I think they are going to composites which are lighter than aluminum and also stronger pound for pound. Titanium is heavier than aluminum and does have a higher melting point, but not necessary on the tanks which is 90% of the body of the booster.
Quote from: spacenut on 08/24/2016 08:22 pmI think they are going to composites which are lighter than aluminum and also stronger pound for pound. Titanium is heavier than aluminum and does have a higher melting point, but not necessary on the tanks which is 90% of the body of the booster. Ah, I see.How do composites compare to titanium? Titanium is 40% stronger than aluminium alloy, pound for pound, so you could use almost 30% less of it by weight and still have the same tank strength.
Quote from: sevenperforce on 08/24/2016 08:59 pmHow do composites compare to titanium? Titanium is 40% stronger than aluminium alloy, pound for pound, so you could use almost 30% less of it by weight and still have the same tank strength.How well understood are the properties of titanium alloys at cryogenic temperatures? Is it compatible with direct LOX contact?
How do composites compare to titanium? Titanium is 40% stronger than aluminium alloy, pound for pound, so you could use almost 30% less of it by weight and still have the same tank strength.
Titanium is not a miracle metal; it's generally more difficult to work for large structural members and actually, I doubt SpaceX could afford the material cost hit even if they could work through the manufacturing and assembly process changes. This isn't a Cold War project like the B-70 (which was ultimately too expensive to produce more than the 3 airframes anyway).
With regard to use on BFS, higher-density (afaik) actually hurts you as the secondary radiation from gamma rays striking the titanium would be far worse than if they strike a less dense material
Quote from: octavo on 08/25/2016 10:10 amWith regard to use on BFS, higher-density (afaik) actually hurts you as the secondary radiation from gamma rays striking the titanium would be far worse than if they strike a less dense materialWouldn't be an issue for the first-stage booster.
Quote from: sevenperforce on 08/25/2016 07:21 pmQuote from: octavo on 08/25/2016 10:10 amWith regard to use on BFS, higher-density (afaik) actually hurts you as the secondary radiation from gamma rays striking the titanium would be far worse than if they strike a less dense materialWouldn't be an issue for the first-stage booster.But having booster and upper stage made of different materials eliminates any production synergism. it would require separate tank production lines.
Well, the MCT is (purportedly) more than just a second stage, so comparing BFR to MCT is less like comparing Falcon 9's stage 1 to stage 2 and more like comparing Falcon 9's stage 1 to the Dragon 2.
Quote from: sevenperforce on 08/25/2016 07:37 pmWell, the MCT is (purportedly) more than just a second stage, so comparing BFR to MCT is less like comparing Falcon 9's stage 1 to stage 2 and more like comparing Falcon 9's stage 1 to the Dragon 2.No, it is still the same comparison. The MCT will have a propulsion system with elements common to the booster.
This isn't a Cold War project like the B-70 (which was ultimately too expensive to produce more than the 3 airframes anyway).
But it will also have a pressure vessel designed for human occupancy, so....
For more than 50 years, heavy metal cryogenic tanks have carried the liquid hydrogen (LH2) and oxygen necessary to launch vehicles into space. But in a joint effort, NASA and The Boeing Co. (Chicago, IL, US) have designed, fabricated and tested a composite cryotank that, if scaled up to current space launch system dimensions, would weigh 30% less and cost 25% less than the best aluminum-lithium cryotanks used today, and could warrant transport of as much as 1,400 kg of additional payload to low-Earth orbit and beyond.The US$25 million Composite Cryotank Technologies and Demonstration (CCTD) project, part of the NASA Space Technology Mission Directorate’s Game Changing Development (GCD) program, involved a team of Boeing and NASA engineers. “This is the first effort to successfully build and test a tank of this scale,” says Douglas McCarville, Technical Fellow at Boeing Research & Technology (BR&T) in Seattle, WA, US. “The tank would work for liquid oxygen or liquid hydrogen on a variety of next-generation launch systems.”
Might make sense to make /portions/ of Falcon out of Titanium. Like the grid fins or maybe parts of the thrust structure. To enhance durability and reduce the amount of TPS you need.But I don't think they'll make the tanks (etc) out of it. Hard to work, not generally as good structure/mass (the lower density of aluminum helps for compressive structures in ways beyond pure strength/weight ratio because of reduced buckling).
But having booster and upper stage made of different materials eliminates any production synergism. it would require separate tank production lines.
Quote from: Herb Schaltegger on 08/24/2016 10:33 pmThis isn't a Cold War project like the B-70 (which was ultimately too expensive to produce more than the 3 airframes anyway).Only two XB-70s were built (the second crashed, the first is in the USAF museum in Dayton, OH), and they were almost entirely made of stainless steel, with titanium just in the most critical parts.The SR-71, on the other hand...
Quote from: Robotbeat on 08/26/2016 07:37 pmMight make sense to make /portions/ of Falcon out of Titanium. Like the grid fins or maybe parts of the thrust structure. To enhance durability and reduce the amount of TPS you need.But I don't think they'll make the tanks (etc) out of it. Hard to work, not generally as good structure/mass (the lower density of aluminum helps for compressive structures in ways beyond pure strength/weight ratio because of reduced buckling).Called it.
Titanium grid fins for supersonic rocket manufacturedQuote from: LIN Industrial3D printed plastic grid fins we currently use can't withstand the dynamic pressure and heating at supersonic. That's why we have started manufacturing titanium grid fins. They are cut from a single piece of titanium with a CNC machine:
3D printed plastic grid fins we currently use can't withstand the dynamic pressure and heating at supersonic. That's why we have started manufacturing titanium grid fins. They are cut from a single piece of titanium with a CNC machine:
Quote from: Robotbeat on 08/18/2017 04:09 amQuote from: Robotbeat on 08/26/2016 07:37 pmMight make sense to make /portions/ of Falcon out of Titanium. Like the grid fins or maybe parts of the thrust structure. To enhance durability and reduce the amount of TPS you need.But I don't think they'll make the tanks (etc) out of it. Hard to work, not generally as good structure/mass (the lower density of aluminum helps for compressive structures in ways beyond pure strength/weight ratio because of reduced buckling).Called it.For historical interest only, mvpel may have called it first. The idea was certainly rattling around:Quote from: mvpel on 06/02/2016 12:19 amTitanium grid fins for supersonic rocket manufacturedQuote from: LIN Industrial3D printed plastic grid fins we currently use can't withstand the dynamic pressure and heating at supersonic. That's why we have started manufacturing titanium grid fins. They are cut from a single piece of titanium with a CNC machine:
shout out to dorkmo for starting that clairvoyant thread
On a slightly more factual note, I was always impressed that the Soviet Union managed to build whole large submarine pressure hulls out of the stuff. None of which is germane to Falcon 9, of course!
Actually they are XB-70A's the original XB-70 programme ended when the B-70 programme was cancelled. XB-70A research programme replaced the XB-70 development programme: http://www.boeing.com/history/products/xb-70-valkyrie.page
Yeah, it's definitely possible to get lower than 4% weight for legs. This is a point HMXHMX often makes.
Quote from: Robotbeat on 08/24/2017 12:27 pmYeah, it's definitely possible to get lower than 4% weight for legs. This is a point HMXHMX often makes.True but that misses the point. It's basically a time honored heuristic of aircraft design. But AFAIK there is no equivalent heuristic for VTOL, although I think Armadillo and Masten have both done enough to have some number in mind depending on wheather you want it to stand on them fully fueled or only deploy when the tanks are nearly empty. That's clearly going to make a big difference to what mass you need to assign given loads. IDK, for a fully fueled VTO stage 4% might be too low, while for gear that's only going to be needed during it's near empty landing it's grossly high, but by how much? "Vertical Landing" (as a thing) is not going to go away any time soon.
Quote from: john smith 19 on 08/24/2017 04:11 pmQuote from: Robotbeat on 08/24/2017 12:27 pmYeah, it's definitely possible to get lower than 4% weight for legs. This is a point HMXHMX often makes.True but that misses the point. It's basically a time honored heuristic of aircraft design. But AFAIK there is no equivalent heuristic for VTOL, although I think Armadillo and Masten have both done enough to have some number in mind depending on wheather you want it to stand on them fully fueled or only deploy when the tanks are nearly empty. That's clearly going to make a big difference to what mass you need to assign given loads. IDK, for a fully fueled VTO stage 4% might be too low, while for gear that's only going to be needed during it's near empty landing it's grossly high, but by how much? "Vertical Landing" (as a thing) is not going to go away any time soon.The F9 is about 27 tonnes (or tons?) at landing according Hans K. The legs are about as much as a Model S (about 2,000 kg) according to Elon. So that's between 7.4% and 8.1% of the landing mass, depending on whether Hans meant short or metric tons.Either way, a lot more than 4%...
Well that's intriguing. Definitely not my instinct would have been. So 7-8+% of gross landing weight. I'm pretty sure one of the (theoretical) benefits of VL was expected to be it's very low landing gear penalty compared to the wheeled landing gear on HTOL or VTOHL systems.This suggests that has not really worked out IRL. Perhaps the new on deck grabber robot will help?
That much weight for the landing gear just seems way to high. Just my opinion.John
The legs are really long. That's why they weigh a lot. A squatter stage could use shorter and more efficient legs.
No comments yet about the ability/complexities to FSW Ti?