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#320 by elmarko on 31 Jul, 2009 18:21
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Thanks for the write up, Danny. What was your plan for any underburn, then? If an engine quits before the targets are met, then you can't prebank anymore.
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#321 by mmeijeri on 31 Jul, 2009 18:26
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That document you linked is from the SCOM, the full version of which is on L2.
Thanks for that! -
#322 by ChrisGebhardt on 31 Jul, 2009 18:35
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Has there ever been a shuttle landing at KSC while a shuttle rollout was in progress?
I do not believe an orbiter has ever landed while another Shuttle vehicle was rolling out to the pad. However, there was an instance where one Orbiter landed while the next Shuttle's crew was in their vehicle conducting their TCDT. -
#323 by oxford750 on 31 Jul, 2009 22:49
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Is there an article (for the layman like me) that explains in which direction each thruster fires, and which way it would make the shuttle move?
I know what the OMS engines do, but what about the others?
If one OMS engine failed for any reason, would firing just one for a "longer" period be enough or would that induce a yaw as the other one can't compensate?
Thanks
Oxford750
Attaching a diagram from the Shuttle Crew Operations Manual which should explain things.
Thanks elmarko.
Would't the body flap negate the momentum of the plumes of thrusters: R4D,R2D,R3d,L4D,L2D,L3D or can the body flap move down 90 degrees, or is it there just to protect the engines
Thanks
Oxford750 -
#324 by Jorge on 31 Jul, 2009 23:22
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Would't the body flap negate the momentum of the plumes of thrusters: R4D,R2D,R3d,L4D,L2D,L3D or can the body flap move down 90 degrees, or is it there just to protect the engines
The body flap is there for entry control. It happens to protect the main engines but that is not what it's there for.
The left and right down-firing thrusters you listed are canted outward. Body flap impingement does cancel some of their thrust, but not enough to be a problem.
Body flap impingement is more noticeable on the down-firing aft vernier thrusters (L5D, R5D) since they point straight down rather than being canted to the sides. They lose almost 40% of their thrust. Still not a problem, though. -
#325 by padrat on 01 Aug, 2009 01:39
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You are the expert on this stuff, so you give me a ray of hope. Is the goal liquid or compressed gas. I understand there some prototype stations working today.
But, I don't recall there ever being that big of an issue in handling gasoline into cars. Heck, we don't even ground our cars like we do planes. It takes about 5 seconds to teach someone to gas up a car. If there is a big spill (which there are), it doesn't quickly boil into an explosive cloud. Detonating a cloud is really, really bad. Probably a gallon turning into vapor will level a whole gas station when it goes off.
I can't imagine my ex ever gassing up her car with liquid hydrogen
In my opinion, even liquid propane is something that shouldn't be taken lightly.
Danny Deger
Most of the concepts I've seen deal with compressed gas. Would probably be similar to gassing a vehicle with propane or LNG nowadays.
One other thing to keep in mind is that hydrogen dissipates much faster than gasoline does. The liquid boils so fast you would probably never see it, just vapor. The biggest concern is if it is in an enclosed space or covered area, so it accumilates more and won't disperse as quickly. Then you may have quite a safety hazard. But for the most part, most experts say that hydrogen is overall safer than gasoline. Biggest concern is the large flammability range (4-74%).
BTW, if anyone is interested, there's a website I've found to be very informative on hydrogen and related topics (hydrogen cars, etc.)
http://www.hydrogenassociation.org -
#326 by mkirk on 01 Aug, 2009 19:26
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Thanks for the write up, Danny. What was your plan for any underburn, then? If an engine quits before the targets are met, then you can't prebank anymore.
I'm not sure I completely understand your question's context, by definition the enigne quiting early would result in an underburn. Which engine are you talking about - an OMS engine? In that case you down-mode to other options such as RCS Completeion, Recovery Pre-bank & Landing Site Redesignation(for ex: can't make KSC then maybe redes to Gander or Shannon).
Entry Flight Procedures Handbook explains much of this in section 4. Chris has a semi current version although it is not accurate about the KSC re-des options since those procedures are relatively new.
Mark Kirkman
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#327 by Danny Dot on 01 Aug, 2009 19:57
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You are the expert on this stuff, so you give me a ray of hope. Is the goal liquid or compressed gas. I understand there some prototype stations working today.
But, I don't recall there ever being that big of an issue in handling gasoline into cars. Heck, we don't even ground our cars like we do planes. It takes about 5 seconds to teach someone to gas up a car. If there is a big spill (which there are), it doesn't quickly boil into an explosive cloud. Detonating a cloud is really, really bad. Probably a gallon turning into vapor will level a whole gas station when it goes off.
I can't imagine my ex ever gassing up her car with liquid hydrogen
In my opinion, even liquid propane is something that shouldn't be taken lightly.
Danny Deger
Most of the concepts I've seen deal with compressed gas. Would probably be similar to gassing a vehicle with propane or LNG nowadays.
One other thing to keep in mind is that hydrogen dissipates much faster than gasoline does. The liquid boils so fast you would probably never see it, just vapor. The biggest concern is if it is in an enclosed space or covered area, so it accumilates more and won't disperse as quickly. Then you may have quite a safety hazard. But for the most part, most experts say that hydrogen is overall safer than gasoline. Biggest concern is the large flammability range (4-74%).
BTW, if anyone is interested, there's a website I've found to be very informative on hydrogen and related topics (hydrogen cars, etc.)
http://www.hydrogenassociation.org
OK last post for me on this thread on this.
Most gas stations are covered
I am not even sure cover is needed. As you said the boil off is so fast an explosive cloud may form. If we go to refueling cars with liquid hydrogen, many people a year will die from REALLY big explosions. Fuel air bombs are more effective than a regular bombs in crushing a concrete bunker.
My guess is compressed gas hydrogen cars will not have enough range to be viable. I will look at the link.
Danny Deger -
#328 by elmarko on 01 Aug, 2009 23:02
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Thanks for the write up, Danny. What was your plan for any underburn, then? If an engine quits before the targets are met, then you can't prebank anymore.
I'm not sure I completely understand your question's context, by definition the enigne quiting early would result in an underburn. Which engine are you talking about - an OMS engine? In that case you down-mode to other options such as RCS Completeion, Recovery Pre-bank & Landing Site Redesignation(for ex: can't make KSC then maybe redes to Gander or Shannon).
Entry Flight Procedures Handbook explains much of this in section 4. Chris has a semi current version although it is not accurate about the KSC re-des options since those procedures are relatively new.
Mark Kirkman
Thanks Mark, but you're misunderstanding me. Danny was advocating a nominal entry with a prebank. Ergo, less fuel required for the deorbit burn, I guess. But then, if you're targetting for that, and then the engines quit, you're already planning to prebank, so you might not be able to prebank anymore (if you were targetting for a 90deg prebank, for instance). -
#329 by Danny Dot on 02 Aug, 2009 03:07
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snip
Thanks Mark, but you're misunderstanding me. Danny was advocating a nominal entry with a prebank. Ergo, less fuel required for the deorbit burn, I guess. But then, if you're targetting for that, and then the engines quit, you're already planning to prebank, so you might not be able to prebank anymore (if you were targetting for a 90deg prebank, for instance).
Even if both engines fail, you can use the RCS. The problem is a failure of the propellant system itself.
Danny Deger -
#330 by elmarko on 02 Aug, 2009 09:19
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Yeah, I do understand that. I was just trying to account for every eventuality, I guess.
This is a fun topic, though
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#331 by rsmath on 02 Aug, 2009 10:48
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I'm sorry if these have been answered before, but a couple things got my curiosity going the last few days:
1) I saw a pic of the SLF and noticed for the first time there is a canal around the runway (broken up by a few roads/access points).
Is that to try to limit wildlife other than alligators from easily accessing the SLF or does it serve some other purpose?
2) If an orbiter was to land in Europe or Africa, how would they return it to KSC? Put it on a ship or does the SCA have the ability to be refueled in-flight?
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#332 by elmarko on 02 Aug, 2009 11:14
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2) It would be ferried with quite a few stops on the way. An orbiter has been carried to and from Europe before.
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#333 by mmeijeri on 02 Aug, 2009 11:15
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If only one engine fails, could you use RCS and the remaining engine simultaneously?
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#334 by elmarko on 02 Aug, 2009 11:41
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You'd have to reorientate to an attitude that would account for the difference in thrust level. Which would probably then be hideously unefficient. Most likely they'd kill the other engine and complete the entire burn in RCS, I guess?
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#335 by DaveS on 02 Aug, 2009 11:41
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2) It would be ferried with quite a few stops on the way. An orbiter has been carried to and from Europe before.
That was Enterprise(OV-101). I believe she was a fair bit lighter than an operational OV would be for a TAL abort ferry.
I believe in order to make the trip viable they would have to undertake some major operations like removing the payloads, SSMEs and completely draining the OMS/RCS and APU prop.
Quite possible that they would need to remove any liquids onboard that could freeze, to make it possible for the SCA to attain the highest altitude possible to extend the range. -
#336 by elmarko on 02 Aug, 2009 12:06
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All of that seems reasonable enough, but a huge task. Blimey.
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#337 by Jim on 02 Aug, 2009 12:14
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1) I saw a pic of the SLF and noticed for the first time there is a canal around the runway (broken up by a few roads/access points).
Is that to try to limit wildlife other than alligators from easily accessing the SLF or does it serve some other purpose?
the rain has to drain some where -
#338 by randomly on 02 Aug, 2009 12:39
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You are the expert on this stuff, so you give me a ray of hope. Is the goal liquid or compressed gas. I understand there some prototype stations working today.
My guess is compressed gas hydrogen cars will not have enough range to be viable. I will look at the link.
You can get sufficient range out of compressed hydrogen systems for passenger cars when coupled with efficient low weight designs (think prius). However many engineers no longer think a Hydrogen economy is viable because of the costs and inefficiencies.
Major problems -
Storage - Liquid hydrogen is right out, it costs you 30% of the energy in the hydrogen to liquify it and you have boil-off issues. Compressed gas is the most viable at 5000-10,000 psi, but it still cost you 12% of your energy. All the adsorption materials like palladium glom on to the hydogen so aggressively that it takes considerable energy to get the hydrogen back out again, the higher the capacity the material the more energy it takes to release the hydrogen.
Transport - Transport is difficult and energy intensive. You cannot use any existing pipelines because of hydrogen embrittlement, you have to lay all new pipe. The pumping energy for pipeline transport is high because of the very low density which is a further drain on your over all energy efficiency. A very busy gas station can be refueled by a single tanker truck a day, to deliver an equivalent mileage of hydrogen fuel would require about 20 tanker trucks a day and the associated impacts and costs of that. Transporting the energy to a hydrogen station by electricity would require all new transmission lines to handle the load, and since electrolyzers are only about 50% efficient you lose half your energy turning it into hydrogen. You also need to dissipate the other 50% of your energy as heat at the station.
Sources of Hydrogen - The only currently economical source of hydrogen is from reforming natural gas, which is quite efficient at about 80% of the original energy in the natural gas. But this doesn't get you away from fossil fuels nor reduce your carbon footprint. The fuel cells are only about 50% efficient and there does not appear yet any way to make them substantially more efficient, especially under the high current densities required for an automotive system. An MIT study found that even with projected improvements in hydrogen fuel cells that by 2020 a simple diesel hybrid car would still be more efficient Well to Wheels than a Hydrogen fuel cell vehicle. Worse yet is production of hydrogen by electrolysis which is only about 50% efficient. If you have any source of electricity the cost of that power in the vehicle is 4x since you lose half in electrolysis and half in the fuel cell for overall efficiency of 25%. This is only 1/3-1/4 as efficient as a battery system which is about 90% efficient for energy storage and return. In short until you have eliminated all your fossil fuel based electrical power generation there will better places to use your electrical power than for hydrogen production.
The only economical source of hydrogen in the future would be from Very High Temperature Nuclear Reactors using a Sulfur-Iodine cycle. That's at least 20-30 years out.
This is before you even get to problems of the very high cost and fragility of fuel cell systems, poisoning of the catalyst by carbon monoxide and other compounds, limited membrane lifetimes etc.
I once had high hopes for hydrogen, but unfortunately given the current and forseeable technology I think it's highly unlikely that a hydrogen economy will arise in the next 50 years, if ever. -
#339 by Jorge on 02 Aug, 2009 19:00
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If only one engine fails, could you use RCS and the remaining engine simultaneously?
No. As long as one OMS engine is firing you are in the TVC DAP and cannot use the THC to perform an RCS translation. In the TVC DAP with a single engine RCS is nominally used only for roll control.
