Falcon 9 launch video

[AstroSmurf]

As seen on APOD, the maiden launch of Falcon 9 took off last week. Good work by SpaceX, and one step closer to a privately run space industry.

antwrp.gsfc.nasa.gov/apod/ap100608.html

What interests me are the dark transient streaks when the second stage engine is burning. Are those normal? As I understood it, the flow is supposed to be completely smooth once you leave atmospheric turbulence behind.

This may not be the right place for this issue, but at least it's marginally Apollo-related.

[PhantomWolf]

All hail the Huge Mutent Insect Overlords that appear about 7 secs in.

[banjomd]

Jun 9, 2010 3:37:18 GMT -4 PhantomWolf said:

All hail the Huge Mutent Insect Overlords that appear about 7 secs in.

Is that one of Florida's famous "Palmetto bugs" ;D
The dropouts and buffer problems make me realize how good NASA's video is.

[AstroSmurf]

The weird thing is that this is a youtube mirror of a video published somewhere else. The buffering was a problem with the original playback. You'd think whoever posted it could have tried until s/he got a good playback.

Not to mention, how come APOD didn't link to the original site?

[banjomd]

I watched the live video stream from SpaceX's website.
When I watched replays from other sites the video problems seemed to be the same (eg. @ staging) making me think that the problems were at the source.

[George Tirebiter]

Jun 8, 2010 20:14:07 GMT -4 AstroSmurf said:

What interests me are the dark transient streaks when the second stage engine is burning. Are those normal? As I understood it, the flow is supposed to be completely smooth once you leave atmospheric turbulence behind.

Yeah, that's perfectly normal. You can also see it in the first stage of the Delta II (and, I would suspect, other LOX/kerosene rockets) once it gets above most of the atmosphere. I don't really know enough about engine design to want to speculate on a cause.

[ka9q]

Jun 8, 2010 20:14:07 GMT -4 AstroSmurf said:

What interests me are the dark transient streaks when the second stage engine is burning. Are those normal? As I understood it, the flow is supposed to be completely smooth once you leave atmospheric turbulence behind.

Yes, I see this kind of plume spreading and turbulent flow on pretty much every rocket engine outside the atmosphere, especially those burning kerosene (e.g., RP-1).

The black streaks are undoubtedly unburned carbon. Every chemical rocket I know burns a fuel-rich mixture to protect the combustion chamber and nozzle from oxidation and to decrease the average molecular weight of the exhaust (with unburned hydrogen) to increase specific impulse.

In the lower atmosphere, this unburned carbon burns on contact with the atmosphere, producing the familiar brilliant yellow-white plume.

As the launcher ascends and ambient air pressure drops, the plume expands and the carbon no longer burns.

Falcon is very unusual in using a kerosene-fueled second stage engine. In fact, I can't think of a single other western space launcher that does. Their upper stages all use either LH2 or hypergolic fuels that produce little (or no) residual carbon and transparent plumes that are nearly invisible even in the lower atmosphere.

This is still relevant to Apollo in serving as yet another illustration of why the LM lacked a visible plume. Here we see that, in a vacuum, even engines burning kerosene and LOX fail to produce the familiar bright glowing plumes that we see in the lower atmosphere.

[ka9q]

Anyone notice the accelerating counterclockwise roll of the second stage that starts halfway through its burn? I've never seen this on any other launcher. Launchers usually keep a precise roll angle as a function of time so the current ground tracking station can see its telemetry antennas.

Every launcher needs 3-axis control. Gimbaling can provide yaw and pitch control. It can also provide roll control on stages with multiple engines, such as the Space Shuttle and the first two stages of the Saturn V. A single engine stage like this one (and the S-IVB) requires auxiliary roll control thrusters. Here you can see a small roll control thruster in front of the main engine. Occasionally it deflects to one side.

So this roll is surprising. I've seen it in earlier Falcon launches, so maybe it's intentional and they have a reason for it.

[Bob B.]

Jun 13, 2010 8:09:14 GMT -4 @KIA9q said:

Here you can see a small roll control thruster in front of the main engine. Occasionally it deflects to one side.

I'm not sure what we have there. It definitely looks and acts like a roll control thruster, or more likely, a vernier engine; however, the Falcon 9 web page states that roll control of the second stage is achieved by actuating the turbine exhaust nozzle. This latter method is nothing new as it was also used on second stage of the Titan 2. I wonder if the web page description was superseded by the addition of a pair verniers.

[ka9q]

Then maybe what looks like a roll control thruster is actually the turbine exhaust. If you want thrust, you might as well shape it like a classical convergent/divergent nozzle, right?

[Bob B.]

Jun 19, 2010 11:45:21 GMT -4 ka9q said:

Then maybe what looks like a roll control thruster is actually the turbine exhaust. If you want thrust, you might as well shape it like a classical convergent/divergent nozzle, right?

That could be, but it doesn't look like the picture in this webpage (about half way down the page).

[ka9q]

Jun 20, 2010 2:23:18 GMT -4 Bob B. said:

Jun 19, 2010 11:45:21 GMT -4 ka9q said:

Then maybe what looks like a roll control thruster is actually the turbine exhaust. If you want thrust, you might as well shape it like a classical convergent/divergent nozzle, right?

That could be, but it doesn't look like the picture in this webpage (about half way down the page).

That's a static firing, and it doesn't look like the turbopump exhaust is steerable. Maybe that's a first stage engine being tested, and the second stage model has some modifications, including a steerable nozzle on the turbopump exhaust?

[Bob B.]

Jul 2, 2010 20:44:45 GMT -4 ka9q said:

Jun 20, 2010 2:23:18 GMT -4 Bob B. said:

That could be, but it doesn't look like the picture in this webpage (about half way down the page).

That's a static firing, and it doesn't look like the turbopump exhaust is steerable. Maybe that's a first stage engine being tested, and the second stage model has some modifications, including a steerable nozzle on the turbopump exhaust?

It looks like I just stumbled across the answer to this question. According to Wikipedia, there are several variants of the Merlin engine in use as described below:

"Three versions of the Merlin 1C engine are in production. The Merlin engine for Falcon 1 has a movable turbo-pump exhaust assembly which is used to provide roll control by vectoring the exhaust. The Merlin engine for the Falcon 9 first stage is nearly identical to the variant used for the Falcon 1 except that the turbo-pump exhaust assembly is not movable. Finally, the Merlin vacuum is used on the Falcon 9 second stage. This engine differs from the Falcon 9 first stage variant in that it uses a larger exhaust nozzle optimized for vacuum operation and can be throttled between 60 and 100 percent."

Source: en.wikipedia.org/wiki/Merlin_(rocket_engine)

So it appears they must have added a pair of vernier engines (one of which we see in the Falcon 9 launch video) for roll control in place of the steerable turbopump exhaust used on Falcon 1.

[ka9q]

Thanks! Maybe the vernier engines give better roll (and attitude) control before the engine starts? As I recall, during at least one of the past Falcon 1 launches the nozzle extension of the second stage impacted the upper skirt of the first stage during separation. They scraped quite hard. If attitude control depended on vectoring the turbopump exhaust of the upper stage, that meant no attitude control until the upper stage was up and running. Hence the staging collision.

In general, attitude control of the upper stage in those earlier launches seemed poor. It wandered all over the place, compared to Delta-II footage that showed a rock-steady attitude during second stage burn with only very slow changes.

[JayUtah]

The skirt-nozzle contact on the Falcon 1 test flight was due to an excessive bending moment at staging, which in turn was caused by an improper angle of attack during first stage boost. The angle of attack parameter was set wrong in the flight control software. The fouled separation caused excessive sloshing in the upper stage propellants which exceeded the ability of the flight control system to correct.

Baffles in the upper stage tanks and improved quality control at launcher integration have solved those problems.