Launch News SpaceX Falcon 9 v1.2 with Dragon CRS-8 April 8 2016

[Urwumpe]

Barge landing attempt according to the article.

The odds on this one are a bit better as there are wider performance margins, but given that the last one seemed to have missed the barge completely and no video was released, I'm not expecting the landing to succeed.

*Humming the theme of "Das Boot"* :hide:

 

[Kyle]

Barge landing attempt according to the article.

The odds on this one are a bit better as there are wider performance margins, but given that the last one seemed to have missed the barge completely and no video was released, I'm not expecting the landing to succeed.

Correct. The ASDS left port yesterday morning to support the landing attempt.

FWIW, I believe this one has a high chance of being successful. Jason-3's first stage would have survived its landing attempt if the leg had not failed to completely deploy during the attempt. SES-9 came in incredibly hot due to mission requirements (GTO mission) and was not expected to survive anyways.

 

[PhantomCruiser]

Well, at least with every failure they gain data. Eventually they'll get it.

 

[RisingFury]

Correct. The ASDS left port yesterday morning to support the landing attempt.

FWIW, I believe this one has a high chance of being successful. Jason-3's first stage would have survived its landing attempt if the leg had not failed to completely deploy during the attempt. SES-9 came in incredibly hot due to mission requirements (GTO mission) and was not expected to survive anyways.

That's fair enough. This one does get to slow down more and yes, the leg really screwed them over the last time.

But it does seem like even if they get this one, there's still a lot of work to do to actually get the thing to reliably land on the ship.


There's one more thing that's been on my mind for all this time:
What exactly prevents the stage from tipping over post launch if the ship rocks with the waves?

 

[Urwumpe]

What exactly prevents the stage from tipping over post launch if the ship rocks with the waves?

See "The Martian": RCS.

 

[Andy44]

See "The Martian": RCS.

I thought one of the failed barge landing videos actually showed the RCS jets on the nose very clearly fighting to keep the booster upright. Or amI misremembering?

 

[Kyle]

I thought one of the failed barge landing videos actually showed the RCS jets on the nose very clearly fighting to keep the booster upright. Or amI misremembering?

That's correct. The question is though how long will the RCS be firing after touchdown?

 

[Urwumpe]

That's correct. The question is though how long will the RCS be firing after touchdown?

Exactly - in the movie, the RCS fired long enough to consume a significant amount of RCS fuel. In the SpaceX landing attempts, it only fired as long as post-landing guidance was still active.

Technically, you need to secure the stage after landing or prevent large list/pitch angles and velocities of the barge. Or both.

 

[Kyle]

It'll be interesting to see what procedure they have for that. I can't imagine they'll allow people on the barge to secure the stage while the RCS is firing.

 

[Urwumpe]

It'll be interesting to see what procedure they have for that. I can't imagine they'll allow people on the barge to secure the stage while the RCS is firing.

I also doubt that, but right now, it is also none of their problems.

Any technical solution to securing the stage after landing for transport adds complexity and can turn a successful landing into a disaster. A flat even surface, not too slippery, is everything that is needed right now, even if the stage could get lost seconds later.

Should I see a live stream of the landing, my expectation of success is that easy: "touchdown, 21, 22, 23, 24, 25 ... VICTORY!" Everything that happens after 5 stable seconds is optional.

For later landings, it would make sense to develop systems that interlock with the landing gear for initial stability. Later you can manually center it and lower it to horizontal position for transport.

 

[Thunder Chicken]

There's one more thing that's been on my mind for all this time:
What exactly prevents the stage from tipping over post launch if the ship rocks with the waves?

Extremely low center of mass of the nearly empty stage, down by the engines. I wouldn't worry so much about rocking, but I'd worry about high wind. I wonder if they have some provision to get crew on board to guy it down after landing.

 

[Notebook]

Some time ago I did a thread about centre of mass change during rocket flight. After a lot of help from here, got some nice graphs:

http://i89.photobucket.com/albums/k207/Notebook_04/Mathcad5.jpg

Be interesting to do it with the Falcon 9.

N.

 

[Andy44]

Run out onto a pitching deck in high wind gusts to try to chain down a rocket booster with hypergolic propellants and possibly still-active RCS jets? Sure I'll do it if you pay me enough. But it's gonna have to be a LOT.

 

[DaveS]

Run out onto a pitching deck in high wind gusts to try to chain down a rocket booster with hypergolic propellants and possibly still-active RCS jets? Sure I'll do it if you pay me enough. But it's gonna have to be a LOT.

Hypergolic propellants? Neither RP-1 (refined kerosene) nor LOX is hypergolic. And the RCS uses gaseous nitrogen of which there is plenty in the atmosphere (80+%). The stage is safed once touchdown is confirmed.

 

[Andy44]

Hypergolic propellants? Neither RP-1 (refined kerosene) nor LOX is hypergolic. And the RCS uses gaseous nitrogen of which there is plenty in the atmosphere (80+%). The stage is safed once touchdown is confirmed.

Ah, I wasn't aware of the RCS propellant. Thought it would have to be hypergolic to have any strength.

 

[DaveS]

Ah, I wasn't aware of the RCS propellant. Thought it would have to be hypergolic to have any strength.

No. It all boils down to the pressure of the gas. I'm not familiar enough with the Falcon to cite any specifics on it, but it's rather high pressure as well as the thrusters being located rather high up which eases the thrust requirements.

The primary control is through the grid fins, the GN2 thrusters are for extra assist when the grid fins doesn't have enough force to control the stage.

 

[Urwumpe]

The primary control is through the grid fins, the GN2 thrusters are for extra assist when the grid fins doesn't have enough force to control the stage.

And for roll control during single engine flight. But AFAIR, the engines use hypergolic starters.

 

[MaverickSawyer]

And for roll control during single engine flight. But AFAIR, the engines use hypergolic starters.

Pyrophoric. TEA/TEB blend is used to provide ignition.

 

[Thunder Chicken]

Press kit is out:

http://www.spacex.com/press/2016/04/07/press-kit-crs-8-dragon-mission

 

[francisdrake]

Why are the unmanned supply missions attached to the ISS by capture and berthing, while the manned Dragon capsule will have a conventional docking port? Wouldn't it be easier to let the Dragon dock like the Progress freighters do?