external tank separation attitude and pitch rate. After main engine cutoff has been commanded, the external tank separation sequence begins, including a reaction control system translation that ensures that the orbiter does not recontact the external tank and that the orbiter has achieved the necessary pitch attitude to begin the glide phase of the RTLS.

From the RTLS workbook. (Emphasis mine).

Having flown more than one RTLS in the SMS, believe me, the tank is almost empty.

 

[statickid]

i'm gonna try and fudge that in orbiter. looks stressful

 

[Urwumpe]

Ok, I would have said 3%, based on testing RTLS flights in SSU and the manual RTLS charts.

2% fuel level is still a lot though (14.5 tons, 53% of the ET dry mass), most nominal MECOs are at less than one percent.

---------- Post added at 12:46 AM ---------- Previous post was at 12:45 AM ----------

i'm gonna try and fudge that in orbiter. looks stressful

Download one of the ascent checklists, it contains pages with hints for manually flying a RTLS.

 

[statickid]

oh thanks for the tip!

....on second thought...

may i inquire what specific ascent checklists you are referring to? are they on O-H?

 

[tblaxland]

may i inquire what specific ascent checklists you are referring to? are they on O-H?

Hours of goodness here: http://www.nasa.gov/centers/johnson/news/flightdatafiles/index.html

 

[Andy44]

I've done an RTLS a few times in Orbiter. Hard, but so much fun. It feels like you're doing an unrealistic sim stunt, hard to believe this could actually happen.