Author Topic: SpaceX Falcon Heavy Discussion (Thread 3)  (Read 249704 times)

Offline punder

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #80 on: 02/18/2015 07:25 PM »


Okay, so forget that part.  (And I do appreciate the smiley.)  Use the ring trusses as the sole thrust structure and align/dock the stages some other way.  Anything else in the "big concept" that's utterly nonsensical?

Back to the boil off issue, if you are only looking for a single impulse from the two stages then, as long as you dock them and get that impulse in the first orbit you should not have lost too much. However, if one of the reasons you wanted all this extra capacity for a probe included a high energy orbit change later on then you still need to solve the boil off (and operation power issues since the main solar panels won't be deployed until after the last high energy burn). 

I am not seeing how this gets you a solution that is cheaper than 3'rd stage.

There may not be a solution.  This is what you guys call "hand-waving" after all!  But:

1.  The 2nd flight US has a bunch of propellant.  It had no payload, after all, other than the weight of the docking mechanism and any rendezvous sensors/computers.  Maybe it only had a small expendable nosecone rather than a big heavy payload shroud.  Seems like that would make for much larger payload than a 3rd stage added to a single launch.

2.  Common stages, common engines, common propellants, common software, common power, common procedures, common personnel.  All from within SpaceX.  No additional companies, personnel, procedures, safety concerns, or pad mods for a non-common stage.  Each interaction between dissimilar items eats money and poops paper + lost time.

3.  The state of the art wrt cryo boiloff may improve.  People have been working on depot tech for awhile now.

Offline Robotbeat

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #81 on: 02/18/2015 07:30 PM »
Maybe we should stop trying to pack all the energy for any given mission into a single launch.  ...
For anything like this, multiple launches don't make any sense.

I'm not sure of the exact figures, but I'm pretty sure a small solid rocket kick motor is in the (perhaps low) single-digits millions of dollars range. Another launch (even fully reusable!) would be more than that.

EDIT: A Star-48 is around $6 million, roughly: http://forum.nasaspaceflight.com/index.php?topic=33084.msg1109467#msg1109467
« Last Edit: 02/18/2015 07:36 PM by Robotbeat »
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Offline nadreck

Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #82 on: 02/18/2015 07:45 PM »


Okay, so forget that part.  (And I do appreciate the smiley.)  Use the ring trusses as the sole thrust structure and align/dock the stages some other way.  Anything else in the "big concept" that's utterly nonsensical?

Back to the boil off issue, if you are only looking for a single impulse from the two stages then, as long as you dock them and get that impulse in the first orbit you should not have lost too much. However, if one of the reasons you wanted all this extra capacity for a probe included a high energy orbit change later on then you still need to solve the boil off (and operation power issues since the main solar panels won't be deployed until after the last high energy burn). 

I am not seeing how this gets you a solution that is cheaper than 3'rd stage.

There may not be a solution.  This is what you guys call "hand-waving" after all!  But:

1.  The 2nd flight US has a bunch of propellant.  It had no payload, after all, other than the weight of the docking mechanism and any rendezvous sensors/computers.  Maybe it only had a small expendable nosecone rather than a big heavy payload shroud.  Seems like that would make for much larger payload than a 3rd stage added to a single launch.

2.  Common stages, common engines, common propellants, common software, common power, common procedures, common personnel.  All from within SpaceX.  No additional companies, personnel, procedures, safety concerns, or pad mods for a non-common stage.  Each interaction between dissimilar items eats money and poops paper + lost time.

3.  The state of the art wrt cryo boiloff may improve.  People have been working on depot tech for awhile now.

But it is going to slightly more than double the launch cost, giving you a maximum price tag for a 3rd stage that offers the same performance to compete against. If your 2nd launch cost $45M for example that would pay for a substantial 3rd stage.

Another solution would be docking not with a bunch of mechanisms and maneuvers that add risk but with an honest to goodness propellant depot. One that did the hard work of docking and connected to both the propellant inlets and vents and insured a full fuel load or as much as was needed for the mission. It could wait to quite close to launch then let go and back off (and side step too).  We are now talking about an orbit inclined about 26degrees  for efficient servicing from the cape or Boca Chica, and of course launch windows would be instantaneous, but we are now only coordinating a single launch, and if we boiled off a little extra, well that is just a little extra that the depot had to supply. Also our craft doesn't need the anti boil off technology (unless it needs subsequent high energy impulses) only the depot does. This craft would benefit from a far better fuel to empty weight ratio than the docked upper stages as well.
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline guckyfan

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #83 on: 02/18/2015 07:51 PM »
The Falcon 9 - Falcon Heavy upper stage would need a major upgrade to enable it for refuelling. A very much longer loiter time would be one of those. I also would worry more about RP-1 freezing than about some LOX boiloff.

Offline IainMcClatchie

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #84 on: 02/18/2015 08:39 PM »
The trouble I see with Punder's scheme is that, for anything like a geostationary orbit (3910 m/s) or Mars transfer (4270 m/s), most of what you need in low earth orbit is fuel.  So the way to think about it is, the FH boosts an upper stage which is mostly fuel to LEO.  You then have a choice: either replace ~10,000 kg of that fuel with a payload, or boost a slightly larger payload, like that of an F9, and mate it up.

Let me posit a scheme like Punder's, perhaps simpler, to demonstrate the problem.

F9 releases a 13,000 kg object into LEO.  The payload adaptor is different to allow in-space mating.

A FH has an upper stage with no payload but extended tanks.  The shroud is reduced to a little nosecone that gets blown off during ascent.  Once in LEO this US has something like 53,000 kg of propellant left.  It rendezvous and mates with the payload, using the same arrangement that the F9 mated with that payload.

The resulting vehicle has an empty mass of ~18,000 kg, full mass of 71,000 kg, and has available delta-V of 4572 m/s, sufficient to get to geosynchronous orbit (needs 3910 m/s) or Mars intercept (4270 m/s).  Sounds good?

Using the same simple math, a 58,000 kg FH upper stage in LEO can deliver 13,000 kg with 3910 m/s delta-V, or 11,200 kg with 4270 m/s delta-V.  So the extra mating step from the F9 doesn't get you much.  If you want to move more stuff to Mars than FH, you'll need to transfer propellants between FH upper stages, or use, as Punder suggested, one FH upper stage as a booster for a second FH upper stage.

Online abaddon

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #85 on: 02/18/2015 08:49 PM »
Maybe we should stop trying to pack all the energy for any given mission into a single launch.  ...
For anything like this, multiple launches don't make any sense.

I'm not sure of the exact figures, but I'm pretty sure a small solid rocket kick motor is in the (perhaps low) single-digits millions of dollars range. Another launch (even fully reusable!) would be more than that.

EDIT: A Star-48 is around $6 million, roughly: http://forum.nasaspaceflight.com/index.php?topic=33084.msg1109467#msg1109467

But a Star-48 wouldn't accomplish the overriding goal of two launches and LEO rendezvous and ...

Wait, that's not the goal?

Offline MP99

Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #86 on: 02/18/2015 08:55 PM »
F1US and it's Kestrel engine flew several times. It could provide the basis for a kick stage, though I believe it's only ~4t. Extra mass would be no problem as gravity losses are not an issue for a kick stage.

But, I wonder about a methalox Kestrel. Assumption is that the engineering that coped with LOX could be co-opted to deal with LCH4.

Big downside - such a large diversion from flight history would basically be a new stage, with no opportunities to demonstrate it before it gets used for something critical. (Unless it could fly as a secondary on F9R-Dev2 flights from NM?)

Cheers, Martin

Offline nadreck

Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #87 on: 02/18/2015 09:09 PM »
The Falcon 9 - Falcon Heavy upper stage would need a major upgrade to enable it for refuelling. A very much longer loiter time would be one of those. I also would worry more about RP-1 freezing than about some LOX boiloff.

Why major, why couldn't the the fuel depot attach to all the existing umbilical points? giving it the ability to circulate propellants (thereby controlling temps) and to provide power to the US and payload to keep it fresh?
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline guckyfan

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #88 on: 02/18/2015 09:20 PM »
The Falcon 9 - Falcon Heavy upper stage would need a major upgrade to enable it for refuelling. A very much longer loiter time would be one of those. I also would worry more about RP-1 freezing than about some LOX boiloff.

Why major, why couldn't the the fuel depot attach to all the existing umbilical points? giving it the ability to circulate propellants (thereby controlling temps) and to provide power to the US and payload to keep it fresh?

At the very least the stage must remain alive and active until docking is achieved.

Also connections to the stage made in the HIF are not the same as needed for automated docking to a fuel depot. It needs a redesign.

I have the very strong opinion it won't be done for a Falcon upper stage. It will need to be done for the BFR upper stage. But that would be designed from the beginning with this in mind.

Online AncientU

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #89 on: 02/18/2015 10:37 PM »
The Falcon 9 - Falcon Heavy upper stage would need a major upgrade to enable it for refuelling. A very much longer loiter time would be one of those. I also would worry more about RP-1 freezing than about some LOX boiloff.

Why major, why couldn't the the fuel depot attach to all the existing umbilical points? giving it the ability to circulate propellants (thereby controlling temps) and to provide power to the US and payload to keep it fresh?

At the very least the stage must remain alive and active until docking is achieved.

Also connections to the stage made in the HIF are not the same as needed for automated docking to a fuel depot. It needs a redesign.

I have the very strong opinion it won't be done for a Falcon upper stage. It will need to be done for the BFR upper stage. But that would be designed from the beginning with this in mind.

Agree that it won't be done for the existing F9 upper stage, but could easily design a new upper for FH with refueling and loiter capability from the beginning.  GS stated that 'lots' of FH launches could head for Mars... Seems that no one would use this launcher for planetary missions with existing configuration.  Refueling is also on the SpaceX docket -- FH is the perfect proving ground before BFR arrives on the scene.
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Offline Ben the Space Brit

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #90 on: 02/19/2015 01:30 PM »
F1US and it's Kestrel engine flew several times. It could provide the basis for a kick stage, though I believe it's only ~4t. Extra mass would be no problem as gravity losses are not an issue for a kick stage.

IMHO, a version of the Kestrel, possibly using F-1e U/S tanking, would be ideal for a lot of in-space applications. Especially if it's modified to use LCH4 rather than RP1, thus removing the 'coking' issue.

That said, I maintain my position that, in the event of the payload needing a kick stage, I think that it is more likely that SpaceX will require the customer to provide it (although they will probably still do the booster/payload integration).
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Offline punder

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #91 on: 02/19/2015 02:31 PM »
Maybe we should stop trying to pack all the energy for any given mission into a single launch.  ...
For anything like this, multiple launches don't make any sense.

I'm not sure of the exact figures, but I'm pretty sure a small solid rocket kick motor is in the (perhaps low) single-digits millions of dollars range. Another launch (even fully reusable!) would be more than that.

EDIT: A Star-48 is around $6 million, roughly: http://forum.nasaspaceflight.com/index.php?topic=33084.msg1109467#msg1109467

But a Star-48 wouldn't accomplish the overriding goal of two launches and LEO rendezvous and ...

Wait, that's not the goal?

Of course it's not the goal, but the snark was funny!   ;D

I'm just thinking about how booster recovery throws a monkey wrench into assumptions that have held since the 1950s.  Three complete boosters, 27 Merlins, that aren't "sunk cost".  (Rimshot) 

That's my main concern.  Concepts long discarded may become feasible with that kind of cost savings.  Maybe not this particular concept from some nobody on the Internet, but you see my point.

Anyway... The 2nd flight US is big.  Extra fuel mass that would otherwise be payload.  It's a super-US.  the partially depleted 1st flight US is now the "kick stage" for what is effectively a bigger rocket.  And because of booster reuse, all youve expended is a second US, NOT a second Falcon Heavy.

You might say that stretching the US tanks for this application is a major cost, and running two FH launches near-simultaneously is difficult and dangerous, or developing and proving the docking scheme is a huge project.  Maybe.  What are they compared to developing and implementing orbital depot infrastructure?

Offline punder

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #92 on: 02/19/2015 03:25 PM »
That's my main concern.  Concepts long discarded may become feasible with that kind of cost savings.  Maybe not this particular concept from some nobody on the Internet, but you see my point.

This!!!

Bring out those retired visionaries from both sides of the Atlantic and dust off those old bindered studies from when cost was no object (until someone actually tried to spend the money). 

We've spend a lot of breath on the economic of reusability, and a good deal of it was conceptualizing missions to take advantage of it....

Thank you!

I guess another idea would be to break up your payload (if possible) and eliminate kick stages altogether.  This would have the added advantage that in case of launch failure, you lose only half your stuff.  For example, a planetary probe with a lander, like Cassini/Huegens.  Send the orbiter on one flight, the lander on another.  Reusable stages lower the overall launch cost, and you are now dividing your eggs between two baskets.  Both payloads can be built with more capability because they no longer have to attach and interface with each other, and trajectories can be optimized for each.

Online abaddon

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #93 on: 02/19/2015 03:50 PM »
This is like talking about moving the house across the street to this side of the street so you don't have to cross the street to get to it.

A Star-48 is proven, relatively cheap, with only minor well-understood integration considerations.  It is a no-brainer way for SpaceX to be able to provide high-energy escape trajectories for the small number of payloads that require it.  Successful booster recovery and reuse doesn't throw any "wrench" into anything.  It makes any mission cheaper.  It doesn't mean it makes it sensible to throw multiple launches and all of the complexity that would entail at something that a $6 million kick stage solves.

There are other concepts that could greatly benefit from something like the proposed architecture, but this isn't one of them.


Offline punder

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #94 on: 02/19/2015 04:05 PM »
This is like talking about moving the house across the street to this side of the street so you don't have to cross the street to get to it.

A Star-48 is proven, relatively cheap, with only minor well-understood integration considerations.  It is a no-brainer way for SpaceX to be able to provide high-energy escape trajectories for the small number of payloads that require it.  Successful booster recovery and reuse doesn't throw any "wrench" into anything.  It makes any mission cheaper.  It doesn't mean it makes it sensible to throw multiple launches and all of the complexity that would entail at something that a $6 million kick stage solves.

There are other concepts that could greatly benefit from something like the proposed architecture, but this isn't one of them.

You are right, I went off on a tangent.  Sorry.

Offline dror

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #95 on: 02/20/2015 06:50 AM »
If WE are thinking about FH upper stage,  the next probabal step is a single raptor.
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Offline Ben the Space Brit

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #96 on: 02/20/2015 10:42 AM »
If WE are thinking about FH upper stage,  the next probabal step is a single raptor.

I've long wondered if any performance advantage can be gained from a methane-fuelled Merlin upper stage.
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Offline Lars-J

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #97 on: 02/20/2015 03:34 PM »
If WE are thinking about FH upper stage,  the next probabal step is a single raptor.

I've long wondered if any performance advantage can be gained from a methane-fuelled Merlin upper stage.

But they have all but ruled it out. It would lose commonality with F9, and FH is already providing more capability than there is demand for.
« Last Edit: 02/20/2015 03:40 PM by Lars-J »

Offline edkyle99

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #98 on: 02/23/2015 04:47 PM »
My first stab at a real Falcon Heavy page, after holding out for a while. 
www.spacelaunchreport.com/falconH.html
Comments and criticisms welcomed, because I expect to edit this page substantially this year.  I expect to be surprised when the thing rolls out and we actually see it for the first time.  I also expect to be surprised by how SpaceX actually uses the machine.

 - Ed Kyle
« Last Edit: 02/23/2015 04:49 PM by edkyle99 »

Offline AJW

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Re: SpaceX Falcon Heavy Discussion (Thread 3)
« Reply #99 on: 02/23/2015 06:04 PM »
You should archive this current page since it will be interesting to see the changes as new details emerge.

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