LIVE: SpaceX Falcon 9 (Flight 2) - COTS-1 - Launch Updates - December 8, 2010

[Namechange User]

But there are 6 forward-facing Draco's. Perhaps the 2 remaining ones are kept in reserve, should the others overheat? 

Actually, while firing, RCS-scale thrusters don't overheat, they are well  cooled by propellant flow into them. It's only after cutoff that the hot nozzles conduct into the thrust chamber and attach points and the temp sensors rise.

Jim O
'Prop' console (OMS/RCS), STS-1, 2

 

It actually depends on the design if they have boundary layer cooling or not.   Even if they do, there are certainly duty cycles that they have tested against and likely cannot fire forever until the prop runs out (assuming the tanks aren't really small )

Also, the number of thrusters provide redundancy Lars.

[rklaehn]

I'm guessing that the forward pointing Draco thrusters are the ones doing the deorbit burn. (Due to the angle of the capsule walls, they would be the most efficient for the purpose)

Yes, that would make sense. The forward-pointing ones are the ones you would use for bigger maneuvers, since they have no "cosine losses" since they point exactly in flight direction.

But there are 6 forward-facing Draco's. Perhaps the 2 remaining ones are kept in reserve, should the others overheat?

They are probably for redundancy. If you need 4 engines in a symmetric pattern for a nominal reentry, having 6 gives you 1 engine out redundancy in any case.

Anyway: congratulations spacex!

[billh]

Jim O
'Prop' console (OMS/RCS), STS-1, 2

Too cool for words

Yes, in the midst of all us "wannabees" it's nice to know we have a few "been there done thats"!

[Chris Bergin]

About 20 minutes to expected splashdown.

[Namechange User]

I don't think we're at loss-of-signal until Dragon starts really hitting the atmosphere and ionizing the air. So, another 5 or so minutes until that.

If there antennas pointing "up" and are communicating through TDRSS there may not be an LOS.  Really don't know if this is the plan or not, just commenting. 

[iamlucky13]

But there are 6 forward-facing Draco's. Perhaps the 2 remaining ones are kept in reserve, should the others overheat?

I   surmise too that the 6-min burn with only 4 thrusters helps with lower Gs.  Astronauts  on board would be forward-facing, pressing outward against  the straps.

Not for this spacecraft. The Draco thrusters are small. 6 x 400 N thrusters = 2400 Newtons.

In a ~3000 kg spacecraft, that's 1/12th of a G. Sleeping on your stomach is more an an eyeballs-out situation. 

[SpacexULA]

Orbital is gonna be shocked when NASA suddenly stops returning their calls.

Hardly, with the shuttle retiring the ISS is going to need more supplies than Dragon could provide by itself.  Orbital is till the tortoise to SpaceX's hare. 

SpaceX,STS, Orbital, and ULA are all on the same team, making sure the US doesn't fall behind in it's ISS commitments.

[brihath]

Jim O
'Prop' console (OMS/RCS), STS-1, 2

Too cool for words

Yes, in the midst of all us "wannabees" it's nice to know we have a few "been there done thats"!

Not only that, he writes excellent books too!

[billh]

SpaceX,STS, Orbital, and ULA are all on the same team, making sure the US doesn't fall behind in it's ISS commitments.

Here, here!! 

[Avron]

Must be passed EI by now.. entry then chutes...

[Chris Bergin]

Standing by for any updates. Parachutes are scheduled to deploy in five minutes.

[Hunts Villain]

Getting video signal through Hawaii.

[iamlucky13]

But there are 6 forward-facing Draco's. Perhaps the 2 remaining ones are kept in reserve, should the others overheat? 

Actually, while firing, RCS-scale thrusters don't overheat, they are well  cooled by propellant flow into them. It's only after cutoff that the hot nozzles conduct into the thrust chamber and attach points and the temp sensors rise.

Jim O
'Prop' console (OMS/RCS), STS-1, 2

 

It actually depends on the design if they have boundary layer cooling or not.   Even if they do, there are certainly duty cycles that they have tested against and likely cannot fire forever until the prop runs out (assuming the tanks aren't really small )

Also, the number of thrusters provide redundancy Lars.

Well, SpaceX have tested these in a thermal vac chamber if I remember right, and this is one of their critical functions, so in this case, I'd hope they've designed a big margin against overheating for the de-orbit burn.

And I think Jim-O was talking more about the mechanical parts of the thruster upstream of the combustion chamber, not boundary layer cooling in the chamber and nozzle.

[spacetraveler]

Must be passed EI by now.. entry then chutes...

Main chute deploy in about 5 min according to NASA.

[dad2059]

SpaceX,STS, Orbital, and ULA are all on the same team, making sure the US doesn't fall behind in it's ISS commitments.

Here, here!! 

Goes without sayin'.

[ugordan]

Standing by for any updates. Parachutes are scheduled to deploy in five minutes.

Is that estimate accurate? Seems to me it would be too early between a deorbit burn (assuming it wasn't a huge one) and being under parachutes...

[Robotbeat]

Getting video signal through Hawaii.

What?

[Avron]

Getting video signal through Hawaii.

music to my ears

[Dave G]

Getting video signal through Hawaii.

On the web? Where?

[Namechange User]

But there are 6 forward-facing Draco's. Perhaps the 2 remaining ones are kept in reserve, should the others overheat?

I   surmise too that the 6-min burn with only 4 thrusters helps with lower Gs.  Astronauts  on board would be forward-facing, pressing outward against  the straps.

Not for this spacecraft. The Draco thrusters are small. 6 x 400 N thrusters = 2400 Newtons.

In a ~3000 kg spacecraft, that's 1/12th of a G. Sleeping on your stomach is more an an eyeballs-out situation. 

It has little to do with g-forces on the crew(unless you burned so quickly you actually went balistic).  The thing just got launched to 17,000 mph in 9 minutes. 

You can deorbit any vehicle with any force given the appropriate length of time to apply it. 

It is all integrated and goes back to mission flight design, amount of prop, duty cycles the thrusters are capable of performing, TPS capability, structural loading for entry, etc