Talk:Space Shuttle Solid Rocket Booster
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- 1 Explosive Bolts
- 2 "Perforated" as an adjective
- 3 Give Source
- 4 The O-rings
- 5 Saturn V and other statements
- 6 SRB thrust graph
- 7 Comment on changes
- 8 SRB vs SRM
- 9 New expanded image
- 10 Thrust?
- 11 Reusable Solid Rocket Motor (RSRM)
- 12 Citations missing
- 13 Seven segment vandalism?
- 14 Five segment boosters
- 15 SRB separation image
- 16 Information to be added
- 17 history?
- 18 Article quality and clarity
- 19 Advanced Solid Rocket Booster section
- 20 Solid Rocket Motor weight or truss-to-weight ratio
- 21 The economics of reuse
- 22 Mixed past-tense and present tense
- 23 Factual dispute
- 24 Morton Thiokol
- 25 Propellant shape needs explanation/diagram
- 26 Photo of the booster
- 27 Capitalization
- 28 Cooling?
From what I have read, The SRBs use frangible nuts, not explosive bolts. I am not 100% on this, but am pretty sure. Just pointing out a possible inaccuracy.. EDIT: on a second look at the article, it states that the srbs are held down by four frangible nuts, and later in the article it states that explosive bolts are used.
"Perforated" as an adjective
I was surfing the NASA website when I found this article (almost word for word) in the NASA NSTS 1988 News Reference Manual http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/stsref-toc.html I realize it is probably public domain, but seeing as how this article is essentially copy-and-pasted straight from the NASA manual, I think a little credit is due.220.127.116.11 06:53, 1 August 2005 (UTC)
I did a little more digging and found that the copy-and-pasting first appeared in Theon's edit (17:11, 17 June 2004)-not that it makes much difference (sorry if I'm going about this the wrong way-it is the first time I have ever written on wiki) 18.104.22.168 07:00, 1 August 2005 (UTC)
It seems perverse in this otherwise very informative article, not to mention either a) The construction of the boosters out of a number of segments joined together with sophisticated double O-ring seals or b) The fact that it was the failure of one of these seals that was directly responsible for the Challenger disaster - particularly, since the latter incident and some of the changes that resulted are detailed in the article. My knowledge is limited to what can be found on the web - and elsewhere in Wikipedia - nevertheless, I have included a modest section on the O-ring sealed construction. I invite others with more knowledge to edit and expand this. Peter M 18:43, 9 October 2005 (UTC)
- Nice pictures of original and new joint are here: http://history.nasa.gov/rogersrep/v6ch1.htm, http://history.nasa.gov/rogersrep/v6p14.htm, http://history.nasa.gov/rogersrep/v6p15.htm —The preceding unsigned comment was added by 22.214.171.124 (talk) 13:46, 28 December 2006 (UTC).
Saturn V and other statements
The shuttle does not have more liftoff thrust than the Saturn V. The 3.3 million lbs (takeoff) thrust figure for the SRB is wrong -- it's vacuum thrust. SRB sea level takeoff thrust is considerably less. Joema 01:22, 8 February 2006 (UTC)
Comment: If you are using that STS-107 graph as proof, then the shuttle reaches as much or more than 3.2 million at sea level. In addition, I have cited below two NASA links which (and they have updated it in the past year) to say 3.3 million sea level specifically. The shuttle produces nearly the same, not much less, than the Saturn V. User CapeCanaveral321.
Also the SRB does not require most of the thrust to reach orbit. Joema 01:22, 8 February 2006 (UTC)
- Well, they provide most of the thrust, and also most of the integral over time of thrust- the impulse. WolfKeeper 04:58, 8 February 2006 (UTC)
- Actually the SSMEs provide most of the impulse. The SRB average vacuum thrust over the 120 sec. firing period is 2.395 million lbs, for a total impulse of 574.8 million lb-sec. The SSME vacuum thrust is about 500,000 lb per engine, total 1.5 million lbs, total impulse over 8.5 minutes (510 sec) is 765 million lb-sec. Thus the SSME total impulse is considerably greater than SRB total impulse.
- The SSMEs are highly optimized for vacuum thrust since most of their firing duration is in vacuum. The SRBs are more optimized for sea level thrust, but their vacuum thrust is still higher, but less increase than the SSMEs. When comparing SSME vs SRB total impulse we must use the thrust figure where each engine spends most of its time. By contrast when comparing liftoff thrust, we must use SRB sea level vs SSME sea level thrust; but that's not the point here. You can see a thrust/time graph of SRB sea level thrust on page 182, figure 3-33 at:  (warning, large PDF). There's a thrust/time graph for SRB vacuum thrust on page 8 of this document:  Joema 14:09, 8 February 2006 (UTC)
Most of the total delta V energy is from the SSMEs, not the SRB.Joema 01:22, 8 February 2006 (UTC)
- I don't know, I've never worked it out. Energy is a funny thing in a rocket. You need to take into account the fact that quite a lot of the kinetic energy of the liquid hydrogen propellant is put there by the SRBs. It all gets very messy very quickly. And the delta-v due to the SRBs is surprisingly high after you account for atmospheric losses and gravity losses. But that wasn't what the piece said anyway.WolfKeeper 04:58, 8 February 2006 (UTC)
- As the above shows the SSMEs provide more of the total impulse, hence more of the energy to reach orbit. You're right due to K=1/2m^v2, the SRBs have imparted a lot of energy despite the low staging velocity since vehicle mass is so great at that point. However the total energy imparted by the SSMEs is significantly greater. Joema 14:09, 8 February 2006 (UTC)
The SRBs do supply over 70% of the initial liftoff thrust, so revised wording to state that. Joema 01:22, 8 February 2006 (UTC)
SRB thrust graph
I'm confused about exactly what the thrust graph is showing. Is this predicted/design thrust, or measurements from an actual mission? I'm guessing the latter, since there are distinct left/right values and I would assume they are designed to be identical. Also, I don't understand what it means to talk about "sea level thrust" at various time points into the mission. It's obviously not at sea level except at t=0. What does sea level thrust at t=60 mean? -- RoySmith (talk) 23:41, 2 March 2006 (UTC)
- Roy, good questions. Yes it's actual thrust data from the Columbia mission, STS-107. However you can't directly measure thrust. Rather it's calculated from other parameters such as chamber pressure. Also the thrust curve is generally corrected to constant sea level or constant vacuum thrust. In actuality the physical thrust would be continuously changing from altitude variation, even if engine design thrust was constant (which it's not for the SRBs). I include below some more info I was preparing to post:
- Because of the frequent confusion on this point, I uploaded a thrust/time graph for the SRBs. I also revised the thrust numbers in the article to reflect this. SRB sea level liftoff thrust is 2.8 million pounds each. Each SSME produces 393,000 pounds sea level thrust at 104% power level. Thus the shuttle total liftoff thrust is: (393,000 * 3) + (2,800,000 * 2) = 6.779 million pounds force, or 3.075 million kgf, or 30.16 MN. Using these numbers the SRBs provide 82.6% of liftoff thrust.
- This is confusing because many sources just blindly copy the 3.3 million pound thrust number, some even erroneously adding "sea level" or "liftoff" thrust. There are six possible thrust numbers for the SRB:
- Sea level liftoff thrust
- Sea level peak thrust
- Sea level average thrust
- Vacuum liftoff thrust
- Vacuum peak thrust
- Vacuum average thrust
- The problem is most references don't state which they are using. This is why references state SRB thrust from 2.65 million lbs (probably sea level average thrust) to 3.4 million lbs (probably vacuum peak thrust).
- When comparing SRB thrust to, say, Saturn V F-1 engine thrust, you must consider the different characteristics of each engine type. The F-1 is not throttlable, so excluding altitude variations always produces the same thrust. At sea level this is 1.5298 million lbs per engine or 7.649 million lbs thrust total. By comparision the SRB thrust changes over the burn time (see chart). Space shuttle total sea level liftoff thrust is 6.779 million pounds force, or about 88.6% of the Saturn V.
- In theory you could compare the SRB thrust at T+20 sec which is somewhat higher, but that wouldn't be liftoff thrust. Joema 23:57, 2 March 2006 (UTC)
Comment on changes
User:Simon Dodds last edit was correct: the correct SRB relative thrust contribution is 83%. Each SRB produces 2.8 million lbf sea level liftoff thrust. Each SSME produces 393,800 lbf sea level liftoff thrust. Thus we calculate: (2.8 million * 2) / ((2.8 million * 2) + (393,800 * 3)) = 82.578%
For more info on SSME thrust, see the specs I added to that article.
- Deleted 83% SRB thrust contribution during 1st stage. Reason: unverified and unlikely, since SRB sea level thrust profile changes over time. See SRB thrust graph.
- Improve wording of SRBs constituting 80% of liftoff mass. Joema 12:43, 12 April 2006 (UTC)
Update based on the discussion above: According to NASA and ATK, the sea level thrust of the SRB is 3.3 million with an average of 2.6 over the duration of the burn. Where does the 2.8 number come from? In addition, for anyone using Astronautix as a source, their numbers are incorrect.
http://www.spaceflight.nasa.gov/shuttle/reference/shutref/srb/srb.html http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/srb.html http://www.atk.com/Customer_Solutions_LaunchSystems/cs_ls_hsf_ssrsrm.asp
It is my opinion, and based on the graph of performance of STS-107, that the article should state that they produce a maximum sea level thrust of 3.3, with a liftoff thrust of 2.8 increasing through the first 20-25 seconds of flight, and that a typical mission (cited 107 graph) produces about 3.2 at sea level.
Just for an aside, if someone who is attending a launch wants to know what they are going to feel and hear, they should know that they will feel and hear 3.2-3.3 million.
SRB vs SRM
I believe that 'Solid Rocket Motor' (SRM) refers solely to the actual solid motor inside the booster, whereas 'Solid Rocket Booster' refers to the whole assembly including the casing, nozzle, parachutes, etc. I've been trying to find a definitive reference on this, but none of the obvious places (e.g. Shuttle News Reference) seem to have one. Mark Grant 20:35, 14 July 2006 (UTC)
- Yep. In Booster Systems Briefs, Final, Rev F, JSC-19041, it states:
- The solid rocket booster (SRB) element of the space shuttle (Figure 4.1-I) is made up of six subsystems:
- The solid rocket motor
- The structural subsystem
- The thrust vector control subsystem
- The separation subsystem containing mechanical and ordnance equipment
- The recovery subsystem containing mechanical and parachute equipment
- The electrical subsystem
- The solid rocket booster (SRB) element of the space shuttle (Figure 4.1-I) is made up of six subsystems:
- Cjosefy 20:53, 14 July 2006 (UTC)
- Yep. In Booster Systems Briefs, Final, Rev F, JSC-19041, it states:
ATK Launch Systems refers to these as the RSRMs - Reusable Solid Rocket Motors. A component of the RSRM is the BSM - Booster Separation Motor. ...don't know if that's helpful or not? —Preceding unsigned comment added by 126.96.36.199 (talk) 23:02, 14 October 2008 (UTC)
New expanded image
I think this page my benifit from a different expanded iamge of the SRB. Perhaps this one will do (in JPG and PNG):
- Nice diagrams, one of them should be included to replace the existing image, but there is a note missing from the "Forward Skirt and Forward IEA"; there is an arrow below it with no note attached. Peter Maggs 07:41, 15 July 2006 (UTC)
Cjosefy 21:06, 14 July 2006 (UTC)
So is there a definitive source for the SRB thrust figure? The cites given in the recent edit do say it's 3,300,000lbs, but that's obviously directly contradicted by the STS-107 thrust graph. I'd tend to believe the latter, but it's odd that NASA sites give the former. Mark Grant 02:16, 3 May 2007 (UTC)
Reply by CapeCanaveral321 02:20 3 May 2007 UTC. First let me note that based on my visits to those reference manuals, NASA has added the words sea level there in the past year or even months. That may be based on discussions here or on certain web forums. It is not out of the question that they see our questions and added that.
This does not directly contradict the STS-107 graph. The graph shows 3.2 million at T+20 which is sea level for all that matters. 3.3 is probably the maximum it can reach at sea level and I would guess it has on some missions of in testing as they would not cite the number otherwise. SRB segments are poured and used in specific sets, and each set is tailored for a specific mission requirement.
Reusable Solid Rocket Motor (RSRM)
The article uses the acronym RSRM, which is presumably "Reusable Solid Rocket Motor". But it never defines the term. Is it a synonym for SRB? Is the motor some subset of the entire booster? If so, and given the diagram in the article doesn't show it, can anyone add some explanatory text? (Sdsds - Talk) 03:22, 4 May 2007 (UTC)
- I think it's Redesigned solid rocket booster, but I'd need to check. --GW_SimulationsUser Page | Talk 21:25, 4 May 2007 (UTC)
- The most common use of RSRM is reusable solid rocket motor, NOT redesigned. This includes many thousands of references within recent NASA documentation. However both forms -- reusable and redesigned -- are very common. For the sake of consistency I suggest we use the most common version -- reusable -- but explain that both nomenclatures are common and either is proper.
- Re the other point about RSRM vs SRB, yes we should make that clear. In general popular usage, both RSRM and SRB are commonly used interchangeably. However, technically RSRM refers to the solid fuel and nozzle, whereas SRB refers to the entire structural assembly (which includes avionics, parachutes, and structural support hardware). Joema 11:59, 14 June 2007 (UTC)
Seven segment vandalism?
This edit in 1995 added the text, "The boosters are assembled from seven individually manufactured segments." Where did that come from? Why, with all the talk of four segment and future five segment SRBs, do we claim there are seven segments? Or does "segments" in this context perhaps refer to something else entirely? (sdsds - talk) 08:20, 21 November 2007 (UTC)
I have no idea what the "seven segment" text is talking about. Boosters are either four segment, or the extant but unflown five. "Segment" is certainly used differently from the usual meaning, and should be clarified or corrected. 188.8.131.52 (talk) 10:15, 2 July 2008 (UTC)
- The explanation is in the sentence immediately after you the one you quoted. The "4-segment" SRB consists of seven segments, six of which are assembled together in pairs at the factory to create 3+1=4 segments as delivered to NASA. From the Challenger disaster article:
Each SRB was constructed of six sections joined in three factory joints and three "field joints". The factory joints were welded, but the field joints--assembled in the Vehicle Assembly Building at Kennedy Space Center--each used two rubber O-rings, a primary and a secondary (backup), to seal them.
Five segment boosters
The more powerful five segment booster was developed and successfully static tested at ATK. It is my understanding that the five segment design was intended to punch the heavier Columbia up to the ISS (which, unlike the other orbiters, it could not reach with the standard boosters), but Columbia's destruction made it superfluous. I'll get details from my sources at ATK and include a paragraph in the article. 184.108.40.206 (talk) 10:15, 2 July 2008 (UTC)
SRB separation image
The image is a faked photo-manipulation, so doesn't belong in an encyclopedia. This is obvious for several reasons:
(1) In general, there is no ground-based or aerial imagery of that clarity. Here is a typical ground-based image of the same separation event: . However after the loss of Columbia, STS-107, specialized high-altitude aircraft with high-resolution imaging devices track each launch. Here is video from one launch: 
(2) The windstream effects on the separation motor exhaust isn't depicted. At SRB sep, the vehicle is 150,000 ft. altitude, moving at Mach 4 (about 3,000 mph). Atmospheric dynamic pressure is fairly low -- about 0.25 pounds per square foot. However this is sufficient to immediately deflect rearward the lateral-firing separation motor exhaust. However the image doesn't show this. By contrast see actual on-board video of the separation event (happens at 2 min. into this video): . Also note the same effects in the above video taken from a high-altitude aircraft. Joema (talk) 11:53, 25 April 2008 (UTC)
Information to be added
The steel case segment from the SRB is made by different forming manufacturing processes. These are starting from As-cast blank, reverse extruding, ring rolling and roll forming. The steel used is D6AC steel.
The case segments are about 3 m diameter and about 13 mm thick. Tolerance from ticknest is 0.25 mm.
Source: Kalpakjian S and Schmid S. R. Manufacturing engineering and technology, 5th edition. Pearson Prentice Hall. USA, 2006. ISBN 0-13-148965-8 —Preceding unsigned comment added by Gengiskanhg (talk • contribs) 14:56, 6 June 2008 (UTC)
Article quality and clarity
Quoted from "Overview" section:
The boosters are composed of seven individually manufactured steel segments. These are assembled in pairs by the manufacturer, and then shipped to KSC by rail for final assembly.
Who/what the heck is "KSC"? This is less than 8th grade composition level here folks. One must introduce/define an entity/location in a written work *BEFORE* identifying said entity/location merely by its initials. If KSC was hyperlinked to a Wiki on KSC then that would be a bit more acceptable. However, it's not. And KSC isn't "Whitehouse" or "NASA". "KSC" isn't already universally known. So, someone needs to edit and make clear very early in the article who/what "KSC" is. "KSC" is mentioned twice in the article, but is never defined. Again, I ask, who/what the heck is "KSC"? Folks, you need to keep in mind that you're writing articles for people who don't already know all this stuff. That the reason why encyclopedias are written. Someone is assuming "the world" already knows who/what KSC is. There are probably other errors like this in the article, but I haven't finished reading it yet. I'm guessing it needs a complete quality control review given the simple but serious mistake I found in the Overview, at the very top of the article. Hardwarefreak (talk) 02:10, 13 May 2009 (UTC)
I just read the "Filament-wound cases" section, which led me to believe KSC was one of the launch sites. Kennedy Space Center comes to mind. Took me the entire length of the article to realize that KSC may be Kennedy Space Center. If indeed this is the case, "Kennedy Space Center" needs to be spelled out in the "Overview" section, not abbreviated. Again, realize that not everyone reading these pages is a NASA junkie, nor can you assume they just read the main Space Shuttle pages before arriving at this page. I'm not in the habit of editing other folks' contributions, so I'll leave it to you. Hardwarefreak (talk) 02:46, 13 May 2009 (UTC)
Advanced Solid Rocket Booster section
The Advanced Solid Rocket Booster section has garbage relating to the current author and previous author that should be edited out. In addition, there are no references for any of the facts in this section. —Preceding unsigned comment added by 220.127.116.11 (talk) 22:27, 11 September 2009 (UTC)
I corrected the assertion that NASA was to manufacture the ASRMs themselves, this was clearly in error. The ASRM development contract was held by Aerojet with Lockheed as an integrator. I've placed Aerojet as the manufacturer with one publicly available reference. I've also removed the assertion about cost growth as the reason for contract cancellation in 1993. There were a wide range of factors that led to the cancellation, price was only one of them and not chief among them. A briefer statement of fact was substituted.
I hoped to find verification for the statement concerning the ASRM motor casings being used on the Pathfinder exhibit at Space Camp, but didn't locate anything. Based on personal communication I've received, I believe it to be true so I left that assertion, hopefully someone else can document it. —Preceding comment added by Saundby (talk • contribs) 00:43, 22 April 2010 (UTC)
Solid Rocket Motor weight or truss-to-weight ratio
The economics of reuse
I am missing information, which I think is one of the most important: Why were the SRBs designed to be reusable? What's the specific economic reason? The cost of recovering and refurbishing the empty hulls is certainly not negligible. So what is that precious part that's more economic to recover than to manufacture? Is it expensive rare earth metals in the hull, turbo pumps, or something else that's so valuable? --18.104.22.168 (talk) 11:58, 6 August 2011 (UTC)
- That's a good question, I've wondered about that myself. In fact I googled on it and found a pdf related to the subject. It said that there were two studies done in the 1990's which concluded that the cost of refurbishing the SRBs is about the same as manufacturing a new one. Not surprising to me. The title of the pdf is 'Economic Model of Reusable Versus Expendable Launch Vehicles'. I can understand how a liquid fueled booster may be economical to recover, because of all the expensive turbopump machinery and cooled combustion chamber. But a solid rocket, I just can't fathom how anyone could have thought it made economic sense to recover and reuse them, being it's mostly just a metal casing. --22.214.171.124 (talk) 02:52, 15 September 2011 (UTC)
This is THE question for all shuttle related discussions. Since this is in the past, the most important judgment history can make is was this reusable? What was the cost of refurbishment over the life of the project and exactly how many were manufactured new? Ideally they would have made two pre-Challenger and two post Challenger. It would have been reasonable to budget 16 (8 pre and 8 post Challenger). How many were actually manufactured and flown? — Preceding unsigned comment added by 126.96.36.199 (talk) 16:03, 31 December 2014 (UTC)
Mixed past-tense and present tense
The article reads as if someone has gone through it and changed present tense to past tense in an almost automatic fashion. I agree that past tense is correct, since the Space Shuttle is no longer operational. The Apollo project articles, for instance, are written in past tense, so we should be consistent.
However, I think the way past tense has been introduced makes the article read funny. I think someone would need to go through it and rewrite whole sections to use past tense. — Preceding unsigned comment added by Avl (talk • contribs) 18:11, 18 March 2012 (UTC)
As the designer of ASRB Handling Rings and the O-Ring Groove Protector, I can definitively state the above sentence is incorrect. The Advanced Solid Rocket Booster was designed using a 3 segment rocket motor with a diameter of 150", held together with 150X 1.25" diameter bolts per field joint. I work across the street from the Pathfinder, and confirmed on 5/26/2012, that the boosters on display at the Space and Rocket Center are 4 segment motor cases with a diameter of 146.146", held together with tang and clevis pinned field joints. To my knowledge the one motor case made, developed a large circumferential crack upon finishing heat treatment, just prior to program termination. The cancellation wasn't in favor of improvement of the SRB. The RSRB was already flying prior to the ASRB program. ASRB was canceled for multiple reasons. The technical reason being the decreased weight of the Super Lightweight External Tank could provide better performance for a longer period of time during the booster phase. The political reason is the program was located in the district of Mississippi Congressman Jamie Whitten. He suffered a stroke in mid 1993, and had to step down from the Head of the Appropriations Committee. The termination of the program soon followed in October 1993, in the same vote as the Super Conducting Super Collider in Texas. - 188.8.131.52 (talk) 05:04, 01 June 2012 (UTC)
- I relocated this commentary and original research about the actual boosters mounted with Pathfinder from the article to the talk page. As it appears this comment was made in good faith and disputed fact is uncited, this claim bears further and rapid investigation and, if true, proper sourcing and a solid edit to this description. - Dravecky (talk) 07:28, 1 June 2012 (UTC)
The full name of Morton Thiokol is used for the company in the critical wikipedia articles on the Challenger disaster, the NASA decision and the engineering assessment of risk.
Why is that full name not found here in this ATK-related article ?
I worked on software used by ATK in the SRB program and so I expected better.
Please remedy without vandalizing the historical accuracy of related articles. They were called Morton Thiokol and they were known as Morton Thiokol. Anything less smells of revisionism.
G. Robert Shiplett 20:48, 24 July 2012 (UTC)
Propellant shape needs explanation/diagram
"The propellant has an 11-point star-shaped perforation in the forward motor segment and a double-truncated-cone perforation in each of the aft segments and aft closure." This really needs explanation and cross-section diagram to make sense to the uninitiated. Rcbutcher (talk) 03:35, 24 December 2013 (UTC)
Photo of the booster
While in an entire article there isn't even a single photograph showing a whole booster? The closest one is showing boosters half-submerged in the ocean, but that's pretty much it. Can we possibly replace drawing in the infobox with a proper photograph? SkywalkerPL (talk) 13:45, 31 July 2014 (UTC)
I think the article should be "Space Shuttle solid rocket booster". We don't capitalize "solid rocket booster" in other uses. "Space Shuttle" is a proper name, but "solid rocket booster" is not. As an example, the Curtiss P-40 Warhawk had an Allison engine, not an "Allison Engine". Any objections? Chris the speller yack 02:30, 28 August 2014 (UTC)
- Yes. NASA is big into acronyms, and the official (and common) name was Space Shuttle Solid Rocket Booster (SSRB). The whole thing is in effect a proper name, not just a composite of "Space Shuttle" and "solid rocket booster". They do this all the time, and some wikieditors have had heartburn with "Command Module" (in context of Apollo program), "Service Module", "Lunar Module", etc. I don't think the argument of common English style applies here. JustinTime55 (talk) 13:16, 28 August 2014 (UTC)
I'm surprised the article has no mention of how the SRBs are cooled. My understanding of traditional rocket engines is that fuel or oxidizer is fed in a spiral path around the throat and bell nozzle, absorbing heat, before being injected into the combustion chamber. But in a SRB, there is no liquid fuel/oxidizer. So how are they cooled? DrZygote214 (talk) 19:22, 3 February 2015 (UTC)
- Uh, the same way all solid-fuel rockets are actively cooled, which would be...not at all. Our SFR article says "The nozzle must be constructed from a material that can withstand the heat of the combustion gas flow. Often, heat-resistant carbon-based materials are used, such as amorphous graphite or carbon-carbon." The only other possible method of passive cooling would be ablative nozzles.