This was asked earlier in the thread but not answered:- has a liquid-propellant LAS ever been developed before?
Quote from: Lee Jay on 10/22/2011 01:30 amQuote from: clongton on 10/22/2011 01:23 amQuote from: Danny Dot on 10/22/2011 12:53 amQuote from: joek on 10/22/2011 12:37 amQuote from: Danny Dot on 10/22/2011 12:07 amHow is the Dragon kept stable during a LAS burn at max q?Is that a concern with pusher in general, or something specific about SpaceX's configuration (at least what we know about it)? E.g., CST-100's LAS appears to be entirely (?predominately?) in the service module (including ACS/RCS), whereas SpaceX's appears to be entirely (?predominately?) in the capsule.It is a problem with pushers in general.Think rear wheel drive vs. front wheel drive on a slippery road.How is this not the pendulum rocket fallacy? I thought stability was only dictated by the location of the CG and the aerodynamic center of pressure (CG must be in front for stability). Thrust location is irrelevant. No?You are correct. Tower LAS systems are not stable because they are pullers, they are stable because they move the CG in front of the center of pressure. And I am doubtfull throttle reaction time is quick enough to stablize the capsule - especially at max q.
Quote from: clongton on 10/22/2011 01:23 amQuote from: Danny Dot on 10/22/2011 12:53 amQuote from: joek on 10/22/2011 12:37 amQuote from: Danny Dot on 10/22/2011 12:07 amHow is the Dragon kept stable during a LAS burn at max q?Is that a concern with pusher in general, or something specific about SpaceX's configuration (at least what we know about it)? E.g., CST-100's LAS appears to be entirely (?predominately?) in the service module (including ACS/RCS), whereas SpaceX's appears to be entirely (?predominately?) in the capsule.It is a problem with pushers in general.Think rear wheel drive vs. front wheel drive on a slippery road.How is this not the pendulum rocket fallacy? I thought stability was only dictated by the location of the CG and the aerodynamic center of pressure (CG must be in front for stability). Thrust location is irrelevant. No?
Quote from: Danny Dot on 10/22/2011 12:53 amQuote from: joek on 10/22/2011 12:37 amQuote from: Danny Dot on 10/22/2011 12:07 amHow is the Dragon kept stable during a LAS burn at max q?Is that a concern with pusher in general, or something specific about SpaceX's configuration (at least what we know about it)? E.g., CST-100's LAS appears to be entirely (?predominately?) in the service module (including ACS/RCS), whereas SpaceX's appears to be entirely (?predominately?) in the capsule.It is a problem with pushers in general.Think rear wheel drive vs. front wheel drive on a slippery road.
Quote from: joek on 10/22/2011 12:37 amQuote from: Danny Dot on 10/22/2011 12:07 amHow is the Dragon kept stable during a LAS burn at max q?Is that a concern with pusher in general, or something specific about SpaceX's configuration (at least what we know about it)? E.g., CST-100's LAS appears to be entirely (?predominately?) in the service module (including ACS/RCS), whereas SpaceX's appears to be entirely (?predominately?) in the capsule.It is a problem with pushers in general.
Quote from: Danny Dot on 10/22/2011 12:07 amHow is the Dragon kept stable during a LAS burn at max q?Is that a concern with pusher in general, or something specific about SpaceX's configuration (at least what we know about it)? E.g., CST-100's LAS appears to be entirely (?predominately?) in the service module (including ACS/RCS), whereas SpaceX's appears to be entirely (?predominately?) in the capsule.
How is the Dragon kept stable during a LAS burn at max q?
No, I was suggesting that SpaceX could develop a new capability to transfer items from the pressurized compartment of the Dragon, to the unpressurized portion of the Dragon, without those items being touched by Human or Robotnaut hands. Of course, there's a whole lot of Dragon components located between the pressurized and unpressurized compartments, including the heatshield, so it's not really possible unless Musk has some Star Trek transporter technology in his back pocket that we don't know about.
And I am doubtfull throttle reaction time is quick enough to stablize the capsule - especially at max q.
Quote from: Danny Dot on 10/22/2011 02:08 amAnd I am doubtfull throttle reaction time is quick enough to stablize the capsule - especially at max q.Considering this is a vehicle designed to land using throttling of the very same thrusters, I would not underestimate their reaction time. Plus, recall that all of Dragon's RCS is on the capsule itself (rather than the trunk), so they still have full RCS authority during abort. Considering that's all CST-100 has for control during abort, I think Dragon is going to be fine.
TECHNICAL ABSTRACT (Limit 2000 characters, approximately 200 words)The innovative High Efficiency, High Output Plastic Melt Waste Compactor (HEHO-PMWC) is a trash dewatering and volume reduction system that uses heat melt compaction to remove nearly 100% of water from trash and reduce the volume by up to 11 times. The HEHO-PMWC system incorporates novel methods to compress the trash, recover water, and remove the resultant plastic tiles. This system requires access to power, data, and cooling interfaces. The system is suitable for recovering water and compacting all trash sources on the ISS. The system has also been designed to recover water from brine solutions produced by primary wastewater processing systems.The HEHO-PMWC works by heating and compressing trash simultaneously to first remove water and then to melt plastic in the trash. The melted plastic encapsulates the trash into a 16 inch square tile, approximately ½ inch thick. The square tile is easier to store than a round tile and is a more effective radiation shield.Variables such as transport vehicle availability, ISS mass, power and space availability, and ISS cooling capabilities were considered. The resulting HEHO-PWMC system, proposed here, was sized to process 3-4 kg of trash per batch while operating three times per day.
As to the ISS trash compactor argument - It seems NASA had a recent SBIR on that: http://www.sbir.nasa.gov/SBIR/abstracts/09/sbir/phase/SBIR-09-2-X2.02-9461.htmlQuoteTECHNICAL ABSTRACT (Limit 2000 characters, approximately 200 words)The innovative High Efficiency, High Output Plastic Melt Waste Compactor (HEHO-PMWC) is a trash dewatering and volume reduction system that uses heat melt compaction to remove nearly 100% of water from trash and reduce the volume by up to 11 times. The HEHO-PMWC system incorporates novel methods to compress the trash, recover water, and remove the resultant plastic tiles. This system requires access to power, data, and cooling interfaces. The system is suitable for recovering water and compacting all trash sources on the ISS. The system has also been designed to recover water from brine solutions produced by primary wastewater processing systems.The HEHO-PMWC works by heating and compressing trash simultaneously to first remove water and then to melt plastic in the trash. The melted plastic encapsulates the trash into a 16 inch square tile, approximately ½ inch thick. The square tile is easier to store than a round tile and is a more effective radiation shield.Variables such as transport vehicle availability, ISS mass, power and space availability, and ISS cooling capabilities were considered. The resulting HEHO-PWMC system, proposed here, was sized to process 3-4 kg of trash per batch while operating three times per day.
...Instead of throwing that mass away, it makes sense to extract all the water and melt the rest into radiation shielding. Good SBIR investment. Technically, the first (purposeful) manufacturing in space.
I'm new here and I must comment this is one of the worst forums I've ever seen for going off topic.
As far as I understand these things, the completion of the PDR for the LAS now allows for the next stage which is actual design and fabrication of the components of the system. Does anyone know which milestone is related to actual testing of the hardware and about how far further on, timewise that is?
Quote from: beancounter on 10/26/2011 01:09 amAs far as I understand these things, the completion of the PDR for the LAS now allows for the next stage which is actual design and fabrication of the components of the system. Does anyone know which milestone is related to actual testing of the hardware and about how far further on, timewise that is?See here (pdf), from the CCDev updates thread.This was milestone 4, "LAS Propulsion Component Initial Test Cycle" is milestone 9 which the current schedule has toward the end of Q2.
Quote from: Confusador on 10/26/2011 01:56 amQuote from: beancounter on 10/26/2011 01:09 amAs far as I understand these things, the completion of the PDR for the LAS now allows for the next stage which is actual design and fabrication of the components of the system. Does anyone know which milestone is related to actual testing of the hardware and about how far further on, timewise that is?See here (pdf), from the CCDev updates thread.This was milestone 4, "LAS Propulsion Component Initial Test Cycle" is milestone 9 which the current schedule has toward the end of Q2.Yes; per the SAA and projected date (per Oct timeline):- Milestone #4 -- LAS Propulsion Components Preliminary Desigh Review (Sep 2011, done)- Milestone #8 -- LAS Propulsion Component Test Articles Complete (Apr 2012)- Milestone #9 -- LAS Propulsion Component Initial Test Cycle (May 2012)
From the beginning the LAS for Dragon's job is a bit different then what the LAS had to do for the Ares I/Orion configuration. When designing the LAS for a Falcon you can factor into it you're on a rocket that can be shut down if something goes wrong. With the Ares I, since you're riding on top of a Roman Candle, with no shut OFF switch. This becomes a major consideration when designing a LAS. The Ares I requires a much more powerful LAS.