Author Topic: Has SpaceX ever discussed using a couple of small SRB's on their F9 1st stage?  (Read 13494 times)

Offline MoDyna

Two recent incidents piqued my interest along that line, for instance the recent launch of the Intelsat 35e which was not recoverable due to performance needs. If SpaceX could use a couple of small SRB's for enhanced performance, then maybe they could save enough fuel to make the 1st stage recoverable. The second incident was the recent contract loss to ULA for a military payload. If I understand correctly the F9 did not have the performance to do the job and SpaceX was bidding with a F9 Heavy. ULA won with a Atlas 5 (541) I think, but not really sure. You would think that with some SRB's attached the F9 could have got the contract. SpaceX could even make the SRB's recoverable as well. Why not, they are trying to recover the fairings and 2nd stage at some point as well.

Offline yokem55

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SpaceX doesn't have any internal capacity to build the SRB's themselves, and the cost of buying them to enable recovery would chew up the savings of recovery. As for missions needing extra performance, that's what Falcon Heavy is for. The structural changes needed to allow for strap on SRB's would be more complicated than just the structural changes needed for the Falcon Heavy core. Altogether, not worth it.

Offline RonM

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Good questions, MoDyna. Welcome to NSF!

I have to agree with yokem55. F9 wasn't designed to use SRBs and heaver payloads will be launched on FH.

Online cppetrie

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Yeah, FH is essentially their solution to what you've outlined, but it draws on internal capabilities with liquid-fueled rockets rather than going external for SRBs. FH wasn't able to compete for the payload awarded to Atlas because it hasn't yet flown. hopefully that won't be an issue in the not very distant future. :)

Offline Welsh Dragon

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Think of it this way: what's going to be cheaper? A few expendable solids or two larger reusable liquid boosters? SpaceX is betting on the latter.

Online pb2000

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I wonder what a couple of Falcon 1 strap on boosters with 1D FT Merlins would add to performance?
Launches attended: Worldview-4 (Atlas V 401), Iridium NEXT Flight 1 (Falcon 9 FT), PAZ+Starlink (Falcon 9 FT)

Offline Comga

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I wonder what a couple of Falcon 1 strap on boosters with 1D FT Merlins would add to performance?

Channeling You-know-who: Rockets are not Lego pieces.

As to the OP, solids are not the SpaceX way.  They won't even use pyro devices or small solids where they would be very helpful, like separating the boosters from the core of Heavy.
« Last Edit: 07/08/2017 10:11 PM by Comga »
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline nicp

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I wonder what a couple of Falcon 1 strap on boosters with 1D FT Merlins would add to performance?

Channeling You-know-who: Rockets are not LEGO pieces.

As to the OP, solids are not the SpaceX way.  They won't even use pyro devices or small solids where they would be very helpful, like separating the boosters from the core of Heavy.
I am a long time lurker, and post rarely.
For some considerable time (and perhaps, no certainly,  I am off topic) I have been considering starting a new thread entitled something like 'LEGO Rockets and why they don't work".
I will add at this point that this is not specifically a response to Comga, more a request to justify _why_ any particular LEGO rocket is a bad idea.

I'm a software engineer with a background in electronics and some physics. I'm 50 and have been fascinated by rocketry and spaceflight for most of my life.
Much as I adore this forum, a long time bugbear for me is such as the above (Rockets are not LEGO pieces). (Actually I understand the reasoning, but let me continue, if you will).

Sometimes it isn't immediately obvious to me why some configuration is not practical. I'm an educated guy so I usually realize for example why a 500 ton solid on top of a Falcon 1 is impractical.
My point is that any response that could be summarized as 'Don't be daft you fool' isn't worth posting (again I am definitely not having a dig at Comga here - but some responses from industry professionals do read that way).

Would anyone else like a 'LEGO rockets that won't work' forum?
As a new thread I'm sort of thinking of Jim's Raptor upper stage thing (I like), a place where impractical ideas - or even potentially practixal ideas can be discussed. With explanations as to _why_ this or that is ridiculous or physically possible but economically impossible (cough cough Helium 3).

Imagine a Centaur on a Falcon 9! Impractical for corporate reasons. (IMHO).
A Saturn 1 style first stage made from Falcon 9 first stages - and lands in one piece.

Ok, I'm blathering now.

Be well all, and have a lovely day,
Best Regards,
Nic

Edit/Lar: Fixed capitalization of LEGO in this post . Also see https://forum.nasaspaceflight.com/index.php?topic=43328 ... which is a thread Jim just started to discuss the topic of when mix and match works and when it doesn't, and why.
« Last Edit: 07/10/2017 07:36 PM by Lar »
Where's my Guinness?

Offline gospacex

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Two recent incidents piqued my interest along that line, for instance the recent launch of the Intelsat 35e which was not recoverable due to performance needs. If SpaceX could use a couple of small SRB's for enhanced performance

Apart from already voiced point about FH, SpaceX may in future also develop a kick stage. Say, based on Dracos and Dragon's navcomp.
Having three-stage LV is not a crime.

Offline ChrisWilson68

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Sure, SpaceX might start using solid rockets at some point in the future.  But it would have to be after Elon Musk is dead and buried.  And, even then, I'm not sure Elon wouldn't come back from the dead and crawl out of his grave just to stop SpaceX from using solids.

Offline ChrisWilson68

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I wonder what a couple of Falcon 1 strap on boosters with 1D FT Merlins would add to performance?
Channeling You-know-who: Rockets are not Lego pieces.
I will add at this point that this is not specifically a response to Comga, more a request to justify _why_ any particular lego rocket is a bad idea.

Saying "rockets are not legos" is a short-hand way of saying that rockets are designed as whole systems and each component of the system has many non-obvious dependences on the design of other components in the system.

If you were designing a new rocket from scratch to use optional solid rocket boosters, you would make many design decisions differently from the way you would make them if you were designing a new rocket to not have the option of solid rocket boosters.  Falcon 9 was designed to not have the option of solid rocket boosters.  As such, it is likely that many design decisions, large and small, were made along the way on the assumption of no solid boosters.  If someone were to go and add solids, it seems likely to many of us that many changes would be needed to Falcon 9 to make that possible.  The changes may be so extensive it's not even worth calling it Falcon 9 any more after the changes.

Some of us might believe it's likely there are many such changes needed, even if we don't know what those needed changes are.  It's just a general rule of thumb that if you swap out a major component of a rocket launch system, it's likely to require many changes in other components.

Online pb2000

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You mean KSP has been lying to me all this time?  ;)

Ah well, it's an easy trap to fall into, even Elon seemed surprised/frustrated at how difficult FH turned out to be.

That being said, wasn't Atlas V originally not designed for SRBs?
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Offline MATTBLAK

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It's simply not part of Elon & SpaceX's design philosophy. The Falcon 9 would need a fair bit of redesign to incorporate expendable solids. However, in the spirit of 'Rocket Lego' it would be interesting to contemplate how capable a Falcon 9, Version 5 etc would be with 6 or 8 GEM-60 solid boosters incorporated with the first stage. I imagine though that the acceleration stresses would be a bit excessive, unless the corestage engines were throttled way back.

Better to leave strap-on solids for the Vulcan family of launchers.
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Offline ChrisWilson68

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You mean KSP has been lying to me all this time?  ;)

Ah well, it's an easy trap to fall into, even Elon seemed surprised/frustrated at how difficult FH turned out to be.

Exactly.  Even the people who designed the thing underestimated how much work it would be to strap three of them together.

That being said, wasn't Atlas V originally not designed for SRBs?

The third Atlas V launch, on July 17, 2003, had two SRBs.  That was less than a year after the first Atlas V launch.  So I find it hard to believe Atlas V wasn't designed for SRBs from the start.  The Atlas V first stage actually has all the structural attachment points for solids and even to do a Falcon Heavy/Delta IV Heavy style triple-first-stage launch, even on launches with no solids at all.

Offline robert_d

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As Falcon was being developed, I thought a set of small side boosters might be a way forward to gain the payload capacity for launches like the latest Intelsat launch. But unless they change their mind and want to compete in the smallsat launcher arena, I think the simpler solution is the idea of launching two cores as one booster unit. Had they chosen this path INSTEAD of a full Falcon Heavy, it would be flying by now, due to far less mods being required. No specialized center core stage or separation systems required. All that would have been needed is a new TEL and interstage to connect to a heavier second stage. All the engineering would be in that interstage to distribute a total weight that is LESS than two boosters can already handle. This booster might well have flown as a "Falcon 16", likely easily RTLS even for big GEOSats.

Then, the path forward ( if larger payloads actually materiralize) would be a Falcon 4 Core. Would require strengthening the center two cores as they did with the center core for Falcon heavy now, but there is no rush. Also, there might be the possibility of an EXTERNAL structure such as narrow, pressurized tanks to augment the center cores. The dual core center could then support a dual tank upperstage. Big enough to at least consider building a reusable, full sized raptor powered version. Also a large payload fairing could be supported in the form of an 8.5 x 5.5 meter elliptical shape.   

Offline ChrisWilson68

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As Falcon was being developed, I thought a set of small side boosters might be a way forward to gain the payload capacity for launches like the latest Intelsat launch. But unless they change their mind and want to compete in the smallsat launcher arena, I think the simpler solution is the idea of launching two cores as one booster unit. Had they chosen this path INSTEAD of a full Falcon Heavy, it would be flying by now, due to far less mods being required. No specialized center core stage or separation systems required. All that would have been needed is a new TEL and interstage to connect to a heavier second stage. All the engineering would be in that interstage to distribute a total weight that is LESS than two boosters can already handle. This booster might well have flown as a "Falcon 16", likely easily RTLS even for big GEOSats.

Then, the path forward ( if larger payloads actually materiralize) would be a Falcon 4 Core. Would require strengthening the center two cores as they did with the center core for Falcon heavy now, but there is no rush. Also, there might be the possibility of an EXTERNAL structure such as narrow, pressurized tanks to augment the center cores. The dual core center could then support a dual tank upperstage. Big enough to at least consider building a reusable, full sized raptor powered version. Also a large payload fairing could be supported in the form of an 8.5 x 5.5 meter elliptical shape.

Or, maybe that would have taken even longer to develop than Falcon Heavy.  Falcon Heavy has the advantage that the second stage still attaches to the top of a first stage in exactly the same way as Falcon 9.  Having that new interstage could be more complicated than Falcon Heavy.  And then you still need the separation system to get the cores back, or else you need them to fly back and land together, which could be much more complicated than a separation system.


Online pb2000

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You mean KSP has been lying to me all this time?  ;)

Ah well, it's an easy trap to fall into, even Elon seemed surprised/frustrated at how difficult FH turned out to be.

Exactly.  Even the people who designed the thing underestimated how much work it would be to strap three of them together.

That being said, wasn't Atlas V originally not designed for SRBs?

The third Atlas V launch, on July 17, 2003, had two SRBs.  That was less than a year after the first Atlas V launch.  So I find it hard to believe Atlas V wasn't designed for SRBs from the start.  The Atlas V first stage actually has all the structural attachment points for solids and even to do a Falcon Heavy/Delta IV Heavy style triple-first-stage launch, even on launches with no solids at all.
I found where I originally heard it - Scott Manly on youtube (skip to 8 mins) :
Not sure what his source is though.
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Online cppetrie

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I feel compelled in Lar's absence thus far in this thread to point out that it is LEGO, not Lego or lego. More specifically it is LEGO pieces or systems, etc. LEGO is an adjective. But I digress.

You do digress, and the single worst thing about this forum is that even the mods encourage getting off topic, when it's their hobby horse.  Can we just drop it?
Relax. It was half in jest. I've been busted on it myself. Point of fact, the rest of my post was on-topic and related to a previous post. I would hardly say the mods encourage getting off topic. They may tolerate it to a certain extent. Their job is hard and figuring out where to draw the line on what is on-topic and where it has drifted off too far is not one I envy.

Offline envy887

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I wonder what a couple of Falcon 1 strap on boosters with 1D FT Merlins would add to performance?

About 700 kg to GTO per booster, if they are Falcon 1e rocket bodies they will conveniently burnout around MECO. 9600 kg to GTO for Block 5 full expendable with two boosters, and 11000 kg to GTO with 4 of them. GEM63 XLs would give about the same boost.

I like this idea a lot better than SRBs: no new or out of house tech; no separation events (I think they could reenter and land the F9 S1 with the boosters still attached); and they would be gas-n-go, just like the Block 5 boosters. Maybe they could attach to and mimic the leg hardpoints, basically as a spacer between the leg and the core.

SRBs are most certainly never going to happen on F9, nor will separable LRBs. Fixed LRBs almost certainly won't either, but it's interesting purely as speculation.

Offline Welsh Dragon

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SRBs are most certainly never going to happen on F9, nor will separable LRBs. Fixed LRBs almost certainly won't either, but it's interesting purely as speculation.
FH?

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