Delta IV launch question

[scooter]

Enjoyed watching the Delta IV/Orion launch, and have a question. or 2...

The craft makes a very slow 90 degree roll during the climb...is there any particular reason for this?
Also, as it leaves the pad, I noticed a LOT of small wires/lines being broken/pulled out as it climbed past the gantry...telemetry/data lines or something?
It was also interesting being able to visually see the throttling of the center engine vs the outboards...great show, and hopefully the beginning of a strong (funded) program.

[Peter B]

Enjoyed watching the Delta IV/Orion launch...

Same here.

...and have a question. or 2...

The craft makes a very slow 90 degree roll during the climb...is there any particular reason for this?

I'm not sure, but I assume it's the rocket rolling from its launch facing to the direction it needs to face to climb to its orbit, given its orbital inclination. Presumably the rocket was aligned N-S or E-W on the launch pad, while its orbit headed off to the south-east. For both Apollo and the Space Shuttle (and I assume Mercury and Gemini) the spacecraft climbed to orbit with the astronauts in a head-down position. That way the astronauts could see the horizon when looking out the window, and it presumably helped blood flow to the head rather than away from it.

Also, as it leaves the pad, I noticed a LOT of small wires/lines being broken/pulled out as it climbed past the gantry...telemetry/data lines or something?

Some of the lines would have been fuel lines, topping up the cryogenic propellants as they boiled off prior to launch. Other lines would have been providing power from the ground, so that if the launch was aborted Mission Control could control the spacecraft.

However, in each of these cases I'm happy for the experts to correct or add to my answer.

It was also interesting being able to visually see the throttling of the center engine vs the outboards...

Yes, I noticed that too, although I wasn't sure whether that was actually what I was seeing.

...great show, and hopefully the beginning of a strong (funded) program.

Agreed.

I have to say I'm ambivalent about the whole thing - what can Orion do that Dragon and the Boeing spacecraft can't? (Apart from keeping a lot of NASA engineers happily employed...?) And I've read a fair bit of criticism of the Space Launch System, although I'll watch it launch as avidly as any Saturn V, Shuttle, Falcon Heavy or Delta IV Heavy launch!

[Echnaton]

For ease of operation, the Saturn V and shuttle had fixed axis labels and always launched with the same orientation to the ground.  So to generalize a bit speculatively, I'd guess that the same thing is true here.  Since the launch direction of any rocket is set to make a specific orbit for the mission needs, there is no one orientation on the pad that will get it into the proper orbit for all missions.  So you need a roll program.  So why not just build the pad in the most efficient configuration for the pad and let the rocket take care of the flight orientation with the roll program. 

[Bob B.]

Adding to what other have said...  The reason the rocket must roll to its intended flight heading before pitching down is to get the pitch and yaw axes properly aligned.  We want the pitch axis to be parallel to the ground and perpendicular to the heading the rocket will fly.  This way when the rocket transitions to horizontal flight it is rotating strictly in pitch, which simplifies the control.

For example, let's say a rocket sits on the launch pad with its pitch axis aligned north-south and its yaw axis aligned east-west.  We want the rocket to fly southeast along a heading of 135 degrees.  After the rocket lifts off we must rotate it 45 degrees to the south (clockwise looking down on it).  This  aligns the rocket so that when we tilt the nose down it is rotating around the pitch axis.  If we didn't execute the roll, bringing the nose down would require movements in both pitch and yaw, which is way more complicated than it needs to be.

[smartcooky]

Every STS launch I have seen had an obvious roll program. Here's a fine example; roll at 1:48 in the video

[Glom]

This of course raises the question of what governs how a space vehicle is oriented on the pad.

[Allan F]

This of course raises the question of what governs how a space vehicle is oriented on the pad.

The pad, mostly.

[Echnaton]

The reason the rocket must roll to its intended flight heading before pitching down is to get the pitch and yaw axes properly aligned.

With the symmetric thrust of the Saturn V, I would guess the axes could be arbitrarily defined, although would be very practical reasons for the specific orientation that was used.  With a side staged rocket like the Delta IV would this make difference?

[Echnaton]

The question I have about the Delta IV is why is the steam exhaust so bright?  The STS main engine exhaust always seemed almost non-existent, aside from the shock diamonds. Was that only by comparison to the very bright exhaust of the solid boosters or is there something in the hydrogen fueled engines that makes them different?

[JayUtah]

It's a zillion times easier to write the guidance programs when there are designated pitch and yaw axes and roll is constrained -- even with symmetrical vehicles.

The civil engineering of the pad and launch site dictates where the hardpoints go, and that dictates the orientation of the vehicle on the pad.  It is impossible to build a pad that doesn't require some roll at launch, since launch azimuths vary from mission to mission, and within the launch window for each individual mission.  Hence launch vehicle orientation is not a consideration when siting launch facility structures.

Von Braun programmed a roll into each of his vehicles' launches specifically to exercise all the flight controls within a few seconds of liftoff, as a safety check.  Pitch and yaw are exercised anyway as part of structure avoidance maneuvers and regular guidance.

Launch Complex 39 oriented the STS stack so that the vertical stabilizer points south.  This was mostly a holdover from Apollo, but it had to do with the way the causeways were built on Merrit Island.  The causeways for the crawler-transporter end with a northbound route, and the orientation of the stack(s) on the MLP was dictated in large part by orienting the most stable of pitch or yaw axes for ground transportation.

The engineering of umbilicals and their associated disconnection strategies is a field unto itself.

[Bob B.]

The question I have about the Delta IV is why is the steam exhaust so bright?  The STS main engine exhaust always seemed almost non-existent, aside from the shock diamonds. Was that only by comparison to the very bright exhaust of the solid boosters or is there something in the hydrogen fueled engines that makes them different?

The RS-68 engines of the Delta IV are ablatively cooled, so maybe that's the reason.  The ablative lining burns away during operation to keep the nozzle cool.  Perhaps it's this material in the exhaust that gives it a different appearance.

[scooter]

Good discussion...

I'm familiar with the "azimuth roll" shortly after launch, but what I noticed in the following minutes is a roughly 90 degree roll that takes the booster from a horizontal alignment (strap on boosters on "either side") to a vertical alignment (with the strap ons above and below the core). Very slow, takes a couple/few minutes, but it's just something interesting I noticed.

I'm familiar with all the propellant feed disconnects pulling away at launch, but there were a lot of smaller "wires", very small, maybe attached further down...perhaps small telemetry feeds or something. Perhaps it's a Delta thing, just never noticed them on other launches.

Boy, that fireball on launch sure is attention getting!!

[gwiz]

The civil engineering of the pad and launch site dictates where the hardpoints go, and that dictates the orientation of the vehicle on the pad.  It is impossible to build a pad that doesn't require some roll at launch, since launch azimuths vary from mission to mission, and within the launch window for each individual mission.  Hence launch vehicle orientation is not a consideration when siting launch facility structures.

The Scout launch vehicle used a rotatable launch pad to set the azimuth, but this was a much smaller vehicle that those we've been discussing.

[ka9q]

When a modern launcher performs a roll after liftoff, it is almost always to point its various antennas in the correct directions.

Launcher antennas include those for the range safety (destruct) receivers, various radar transponders, telemetry transmitters and often a TDRSS antenna. I think this last one accounts for most of the roll maneuvers on US launches as there still aren't that many TDRSS satellites and you usually want to remain on one for as long as you can, at least during critical mission events, to avoid the interruption that occurs when handing off from one satellite to the next.

It's not just a matter of where the antennas are mounted; sometimes plume obstruction is an issue too.

The shuttle used to remain heads-down for its entire ride into orbit, but later missions often rolled into a heads-up position specifically for better TDRSS coverage.

Range safety reception usually isn't a serious constraint as there are multiple antennas (and receivers) arrayed around the vehicle specifically so the destruct command will be reliably received no matter what the rocket happens to be doing.

[ka9q]

I tried to start a thread specifically on the question of the appearance of the Delta IV's plume, but I couldn't find the new topic button. I've since seen LO's note about accidentally disabling it.

I thought to bring it up not only for my own curiosity, but because I expect the hoaxers will eventually seize on it as "proof" the LM ascent plumes should also have been visible.

An ablative nozzle lining occurred to me too, especially since the onboard camera shows quite a few 'sparks' being thrown off. But that orange color is also the color of hydrogen burning in air, so I didn't want to jump to that conclusion. OTOH, all rocket engines run rich, including the LH₂-burning SSMEs, but I never saw them produce orange plumes. As reusable engines, I don't think they used ablative coatings.