Author Topic: SpaceX complete PDR on LAS  (Read 66376 times)

Offline yg1968

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Re: SpaceX complete PDR on LAS
« Reply #100 on: 10/22/2011 02:19 pm »
This was asked earlier in the thread but not answered:
- has a liquid-propellant LAS ever been developed before?

I believe that pusher LAS was considered for the Appollo program but the tractor LAS was considered to be safer. I suspect that the pusher LAS is prefered by Boeing and SpaceX because of its cost and versatility. 
« Last Edit: 10/22/2011 02:23 pm by yg1968 »

Offline SF Doug

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Re: SpaceX complete PDR on LAS
« Reply #101 on: 10/22/2011 03:08 pm »
How 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.
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Offline JayP

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Re: SpaceX complete PDR on LAS
« Reply #102 on: 10/22/2011 04:02 pm »
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.
From a purly technical standpoint, it wouldn't require anything from Star Trek. All of the rquired technology has flown in space before. Skylab and Salyut had trash airlocks. The ISS has 2 airlocks for moving small loads outside roboticaly without doing an EVA (admitedly, one isn't installed yet, but it is up there). Gemini-MOL tested a hatch thru a heat shield.

All they would need to do is mount a small airlock in the aft section of the presurised compartment with it's outer hatch thru the heat shield. In the trunk, they mount a big bag with its opening up against the hatch. The bag is folded up against the forward face on the way up and allowed to open up after the cargo is removed from the trunk. The bag keeps the trash in place until the trunk burns up.

As others have pointed out, they would never ACTUALLY do this. There are much better way of getting rid of the staton's trash.

Offline baldusi

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Re: SpaceX complete PDR on LAS
« Reply #103 on: 10/22/2011 04:32 pm »
How 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.
I'm totally ignorant on this, but wouldn't you want to push forward and slightly above the rocket's vector to let it pass above you in case you have turned it off or is a catastrophic explosion, and the other way if it has lost it's attitude control?

Offline simonbp

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Re: SpaceX complete PDR on LAS
« Reply #104 on: 10/22/2011 05:10 pm »
And 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.

Offline Downix

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Re: SpaceX complete PDR on LAS
« Reply #105 on: 10/22/2011 05:31 pm »
This was asked earlier in the thread but not answered:
- has a liquid-propellant LAS ever been developed before?

Yes.  The Almaz recovery capsule abort system was a Hypergolic liquid fueled system.
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Offline joek

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Re: SpaceX complete PDR on LAS
« Reply #106 on: 10/22/2011 09:24 pm »
And 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.

CST-100 appears to have 4 main LAS engines, 16 SM LAS control thrusters, 24 SM RCS thrusters. and 12 CM RCS thrusters.  Some may do double duty, but there certainly seem to be quite a few of them, with a number apparently dedicated to LAS.  (Excluding the LAS main engines, a total of 12 thrusters on the CM, and 40 on the SM.)

That appears to be a significant difference between CST-100 and Dragon (at least from what we've seen) and suggests Boeing believes LAS control requires a significantly different approach that what can be provided alone by dual-purposing RCS thrusters (?).
« Last Edit: 10/22/2011 09:31 pm by joek »

Offline watermod

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Re: SpaceX complete PDR on LAS
« Reply #107 on: 10/24/2011 09:23 pm »
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.html

Quote
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.

Offline pippin

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Re: SpaceX complete PDR on LAS
« Reply #108 on: 10/24/2011 10:49 pm »
How 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.

Actually the pendulum rocket fallacy applies to cars in a similar way.
It's generally the REAR wheel drives that are stable on a slippery road, not the front-wheel ones. Try riding a forklift truck at speed and you know what I mean.

Apart from that you can tweak a lot with how you set up the chassis and actually the same is probably true for capsules.

Anyway, a tractor LAS should in no case be much better off maybe except for initially carrying a heavy solid up in the front (if you use solids) but in both cases you have a "big end" which helps a lot to get CP back.

Offline Robotbeat

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Re: SpaceX complete PDR on LAS
« Reply #109 on: 10/25/2011 03:08 am »
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.html

Quote
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.
GREAT idea!
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.
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Offline kkattula

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Re: SpaceX complete PDR on LAS
« Reply #110 on: 10/25/2011 03:17 am »
...
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 suspect the oxygen generating equipment on ISS could be defined as (purposeful) manufacturing in space.

It too takes a waste product, (water), and makes something useful.

Offline Lars_J

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Re: SpaceX complete PDR on LAS
« Reply #111 on: 10/25/2011 03:22 am »
This is going off-topic. Again.

Offline spectre9

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Re: SpaceX complete PDR on LAS
« Reply #112 on: 10/25/2011 03:49 am »
I'm new here and I must comment this is one of the worst forums I've ever seen for going off topic.

If you want to discuss something else start a new thread. Not that hard I would've thought.

Mods can delete this post when they see it as it's off topic too.

The people on this board need to learn how to use a forum.

Offline Crispy

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Re: SpaceX complete PDR on LAS
« Reply #113 on: 10/25/2011 07:30 am »
I'm new here and I must comment this is one of the worst forums I've ever seen for going off topic.
Then you can't have been here long (or have spent time on some severely strict forums!). The moderation is generally excellent

Offline beancounter

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Re: SpaceX complete PDR on LAS
« Reply #114 on: 10/26/2011 01:09 am »
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?
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Offline Confusador

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Re: SpaceX complete PDR on LAS
« Reply #115 on: 10/26/2011 01:56 am »
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?

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.

Offline joek

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Re: SpaceX complete PDR on LAS
« Reply #116 on: 10/26/2011 02:20 am »
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?
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)

Offline PhillyJimi

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Re: SpaceX complete PDR on LAS
« Reply #117 on: 10/26/2011 04:25 am »
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.

I am not a rocket scientist but I would think getting the Dragon and crew away from danger is less of a challenge when the booster can be shut down.  Not saying aborting a launch is easy.  I would also think even if the Dragon LAS fails, as long as the main engines shut down and if Dragon can just detach, the capsule could still have a chance of floating clear of the danger of smacking into the shut down booster stage. 

I also like the push style system just because if there was a problem with the tractor style system detaching from the capsule it would create a situation where you're going to have a really bad day.  The least not being you're parachutes can't deploy.  So with with a tractor system the LAS, MUST work perfectly every time. 

Offline beancounter

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Re: SpaceX complete PDR on LAS
« Reply #118 on: 10/26/2011 07:47 am »
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?
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)


Thanks for the info'. :)
Beancounter from DownUnder

Offline Nomadd

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Re: SpaceX complete PDR on LAS
« Reply #119 on: 10/26/2011 11:24 am »
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.

I don't think that's true. I'm pretty sure the LAS has to be able to pull Dragon away from a still accelerating stage.
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