Launch News SpaceX Falcon 9 F3 COTS2+ Updates

[Screamer7]

Why is the second stage Merlin engine glow red hot?
Is it not supposed to be cooled with propellant, and if not what prevent the nozzle metal from melting.
I did a search, but can't get any info about the second stage engine cooling.
All I get is that the first stage engines are regeneratively cooled.
As they are the same engines as used in the second stage, what is the difference?

 

[Urwumpe]

Why is the second stage Merlin engine glow red hot?
Is it not supposed to be cooled with propellant, and if not what prevent the nozzle metal from melting.
I did a search, but can't get any info about the second stage engine cooling.
All I get is that the first stage engines are regeneratively cooled.
As they are the same engines as used in the second stage, what is the difference?

It is made of Niobium*, a metal that does not get soft at relatively high temperatures. The Apollo Service Module Propulsion System nozzle was also made of it. It is NOT cooled by propellant at all, but by permitting it to radiate heat away. The bright red glow means that every square meter of nozzle surface is radiating over 30 Kilowatts of heat into space at 730°C. The inside of the nozzle is possibly film cooled, but I don't know it with certainty.



Note that even steel can be red glowing in the visible light spectrum without melting, for example the exhaust manifolds of a better car engine.

* Actually, they use a Niobium-Titanium alloy for such applications, which is much more elastic than the relatively brittle Niobium itself.

 

[Notebook]

Yup- the MVac gas generator exhaust is used for roll control of the second stage.

I assume there is another exhaust 180 degrees away for symmetry? Also, the nozzle aways seemed to move to the left of picture, did I miss some movement?

N.

 

[C3PO]

I assume there is another exhaust 180 degrees away for symmetry? Also, the nozzle aways seemed to move to the left of picture, did I miss some movement?

Negatory. There's only one gas-generator nozzle.

When the engine is running it produces a small amount of torque.

Wikipedia provides a good overview of the Merlin models.
http://en.wikipedia.org/wiki/Merlin_(rocket_engine)

 

[Screamer7]

Thanks Urwumpe.
Now I understand it better.
Johan

 

[Codz]

! I missed the launch!

Hopefully I won't be in school during docking.

I just barely caught it with about an hour to spare.

 

[orb]

SPACE.com:

• SpaceX's Commercial Spaceship Chasing Space Station in Orbit
  
  
• SpaceX Launch Success 'Like Winning Super Bowl,' Billionaire CEO Elon Musk Says

Spaceflight Now: Falcon 9 rocket roars to space (PHOTO GALLERY)

Universe Today: SpaceX Dragon Spies Earth

Florida Today: SpaceX's Dragon capsule doing well after day in orbit

 

[Codz]

I saw a pass of it this morning in the night sky.

 

[Cosmic Penguin]

! I missed the launch!

Hopefully I won't be in school during docking.

Unfortunately the docking is current scheduled at around 11 am CDT on Friday.

Sick-leave?

 

[Notebook]

Negatory. There's only one gas-generator nozzle.

When the engine is running it produces a small amount of torque.

Wikipedia provides a good overview of the Merlin models.
http://en.wikipedia.org/wiki/Merlin_(rocket_engine)

Bit confused now looked at the diagrams, how does the engine produce torque?

N.

 

[C3PO]

Bit confused now looked at the diagrams, how does the engine produce torque?

My guess would be that the exhaust gasses do not travel in a perfectly straight line.

The first Dragon launch had a larger than expected roll on liftoff.

 

[Notebook]

Well, if the first stage leaves the second with no roll? And the second has to leave the Dragon with no roll? I'm guessing these are parameters?

I haven't looked at any of the control systems for these stages, does the Dragon have attitude control as it leaves the second stage?

Edit: To C3PO above, as I understand it a torque is always around an axis, if the engine(main engine) is not on that axis, it will give a moment, or couple?

N.

 

[Urwumpe]

My guess would be that the exhaust gasses do not travel in a perfectly straight line.

The first Dragon launch had a larger than expected roll on liftoff.

Another option would be installing the main combustion chamber a few millimeters off the center line. it is then simple levers and high school physics.

[math]\vec{d}_1 \times \vec{F}_1 + \vec{d}_2 \times \vec{F}_2 = \vec{0} [/math]

 

[NovaSilisko]

The little exhaust nozzle on the upper stage engine gimbals to control roll.

 

[C3PO]

Another option would be installing the main combustion chamber a few millimeters off the center line. it is then simple levers and high school physics.

[math]\vec{d}_1 \times \vec{F}_1 + \vec{d}_2 \times \vec{F}_2 = \vec{0} [/math]

That will produce pitch and yaw (or [math]\alpha[/math] and [math]\beta[/math]) in a single engine setup.

But if the flow through the exhaust nozzle isn't 100% laminar the sum force can produce a small roll torque. The force is tiny compared to the thrust, and the roll nozzle only needs to make small corrections to compensate. I believe that's what Notebook was asking about.

 

[Notebook]

Indeed it is, I can see if the rocket exhaust has a "twist" to it, then torque could be produced, bit like rifling in a... rifle..

I'll have bit of research and see what turns up.

Edit:

got this

Staging and second stage engine start - the first in-space start of a Merlin engine - appeared nominal, but a roll developed during the five minute long burn of the second stage Merlin Vacuum engine. It was not clear if the roll had any effect on velocity performance. The roll began about 5 minutes after liftoff, after the turbopump exhaust nozzle stopped vectoring. Merlin shut down about 517 to 524 seconds after liftoff, just as the stage completed its fourth roll. The stage was rolling about three times per minute at second stage engine cutoff.

from here:
http://www.spacelaunchreport.com/falcon9.html#components

Implying the roll control wasn't?

Edit: that was from the Inaugural Launch(updated June9,2010)


N.

 

[IronRain]

Spaceflight Now:

After a succession of rocket burns to fine-tune its pursuit of the International Space Station, the commercial Dragon spacecraft is due for a flyby of the complex Thursday, a crucial prerequisite for the ship's arrival at the outpost Friday.

Live coverage should start in 9 minutes (6:30 UTC).

 

[IronRain]

Elon Musk tweeted:

SpaceX chief Elon Musk just tweeted: "About 110 miles away and the spacecraft is now in direct communication with the space station."

 

[Urwumpe]

That will produce pitch and yaw (or [math]\alpha[/math] and [math]\beta[/math]) in

But that isn't caused if you have two thrust sources that are balanced by the lever lengths.

You still need to gimbal the main engines to compensate thrust inbalances (eg, gas generator thrust dropping stronger than main combustion chamber thrust, or gas generator thrust vector is gimballed), but you have lower loads on the thrust structure and thus a lot of weight saved, since the main combustion chamber does not need to be gimballed all the time.

 

[Notebook]

Urwumpe, if I understand you correctly, are you saying the main engine and gas-generator exhaust(roll-control) are set apart such that their thrusts (and torques)nominally balance?

Not sure I've phrased that well

N.