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Falcon Heavy Static Fire
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#12
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Falcon Heavy Static Fire
JF Mezei wrote:
On 2018-01-28 08:44, Jeff Findley wrote: In article , says... Musk just Tweeted that they are aiming for Feb 6 launch for Falcon Heavy I saw that last night. So only a bit more than a week away. Exciting times. Would it be fair to state that in terms of "spectacular" rocket-goes-kablooie" during launch and near the pad, majority would be the engine turbines that go amok and break apart causing a great big ball of fire ? No. Much more likely is that simultaneous ignition of all engines fails and this stresses the connections between the cores to the point where the booster breaks up. Considering the Merlin engines have been tested quite a bit, shouldn't there be a good confidence level and Musk's "it will likely fail" is just PR stunt to make the lanch more "interesting" ? No. He's just 'managing expectations' on a very challenging initial launch. I'm sure that SpaceX is much more interested in data they'll collect during the flight than they are in getting a Tesla roadster to Mars orbit. Space X web site shows that the stage 2 for Falcon Heavy will be identical to Stage 2 from Falcon 9 (397s of burn time, 934kN thrust). So if Falcon Heavy is able to throw a car out of Earth orbit into Sun, something Falcon 9 can't do, it would mean that Falcon Heavy will be dropping stage2 and the car at higher orbit/velocity, right ? Who said anything about putting a car out of Earth orbit into the Sun? Here's a hint. Falcon 9 FT can put around 4 MT into TMI. That's easily a car to Mars. Falcon Heavy can put 16.8 MT into TMI. Falcon 9 Stage 1 burns for ~160 seconds. Will the side boosters on Falcon Heabvy burn for same amount of time and detach at roughly same altitude/speed as Falcon 9 (somewhere between 80 and 100km altitude) ? I would expect the separation TIME to be the same, since the side boosters burn at 100% from launch to burnout. The difference, of course, is that once the side boosters separate a Falcon Heavy still has a big chunk of a Falcon 9 core performance left, since the center core throttles back until separation of the side boosters. If so, correct to state that this operation will occur in much thinner almosphere than the Shuttle SRB separation and this far less aerodynamic challenges? Yes, the separation will be higher than Shuttle SRBs. However, your conclusion doesn't follow, since the concern is Q rather than just air density and Q is affected by velocity. Falcon Heavy separation will be higher than Shuttle SRB separation, but will occur at higher velocity. Since the core stage will throttle down early on which will allow it to continue to push the stack after the boosters have left, it also means that it will be dropping its payload at far higher and faster (and more distance from launch site) than a Falcon 9 would have. Only for identical payloads. What you really buy is more payload to the same place. If you don't need the extra payload capability you just shut the stage down early. Does this imply that the core stage will have to keep a lot more reserve fuel to "brake" to drop out of the sky? Would the barge be located signifancly more downrange from the pad so that the core stage wouldn't have to travel as much on its return trajectory? No. -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
#14
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Falcon Heavy Static Fire
In article ,
says... On 2018-01-29 06:21, Jeff Findley wrote: Entering earth orbit would be pointless on a flight without a crew. I was thinking more in terms of going around until it is aligned to the path to escape Earth and become in orbit around the sun. (aka: liberal launch window because you adjust when you start the escape engine burn). You can also do that by carefully choosing the time of the launch. We'll see on launch day, won't we? SpaceX usually does a good job with their live coverage (of non-classified) missions. would also be a waste of fuel/oxidizer, so I seriously doubt they'd do that. In what way would it be a waste? Because it might slow down at perigee due to some thin atmosphere? That and if you're aiming for an escape trajectory, you don't care how low "perigee" is, because you're never going to experience it. So why waste fuel on raising it about the ground at all? The latter. Lingering doesn't do anything but use up some of the limited (battery and LOX boil off) lifetime of the upper stage. Fair enough. But... Earth is ~150 million km orbit, Mars is ~228 million km. Or roughly 78 million km difference in diametre. If Stage 2 only has "hours" autonomy on batteries, how does it expect to not onlu escape Earth's travity, but also increase its orbit around the sun by som 78 million km and circularize it? It's not going to be in a circular orbit. It's going to be in a Hohmann transfer orbit between earth's orbit and Mars' orbit. It's just that Mars won't be there when it gets there. Presumably earth won't be there either With all the fancy orbital mechanic tricks, doesn'it need at least a quarter orbit around the sun to get into mostly circular orbit? (which would be 171 days. (Mars tear is 687). Seems to me that spending an extra 900 minutes for 1 spin around the Earth shouldn't be a big deal in terms of autonomy. No, as long as you escape earth's orbit, you're in a solar orbit. SpaceX doesn't care if it's circular, why would they? They're simulating a Mars mission, without entering Mars orbit. Again Hohmann transfer orbit between earth orbit and Mars orbit. That tells you nothing of second stage performance. If all they wanted was performance of the boosters and core, they'd have put a dummy upper stage on top. They didn't. Surely they'll want to measure the final orbital parameters of the combined upper stage and dummy payload. Since second stage is allegedly identical to that of Falcon 9, don't they already have full performance data on it? Not in this configuration. From engine performance point of view, is there much difference in "vacuum" between where Falcon 9 normally delivers stage2 and where Falcom Heavy will deliver it ? USAF is certifying Falcon Heavy for launches, so they want to test the entire system "end to end". As do the ULA EELVs. But EELVs don't land back at a designated spot. So the big diffrerences in what Falcon Heavy can do (high/fast for light loads) or low/slow for heavy loads) would result in very different parameters for the stages to re-enter and land. USAF doesn't much care about landings, unless it screws up their launch. So SpaceX wants to test the entire system "end to end", including landings so that the USAF will have confidence in the entire system, including landings. Google broken? SSME's got tweaked a bit but more or less remained the same from a performance perspective. Orbiters later than Columbia were built a tad bit lighter, but in the overall scheme of things that wasn't very much mass saved. Wasn't there much weight saved when top skin was changed from tiles to blankets? Wight saved when buil-in airlock removed ? glass cockpit upgrades and many structural changes and some insyrumentation removed in the structure ? A tiny amount in all those cases, except "structural changes". That's why Columbia is heavier. It was the first space-worthy orbiter, so didn't get the full benefit of the structural weight reduction program. Also, didn't SSMEs get performance upgrades of somewhere around 5% since they would go to 105% of rated performance during launch ? Yep, another small amount there as well. The program was pretty desperate to reduce mass on the orbiter and the ET. They were scrubbing mass from the most insignificant of things to save a kg or two here and there. As far as I know, the program never quite met it's original payload goals (as set by the USAF). Doubly true with Columbia. It was the "heavy" orbiter and was relegated to missions that were on the low end of the performance spectrum. Easier. But easier still isn't a sure thing. There really is no perfect substitute for flight testing in a scenario like this. You simply can't test this on the ground. You run your simulations and you fly a test flight. At altiutude boosters are expected to pop out, is atmosphere/drag a consideration for the few moments where there is danger? Or Is this basically a newtonian process of pusging the boosters out gently and they continue to gently move away as core accelerates ahead ? It depends on Q, which is the dynamic pressure experienced at the speed and altitude that the boosters drop off. It'll be higher than SRB sep on the shuttle, but will surely be faster as well. Dynamic Pressure https://www.grc.nasa.gov/www/k-12/ai.../dynpress.html See that squared term on velocity in the dynamic pressure equation? The devil is in the details here. We'll know more come launch day when the live feed will show altitude and velocity at booster separation. Then you can "plug and chug" to get Q. I guess the one big variable is that since the boosters are not expandable, it isn't just ensuring they don't cause damage to core stage, but also that the core stage's engines don't burn the boosters as it accelerates ahead of them. Well, yeah, if you want to reuse them that's a consideration, isn't it? I wonder what sort of video feeds we'll have of that operation. Falcon 9 typically has at least one rear facing camera on the "interstage" section of the first stage. I'd imagine for Heavy, they'll have at least one camera on the "interstage" for each booster (maybe more for redundancy). The engineers are going to want data on the separation. Cameras are a great way to get some of that data. Google it. Look for the exclusion zones for boats and aircraft. I googled exclusion zone atlantic falcon and it gave me unexpected results... some footbal team :-) OK, so he core still lands well inside the US territorial waters. Does this mean that it kills forwards velocioty and starts to travel back to KSC on its way down like Falcon 9s ? Or could this distance still allow a ballistic of rapid up, drop stage 2, and rapid down, always with eastbound horizontal speed ? Sorry, I don't have time to look this up. I need to get to work on time. I did see a pic on Twitter, surely taken from whatever US Government website issues warnings to ships and the like. The information is out there, you just have to look for 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. |
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Falcon Heavy Static Fire
Jeff Findley wrote:
In article , says... JF Mezei wrote: On 2018-01-28 08:44, Jeff Findley wrote: In article , says... Musk just Tweeted that they are aiming for Feb 6 launch for Falcon Heavy I saw that last night. So only a bit more than a week away. Exciting times. Would it be fair to state that in terms of "spectacular" rocket-goes-kablooie" during launch and near the pad, majority would be the engine turbines that go amok and break apart causing a great big ball of fire ? No. Much more likely is that simultaneous ignition of all engines fails and this stresses the connections between the cores to the point where the booster breaks up. The Falcon Heavy hot fire test already happened and was successful, so I personally think that's unlikely to happen. True, but it's probably still the most likely 'dramatic' failure close to the pad. Also, from what I've read, ignition of the Merlin engines does not occur simultaneously on Falcon Heavy. It certainly didn't during the hot fire test. There was significant time (seconds) between core starts. -- "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 |
#16
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Falcon Heavy Static Fire
JF Mezei wrote:
On 2018-01-29 06:21, Jeff Findley wrote: Entering earth orbit would be pointless on a flight without a crew. I was thinking more in terms of going around until it is aligned to the path to escape Earth and become in orbit around the sun. (aka: liberal launch window because you adjust when you start the escape engine burn). Just use a reasonable launch window and that's not necessary. would also be a waste of fuel/oxidizer, so I seriously doubt they'd do that. In what way would it be a waste? Because it might slow down at perigee due to some thin atmosphere? Because you have to do a high burn to get an orbit that you wouldn't need to do if you go directly to a transfer path. The latter. Lingering doesn't do anything but use up some of the limited (battery and LOX boil off) lifetime of the upper stage. Fair enough. But... Earth is ~150 million km orbit, Mars is ~228 million km. Or roughly 78 million km difference in diametre. If Stage 2 only has "hours" autonomy on batteries, how does it expect to not onlu escape Earth's travity, but also increase its orbit around the sun by som 78 million km and circularize it? With all the fancy orbital mechanic tricks, doesn'it need at least a quarter orbit around the sun to get into mostly circular orbit? (which would be 171 days. (Mars tear is 687). Seems to me that spending an extra 900 minutes for 1 spin around the Earth shouldn't be a big deal in terms of autonomy. Since they're just going out to Mars orbit (in a transfer ellipse) and not actually going anywhere near Mars, why would they get any kind of 'circular orbit'. That tells you nothing of second stage performance. If all they wanted was performance of the boosters and core, they'd have put a dummy upper stage on top. They didn't. Surely they'll want to measure the final orbital parameters of the combined upper stage and dummy payload. Since second stage is allegedly identical to that of Falcon 9, don't they already have full performance data on it? But they don't have any data on its performance starting from where a Falcon Heavy launch leaves it. From engine performance point of view, is there much difference in "vacuum" between where Falcon 9 normally delivers stage2 and where Falcom Heavy will deliver it ? Depends on a lot of things. There certainly could be. As do the ULA EELVs. But EELVs don't land back at a designated spot. So the big diffrerences in what Falcon Heavy can do (high/fast for light loads) or low/slow for heavy loads) would result in very different parameters for the stages to re-enter and land. Would it? Returning stages hit terminal velocity due to air drag on the way down, regardless of how 'fast' and 'high' they start from. snip remaining bootless speculation -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
#17
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Falcon Heavy Static Fire
JF Mezei wrote:
On 2018-01-30 06:09, Jeff Findley wrote: That and if you're aiming for an escape trajectory, you don't care how low "perigee" is, because you're never going to experience it. So why waste fuel on raising it about the ground at all? Side question: If you are in orbit for a few hours and then leave to Jupiter and beyond. Does spending fuel to circularize that orbit at apogee for those few hours end up reducing fuel needed once you fire engines to get to espape velocity? No. In fact, it's usually the reverse. Since a craft in circular orbit at altitude X has more energy than same craft at elliptical orbit with apogee at X, I am wondering if that extra energy offers *any* help when leaving to escape Earth. Your premise is faulty and poorly thought out. And the answer is essentially 'no'. It's not going to be in a circular orbit. It's going to be in a Hohmann transfer orbit between earth's orbit and Mars' orbit. It's just that Mars won't be there when it gets there. Presumably earth won't be there either Hohmann, from what that Internet thing tells me is to transfer from one circular to another circular orbit and requires a burn once you reach the destination altitude to "stay there". Correct. This is the difference between TMI and Mars orbit. If the Tesla is going to be in elliptical orbit with perigee at Earth and Apogee at Mars altitudes, doesn't that have a risk that it will come back to Earth at some point ? Odds are tiny and it's easily prevented. (this is in a context of battery autonomy and ability to fire engines much later to at least raise perigee to above earth's orbit around sun) simulating a Mars mission, without entering Mars orbit. Again Hohmann transfer orbit between earth orbit and Mars orbit. I was confused by reading that they would send the Tesla into an orbit around the sun matching Mars. (as opposed to stating it was a highly elliptical orbit around the sun between Earth and Mars altitudes). They didn't say that. Hence your confusion. Since second stage is allegedly identical to that of Falcon 9, don't they already have full performance data on it? Not in this configuration. So what is different in terms of Stage 2's performance if the hardware is identical? What is the difference in terms of your car's performance in accelerationg from 30 MPH on a road 2,000 feet MSL and accelerating from 50 MPH on a road 5,000 feet MSL if the hardware is identical? snip usual Mayfly Mauling a Mortified Mare -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
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Falcon Heavy Static Fire
JF Mezei wrote:
On 2018-01-30 08:12, Fred J. McCall wrote: Would it? Returning stages hit terminal velocity due to air drag on the way down, regardless of how 'fast' and 'high' they start from. Re-usable stages, compared to EELVs, need to consider heat of re-entry, keeping enough fuel to return to land, and attitude control with thrusters and then aerodynamic devices. So there are plenty of differences when a stage goes up much higher and farther and needs to return to land compared to expandable stages who want to burn up on re-entry. You think so, do you? Do the math. -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
#19
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Falcon Heavy Static Fire
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#20
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Falcon Heavy Static Fire
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