<font color="yellow">Boat motors and rocket motors are made of metal. Are you telling me that rocket motor metals, made to withstand much higher temps and higher oxidizing environments, will be less durable to exposure to sea salt than a stock evinrude or cat? Gimme a break. Shuttle motors stand out in the open air exposed to atmospheric sea salt for months at a time. This is a bogus argument. </font><br /><br />It's not a bogus argument.<br /><br />Are you arguing that metals are metals and they are all the same? <img src="/images/icons/laugh.gif" /> I would not have laugh if I did not know that you're a self-professed engineer/ scientist. <img src="/images/icons/smile.gif" /><br /><br />For one, the SSME does not combust in an "oxidizing environment". The chamber combustion is in a "fuel rich" environment so the metal would not see any hot gaseous oxygen. In fact, extra fuel are injected along sidewall of chamber in order to cool and protect the metal from reacting with oxygen. As you [should have] known, metal is a very good "fuel" for pure oxygen.<br /><br />Just to show you the sensitivity of SSME, the hotest part is at the throat of SSME where 6,000 deg. F of combusted gases "fly" by at Mach 1, the metall is made of copper alloy, called North American Alloy-Z, e.g., NARLoy-Z, it is similar to the commercial grade of copper alloy called Amzirc. The thin piece of NARLoy that separates the 6,000 deg. F combustion gases on one side from the -300 deg. F gaseous hydrogen from the other side is only 0.10 inch thin. The temperature gradient across this 0.10 inch thin copper alloy is 800 deg. F. <br /><br />Upon contact with a corrosive fluid, such as saltwater, pitting corrosion will start to occur and eats away precious metals. Any reduction of its thickness, such as cause by corrosion, will quickly generate hot spot and potentially cause a burn through in the coolant channel.<br /> <br /><br />Marine outboard engines such as Envirude, Mercury, Johnson, Honda, etc. <div class="Discussion_UserSignature"> </div>
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I read about it 2 years ago, I am aware it happened longer ago than that. I was putting into context the age of the information I knew...
Actually, propforce, the SSME combusts in an oxidizer rich environment. Compared to ambient atmosphere, which is less than 1/5th O2, the combustion chamber sees a 50% molecular ratio of O2, and 85%+ by mass oxygen environment, which is 6000 degrees, by your own admission. That is far more hazardous than a dunk in the ocean.<br /><br />NASA seems to agree: "Due to their high thermal conductivity, copper alloys make excellent liners for the hot sections of high-heat-flux engines, such as combustion chambers of rocket engines for launching space payloads. However, in that aggressive service environment Cu alloys are prone to degradation by oxidation-related phenomena. In a combustor there are always issues of static and cyclic oxidation; in a hydrogen-fueled (“LH2-LOX”
rocket engine there is the additional issue of blanching, which causes the most serious oxidation-related damage to the liners [1–4]. Blanching is caused by spatial and temporal variations in oxidant-to-fuel (O/F) ratio, which change the local<br />ambient from oxidizing to reducing and back [3]. Oxide film formed in the fuel-lean cycle is reduced and removed in the fuel-rich cycle, thus exposing the metal to further attack. Therefore, blanching is somewhat analogous to cyclic oxidation, except that the duration of an oxidationreduction cycle may be in microseconds, rather than the minutes or hours that characterize cyclic oxidation. The “blanched” (i.e., bleached) spots indicate accelerated degradation, which has serious consequences for the impairment of cooling systems beneath the liner."<br />http://gltrs.grc.nasa.gov/reports/2003/CR-2003-212549.pdf<br /><br />Pitting happens because of poor granular integrity of the alloy.<br /><br />I'm quite aware that metal is a good fuel for pure oxygen. I've cut inch thick metal with nothing but an o2 feed once I got the initial start of t
rocket engine there is the additional issue of blanching, which causes the most serious oxidation-related damage to the liners [1–4]. Blanching is caused by spatial and temporal variations in oxidant-to-fuel (O/F) ratio, which change the local<br />ambient from oxidizing to reducing and back [3]. Oxide film formed in the fuel-lean cycle is reduced and removed in the fuel-rich cycle, thus exposing the metal to further attack. Therefore, blanching is somewhat analogous to cyclic oxidation, except that the duration of an oxidationreduction cycle may be in microseconds, rather than the minutes or hours that characterize cyclic oxidation. The “blanched” (i.e., bleached) spots indicate accelerated degradation, which has serious consequences for the impairment of cooling systems beneath the liner."<br />http://gltrs.grc.nasa.gov/reports/2003/CR-2003-212549.pdf<br /><br />Pitting happens because of poor granular integrity of the alloy.<br /><br />I'm quite aware that metal is a good fuel for pure oxygen. I've cut inch thick metal with nothing but an o2 feed once I got the initial start of tSupersonic parachute links...<br /><br />http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=35017<br />http://athena.cornell.edu/mars_facts/sb_punch.html<br />http://www.mtu-net.ru/mosseev/vasiljev.htm<br />http://www.paratech-parachutes.com/ParachuteSystems/FlightTesting.html<br /><br />One reason I don't address the engines being exposed nozzle up is that I do not anticipate that we'd drop a pod into a hurricane. I don't recall the Shuttle ever launching when the SRB landing area wasn't clear. That seems to be a standard part of the countdown procedure...
Even more reason for a two stage rocket. Use existing Shuttle facilities, on the East coast and pretty much completed facilities on the West coast, for Polar orbits. I don't see any reason to land in water either. Use turbofan engines to assist initial launch and then use them for approach and landing of the first stage.<br /><br />The second stage could be anything. Various size Propellant Modules, number and types of engines and payloads. You want a capsule you get a capsule, if you want a lander you get a lander. As long as it attaches to a second stage it works.<br /><br /> <br /><br /><br /><br /><br /> <div class="Discussion_UserSignature"> </div>
<font color="yellow">Actually, propforce, the SSME combusts in an oxidizer rich environment....</font><br /><br />I can see you're in a desperate need of a tutorial course in combustion chemistry. Please pick up a book and learn the difference between "stoichiometric" from "fuel-rich" and "fuel-lean".<br /><br /><font color="yellow">NASA seems to agree:...... </font><br /><br />Please understand the quote before you copy & paste them. You'll need to understand the <i>issues</i> before you can address them which, in this case, you've demonstrated that you have no clue. We were addressing post engine opeation and the exposure to saltwater, not during engine operation. The fundamental failure mode mechanism is totally different. <br /><br />By the way, did you notice the irony that, for someone like you who's constantly criticizing NASA's mismanagement of programs and waste of money, you had to go to a NASA website to get some education? <img src="/images/icons/wink.gif" /><br /><br /><font color="yellow">Your previous calculations on drop time are also okay, 16.5 minutes is about what I'd figure</font><br /><br />It doesn't take a rocket scientist to divide 200,000 feet altitude by 200 ft/sec to get 1,000 sec of air time, which is 16.7 minutes. But I am glad that your calculation confirmed my number. So where was this "... several hours.." of air time that you quoted inititially come from? <br /><br /><font color="yellow">But I have to ask: given how copper is one of the most thermally conductive metals, what makes you think it, or any of the engine, will not be at ambient temperature after dropping through frigid stratospheric conditions at a hundred mph??? I mean geez, this stuff is obvious. </font><br /><br />I can see your ADD is kicking in here. Please go back and review my post stating <i>where</i> and <i>how</i> cooling mechanism is on the SSME. This stuff is obvious for those of us who have the background and that's what <div class="Discussion_UserSignature"> </div>
<font color="yellow">"Upon contact with a corrosive fluid, such as saltwater, pitting corrosion will start to occur and eats away precious metals. "</font><br /><br />Would a thin layer of sacrificial zinc anode near the bell help a stage that plunges into the sea nozzles down? I recon it wouldn't help if nozzles are up and some seawater just splashes into the reaction chamber, it wouldn't form the necessary circuit with the zinc anode outside the bell, hard to imagine it inside it!. Then again hard to imagine a stage coming down engines upward because they are usually the heaviest part of empty stage.
<font color="yellow">"The thin layer of zinc would be gone about .02 seconds after engine start."</font><br /><br />Exactly, and that's why the zinc anode would have to be outside of the nozzle, possibly on the bell or somewhere in the supporting structure as long as there's electrical conductance between the anode and the area it's supposed to protect. When the whole thing becomes submerged in salt water the 'sacrificial' zinc and copper alloy in the bell form a kind of giant galvanic cell where zinc prefers to corrode instead of copper. AFAIK this phenomenon is widely exploited to protect the propellers and shafts of seagoing boats. <br /><br />edit: I'm not suggesting that this would magically turn SSME seawater proof, but it might help in designing an engine from the beginning to withstand relatively short exposures to such environment.
How about installing a water-tight valve at the free end...<br /><br />Yes, I know that saying "just install a water tight valve at the free end" is a gross oversimplification. Not saying it's an afternoon project or anything.<br /><br />But lets face it... if the rest of the engine doesn't leak fluids OUT ('cept from that open end at the bottom), then sea water shouldn't leak IN from any hole 'cept that one at the bottom. Find a way to close that off after you're done "leaking propellant under extreme force" as it were... and you're mostly there.<br /><br />Heck, might be impossible... <br />But I live on a coast, and know what salt water can do.<br />The only way to not wreck anything made of metal is to not get sea water on it in the first place... if you can't "seal" it up, you're not going to "refurbish" it after a swim in the ocean.<br /><br />Paul F.
Like I said... gross oversimplification..<br />But here's just one nutty idea thats probably impractical; After the engine is done blowing important stuff out the back end, have a separate system blow some sort of waterproof material (an expanding hardening foam comes to mind, even though that would probably not resist heat ) throught the piping to keep water out.<br />Of course, then getting that stuff OUT is a task by itself... <br />Maybe something that dissolves in a solvent that is otherwise harmless to the engine components.<br /><br />Also, like I said, maybe it IS impossible or impractical..<br />But you ARE correct that one sea water gets in there, it'll make a fine door stop.<br /><br />Paul F.
Somewhere, years ago, I saw a proposal for seperating the engines from a booster and parachuting them into the ocean. This particular proposal involved a folding domelike cover that shielded the engines on landing. It worked a bit like the folding helmets on the Russian launch and entry suits. Anyone remember this?<br />
Before everyone start to think about how to 'water-proof' the SSME, think about how difficult it is to separate the engine from the booster.<br /><br />Each SSME has 11 prop/fluids interfaces with the vehicle, not counting electrical power, commands, and telemetry (data links). Two main ones, LOX and LH2 low pressure turbopumps are attached to each feedline. The fuel inlet is secured with 0.408 inch diameter bolt in 36 places, while the oxidizer inlet with 48 likewise bolts. The 2 interfaces are designed to take the engine gimbal loads, they also must be able to partially support the engine weight in a horizontal position, so they were designed to be as strong as hell. The other fluid lines include pure GH2/ GO2, hydraulic and pure GHe interface, some with very high pressure connections. <br /><br />How does one propose to place explosive shape charges at the engine interface without damage the hardware? Think about the environment when the engine is operating, e.g., highest vibration, acoustic, and thermal environment on the vehicle. Think about the "unusable propellant" left in the feedlines and engine as "wet", what will happen to these "unusable propellant" upon experiencing a highly explosive separation? <br /><br />Upon 'successful separation', all interfaces will have open path for saltwater to free-flow into and include the high pressure turbopumps - the heart of SSME. <br /><br />On the exist of SSME, in additon to the main nozzle, there are at least 8 "drain lines" at exit. All can be subjected to saltwater intrusion with the most damaging one being directly through the nozzle as injectors are openly exposed. <br /><br />The saltwater corrosion problem is not just what you can see, it's what you can not see that worries you. Will there be any reduction of material strength that degrades SSME margins of safety? How does one diagnose? How does one even repair? <br /><br />This thing is not a simple RSRM, this thing has the world most sophisticated plumbi <div class="Discussion_UserSignature"> </div>
I'll take this opportunity to remention a couple of thought I had in the past, looking for some comments.<br /><br />Coaxial Staging.<br />This config would have the first stage surround the second stage like a sleeve. This is analagous to the solids arrayed around the perimeter of some rockets, only it would be a larger liquid propellent stage. The idea would be that when burned out, the exterior coaxial first stage would fall away and the inner second stage would ignite when clear.<br /><br />Some useless tech details (considering the source)...<br />Perhaps the stage would be manufactured by coiling fuel and oxidizer tanks at a gradual angle. The rocket engines themselves would be throttled like the N1 and not gimbled. Thus, there would be a large number of them /> 6.<br /><br />Benefits<br />The structural strength required for the first stage would be significantly reduced since it would not have to support the second stage and the payload. The loading point for the second stage would be arrayed around the base. The insulation requirements would be simplified since the coaxial rocket would have far less surface area exposed compared to a conventional stack. It may be that the second stage and inner facing surface of the first stage would require only minimal insulation being in a cold well.<br /><br />Payload at Bottom<br />This configuration would place the payload under the fuel tanks with a reusable engine module underneath the payload. At burnout, the tank would be jetosoned along with the engine module, the latter would reenter with a heat shield and parachute to a landing.<br /><br />Benefits<br />This would elliminate the need for the large fuel tanks to support the weight of the payload.<br />
I would think a TSTO system with a flyback booster would be a whole lot cheaper and have a far greater payload. I think this was one of the Shuttle proposals to begin with.<br /><br />When you start talking about parachuting the engines and protecting them from the salt water you are adding a lot of weight to your rocket, pretty soon you don't have enough left for payload. <div class="Discussion_UserSignature"> </div>
<font color="yellow">All that plus the gimble joint and the 2 Thrust Vector Control actuators. All the fluid, electrical and structural interfaces and dropping it in sea water. Then refurbish it for $750,000 makes for a impossible task. </font><br /><br />Exactly. This is the STRONGEST and the MOST COMPLEX part of interface. This is where the thrust of engine goes through the gimbal block pushing the entire vehicle forward.<br /><br />Proposing to separate safely and cleanly is just not possible without a whole lot of complexity and reduced mission reliability. It is far easier to recover the entire stage than attempt to separate engines from the booster. <div class="Discussion_UserSignature"> </div>
<font color="yellow">Coaxial Staging. <br />This config would have the first stage surround the second stage like a sleeve. This is analagous to the solids arrayed around the perimeter of some rockets, only it would be a larger liquid propellent stage. The idea would be that when burned out, the exterior coaxial first stage would fall away and the inner second stage would ignite when clear. </font><br /><br />Actually a smiliar concept was proposed during the SLI program, called "cross-feed". Imagine something like a Delta IV heavy (core with 2 liquid strap-on), or a "bimese" (parallel first and second stage), with all engines going during lift-off; except the propellant for the core engine (or 2nd stage engine) are "drained" from strap-on tanks (or 1st stage tanks) first so that they are first to be jettisoned (or separated). The core stage will then act as 2nd stage and continue to burn using its own propellant. Analyses have shown there's actual payload performance increase this way as a result. <br /><br /><font color="yellow">Some useless tech details (considering the source)... <br />Perhaps the stage would be manufactured by coiling fuel and oxidizer tanks at a gradual angle. The rocket engines themselves would be throttled like the N1 and not gimbled. Thus, there would be a large number of them /> 6. </font><br /><br />Well... that's not so good from a vehicle control point of view. Engine gimbal rate must be fast enough as a part of vehicle TVC system, e.g., don't wait till vehicle veer off course before the gimbal turned enough, otherwise one risks of over-correcting (flying like an "S" shape trajectory). <br /><br />Vehicle TVC using engines throttling, especially with engines feeding from different propellant tanks, can create complex vehicle dynamics that's difficult to control. First, the throttling process is transient in nature. Therefroe the time require to throttle must be tanken into account of the overall vehicle response ti <div class="Discussion_UserSignature"> </div>
Thanks Prop, I've never actually read about the interfaces between a SSME and the shuttle. I've always known its a complicated process to detach and reattach SSMES, but that gives me a lot more respect.<br /><br />What materials are the gymbal-joints made from? Ti? My mind has a hard time visualizing how such a part can be ON(or THE) the thrust vector, and yet still be expected to traverse under load. <div class="Discussion_UserSignature"> </div>
<font color="yellow">What materials are the gymbal-joints made from? Ti? </font><br /><br />Yes, it's a form of Titanium alloy. <div class="Discussion_UserSignature"> </div>
How about a booster that recycles some of the good things about the STS transportation system? 16 years ago I studied a conceptual design for a Space Shuttle Derived Vehicle that used a modified (extended/reinforced) shuttle ET setup for a vertical stack. Instead of the forward Ogive Liquid Oxygen Tank, a more conventional cylindrical tank with ellipsoidal forward and back domes were used, with a forward interstage connected to a payload faring. The original monster used a detachable engine module at the bottom with 8 SSME's and with its own dedicated RCS system, reentry heatshield, and parachutes for Ocean splash down. The pod could be ballasted for stable ocean recovery (engine up configuration by placing a ballast mass on the end of a suspension cable to shift the CG forward) however, I never got as far as figuring out how to keep the sea gulls from roosting on the engine bells! The original plan was to use 4 four segment SRB's for boosting, and the vehicle would come very close to orbiting 300,000 kg.<br /><br />More recently, re-examining the idea, I've come to the conclusion the design could be more effective if 4 RS-68's were used instead of a cluster of 8 SSME's, and instead of using 4 SRBs, using a cluster of 4 boosters using modifed Russian RD-170's utilizing a small amount of liquid hydrogen for coolant to prevent coking inside the cooling channels (to enhance reusability,) and using LOX and RP-1 as main propellants. I guess such a vehicle would probably be akin to the Russian Energya booster, but would have a little more payload capacity.
Thanks for the response, that's good analysis. I wasn't thinking so much of multiple tanks on the coaxial outter stage. I was suggesting a fuel and oxidizer tanks coiled around to make up the stage. In my mind it would have significant girth to be worthwhile. Concerning the complexity of the control system, I'm sure you are right. However, I will point out that this arrangement was successfully flown on the N-1 with PDP8 equivalent control computers. We haven't made much progress with rockets, but our control computers are awesome.<br /><br />It sounds like the payload at the bottom would be in for a shake-n-bake experience from hell. I'm sure American Airlines will one day adopt this configuration to torture space tourists in coach. But, I'll scratch that one off my list...<br />
<font color="yellow">Concerning the complexity of the control system, I'm sure you are right. However, I will point out that this arrangement was successfully flown on the N-1 with PDP8 equivalent control computers.</font><br /><br />Are you talking about this N-1?<br /><br />http://www.astronautix.com/lvs/n1.htm<br /><br />Launches: 4. Failures: 4. Success Rate: 0.000 pct. <br /><br />The type of throttling control system might work, but my gut feeling tells me that it is not optimum. However, the Russians have had brilliant rocket scientists and they probably figured out that, when you have 30 FRICKING ROCKET ENGINES ON THE FIRST STAGE !! It's probably easier to do differential throttling, than try to put hydraulic gimbal actuators (what's available at the time) on 30 engines and expect them to gimbal within the same tolerances !! <img src="/images/icons/smile.gif" /><br /> <div class="Discussion_UserSignature"> </div>
<font color="yellow">"that layout would enormously complicate escape scenarios."</font><br /><br />I think sitting next to the engines would greatly simplify escape scenarios; there would be none...
General questions for the history types: on the older Atlas, did the outside booster engines (the ones the dropped off) gimble? Also did the separating of those two engines (while the center and vernier engines contiued to operate) from what was just about an SSTO ever cause a loss of vehicle? I was alway impressed by that vehicle, it was very impressive for its time (1950's).
The N-1 never made orbit, but of all the launches the problems were not the direct result of the control system. As I recall, one of the failures was a staging problem after burn out. Engines exploding and the like took out a couple of the N-1s. The engines on the N-1 were incredibly advanced closed-loop design that shocked Aerojet with their efficiency. The Atlas (or maybe the Delta, I forget) heavy lifter derrived its engines from N-1 ancestry. Failure prone initial test flights weren't unsual for Soviet rocket developers, too much too soon perhaps, and It probably didn't help that one of the failures wiped out most of the staff. If the russians had continued test flights they likely would have gotten it right. What a difference that would have made for a continued presence on the moon! The N-1 is a great story to read about.<br />
I think it is like an opportunity staring us in the face. A Shuttle derived flyback First Stage and a Second Stage that would carry a variety of payloads into orbit and to an orbital destination. A big, vertically launched White Knight and an independant Second Stage. It could be built to any scale you wanted, four SSME's and two SRB's would probably put 100,000 pounds into orbit comfortably and be ready for re-use in weeks. <div class="Discussion_UserSignature"> </div>
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