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#11
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BFR early next year.
On Mar/13/2018 at 6:09 PM, Niklas Holsti wrote :
On 18-03-13 23:01 , Alain Fournier wrote: Â*Â* ... I would be very surprised if BFS had anything close to SSTO capability. It is a spaceship not a launch vehicle. Musk has said the BFS can do SSTO. Quotes from Musk's answer at https://www.teslarati.com/elon-musks...bfs-spaceship/, section headed "DEVELOPMENT SCHEDULE": --- start quote: Q: ... Will we see BFS hops or smaller test vehicles similar to Grasshopper/F9R-Dev? Facilities being built? Propellant plant testing? etc. etc. A (Elon): Will be starting with a full-scale Ship doing short hops of a few hundred kilometers altitude and lateral distance. Those are fairly easy on the vehicle, as no heat shield is needed, we can have a large amount of reserve propellant and don’t need the high area ratio, deep space Raptor engines. Next step will be doing orbital velocity Ship flights, which will need all of the above. Worth noting that BFS is capable of reaching orbit by itself with low payload, but having the BF Booster increases payload by more than an order of magnitude. Earth is the wrong planet for single stage to orbit. No problemo on Mars. --- end quote. Thanks for that. The web page you cited is very interesting. Alain Fournier |
#12
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BFR early next year.
JF Mezei wrote on Tue, 13 Mar 2018
17:01:25 -0400: On 2018-03-13 05:53, Jeff Findley wrote: BFS. It could be that the first BFS would be similar to Grasshopper or Enterprise in that it won't have all the systems necessary for supporting a crew in space. Automated testing only. Thanks. Hadn't thought of that. Does the ability to land on Earth absolutely imply the ability to take off from Earth? (I know BFS is to be able to take off from Mars). It can certainly take off from Earth. Remember, it's intended to be able to do transcontinental flight without a booster. It's also intended to be able to take off from Mars into TEI and then do the insertion and land on Earth. (I realise the prototype will be empty shell and much lighter so usable for tests, just curious about whether the ability to take off from Earth comes automatically with ability to land on Earth). For some definition of 'take off' it does, but in this case BFR Spaceship is capable of flying to orbit (if it has all its engines) without a booster. I question the 'empty shell' assumption. Musk has stated that it probably won't have the vacuum engines installed, since they're not needed initially. I know that spaceX has been pushing composite tank size limits by a huge margin for the first stage. Is the 2nd stage/BFS also beyond current "commodity" tech for tanks? I'm guessing, but I would say yes. BFR Spaceship carries 1,000 tonnes of fuel and oxidizer. You can do a partial fill for short "hops". Does your car's gas tank need to be full to make a trip to the grocery store? Thinking in terms of keeping the methane liquid long enough in such a large tank. Will the tanks be pressurized to maintain the methane liquid, or will it be a "reduce the boiling rate and vent excess pressure" on pad like for shuttle's ET? There will presumably be some boil off, although that's more manageable given the liquification point of propane as compared to hydrogen. The bulk of the fuel in the tanks will still be liquid, right up until you're out of fuel entirely. Note: you car may not worry about fuel sloshing around in a small car tank, but fuel trucks worry very much about it when the tanks are not full, which is why they have separate tanks in the big one, and each of those smaller tanks have baffles to reduce movement as truck accelerates/brakes/turns. The rocket is under acceleration. Fuel won't 'slosh' much, if at all. -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
#14
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BFR early next year.
Jeff Findley wrote on Tue, 13 Mar 2018
18:40:53 -0400: The prototypes had better be close to BFR/BFS in many ways, or it wouldn't be very useful would it? It will probably fly without the vacuum engines or a heat shield, as those aren't necessary for 'grasshopper' tests. However, Musk is talking quickly moving to orbital testing, where both those things ARE necessary. -- "The reasonable man adapts himself to the world; the unreasonable man persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." --George Bernard Shaw |
#15
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BFR early next year.
On Mar/13/2018 at 5:01 PM, JF Mezei wrote :
Does the ability to land on Earth absolutely imply the ability to take off from Earth? (I know BFS is to be able to take off from Mars). (I realise the prototype will be empty shell and much lighter so usable for tests, just curious about whether the ability to take off from Earth comes automatically with ability to land on Earth). Not really. You land with the tanks nearly empty. If you have only enough thrust to land with nearly empty tanks, you won't have enough thrust to take off with tanks full. Alain Fournier |
#16
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BFR early next year.
On 18-03-14 00:36 , Jeff Findley wrote:
In article , lid says... ... For small, Grasshopper-like hops, it would be enough to mount just one of the two (or are there now more than two?) BFS sea-level engines. Agreed. Two, from this pictu On the other hand, at https://www.teslarati.com/elon-musks...bfs-spaceship/, Musk is quoted as follows (in the section headed "Raptor and rocket propulsion"): "If you just have two engines that do everything, the engine complexity is much higher and, if one fails, you’ve lost half your power. Btw, we modified the BFS design since IAC to add a third medium area ratio Raptor engine partly for that reason (lose only 1/3 thrust in engine out) and allow landings with higher payload mass for the Earth to Earth transport function." (Gosh, perhaps the "Earth to Earth transport function" is to be taken seriously...) -- Niklas Holsti Tidorum Ltd niklas holsti tidorum fi . @ . |
#17
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BFR early next year.
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#18
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BFR early next year.
In article ,
lid says... On 18-03-14 00:36 , Jeff Findley wrote: In article , lid says... ... For small, Grasshopper-like hops, it would be enough to mount just one of the two (or are there now more than two?) BFS sea-level engines. Agreed. Two, from this pictu On the other hand, at https://www.teslarati.com/elon-musks...bfs-spaceship/, Musk is quoted as follows (in the section headed "Raptor and rocket propulsion"): "If you just have two engines that do everything, the engine complexity is much higher and, if one fails, you?ve lost half your power. Btw, we modified the BFS design since IAC to add a third medium area ratio Raptor engine partly for that reason (lose only 1/3 thrust in engine out) and allow landings with higher payload mass for the Earth to Earth transport function." (Gosh, perhaps the "Earth to Earth transport function" is to be taken seriously...) This is all very fluid right now, isn't it? Jeff -- All opinions posted by me on Usenet News are mine, and mine alone. These posts do not reflect the opinions of my family, friends, employer, or any organization that I am a member of. |
#19
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BFR early next year.
In article ,
says... On 2018-03-13 18:40, Jeff Findley wrote: They built a full scale composite tank and pressure tested it to destruction a couple years ago. http://www.businessinsider.com/space...nk-ocean-ship- test-2016-11 But correct to state that the destructive test was only a few months ago? I seem to recal some tank video that was much more recent than 2016. The prototypes had better be close to BFR/BFS in many ways, or it wouldn't be very useful would it? Depends on the goal of that test flight. It could very well be that a real BFS ship is ready to be built with the structural aspects all done, but will go without payload (the crew compartment) On the other hand, there maty be PR/marketing pressres to have a flight early, at which point engineers are told to focus on engines/tanks and just build a epty shell around iot that looks like BFS. (the real structsures/shell can be designed/built later). Or, we could see naked engines/tanks go up and down. It really depends on how far they are in the design. The article was dated November 16, 2016 and said: SpaceX announced on Wednesday that it had successfully completed a critical test of a huge piece of its Mars spaceship ? a giant and potentially explosive black orb. Also, the Twitter video of them loading the tank on the barge is dated 16 months ago. That is consistent with the news article being put out in November 2016. So, it was only 16 months ago, not two years. Still, the tank was built and was tested. That "retired" much of the risk of using such large composite tanks. At least their shape is simple compared to the failed X-33 tanks (which was a geometrically complex multi-lobed design). Jeff -- All opinions posted by me on Usenet News are mine, and mine alone. These posts do not reflect the opinions of my family, friends, employer, or any organization that I am a member of. |
#20
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BFR early next year.
Niklas Holsti wrote on Wed, 14 Mar
2018 09:22:15 +0200: On 18-03-14 00:36 , Jeff Findley wrote: In article , lid says... ... For small, Grasshopper-like hops, it would be enough to mount just one of the two (or are there now more than two?) BFS sea-level engines. Agreed. Two, from this pictu On the other hand, at https://www.teslarati.com/elon-musks...bfs-spaceship/, Musk is quoted as follows (in the section headed "Raptor and rocket propulsion"): "If you just have two engines that do everything, the engine complexity is much higher and, if one fails, you’ve lost half your power. Btw, we modified the BFS design since IAC to add a third medium area ratio Raptor engine partly for that reason (lose only 1/3 thrust in engine out) and allow landings with higher payload mass for the Earth to Earth transport function." (Gosh, perhaps the "Earth to Earth transport function" is to be taken seriously...) Yeah, I thought all the later drawings and such that I'd seen showed 3 atmospheric engines vice 2. I believe it can still land on a single engine, though. -- "The reasonable man adapts himself to the world; the unreasonable man persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." --George Bernard Shaw |
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