SpaceX: Advanced Launch Abort System (LAS)

[dcporter]

Sure, the videos are still a PR exercise. I guess I should have said, they seem to get less idealized over time.

[Robotbeat]

I guarantee SpaceX knows where the abort thrusters can fit and where they can't and basically what they need to do to fit them. Heck, they probably have the CAD files already drafted, and NASA has probably already seen some of them. People here are acting like they discovered some fatal flaw in their plan, and that's just ridiculous on the face of it. They've already test fired several versions of SuperDraco, after all.

[Jason1701]

I guarantee SpaceX knows where the abort thrusters can fit and where they can't and basically what they need to do to fit them. Heck, they probably have the CAD files already drafted, and NASA has probably already seen some of them. People here are acting like they discovered some fatal flaw in their plan, and that's just ridiculous on the face of it. They've already test fired several versions of SuperDraco, after all.

Not disputing that, just that the animations rarely reflect the actual design, and significant modifications to Dragon's moldline may be required.

[go4mars]

True, but SpaceX probably wants to keep the pressure vessel as similar to the cargo version as possible. Doing otherwise would add to cost and schedule.

I suspect that they will be the same.  ie. The cargo dragons will propulsively land also, once the ability is demonstrated.  Probably before crewed actually. 

[Lurker Steve]

True, but SpaceX probably wants to keep the pressure vessel as similar to the cargo version as possible. Doing otherwise would add to cost and schedule.

I suspect that they will be the same.  ie. The cargo dragons will propulsively land also, once the ability is demonstrated.  Probably before crewed actually. 

If they are counting on propulsive landing, then they are going to have challenges making even the 2017 date.

[MP99]

The recent update about the safety advisory panel contains a new graphic of a crewed Dragon spacecraft.

http://www.spacex.com/press.php?page=20120329

In that graphic the abort/landing engines are housed in protruding boxes on the sidewalls with a recessed area below instead of being fully sleek with the sidewalls as previously shown in the RTLS video.
I assume this graphic shows a relatively recent design since it also has the attachments for the solar panel fairings on the trunk.

I know that I shouldn't read to much into these graphics...

Nice spot.

Good first post - welcome.

cheers, Martin

[go4mars]

If they are counting on propulsive landing, then they are going to have challenges making even the 2017 date.

Sorry for not being clear.   I should have said that propulsive landing will likely be operationally attempted on unmanned dragons prior to crews being propulsively landed.  I think that manned and unmanned dragons will have the same pressure vessel mold-line because they will eventually both land propulsively (one with biological cargo, and one without). 

[dcporter]

Right. COTS is a development program, as is CCDev. Each is going to fund improvements to the Dragon, but I suspect that at the end of the day there will be one model of Dragon which acts basically the same whether it has racks or seats.

[beancounter]

Right. COTS is a development program, as is CCDev. Each is going to fund improvements to the Dragon, but I suspect that at the end of the day there will be one model of Dragon which acts basically the same whether it has racks or seats.

Well I think that was always the intention.  Utilising the same basic structures et al provides for reduced costs over unique items for each separate use.  That's been their philosophy since start up and they seem to have kept pretty much to it.

[go4mars]

Right. COTS is a development program, as is CCDev. Each is going to fund improvements to the Dragon, but I suspect that at the end of the day there will be one model of Dragon which acts basically the same whether it has racks or seats.

Exactly.  The next development program which would expand dragon's capability would be Red Dragon (if it happens).  Based on the projected cost including science instruments ($500M), it seems that related changes/upgrades to dragon would likely be less than $200M-$300M.  What new features might this include?  I suspect it would be focussed on software (including automated descent propulsion) and communications hardware.  Perhaps the trunk would get an option for a larger solar array too.  Whatever changes it brought, I suspect it would bring most (if not all) changes necessary for dragon rider trips around the moon.       

Other than perhaps re-examination of  NOFBX or other alternatives (if the need arises for a specific purpose) may be the only remaining upgrade for this version of dragon, but I see that as low probability. 

I do see potential for a much larger methane ISRU version of dragon in the future.  But that probably wouldn't be even discussed until Elon feels ready to make a Mars architecture public.  And that probably won't be until he either wants to IPO SpaceX, or has at least propulsively landed a rocket stage (operationally and not just grasshopper). 

[SF Doug]

I know that I shouldn't read to much into these graphics...

They do seem to get more accurate over time though.

Does this mean they're changing the nozzle angle to decrease cosine losses?   Even 10 degrees would give you roughly 10% overall improvement.. That is significant and could close the gap or increase margins for some abort/landing scenarios.

Perhaps they no longer think they need the individual thrust vectors to be through the center of mass.

[RDoc]

Perhaps they no longer think they need the individual thrust vectors to be through the center of mass.

It doesn't seem from the earlier illustrations they ever were designed to go through the center of mass does it? It seems likely the center of mass, particularly with cargo, would be well below the vertical midpoint and roughly radially centered. The thrust vectors I believe always intersected the radial center well above the midpoint, actually near the top of the pressure vessel.

[kttopdad]

Does anyone have an educated guess on whether the Dracos are individually tanked or fed from common tanks?

Dean

[Ben the Space Brit]

Does anyone have an educated guess on whether the Dracos are individually tanked or fed from common tanks?

It's been established that the Dracos and Superdracos will be fuelled from a single common system.  FWIW, I think building the RCS/LAS system in self-contained pods that could be swapped, reconditioned and possibly applied to other spacecraft might be a good idea.

[jwade]

Does anyone have an educated guess on whether the Dracos are individually tanked or fed from common tanks?

It's been established that the Dracos and Superdracos will be fuelled from a single common system.  FWIW, I think building the RCS/LAS system in self-contained pods that could be swapped, reconditioned and possibly applied to other spacecraft might be a good idea.

From all of the various cutaway CAD drawings, the Draco set test fire video, the shots of the partly exposed dracos on the COTS1 dragon on display in DC,  it really looks like each set of dracos is basically a self contained module with separate tanks and plumbing that are then cross connected.   Interestingly there appear to be two different modules, a 4 draco set for the hatch side of the dragon and a 5 draco set for the back side.   There are a total of 4 modules (4+4+5+5=18 total dracos per dragon)

The 2010 Spacex archived updates page. http://www.spacex.com/updates_archive.php?page=2010 states: "A system of valves provides redundant cross-connection between the propellant tanks for maximum reliability", although I have never seen a picture that clearly shows this.    Do you have a better source or picture?   

Edit: clarified draco quantities

[Kaputnik]

Sounds a bit like the Shuttle's OMS pods. Essentially self-contained units, but with a propellant transfer capability. Seems to be the best of all worlds. Especially on a capsule where you need to have control over the centre of gravity and therefore want an even distribution of propellant across all of the tanks.

[Chris-A]

There is a photo from a powerpoint that displayed the center section of dragon with aluminum hydraulic lines.

[jwade]

I guarantee SpaceX knows where the abort thrusters can fit and where they can't and basically what they need to do to fit them. Heck, they probably have the CAD files already drafted, and NASA has probably already seen some of them. People here are acting like they discovered some fatal flaw in their plan, and that's just ridiculous on the face of it. They've already test fired several versions of SuperDraco, after all.

I don't mean to be disrespectful, but I am not sure this is true.    SpaceX clearly uses an iterative design process and we have seen significant changes in components that have already flown.    For example, the dragon trunk/solar panel farings.    They clearly investigated significant resources designing and builiding at least test articles of a composite trunk before switching to the current aluminum design.  (See the picture from corroded nut).    The addition of the solar panel fairings extending out from the trunk and the change in mold line and aerodynamics does not look to me like something that was planned for in the original design but was forced by the reality of the solar panel deployment design and volume requirements.    I could be wrong but I would think they would have at least done a more acurate simulated trunk for either of the first two flights had they known what it was going to look like.

I am speculating of course, but I would bet that some propulsion and mechanical engineers at SpaceX are sitting in a conference room still trying to identify a final pipeing and manifold configuration for the flight superdracos that will actually fit into the structure.    The switch to a pusher LAS was clearly done long after the initial dragon design and engineering pathfinder construction so I would still be very surprised if the final propulsively landed dragon ends up sharing the same basic moldline with the current version.   Unfortunately, we can speculate all we want to, but we will probably never know the answer about where SpaceX is in the design process and we will have to wait to see the first real crewed dragon hardware to know for sure how they have solved this.

[Robotbeat]

Yeah, I'm not trying to say I think the SpaceX design is completely set in stone, only that they surely have thought a lot about exactly how big the thrusters need to be, where they can fit, and probably have detailed CAD files of one possible solution to the problem. Considering their pretty impressive past accomplishments (from largely clean-sheet designs), they're at least competent enough to have thought about where the thrusters can fit.

[corrodedNut]

At 1:16:50 Elon says "...even when we have propulsive landing capability, there will still be an emergency parachute...kind of like the Cirrus aircraft"

That system uses a small rocket to ensure proper parachute deployment, even in a stall or at very low airspeeds.

http://cirrusaircraft.com/innovation/?item=parachute#products

Let the speculation begin!