Atlas 5/ASTRA 1KR Launch, Atlas 5/ASTRA 1KR Launch Options

[hal_9000]

Atlas 5/ASTRA 1KR Launch

http://video.google.com/videoplay?docid=-6201184353787535479

[BPCooper]

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And here are the photos I got for SFN:

http://www.launchphotography.com/ASTRA_1KR.html

It was a nice launch, but certainly unique with that one SRB!

[Bob Shaw]

Ben:

Bloody 'ell! Unique isn't the word for it - it looks about as sensible as a three-legged dog trying to pee against a lamp-post! And it worked? Wow!

Seriously, imagine the mechanical stresses, or the way the main engine myst have had to gimball from even before liftoff, or the trouble they'd have had if it hadn't, or... ...I'm amazed they got insurance (or maybe they just charged the ASTRA folk a bit less for the fun of (potentially) launching the record-breaking pinwheel!).

Bob Shaw

[ugordan]

Seriously, imagine the mechanical stresses, or the way the main engine myst have had to gimball from even before liftoff, or the trouble they'd have had if it hadn't

Actually, this wasn't all that remarkable from the steering point of view. The SRB boosters are set up so their thrust passes through the center of mass of the entire vehicle. This way, the SRB booster imparts no rolling/tumbling torques, only a slight sideways movement of the rocket. In terms of RD-180 gimbals, they probably had much more control authority here than for example the New Horizons 5 SRB configuration since here the RD-180 had a greater fraction of the total thrust.

Ben, as usual, your photos are outstanding, leaving me only to wish you provided some higher resolution views to marvel at!

[BPCooper]

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Thanks!

They said the RD-180 only had to steer half a degree off to account for the SRB (out of eight degrees it could swivel maximum). Pretty good, as always for Atlas.

[Guest_Analyst_*]

About 20% of the shuttle's trust at lift off is not aligned with it's roll axis, actually the intire stack swings about 0.5m at the top of the ET after SSME ignition. The SRBs fire after 6.6 seconds when the stack is back in it's vertical (initial) position.
Cassini's main engines are off axis too, because there are two and only one is used at a time (the other is a backup). And AV-010 (New Horizons) had two SRBs on one side and three at the other. So off axis trust is not this unusual as it seems.

Great pictures, btw.
Analyst

[ugordan]

So off axis trust is not this unusual as it seems.

By that definition any rocket that has more than one engine chamber is necessarily off-axis aligned. There's really nothing weird and unconventional about it. In fact, if you could be sure that each engine will produce exactly the same amount of thrust, you wouldn't even needto align their thrust vectors through the center-of-mass, merely being parallel to the axis would suffice. Of course, in the real world this is not possible so they are aligned through CoM with the final result being a much stabler vehicle while only losing a few percent of the total useful thrust.
Using only one SRB might seem counter-intuitive, but it really isn't much different than for example using two SRBs on the space shuttle.

[Bob Shaw]

OK guys, point made - but it *still* looks like that three-limbed canine!

Bob Shaw

[djellison]

What's more odd is the post SRB-sep dogleg. You get that with West coast launches a lot, and sometimes it's visible with East Coast launches, but I dont remember seing such an obvious dog leg as that.

A lot of Delta II onboard vids, if you play them at 4x speed, you can see a big of a dogleg

Doug

[ugordan]

What's more odd is the post SRB-sep dogleg. You get that with West coast launches a lot, and sometimes it's visible with East Coast launches, but I dont remember seing such an obvious dog leg as that.

In case of New Horizons the vehicle appeared to level-off after SRB sep, as if it was only trying to gain altitude in the first phase, but in this case it was obvious as a sharp right turn. That doesn't strike me as being an optimal flight path at all. As you said, some Delta IIs also exhibited this, notably the Mars Odyssey vehicle.

The only logical reason I can come up with has to do with aerodynamic forces as the Earth rotates and the atmosphere with it, the whole thing already moves at several hundred m/s eastward, which might not be the desired flight path. So a compromise is made that during the early ascent the vehicle doesn't "slide sideways" through the atmosphere as that might rip it apart. Once the vehicle enters stratosphere it can take the optimal path from thereon.
Then again, I might be talking rubbish here... During the NH launch the telemetry engineer said "vehicle steering has been enabled, right on time" which might simpy mean a different guidance algorithm takes over?

[djellison]

I think it's to do with range geometry - someone may be able to correct me

Doug

[tty]

I think it is mostly aerodynamic. A rocket is really rather fragile and it is best to get up and out of the densest part of the atmosphere while still moving fairly slowly. In a normal launch the maximum dynamic pressure (Max Q) is reached at about Mach 2 and 50,000 feet.
Also air resistance (and frictional heating) increases very quickly with speed, so from this point of view too it's best to gain altitude first and speed afterwards. Since you need to gain a fixed amount of both speed and altitude to reach a given orbit it does not really matter that much efficiency-wise. The main drawback is that a dog-leg trajectory takes slightly longer to reach orbital speed which in principle costs 10 ms-1 for each extra second.

tty

[Jim from NSF.com]

It is for SRM disposal Also it was more of a pitch than yaw.