Author Topic: SpaceX Falcon 9 v1.1 - Dragon - CRS-5/SpX-5 -Jan. 10, 2015 - DISCUSSION (Read 618065 times)

rpapo · « **Reply #960 on:** 01/12/2015 09:56 am »

When did the SSRMS start coming in to grapple the Dragon so quickly? I remember on earlier missions it was like watching paint dry. This time it was downright fast.

RotoSequence · « **Reply #961 on:** 01/12/2015 11:01 am »

Quote from: rpapo on 01/12/2015 09:56 am

When did the SSRMS start coming in to grapple the Dragon so quickly? I remember on earlier missions it was like watching paint dry. This time it was downright fast.

I'm not going to complain; space is more practical when not everything needs to be treated delicately!

king1999 · « **Reply #962 on:** 01/12/2015 02:06 pm »

Quote from: rpapo on 01/12/2015 09:56 am

When did the SSRMS start coming in to grapple the Dragon so quickly? I remember on earlier missions it was like watching paint dry. This time it was downright fast.

They are hungry

Already ran out of spices, making the food hard to swallow

justineet · « **Reply #963 on:** 01/12/2015 02:07 pm »

Actually the issue with the landing is not clear to me. Not sure if the rocket was coming too fast or was a bit off target and landed on the support equipments instead of the flat surface. I know Elon said it landed hard. But that could be interpreted also as landing off target on the support equipments.

Herb Schaltegger · « **Reply #964 on:** 01/12/2015 02:12 pm »

Quote from: justineet on 01/12/2015 02:07 pm

Actually the issue with the landing is not clear to me. Not sure if the rocket was coming too fast or was a bit off target and landed on the support equipments instead of the flat surface. I know Elon said it landed hard. But that could be interpreted also as landing off target on the support equipments.

You need to pay more attention - Elon's subsequent tweets provided more info (e.g., ran out of hydraulic fluid for grid fins during the landing). The threads have been full of discussion about hydraulic systems, control algorithms, proposed impact/hard landing scenarios and Kreminology of barge damage pics ever since ...

sghill · « **Reply #965 on:** 01/12/2015 03:12 pm »

The video posted earlier in this thread of the Brazilian YouTube CRS-5 launch video has some interesting shots of the SpaceX launch control as others have already pointed out. I didn't see anyone else post it (forgive me if someone did), but one of the shots clearly shows end of the retro-propulsion burn with the grid fins deployed in the rocketcam shot.

You can see the video feed over the technician's shoulder up on the wall monitor on the far left, and also projected on the far wall to the right. He turns around and notices the webcam right after the burn ends followed by a shot of lots of clapping in Hawthorne- at which point, we don't see that launch control room anymore for the remainder of the video.

Fast forward to 7:40 in the video (T+ 7:02 for the launch itself) to see the retro-propulsion burn. At 8:33 in the video, everyone's attention in Hawthorne quickly jerks towards their monitors, and then we see more the engine bell and lox shots for a while with a bummed out looking-Elon leaning back in his center-front Captain's chair for the remainder of the launch.

Kabloona · « **Reply #966 on:** 01/12/2015 03:32 pm »

Quote

. At 8:33 in the video, everyone's attention in Hawthorne quickly jerks towards their monitors, and then we see more the engine bell and lox shots for a while with a bummed out looking-Elon leaning back in his center-front Captain's chair for the remainder of the launch.

I think you meant 9:33 instead of 8:33. At 9:45 the guy next to Elon throws his hands onto his head in the universal sign of "Doh!" and the leans over to confer with Elon (speculation: about the fireball they just saw from the ASDS video feed.)

Aerospace Dilettante · « **Reply #967 on:** 01/13/2015 01:41 am »

Can't figure out what the second dude is saying about the booster when he talks over the first dude in the above video at:

7:52 "T + 7 minutes, 15 seconds, altitude 205 km, 4.2km/s, downran..."

8:00 "Stage 1 blah blah stage"

Anyone have any idea what he said?

NovaSilisko · « **Reply #968 on:** 01/13/2015 01:49 am »

Here's a gif showing the retroburn on the monitor, for easier watching.

johnmoe · « **Reply #969 on:** 01/13/2015 02:16 am »

Quote from: Aerospace Dilettante on 01/13/2015 01:41 am

Can't figure out what the second dude is saying about the booster when he talks over the first dude in the above video at:

7:52 "T + 7 minutes, 15 seconds, altitude 205 km, 4.2km/s, downran..."

8:00 "Stage 1 blah blah stage"

Anyone have any idea what he said?

"Stage 1 FTS is safed."?

rickl · « **Reply #970 on:** 01/13/2015 02:25 am »

Quote from: Kabloona on 01/12/2015 03:32 pm

Quote
. At 8:33 in the video, everyone's attention in Hawthorne quickly jerks towards their monitors, and then we see more the engine bell and lox shots for a while with a bummed out looking-Elon leaning back in his center-front Captain's chair for the remainder of the launch.

I think you meant 9:33 instead of 8:33. At 9:45 the guy next to Elon throws his hands onto his head in the universal sign of "Doh!" and the leans over to confer with Elon (speculation: about the fireball they just saw from the ASDS video feed.)

I'm confused. Is Elon in the first or second row? I can't see the faces clearly enough to tell.

Kabloona · « **Reply #971 on:** 01/13/2015 03:02 am »

Quote from: rickl on 01/13/2015 02:25 am

Quote from: Kabloona on 01/12/2015 03:32 pm
Quote
. At 8:33 in the video, everyone's attention in Hawthorne quickly jerks towards their monitors, and then we see more the engine bell and lox shots for a while with a bummed out looking-Elon leaning back in his center-front Captain's chair for the remainder of the launch.

I think you meant 9:33 instead of 8:33. At 9:45 the guy next to Elon throws his hands onto his head in the universal sign of "Doh!" and the leans over to confer with Elon (speculation: about the fireball they just saw from the ASDS video feed.)

I'm confused. Is Elon in the first or second row? I can't see the faces clearly enough to tell.

I was probably mistaken. More likely Elon is in the center front row as sghill said.

cscott · « **Reply #972 on:** 01/13/2015 03:28 am »

Quote from: cscott on 01/04/2015 09:19 pm

It will be interesting to see how the grid fins will be used, that's for sure. At hypersonic speeds they work, but might not generate enough force given the altitude. As the stage descends there's a tricky transition to transonic flow, where they aren't effective as fins but do generate spoiler drag -- and quite substantial forces on the actuators, presumably. Then there's another tricky transition to subsonic flow, where the fins are again low drag but can generate substantial aerodynamic forces with minimal actuator force.

Because of the difficulties with symmetrical transitions through flow regimes (this is what Carmack was referencing) and the potentially large actuator forces, most folks (me included) assume the fins will be stowed during transonic flight (and a comfortable margin of velocities around that transition). This is why I mentioned that the fins are likely not being used for high drag.

But it is probable that they will be deployed in hypersonic flight, even though fin effectiveness may be low due to the altitude and thin atmosphere. If they weren't interested in using them supersonic they wouldn't have bothered using grid fins in the first place.

And if SpaceX is really confident in their modeling (and it is true that grid fins are fairly well-understood analyticly) and in the strength of their actuators, then they may well keep them extended through the transonic transition region. It would be pretty gutsy to do so, considering the aerodynamic and mechanical unknowns, the risk of control inversion, etc. Perhaps the actuators can be locked through transition. SpaceX do take risks, and the extra transonic drag might make it worth it. Maybe not on the first flight, though?

It will be exciting to find out!

Well, we know now that the grid fins were deployed in the hypersonic region. And they were deployed subsonic... at least until they ran out of fluid.

I don't think we have any direct evidence about what happened in the transonic transition region. Did the fins fold back in, did they leave them out but lock them in position, or what?

This morning I realized that SpaceX have a third option: they can use the "fold down" axis of the fins to skip through the transonic region entirely. Folding down the fins changes the effective grid spacing. From this reference (pg 19-21) we can confirm that the critical transonic speed where choked flow occurs is dependent on the lattice cell size.

So my theory is that SpaceX does not completely fold up the grid fins at any point once they've been deployed, but instead the core varies the deploy angle to ensure that the fins are never in a transonic critical region. That is, I expect the grid fins to 'droop' slightly when the speed reaches the high end of the transonic critical region, avoiding transonic flow, then 'undroop' once the speed reaches the low end of the transonic critical region.

Comga · « **Reply #973 on:** 01/13/2015 04:31 am »

Quote from: NovaSilisko on 01/13/2015 01:49 am

Here's a gif showing the retroburn on the monitor, for easier watching.

This is very neat but does not show the structure visible in at least two of the previous hypersonic retro-propulsion burns, including the first for CASSIOPE.
These involved quasi-periodic patterns, like repeated bars of flame, although they were only present for parts of the burns.
As others have noted, the color here is blue, where in previous burns it was decidedly yellow.
I wonder what is different this time.

Comga · « **Reply #974 on:** 01/13/2015 04:34 am »

On a different subject, did anyone notice that there seemed to be another fire on the TEL?
It appears at 0:52-0:58 in the video, 14 to 18 seconds after launch.
It looks even more like a flame in the video than in these stills.

Kabloona · « **Reply #975 on:** 01/13/2015 04:36 am »

Quote

. So my theory is that SpaceX does not completely fold up the grid fins at any point once they've been deployed, but instead the core varies the deploy angle to ensure that the fins are never in a transonic critical region. That is, I expect the grid fins to 'droop' slightly when the speed reaches the high end of the transonic critical region, avoiding transonic flow, then 'undroop' once the speed reaches the low end of the transonic critical region.

Wouldn't that require another level of complexity: stage has to know its own Mach number? If so, how would they implement?

If not, maybe they just design for the worst case loads and hope for the best during transonic? Even if resultant control authority is not good during transonic, there's still plenty of time in subsonic flight afterwards to recover.

Asking to be educated from a position of genuine ignorance, obviously.

cscott · « **Reply #976 on:** 01/13/2015 05:20 am »

Quote from: Kabloona on 01/13/2015 04:36 am

Quote
. So my theory is that SpaceX does not completely fold up the grid fins at any point once they've been deployed, but instead the core varies the deploy angle to ensure that the fins are never in a transonic critical region. That is, I expect the grid fins to 'droop' slightly when the speed reaches the high end of the transonic critical region, avoiding transonic flow, then 'undroop' once the speed reaches the low end of the transonic critical region.

Wouldn't that require another level of complexity: stage has to know its own Mach number? If so, how would they implement?

If not, maybe they just design for the worst case loads and hope for the best during transonic?

It's not a question of loads, it's stability. The fin loses all control authority when in the critical transonic region. If this happens asymmetrically this can be even badder.

The stage knows its speed and altitude. That's all you need. And yes, there may be some uncertainty about your exact Mach number, just like there will be uncertainly about the exact critical Mach number for each grid fin (which may vary based on roughness, angle of attack, etc). That's why you sandbag the range with a comfortable margin on each side. Start the droop "comfortably above" the troublesome region, end the droop when you are "comfortably below" it. The amount of droop is calculated to keep you safely out of trouble while drooped.

cleonard · « **Reply #977 on:** 01/13/2015 05:27 am »

There is still control authority during the transonic regime, but it is drag only. Just setting them to straight out and flat would get stabilizing drag at the top of the falling stage. When the speed drops below some critical value they can start using them for steering again.

ugordan · « **Reply #978 on:** 01/13/2015 11:48 am »

This video shows the best view of a 1st stage recovery burn I've seen, at 3 minutes in:

I can't figure out if it's the boostback or reentry burn. Correlating it with the CRS-4 IR video and atmospheric disturbances, I'd say it's a better match to the reentry burn - exhaust wake is more disturbed and collimated, while the boostback burn seems to be occuring in near-vacuum at low dynamic pressure.

cscott · « **Reply #979 on:** 01/13/2015 01:21 pm »

@cleonard: locking the grid fins was my original theory. What I realized is that it is not necessary to give up control through the transonic region if you droop the fins. This also explains why we saw active control of droop angle in the F9dev1 test video.