Author Topic: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION  (Read 1087827 times)

Offline JamesH

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #200 on: 12/27/2015 10:28 am »
Also, I believe the entry burn is designed to create a plasma sheath between the atmospheric heating region and the octoweb.  In other words, it acts to provide protection against entry heating.  And trust me, at the altitude from, and speed at which the first stage comes in, there is significant entry heating.  The entry burn keeps that from affecting the stage itself, without needing to cover the base of the stage with some additional TPS rated for entry heating.

That's likely, plus I believe it also provides stability in a region where the fins are still not effective.

This is the biggest piece of secret sauce they developed.  When and how much.  They were lucky and got it to work on the first try (CASSIOPE IIRC) but then made it work on the subsequent launch that had much lower margins...  And it has worked on each and every subsequent launch.

I don't believe they were lucky.

I believe they have good engineers, who know what they are doing.  As shown by the fact it has worked on every launch. Including the first.

Offline AncientU

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #201 on: 12/27/2015 12:18 pm »
Also, I believe the entry burn is designed to create a plasma sheath between the atmospheric heating region and the octoweb.  In other words, it acts to provide protection against entry heating.  And trust me, at the altitude from, and speed at which the first stage comes in, there is significant entry heating.  The entry burn keeps that from affecting the stage itself, without needing to cover the base of the stage with some additional TPS rated for entry heating.

That's likely, plus I believe it also provides stability in a region where the fins are still not effective.

This is the biggest piece of secret sauce they developed.  When and how much.  They were lucky and got it to work on the first try (CASSIOPE IIRC) but then made it work on the subsequent launch that had much lower margins...  And it has worked on each and every subsequent launch.

I don't believe they were lucky.

I believe they have good engineers, who know what they are doing.  As shown by the fact it has worked on every launch. Including the first.

Talent, no doubt... but an environment that thrives on innovation and empirical testing (with its associated kabooms) is as vital.  They don't study problems to death -- they try things that will probably be close to the answer, watch the response, and adjust before trying again.  Brilliant.
"If we shared everything [we are working on] people would think we are insane!"
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Online Jakusb

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #202 on: 12/27/2015 12:40 pm »

Also, I believe the entry burn is designed to create a plasma sheath between the atmospheric heating region and the octoweb.  In other words, it acts to provide protection against entry heating.  And trust me, at the altitude from, and speed at which the first stage comes in, there is significant entry heating.  The entry burn keeps that from affecting the stage itself, without needing to cover the base of the stage with some additional TPS rated for entry heating.

That's likely, plus I believe it also provides stability in a region where the fins are still not effective.

This is the biggest piece of secret sauce they developed.  When and how much.  They were lucky and got it to work on the first try (CASSIOPE IIRC) but then made it work on the subsequent launch that had much lower margins...  And it has worked on each and every subsequent launch.

I don't believe they were lucky.

I believe they have good engineers, who know what they are doing.  As shown by the fact it has worked on every launch. Including the first.

Talent, no doubt... but an environment that thrives on innovation and empirical testing (with its associated kabooms) is as vital.  They don't study problems to death -- they try things that will probably be close to the answer, watch the response, and adjust before trying again.  Brilliant.
I guess that is one of the most intriguing aspects of SpaceX: the pushing the envelope at any chance they get. Balancing almost perfectly between science and practice. Failure is not only an option, it is part of shifting boundaries almost no-one seems to dare.
A bit of luck is needed at this too, but they seem to minimize the luck factor to a minimum. And very successfully as it seems.

Offline Jcc

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #203 on: 12/27/2015 12:43 pm »
Here's a question to which I don't have the answer, though -- is the ballistic trajectory worse in terms of heating regime than the looped-back trajectory achieved with the boostback burn?  The boostback does cancel out the rather significant downrange velocity, after all.

I recall that ballistic trajectories have high deceleration rates; do they also have hotter entries than a loop-back?  If so, would that limit the speed and angle at which a falcon can enter on a ballistic trajectory, even with an engine's exhaust pushing back the entry heating?

At staging, S1 has a significant upward velocity, but that will be diminished by about 10m/s per sec., or add to downward velocity 1000m/s for every 100 s of free flight. For boostback, they have to calculate the amount of time it will take to get to the landing site at the planned horizontal velocity and make sure they have enough upward velocity to stay above the atmosphere for most of that distance. That could include adding upward v in the boostback if needed, but all the added upward v will come back in downward v due to gravity, and need to be killed propulsively. For landing at sea, they don't have to do a boostback burn unless they want to keep the landing site  closer to shore, just let it follow the ballistic arc and do a reentry burn to make it survivable.

Offline the_other_Doug

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #204 on: 12/27/2015 01:36 pm »
OK --to try and wrap up this little side-thread, here, let me try and put the question a little better:

Will a ballistic landing downrange, with little to no boostback burn (as will be required for some heavier payloads), create a more challenging entry environment, in terms of both entry heating and deceleration stresses, than entry after a boostback to an RTLS, or near-RTLS, profile?  And does the Falcon have limits beyond which it can't survive a ballistic entry without a boostback (or at least a lofting/shaping) burn?  Or is the entry burn capable of handle all possible conditions, from pure unmodified ballistic entries to full boostback RTLS trajectories?

I guess I'm trying to visualize the boundary between the case of being able to recover a first stage, and the case where the stage must be expended.  I know there's a line out there, defined by the remaining delta-V in the stage after BECO, below which there is not enough energy left to achieve both an entry burn and a landing burn.  But are there ballistic trajectories that are non-survivable, even if there is theoretically enough energy left in the stage to accomplish a downrange recovery?  In other words, is the definition of "must be expended" entirely defined by the remaining delta-V in the stage, or does the entry environment also play a role in defining a mission where the first stage cannot be recovered?
-Doug  (With my shield, not yet upon it)

Offline Jcc

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #205 on: 12/27/2015 01:51 pm »
By environmental conditions do you mean air temp, pressure and wind speed? I'm guessing wind speed and sea state may be significant, but not temperature and barometric pressure. Apart from that, it is also a matter of probabilities as far as actual engine performance that may leave more or less fuel once the velocity target is reached for MECO.

Offline the_other_Doug

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #206 on: 12/27/2015 02:09 pm »
By environmental conditions do you mean air temp, pressure and wind speed? I'm guessing wind speed and sea state may be significant, but not temperature and barometric pressure. Apart from that, it is also a matter of probabilities as far as actual engine performance that may leave more or less fuel once the velocity target is reached for MECO.

No -- I'm talking about the entry conditions -- speed, angle of entry, tie of peak heating, and deceleration stresses.  For example, let's say that a boostback to an RTLS trajectory results in deceleration stresses of about 5G to 6G, whereas a ballistic entry results in 15G to 20G stresses.  Or there is a difference between 30 seconds of entry heating and, say, two minutes, or a significant increase in entry heating, from a ballistic to an RTLS trajectory?  Are there outlier conditions on ballistic entries where the deceleration and thermal stresses result in breakup of the stage?

Again, not talking about the wind conditions at the desired landing point, or the sea state.  I'm talking about surviving the entry back into the atmosphere, and whether or not there is a point at which a Falcon stage will not survive a ballistic entry, even if it has enough delta-V on paper to perform entry and landing burns.  Or is the question of whether or not a given trajectory allows stage recovery based solely on the remaining delta-V in the stage, and the entry conditions are not ever going to be a limiting factor?
-Doug  (With my shield, not yet upon it)

Offline cro-magnon gramps

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #207 on: 12/27/2015 02:18 pm »
Is there an update thread for the SES-9 SpaceX Mission... I'd like to know more details about where this all stands in terms of Launch Readiness ie is the LV ready, is the PL ready, what is the hold up...
Gramps "Earthling by Birth, Martian by the grace of The Elon." ~ "Hate, it has caused a lot of problems in the world, but it has not solved one yet." Maya Angelou ~ Tony Benn: "Hope is the fuel of progress and fear is the prison in which you put yourself."

Offline Jcc

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #208 on: 12/27/2015 02:27 pm »
By environmental conditions do you mean air temp, pressure and wind speed? I'm guessing wind speed and sea state may be significant, but not temperature and barometric pressure. Apart from that, it is also a matter of probabilities as far as actual engine performance that may leave more or less fuel once the velocity target is reached for MECO.

No -- I'm talking about the entry conditions -- speed, angle of entry, tie of peak heating, and deceleration stresses.  For example, let's say that a boostback to an RTLS trajectory results in deceleration stresses of about 5G to 6G, whereas a ballistic entry results in 15G to 20G stresses.  Or there is a difference between 30 seconds of entry heating and, say, two minutes, or a significant increase in entry heating, from a ballistic to an RTLS trajectory?  Are there outlier conditions on ballistic entries where the deceleration and thermal stresses result in breakup of the stage?

Again, not talking about the wind conditions at the desired landing point, or the sea state.  I'm talking about surviving the entry back into the atmosphere, and whether or not there is a point at which a Falcon stage will not survive a ballistic entry, even if it has enough delta-V on paper to perform entry and landing burns.  Or is the question of whether or not a given trajectory allows stage recovery based solely on the remaining delta-V in the stage, and the entry conditions are not ever going to be a limiting factor?

I think the answer is yes, there are limits to all these parameters, and the model the reentry using computational flow dynamics simulations to work out the optimal trajectory. The remaining variation can mostly be made up with grid fin control to adjust stage attitude, lift and drag.

Offline ugordan

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #209 on: 12/27/2015 02:32 pm »
No -- I'm talking about the entry conditions -- speed, angle of entry, tie of peak heating, and deceleration stresses.  For example, let's say that a boostback to an RTLS trajectory results in deceleration stresses of about 5G to 6G, whereas a ballistic entry results in 15G to 20G stresses.  Or there is a difference between 30 seconds of entry heating and, say, two minutes, or a significant increase in entry heating, from a ballistic to an RTLS trajectory?

Maybe I'm missing something and perhaps this is just semantics, but the only entry type a F9 stage can perform is effectively a ballistic entry. It has no significant lift, the grid fins serve only to fine-tune the landing point, I don't think they have enough control authority to significantly shallow-up the trajectory. The only difference between trajectories it can do is the entry angle you set up.

Also, dynamic pressure loading on reentry is likely to be the driving factor (trying to crush the stage, i.e. the G loading you mention), not reentry heating. The part that would experience most heating is the engine section and it already carries TPS anyway.

Offline Jcc

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #210 on: 12/27/2015 02:54 pm »
Lift is quite significant in that a small amount of lift from high altitude can make a difference of several km to the landing point. They adjust the stage orientation control that lift.

Online FutureSpaceTourist

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #211 on: 12/27/2015 03:34 pm »
Is there an update thread for the SES-9 SpaceX Mission... I'd like to know more details about where this all stands in terms of Launch Readiness ie is the LV ready, is the PL ready, what is the hold up...

Not yet, it's too early. The Jason-3 update thread was only created yesterday.

Offline Lars-J

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #212 on: 12/27/2015 05:01 pm »
No -- I'm talking about the entry conditions -- speed, angle of entry, tie of peak heating, and deceleration stresses.  For example, let's say that a boostback to an RTLS trajectory results in deceleration stresses of about 5G to 6G, whereas a ballistic entry results in 15G to 20G stresses.  Or there is a difference between 30 seconds of entry heating and, say, two minutes, or a significant increase in entry heating, from a ballistic to an RTLS trajectory?

Maybe I'm missing something and perhaps this is just semantics, but the only entry type a F9 stage can perform is effectively a ballistic entry. It has no significant lift, the grid fins serve only to fine-tune the landing point, I don't think they have enough control authority to significantly shallow-up the trajectory. The only difference between trajectories it can do is the entry angle you set up.

...Which is exactly what the poster is asking about. A relatively shallow re-entry (from no boost-back) is quite different from an almost vertical re-entry. (which this last landing used)

My guess would be that it would be handled by making the braking/re-entry burn as long as needed, to reach a target velocity at ~40km. Didn't the CASSIOPE mission skip the boost-back burn? See the CASSIOPE video here, starting at 2:40:

« Last Edit: 12/27/2015 05:05 pm by Lars-J »

Online meekGee

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #213 on: 12/27/2015 05:06 pm »
Boost-back zeroes out the horizontal velocity component, and then adds the minimal possible reverse horizontal velocity.

So a forward reentry will be faster and shallower, unless they correct it.

Again - the reentry parameters are the secret sauce.
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Offline ugordan

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #214 on: 12/27/2015 05:07 pm »
No -- I'm talking about the entry conditions -- speed, angle of entry, tie of peak heating, and deceleration stresses.  For example, let's say that a boostback to an RTLS trajectory results in deceleration stresses of about 5G to 6G, whereas a ballistic entry results in 15G to 20G stresses.  Or there is a difference between 30 seconds of entry heating and, say, two minutes, or a significant increase in entry heating, from a ballistic to an RTLS trajectory?

Maybe I'm missing something and perhaps this is just semantics, but the only entry type a F9 stage can perform is effectively a ballistic entry. It has no significant lift, the grid fins serve only to fine-tune the landing point, I don't think they have enough control authority to significantly shallow-up the trajectory. The only difference between trajectories it can do is the entry angle you set up.

...Which is exactly what the poster is asking about.

Yeah, but he was talking about RTLS and ballistic trajectories as if they're somehow different. My point was that they're both really ballistic.

Offline nadreck



Yeah, but he was talking about RTLS and ballistic trajectories as if they're somehow different. My point was that they're both really ballistic.

Until the super/hypersonic retropulsion starts

The original question we drifted on to this really boils down (at least as I understand it) to "what significant differences are there between the supersonic retropulsion phase and landing in a downrange landing or an RTLS landing".

I would agree that the RTLS case has the stage moving somewhat slower against the surrounding air but add that it is going from low pressure to higher pressure quicker because the vertical velocity is much higher. The ADSL case should be going as much as 1km/s higher in absolute velocity but with a rate of descent that is much lower when that retropulsion starts. Once retropulsion is complete the coast phase at (anyone with a better number correct me please) about 800m/s slowing towards terminal velocity before the final landing burn should be steeper for the RTLS but the forces and stresses should not be much different.

Lastly the shape of the course from the start of the final burn is slightly different

Note that the  ΔV required for RTLS vs downrange landing is about double given the rest of the course elements being the same and that in absolute terms if your stage has a downrange velocity of 2km/s then it needs to boost back with more than 3kms with a slight upward component to the vector as soon as it can after stage separation and then do a supersonic retro burn from about 2km/s to 0.8 with probably more than 50% component of vertical velocity compared to a single retropulsion burn from about 3km/s (vertical plus horizontal component) to 0.8. Then in both cases about the same landing burn will be made.
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline cro-magnon gramps

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #216 on: 12/27/2015 06:26 pm »
Is there an update thread for the SES-9 SpaceX Mission... I'd like to know more details about where this all stands in terms of Launch Readiness ie is the LV ready, is the PL ready, what is the hold up...

Not yet, it's too early. The Jason-3 update thread was only created yesterday.

Thx FST with it being NET JAN I was hoping that there might actually be some news about it's progress...
Gramps "Earthling by Birth, Martian by the grace of The Elon." ~ "Hate, it has caused a lot of problems in the world, but it has not solved one yet." Maya Angelou ~ Tony Benn: "Hope is the fuel of progress and fear is the prison in which you put yourself."

Offline OxCartMark

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #217 on: 12/28/2015 03:51 am »
OK --to try and wrap up this little side-thread, here, let me try and put the question a little better:

Will a ballistic landing downrange, with little to no boostback burn (as will be required for some heavier payloads), create a more challenging entry environment, in terms of both entry heating and deceleration stresses, than entry after a boostback to an RTLS, or near-RTLS, profile?  And does the Falcon have limits beyond which it can't survive a ballistic entry without a boostback (or at least a lofting/shaping) burn?  Or is the entry burn capable of handle all possible conditions, from pure unmodified ballistic entries to full boostback RTLS trajectories?

I guess I'm trying to visualize the boundary between the case of being able to recover a first stage, and the case where the stage must be expended.  I know there's a line out there, defined by the remaining delta-V in the stage after BECO, below which there is not enough energy left to achieve both an entry burn and a landing burn.  But are there ballistic trajectories that are non-survivable, even if there is theoretically enough energy left in the stage to accomplish a downrange recovery?  In other words, is the definition of "must be expended" entirely defined by the remaining delta-V in the stage, or does the entry environment also play a role in defining a mission where the first stage cannot be recovered?

Well, your first comment about wrapping up the side-thread, now a dozen or so posts later looks like the side thread is still going on.  Including this-

I seem to have some knowledge relevant to the necessity of boostback but my memory is foggy and a quick search didn't come up with anything useful.  Posting here in hopes that it triggers someone else to remember and flush out the details.  [IIRC] All ocean recovery experiments including the ones prior to ASDS platforms have had what SpaceX has called a boostback burn even though that burn was only to slow horizontal velocity not reverse it (as was done with the CCAFS landed Orbcomm-2) - with one exception.  The one exception was relatively recently, approximately Eutelsat, in March.  That heavy payload took too much energy to do a boostback burn.  It seems as if  there was a tweet or some other source that stated the kinetic energy being carried into the re-entry burn was to be 8x what had succeeded on previous recovery attempts.  And it made it through.[/IIRC]

I can't emphasize enough that this is only foggy memory stuff, not necessarily fact.
Actulus Ferociter!

Offline John Alan

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #218 on: 12/28/2015 05:40 am »
OK --to try and wrap up this little side-thread, here, let me try and put the question a little better:

Will a ballistic landing downrange, with little to no boostback burn (as will be required for some heavier payloads), create a more challenging entry environment, in terms of both entry heating and deceleration stresses, than entry after a boostback to an RTLS, or near-RTLS, profile?  And does the Falcon have limits beyond which it can't survive a ballistic entry without a boostback (or at least a lofting/shaping) burn?  Or is the entry burn capable of handle all possible conditions, from pure unmodified ballistic entries to full boostback RTLS trajectories?

I guess I'm trying to visualize the boundary between the case of being able to recover a first stage, and the case where the stage must be expended.  I know there's a line out there, defined by the remaining delta-V in the stage after BECO, below which there is not enough energy left to achieve both an entry burn and a landing burn.  But are there ballistic trajectories that are non-survivable, even if there is theoretically enough energy left in the stage to accomplish a downrange recovery?  In other words, is the definition of "must be expended" entirely defined by the remaining delta-V in the stage, or does the entry environment also play a role in defining a mission where the first stage cannot be recovered?

Well, your first comment about wrapping up the side-thread, now a dozen or so posts later looks like the side thread is still going on.  Including this-

I seem to have some knowledge relevant to the necessity of boostback but my memory is foggy and a quick search didn't come up with anything useful.  Posting here in hopes that it triggers someone else to remember and flush out the details.  [IIRC] All ocean recovery experiments including the ones prior to ASDS platforms have had what SpaceX has called a boostback burn even though that burn was only to slow horizontal velocity not reverse it (as was done with the CCAFS landed Orbcomm-2) - with one exception.  The one exception was relatively recently, approximately Eutelsat, in March.  That heavy payload took too much energy to do a boostback burn.  It seems as if  there was a tweet or some other source that stated the kinetic energy being carried into the re-entry burn was to be 8x what had succeeded on previous recovery attempts.  And it made it through.[/IIRC]

I can't emphasize enough that this is only foggy memory stuff, not necessarily fact.

DSCOVR was the fast and hot one way downrange...  ;)

Offline OxCartMark

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #219 on: 12/28/2015 05:26 pm »
DSCOVR was the fast and hot one way downrange...  ;)

Can you confirm or deny my recollections of no boostback burn and 8x kinetic energy at atmospheric interface for DSCOVR?  Looking back I see that DSCOVR was the one that was headed to the ASDS but the ASDS was not in position due to a severe storm out there.  It did have a landing on the water surface that was within 10M, which is IIRC, the first to do so.

Interesting discussion but very OT, so I'll just throw this in "SES-9".
Actulus Ferociter!

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