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SpaceX video showing Falcon 9 stages and Dragon performing avertical landing
On Sep 29, 4:15*pm, Jeff Findley wrote:
SpaceX video showing Falcon 9 stages and Dragon performing a vertical landinghttp://www.youtube.com/watch?v=p176UpWQOs4&feature=player_embedded SpaceX Reusable Planshttp://nasawatch.com/archives/2011/09/spacex-reusable.html So, this shows VTVL for a reusable TSTO (Falcon 9) plus Dragon landing vertically. For the first stage, it looks like they're using propulsion from three of the engines to head back to KSC where it would land vertically on one engine. *Since there is only TPS on the very end of the first stage, it does not look like they're using any hypersonic lift to gain cross- range. For the second stage, the TPS looks like it extends further down the side of the stage on one side. *This would indicate that they plan on using hypersonic lift to gain cross-range and/or more accurately control the landing location. *Similar to the first stage, the video shows the second stage landing vertically under power of its engine. In other words, their approach is a fully reusable VTVL TSTO. *I wish them luck. *Since their test vehicle is reportedly based on the Falcon 9 first stage, it would appear that they're going to implement reusability on it first. *This is *exactly* what I've been advocating for an incremental approach to developing a fully reusable launch vehicle. * As for landing Dragon under rocket power, this is a plus because (as I've said in other posts) it eliminates the costs associated with landing and recovery in the ocean. *Besides the costs associated with a recovery ship, dunking a spacecraft in salt water might not be good for reusability. *There would be costs associated with cleaning off the salt water and verifying that it didn't get anywhere it shouldn't. *On top of that, there would be the additional cost of testing and re-certifying anything on the spacecraft that was exposed to salt water. Jeff -- " Ares 1 is a prime example of the fact that NASA just can't get it * up anymore... and when they can, it doesn't stay up long. " * *- tinker The part that shows the Dragon landing, I couldn't help but wondering, where all the fuel is stored for landing or how much does that eat up in payload? Just my $0.02 Space Cadet Moon Society - St. Louis Chapter http://www.moonsociety.org/chapters/stlouis/ The Moon Society is a non-profit educational and scientific foundation formed to further scientific study and development of the moon. |
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SpaceX video showing Falcon 9 stages and Dragon performing a vertical landing
In article 73112da4-3bed-482e-a546-01c02f3a48f3
@d28g2000vby.googlegroups.com, says... The part that shows the Dragon landing, I couldn't help but wondering, where all the fuel is stored for landing or how much does that eat up in payload? The landing engines only need to slow the capsule from its terminal velocity to zero. We're not talking about "a lot" of fuel here. Also, parachutes "eat up" payload too. Jeff -- " Ares 1 is a prime example of the fact that NASA just can't get it up anymore... and when they can, it doesn't stay up long. " - tinker |
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SpaceX video showing Falcon 9 stages and Dragon performing a vertical landing
Jeff Findley writes:
In article 73112da4-3bed-482e-a546-01c02f3a48f3 @d28g2000vby.googlegroups.com, says... The part that shows the Dragon landing, I couldn't help but wondering, where all the fuel is stored for landing or how much does that eat up in payload? The landing engines only need to slow the capsule from its terminal velocity to zero. We're not talking about "a lot" of fuel here. Doesn't matter how fast the thing is falling down -- Dragon weights about 15000 lb when returning, so you need engines with 15000 lbf thrust to hover. The existing OMS/RCS engines (Draco) have 4x90 lbf. You'd need fourty of them to brake the thing. And of course you'd need fuel not only for slowing down vertically. Even if you can target reentry and descent to about a mile around the landing pad you still need to nudge the capsule around quite a bit in the last stages of descent. Without any kind of control surfaces you'll need to expend fuel for that. Also, parachutes "eat up" payload too. True. But if the landing engines and fuel are meant to serve also as a "pusher" escape system for manned launches you'll need to carry a parachute anyway if you don't want to have the capsule plummet down to the ground with empty fuel tanks afterwards. And if they're really serious about that kind of escape system, they will need to be able to accelerate with more than 1 g in case of a catastrophic booster failure. 10 g would require 150000 lbf thrust, or the equivalent of 400 Draco engines. And the fuel to feed them. Jochem -- "A designer knows he has arrived at perfection not when there is no longer anything to add, but when there is no longer anything to take away." - Antoine de Saint-Exupery |
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SpaceX video showing Falcon 9 stages and Dragon performing a vertical landing
Jeff Findley writes:
And if they're really serious about that kind of escape system, they will need to be able to accelerate with more than 1 g in case of a catastrophic booster failure. 10 g would require 150000 lbf thrust, or the equivalent of 400 Draco engines. And the fuel to feed them. You're just being silly. Obviously the engineers at SpaceX have thought of this. I surely hope so, but *what* did they think? ;-) The point is that as clean and nice and easy all this looks in a video, as soon as you look at the numbers all of this looks very dubious. And a liquid fueled pusher escape system needs some engines with *massive* thrust. If they use 400 Draco engines (obviously not really an option) or just 4 new engines with each 100 times the thrust of a Draco engine, the required thrust stays the same. Squeezing something with 150000 lbf thrust into the bottom of a Dragon capsule along with the fuel tanks for it just seems impossible to me. Jochem -- "A designer knows he has arrived at perfection not when there is no longer anything to add, but when there is no longer anything to take away." - Antoine de Saint-Exupery |
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SpaceX video showing Falcon 9 stages and Dragon performing a vertical landing
In article , says...
Jeff Findley writes: And if they're really serious about that kind of escape system, they will need to be able to accelerate with more than 1 g in case of a catastrophic booster failure. 10 g would require 150000 lbf thrust, or the equivalent of 400 Draco engines. And the fuel to feed them. You're just being silly. Obviously the engineers at SpaceX have thought of this. I surely hope so, but *what* did they think? ;-) The point is that as clean and nice and easy all this looks in a video, as soon as you look at the numbers all of this looks very dubious. Really? And just where are these "dubious" numbers? Care to share? Obviously SpaceX isn't going to share much, since that's all their intellectual property. But having seen papers on landing using propulsion, the numbers just aren't as bad as you're making them out to be. Yes you lose payload, but that's not the point. A launch vehicle can afford to "lose payload" when it's being reused several times. LOX and kerosene are a tiny fraction of today's launch costs. The lion's share of today's launch costs are to replace the *entire launch vehicle* after each and every flight. And a liquid fueled pusher escape system needs some engines with *massive* thrust. If they use 400 Draco engines (obviously not really an option) or just 4 new engines with each 100 times the thrust of a Draco engine, the required thrust stays the same. True, so it is a good thing LOX/kerosene rocket engines have excellent thrust to weight ratios. The Merlin IC reportedly has a thrust to weight ratio of nearly 100. Using that as a yardstick, 150,000 lbs of thrust requires an engine weight of about 1,500 lbs. Here is a report on the Apollo launch escape system: http://klabs.org/history/apollo_expe...ports/tn-d7083 _apollo_launch_escape_propulsion.pdf Curiously, it had a thrust of 155,000 lbs, which is just about what you're saying Dragon would need, so this ought to be interesting. Total impulse of the launch escape motor was 515,000 lb-sec, which works out to about 3.3 seconds of thrust at 155,000 lbs. The launch escape motor had a weight of 4850 lbs. Now compare it to LOX/kerosene numbers: According to Wikipedia, when configured for Falcon 1, Merlin IC's thrust was 78,000 lbs at sea level, and its fuel consumption is about 300 lb of propellant per second. Scaling that up to 155,000 lbs of thrust gives a fuel consumption number of about 600 lbs per second which is about 2000 lbs for 3.3 seconds of thrust. So, the total weight of LOX/kerosene engines plus propellant would be 3500 lbs, which is 1350 lbs lighter than the solid. Obviously we've got to add in the weight of tanks, plumbing, and etc., so there may not be much in the way of weight savings. This back of the envelope calculation shows that liquid fueled engines for launch escape isn't ridiculous at first glance. I know that "the devil is in the details", so this may be quite a challenge to work out. Pluse, if these liquid fueled engines double as landing engines, that's a "win" over a solid system which is simply discarded if it's not needed. Squeezing something with 150000 lbf thrust into the bottom of a Dragon capsule along with the fuel tanks for it just seems impossible to me. We'll see what SpaceX comes up with. Results are what will matter. Jeff -- " Ares 1 is a prime example of the fact that NASA just can't get it up anymore... and when they can, it doesn't stay up long. " - tinker |
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SpaceX video showing Falcon 9 stages and Dragon performing a vertical landing
Jeff Findley writes:
Curiously, it had a thrust of 155,000 lbs, which is just about what you're saying Dragon would need, so this ought to be interesting. Total impulse of the launch escape motor was 515,000 lb-sec, which works out to about 3.3 seconds of thrust at 155,000 lbs. The launch escape motor had a weight of 4850 lbs. The Apollo CM had less mass than dragon with down payload, so to attain about the same escape acceleration as Apollo, Dragon needs about the same thrust, yes. Now compare it to LOX/kerosene numbers: According to Wikipedia, when configured for Falcon 1, Merlin IC's thrust was 78,000 lbs at sea level, and its fuel consumption is about 300 lb of propellant per second. Scaling that up to 155,000 lbs of thrust gives a fuel consumption number of about 600 lbs per second which is about 2000 lbs for 3.3 seconds of thrust. So, the total weight of LOX/kerosene engines plus propellant would be 3500 lbs, which is 1350 lbs lighter than the solid. Obviously we've got to add in the weight of tanks, plumbing, and etc., so there may not be much in the way of weight savings. 3500 lbs is about half of the Dragon down payload and a quarter of the up payload. And you'll need turbopumps (which might be a bit slow to spin up in an escape system and anyway heavy) or pressurized tanks (which also are heavy). And plumbing and then there's the landing gear. And getting away with about 30 seconds worth of fuel for a landing seems to be a bit daring, too. Especially if you don't have any other way to control your descent (like control surfaces), you'll need the fuel for more than just breaking. And for a manned landing there will be a very nasty black zone where you're too low to switch to the backup parachute and still high enough to have a failing engine or control system lead to loss of vehicle and crew. But if you have thrust enough for accelerating with 10 g, you may have got enough engines and redundancy to compensate for many failure modes, OK. This back of the envelope calculation shows that liquid fueled engines for launch escape isn't ridiculous at first glance. I know that "the devil is in the details", so this may be quite a challenge to work out. Pluse, if these liquid fueled engines double as landing engines, that's a "win" over a solid system which is simply discarded if it's not needed. I think solids are better for escape systems if you throw them away unused nearly all the time. Just because they're probably cheaper. Maybe more reliable, too. For a reusable capsule liquid fueled is certainly a good idea. Dragon is a great spacecraft and would totally deserve powered precision landings. I'm just saying that this is nothing anyone would dare to try. If it works out: Great! Squeezing something with 150000 lbf thrust into the bottom of a Dragon capsule along with the fuel tanks for it just seems impossible to me. We'll see what SpaceX comes up with. Results are what will matter. I'm certainly looking forward to that and in any case trying and failing is totally better than not even trying. Jochem -- "A designer knows he has arrived at perfection not when there is no longer anything to add, but when there is no longer anything to take away." - Antoine de Saint-Exupery |
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SpaceX video showing Falcon 9 stages and Dragon performing a vertical landing
In sci.space.policy message , Wed, 5 Oct 2011
10:59:39, Jochem Huhmann posted: I think solids are better for escape systems if you throw them away unused nearly all the time. Just because they're probably cheaper. Maybe more reliable, too. For a reusable capsule liquid fueled is certainly a good idea. An escape TOWER is a waste of mass; there may be need for a light fairing to protect the capsule. The capsule should have a ring of motors at the bottom of its sides, sized overall to give the necessary but uncomfortable escape thrust for the escape period. As soon as there is no need for such an escape system, or when the lower stages have been dropped, or after a subsequent coast period, then those motors should be used, a comfortable few at a time, for the final insertion into orbit or for subsequent orbit raising. Everything that lifts off the launch pad should be used before it is abandoned. -- (c) John Stockton, nr London, UK. Turnpike v6.05 MIME. Web http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms and links; Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc. No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News. |
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