Author Topic: SpaceX Falcon 9 : SES 11/Echostar 105 : Oct 11, 2017 : Discussion  (Read 55928 times)

Offline meekGee

  • Senior Member
  • *****
  • Posts: 7757
  • N. California
  • Liked: 4050
  • Likes Given: 830
Looks like another stage that won't fly again.  There have been 12 first stage recovery flights this year, but only three of them were GTO missions and all three were first stage reflights (using "used" first stages).  My guess is that these are R&D flights on the reuse side that won't see their stages used again (the SES-10 and Bulgariasat stages have been retired or mothballed).  They would have been expendable flights otherwise.  The other three GTO missions this year were expendable missions.

A bit of a weenie roast after this landing!

 - Ed Kyle

People have been saying that on every core that comes down a little stressed.

Remember Thaicom 8? 

Not sure what the point is, but it's a popular refrain.
Regardless of if it can be reflown, they won't do any 3rd flights for anything as long as they have single flight cores hanging around everywhere or it makes more sense to fly/refly block 5 cores.
With that I agree. Just got tired of all the internet experts declaring with such confidence (and no evidence) that "this landing was so rough, clearly the stage will never fly again".

These are the same people that also claim how uneconomical the whole endevour is.

So, you know, had to point out the obvious.
ABCD - Always Be Counting Down

Offline llanitedave

  • Senior Member
  • *****
  • Posts: 2102
  • Nevada Desert
  • Liked: 1280
  • Likes Given: 1487
If you think about it, the control algorithms must be awfully impressive to deal with the rapidly changing flight dynamics! They deal with essentially no atmosphere, supersonic thin through thicker atmosphere, transoceanic, and subsonic with three different control methods of varying power all of which substantially change over time. I mean, the rocket flies beautifully with the grid fins vaporizing during flight! Imagine how the system must deal with some fins producing more drag (but not predictable before hand drag) from worse and worse flow properties (due to some parts no longer being there). I mean, adaptive controls have been in flight systems for ages but its still amazing just how controlled these flights are with so much changing!

Somebody did their calculus homework in school!
"I've just abducted an alien -- now what?"

Online deruch

  • Full Member
  • ****
  • Posts: 1579
  • California
  • Liked: 1186
  • Likes Given: 1697
It seems that telemetry (not just video) from the 1st stage was lost towards the end of the entry burn (?) and those monitoring had to use external sources to keep track of it (??).
Had that happened before AFTS on that stage had been safe, would it blew the stage up?  :-\
No, that's exactly one of the benefits of AFTS.  It doesn't matter if the ground receives zero telemetry from the rocket so long as the rocket can still "compute" its position.  Then the AFTS just determines that the rocket's position and vectors aren't violating any of the preloaded safety rules. 
Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

Offline yokem55

  • Full Member
  • ****
  • Posts: 443
  • Oregon (Ore-uh-gun dammit)
  • Liked: 247
  • Likes Given: 12
42967/2017-063A: 309 x 40519 km x 27.89 deg
42968/2017-063B: 313 x 40517 km x 27.88 deg
Using this calculator I get a detla-v to GEO of 1773m/s. Right on target.

Offline Kaputnik

  • Extreme Veteran
  • Senior Member
  • *****
  • Posts: 2795
  • Liked: 447
  • Likes Given: 381


I was thinking the same thing about the plasma, but then got worried when it didn't pick up again. Held my breath until I started hearing the descent callouts.

I was really amazed to see that it was showing 6,000 km/h when the entry burn ended, is that a record?
I am sure some of the spacex stats geeks around here will have that info soon!   But yeah 6000 seems pretty quick.  Also since they arent doing 3 engine landing burn attempts anymore (for now) They could be hunting for ways to trim down on the entry burn requirements by seeing how little they need to slow the stage down :) "This one wasnt burned up that badly?  Hmmm, cut the burn off another 2 seconds early and see what happens!  Its just a block 3!"

I'm sure Chris G's article said this was a three engine landing burn.
Waiting for joy and raptor

Offline joncz

  • Veteran
  • Full Member
  • ***
  • Posts: 358
  • Atlanta, Georgia
  • Liked: 47
  • Likes Given: 127
The titanium fins are slightly longer and cover the bottom-of-fin attach point protrusion on the body completely, Have a scalloped front face, And for the moment are unpainted and dark grayish instead of white.

As far as the glow, I'm halfway surprised I never saw big chunks blowing by the camera. Whatever ablative coating is used on them earned it's pay today.

The aluminum fins also have these longitudinal ribs:



Offline vanoord

  • Full Member
  • ****
  • Posts: 479
  • Liked: 287
  • Likes Given: 38
I'm sure Chris G's article said this was a three engine landing burn.

I don't think we saw the landing burn, but my understanding has been that the stage lands on a single engine, even if three have been lit during the burn - they are ramped up and down 1 engine / 3 engines / 1 engine, hence the description as a 1-3-1 burn.

To me, that makes sense as a change in throttle level on a single engine gives a less aggressive thrust change, particularly at the point of touch-down - and from memory, the attempts to touch down with three engines lit haven't been particularly easy viewing.

That said, a quick skip through the recent landings is pretty inconclusive, as the moment of landing is either not seen either due to video drop-out on the ASDS - or from too far away for RTLS.

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 27033
  • Minnesota
  • Liked: 6927
  • Likes Given: 4886
Looks like another stage that won't fly again.  There have been 12 first stage recovery flights this year, but only three of them were GTO missions and all three were first stage reflights (using "used" first stages).  My guess is that these are R&D flights on the reuse side that won't see their stages used again (the SES-10 and Bulgariasat stages have been retired or mothballed).  They would have been expendable flights otherwise.  The other three GTO missions this year were expendable missions.

A bit of a weenie roast after this landing!

 - Ed Kyle

People have been saying that on every core that comes down a little stressed.

Remember Thaicom 8? 

Not sure what the point is, but it's a popular refrain.
Regardless of if it can be reflown, they won't do any 3rd flights for anything as long as they have single flight cores hanging around everywhere or it makes more sense to fly/refly block 5 cores.
Exactly.

Doesn't make sense to reuse this stage, perhaps, but doesn't mean it can't be done.
« Last Edit: 10/12/2017 11:43 AM by Robotbeat »
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline hans_ober

  • Full Member
  • *
  • Posts: 100
  • Somewhere
  • Liked: 52
  • Likes Given: 1
I'm sure Chris G's article said this was a three engine landing burn.

I don't think we saw the landing burn, but my understanding has been that the stage lands on a single engine, even if three have been lit during the burn - they are ramped up and down 1 engine / 3 engines / 1 engine, hence the description as a 1-3-1 burn.

To me, that makes sense as a change in throttle level on a single engine gives a less aggressive thrust change, particularly at the point of touch-down - and from memory, the attempts to touch down with three engines lit haven't been particularly easy viewing.

That said, a quick skip through the recent landings is pretty inconclusive, as the moment of landing is either not seen either due to video drop-out on the ASDS - or from too far away for RTLS.

IIRC the callout from landing burn start to us seeing the booster exhaust on the barge was ~10s, which makes it a 3 engine landing burn.
Single engine landing burns take around 30 seconds, 3 engine ones take around 10-15.

I'm guessing the reason for starting with one engine (1-3-1) is to decrease the jerk on the stage, but more importantly improve stability. The 2 side engines are off axis, and if one starts faster than the other (or even fails to start), you've got a large off axis thrust that would require a quick gimbal correction, and result in the rocket veering off course. While this might be tolerable for the boost back and reentry burns (since they can always correct), it will be close to impossible to correct when dealing with the very tight margins of a 3 engine burn: they've gotta deal with vertical velocity, horizontal velocity, pitch and position the stage over the ASDS in ~10 seconds. Any off axis thrust will make it veer off course and require additional fuel to correct - something that do not have.
They probably shutdown the 2 outer engines at the end of the 1-3-1 for accuracy. It's difficult to do a suicide burn when accelerating at 4.5Gs (since distance is the double integral of acceleration.. at 4.5Gs, a fraction of a second puts them off by a couple of meters - so they crash hard, or end up hovering).

Offline hans_ober

  • Full Member
  • *
  • Posts: 100
  • Somewhere
  • Liked: 52
  • Likes Given: 1
Ready for a scary thought....BulgariaSat-1 was going ~600km/h faster at the end of the entry burn then this one!!

Bulgariasat entered at ~1.8kms. Normal GTO MECO velocity is usually around 2.3km/s, split between ~2.1km/s horizontal & 1 km/s vertical components.
Any idea what the velocities were on the early experimental flights they did with F9 where the stage broke up as soon as it hit the atmosphere (early recovery days)? Bulgariasat reentry points to them being able to do >2km/s reentries with Ti gridfins.

The main factor here is the vertical velocity: prior to the reentry burn they're probably doing >1km/s which makes the stage hit the atmosphere too quickly. Reduce that, and they'll be able to use the larger grid fins to make F9 a lifting body and bleed off even >2.5km/s horizontal velocity.

They'll need this for FH. Core will probably MECO >3km/s, so as long as they reduce vertical velocity during the reentry burn, they'll manage to bleed off the horizontal velocity without any problem.

Online Herb Schaltegger

... so as long as they reduce vertical velocity during the reentry burn, they'll manage to bleed off the horizontal velocity without any problem.
I donít know that that follows axiomatically. The longer the stage is bleeding off velocity through the atmosphere, the longer itís exposed to heating; that can affect the bulk prop temps and the overall temp regime inside the octoweb, which affect startup of the engine for landing. Further, the longer the stage is being heated by high speed atmospheric flight, the more net heat load the structure is exposed to; you donít want your composites and grid fin hydraulics to get too hot either.

So yeah, core landings will be a balancing act of many factors and will almost certainly be pretty sporty, aside from very light payloads when SpaceX trajectory designers have lots of prop to burn for slower entry and longer landing burns.
Ad astra per aspirin ...

Offline edkyle99

  • Expert
  • Senior Member
  • *****
  • Posts: 12849
    • Space Launch Report
  • Liked: 3606
  • Likes Given: 616
Looks like another stage that won't fly again.  There have been 12 first stage recovery flights this year, but only three of them were GTO missions and all three were first stage reflights (using "used" first stages).  My guess is that these are R&D flights on the reuse side that won't see their stages used again (the SES-10 and Bulgariasat stages have been retired or mothballed).  They would have been expendable flights otherwise.  The other three GTO missions this year were expendable missions.

A bit of a weenie roast after this landing!

 - Ed Kyle

People have been saying that on every core that comes down a little stressed.

Remember Thaicom 8? 

Not sure what the point is, but it's a popular refrain.
Thaicom 8 weighed only 3 tonnes.  The other reused boosters flew LEO missions first, then launched heavier-than-Thiacom 8 satellites to GTO.

Remember NROL 76?  LEO mission, stage reportedly mothballed after LZ 1 landing.  What about JCSAT 16's stage, scrapped after a GTO launch?  I count at least five stages retired, mothballed, or scrapped to date out of 15 stages recovered to date, six if B1031.2 ends up retired.

 - Ed Kyle
« Last Edit: 10/12/2017 06:42 PM by edkyle99 »

Offline dedead

  • Member
  • Posts: 25
  • Liked: 9
  • Likes Given: 0
Hello,

I'm here for the 1st time at Cape Canaveral.
Do you know when the drone ship is planned to go back at the port with the first stage ? :)

Online envy887

  • Senior Member
  • *****
  • Posts: 2765
  • Liked: 1277
  • Likes Given: 803
Hello,

I'm here for the 1st time at Cape Canaveral.
Do you know when the drone ship is planned to go back at the port with the first stage ? :)

It usually takes 3 or 4 days IIRC, so I'd expect it Saturday or Sunday.

Online abaddon

  • Full Member
  • ****
  • Posts: 1513
  • Liked: 947
  • Likes Given: 765
Hello,

I'm here for the 1st time at Cape Canaveral.
Do you know when the drone ship is planned to go back at the port with the first stage ? :)
Welcome to the forum!  I'd suggest following this thread: https://forum.nasaspaceflight.com/index.php?topic=39766, which is specific to tracking the ASDSs (ASDI?).

Offline dedead

  • Member
  • Posts: 25
  • Liked: 9
  • Likes Given: 0
Thank you :)

Online Prettz

  • Full Member
  • *
  • Posts: 137
  • Atlanta, GA
  • Liked: 65
  • Likes Given: 13
Was it just because it was dark out the heat on the grin fins was more visible? Was the Iridium launch using titanium?
Iridium was also aluminum
Was stated during the launch webcast due to lower energy trajectory.

This SES-11 was obviously not a lower energy trajectory, so we can assume they are using (or rather burning) up their stock of aluminum ones.
I got the impression that they reeeally didn't care too much if they got this old booster back or not.

Or, that there was a risk of not getting the booster back anyway, and they didn't want to risk losing the titanium fins for no reason.

Online nacnud

  • Extreme Veteran
  • Senior Member
  • *****
  • Posts: 2021
  • Liked: 221
  • Likes Given: 145
Oh come on, don't be daft. The stage is worth $$$, just the engines alone are probably worth the recovery attempt. So they didn't use the titanium fins, well if they have the aluminum fins knocking around and they're good for one used only at these entry velocities then why not use them?

Offline Orbiter

  • Senior Member
  • *****
  • Posts: 2186
  • Florida
  • Liked: 386
  • Likes Given: 911
My shot from Playalinda Beach
Attended space missions: STS-114, STS-124, STS-128, STS-135, Atlas V "Curiosity", Delta IV Heavy NROL-15, Atlas V MUOS-2, Delta IV Heavy NROL-37, SpaceX CRS-9, SpaceX JCSAT-16, Atlas V GOES-R, SpaceX SES-11.

Offline meekGee

  • Senior Member
  • *****
  • Posts: 7757
  • N. California
  • Liked: 4050
  • Likes Given: 830
Looks like another stage that won't fly again.  There have been 12 first stage recovery flights this year, but only three of them were GTO missions and all three were first stage reflights (using "used" first stages).  My guess is that these are R&D flights on the reuse side that won't see their stages used again (the SES-10 and Bulgariasat stages have been retired or mothballed).  They would have been expendable flights otherwise.  The other three GTO missions this year were expendable missions.

A bit of a weenie roast after this landing!

 - Ed Kyle

People have been saying that on every core that comes down a little stressed.

Remember Thaicom 8? 

Not sure what the point is, but it's a popular refrain.
Thaicom 8 weighed only 3 tonnes.  The other reused boosters flew LEO missions first, then launched heavier-than-Thiacom 8 satellites to GTO.

Remember NROL 76?  LEO mission, stage reportedly mothballed after LZ 1 landing.  What about JCSAT 16's stage, scrapped after a GTO launch?  I count at least five stages retired, mothballed, or scrapped to date out of 15 stages recovered to date, six if B1031.2 ends up retired.

 - Ed Kyle

Maybe, but the re-entry was hot, and all the experts lined up and declared it a total loss because of the rough touch-down.

It wasn't.

There's no argument that early recovered F9s are less likely to refly.  That's obvious.  If only because there are more recovered stages that options to re-fly.

But this will clearly change - SpaceX has only re-flown 3 times this year. The direction it's heading, especially with more advanced revisions of F9, is clear...
ABCD - Always Be Counting Down

Tags: