Author Topic: Refurbishment of Used Stages/Vehicles  (Read 211290 times)

Offline rsdavis9

Re: Refurbishment of Used Stages/Vehicles
« Reply #660 on: 04/02/2017 10:12 PM »
So if you have the fuel for RTLS, do that and maybe only reduce the reentry burn to 1 engine. But on marginal missions for downrange landing do a lower  trajectory, that is where saving is most needed.

No, you don't seem to understand. The higher trajectory *IS* the optimal one. The stage isn't thrusting upwards... It merely cancels and reverses its horizontal vector. The same apogee would have been reached with or without a boost-back burn. Doing a shallower boost-back profile does in fact consume MORE propellant.

So with the standard boost back the better L/D would enable less horizontal cancellation because they can stretch the in atmosphere part with the better L/D.
With ELV best efficiency was the paradigm. The new paradigm is reusable, good enough, and commonality of design.
Same engines. Design once. Same vehicle. Design once. Reusable. Build once.

Offline Lar

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Re: Refurbishment of Used Stages/Vehicles
« Reply #661 on: 04/02/2017 10:12 PM »
I am wondering if with the new larger and more heat resistant grid fins there is enough control authority to actually turn, not just slow down by getting some lift. If you could turn around you might be able to RTLS without a boostback burn.

Wings by any other name?

Probably not.  But airplanes turn all the time.
« Last Edit: 04/02/2017 10:29 PM by Lar »
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Online Lars-J

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Re: Refurbishment of Used Stages/Vehicles
« Reply #662 on: 04/02/2017 10:17 PM »
So if you have the fuel for RTLS, do that and maybe only reduce the reentry burn to 1 engine. But on marginal missions for downrange landing do a lower  trajectory, that is where saving is most needed.

No, you don't seem to understand. The higher trajectory *IS* the optimal one. The stage isn't thrusting upwards... It merely cancels and reverses its horizontal vector. The same apogee would have been reached with or without a boost-back burn. Doing a shallower boost-back profile does in fact consume MORE propellant.

I am wondering if with the new larger and more heat resistant grid fins there is enough control authority to actually turn, not just slow down by getting some lift. If you could turn around you might be able to RTLS even with a less lofted profile. Wings by any other name?

Probably not.

Sigh, I'm not sure how to keep explaining this any better.  ???  The 'lofting' of the return trajectory is primarily an artifact of the upward momentum at staging. To 'loft less' requires MORE propellant to cancel this out! (boost-back burn pointing downward)

So you spend more propellant to save propellant later!
« Last Edit: 04/02/2017 10:19 PM by Lars-J »

Offline rsdavis9

Re: Refurbishment of Used Stages/Vehicles
« Reply #663 on: 04/02/2017 10:18 PM »
Totally off topic...

Whats the difference between LARS and LARS-J.
This is the first time I noticed you were different people.
You both seem very knowledgeable.
 
Edit/Lar: Answered in the party thread because it IS off topic
http://forum.nasaspaceflight.com/index.php?topic=42585.msg1662592#msg1662592
« Last Edit: 04/02/2017 10:25 PM by Lar »
With ELV best efficiency was the paradigm. The new paradigm is reusable, good enough, and commonality of design.
Same engines. Design once. Same vehicle. Design once. Reusable. Build once.

Offline Lar

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Re: Refurbishment of Used Stages/Vehicles
« Reply #664 on: 04/02/2017 10:21 PM »
Sigh, if something has lift and has control authority why can't it turn? Things with actual wings turn all the time. They bleed off speed turning and they bleed off altitude too (or more speed if you "set the flaps" higher). If you can actually turn all the way around, voila, you don't have to boost back any more, you're already headed the right way. Elon hates wings but large enough grid fins are a lot like wings :)

I'm not responding to your argument with Guckyfan, I was throwing a new idea out there. (probably to sink but..). I'l cut the quote away if it's really confusing you.

Edit: I did.
« Last Edit: 04/02/2017 10:28 PM by Lar »
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline Space Ghost 1962

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Re: Refurbishment of Used Stages/Vehicles
« Reply #665 on: 04/02/2017 10:33 PM »
Sigh, if something has lift and has control authority why can't it turn? Things with actual wings turn all the time. They bleed off speed turning and they bleed off altitude too (or more speed if you "set the flaps" higher)

Different answers hypersonic, sonic, transonic. First two have stability issues, you'll tumble easy.

When you bleed off energy, control surfaces heat at super linear rates, increasing costs. Shuttle's was carefully done to never push up temps too high in certain edges.

Lifting only works with certain geometries - shallow ones are best, so loong downrange and not lofted. There are some cases, like with RD, where you need to force it to stay within a corridor/ceiling height too, which depends on atmospheric density, which might change daily.

Offline Herb Schaltegger

Re: Refurbishment of Used Stages/Vehicles
« Reply #666 on: 04/02/2017 10:34 PM »
Sigh, if something has lift and has control authority why can't it turn? Things with actual wings turn all the time.

Those wings have a much higher control authority than the grid fins of rocket, and they have actual power (thrust) to help them maintain their kinetic energy through the turn. Something like an SR-71, with those two ginormous afterburning turboramjets still needed something like over 90 miles to make a U-turn at speed, and that's in the much (relatively) denser atmosphere is 70 - 80Kft.
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Offline Lar

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Re: Refurbishment of Used Stages/Vehicles
« Reply #667 on: 04/02/2017 11:18 PM »
Thanks for the clarification. So basically Hypersonic and Transsonic are far different regimes than the 100 kps that a glider (no engine yet it still can turn) does when turning so no, turning isn't going to work. Not without gynormous wings that have special heat shedding properties. Which we know they're not doing. because Elon hates wings.

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"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline Rocket Science

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Re: Refurbishment of Used Stages/Vehicles
« Reply #668 on: 04/02/2017 11:30 PM »
a few months back I toyed with the idea of using the legs to generate lift and control...
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Offline Lar

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Re: Refurbishment of Used Stages/Vehicles
« Reply #669 on: 04/02/2017 11:51 PM »
I'm partly (ok, a lot) at fault here, but the actual reentry stuff is probably not really on topic for refurbishment discussions.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline john smith 19

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Re: Refurbishment of Used Stages/Vehicles
« Reply #670 on: 04/03/2017 06:31 AM »
I the presser Musk said the refurb took about 4 months of actual time and the replaced pretty much everything that looked even slightly worn.

The jokers in this process are
1)How many staff did it take
2)How variable can it be. Consistency really helps in staff planning.
3)Once they are satisfied most stuff does not need replacing what could it go down to?

At present that suggests the refurb team can do 3 stages a year, but we don't know how big that team is or how many teams they can form. If it's 100 strong you don't want too many such teams. If it's just a couple of guys then you could have dozens of them.

BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline guckyfan

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Re: Refurbishment of Used Stages/Vehicles
« Reply #671 on: 04/03/2017 02:02 PM »
At present that suggests the refurb team can do 3 stages a year, but we don't know how big that team is or how many teams they can form. If it's 100 strong you don't want too many such teams. If it's just a couple of guys then you could have dozens of them.

Did you miss that the refurbishment time is already down to 6 weeks, even ahead of block 5 which is supposed to make it much easier?

Offline JamesH65

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Re: Refurbishment of Used Stages/Vehicles
« Reply #672 on: 04/03/2017 02:23 PM »
I the presser Musk said the refurb took about 4 months of actual time and the replaced pretty much everything that looked even slightly worn.

The jokers in this process are
1)How many staff did it take
2)How variable can it be. Consistency really helps in staff planning.
3)Once they are satisfied most stuff does not need replacing what could it go down to?

At present that suggests the refurb team can do 3 stages a year, but we don't know how big that team is or how many teams they can form. If it's 100 strong you don't want too many such teams. If it's just a couple of guys then you could have dozens of them.

The first time you do anything, it always takes longer whilst you get the processes sorted. Not only that, but in this one they also would have been testing EVERYTHING as it was dealt with, a lot of which, as I think Musk has said, will be replaced by more effective sensor suites. I think making any assessment of future times from this one example is foolhardy.

Online envy887

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Re: Refurbishment of Used Stages/Vehicles
« Reply #673 on: 04/04/2017 03:22 AM »
I the presser Musk said the refurb took about 4 months of actual time and the replaced pretty much everything that looked even slightly worn.

The jokers in this process are
1)How many staff did it take
2)How variable can it be. Consistency really helps in staff planning.
3)Once they are satisfied most stuff does not need replacing what could it go down to?

At present that suggests the refurb team can do 3 stages a year, but we don't know how big that team is or how many teams they can form. If it's 100 strong you don't want too many such teams. If it's just a couple of guys then you could have dozens of them.

SpaceX said it will be 2-4 weeks soon, and then go down from there based on resources. So the current team could do as many as 26 in a year.

Offline john smith 19

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Re: Refurbishment of Used Stages/Vehicles
« Reply #674 on: 04/04/2017 12:10 PM »
At present that suggests the refurb team can do 3 stages a year, but we don't know how big that team is or how many teams they can form. If it's 100 strong you don't want too many such teams. If it's just a couple of guys then you could have dozens of them.

Did you miss that the refurbishment time is already down to 6 weeks, even ahead of block 5 which is supposed to make it much easier?
Yes. Where was it reported?
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline Lar

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Re: Refurbishment of Used Stages/Vehicles
« Reply #675 on: 04/04/2017 12:18 PM »
At present that suggests the refurb team can do 3 stages a year, but we don't know how big that team is or how many teams they can form. If it's 100 strong you don't want too many such teams. If it's just a couple of guys then you could have dozens of them.

Did you miss that the refurbishment time is already down to 6 weeks, even ahead of block 5 which is supposed to make it much easier?
Yes. Where was it reported?

Same place you got your quotes I think...
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline sevenperforce

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Re: Refurbishment of Used Stages/Vehicles
« Reply #676 on: 04/04/2017 05:26 PM »
a few months back I toyed with the idea of using the legs to generate lift and control...
Mechanically, current legs are a non-starter on this. I don't know whether Block 5 will have automatically retractable legs, but probably not.

And aerodynamically...no, I don't think this works. Even with the COM being so far forward, the drag on those legs at anything over a few km/s would flip the stage like a shuttlecock.

Offline guckyfan

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Re: Refurbishment of Used Stages/Vehicles
« Reply #677 on: 04/04/2017 05:33 PM »
a few months back I toyed with the idea of using the legs to generate lift and control...
Mechanically, current legs are a non-starter on this. I don't know whether Block 5 will have automatically retractable legs, but probably not.

And aerodynamically...no, I don't think this works. Even with the COM being so far forward, the drag on those legs at anything over a few km/s would flip the stage like a shuttlecock.

Elon Musk has just said, the gridfins become a lot larger and provide more drag. That could counter some more drag of the legs. Or just one leg. He did announce too that the rocket can do some more lift as well. I don't believe that helps on ascent but can increase drag on the way down. The increase of capability must come from somewhere and not from more engine thrust alone.

Offline Kabloona

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Re: Refurbishment of Used Stages/Vehicles
« Reply #678 on: 04/04/2017 07:40 PM »
a few months back I toyed with the idea of using the legs to generate lift and control...
Mechanically, current legs are a non-starter on this. I don't know whether Block 5 will have automatically retractable legs, but probably not.

And aerodynamically...no, I don't think this works. Even with the COM being so far forward, the drag on those legs at anything over a few km/s would flip the stage like a shuttlecock.

Elon Musk has just said, the gridfins become a lot larger and provide more drag. That could counter some more drag of the legs. Or just one leg. He did announce too that the rocket can do some more lift as well. I don't believe that helps on ascent but can increase drag on the way down. The increase of capability must come from somewhere and not from more engine thrust alone.


They may be figuring the bigger titanium grid fins will reduce terminal velocity, thus shortening the landing burn. Maybe also shortening the entry burn. That could free up some propellant for more payload.


Offline sevenperforce

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Re: Refurbishment of Used Stages/Vehicles
« Reply #679 on: 04/04/2017 09:23 PM »
I wonder if they will go with diamond-shaped grid fins a la ITS.

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