Author Topic: SpaceX Falcon 9 First Landing Discussion--Historic!  (Read 114985 times)

Offline Hauerg

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Re: SpaceX Falcon 9 First Landing Discussion--Historic!
« Reply #180 on: 12/23/2015 08:32 pm »
Now that a stage has landed, the real work begins.  There is still a long way between this experimental landing and the ideal of saving money by reusing stages.  So far, reuse is adding to SpaceX costs. 

 - Ed Kyle
As all R&D projects... first you spend, then you take benefits.

And in fact this is not completely true. One of the biggest benefits for now will not be stage reusing. It will be the learning from used stages.
Checking structural components would be one of the most important areas for future improvement. Let's say they had pulled this off in April, on a barge landing. And after the flight they could have seen that the helium tank support structure was not in good conditions, thus preventing the later failure.

also, don't forget stock value. I'd bet the increase in the stock value after such a successful night is more than sufficient to cover up the extra costs of the  landing of tonight.

There is no SpaceX stock.
And there will not be an IPO before there are lots of regular flights to and from Mars, the Elon said.

Offline cebri

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Re: SpaceX Falcon 9 First Landing Discussion--Historic!
« Reply #181 on: 12/23/2015 08:44 pm »
Wow. Amazing stuff. I woke up at 2 am (living in Spain) just to watch it live. I'll admit i cried.

BTW, probably this has been answered a thousand times, do we know how much it costs to manufacture a F9? I've read figures that go from 16 to 60 million dollars.

Can't wait for Elon to tell us what have they found after they carefully examining the 1st stage.
"It's kind of amazing that a window of opportunity is open for life to beyond Earth, and we don't know how long this window is gonna be open" Elon Musk
"If you want to see an endangered species, get up and look in the mirror." John Young

Offline QuantumG

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Re: SpaceX Falcon 9 First Landing Discussion--Historic!
« Reply #182 on: 12/23/2015 08:45 pm »
There is no SpaceX stock.

There is, it's just that the public can't buy it.

Quote from: Hauerg
And there will not be an IPO before there are lots of regular flights to and from Mars, the Elon said.

That just means the SEC will decide when SpaceX goes public, not Elon.  :(
Human spaceflight is basically just LARPing now.

Offline CorvusCorax

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Re: SpaceX Falcon 9 First Landing Discussion--Historic!
« Reply #183 on: 12/23/2015 10:58 pm »
Technically, the rocket can do even better.  Since the engines are known to re-start, you could shut down the center core in early flight, then restart the engines and use the saved fuel after the size boosters separate.  This would take a lot of engineering courage, but gets most of the benefit of cross-feed without any hardware changes.

No it doesn't. It wastes Delta-V, as you lift weight (unburnt fuel, turned off engines) to higher energy level (in this case altitude)

Any engine that doesn#t run at full throttle reduces thrust to weight ratio. At launch, it's effectively dead weight that eats up payload.

From a efficiency point of view you want to get rid of as much mass as early as possible, so you don't waste propellant on getting that mass to a high energy level. That means both propellant as well as ballast (engines, tanks, ...) thats why most rockets do staging.

Especially at liftoff and during the early alost vertical flight phase, you loose 1g of acceleration to overcome static gravity, as such you want as much thrust as possible to make that 1g as low a percentage of your overall achievable acceleration as possible.

From an efficiency standpoint (if you don't have crossfeed) it would be best to have all 3 cores run at full power, stage when they are empty to get rid of their mass and let the lighter 2nd stage take over. That would make the entire rocket 2 stage and have the 3 1st stage cores return simultaneously.

The only reason this isn't possible is that all 3 cores together would pull far too many g's when they are nearly empty. (You have an upper g limit, as well as friction losses if you become too fast too early in the flight envelope)

So what you do is, you give full thrust with all 3 cores until the g loads  become too high (or to prevent atmospheric loads from becoming too great), only then you throttle down the center core at a time the rocket is already flying almost horizontal and has much less cosine losses. (Either by deep throttling or by turning off some of its engines) You can throttle it back up once the side boosters separated, but you don't have to, as this should be a relatively short flight phase anyway.

Cross feed would be much more efficient, since you can shed dead weight (side cores + engines) earlier in the flight envelope. Any propellant that is crossfed from the side cores to keep the center core full is propellant not wasted to accelerate the side cores (which then you need to use more propellant to bring them back to launch site) and you end up with a fully fueled falcon 9 rocket basically outside the atmosphere and already at significant speed


Offline Ludus

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Re: SpaceX Falcon 9 First Landing Discussion--Historic!
« Reply #184 on: 12/24/2015 02:42 am »
There is no SpaceX stock.

There is, it's just that the public can't buy it.

Quote from: Hauerg
And there will not be an IPO before there are lots of regular flights to and from Mars, the Elon said.

That just means the SEC will decide when SpaceX goes public, not Elon.  :(

The SEC rule involved for example with Facebook, specifies 500 shareholders "of record". Most shareholders, including employees are typically beneficial shareholders who don't count for that rule. EM owns 60% and can control that detail. He won't be pushed into an IPO by the SEC before he's ready.

Offline LouScheffer

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Re: SpaceX Falcon 9 First Landing Discussion--Historic!
« Reply #185 on: 12/24/2015 02:48 am »
Technically, the rocket can do even better.  Since the engines are known to re-start, you could shut down the center core in early flight, then restart the engines and use the saved fuel after the size boosters separate.  This would take a lot of engineering courage, but gets most of the benefit of cross-feed without any hardware changes.
From an efficiency standpoint (if you don't have crossfeed) it would be best to have all 3 cores run at full power, stage when they are empty to get rid of their mass and let the lighter 2nd stage take over. That would make the entire rocket 2 stage and have the 3 1st stage cores return simultaneously.
This is not correct, since it ignores the benefits of saving some fuel until the accelerated dead mass is less.  Here's a numerical example:

Assume each core is 30 t empty, holds 420 t of fuel, ISP = 311, and a second stage mass of 125 t.  The three boosters combined mass 90 t at burnout.  So running all of them in parallel, as you suggest, the delta-V is 311*9.8*ln(1260 + 90 + 125)/(90 + 125)) = 5869 m/s imparted to the second stage.

Now alternatively, use the two side cores to loft a full middle core.  The the side cores burn 840 t of fuel to lift a payload of 575 t (420 fuel + 30 middle core + second stage).  Thus the delta-V when the 2 cores burn out is: 311*9.8*ln((840+60+575)/(60+575)) = 2568 m/s. Then  the middle core burns, adding 311*9.8*ln((420+30+125)/(30+125)) = 3995 m/s.  That's a total of 6563 m/s imparted tp the second stage, about 700 m/s more than parallel staging. Of course your gravity losses are higher in the second case.  You compromise by using full thrust at first, then throttle back to save more fuel for after staging.

You don't need to take my word (or calculations) for this.  Look at the Delta-IV heavy ( http://spaceflight101.com/spacerockets/delta-iv-heavy/ ).  It takes off at full power, then throttles down the middle core at about 50 sec, well before acceleration limits kick in.  The side cores run at full power until they run out of fuel, then they stage away and the center core resumes at full thrust.  They do this precisely to maximize the delta-V in a non-crossfeed situation.  Exactly the same logic will apply to the Falcon Heavy.

Offline QuantumG

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Re: SpaceX Falcon 9 First Landing Discussion--Historic!
« Reply #186 on: 12/24/2015 03:23 am »
The SEC rule involved for example with Facebook, specifies 500 shareholders "of record".

Those rules have a habit of changing overnight.

Quote from: Ludus
EM owns 60% and can control that detail. He won't be pushed into an IPO by the SEC before he's ready.

Dunno where that number comes from.
Human spaceflight is basically just LARPing now.

Offline watermod

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Re: SpaceX Falcon 9 First Landing Discussion--Historic!
« Reply #187 on: 12/24/2015 03:51 am »
There is no SpaceX stock.

There is, it's just that the public can't buy it.

Quote from: Hauerg
And there will not be an IPO before there are lots of regular flights to and from Mars, the Elon said.

That just means the SEC will decide when SpaceX goes public, not Elon.  :(
Just a nit. The SEC never forced Bechtel pubic so I wouldn't bet on them doing so to SpaceX.

Offline Ludus

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Re: SpaceX Falcon 9 First Landing Discussion--Historic!
« Reply #188 on: 12/24/2015 04:29 am »
The SEC rule involved for example with Facebook, specifies 500 shareholders "of record".

Those rules have a habit of changing overnight.

Quote from: Ludus
EM owns 60% and can control that detail. He won't be pushed into an IPO by the SEC before he's ready.

Dunno where that number comes from.

You may be right. There is some risk and SEC interpretation. The intent though isn't to penalize companies for employee shareholding, it's to apply reporting rules to companies that are widely held by investors.

The 60% is just a guess. It was over 65% a couple years ago before the recent round lead by Google and Fidelity that would have diluted it some. Just based on googling around. SpaceX wasn't mostly funded by venture capital. EM put in $100M of his own from the PayPal sale. His brother Kimbal invested too.

Offline TheTraveller

Re: SpaceX Falcon 9 First Landing Discussion--Historic!
« Reply #189 on: 12/24/2015 04:35 am »
Pure goosebump stuff:

It Is Time For The EmDrive To Come Out Of The Shadows

Offline Jakusb

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SpaceX Falcon 9 First Landing Discussion--Historic!
« Reply #190 on: 12/24/2015 09:00 am »
Pure goosebump stuff:


Goosebumps indeed, but honestly a little one-sided, isn't it?
I guess we would have to acknowledge at least some of the amazing stuff the Russians did too... They had a lot of firsts and breakthroughs.
If you talk about Human Race... Talk about all of it and acknowledge all achievement equal and openly, regardless of where on earth it originated.

Ps: I am from Europe and only discovered in my teens that Russians have at least as amazing breakthroughs by brilliant scientists as "the west" has. Strangely enough that part was missed out in my early education. Most of it was USA/Europe oriented and thus very one sided. It might still be the same. I really hope not. It should not.
« Last Edit: 12/24/2015 09:07 am by Jakusb »

Offline NovaSilisko

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Re: SpaceX Falcon 9 First Landing Discussion--Historic!
« Reply #191 on: 12/24/2015 09:39 am »
And it portrays it as if SpaceX is the only one doing anything in space...

Offline Jakusb

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Re: SpaceX Falcon 9 First Landing Discussion--Historic!
« Reply #192 on: 12/24/2015 09:50 am »

And it portrays it as if SpaceX is the only one doing anything in space...
Haha, this is a SpaceX thread and they are taking steps everyone thought impossible or uneconomical.
But they build upon a lot of existing stuff.

Offline brettreds2k

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Re: SpaceX Falcon 9 First Landing Discussion--Historic!
« Reply #193 on: 12/24/2015 12:17 pm »
I hope SpaceX releases some up close daylight pictures of the first stage, The only ones I have seen are from a distance. Id love to see where on the X it landed and how the X fared after being blasted by the engines :)
Brett
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Orbiters I have visited in retirement:

[ ] Enterprise
[X] Discovery
[X] Atlantis
[ ] Endeavour

Offline LouScheffer

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Re: SpaceX Falcon 9 First Landing Discussion--Historic!
« Reply #194 on: 12/24/2015 01:58 pm »
SpaceX is building it's own version of STS.  Falcon Heavy will weigh close to 1,500 tonnes at liftoff and only lift 6.5 tonnes to GTO.  A little better than Shuttle, and freed of the need to launch humans along with the cargo, but still a very big rocket.

 - Ed Kyle

[...] Also, I'm pretty sure SpaceX is sand-bagging the GTO recoverable numbers. [Calculations deleted...]   There is still some gravity loss involved, but staging should be at 3200 m/s or better.  [More calcs deleted...]  that's at least 8 t to a 1500 m/s deficit GTO.

We now have more info from Musk's post-landing comments.  He said:
Quote
The transfer energy of Falcon Heavy will more than double that of Falcon 9. The maximum transfer energy is approaching a terajoule.
So we know staging is at more than 600 GJ (twice Falcon 9) and less than 1000GJ.  More than twice is not very precise, but 700 GJ = 3346 m/s, and 800 GJ, what I would consider "approaching a TJ", is 3577 m/s.  At this speed, only 7 km/sec more is needed to get to a 1500 m/s deficit GTO.  With an ISP of 348, that's a mass ratio of 8, a burnout mass of 15 t, and hence a payload mass of roughly 10 t.

If they can really get 3500 m/s (765 GJ) at staging, you can even get very useful mass to GSO, not GTO, while still having stage recovery.   To do this requires (in a canonical 3 burn sequence) 7.79 km/sec for LEO, 2.34 km/s for GTO injection, then 1.80 km/sec to circularize and remove inclination.  That's a total of 11.93 km/sec, so if the booster supplies 3.5 km/sec, that leaves 8.43 km/sec for the second stage.  That's a mass ratio of 11.85 at an ISP of 348, so a burnout mass of 10.2 tonnes.  If the stage plus residuals is 5.2 tonnes, that's 5 tonnes direct to GSO.  Of course the additions for the long coast, and disposal of the upper stage, will eat into this, but it's clear it could be a useful payload.
« Last Edit: 12/24/2015 02:00 pm by LouScheffer »

Offline cambrianera

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Re: SpaceX Falcon 9 First Landing Discussion--Historic!
« Reply #195 on: 12/24/2015 02:42 pm »
Technically, the rocket can do even better.  Since the engines are known to re-start, you could shut down the center core in early flight, then restart the engines and use the saved fuel after the size boosters separate.  This would take a lot of engineering courage, but gets most of the benefit of cross-feed without any hardware changes.
From an efficiency standpoint (if you don't have crossfeed) it would be best to have all 3 cores run at full power, stage when they are empty to get rid of their mass and let the lighter 2nd stage take over. That would make the entire rocket 2 stage and have the 3 1st stage cores return simultaneously.
This is not correct, since it ignores the benefits of saving some fuel until the accelerated dead mass is less.  Here's a numerical example:

Assume each core is 30 t empty, holds 420 t of fuel, ISP = 311, and a second stage mass of 125 t.  The three boosters combined mass 90 t at burnout.  So running all of them in parallel, as you suggest, the delta-V is 311*9.8*ln(1260 + 90 + 125)/(90 + 125)) = 5869 m/s imparted to the second stage.

Now alternatively, use the two side cores to loft a full middle core.  The the side cores burn 840 t of fuel to lift a payload of 575 t (420 fuel + 30 middle core + second stage).  Thus the delta-V when the 2 cores burn out is: 311*9.8*ln((840+60+575)/(60+575)) = 2568 m/s. Then  the middle core burns, adding 311*9.8*ln((420+30+125)/(30+125)) = 3995 m/s.  That's a total of 6563 m/s imparted tp the second stage, about 700 m/s more than parallel staging. Of course your gravity losses are higher in the second case.  You compromise by using full thrust at first, then throttle back to save more fuel for after staging.

You don't need to take my word (or calculations) for this.  Look at the Delta-IV heavy ( http://spaceflight101.com/spacerockets/delta-iv-heavy/ ).  It takes off at full power, then throttles down the middle core at about 50 sec, well before acceleration limits kick in.  The side cores run at full power until they run out of fuel, then they stage away and the center core resumes at full thrust.  They do this precisely to maximize the delta-V in a non-crossfeed situation.  Exactly the same logic will apply to the Falcon Heavy.

Unfortunately your example with only two side cores firing is impossible.
The rocket would not lift off.
Bad assumptions -> invalid results.
Waiting for someone with more convincing arguments.

Oh to be young again. . .

Offline punder

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Re: SpaceX Falcon 9 First Landing Discussion--Historic!
« Reply #196 on: 12/24/2015 02:48 pm »
And it portrays it as if SpaceX is the only one doing anything in space...

I saw Gemini, Apollo, Shuttle, and ISS in addition to SpaceX.  And this is a SpaceX promotional video!  What more should they do--include video of ULA launches?

Offline Mongo62

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Re: SpaceX Falcon 9 First Landing Discussion--Historic!
« Reply #197 on: 12/24/2015 02:55 pm »
Technically, the rocket can do even better.  Since the engines are known to re-start, you could shut down the center core in early flight, then restart the engines and use the saved fuel after the size boosters separate.  This would take a lot of engineering courage, but gets most of the benefit of cross-feed without any hardware changes.
From an efficiency standpoint (if you don't have crossfeed) it would be best to have all 3 cores run at full power, stage when they are empty to get rid of their mass and let the lighter 2nd stage take over. That would make the entire rocket 2 stage and have the 3 1st stage cores return simultaneously.
This is not correct, since it ignores the benefits of saving some fuel until the accelerated dead mass is less.  Here's a numerical example:

Assume each core is 30 t empty, holds 420 t of fuel, ISP = 311, and a second stage mass of 125 t.  The three boosters combined mass 90 t at burnout.  So running all of them in parallel, as you suggest, the delta-V is 311*9.8*ln(1260 + 90 + 125)/(90 + 125)) = 5869 m/s imparted to the second stage.

Now alternatively, use the two side cores to loft a full middle core.  The the side cores burn 840 t of fuel to lift a payload of 575 t (420 fuel + 30 middle core + second stage).  Thus the delta-V when the 2 cores burn out is: 311*9.8*ln((840+60+575)/(60+575)) = 2568 m/s. Then  the middle core burns, adding 311*9.8*ln((420+30+125)/(30+125)) = 3995 m/s.  That's a total of 6563 m/s imparted tp the second stage, about 700 m/s more than parallel staging. Of course your gravity losses are higher in the second case.  You compromise by using full thrust at first, then throttle back to save more fuel for after staging.

You don't need to take my word (or calculations) for this.  Look at the Delta-IV heavy ( http://spaceflight101.com/spacerockets/delta-iv-heavy/ ).  It takes off at full power, then throttles down the middle core at about 50 sec, well before acceleration limits kick in.  The side cores run at full power until they run out of fuel, then they stage away and the center core resumes at full thrust.  They do this precisely to maximize the delta-V in a non-crossfeed situation.  Exactly the same logic will apply to the Falcon Heavy.

Unfortunately your example with only two side cores firing is impossible.
The rocket would not lift off.
Bad assumptions -> invalid results.
Waiting for someone with more convincing arguments.

Are you sure about that? He has a total delta-V using just the two side full-thrust boosters of 2568 m/s, over a period of maybe 150 seconds. That an average acceleration before gravity losses of about 17.1 m/s/s, minus gravity is an acceleration upward of 7.3 m/s/s. Of course it would be lower to start, since the two side boosters would be full of propellant. What is the initial acceleration, using just the two side boosters?

Offline Kabloona

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Re: SpaceX Falcon 9 First Landing Discussion--Historic!
« Reply #198 on: 12/24/2015 03:17 pm »
Quote
From an efficiency standpoint (if you don't have crossfeed) it would be best to have all 3 cores run at full power,

No, it isn't, as the Delta IV Heavy example given by LouScheffer shows. It's most efficient to throttle down the center core, stage the side boosters, then throttle up the center core. It's "quasi cross-feed."

Perhaps you missed this part of his post:

Quote
You don't need to take my word (or calculations) for this.  Look at the Delta-IV heavy ( http://spaceflight101.com/spacerockets/delta-iv-heavy/ ).  It takes off at full power, then throttles down the middle core at about 50 sec, well before acceleration limits kick in.  The side cores run at full power until they run out of fuel, then they stage away and the center core resumes at full thrust.  They do this precisely to maximize the delta-V in a non-crossfeed situation.  Exactly the same logic will apply to the Falcon Heavy.
« Last Edit: 12/24/2015 03:24 pm by Kabloona »

Offline LouScheffer

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Re: SpaceX Falcon 9 First Landing Discussion--Historic!
« Reply #199 on: 12/24/2015 03:30 pm »

Unfortunately your example with only two side cores firing is impossible.
The rocket would not lift off.
Bad assumptions -> invalid results.
Waiting for someone with more convincing arguments.

You are correct my simple exaggerated example ignored gravity, and is not possible (or desirable, even if barely possible).  It was just meant to show the total delta-V is higher if you save core fuel for later.  When you count gravity losses, you will need to do what the Delta-IV does - all engines at lift off, throttle down to save center core fuel when possible, then throttle center core up after the side boosters stage.  But this more realistic case takes a lot more calculation.  I was just trying to show the benefits of pseudo-staging.

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