Author Topic: SpaceX Falcon Heavy Discussion (Thread 4)  (Read 522510 times)

Offline Jim

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1520 on: 08/03/2016 04:42 PM »

No one thinks that strapping together a total of 27 engines, in three different thrust structures and three discrete-but-interacting flight control systems, and igniting all of them for lift-off has any potential engineering challenges that might still be looking for hard solutions?

No,
a.  They haven't have any issues for 9 engine starts for awhile.  Doing 27, it isn't going to change much
b.  They aren't 3 different, but two exactly the same,with the other similar.
c.  Flight control systems are any different.  They are all slaved to the second stage until after separation, just like a single stick launch.

Offline the_other_Doug

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1521 on: 08/03/2016 05:00 PM »

No one thinks that strapping together a total of 27 engines, in three different thrust structures and three discrete-but-interacting flight control systems, and igniting all of them for lift-off has any potential engineering challenges that might still be looking for hard solutions?

No,
a.  They haven't have any issues for 9 engine starts for awhile.  Doing 27, it isn't going to change much
b.  They aren't 3 different, but two exactly the same,with the other similar.
c.  Flight control systems are any different.  They are all slaved to the second stage until after separation, just like a single stick launch.

Thanks, Jim!  To clarify, I wasn't trying to suggest that SpaceX must be having problems in integrating the three cores that they're not talking about.  I was just tossing out a couple of examples of the kinds of things one might think would need to be explored and addressed.

Glad to hear, from someone who knows, that there seem to be no insurmountable engineering issues to be solved before they strap three of these things together and light 'em all off.  And thanks for the reminder that the three boost stages will be slaved to the FCS in stage 2 until they separate.

I know the separate FCS systems in each booster are identical (with possibly small alterations to the center core's FCS), but I've seen two (granted, commercial) identical GPS receivers sitting side-by-side disagree in their position by several meters.  Obviously, the side boosters on each FH launch will have to be in very close agreement on their position, both via GPS and inertial, once their separate flight control systems take over upon separation.

Also, the side cores will need to fly avoidance maneuvers to ensure no recontact with either the remaining center core, or each other, that initiate immediately upon side booster separation, etc. -- all I was suggesting is that these are things SpaceX has never done before, and that have never been done with this specific booster, and I wondered if they would pose engineering challenges that could still be in the process of being addressed.

Good to know, as you seem to intimate, that these will not be show-stoppers.  I'm hoping SpaceX isn't working any other show-stoppers on the engineering side -- it's not like they would be publicizing it, if they were.

I do still wonder about Elon stating the two side boosters will RTLS "nearly simultaneously."  I'd think you would want to maintain some distance between the two stages, to avoid any possibility of interaction between the two.  Each stage is generating sonic booms, after all -- I wouldn't think you'd want them within a kilometer of each other when they each go subsonic.  A little separation, please...?
-Doug  (With my shield, not yet upon it)

Offline Jim

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1522 on: 08/03/2016 05:24 PM »
1.    Obviously, the side boosters on each FH launch will have to be in very close agreement on their position, both via GPS and inertial, once their separate flight control systems take over upon separation.

2.  Also, the side cores will need to fly avoidance maneuvers to ensure no recontact with either the remaining center

1.  Not really, they already are further apart than the standard GPS error and they will never get closer.

2.  Not really, they will be separated by solid motors and/or gas thrusters (just like other vehicles).  Just as the single core booster doesn't do anything right after separation, neither will the side boosters.  Aerodynamics will take over as the booster angle away and increase the separation.


  Each stage is generating sonic booms, after all -- I wouldn't think you'd want them within a kilometer of each other when they each go subsonic.  A little separation, please...?

That should have no bearing on the matter. 
« Last Edit: 08/03/2016 05:26 PM by Jim »

Offline Dante80

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1523 on: 08/03/2016 05:50 PM »
2.  Not really, they will be separated by solid motors and/or gas thrusters (just like other vehicles).  Just as the single core booster doesn't do anything right after separation, neither will the side boosters.  Aerodynamics will take over as the booster angle away and increase the separation.

Do we have any more info on this procedure? I think that SpaceX would use a hydraulic system initially for separation, and maybe couple it with the nitrogen thrusters for adding some distance after that.

Offline Jim

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1524 on: 08/03/2016 05:53 PM »
2.  Not really, they will be separated by solid motors and/or gas thrusters (just like other vehicles).  Just as the single core booster doesn't do anything right after separation, neither will the side boosters.  Aerodynamics will take over as the booster angle away and increase the separation.

Do we have any more info on this procedure? I think that SpaceX would use a hydraulic system initially for separation, and maybe couple it with the nitrogen thrusters for adding some distance after that.

Gas thrusters/gas pistons   

A large impulse is needed.

Offline the_other_Doug

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1525 on: 08/03/2016 05:59 PM »
2.  Not really, they will be separated by solid motors and/or gas thrusters (just like other vehicles).  Just as the single core booster doesn't do anything right after separation, neither will the side boosters.  Aerodynamics will take over as the booster angle away and increase the separation.

Do we have any more info on this procedure? I think that SpaceX would use a hydraulic system initially for separation, and maybe couple it with the nitrogen thrusters for adding some distance after that.

Gas thrusters/gas pistons   

A large impulse is needed.

Have side boosters (LRB or SRB) on any large rockets ever been jettisoned with anything except explosive bolts and solid-fuel separation motors?
-Doug  (With my shield, not yet upon it)

Offline Silmfeanor

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1526 on: 08/03/2016 06:24 PM »
2.  Not really, they will be separated by solid motors and/or gas thrusters (just like other vehicles).  Just as the single core booster doesn't do anything right after separation, neither will the side boosters.  Aerodynamics will take over as the booster angle away and increase the separation.

Do we have any more info on this procedure? I think that SpaceX would use a hydraulic system initially for separation, and maybe couple it with the nitrogen thrusters for adding some distance after that.

Gas thrusters/gas pistons   

A large impulse is needed.

Have side boosters (LRB or SRB) on any large rockets ever been jettisoned with anything except explosive bolts and solid-fuel separation motors?
Soyuz boosters just drop away and vent some gas near the top I think; no solids involved.

a thread about it can be found here:
https://forum.nasaspaceflight.com/index.php?topic=12437.0
« Last Edit: 08/03/2016 07:20 PM by Silmfeanor »

Online wannamoonbase

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1527 on: 08/03/2016 06:30 PM »
So -- it's the consensus of all the engineering types around here that SpaceX is deliberately delaying FH for their own internal reasons, and not because they are still addressing potential engineering issues?

No one thinks that strapping together a total of 27 engines, in three different thrust structures and three discrete-but-interacting flight control systems, and igniting all of them for lift-off has any potential engineering challenges that might still be looking for hard solutions?

Just wonderin'... :)

Not to mention the manpower/schedule challenge of trying to catch up on a severe F9 launch backlog...and getting crewed Dragon done, which has also been slipping, BTW...

Their workload has been increasing at a rapid rate, and increasing staffing to match in an extremely demanding work environment like that can be very difficult to manage. Often the hiring lags behind the actual headcount need. We've already heard that 80-hour work weeks are common. It wouldn't surprise me if the delays in FH and crewed Dragon are simply the result of too few people trying to do too much work.

I think a likely reason for the FH delay is exactly what you mentioned.  The F9 backlog of paying customers who have been waiting a long time.

Resources, such as people, money and equipment, being stretched by other projects like Dragon (that will generate large revenues).

Waiting until recovery is understood a little more and increases the likelihood of being successful in recovering all 3 boosters. 

I want to see the FH fly, it's going to be a crazy machine, and I have been critical of SpaceX's delays and schedule slips.  But this one doesn't trouble me that much.  It's getting closer, there is hardware and I don't believe there is a design or engineering hold up, just getting it through the system.
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Offline oldAtlas_Eguy

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1528 on: 08/03/2016 06:52 PM »
I remember seeing somewhere that range tracking system needs to be upgraded to support tracking multiple inbound boosters at the same time. Totally unconfirmed rumor, but makes certain amount of sense...

Ah, that makes sense. Need someone to confirm that rumour then!
Since Shuttle in the 1980's both ranges needed capability to track and have backups for three simultaneous objects which not only was radar but 3 independent telemetry streams with additional backup telemetry receiver station or stations. With the F9/FH as well as other LVs going forward with AFTS the critical of radar drops such that each object must be able to be tracked by a combination of radar or telemetry assets not both with backups. Less assets but an FH still has more range assets required than a F9 creating a launch constraint more sensitive to range assets health than for F9.

Online FutureSpaceTourist

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1529 on: 08/09/2016 05:18 PM »
Quote
Shotwell on Falcon Heavy: “sorry we’re late” on it; harder problem to develop than we thought. #smallsat

https://twitter.com/jeff_foust/status/763060905886167040

Offline Shanuson

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1530 on: 08/09/2016 05:46 PM »
Quote
David Hurst
‏@OrbitalDave

Shotwell: 1st Falcon Heavy mission expected Q3 of 17 #smallsat

https://twitter.com/OrbitalDave/status/763060858528215040

The guy posting from the conference on Reddit said that's the STP-2 mission in Q3 2017, which would be the second or third FH flight.  Can't wait until they post a video of the talk so we don't have to rely on a bunch of possibly misleading tweets.

I think you are right that the qualification flight will be before that and she did not mean the first F9H flight with her comment.
Still have the feeling F9H shifts right one month each month. Has someone already collected data on that feeling?

Offline cebri

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1531 on: 08/09/2016 07:03 PM »
Ok. I asked jeff foust. Demo still planned for late this year, early next. However delay in the FH development pushing other missions forward.

Offline Mike_1179

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1532 on: 08/23/2016 05:38 PM »
Is it useful to create a FH with three cores that might not be the final design (how to jettison side boosters, flight software, thermal protection, etc.) to test out the GSE? Is there a benefit to getting a WDR done without waiting for the boosters and core to be complete?

Offline oldAtlas_Eguy

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1533 on: 08/23/2016 09:55 PM »
Is it useful to create a FH with three cores that might not be the final design (how to jettison side boosters, flight software, thermal protection, etc.) to test out the GSE? Is there a benefit to getting a WDR done without waiting for the boosters and core to be complete?
SpaceX adopted mantra "Test as you fly. Fly as you test." So no. Only if the use will gain them something very significant is the only exception. The only exception that comes to mind is that the M1D FTs are not yet the M1D maxFTs. M1D max FTs are to supposed start being used sometime after Oct on F9.

But this is not to say that they will not tweak the designs once the FH starts flying either. Its just that intentionally not flying the current design is not likely to gain them anything. A BTW on the engines is that their impact if the non maxFT ones are used is use of different constants in the software and a smaller payload but not much else.

Offline cambrianera

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1534 on: 08/25/2016 07:40 PM »
I realized that, with latest improvements of M1D, FH would still have a good T/W at liftoff with a five engine center core.
This would be 2000 kg dry mass reduction; not saying it is simple, but improving mass ratio on the center core would be a very good thing for reusability.
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Offline Nomadd

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1535 on: 08/25/2016 07:46 PM »
I realized that, with latest improvements of M1D, FH would still have a good T/W at liftoff with a five engine center core.
This would be 2000 kg dry mass reduction; not saying it is simple, but improving mass ratio on the center core would be a very good thing for reusability.
The lighter the core, the more overpowered the last part of the landing. They can do it, but the benefit might be marginal compared to the job of designing a different stage. it might also cost them engine out capabilty for much of the flight.

Offline cambrianera

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1536 on: 08/25/2016 08:06 PM »
The lighter the core, the more overpowered the last part of the landing.
Can't follow your logic, mass reduction is a good thing, and SpaceX seems perfectly capable of landing a stage with about 10% reduced mass compared to actual.

They can do it, but the benefit might be marginal compared to the job of designing a different stage.
Center core already is a different stage, and about 10% reduced mass seems not marginal to me.
Less engines means also less cost.


It might also cost them engine out capabilty for much of the flight.
Losing 1/23 is not that different than losing 1/29.
Maybe losing 1/5 is, compared to 1/9.
No free lunch anyway...
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Online wannamoonbase

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1537 on: 08/25/2016 08:11 PM »
Is it useful to create a FH with three cores that might not be the final design (how to jettison side boosters, flight software, thermal protection, etc.) to test out the GSE? Is there a benefit to getting a WDR done without waiting for the boosters and core to be complete?
SpaceX adopted mantra "Test as you fly. Fly as you test." So no. Only if the use will gain them something very significant is the only exception. The only exception that comes to mind is that the M1D FTs are not yet the M1D maxFTs. M1D max FTs are to supposed start being used sometime after Oct on F9.

But this is not to say that they will not tweak the designs once the FH starts flying either. Its just that intentionally not flying the current design is not likely to gain them anything. A BTW on the engines is that their impact if the non maxFT ones are used is use of different constants in the software and a smaller payload but not much else.

Agreed with OAG.  Using a test article is something you do if you have time and money to burn.  Modern design tools and computer modeling have eased or eliminated many of the things that a test article would be used to evaluate.  Design, fabrication and testing has improved ridiculously, I'm constantly in awe.

SpaceX is flying a similar vehicle and learning each flight.  The FH will require some new steps but nothing that can't be figured out with flight hardware.

After seeing the returned core with what appears to be no engines I started to think that maybe the FH slip is partly so that it only ever flies with the maxFT engines. 

SpaceX is likely planning to reuse this first FH a number of times as nothing up to Red Dragon needs expendable performance.  May as well be the final configuration.  Heck this first FH maybe the Red Dragon vehicle.

Edit: My bad, I just remembered I was 'corrected' a while ago by others saying that the Red Dragon FH was going to be recovered. 
« Last Edit: 08/25/2016 08:18 PM by wannamoonbase »
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Online envy887

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1538 on: 08/25/2016 08:14 PM »
Direct GSO insertion of large sats needs expendable performance (and 2nd stage endurance). I know they have said they are working on the endurance, but don't think they have any direct GSO payloads manifested.

Online Robotbeat

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #1539 on: 08/25/2016 08:24 PM »
Direct GSO insertion of large sats needs expendable performance (and 2nd stage endurance). I know they have said they are working on the endurance, but don't think they have any direct GSO payloads manifested.
I think you underestimate just how powerful Falcon Heavy is even in partially reusable mode. Yes, even for high energy missions...
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