Author Topic: SpaceX Falcon 9 v1.1 - SpX-6/CRS-6 DRAGON - Discussion Thread  (Read 508749 times)

Offline GalacticIntruder

  • Full Member
  • ****
  • Posts: 513
  • Pet Peeve:I hate the word Downcomer. Ban it.
  • Huntsville, AL
  • Liked: 247
  • Likes Given: 70
Not sure about this hover-slam idea on a very small target. I don't see how they will ever get the time to correct for their late (or unexpected) lateral movements if they are falling/landing that fast that close to the target.  I would have assumed almost zero velocity well above the lander. Might need a larger landing area, and better landing gear.
"And now the Sun will fade, All we are is all we made." Breaking Benjamin

Offline Elmar Moelzer

  • Senior Member
  • *****
  • Posts: 3670
  • Liked: 855
  • Likes Given: 1074
Just look at how tiny the barge is compared to the stage! It is no wonder that they are having such a hard time getting right on top of it (especially with strong cross winds, etc). To me it seems very obvious that landing on a (MUCH larger) landing pad on land, would be trivial compared to this and would have probably succeeded.

Offline abaddon

  • Senior Member
  • *****
  • Posts: 3175
  • Liked: 4156
  • Likes Given: 5614
Oh man that was so close.  Much closer than I had thought from the barge pics.

Offline sanman

  • Senior Member
  • *****
  • Posts: 6077
  • Liked: 1363
  • Likes Given: 8
Gee, I would hate to be a human passenger in that thing. Even if it hadn't toppled over, it would still feel like a "brown pants" landing. They should slow the vertical descent rate near the end.
« Last Edit: 04/15/2015 01:22 am by sanman »

Offline jabe

  • Regular
  • Full Member
  • ****
  • Posts: 1227
  • Liked: 184
  • Likes Given: 12
Just look at how tiny the barge is compared to the stage! It is no wonder that they are having such a hard time getting right on top of it (especially with strong cross winds, etc). To me it seems very obvious that landing on a (MUCH larger) landing pad on land, would be trivial compared to this and would have probably succeeded.
my thoughts too...if off target 10 m on land just land it..not so for barge...have to adjust.. Amazing how close they got!! higher resolution vid is going to be awesome!!
jb

Offline butters

  • Senior Member
  • *****
  • Posts: 2402
  • Liked: 1701
  • Likes Given: 608
It looks like the leg deploy upset the attitude control. The mark 2 legs with early deploy might help quite a bit.

Offline CameronD

  • Senior Member
  • *****
  • Posts: 2425
  • Melbourne, Australia
    • Norton Consultants
  • Liked: 900
  • Likes Given: 562
So.. I suppose the ASDS Landing Bingo jackpots again?
With sufficient thrust, pigs fly just fine - however, this is not necessarily a good idea. It is hard to be sure where they are
going to land, and it could be dangerous sitting under them as they fly overhead.

Offline sanman

  • Senior Member
  • *****
  • Posts: 6077
  • Liked: 1363
  • Likes Given: 8
Infrared would have been awesomer, to penetrate that exhaust cloud at the end.

Offline Space Ghost 1962

  • Senior Member
  • *****
  • Posts: 2780
  • Whatcha gonna do when the Ghost zaps you?
  • Liked: 2925
  • Likes Given: 2247
Also, somehow it looks like this stage is descending at a much faster rate at the end, compared to Grasshopper. Can't they spare a bit more fuel to slow the vertical descent just before the end?

It's like the equivalent of a guy screeching into his parking spot and slamming on the brakes.

Could be easier to control coming in fast - not as susceptible to gusts.

The lateral/pitching is more worry some.

The video is impressive, especially when you know the size/weight of the vehicle.

Offline MarekCyzio

Regarding Vine movie:
https://vine.co/v/euEpIVegiIx

This is a book example of an uncontrolable, unstable system with long delay between measurements and controls. 

Offline Lars-J

  • Senior Member
  • *****
  • Posts: 6809
  • California
  • Liked: 8487
  • Likes Given: 5385
To me, it looks like part of the problem is overcorrection.

Yes, it does appear so.

But one cool thing you can see in the Vine is how the RCS thrusters fire just before touchdown. It wasn't enough, obviously. But this data will be immensely helpful it improving the landing algorithm.

Offline NWade

  • Member
  • Posts: 57
  • United States
  • Liked: 74
  • Likes Given: 626
Anyone else notice the top of the stage as it nears the barge? I'm assuming we're seeing the N2 thrusters going full-bore trying to adjust the vehicle and either assist (or compensate for) the gimballed-dance that the main engine is doing...
 
[Answer: Yes, and Lars is just a bit faster on the "Post" button than I am, apparently!]  ::)

--Noel
« Last Edit: 04/15/2015 01:34 am by NWade »

Offline Lars-J

  • Senior Member
  • *****
  • Posts: 6809
  • California
  • Liked: 8487
  • Likes Given: 5385
Not sure about this hover-slam idea on a very small target. I don't see how they will ever get the time to correct for their late (or unexpected) lateral movements if they are falling/landing that fast that close to the target.  I would have assumed almost zero velocity well above the lander. Might need a larger landing area, and better landing gear.

No, hovering solves very little of the actual problem - it just wastes fuel. The targeting/landing algorithm will just need tweaking.

Offline meekGee

  • Senior Member
  • *****
  • Posts: 14618
  • N. California
  • Liked: 14579
  • Likes Given: 1418
Regarding Vine movie:
https://vine.co/v/euEpIVegiIx

This is a book example of an uncontrolable, unstable system with long delay between measurements and controls.

It might just be.   I can't tell if there's a sudden external forcing input (wind gust, failed leg deploy, etc) or just a rocket-induced-oscillation..

I think at the end it wasn't just lateral velocity - the tip rate at touch-down was not zero.
ABCD - Always Be Counting Down

Offline Lars-J

  • Senior Member
  • *****
  • Posts: 6809
  • California
  • Liked: 8487
  • Likes Given: 5385
Regarding Vine movie:
https://vine.co/v/euEpIVegiIx

This is a book example of an uncontrolable, unstable system with long delay between measurements and controls.

Unstable? Yes. Uncontrollable? Give me a break!  ::) (you've never seen the grasshopper videos??)

If this was a piece of cake it would have been done before... But it certainly is possible.
« Last Edit: 04/15/2015 01:36 am by Lars-J »

Offline sanman

  • Senior Member
  • *****
  • Posts: 6077
  • Liked: 1363
  • Likes Given: 8
Were these landing conditions a worst case example? Or would landings be expected under even worse wind/sea conditions?

Offline matthewkantar

  • Senior Member
  • *****
  • Posts: 2176
  • Liked: 2640
  • Likes Given: 2308
A few notes on the amazing Vine Spacex posted:

-One can see the thrusters at the top of the stage doing their thing at the last second.
-The camera seems to have been 'sidewind' to the barge not upwind or downwind, and the wind seems to have been a problem. The gimbal on the landing engine goes from hard left to hard right in the short video.
-I have no confidence at all that I am not seeing things, but it looks like the stage is bending in response to the maneuvering.
-A much larger landing surface would seem to be helpful, but the horizontal component of velocity is still going to have to be zeroed with rocket nearly plumb at the moment of touchdown.
-The video took away any notion that I had that there is a problem with the steadiness of the barge, the amplitude of the stage's movements are off the charts compared to the barge.

It would seem they have lots of work to do.

Matthew




Offline Ohsin

  • Full Member
  • ****
  • Posts: 1469
  • Liked: 1453
  • Likes Given: 2379
To me, it looks like part of the problem is overcorrection.

Yes, it does appear so.

But one cool thing you can see in the Vine is how the RCS thrusters fire just before touchdown. It wasn't enough, obviously. But this data will be immensely helpful it improving the landing algorithm.

Those could be grid fins catching the sunlight. Btw this all feels unreal amazing stuff we are witnessing.

EDIT: Nah too far up to be grid fins. You're right :)
« Last Edit: 04/15/2015 01:38 am by Ohsin »
"Well, three cheers to Sharma, but our real baby is INSAT."

Offline Herb Schaltegger

Also, somehow it looks like this stage is descending at a much faster rate at the end, compared to Grasshopper. Can't they spare a bit more fuel to slow the vertical descent just before the end?

It's like the equivalent of a guy screeching into his parking spot and slamming on the brakes.

Could be easier to control coming in fast - not as susceptible to gusts.

The lateral/pitching is more worry some.

The video is impressive, especially when you know the size/weight of the vehicle.

I need to watch the video a few more times to see if I can make out the moment of leg deploy, but I have to wonder if the late deploy, into a steady sea breeze, isn't what causes the pitch excursion due to the sudden increase in drag at the base of the vehicle relative to the wind. Those rapidly-telescoping legs and their bases have much greater area drag than the relatively featureless cyclinder of the rest of the stage.
Ad astra per aspirin ...

Offline meekGee

  • Senior Member
  • *****
  • Posts: 14618
  • N. California
  • Liked: 14579
  • Likes Given: 1418

2.  No, they are not.  Again, the rocket flies to a coordinate and not an object.


We haven't seen any evidence that there is or isn't a closed loop terminal guidance system.

Clearly most of the descent is towards an absolute coordinate, but we don't know about the last mile.

It is unarguable that active guidance (the rocket doesn't need to communicate with the barge for that) is more precise, since by using absolute coordinates you add the errors in barge and rocket station navigation.

The only question is whether SpaceX implemented a last mile terminal guidance system of some sort.

So far, all we have are opinions.
ABCD - Always Be Counting Down

Tags: CRS-6 
 

Advertisement NovaTech
Advertisement Northrop Grumman
Advertisement
Advertisement Margaritaville Beach Resort South Padre Island
Advertisement Brady Kenniston
Advertisement NextSpaceflight
Advertisement Nathan Barker Photography
1