SpaceX: Advanced Launch Abort System (LAS)

[Robotbeat]

I see no reason why SpaceX, with their pretty extensive in-house design and manufacturing capabilities and vertical integration, wouldn't just develop a custom lunar lander more like the Soviet or Apollo lander designs. You have to do all the manufacturing and certification and design anyway, might as well do it right.

[balan h20]

I may be dense but I dont see how you can not change the angle of descent if you add two manuvering draco pointinting up on one side and two pointing down on the other. That has to chang the angle a hair or two and that would make the dragon creep in the direction of the dangle. All factors being even if you add an upward element to on side and a downward to the other it has to change the angle.

[ugordan]

I may be dense but I dont see how you can not change the angle of descent if you add two manuvering draco pointinting up on one side and two pointing down on the other.

It's not a matter of changing the angle, it's a matter of actually *keeping* that angle. In the real world there is no way to *perfectly* aim thrust of an engine through the center of mass of a vehicle and even the slightest mispointing will induce a rotational torque on the vehicle. What happens if this torque is greater than the lowly Dracos can counter?

[balan h20]

You are already through the atmosphere and approaching the ground. What you want to do is to change the angle to move the craft latteraly across the surface prior to setting down. You do this at three or four kilo above the surface to land in a more appropriate area. No different than changing the landing area on a water landing in an airplane or switching to a different runway  or doing a go round. I had to do a go round at Jeckel Island GA because of a fishing trawler in the inland seaway on final crossing the runway. If they plan to land this thing on planets they are going to have to manuver like the lunar alnder to keep from landing on a boulder or on a the side of a incline.

[ugordan]

If they plan to land this thing on planets they are going to have to manuver like the lunar alnder to keep from landing on a boulder or on a the side of a incline.

I imagine they would use throttling of the 4 sections of SDs to do that and only possibly use Dracos for finer attitude adjustments. You're talking about using a single Super Draco (or two) on the same side of the spacecraft to eliminate cosine losses. That's a different beast control-wise.

[HMXHMX]

Can anyone draw any useful design insights from these cropped stills from the video?  Interested in the rectangular features between where the fuel lines enter.

It's underexpanded, very low area ratio (but that's expected). The rectangular features look like a thermal standoff to me (if I'm looking at what you're looking at). Might have been necessary because these things give off a lot more heat than a regular Draco, so they have to be more concerned about the surrounding hardware.

Can you estimate what the area ratio may be?

[darkenfast]

Here's a question: are there any figures for the ignition reliability of pressure-fed bi-propellant engines versus solid-fuel motors? These are both mature technologies, but I wonder how they compare.

[Robotbeat]

Here's a question: are there any figures for the ignition reliability of pressure-fed bi-propellant engines versus solid-fuel motors? These are both mature technologies, but I wonder how they compare.

The bipropellant is hypergolic in this case. As long as both fuel and oxidizer make contact, they will ignite. So bipropellant in this case needs no ignition system.

[sanman]

The bipropellant is hypergolic in this case. As long as both fuel and oxidizer make contact, they will ignite. So bipropellant in this case needs no ignition system.

Well, then what about the safety of this arrangement? If its hypergolic, then isn't there also the danger of unwanted ignition or explosion? Did they investigate any alternatives, or did they just decide that whatever works for Draco is good enough for SuperDraco?

[ugordan]

If its hypergolic, then isn't there also the danger of unwanted ignition or explosion?

Ignition occurs when they mix and they mix in the combustion chamber after valves upstream open.

You also have to let go of the notion that a LAS will be 100% safe with no failure modes of its own. NASA expects any abort system to be at least 90% reliable, i.e. less than 1/10 chance of a failed abort once it's initiated. A LAS is not a silver bullet to *guarantee* you won't have a bad day.

Isn't there a saying in the fighter pilot world that an ejection is an attempted suicide to escape certain death...

[Maciej Olesinski]

Not sure if that one was posted before - not in this topic for sure.
Super Draco testing without fancy music

[SebastianB]

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...

[dcporter]

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

They do seem to get more accurate over time though.

[Jason1701]

I don't see how the SuperDracos could be housed in those fairings without protruding into the pressure vessel.

[Robotbeat]

I don't see how the SuperDracos could be housed in those fairings without protruding into the pressure vessel.

That's not without precedent. The Apollo lunar lander ascent engine protruded into the crew cabin.

[Jason1701]

I don't see how the SuperDracos could be housed in those fairings without protruding into the pressure vessel.

That's not without precedent. The Apollo lunar lander ascent engine protruded into the crew cabin.

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. Also, the first round of crew accommodation tests did not show a modified pressure vessel; we'll see if the second round does. I think SpaceX will increase the height of Dragon without changing the pressure vessel, so as to create space in the service section for the SuperDracos.  If they add a cylindrical rather than conical section, they wouldn't have to modify the heat shield.

[Robotbeat]

I don't see how the SuperDracos could be housed in those fairings without protruding into the pressure vessel.

That's not without precedent. The Apollo lunar lander ascent engine protruded into the crew cabin.

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. Also, the first round of crew accommodation tests did not show a modified pressure vessel; we'll see if the second round does. I think SpaceX will increase the height of Dragon without changing the pressure vessel, so as to create space in the service section for the SuperDracos.  If they add a cylindrical rather than conical section, they wouldn't have to modify the heat shield.

Changing the pressure vessel is less of a concern than you make it sound like, certainly less than your alternative, which would significantly change the reentry dynamics, etc.

[TrueBlueWitt]

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.

[cuddihy]

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...

I would take this as confirmation that the guy who said he had seen the service section and that there wasn't room for 8 estes motors much less eight abort engines was correct.

[Comga]

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

They do seem to get more accurate over time though.

I wouldn't say that.  There are many questionable elements in this graphic.  The Trunks have pontoon-ish items for the solar panels, but they don't protrude sufficiently into the volume of the Trunks to provide volume for the folded solar panels.  In the upper right there is the end of the original centered ISS solar panel that was moved long ago to an end of the Truss.  The JEM is not quite correct, with too many, too prominent EVA handles.  Lots of little things.

It is interesting that new features were added specificaly to the Crew Dragon depiction, but I would not rely on that as what will be built.