SpaceX: Advanced Launch Abort System (LAS)

[Lars_J]

Perhaps this is a better thread for it - A new tweet from Elon Musk that just went out: https://twitter.com/elonmusk/status/214831794103664640

Elon Musk ‏@elonmusk
Just fired our Superdraco escape rocket engine at full thrust! Needed to carry astronauts on Dragon pic.twitter.com/ef86qbWF

[Lars_J]

This appears to be a new vertical SD test stand at McGregor, TX. It looks different than the Merlin stands, and I assume the hole is too small for Merlin firings as well.

Can anyone guess a size of the engine based on this image?

[Halidon]

In my head, I just heard Crocodile Dundee say "now that's a thruster."

I wonder if they will test paired thrusters on the stand before progressing to "hopper"-style tethered testing.

[Alpha Control]

This appears to be a new vertical SD test stand at McGregor, TX. It looks different than the Merlin stands, and I assume the hole is too small for Merlin firings as well.

Can anyone guess a size of the engine based on this image?

Lars,
I see a blue staircase in the background that gives a sense of the scale of the platform. To my eyes then, the engine doesn't seem large - 1-2 ft high? (just my very rough guess).

[modemeagle]

I calculated, using some educated guesses on some parameters, that the chamber is ~ 14" dia and ~18" long, which is very close to the size of the chamber for the 1D (also calculated with a few guesses).  The nozzle should be ~16 inches for Pe=Pa.

[HMXHMX]

I calculated, using some educated guesses on some parameters, that the chamber is ~ 14" dia and ~18" long, which is very close to the size of the chamber for the 1D (also calculated with a few guesses).  The nozzle should be ~16 inches for Pe=Pa.

Based on the mockup exhibited at Space Tech Expo, I'd estimate the exit is 8 inches in diameter.

[Lars_J]

This may help... Using the camera position and perspective, I have highlighted two vertical red bars that would be the same actual height.

Now all we need to know is the height of the guide rail to know the dimensions of the SD thrust chamber.

Does anyone know what the standard height is of a guide/safety rail like that?

[MikeAtkinson]

The nozzle should be ~16 inches for Pe=Pa.

It looks underexpanded to me.

[MikeAtkinson]

This may help... Using the camera position and perspective, I have highlighted two vertical red bars that would be the same actual height.

Now all we need to know is the height of the guide rail to know the dimensions of the SD thrust chamber.

Does anyone know what the standard height is of a guide/safety rail like that?

That helps, but I think the camera is slightly above the top of the thrust chamber, so that the red scale line on the rail should be a bit smaller.

[edit: the horizon is 2/3 up the picture, so the camera is pointing down slightly.]

[HMXHMX]

The nozzle should be ~16 inches for Pe=Pa.

It looks underexpanded to me.

This engine is also used for landing.  In that mode, it has to be able to deeply throttle.  I estimate it throttles about 8:1, maybe 10:1, from the max abort thrust level.  They will have designed for no separation at the most deeply throttled sea level condition.

[Lars_J]

That helps, but I think the camera is slightly above the top of the thrust chamber, so that the red scale line on the rail should be a bit smaller.

Nope - pay attention to the horizon. Both of the red bars end at the same level - the horizon. If the camera was above the thrust chamber, the horizon would be above it.

[edit: the horizon is 2/3 up the picture, so the camera is pointing down slightly.]

It doesn't matter - if a picture includes a horizon line - that line is exactly horizontal. (and the virtual triangle formed from the camera to the edge horizon points is 100% even/flat) It doesn't matter if the camera was pointing mostly up or down.

[modemeagle]

My numbers were based on a 132psi chamber pressure (just a guess).
I have been thinking for a while that their system is much higher which would make the chamber smaller then my estimated size.

[DigitalMan]

This is nice:

http://twitter.com/elonmusk/status/214831794103664640/photo/1

[modemeagle]

This may help... Using the camera position and perspective, I have highlighted two vertical red bars that would be the same actual height.

Now all we need to know is the height of the guide rail to know the dimensions of the SD thrust chamber.

Does anyone know what the standard height is of a guide/safety rail like that?

quick search came up with 42" for railing

[go4mars]

Would need to throttle more than 10:1 for Red Dragon I think.  Or maybe they'll only fire 4 superdracos instead of all 8 for that.

[docmordrid]

IIRC at the Mars Concepts and Approaches conference they were talking an SD throttling range of 5% to 100%.

[Robotbeat]

Of course with the very low Martian pressure, separation isn't an issue.

[kevin-rf]

Considering the level of under expansion, you would have to be landing Dragons on Venus before you have a separation issue.

[baldusi]

On Red Dragon it was going to make 7g. At 5 tonnes, 0.375g of Mars gravity, that's 368kN? That's 82.7klbf. That's 69% of throttle.
Hover on Earth's sea level would require just 49kN, or 11klbf, that's 9.1% with eight SD, 18.2% for four. More reasonable.

[go4mars]

On Red Dragon it was going to make 7g. At 5 tonnes, 0.375g of Mars gravity, that's 368kN? That's 82.7klbf. That's 69% of throttle.
Hover on Earth's sea level would require just 49kN, or 11klbf, that's 9.1% with eight SD, 18.2% for four. More reasonable.

Red dragon planned to have a very slow final descent after the 7 g phase.  Hover on Mars = .38 g or lower. 

6.9% using only 4... 

That's throttling from 100% to less than 3.5% if using all 8.