Author Topic: SpaceX: Advanced Launch Abort System (LAS)  (Read 222509 times)

Online Zed_Noir

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Re: SpaceX: Advanced Launch Abort System (LAS)
« Reply #40 on: 04/29/2011 02:39 am »
Gentle? 

Gentle compared to the LES acceleration. Not when used as normal main propulsion.

Link doesn't seem to work, goes to a 404 for me. Can someone attach it here?

Hmm. Still works for me. Have you tried copying the URL text manually into the address bar?

Yes, didn't work. Maybe SpaceX took it down but it's still in your browser cache, so the link still "works" for you?

Here.

Thanks.

SpaceX  change the URL. A "-" character is inserted between STS and 134 near the end of the URL. The current URL link to the press kit follows.

http://www.spacex.com/downloads/20110428-spacex-sts-134.pdf

Offline Downix

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Re: SpaceX: Advanced Launch Abort System (LAS)
« Reply #41 on: 04/29/2011 02:58 am »
And to be honest, I agree with the CCDev2 reviewer that using a hybrid rocket is risky for abort. Dreamchaser is cool, but is more difficult to develop.
I don't see it as risky, it depends on the particulars of the hybrid system doesn't it?  I made one, once, which was Hypergolic, so no concern over ignition there.

*edit* Come to think of it, my particular design would not be smart for the Dream Chaser in any case, as I used a 5% formula of Chlorine TriFlouride as the oxidizer.  That stuff is dangerous in the highest degree, so falls under the "Don't do this at home kids" category.

In my view, the problem with a hybrid for abort is start up time.  You really want something that can deliver 100 ms or less to full thrust, and all hybrids I've seen are more like 1500 ms.
You've never worked with Chlorine TriFlouride then.  That stuff is insta-on. (I did not have a fine enough fidelity camera when testing it, so all I can say is that it was faster than 200ms.
I am pretty sure DreamChaser doesn't use anything that sounds like "Chlorine TriFlouride." They use nitrous.
Then it's darn easy to get such a reaction started.  Have inside the solid fuel combustion chamber a pellet of EPDC rubber filled with Monomethylhydrazine, use a plug holding red fuming Nitric acid in the feed line, and BAM, you have start in under 100ms.  You turn on the engine, the pump forces the plug into the engine, where the RFNA meets the EPDC, immediately dissolving it and exposing it to the MMH producing a hypergolic reaction, kicking the hybrid engine into starting for the LAS.  Once you no longer need it for a LAS, drop the EPDC rubber pellet, as RFNA does not intact with the HTPD and would just be expelled out the back harmlessly.
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Offline Proponent

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Re: SpaceX: Advanced Launch Abort System (LAS)
« Reply #42 on: 04/29/2011 03:01 am »
Right, escape being possible doesn't mean it's guaranteed to save you in every scenario. This is true whether you have high power escape motors or not.

I agree and I'm not saying having a LAS would necessarily have worked in that case, either.

Quote
I'm not saying that SpaceX system couldn't be better than what Apollo had, I'm just disappointed by the needless conflation of an *escape tower* with an *escape system*. SpaceX should know better.

Maybe there's a fine distinction between "escape" and "abort" to be made? SPS could have aborted away from let's say a gracefully shut down stage, but it probably wouldn't have worked that well if the vehicle executed a RUD.

In the end, this is all spin and I don't personally get too excited over it.

I agree it's not a huge deal, but SpaceX does have a habit of presenting the ordinary as extraordinary, and it's good to be aware of that.

Offline jak Kennedy

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Re: SpaceX: Advanced Launch Abort System (LAS)
« Reply #43 on: 04/29/2011 03:08 am »
Just saw what I believe is a new article from Elon in Business Week.

"We're entering the era of commercial space flight, which will advance dramatically faster than in the past. But I made the decision to patent almost nothing: Our competition is the Chinese and Russian governments, against whom patents are unenforceable and can simply be used as a recipe. It's much better for our technology to be trade secrets. I'd rather keep the information to myself. There could be a Chinese spy or a cyber attack, but my CIO is from PayPal, which never got cracked."

http://www.businessweek.com/magazine/content/11_19/b4227076914379.htm

Offline QuantumG

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Re: SpaceX: Advanced Launch Abort System (LAS)
« Reply #44 on: 04/29/2011 03:46 am »
Means you can move a lot faster too..
Human spaceflight is basically just LARPing now.

Offline wally

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Re: SpaceX: Advanced Launch Abort System (LAS)
« Reply #45 on: 04/29/2011 05:26 am »
Isn't Dragon to cramped for a trip to Mars?

Offline Proponent

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Re: SpaceX: Advanced Launch Abort System (LAS)
« Reply #46 on: 04/29/2011 05:40 am »
You wouldn't have to make the whole trip in the Dragon; there would probably be a hab module as well, and Dragon would be used just during descent to the martian surface.

On the other hand, I'm sure you could find volunteers who would be willing to make the whole trip in the Dragon.

Online Zed_Noir

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Re: SpaceX: Advanced Launch Abort System (LAS)
« Reply #47 on: 04/29/2011 01:21 pm »
Isn't Dragon to cramped for a trip to Mars?

That depends on how many crew members you got on a Mars Dragon. It's likely a Mars Dragon mission will have 3 crew like Apollo.

Offline yg1968

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Re: SpaceX: Advanced Launch Abort System (LAS)
« Reply #48 on: 04/29/2011 03:17 pm »
And to be honest, I agree with the CCDev2 reviewer that using a hybrid rocket is risky for abort. Dreamchaser is cool, but is more difficult to develop.
I don't see it as risky, it depends on the particulars of the hybrid system doesn't it?  I made one, once, which was Hypergolic, so no concern over ignition there.

*edit* Come to think of it, my particular design would not be smart for the Dream Chaser in any case, as I used a 5% formula of Chlorine TriFlouride as the oxidizer.  That stuff is dangerous in the highest degree, so falls under the "Don't do this at home kids" category.

Isn't the risk more related to the fact that Dream Chaser can't land in water?
« Last Edit: 04/29/2011 03:25 pm by yg1968 »

Offline Downix

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Re: SpaceX: Advanced Launch Abort System (LAS)
« Reply #49 on: 04/29/2011 05:51 pm »
And to be honest, I agree with the CCDev2 reviewer that using a hybrid rocket is risky for abort. Dreamchaser is cool, but is more difficult to develop.
I don't see it as risky, it depends on the particulars of the hybrid system doesn't it?  I made one, once, which was Hypergolic, so no concern over ignition there.

*edit* Come to think of it, my particular design would not be smart for the Dream Chaser in any case, as I used a 5% formula of Chlorine TriFlouride as the oxidizer.  That stuff is dangerous in the highest degree, so falls under the "Don't do this at home kids" category.

Isn't the risk more related to the fact that Dream Chaser can't land in water?
The HL-20 could land in water as a ditch landing.  I do not know if the DC kept this capability.  But that would be better discussed on the DC thread. 
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Offline sanman

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Re: SpaceX: Advanced Launch Abort System (LAS)
« Reply #50 on: 04/29/2011 06:33 pm »
You wouldn't have to make the whole trip in the Dragon; there would probably be a hab module as well, and Dragon would be used just during descent to the martian surface.

On the other hand, I'm sure you could find volunteers who would be willing to make the whole trip in the Dragon.

How long would that trip be again? Everybody seems to have different trip plans, and it's unclear to me whether a SpaceX manned trip would be identical to what's specified in Mars Direct.

What's the shortest possible trip that could be made in a manned vehicle/hab?

How much would this cost? (under SpaceX everyday low prices, as opposed to rug bazaar prices)

Offline spacetraveler

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Re: SpaceX: Advanced Launch Abort System (LAS)
« Reply #51 on: 04/29/2011 06:42 pm »
What NASA needs is lunar , mars landing modules and EDS, Tugs,Fuel depot
and put back the moon and mars plan that was taken away.

I agree, if NASA could spend $11.5 billion on this stuff instead of a BFR, we would be much further ahead in exportation.

Multiple EELV or FH launches could lift it.

Offline Michael Bloxham

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Re: SpaceX: Advanced Launch Abort System (LAS)
« Reply #52 on: 05/22/2011 02:22 am »
I have a question. How much propellant would the LAS on Dragon be expected to hold?

Thanks,

- Mike

Offline strangequark

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Re: SpaceX: Advanced Launch Abort System (LAS)
« Reply #53 on: 05/22/2011 01:26 pm »

How long would that trip be again? Everybody seems to have different trip plans, and it's unclear to me whether a SpaceX manned trip would be identical to what's specified in Mars Direct.

What's the shortest possible trip that could be made in a manned vehicle/hab?

How much would this cost? (under SpaceX everyday low prices, as opposed to rug bazaar prices)

Tough questions to answer well, but I'll take the first part, at least. I'm assuming you mean shortest practical trip, as what's possible depends on how many gigatonnes of propellant you're willing to launch. Duration depends on the type of trajectory. Mars Direct recommended a conjunction class mission. That is, you launch when Mars and Earth are on opposite sides of the sun from one another. This is the lowest energy path, and results in a longer surface stay (a year or more). Conjunction transfers are between about six and nine months, depending on the amount of energy you want to sink into it, and the year you are launching.

If I costed it, I'm afraid it would only be a step above a WAG.
« Last Edit: 05/22/2011 01:35 pm by strangequark »

Offline Nomadd

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Re: SpaceX: Advanced Launch Abort System (LAS)
« Reply #54 on: 05/22/2011 03:05 pm »
I have a question. How much propellant would the LAS on Dragon be expected to hold?

Thanks,

- Mike

 A huge advantage of this LAS is that it wouldn't need any extra fuel mass. It will use the 1200kg or so manuevering fuel that the capsule already carries.
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Offline Jason1701

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Re: SpaceX: Advanced Launch Abort System (LAS)
« Reply #55 on: 05/22/2011 07:55 pm »
I have a question. How much propellant would the LAS on Dragon be expected to hold?

Thanks,

- Mike

 A huge advantage of this LAS is that it wouldn't need any extra fuel mass. It will use the 1200kg or so manuevering fuel that the capsule already carries.

If they didn't carry any extra fuel, they couldn't do a propulsive landing. Also, there were some rumors that the LAS might be monopropellant, whereas Draco is bipropellant. Both of these provide reasons for them to carry extra fuel.

Offline Downix

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Re: SpaceX: Advanced Launch Abort System (LAS)
« Reply #56 on: 06/22/2011 03:16 am »
On the Lunar Lander thread we got onto a tangent about the Dragon LAS, and if the Draco thruster system or a derivative of it could be part of the LAS. 

So I dug up what information I could, the Draco thruster as it is now has a chamber pressure of ~6 bar/~100 psia.  The chamber itself, however, based on what I can observe should be able to handle 30 bar/~500 psia.  This level of chamber pressure difference is not unknown, the RS-36 handled a pressure differential of almost twice this and had a very similar chamber design and an almost identical fuel mixture. 

So, calculating out the thrust of a 500 psia in this chamber, by changing the pressure going in (not a difficult thing to do in my experience if you design for it with a pintle system) and you would wind up with a 2.6klbf thruster, at the cost of your isp dropping like a rock, to ~250.  8 x 2.6k == 20.8 klbf, a little over 90kN, more than the Soyuz abort system.  This would require other changes to the system, of course, and is likely not the solution they would use, but it was an interesting academic exercise.
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Offline Robotbeat

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Re: SpaceX: Advanced Launch Abort System (LAS)
« Reply #57 on: 06/22/2011 05:42 am »
On the Lunar Lander thread we got onto a tangent about the Dragon LAS, and if the Draco thruster system or a derivative of it could be part of the LAS. 

So I dug up what information I could, the Draco thruster as it is now has a chamber pressure of ~6 bar/~100 psia.  The chamber itself, however, based on what I can observe should be able to handle 30 bar/~500 psia.  This level of chamber pressure difference is not unknown, the RS-36 handled a pressure differential of almost twice this and had a very similar chamber design and an almost identical fuel mixture. 

So, calculating out the thrust of a 500 psia in this chamber, by changing the pressure going in (not a difficult thing to do in my experience if you design for it with a pintle system) and you would wind up with a 2.6klbf thruster, at the cost of your isp dropping like a rock, to ~250.  8 x 2.6k == 20.8 klbf, a little over 90kN, more than the Soyuz abort system.  This would require other changes to the system, of course, and is likely not the solution they would use, but it was an interesting academic exercise.
If the throat is the same size, then to a first order estimate, having five times the chamber pressure will get you five times the thrust. So, not 2.6klbf but 450lbf (original Draco is 90lbf).

Except it will likely be worse than that since the 90lbf is in vacuum with the vacuum-optimized nozzle (alleviated a bit by the higher pressure...).

Also, you generally don't want to design an engine with a Factor of Safety of 1... you'll kill it with just the start-up transient, most likely.

Also, with higher chamber pressure comes higher thermal loads, thus higher temperatures and lower material strengths...

...and, since we're being pressure-fed, here... much heavier tanks and valves... with the same factor of safety, the tanks just got about 5 times heavier for the same amount of propellant

And after all this, we're still a good ten times less thrust than is needed per abort engine.
« Last Edit: 06/22/2011 05:59 am by Robotbeat »
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Offline Chris-A

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Re: SpaceX: Advanced Launch Abort System (LAS)
« Reply #58 on: 06/22/2011 06:00 am »
Pretty much "Rockets and Spacecraft are not Lego blocks" apply here.

Offline Downix

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Re: SpaceX: Advanced Launch Abort System (LAS)
« Reply #59 on: 06/22/2011 06:25 am »
On the Lunar Lander thread we got onto a tangent about the Dragon LAS, and if the Draco thruster system or a derivative of it could be part of the LAS. 

So I dug up what information I could, the Draco thruster as it is now has a chamber pressure of ~6 bar/~100 psia.  The chamber itself, however, based on what I can observe should be able to handle 30 bar/~500 psia.  This level of chamber pressure difference is not unknown, the RS-36 handled a pressure differential of almost twice this and had a very similar chamber design and an almost identical fuel mixture. 

So, calculating out the thrust of a 500 psia in this chamber, by changing the pressure going in (not a difficult thing to do in my experience if you design for it with a pintle system) and you would wind up with a 2.6klbf thruster, at the cost of your isp dropping like a rock, to ~250.  8 x 2.6k == 20.8 klbf, a little over 90kN, more than the Soyuz abort system.  This would require other changes to the system, of course, and is likely not the solution they would use, but it was an interesting academic exercise.
If the throat is the same size, then to a first order estimate, having five times the chamber pressure will get you five times the thrust. So, not 2.6klbf but 450lbf (original Draco is 90lbf).

Except it will likely be worse than that since the 90lbf is in vacuum with the vacuum-optimized nozzle (alleviated a bit by the higher pressure...).

Also, you generally don't want to design an engine with a Factor of Safety of 1... you'll kill it with just the start-up transient, most likely.

Also, with higher chamber pressure comes higher thermal loads, thus higher temperatures and lower material strengths...

...and, since we're being pressure-fed, here... much heavier tanks and valves... with the same factor of safety, the tanks just got about 5 times heavier for the same amount of propellant

And after all this, we're still a good ten times less thrust than is needed per abort engine.
If everything else were the the same, you would be correct.  However, I was focusing on the various bits TRW developed for the LCPE, to enable that engine to throttle so widely without a dramatic pressure change.  By changing the pintle arrangement, they produced differing thrust envelopes at the same pressure within the chamber itself.  SpaceX uses a similar pintle design, so logic says that they too can take advantage of these differing thrust envelopes.

As for heavier tanks, only if they are to hold the load.  If instead it was to be a forced emergency pressurization, that is the extra pressure was not added until needed, you could get by with the existing tankage.  Old trick I used to use for my step-brothers dragster, to enable him to utilize the same fuel tank as other racers but gain the advantage of a pressurized system when he needed it. I strapped a bottle of Nitrogen gas, which would be forced into the tank body, putting pressure on the outside of the bladder, pushing the fuel up the pipe, pressurizing it to ensure that the system regulated the fuel flow, and not the fuel-flow regulating the system.  So long as the duration of the added pressure was not overly long (which a LAS situation should not be), it would not be an issue.

And why would someone do all this when they could introduce their own LAS motors?  Weight, by dual-purpose, they could save a lot of weight.  They may be going about their own custom LAS motors, who knows.  But it is an interesting thought to see how one could accomplish the job.
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