SpaceX: Advanced Launch Abort System (LAS)

[meekGee]

Red Dragon might have a 50% strong version of the SDs.  And only 4, since LAS is not really needed.
(I realize a presentation last week said 7 g slow-down, but I don't know if that's SpaceX's plan, or is just carrying over the LAS acceleration, as-is, to the Mars scenario.)

[Lars_J]

I think the 7G slow-down was just the result of using existing Dragon capabilities with the least change... In the thin martian air, you want to make the heat shield and atmosphere friction do as much work as possible to slow down. (no chutes in this scenario)

So with the thrust available, a last-ditch 7G burn of most of the propellant is the most efficient use of the SD thrusters.

(I don't think SpaceX were behind this, this seems to be more of an outside analysis of how best to use a Dragon to land cargo on Mars)

[meekGee]

As long as you're near terminal velocity when you start firing, you haven't wasted any aerobraking, and since the approach is very shallow, you can afford a longer burn.

The delta-V is of course in the propellant, not the engines, but having less engine weight means you have more payload mass.

I think less engines is definitely under "minimum change", and maybe even "weaker engines" - but I'm not an expert on this last one.

[DavidH]

So here's a novice question:
Q: The SuperDraco is a hypergolic engine right? That means horribly nasty chemicals (ie, hydrazine), right? So with a hypergol engine this size, how far from humanity does this test have to take place and how long do you have to wait before a human can access the test stand? Do you have to flush the scene with sprinklers and then wait for an hour? That's a GOB (not an acronmym) of hydrazine. I'd imagine there to be some unburnt fuel lying around even if burnt hydrazine is safe (which I don't know is the case.)

[WmThomas]

(I don't think SpaceX were behind this, this seems to be more of an outside analysis of how best to use a Dragon to land cargo on Mars)

Steve Davis of SpaceX, one of the senior engineers on Dragon, was a co-author of the "Ice Dragon" proposal. It would be surprising to learn that he didn't know about this 7g burn concept. I'll ask him when I see him weekend after next.

[Lars_J]

They certainly could have been involved. It was just my (probably erroneous) impression.

[yg1968]

https://twitter.com/elonmusk/status/215478323147575297

Dragon will use four pairs of side mounted Superdraco engines. Can function with up to four out.

[plank]

https://twitter.com/elonmusk/status/215478323147575297

Dragon will use four pairs of side mounted Superdraco engines. Can function with up to four out.

How will they be protected them from reentry?

[Crispy]

https://twitter.com/elonmusk/status/215478323147575297

Dragon will use four pairs of side mounted Superdraco engines. Can function with up to four out.

How will they be protected them from reentry?

They should be well behind the shock wave and won't require additional protection.

[Prober]

https://twitter.com/elonmusk/status/215478323147575297

Dragon will use four pairs of side mounted Superdraco engines. Can function with up to four out.

How will they be protected them from reentry?

They should be well behind the shock wave and won't require additional protection.

thought one side of the Dragon takes the heat?

[DigitalMan]

https://twitter.com/elonmusk/status/215478323147575297

Dragon will use four pairs of side mounted Superdraco engines. Can function with up to four out.

How will they be protected them from reentry?

They should be well behind the shock wave and won't require additional protection.

thought one side of the Dragon takes the heat?

Look more closely.

[peter-b]

thought one side of the Dragon takes the heat?

Um, isn't that what Crispy's image shows?

[Crispy]

The base takes the heat. You might be thinking of the blackening of the sides of the capsule visible immediately after recovery.

This is not due to direct heating by the extremely hot plasma. It's part radiative heating of the paint, from the hot plasma passing by, and part deposition of particles from the ablating heat shield. Neither of which are going to be any problem for the superdraco pods.

[kirghizstan]

so the albative material getting into the super dracos won't have any impact on their performance?

[go4mars]

so the albative material getting into the super dracos won't have any impact on their performance?

Not sure we know enough about it.  It might be a benefit.  It might be a detriment.  It might be neither.

[SpacexULA]

The black dust on the Dragon is not from the sides being super heated, it's from all the ablation of the thermal protective system.

As you can see from the COTS1 and COTS2 dragons, anything brushing the capsule wipes the powder right off.

If you really wanted to upset SpaceX, go after the Dragon with soap and water and it will likely look like it's barely been used (and not be nearly as interesting to look at).

The nozzle for the superdraco is also ablative, it should already be signed for a much ruffer life than some dust coming off the ablative.  (Ok, it's most likely not ablative after reading back, thanks ugordan!)

[mr. mark]

In other words, it's not burnt its dirty.

[ugordan]

The nozzle for the superdraco is also ablative

It is?

[Crispy]

so the albative material getting into the super dracos won't have any impact on their performance?

I'd be amazed if it made any measurable difference whatsoever.

[ugordan]

so the albative material getting into the super dracos won't have any impact on their performance?

I'd be amazed if it made any measurable difference whatsoever.

Quite likely, but when it comes to spaceflight one should never underestimate the ability of "insignificant" things to ruin your day.