Author Topic: Musk lays out plans for reusability of the Falcon 9 rocket  (Read 103288 times)

Offline Lourens

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Re: Musk lays out plans for reusability of the Falcon 9 rocket
« Reply #220 on: 12/09/2013 08:10 PM »
If they are going land it at a remote location. It will need to have good road access so they can truck it out.
Spacex may need to demo a few successful landings before being allowed to land at pad.

One can assume it will not be landing to far inland, so all they need is a good hovercraft ;)
I've been thinking that a cargo airship would be ideal for retrieving stages that land downwind. Launch from Boca Chica, then put the first stage down somewhere on an islet at the very southern tip of Florida. Float in with your airship, attach some kind of bridle, and winch it right up into the air, then fly back to the launch point.

Unfortunately, it appears that this particular project is dead, and that there's not a lot of development in this area at the moment. But it would be a neat way to do the logistics associated with reusability...

Offline IRobot

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Re: Musk lays out plans for reusability of the Falcon 9 rocket
« Reply #221 on: 12/09/2013 08:30 PM »
I know Elon said F9R performed better than expected, but we don't know how much better !

He quoted the engines running at about 85% capacity.  Not sure how exactly that translates to fuel efficiency though.
Less thrust, more gravity losses.

Offline Wetmelon

I know Elon said F9R performed better than expected, but we don't know how much better !

He quoted the engines running at about 85% capacity.  Not sure how exactly that translates to fuel efficiency though.
Less thrust, more gravity losses.

Due to what, the increased fuel mass at each point in the profile?

Offline Joffan

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Re: Musk lays out plans for reusability of the Falcon 9 rocket
« Reply #223 on: 12/09/2013 09:15 PM »
I know Elon said F9R performed better than expected, but we don't know how much better !

He quoted the engines running at about 85% capacity.  Not sure how exactly that translates to fuel efficiency though.
Less thrust, more gravity losses.

Due to what, the increased fuel mass at each point in the profile?

Essentially, higher thrust reduces gravity losses because of quicker ascent. More time spent fighting gravity means more propellant used just to "hold the rocket up".
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Offline TrevorMonty

Does anybody know how much of a fuel saving the +15% increase in thrust would result in.

Offline macpacheco

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Re: Musk lays out plans for reusability of the Falcon 9 rocket
« Reply #225 on: 12/10/2013 04:32 AM »
I know Elon said F9R performed better than expected, but we don't know how much better !

He quoted the engines running at about 85% capacity.  Not sure how exactly that translates to fuel efficiency though.

85% capacity in which point ?
Most rockets (I believe F9R included) must throttle down around Maximum Dynamic pressure, and afterwards can throttle back up again.

Did his statement pointed to SES-8 launch using only 85% or less of available thrust all the way through the launch ? Given the resulting 80000x300 Km orbit, this would be nothing short of astonishing.

If the engines were limited at 85% all the way, increasing to 100% should reduce fuel utilization by more than 15%, given a significant reduction in time spent at lower speeds (consider how much fuel is "wasted" just holding the rocket against gravity from clearing the tower and accelerating to Mach 2 when rockets begin to perform very efficiently), I'm no rocket scientist/engineer, but it's entirely possible the fuel savings at least 20% given the profile is cumulative (speed is integral of acceleration, simplifying to a linear acceleration and 85% to 100% thrust resulting in the same proportional acceleration the extra fuel spent over time is compensated by a squared gain in distance over time, and total time for the same distance is also less). Even with the throttle limitation around MaxQ, still over 20% gains possible (given the F9R is very slender, it probably requires less throttle down than other rockets, less cross section exposed to the wind).

Sorry for the convoluted through process, 20 years since I took Physics and Calculus, explaining the through process might be useful for others, and I'm unsure of lots of aspects.
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Offline cleonard

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Re: Musk lays out plans for reusability of the Falcon 9 rocket
« Reply #226 on: 12/10/2013 04:47 AM »
Rocket engines are designed for a specific thrust.  It's generally known as 100%.  Now after they are actually built, tested, and flown it is often found that they have some extra reserve preformance.  The Space Shuttle main engines were this way.  Later in the program they would run at 104% with the abort option of 109%. 

Elon's comment indicates that SpaceX thinks that the Merlin 1D can run up to 115%.   To make maximum use the rocket would need to grow by that same 15%.   Without changing the rocket it only gets you a little extra performance.   You get a little less gravity losses because the rocket can climb out faster and burn out sooner.  It also helps a lot with an engine out.   Since 9 engines at 100% is actailly slightly less than 8 at 115% you have great engine out capability.

A oversimplified first order approximation would be the stage burns out 15% sooner.  If I remember correctly the first stage runs for about 180 seconds.  At 115% fuel use it would be 154 seconds.  That cuts 9.8 * 27 seconds or 264 m/s of gravity loss.  It's actually less since the first stage throttles some at the end.  Maybe 250 m/s.  That's not insignificant.  A good use might be adding some more fuel to the second stage and reducing the staging velocity to make recovery easier..
« Last Edit: 12/10/2013 05:32 AM by cleonard »

Offline QuantumG

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Re: Musk lays out plans for reusability of the Falcon 9 rocket
« Reply #227 on: 12/10/2013 05:11 AM »
To reiterate what he actually said:

Quote from: Elon Musk
I'm really happy with this rocket design. It's an incredibly capable vehicle. It's actually one of the biggest rockets in the world, it's worth noting, at about 1.3 million pounds of thrust, and we're only actually operating the engines at about 85% of their potential. Down the road, in future missions, we anticipate being able to crank them up to their full thrust capability, which would give about 165,000 pounds of sea-level thrust per engine. Anyway, it really is something that is, I think, going to serve really well for the commercial launch market, for government satellites and for Dragon, both crew and cargo.  I believe its inherent reliability potential is better than any other rocket in the world. It will be up to us to show that it lives up to that reliability potential.

http://shitelonsays.com/transcript/spacex-ses-8-pre-launch-conference-2013-11-24

I'm not sure why there's any need to "interpret" what he said.. he did use numbers.
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Offline beancounter

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Re: Musk lays out plans for reusability of the Falcon 9 rocket
« Reply #228 on: 12/10/2013 07:01 AM »
To reiterate what he actually said:

Quote from: Elon Musk
I'm really happy with this rocket design. It's an incredibly capable vehicle. It's actually one of the biggest rockets in the world, it's worth noting, at about 1.3 million pounds of thrust, and we're only actually operating the engines at about 85% of their potential. Down the road, in future missions, we anticipate being able to crank them up to their full thrust capability, which would give about 165,000 pounds of sea-level thrust per engine. Anyway, it really is something that is, I think, going to serve really well for the commercial launch market, for government satellites and for Dragon, both crew and cargo.  I believe its inherent reliability potential is better than any other rocket in the world. It will be up to us to show that it lives up to that reliability potential.

http://shitelonsays.com/transcript/spacex-ses-8-pre-launch-conference-2013-11-24

I'm not sure why there's any need to "interpret" what he said.. he did use numbers.

I like the last sentence.  "It will be up to us ...",   and earlier concerning a force for change in their competitors, that already seems to be happening, not entirely due to SpaceX but EADS has released a restructuring program cutting costs (and jobs of course) by significant numbers. 
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Offline RigelFive

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Re: Musk lays out plans for reusability of the Falcon 9 rocket
« Reply #229 on: 12/10/2013 07:16 AM »
To reiterate what he actually said:

Quote from: Elon Musk
I'm really happy with this rocket design. It's an incredibly capable vehicle. It's actually one of the biggest rockets in the world, it's worth noting, at about 1.3 million pounds of thrust, and we're only actually operating the engines at about 85% of their potential. Down the road, in future missions, we anticipate being able to crank them up to their full thrust capability, which would give about 165,000 pounds of sea-level thrust per engine. Anyway, it really is something that is, I think, going to serve really well for the commercial launch market, for government satellites and for Dragon, both crew and cargo.  I believe its inherent reliability potential is better than any other rocket in the world. It will be up to us to show that it lives up to that reliability potential.

http://shitelonsays.com/transcript/spacex-ses-8-pre-launch-conference-2013-11-24

I'm not sure why there's any need to "interpret" what he said.. he did use numbers.
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Offline macpacheco

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Re: Musk lays out plans for reusability of the Falcon 9 rocket
« Reply #230 on: 12/10/2013 10:01 AM »
Rocket engines are designed for a specific thrust.  It's generally known as 100%.  Now after they are actually built, tested, and flown it is often found that they have some extra reserve preformance.  The Space Shuttle main engines were this way.  Later in the program they would run at 104% with the abort option of 109%. 

Elon's comment indicates that SpaceX thinks that the Merlin 1D can run up to 115%.   To make maximum use the rocket would need to grow by that same 15%.   Without changing the rocket it only gets you a little extra performance.   You get a little less gravity losses because the rocket can climb out faster and burn out sooner.  It also helps a lot with an engine out.   Since 9 engines at 100% is actailly slightly less than 8 at 115% you have great engine out capability.

A oversimplified first order approximation would be the stage burns out 15% sooner.  If I remember correctly the first stage runs for about 180 seconds.  At 115% fuel use it would be 154 seconds.  That cuts 9.8 * 27 seconds or 264 m/s of gravity loss.  It's actually less since the first stage throttles some at the end.  Maybe 250 m/s.  That's not insignificant.  A good use might be adding some more fuel to the second stage and reducing the staging velocity to make recovery easier..

Ok, now we're talking. Considering reusability, running at 115% could have thermal stress issues and other things, 100% to 115% very different than 85% to 100% ! So it might only be use to use that in engine out situation (perhaps for 2nd stage, since no plans to reuse for now).

Thanks for the important clarification.
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Offline Nomadd

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Re: Musk lays out plans for reusability of the Falcon 9 rocket
« Reply #231 on: 12/10/2013 11:34 AM »
I don't think that the term "potential" means they can just step on the gas pedal harder with existing engines, but that they have the potential to be upgraded to 165,000.
« Last Edit: 12/10/2013 11:38 AM by Nomadd »

Offline IRobot

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Re: Musk lays out plans for reusability of the Falcon 9 rocket
« Reply #232 on: 12/10/2013 01:01 PM »
To reiterate what he actually said:

Quote from: Elon Musk
I'm really happy with this rocket design. It's an incredibly capable vehicle. It's actually one of the biggest rockets in the world, it's worth noting, at about 1.3 million pounds of thrust, and we're only actually operating the engines at about 85% of their potential. Down the road, in future missions, we anticipate being able to crank them up to their full thrust capability, which would give about 165,000 pounds of sea-level thrust per engine. Anyway, it really is something that is, I think, going to serve really well for the commercial launch market, for government satellites and for Dragon, both crew and cargo.  I believe its inherent reliability potential is better than any other rocket in the world. It will be up to us to show that it lives up to that reliability potential.

http://shitelonsays.com/transcript/spacex-ses-8-pre-launch-conference-2013-11-24

I'm not sure why there's any need to "interpret" what he said.. he did use numbers.
I think Elon likes to play with us by given incomplete information :)

When he talks about 85% and "full thrust capability" is he using the design requirement as the 100% reference?

Looking at their site, they advertise 147,000 lbf per engine at sea level. That is 89%, close to the 85% mark.

So the current F9 at 147,000 lbf seems to be the 100% rated and the future upgrades will enable a jump to 112%.

Offline Garrett

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Re: Musk lays out plans for reusability of the Falcon 9 rocket
« Reply #233 on: 12/10/2013 04:06 PM »
Bringing this over from the Grasshopper thread as it would have been off-topic:
If 2 out of 3 launches uses a recovered 1st stage, they only need to build 7 stages a year to support a 21 core a year launch rate which should be with in their current manufacturing capablities. No need to build another factory which is another big saving.
Their current factory capability is already being ramped up to 40 v1.1 cores per year.
Elon expects "without any miracles" a launch rate of 20 per year (10 F9 and 10 FH), which works out at 40 cores per year.

Recovery, if they succeed, may allow them to continue to sell flights on F9 and FH, while developing and building another more capable rocket using their current factory.
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Offline kirghizstan

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Re: Musk lays out plans for reusability of the Falcon 9 rocket
« Reply #234 on: 12/10/2013 05:05 PM »
Not to be too technical but...

85/100% is not the same as 100/115%. 

While it is close there is a difference so if Elon is saying 85/100% then can we agree to use his numbers going forward. 

even if they were designed to the 85% number but it turned out that they did the 100% number these are the numbers SpaceX is using. 

Math Nazi signing off
« Last Edit: 12/10/2013 05:06 PM by kirghizstan »

Offline cleonard

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Re: Musk lays out plans for reusability of the Falcon 9 rocket
« Reply #235 on: 12/10/2013 06:05 PM »
When engineering says that we should be able to get another 15%, management hears "we were only running at 85%."

Offline Owlon

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Re: Musk lays out plans for reusability of the Falcon 9 rocket
« Reply #236 on: 12/10/2013 06:11 PM »
When engineering says that we should be able to get another 15%, management hears "we were only running at 85%."

To a large degree, Elon is both engineering and management. Its a pretty safe bet that he knows the difference between 85/100 and 100/115.

Offline oldAtlas_Eguy

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Re: Musk lays out plans for reusability of the Falcon 9 rocket
« Reply #237 on: 12/10/2013 06:12 PM »
I think Elon is thinking way ahead of us about the needs to do US reusable. By going to 165klbf and stretching the US tank size the payload loss for making the US and 1st stage can be mitigated. Allowing for F9R (full reusable) to have a 10+mt payload, enough capability to meet all current customers requirements even SpaceX's Dragon and DragonRider.

BTW a 15% increase can mean for a non reusable FHwCF(with Cross-Feed) with stretched US tanks a 60mt max payload.
« Last Edit: 12/10/2013 06:13 PM by oldAtlas_Eguy »

Offline macpacheco

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Re: Musk lays out plans for reusability of the Falcon 9 rocket
« Reply #238 on: 12/10/2013 06:57 PM »
To reiterate what he actually said:

Quote from: Elon Musk
I'm really happy with this rocket design. It's an incredibly capable vehicle. It's actually one of the biggest rockets in the world, it's worth noting, at about 1.3 million pounds of thrust, and we're only actually operating the engines at about 85% of their potential. Down the road, in future missions, we anticipate being able to crank them up to their full thrust capability, which would give about 165,000 pounds of sea-level thrust per engine. Anyway, it really is something that is, I think, going to serve really well for the commercial launch market, for government satellites and for Dragon, both crew and cargo.  I believe its inherent reliability potential is better than any other rocket in the world. It will be up to us to show that it lives up to that reliability potential.

http://shitelonsays.com/transcript/spacex-ses-8-pre-launch-conference-2013-11-24

I'm not sure why there's any need to "interpret" what he said.. he did use numbers.
I think Elon likes to play with us by given incomplete information :)

When he talks about 85% and "full thrust capability" is he using the design requirement as the 100% reference?

Looking at their site, they advertise 147,000 lbf per engine at sea level. That is 89%, close to the 85% mark.

So the current F9 at 147,000 lbf seems to be the 100% rated and the future upgrades will enable a jump to 112%.

1 - This might not be a firm thing (remember hunt for the red october, 110% of the reactor possible but not recomendable) ! This extra thrust might be exploited a little bit at a time
2 - Elon needs to contend with ITAR and competitive issues, so some obfuscation might be by design instead of by a sadistic feelings
3 - I learnt with a very successful Brazilian software developer, always under promise and over deliver ! Leave yourself room for breathing. The only reason to promise with no safety margin is if you'll loose a very important deal in consequence, SpaceX right now has performance to spare, having a spotless 2014 would put them on par safety wise with ULA (about 20 launches failing only a single secondary payload).
« Last Edit: 12/10/2013 06:59 PM by macpacheco »
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Offline TrevorMonty

Wording is important. Would you buy an engine that runs at 85% of its tested rating or an engine that runs at 100% of its tested rating but can give 115% if need be.

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