# How does a single SRB control attitude?

The Ares I-X was a test flight from the Constellation program for crewed Ares I-launched Orion capsules.

If liquid fueled rocket motors can gimbal, how do solid rocket motor-propelled spacecraft control their attitude, especially when performing a "pad avoidance maneuver" directly after ignition?

• I can't quite decide if this is a duplicate or not, but it's about the same rocket (Ares I-X) and the answers to the existing question do discuss how attitude control is achieved in SRBs, but not to the same depth as the answers here. So I'm throwing this into the review queues and we'll see how it fares (no pun intended)... – user Mar 21 '17 at 13:08
• If we look at this from the scope in particular of single SRBs, as opposed to strap-on or ganged SRBs, it provides an opportunity to discuss roll control authority in particular, which is present in one answer. Maybe an edit to the question to slightly tweak its scope is more useful than closing and redirecting to the other question. – Tristan Mar 21 '17 at 14:06
• I agree that the issue of roll control makes this a non-duplicate. – Russell Borogove Mar 21 '17 at 20:22
• @MichaelKjörling Throwing things into the review queues is a good way to get things closed without due consideration. Rightly or wrongly, people will tend to think that Michael Kjörling must think it should be closed, even if you leave a comment denying that you think so. I don't think things should be put in review queues by anyone except someone who is fairly sure it should be closed and can articulate why they feel so. What is the utility of an ambivalent nomination? If you are not sure, why not just leave it alone. It's not like you've lost a valuable opportunity to close something. – uhoh Mar 22 '17 at 11:33
• @MichaelKjörling the other question is about thrust vectoring of SRB's - the boosters mounted on other rockets. The use of a stand-alone SRB is mentioned only as background; "Here is where I have seen it said that a particular SRB has thrust vectoring - is it unusual for SRBs in general to have thrust vectoring?" These are really clearly different questions, and have distinctly different answers. This is specifically about SRBs as stand-alone launch vehicles, that one is clearly about SRBs in general. Should have taken the time to read it before "throwing" this one into the gauntlet. – uhoh Mar 22 '17 at 11:34

The Ares 1-X used stock Shuttle program SRB thrust vector control (TVC) - hydrazine fueled power units drove hydraulic pumps which powered actuators that could tilt and rock the nozzle, which incorporated a flexible bearing in its design.

(Pictures from "Space Shuttle", Jenkins, 1992 edition p.263 and here - p 2.13-48 of linked PDF)

However, unlike the Shuttle system with its 2 SRBs, a single SRB with articulating nozzle cannot provide roll control, only pitch and yaw. So Ares 1-X had 2 unique modules containing hypergolic thrusters (derived from the Peacekeeper missile) mounted on it to provide control in the roll axis.

(Picture from here)

• Very nice graphic! – uhoh Mar 21 '17 at 16:31

Solid rocket booster nozzles can gimbal. If you take the SRB of the Space Shuttle:

Each SRB had two hydraulic gimbal servoactuators, to move the nozzle up/down and side-to-side. This provided thrust vectoring to help control the vehicle in all three axes (roll, pitch, and yaw).

You will find more explanation on this Wikipedia article, where I found this picture:

In addition, rockets can board several devices, as:

• Both answers to the question Is it unusual to vector the thrust from an SRB? are also informative. – uhoh Mar 21 '17 at 9:12
• @uhoh absolutely. SE algorithm for "linked question" is pretty accurate – le_daim Mar 21 '17 at 12:12
• I think Linkedonly reflects things that have been actually linked already. Do you mean Related? Sometimes both categories display, sometimes just one or the other. It took me a while to figure that out. – uhoh Mar 21 '17 at 16:30
• @uhoh you are absolutly right. No algorithm at all with the "linked question but Michael Kjörling comment on the question :) Anyway, "related questions" algorithm is not bad, though. – le_daim Mar 21 '17 at 16:44

Apart from having an actuated nozzle, an inert gas or reactive liquid can be injected into the nozzle of an SRB to dynamically deflect or shape the exhaust, thereby vectoring the thrust.

ISRO's Polar Satellite Launch Vehicle (PSLV) uses strontium perchlorate from N2 pressure-fed tanks attached on side of core introduced into the SRB exhaust through an array of injectors around the exhaust nozzle. The Secondary Injection Thrust Vector Control (SITVC) system is shown on page 8 of the Oct-92-Mar-93 issue of Space India (view online), and is shown below, where engineers can be seen working on the ring of injectors near the top of the nozzle.

SITVC is also present on a few of the strapon SRBs of PSLV; two strapons (PSOM-4,5) in PSLV-XL and one in PSLV-G.

Similarly, N2O4 powered Liquid injection thrust vector control (LITVC) was used on Titan IIIC.

• "... numerous injectors present around the exhaust nozzle (as seen in following issue of Space India Oct-92-Mar-93 on Page 8) " I don't see numerous injectors in the photos on page 8, but I would really like to! Are they shown somewhere else? I see this: i.stack.imgur.com/1ytlV.png but it seems to be something different (but equally interesting). – uhoh Mar 22 '17 at 11:30
• @uhoh Added image in answer. – Ohsin Mar 22 '17 at 12:08
• That picture of the injectors is very nice indeed. – Organic Marble Mar 23 '17 at 1:46