Author Topic: SpaceX Falcon Heavy Discussion (Thread 4)  (Read 344599 times)

Offline QuantumG

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #20 on: 12/30/2015 09:24 PM »
This may seem obvious to some, but I don't think it actually can launch 53 tons to LEO.. it's just a reference orbit. That said, the best number I've seen for the fairing mass is 1,750 kg, so if you really want to squeeze a maximum payload to LEO number out of the Falcon Heavy you could probably imagine a payload that doesn't need to go inside the fairing (like some mega-Dragon). Also, this is all old numbers with cross-feed. Maybe this year SpaceX will release a press kit and we'll actually find out what the real vehicle on the pad can do.

When someone is wishing for a pony, there's little to be gained by suggesting a unicorn would be ever better.. ya know, unless it's sarcasm.

Offline Nathan2go

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #21 on: 12/30/2015 10:47 PM »
I agree the F9H could have a huge impact on manned Mars exploration.  In the same way that the COTS program was very successful at allowing NASA to help fund companies that wanted to get into the LEO cargo business (i.e. SpaceX and Orbital Sciences), commercial companies can now demand a piece of the manned Mars program, with a con-ops optimized for numerous flights with reusable rockets.

1) One of the core principles of the Mar Direct concept was that Mars-Surface-Rendezvous was better than building large mono-ships in LEO.  This principle was only used to justify having the crew fly out separately from their Mars Ascent Vehicle (MAV/ERV); but we could take the idea further and deliver most of the mission mass to Mars in 1-5 ton landers, which could then be retrieved by truck (everything except the nearly empty Hab and empty MAV).  These could be sent out 2 years ahead of the crew, by vehicles in the F9H class.

2) The 2013 Mars DRM-5 from NASA  included nuclear thermal engines, which were rejected from Mars Direct in order to speed the schedule etc.  On orbit-transfer of LOX (from a commercial space company) provides the same ability to boost the capabilities of the SLS, without the difficulty of large nuclear developments.  For a 130 ton Earth Departure Stage to throw a 130 ton payload to Mars on a 6 month trajectory, it would need to top-off with an extra 210 tons of propellant.   Commercial companies offering F9H class rockets could credibly provide this amount of LOX to LEO to support anticipated SLS launch rates.

With those two markets, companies like SpaceX and Blue Origin could get funding (from NASA and investors) to develop a new generation of larger (colonization-class) rockets.

Online Jcc

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #22 on: 12/30/2015 11:52 PM »
This may seem obvious to some, but I don't think it actually can launch 53 tons to LEO.. it's just a reference orbit. That said, the best number I've seen for the fairing mass is 1,750 kg, so if you really want to squeeze a maximum payload to LEO number out of the Falcon Heavy you could probably imagine a payload that doesn't need to go inside the fairing (like some mega-Dragon). Also, this is all old numbers with cross-feed. Maybe this year SpaceX will release a press kit and we'll actually find out what the real vehicle on the pad can do.

Better still, launch it.

Online oldAtlas_Eguy

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #23 on: 12/31/2015 02:17 AM »
I just looked at the SpaceX FH description page and it describes an FH that is based on the F9FT: 170klbf M1DFT engines, larger US and higher GLOW than the FHv1.1 based version. The problem is the some of the text, performance values and prices don't seem to be updated to reflect the FHFT physical description.

One of the items with the text is cross feed is still mentioned. That questions is there still a long term cross feed in the works or not? The many statements recently is that there will not be a cross feed. But that may not be correct. B ut that for now and until sometime in the future when a cross-feed is deemed useful it will be an option.

One of the items is that the 53mt is seemingly possible by a FHFT expendable, but if there was a FHFTcrossfeed it would be possible to have a 53mt reusable vehicle.

BTW if there was eventually a FHFT crossfeed what would its max LEO payload be? 70mt?
« Last Edit: 12/31/2015 02:20 AM by oldAtlas_Eguy »

Offline Dave G

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #24 on: 12/31/2015 02:25 AM »
How close to the cross-fed enabled 53mt payload to LEO is the non-cross-fed fully expended full thrust falcon heavy? I'm guessing it's fairly close...

This may have changed, but last I heard there were 3 flavors of Falcon Heavy:
1) Fully expendable, cross-fed: 21mt GTO, 53mt LEO
2) Reusable boosters RTLS, expendable center core, cross-fed: 14mt GTO
3) All 3 first stages RTLS, not cross-fed: 7mt GTO

Of these, I believe 3) will be most important, as it covers virtually all current comsats with a fully reusable set of first stages that RTLS.  If refurbishing the stages is relatively easy, as SpaceX suggests, then this configuration should end up being less expensive than an expendable Falcon 9.
« Last Edit: 12/31/2015 02:35 AM by Dave G »

Offline QuantumG

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #25 on: 12/31/2015 02:37 AM »
1) Ghost of Elon past
2) Ghost of Elon present
3) Ghost of Elon future

When someone is wishing for a pony, there's little to be gained by suggesting a unicorn would be ever better.. ya know, unless it's sarcasm.

Online oldAtlas_Eguy

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #26 on: 12/31/2015 02:49 AM »
How close to the cross-fed enabled 53mt payload to LEO is the non-cross-fed fully expended full thrust falcon heavy? I'm guessing it's fairly close...

This may have changed, but last I heard there were 3 flavors of Falcon Heavy:
1) Fully expendable, cross-fed: 21mt GTO, 53mt LEO
2) Reusable boosters RTLS, expendable center core, cross-fed: 14mt GTO
3) All 3 first stages RTLS, not cross-fed: 7mt GTO

Of these, I believe 3) will be most important, as it covers virtually all current comsats with a fully reusable set of first stages that RTLS.  If refurbishing the stages is relatively easy, as SpaceX suggests, then this configuration should end up being less expensive than an expendable Falcon 9.
The item not discussed is that your options is based on FHv1.1 performance and not the additional 33% that is a possible increase provided by a FHFT. If you straight X 33% the performance values you get
1) Fully expendable, cross-fed: 27mt GTO, 70mt LEO
2) Reusable boosters RTLS, expendable center core, cross-fed: 18.5mt GTO
3) All 3 first stages RTLS, not cross-fed: 8.7mt GTO

Unfortunately performance values don't usually scale like that so these new values are only a guide not anything more. In some case there could be more and others less due to the interactions of what the changes are and how they affect the flight performance to an orbit.

Online Lars-J

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #27 on: 12/31/2015 06:52 AM »

How close to the cross-fed enabled 53mt payload to LEO is the non-cross-fed fully expended full thrust falcon heavy? I'm guessing it's fairly close...

This may have changed, but last I heard there were 3 flavors of Falcon Heavy:
1) Fully expendable, cross-fed: 21mt GTO, 53mt LEO
2) Reusable boosters RTLS, expendable center core, cross-fed: 14mt GTO
3) All 3 first stages RTLS, not cross-fed: 7mt GTO

Of these, I believe 3) will be most important, as it covers virtually all current comsats with a fully reusable set of first stages that RTLS.  If refurbishing the stages is relatively easy, as SpaceX suggests, then this configuration should end up being less expensive than an expendable Falcon 9.

Nope. That was the plan, cross feed is not in the current iteration of FH. It could still be added in the future, but I doubt it.

So the only question for an FH launch is where the core booster will end up. RTLS, on a barge, or expended.

Offline hkultala

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #28 on: 12/31/2015 07:21 AM »

The item not discussed is that your options is based on FHv1.1 performance and not the additional 33% that is a possible increase provided by a FHFT.

Any credible source for this claim?

Even though they released the 53t number many years ago, they already knew then what their M1D will finally be capable of.

And even if the original numbers were for the reduced-thrust version of M1D, your 33% scaling factor is way too high for the payload increase for that 15% engine thrustupgrade.

Online guckyfan

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #29 on: 12/31/2015 07:52 AM »
And even if the original numbers were for the reduced-thrust version of M1D, your 33% scaling factor is way too high for the payload increase for that 15% engine thrustupgrade.

Much of the performance increase is in the upper stage enlargement and the larger M-vac nozzle.

Offline hkultala

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #30 on: 12/31/2015 08:38 AM »
And even if the original numbers were for the reduced-thrust version of M1D, your 33% scaling factor is way too high for the payload increase for that 15% engine thrustupgrade.

Much of the performance increase is in the upper stage enlargement and the larger M-vac nozzle.

Larger M-vac nozzle? where is this information from?

And upper stage enlargement helps payload to higher orbits more than payload to LEO. 30% increase in GTO payload may mean 24% increase in LEO payload.

And, if spaceX knew they were going to expand the second stage again before FH, I think the effect of this is already calculated in the original FH capasity numbers.

Online guckyfan

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #31 on: 12/31/2015 08:48 AM »
Larger M-vac nozzle? where is this information from?

They made the interstage longer and upgraded the pushers for stage separation to accomodate a larger nozzle extension.

And upper stage enlargement helps payload to higher orbits more than payload to LEO. 30% increase in GTO payload may mean 24% increase in LEO payload.

And, if spaceX knew they were going to expand the second stage again before FH, I think the effect of this is already calculated in the original FH capasity numbers.

Yes.

Maybe.

Offline Darkseraph

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #32 on: 12/31/2015 09:08 AM »
Has SpaceX said anything about engine out capability with reuse? 



"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." R.P.Feynman

Offline Dave G

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #33 on: 12/31/2015 09:55 AM »
Has SpaceX said anything about engine out capability with reuse?

Excellent question!

I haven't heard anything specifically from SpaceX on this, but I always assumed the extra propellant required for engine out capability was dual use. This is similar in concept to Dragon v2, where the SuperDraco propellant is used for either LAS or RTLS, but not both.

Last I heard, the first stage uses 3 Merlin engines for supersonic retrograde propulsion, and 1 Merlin engine (the center one) for landing.  So if the center engine fails during ascent, there's no way they could return the stage. 

But again, if an engine fails during ascent, they'll need to burn the first stage longer to make the intended orbit with less total thrust, which ends up requiring more propellant.  And SpaceX says they can tolerate 2 engine failures during ascent, which would require even more extra propellant to make the intended orbit with the remaining 7 engines.

My bet: If an engine fails, they won't have enough propellant left to land the first stage anywhere, either RTLS or a barge.  So the extra fuel for engine out is that same fuel for reuse.
 

Offline StuffOfInterest

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #34 on: 12/31/2015 10:17 AM »
Although an engine out may not leave enough fuel for RTLS I don't think it is a certainty.  If the engine out occurs late during first stage flight then it may leave enough fuel to still make it back.  Beyond that, I don't think there is fine grained enough monitoring of the fuel level to decide if there is enough to make it so the computer will likely just try to land and if fuel runs out during one of the three burns then the rocket drops either just off shore or on the landing pad.  Even with a hard landing I bet SpaceX would love to get back a failed engine to figure out what went wrong with it.

Offline Dave G

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #35 on: 12/31/2015 10:33 AM »
The item not discussed is that your options is based on FHv1.1 performance and not the additional 33% that is a possible increase provided by a FHFT.

Even though they released the 53t number many years ago, they already knew then what their M1D will finally be capable of.

Originally, way back with Falcon 5, they were already talking about a heavy version.  Then when they went to Falcon 9, then called it "Falcon 9 Heavy". 

Then when they did a press event for "Falcon Heavy" (leaving the "9" out of the name), that was where they first mentioned 53mt to LEO.  I'm pretty sure this number was based on the Falcon 9 v1.1 improvements that they were just about to test at VAFB.  At that time, the 53mt included a cross-fed center core, and that configuration was fully expendable.  I believe the other numbers Elon mentioned back then (7mt GTO with 3 cores RTLS, 14mt GTO with 2 cores RTLS) are all based on the Falcon 9 v1.1 improvements.

But since then, they've made even more performance improvements with Falcon 9.  My guess: Elon probably wanted to call this Falcon 9 v1.2, but that would tend to scare some customers, so he mentions these performance improvements only in passing without any specific numbers.

I've also heard the first versions of Falcon Heavy will not be cross-fed, but they haven't ruled out using this in the future.

So the bottom line is that we don't really know what the FH numbers will be exactly.  I suspect SpaceX will revise the numbers when they get closer to launch.
« Last Edit: 12/31/2015 12:21 PM by Dave G »

Offline Dave G

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #36 on: 12/31/2015 11:18 AM »
Although an engine out may not leave enough fuel for RTLS I don't think it is a certainty.  If the engine out occurs late during first stage flight then it may leave enough fuel to still make it back.  Beyond that, I don't think there is fine grained enough monitoring of the fuel level to decide if there is enough to make it so the computer will likely just try to land and if fuel runs out during one of the three burns then the rocket drops either just off shore or on the landing pad.  Even with a hard landing I bet SpaceX would love to get back a failed engine to figure out what went wrong with it.

I'm sure SpaceX would love to get back a failed engine to figure out what went wrong, but without enough fuel to control descent, a RTLS attempt could land the stage significantly off course.  If it blew up some building, RTLS would be set back for years...

They could attempt to land it on a barge, but now that RTLS is working, I doubt SpaceX will want the added expense of deploying a landing barge for every flight.

Remember, reusability is all about cost savings.  It's not mission critical, so it doesn't need to be highly reliable to work.  It's a just numbers game.  If an engine fails 1 out of every 100 flights, I suspect the safest, least cost option is to ditch it in the ocean, like a regular expendable launcher.  If an engine fails 1 out of every 10 flights, then they have a problem with their engine, so that would need to be fixed.

In other words, an engine failure should be a rare event.  In such rare events, since reuse isn't mission critical, I suspect the best option will be to expend the stage.

Online oldAtlas_Eguy

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #37 on: 12/31/2015 02:30 PM »
Just by the math if the engine throttle position of the 9 engines is 88% or less the loss of a single engine (shutdown) will not result in any additional prop use. In fact it may result in more residual prop since the remaining 8 engines would throttle back up to 100% and operate at a slightly higher ISP.

It is only when the throttle position is greater than 88% that the additional prop for RTLS would be consumed partially because of increased gravity losses (less acceleration due to the engine loss).

The difficulty is which engine fails and what contingencies the software has for doing RTLS to work around using a failed engine (a different set of 3)?

Offline Im_Utrecht

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #38 on: 12/31/2015 02:34 PM »
FH will be manrated like F9
FH's first version will be based on F9v1.1FT but will upgraded in the future.
Probably they will use more composites to save weight, introduce crossfeed and first stage engines that do not dump the exhaust from the turbopumps. (like the merlin 1D vac from s2)


Online oldAtlas_Eguy

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Re: SpaceX Falcon Heavy Discussion (Thread 4)
« Reply #39 on: 12/31/2015 03:11 PM »
FH will be manrated like F9
FH's first version will be based on F9v1.1FT but will upgraded in the future.
Probably they will use more composites to save weight, introduce crossfeed and first stage engines that do not dump the exhaust from the turbopumps. (like the merlin 1D vac from s2)
There are a lot of don't knows!
1) performance expendable?
2) performance RTLS?
3) performance with crossfeed?
4) possible upgrades?
5) the higher delta V orbit performce due to having a "larger" US?

The last one is something we have been discussing about a short fall of the FHv1.1 having a too small US. Was the size increase of the F9 US optimized for FH performance or for F9 performance?

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