Author Topic: While We're waiting - Falcon Medium  (Read 19831 times)

Offline robert_d

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While We're waiting - Falcon Medium
« on: 02/25/2016 03:24 pm »
All of the current activities for the SES-9 mission highlight the difficulties that the Falcon 9 has completing a true return-to-launch-site mission with the largest commercial payloads. So I began to wonder if there would be a relatively “simple” solution that could be fielded near term in advance of any methane powered replacements for the F-9.

My current suggestion would be for Space-X to create a “Falcon Medium”. This would basically be a two core version for the first stage with an enhanced second stage centered over the two cores. The two cores would stay connected, and return as a unit. The enhancement to the second stage would be to add two 5.5 ft. diameter tank sets, one on each side.

The first stage might lift off with say 16 engines running, or with all 18 running with two shut down prior to max Q.  Or two might be removed entirely. The fuel not used would be the RTLS reserve. The additional second stage tanks would be partially obstructed by the faring so would not cause much extra drag, and would help the flow over the “double-wide” first stage. The first stage would have to land on six legs, so they might have to be upgraded.

I would hope that ground operations would not be horribly impacted as the integration of two cores should be somewhat similar to the Falcon Heavy with only the addition of a new interstage unit to connect the two cores and the second stage. I would hope that only a new top of the TEL would need to be created to offset the second stage and payload by 6.4 ft. from the prior centerline. An additional support scaffold might be added to the current Heavy TEL if needed.

This would only work if it completely removed the need for any ASDS missions. Falcon Heavy center cores would be expended. A trade would have to be made against expending a few (<1 a year) FH cores versus using standard cores for the Falcon Medium and returning all of them as RTLS. It might even be that a “four core” Falcon Heavy would be possible (yes, new TEL) where two outboard cores support the central Falcon Medium with enough reserves to RTLS.     

Now back to the regular scheduled program...

Offline whitelancer64

Re: While We're waiting - Falcon Medium
« Reply #1 on: 02/25/2016 03:35 pm »
The several millions needed for redesigning the second stage and interstages and all the ground support equipment and retrofitting the first stages to hodge-podge all of this together ... would be better spent supporting several years of ASDS operations.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
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Offline matthewkantar

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Re: While We're waiting - Falcon Medium
« Reply #2 on: 02/25/2016 04:02 pm »
I have thought for some time that a two core Falcon could be done with the upper stage and fairing above one core. Vectored first stage thrust is capable of keeping course. This is speculation only, I use the Shuttle hanging off of the external tank as an example.

Matthew

Offline TrueBlueWitt

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Re: While We're waiting - Falcon Medium
« Reply #3 on: 02/25/2016 04:13 pm »
I have thought for some time that a two core Falcon could be done with the upper stage and fairing above one core. Vectored first stage thrust is capable of keeping course. This is speculation only, I use the Shuttle hanging off of the external tank as an example.

Matthew

Raptor based S2 will be more effective use of resources.  likely similar performance gain. Plus option of S2 recovery and reuse.

Offline Robotbeat

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Re: While We're waiting - Falcon Medium
« Reply #4 on: 02/25/2016 04:21 pm »
Bad idea. There's already plenty of granularity in performance between full RTLS and full droneship with various fuel margins. Adding this configuration would simply add cost and reduce reliability.
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Offline chrisking0997

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Re: While We're waiting - Falcon Medium
« Reply #5 on: 02/25/2016 04:26 pm »
seems like this solution creates alot of problems...which one(s) is it supposed to solve?
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Online spacenut

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Re: While We're waiting - Falcon Medium
« Reply #6 on: 02/25/2016 04:41 pm »
What about a Falcon medium with two outer first stage cores, then a single middle second stage core, same diameter, but with a metholox upper stage engine.  Rocket would be short, kind of like the old Stumpy idea, but as tall as the existing first stage.  Second stage could be mounted higher up so the fairing would clear the first stage engines.  I figure this could get in the 30-40 ton range, or even help with high altitude GSO satelites, without going completely to heavy.  No retooling from the 3.7m stages.  Would not have the capability of a FH but in between F9 and FH. 

Like this:     
 booster >     ====               
 second stage >  ===< payload
 booster >      ==== 
   
« Last Edit: 02/25/2016 04:47 pm by spacenut »

Offline robert_d

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Re: While We're waiting - Falcon Medium
« Reply #7 on: 02/25/2016 04:51 pm »
seems like this solution creates alot of problems...which one(s) is it supposed to solve?

TODAY! You have a high probability of losing a first stage that could be saved and RTLS as a Falcon Medium. I have always hated the barge concept. Lots of expense not in their primary area of expertise. Weather issues. Possible corrosion. Time delays. Likely easier operations with one RTLS for some missions that would otherwise require a full Falcon Heavy. Better engine out if all 18 fly on a mission.

And having an upgrade path (Falcon 4 Core) to a two engine second stage which would THEN have the volume to support a FULLY FUNCTIONAL methane Raptor.

Offline matthewkantar

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Re: While We're waiting - Falcon Medium
« Reply #8 on: 02/25/2016 04:51 pm »
With a Falcon Medium utilizing off of the shelf parts as i described above, I think for instance, the current SES-9 mission would benefit. Both lower stages could return to landing site requiring no barging. There would be a range of payloads that could benefit from the extra capacity without having to develop any new elements. If it works structurally, it would add capacity and economy to SpaceX's product line.

There are plenty of good reasons to develop a Raptor upper stage, but if you want to get the most money and performance out of extant gear, i would guess this would do it.

Enjoy, Matthew

Offline robert_d

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Re: While We're waiting - Falcon Medium
« Reply #9 on: 02/25/2016 05:07 pm »
What about a Falcon medium with two outer first stage cores, then a single middle second stage core, same diameter, but with a metholox upper stage engine. 

Like this:     
 booster >     ====               
 second stage >  ===< payload
 booster >      ==== 
   
Wow. I like it. Better than my idea, because it requires no new interstage. Payload stays on centerline. TEL only requires handling PLF and payload lower down. Two RTLS, but they were planning on that for Falcon Heavy anyway. Put two Merlins in the center while waiting for the debut of the Raptor.

Offline Jim

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Re: While We're waiting - Falcon Medium
« Reply #10 on: 02/25/2016 05:11 pm »
This is just nonsense.  There is no redeeming value.   It just adds costs.  It can't use existing TELs.  It doesnt fit in the 40 hangar.  Keeping the boosters apart like that would require structure at the base to hold them together.
« Last Edit: 02/25/2016 05:17 pm by Jim »

Offline robert_d

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Re: While We're waiting - Falcon Medium
« Reply #11 on: 02/25/2016 05:25 pm »
This is just nonsense.  There is no redeeming value.   It just adds costs.  It can't use existing TELs.  It doesnt fit in the 40 hangar
Yes, it would have to fly out of 39A. How much have they spent on ASDS activities so far? So let's turn it over to the manifest analysis people to see how many of these large birds there are to fly.

Offline Jim

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Re: While We're waiting - Falcon Medium
« Reply #12 on: 02/25/2016 05:29 pm »

Yes, it would have to fly out of 39A. How much have they spent on ASDS activities so far? So let's turn it over to the manifest analysis people to see how many of these large birds there are to fly.


Not as much as the engineering and operations to maintain another seldom used configuration that doesn't use existing stages.
« Last Edit: 02/25/2016 05:30 pm by Jim »

Offline abaddon

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Re: While We're waiting - Falcon Medium
« Reply #13 on: 02/25/2016 05:36 pm »
Days like these I think we need a SpaceX Crackpot Ideas forum.


Offline whitelancer64

Re: While We're waiting - Falcon Medium
« Reply #14 on: 02/25/2016 05:46 pm »
Days like these I think we need a SpaceX Crackpot Ideas forum.

Asking silly questions and making up silly ideas, and then having people who know better explain why those questions and ideas are silly is how people learn.

Hopefully there is learning going on here, anyway.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Offline Lars-J

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Re: While We're waiting - Falcon Medium
« Reply #15 on: 02/25/2016 05:48 pm »
This is just nonsense.  There is no redeeming value.   It just adds costs.  It can't use existing TELs.  It doesnt fit in the 40 hangar
Yes, it would have to fly out of 39A. How much have they spent on ASDS activities so far? So let's turn it over to the manifest analysis people to see how many of these large birds there are to fly.

Probably not as much as they would have to spend on realizing your idea. F9 is here, and FH will be soon. Why in the world would they do this? With FH they can do RTLS with all cores, putting even less stress on them.

And if you think FH will be too much rocket - why? Are you upset that deliveries sent to you comes on a vehicle that is oversized? Matching LV performance exactly for each payload is not practical, and will only add costs. (ULA can do this by adding small solids, but it still costs them to have many configurations)

And no, you cannot fit two M1D-Vac's on an upper stage. Not even a 5.2m diameter upper stage. (see image)

Offline whitelancer64

Re: While We're waiting - Falcon Medium
« Reply #16 on: 02/25/2016 05:48 pm »
This is just nonsense.  There is no redeeming value.   It just adds costs.  It can't use existing TELs.  It doesnt fit in the 40 hangar
Yes, it would have to fly out of 39A. How much have they spent on ASDS activities so far? So let's turn it over to the manifest analysis people to see how many of these large birds there are to fly.

The amount of money it would cost to make and test all these new designs and modifications of existing components would very rapidly EXCEED how much the ASDS program costs, and could, in fact, pay for ASDS operations for several years.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Offline intrepidpursuit

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Re: While We're waiting - Falcon Medium
« Reply #17 on: 02/25/2016 06:18 pm »
Why do people keep having this bright idea? Adding boosters to a central rocket can leave the central rocket infrastructure untouched except some reinforcement and attachment points. The outer rockets then have much less stress and can be identical. Then you shed the outer boosters partway through flight to shed weight and continue burning the central booster. Then the second stage takes over when the vehicle is significantly higher up and/or going faster than it would be on a single stick. This is often called a 2.5 stage arrangement.

With a dual booster arrangement you now have to split the weight of the upper stage across two boosters, requiring a bunch of extra structure in an entirely new interstage. All you get is double the first stage power along with almost double the total weight, leaving you with a nearly identical separation event. If the upper stage is now left at the same height and going the same speed, the only way to take advantage of the additional lift is with a larger second stage. So now you need to build a new interstage, and a new second stage. The maximum benefit is less than 2x the payload when you have redesigned half of your rocket and added at least two entirely new items to your production line.

There is a reason there are ZERO instances of people strapping 2 boosters together without a central core. It just doesn't give a worthwhile return on investment from an infrastructure or cost savings perspective.
« Last Edit: 02/25/2016 06:20 pm by intrepidpursuit »

Online spacenut

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Re: While We're waiting - Falcon Medium
« Reply #18 on: 02/25/2016 06:46 pm »
My idea was to place a 3.7 central core UPPER stage using metholox, same diameter as the other cores.  The outer two cores boost, separate off to fly back, then the upper central stage goes on to orbit where ever.  Only problem I see it the diameter of a Raptor Vacuum.  This would be a medium Falcon, with in between capacity of Falcon 9 and Falcon Heavy.  Height wouldn't be a problem so the upper stage could be as long as needed.  It would fit the Falcon heavy infrastructure.  It could even be an extended kerolox upper stage that would fit in between for longer burning.  Even if the stage is only half as long as a first stage, a bar could be placed near the bottom between the outer boosters to keep them stable and fall away with separation of the upper stage.  Having more length could allow for more fuel for longer duration second stage.  It is all just an exercise trying to use existing infrastructure, manufacturing, and launch facilities at 39A, as a go between.  Only two boosters, an extended upper, or a metholox upper in between them.  No interstage would be needed.
« Last Edit: 02/25/2016 06:47 pm by spacenut »

Offline Jim

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Re: While We're waiting - Falcon Medium
« Reply #19 on: 02/25/2016 06:51 pm »
1.   a bar could be placed near the bottom between the outer boosters to keep them stable and fall away with separation of the upper stage. 
2.  It is all just an exercise trying to use existing infrastructure, manufacturing, and launch facilities at 39A, as a go between. 

3. Only two boosters, an extended upper, or a metholox upper in between them.  No interstage would be needed.


1.  The "bar" isn't that simple
2.  It doesn't.  see 1 & 3
3.  New interstage is required because there is no core to support it.

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