Delta IV launch question

[ka9q]

I also noticed those fine lines pulling away at liftoff. I can't imagine they were any kind of propellant lines, as that's what the gantry arms are for. They don't detach until liftoff.

All I can think of is that they pulled away some sort of protective insulation or cover at liftoff. The early versions of the Ariane launcher dropped a layer of insulation around their second stages at liftoff. The second stage burned hypergolic (storable) propellants, but they were cooled to cram more into the tanks in the tropical French Guiana heat. I always thought it was bad form for your launcher to drop bits of itself onto the pad at liftoff.

The tip of the Q-ball at the top of the Apollo stack also had a protective cover, but I think it was pulled away by a line a few minutes before launch.

And yeah, that hydrogen fireball around the base of the Delta IV has always bothered me. The engines are started with a fuel lead, and the excess hydrogen burns in air as it rises. In previous launches it actually scorched the insulation on the three sections. To minimize that effect, the three engines were stagger-started on the Orion launch for the first time and it seems to have worked; I noticed very little if any scorching of the insulation this time.

[gwiz]

The first time I noticed such a thing was the maiden launch of the Titan 3 in 1965.  This famously had a camera that took a series of pictures looking down the length of the rocket and documenting the jettison of the solid boosters.  The line appeared to lead to the position that this camera had to be in and I would guess that it switched the camera on as the vehicle left the pad.

[Sus_pilot]

The first time I noticed such a thing was the maiden launch of the Titan 3 in 1965.  This famously had a camera that took a series of pictures looking down the length of the rocket and documenting the jettison of the solid boosters.  The line appeared to lead to the position that this camera had to be in and I would guess that it switched the camera on as the vehicle left the pad.

Link, please?  Thanks.

[Bob B.]

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.

The SSME used regenerative cooling.  The reason the RS-68 uses ablative cooling is cost reduction.  The trade off for lower cost was higher mass.  The RS-68 has a thrust-to-weight ratio of 51:1 while the SSME is 67:1 (based on vacuum thrust).
 

[gwiz]

Link, please?  Thanks.

The line is visible about 15 to 20 s into this video:

I can't find any on-line pictures from the camera, but they were in the press at the time and also in this article:
http://adsabs.harvard.edu/abs/1993JBIS...46..122R

[JayUtah]

It's a gazillion times cheaper to build an ablatively-cooled or radiatively-cooled nozzle than a regeneratively-cooled one.  Regeneratively-cooled thrust assemblies are monumentally difficult, monumentally expensive, and have a high rejection rate during manufacturing.

[JayUtah]

Okay, I finally got a good look at them and I think they're almost certainly safing lanyards.  Signals and power go through the hardpoint umbilicals -- the big ones that get pulled away by mechanical arms and are properly deadfaced at liftoff.  But certain range safety and ordnance systems require either 2- or 3-factor inhibitors for safety reasons (depending on the consequences of premature activation).  Looking at where the lanyards attach to the vehicle, I'm thinking at least half of them are range-safety destruct inhibitors.  After the rocket has climbed high enough, they pull loose and operate by severing breakwire inhibitors as one of the safing factors.  That's confirmation to the simple-as-dirt range safety systems that the rocket is moving and has climbed high enough to allow a commanded destruction.

One of the lanyards goes to the middle of the second stage, where the instrument unit is on this vehicle.  That would an additional breakwire trip that confirms vehicle motion to the guidance system.  Basically you program the rocket to expect a breakwire event within a few seconds after commencing the launch.  That would be the second confirmation factor of vehicle motion, whereas IMU reports would be the first.  It can also be a dirt-simple confirmation of vehicle altitude to allow pitch and yaw manuevers that would otherwise be restricted when the vehicle is near the umbilical tower.

Incidentally I went over the flight dynamics specifically for the Delta IV H and was reminded that because of its unique profile it rolls in order present its most drag-insensitive aspect to the wind.  This minimizes wind dispersion which, frankly, isn't that much of an issue for smaller vehicles.  It fixes wind dispersions after staging and consequently after wind is no longer a factor.

[ka9q]

So what about antennas? If the vehicle has to roll to minimize wind forces, which vary unpredictably with the weather, it would need extra antennas to communicate regardless of the roll.

I know several range safety antennas and receivers are always arrayed around the vehicle to ensure a rock-crushing signal regardless of attitude, but I don't know about telemetry transmitters, radar transponders, TDRSS terminals, TV transmitting antennas, etc.

You're right about those range safety systems being as simple as dirt. The commands consist of simple tone sequences, not much different from telephone Touch Tones. Last I heard, the frequency was somewhere around 410 MHz, with ground transmitters generating some tens of kilowatts -- there's no hiding them. (I'm told that listening for them was a good way to tell when a secret launch was coming up, before they lightened up and began to announce them a few hours before the event.) The range safety received signal strengths are telemetered to the ground, and anything less than full-scale at any time on any receiver is considered cause for concern.

[ka9q]

I wonder what the range safety profile is for the Delta IV. The Saturn V had a rather complicated one that inhibited engine shutdown for the first 30 seconds so that the vehicle would not fall back on the pad. I'm not sure how this would have worked given that a single engine failure at liftoff left a total remaining thrust less than the vehicle weight. But the S-IC gobbles its propellants pretty quickly, so it probably didn't take long for this particular vulnerability to go away.

They seemed as concerned about engine gimbal hardovers as premature shutdown, and some of the failure scenarios looked pretty bad no matter what you did. Still, they took some precautions such as canting the four outboard engines slightly outward. This was said to make it easier in case of an engine hardover, but I'm not sure how.

[JayUtah]

So what about antennas?

Patches around the circumference.  It's literally impossible for there not to be a range-safety antenna available.

but I don't know about telemetry transmitters, radar transponders, TDRSS terminals, TV transmitting antennas, etc.

The Delta guidance system and ground-support has a real-time ongoing telemetry margin monitor.  If you invade the link margin, that becomes a guidance input.  Naturally it's prioritized among wind and ordinary trajectory management, but Boeing really thought this through.  That's why it was a pleasure to work with both their launch-vehicle team and their spacecraft engineering team.

Last I heard, the frequency was somewhere around 410 MHz, with ground transmitters generating some tens of kilowatts -- there's no hiding them.

ULA has put practically everything in the C- and S-bands these days, and there's an ongoing effort to uniformalize with the Atlas.  Within then next 10 years they will fly the same guidance software and the same telemetry and up-/downlink systems.

[JayUtah]

I wonder what the range safety profile is for the Delta IV.

Very hard to find these days.  I had to go back to my old Boeing documentation for Delta II and III to get the designs for ordnance safeties, and I can't find any detailed information online.  The Delta IV User Guide describes the range safety procedures at a very high level, but that material is aimed at payload designers and doesn't really go into detail about launch vehicle design policies.

They seemed as concerned about engine gimbal hardovers as premature shutdown, and some of the failure scenarios looked pretty bad no matter what you did.

Bending moments for launch vehicles are heinous and unforgiving.  You don't hardover an engine on a large launch vehicle unless several important people are going to die otherwise.

Still, they took some precautions such as canting the four outboard engines slightly outward. This was said to make it easier in case of an engine hardover, but I'm not sure how.

The ratio of hardovered engine to the opposing moment in the same plane would be reduced.  But I agree with you; it still seems puzzling.

[ka9q]

But doesn't the Air Force dictate the range safety requirements, and aren't they more than a little conservative when it comes to technology?

I've heard people complain about the ancient design and high cost of these receivers, but given the consequences of their not working when required I can sort of understand the Air Force's concern. The US has a perfect record of protecting uninvolved persons and private property on the ground. Several other spacefaring countries can't make this claim.

[JayUtah]

But doesn't the Air Force dictate the range safety requirements...

Yes.  But a fair amount of that isn't static.

...and aren't they more than a little conservative when it comes to technology?

Yes.  And for every iota of effort toward, "The vehicle must explode completely when told to," there are two iotas of, "Ordnance on your rocket may not explode prematurely or pose a hazard to integration and ground crews."

Both of those imperatives practically dictate a dirt-simple method of handling ordnance, both on the ground and in flight.  So yes, three-factor safety where one of the factors is a physical pin pulled by a physical lanyard when the vehicle clears the tower is not at all out of keeping with the Air Force philosophy.

Some of the components we build for rocketry do indeed achieve or exceed "five nines" of reliability.  We do not lightly set aside those designs, no matter who archaic or simplistic they may seem to the layman.

[Kiwi]

...a physical pin pulled by a physical lanyard when the vehicle clears the tower...

Whenever there's a question like, "How can we best get these two things working together?" there's a certain nobility and excellence in the best answer being, "Piece of string."

[BazBear]

But doesn't the Air Force dictate the range safety requirements, and aren't they more than a little conservative when it comes to technology?

I've heard people complain about the ancient design and high cost of these receivers, but given the consequences of their not working when required I can sort of understand the Air Force's concern. The US has a perfect record of protecting uninvolved persons and private property on the ground. Several other spacefaring countries can't make this claim.

I'm not so sure about the private property part. On Jan. 17 1997 a Delta II carrying a GPS satellite "auto destructed" 13 seconds into flight after a SRB casing failed. Debris fell on a parking lot near the blockhouse complex, and damaged or destroyed 20 cars parked there. https://en.wikipedia.org/wiki/GPS_IIR-1#Debris