tag:blogger.com,1999:blog-7598615455712402973.post4471202075357192049..comments2024-03-25T11:14:45.840-04:00Comments on Polymath: The Coming SSTO's: multi-Vulcain Ariane.Robert Clarkhttp://www.blogger.com/profile/16114043697010364282noreply@blogger.comBlogger5125tag:blogger.com,1999:blog-7598615455712402973.post-43317886964360322282013-04-01T13:21:22.939-04:002013-04-01T13:21:22.939-04:00Thanks for that. I had some questions on using sol... Thanks for that. I had some questions on using solids in some other applications I want to run by you that I'll discuss in an email.<br /><br /> Bob ClarkRobert Clarkhttps://www.blogger.com/profile/16114043697010364282noreply@blogger.comtag:blogger.com,1999:blog-7598615455712402973.post-1439331687854257402013-04-01T13:16:31.279-04:002013-04-01T13:16:31.279-04:00Research has already been done on replacing the cu... Research has already been done on replacing the current Al 2219 aluminum alloy of the Ariane 5 core with Al 2195, a lighter, but stronger, aluminum-lithium alloy:<br /><br />NASA Uses Twin Processes to Develop New Tank Dome Technology.<br />12.02.09<br />[quote] <br />Spherical tank dome combines friction stir welding and spun formation.<br />A full-scale spherical tank dome measuring 18 feet in diameter was produced from high-strength 2195 aluminum-lithium using twin manufacturing processes. Image credit: MT Aerospace<br />NASA has partnered with Lockheed Martin Space Systems in Denver, Colo., and MT Aerospace in Augsburg, Germany, to successfully manufacture the first full-scale friction stir welded and spun formed tank dome designed for use in large liquid propellant tanks.<br />The NASA and Lockheed Martin team traveled to Germany to witness the first successful aerospace application of two separate manufacturing processes: friction stir welding, a solid-state joining process, and spin forming, a metal working process used to form symmetric parts.<br />The twin processes were used by MT Aerospace to produce an 18-foot-diameter tank dome using high-strength 2195 aluminum-lithium. The diameter of this development dome matches the tank dimensions of the upper stage of the ARES I launch vehicle under development by NASA, as well as the central stage of the European Ariane V launcher.<br />"This new manufacturing technology allows us to use a thinner, high-strength alloy that will reduce the weight of future liquid propellant tanks by 25 percent, compared to current tank designs that use a lower-strength aluminum alloy that weighs more," said Louis Lollar, project lead for the Friction Stir Weld Spun Form Dome Project at NASA's Marshall Space Flight Center in Huntsville, Ala.[/quote]<br />http://www.nasa.gov/topics/technology/features/twin_dome.html <br /><br /> This could bring the payload of this SSTO into the 9,000 kg range.<br /><br /> Bob ClarkRobert Clarkhttps://www.blogger.com/profile/16114043697010364282noreply@blogger.comtag:blogger.com,1999:blog-7598615455712402973.post-33609619347203024442013-04-01T11:40:26.101-04:002013-04-01T11:40:26.101-04:00Well, as near as I can tell, from what little wa...Well, as near as I can tell, from what little was publicly released, the thrust oscillations were very bad with all the 5 segment motors. There was talk of lethality to an astronaut, until they added a big damping mass (a payload penalty). The real solution to combustion instability in a solid is a redesign of the propellant grain and internal volume shape in the motor. They didn't do that. Due diligence would say they should have, but pride rarely admits to an error. <br /><br />Solids have good application about the first half of a typical 1st stage burn of 2 stages. That's where thrust is a whole lot more important than high Isp. The rapid weight burnoff is also very important to vehicle acceleration in that early flight. Plus, there's also higher thrust per unit stage blockage area available, in spite of the much-higher inert weight, partly due to the internal-burning grain design, and partly due to the heavier molecular-weight gas properties. <br /><br />The best (and safest) are aluminized HTPB-AP propellants, with burn rates that fall in the 0.1 to 1 inch/sec range at 1000 psia, and Isp's in the 255-260 sec range in very large sizes. Shuttle SRB's used that stuff. So did we in the tactical missile business. That technology hasn't changed much since the 1960's. It's very mature. <br /><br />The longer 5-segment design simply brought into resonance a longer bore space to interact with the natural variability of solid surface burning. It's most likely a first longitudinal mode thing, although other, higher modes have been known. <br /><br />It was probably greatly exacerbated by the erosive-burning effects of a higher mass flux at the exit to the longer grain design. I've seen that many times before. The first thing to have tried would have been a larger (or better-yet, tapered) bore in the aft segment. But, they didn't do that.<br /><br />GW<br /><br />Gary Johnsonhttps://www.blogger.com/profile/06723964751681093047noreply@blogger.comtag:blogger.com,1999:blog-7598615455712402973.post-89206691207544334522013-04-01T01:01:17.323-04:002013-04-01T01:01:17.323-04:00 Thanks for the info. I am not a fan of solids bec... Thanks for the info. I am not a fan of solids because I feel they do not advance the technology. <br /> Ground tests have been done of the 5-segments. I wonder what the thrust oscillations look like in those tests.<br /><br /><br /> Bob ClarkRobert Clarkhttps://www.blogger.com/profile/16114043697010364282noreply@blogger.comtag:blogger.com,1999:blog-7598615455712402973.post-47824271620997612432013-03-29T18:37:09.236-04:002013-03-29T18:37:09.236-04:00What usually sets case thickness on a solid is max...What usually sets case thickness on a solid is max expected operating pressure (as hoop stress). This is especially true in larger sizes like SRB's, but largely true even in the far smaller sizes of tactical rockets. <br /><br />Man-rating with a solid merely requires a lot of tests with no problems experienced, something the 5-segment SRB/Liberty was not honestly able to claim. That "thrust oscillation" they "solved" with a damper did not fool me: that was a fundamental solid motor longitudinal-mode combustion instability, induced by the extra length of the 5-segment motor, with otherwise the same 4-segment solid propellant grain design. <br /><br />Instabilities like that tend to blow up solid motors, sooner or later. Better sooner than later, but it didn't happen (yet) in the ground tests of the 5 segment motor. <br /><br />Interesting, is it not, that the motor NASA actually did fly was 4 live segments and one inert dummy segment ??!!?? Wanna guess why?<br /><br />Solid motor combustion instability is something the liquid guys at NASA (and ULA) know nothing about: their liquid-engine combustion instabilities are quite different physics entirely. <br /><br />NASA has no long-experienced solid motor guys. And they never have. Those guys were at Thiokol, UTC, ATK, etc. Still are, if not dead or retired. Or working in some other industry, like me. <br /><br />The 4-segment SRB on Space Shuttle was indeed "man-rated", in spite of what I always considered to be a defective segment joint design mandated by a NASA not qualified to judge the merits of the design. They simply made it even worse after the Challenger accident, with that idiotic 3-O-ring design. <br /><br />Even the 2-O-ring design before Challenger was idiotic. And I really do mean idiotic. Idiotic! Truly idiotic!!!! It really was a very egregious mis-design mandated by idiots who very clearly knew no better. <br /><br />The only reason it (that awful 3-O-ring "design") flew successfully for all those flights after Challenger was that "they never again flew cold" (just as Chuck Yeager recommended to the Rogers Commission in its very first meeting), not because of the egregiously-mis-designed post-Challenger 3-O-ring SRB segment joint.<br /><br />NASA still (to this very day) does not know anything truly useful about solid rocket design. I do, I worked in a for-profit solid rocket company for 16 years. <br /><br />ESA knows incredibly-little about solid rockets, basically they know only what NASA has told them. NASA? Really?<br /><br />So, who would you believe? NASA? Or someone like me, who did it for a living in a for-profit company?<br /><br />GW<br /><br /><br /><br /> Gary Johnsonhttps://www.blogger.com/profile/06723964751681093047noreply@blogger.com