Atlas V Asymmetrical Boosters

[Bioman222]

I've been working on a New Horizons mission copy recently, and while researching the Atlas V I noticed its asymmetrical booster placement:

So here are my questions: Why is it set up like this? How does it work? Why not use a normal symmetrical placement?

[Kibble]

Atlas V core wasn't originally designed for boosters - the oxygen line and avionics package ended up getting in the way of SRM placement.

[SciMan]

Yeah but why do they have an option that uses only ONE SRM?

Sure looks funny, but I guess if the control systems can compensate for it it won't have any problems.

[Redjoker]

Yeah but why do they have an option that uses only ONE SRM?

Sure looks funny, but I guess if the control systems can compensate for it it won't have any problems.

It is likely because there are payloads that only need the additional thrust of one SRB. Why add another booster that will increase the cost of the rocket if the SRB nozzle is tilted and RD-180 can gimble enough to compensate for it.

[bs1110101]

What ever happened to the Atlas 5 heavy? And did they look into mixing Atlas 5 and and Delta 4 cores at all?

[Lime]

Yeah but why do they have an option that uses only ONE SRM?

Sure looks funny, but I guess if the control systems can compensate for it it won't have any problems.

The Atlas V 411 have 1 srb for a number of reasons. 1 it works 2. It gives it 3 tonnes of more payload. Fun fact an Atlas V 411 will launch Osiris-Rex next year.

[Hcube]

The single SRB configuration works in KSP, too ! you may need a little bit of effort to adjust the thrust and gimbals/tilt of the engines, though

EDIT : nice picture :

Edited July 15, 2015 by Hcube

[Budgie]

There are some great videos of Atlas V 411 launches where, once the rocket leaves the pad, it visibly translates horizontally as it goes up.

Here's one!:

[radonek]

Why add another booster that will increase the cost of the rocket if the SRB nozzle is tilted and RD-180 can gimble enough to compensate for it.

Aint that less efficient?

[Redjoker]

Aint that less efficient?

I probably could have phrased that better. If one SRB adds enough thrust, why add another booster that will increase the cost of the rocket if you can tilt the SRB's nozzle and gimbal the RD-180 so you are still thrusting through your center of mass. Doing it this way is probably less fuel efficient than adding a second booster, but the lower cost makes it a better option.

[shynung]

It's also for practical reasons.

Suppose that the extra thrust of only one booster is needed. If the manufacturer insists on using two boosters for stability, they'd have to manufacture half-length boosters.

[pincushionman]

It would probably be better all around if they instead used two boosters of roughly half the capability.

Thing is, there isn't a booster of half the capability that's compatible with the core, and it's probably not cost-effective to make one. The payloads that need one booster's worth of thrust may just be a niche market within the Atlas V's own niche market.

It'd be like "I'd like to use two BACC's here, but the only SRB that will fit on the rocket is the SRB-KD25k, so we're gonna have to get creative!"

[winged]

5char

Edited September 8, 2016 by winged

[shynung]

It'd be like "I'd like to use two BACC's here, but the only SRB that will fit on the rocket is the SRB-KD25k, so we're gonna have to get creative!"

Actually, it's more like "We need half-strength SRBs, but we can't change the thrust profile of the SRBs, and our factory cannot produce half-length SRBs without a significant upgrade. Let's stick only one SRB to the side and adjust nozzle geometries to compensate."

Like that, the factory can focus on building only one type of SRB, reducing production machinery requirements (only one product is expected) and cost.

[basic.syntax]

They say you (should?) learn something new every day... this thread makes it one of those days

[MinimumSky5]

The Delta II does it too, with four boosters one is placed offset, so that the three booster variant has less of an symmetric thrust.

[AlphaKerman]

Here a video from recent MUOS - 5 launch. Well, someone ask very good question there. According to them, to balance the 5 SRB used on Atlas V, they angled the engine yaw 1,5 degree. Explanation at 44:40  

 

[wumpus]

On 7/14/2015 at 0:54 PM, Kibble said:

Atlas V core wasn't originally designed for boosters - the oxygen line and avionics package ended up getting in the way of SRM placement.

They just happened to have enough gimbal to handle asymmetric boosters???  I don't think its a shuttle derivative, was it based on submarines (which would have funky launch angle issues)?

[DDE]

On ‎13‎.‎07‎.‎2016 at 9:28 PM, wumpus said:

They just happened to have enough gimbal to handle asymmetric boosters???  I don't think its a shuttle derivative, was it based on submarines (which would have funky launch angle issues)?

RD-180 is a half-size variant of the RD-170, which was one of the two engines used in the pronouncedly asymmetric Energiya.

Nobody uses kerolox on submarines.

Edited July 31, 2016 by DDE

[cryogen]

On 7/15/2015 at 1:47 AM, bs1110101 said:

What ever happened to the Atlas 5 heavy? And did they look into mixing Atlas 5 and and Delta 4 cores at all?

Here's a useful article about super-sized EELV derivatives:

https://www.cbo.gov/sites/default/files/109th-congress-2005-2006/reports/10-09-spacelaunch.pdf

Quote

At the inception of the EELV program, the plan was to develop both Delta IV Heavy and Atlas V Heavy launchers capable of lifting about 25 mt into low earth orbit. Subsequently, the Department of Defense and Lockheed Martin agreed to forgo production of the A5H. Although the most capable version of the Atlas V is not designated a “heavy” launcher, its lift capacity places it in the heavy-lift launch category as defined by the Federal Aviation Administration.

I don't think there's much market for heavy EELV's (at least at ULA pricing), given that Delta IV Heavy launched only 9 times in the past 12 years. And none of them were commercial launches. As for USAF, they can't buy many more Atlas V's because of the RD-180 embargo.

Edited August 1, 2016 by cryogen

[DDE]

@Bioman222, I found another case of the RD-170 being a miracle worker. That would be an augmented Zenit.

[Bloojay]

Holy crap, I accidentally made that in KSP-ish

[KSPNerd]

Here's your proof that both the augmented Zenit & the Atlas V 411 work!!!!

Atlas V 411: http://imgur.com/gallery/ghw6b

Zenit-Augmented: http://imgur.com/gallery/kLuqt