Author Topic: Full diameter shortened ITS as FH replacement?  (Read 10367 times)

Offline KelvinZero

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Full diameter shortened ITS as FH replacement?
« on: 10/03/2016 11:55 am »
This is a spin off of the SFR (mini-BFR) as fully reusable Falcon Heavy replacement thread.

Someone has probably already asked this but I wouldn't know how to find it: How short could you plausibly make the full-diameter BFR? Im just thinking a lot shorter and symmetrically remove some engines.

Yes, if you could make it wide but short for a Mini-BFR with say 9 Raptors, then stretch the tanks and add the remaining engines for a full BFR.  Same with a second stage, one Raptor and a short reusable stage, then stretch with more engines for an MCT or tanker.  I would say at least 10-12m in diameter.   3.7m tankage could be made at Hawthorn to fit inside the upper stage with remaining space on a stretched MCT version for cargo or crew.

I can't shake this idea. Now we have exact ITS numbers to deal with.

Im sure you would lose some efficiency; there is a reason rockets are tall and thin, but the Shuttle suggests it is not the only design consideration.

You would be testing so much of the final ITS. By past history im not sure I want to ride on any SpaceX rocket until they have blown up at least two of them  8) .

It could be simpler and cheaper than the FH: probably a bit more fuel but many less components. It would have huge volume advantages over the FH. Even without the Mars colonisation goal you would be developing a BFR of very adaptable performance without going back to the drawing board. No need for crossfeed. With half the number of engines, but still about as many as the FH, you still have redundancy but even less risk of one rocket taking out neighbours. It would let you start with much wider safety margins and evolve towards the requirements of the ITR.
« Last Edit: 10/14/2016 03:57 am by KelvinZero »

Offline Paul451

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Re: Full diameter shorted ITS as FH replacement?
« Reply #1 on: 10/03/2016 04:38 pm »
What kind of performance would you get out of a 9+1 Raptor, 12m diameter, TSTO launcher?

It seems like a reasonable stepping stone to ITS, same engines, same diameter tanks, etc. And switching to 9 vac-Raptors, the mini-ITS first stage becomes the first version of an ITS second stage when you develop the BDB.

But Musk's timeline pretty much rules it out.

Offline envy887

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Re: Full diameter shorted ITS as FH replacement?
« Reply #2 on: 10/03/2016 04:52 pm »
The only way I could see this being worthwhile is if it used almost all the same major components from the ITS spaceship. Use the same tanks, convert the thrust structure to hold 21 Raptors: same gimballing center cluster of 3, and each of the 6 fixed vacuum engines replaced with a fixed cluster of 3 SL Raptors. Convert the cargo section into an interstage. The PICA layer could be a lot lighter.

That would still be big enough to put 150 tonne payloads in LEO, probably closer to 200t of fuel with the tanker version.

Offline Paul451

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Re: Full diameter shorted ITS as FH replacement?
« Reply #3 on: 10/03/2016 05:14 pm »
The only way I could see this being worthwhile is if it used almost all the same major components from the ITS spaceship.

Well that is the idea. Essentially the propulsion section of ITS (second stage) starts life as the first stage of smaller beast.

Same tanks, same engines, same handling and transport systems.

convert the thrust structure to hold 21 Raptors

21?

Offline envy887

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Re: Full diameter shorted ITS as FH replacement?
« Reply #4 on: 10/03/2016 06:25 pm »
21 SL Raptors is based on the idea that the second stage is the same as the ITS ship. The total GTOW would be about 4500 tonnes, so at least 20 Raptors are needed. 21 packs a little better.

I don't see the point of wasting resources making a smaller dedicated second stage. Just put the big ITS upper stage on top and stage lower. As long as the booster gets it up 30 km they can light the Raptor vacs.

Offline Impaler

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Re: Full diameter shorted ITS as FH replacement?
« Reply #5 on: 10/04/2016 05:30 am »
Simply utilizing the amazing engine technology and carbon composite construction in the Falcon family seems like the more straightforward way to improved the existing vehicle performance and serve as sub-scale demonstrators at the same time.  Also allows Merlin engine to be retired which saves overhead

Offline hkultala

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Re: Full diameter shorted ITS as FH replacement?
« Reply #6 on: 10/04/2016 06:09 am »
The only way I could see this being worthwhile is if it used almost all the same major components from the ITS spaceship.

Well that is the idea. Essentially the propulsion section of ITS (second stage) starts life as the first stage of smaller beast.

Same tanks, same engines, same handling and transport systems.

convert the thrust structure to hold 21 Raptors

21?

21 means just dropping the outer ring of engines of ITS booster. More compatibility with it.

In ITS booster there is 1 center engine, 6 other around it. And 14 on the next ring. This makes 21.



Online guckyfan

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Re: Full diameter shorted ITS as FH replacement?
« Reply #7 on: 10/04/2016 10:17 am »
To me it makes much sense to use the ITS, the upper stage and replace the vac engines with first stage engines. Keep the propulsion system basically the same as ITS  and put a second stage with 1 Raptor on top. Or fly with cargo section on top as SSTO with smaller LEO payloads.

Offline KelvinZero

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Re: Full diameter shorted ITS as FH replacement?
« Reply #8 on: 10/09/2016 02:17 am »
21 SL Raptors is based on the idea that the second stage is the same as the ITS ship. The total GTOW would be about 4500 tonnes, so at least 20 Raptors are needed. 21 packs a little better.

I don't see the point of wasting resources making a smaller dedicated second stage. Just put the big ITS upper stage on top and stage lower. As long as the booster gets it up 30 km they can light the Raptor vacs.
(Sorry for bumping this with such a late reply. Partially because a whole bunch of interesting proposals where thrown in that I hadn't thought of.. and that might drag this back to the mini-bfr thread.)

This above is probably the closest to what I was imagining. I was (probably naively) considering shortening both stages but that may be more like "just shortening" the space shuttle than a typical rocket tank.

I would still like to take some weight off the upper stage. 150 tons dry mass (90 tons for propellant variation) is not super absurd, only double the dry mass of the shuttle, which delivered less than 30 tons to orbit. I would like to start smaller if possible though. Between the fuel and mars version I think there could be room for a cargo version. It's goal is to do the same job as the falcon heavy but be totally reusable including the fairing. It also has room to grow to much much larger payloads.

People have also mentioned using the upper stage as a SSTO, which technically fits on this thread. I haven't done the numbers but it is the opposite of the philosophy Im aiming for here: Start easy with large margins. Feel your way forwards. If an SSTO pops out at the end, great.

Im wondering if the reasons that make 12 meters absurd are not such a big deal now that SpaceX is confident of returning to landing site. Could a squat kettle of a rocket serve current uses (ie FH cargos) competitively while being evolvable to a full size ITS? I don't think Elon has ever said the ITS was other than an ultimate goal, but at the same time there does not seem to be room for a totally different intermediate rocket as part of the learning process.
« Last Edit: 10/09/2016 02:56 am by KelvinZero »

Online guckyfan

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Re: Full diameter shorted ITS as FH replacement?
« Reply #9 on: 10/09/2016 06:41 am »
It seems to me that using only the propulsion unit of the upper stage/ITS and replacing the vac engines with sea level engines would be a good first stage for a smaller vehicle though still large. Then put a new second stage on top with one vac Raptor and 3 of the 10t RCS thrusters as landing engines.

Not an optimal design but utilizing much "existing" capabilities.

Offline sdsds

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Re: Full diameter shorted ITS as FH replacement?
« Reply #10 on: 10/09/2016 06:55 am »
It doesn't sound like everyone is on the same page as SpaceX. They intend to build and sub-orbitally test the Ship first. Once that's accomplished there will be time for them to decide whether going for the final Booster design, or building a shorter "Booster Block 0" makes more sense.
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Offline KelvinZero

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Re: Full diameter shorted ITS as FH replacement?
« Reply #11 on: 10/09/2016 07:33 am »
It doesn't sound like everyone is on the same page as SpaceX. They intend to build and sub-orbitally test the Ship first. Once that's accomplished there will be time for them to decide whether going for the final Booster design, or building a shorter "Booster Block 0" makes more sense.
Oh, ok. I missed that. Does ship mean upper stage? Where can I read about this?

Offline sdsds

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Re: Full diameter shorted ITS as FH replacement?
« Reply #12 on: 10/09/2016 08:02 am »
They intend to build and sub-orbitally test the Ship first.
Does ship mean upper stage? Where can I read about this?

Well yes it would mean that, if it were a standard launch system. It's an upper stage of a launch vehicle, a trans-planetary habitat, a planetary lander, and a single-stage-to-orbit (from Mars at least) ascent vehicle. You can hear more about it in ... the speech Musk gave announcing the ITS. Look particularly at the timeline graphic which shows which systems are developed when....
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Offline KelvinZero

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Re: Full diameter shorted ITS as FH replacement?
« Reply #13 on: 10/09/2016 12:25 pm »
They intend to build and sub-orbitally test the Ship first.
Does ship mean upper stage? Where can I read about this?
Well yes it would mean that, if it were a standard launch system. It's an upper stage of a launch vehicle, a trans-planetary habitat, a planetary lander, and a single-stage-to-orbit (from Mars at least) ascent vehicle. You can hear more about it in ... the speech Musk gave announcing the ITS. Look particularly at the timeline graphic which shows which systems are developed when....
I just meant the top bit (as distinguished from the bottom bit)  :)

Ok, I found the timeline inside the speech.
https://www.youtube.com/watch?v=IFA6DLT1jBA?t=3157

It is saying top bit first, possibly in 4 years, mentions vague possibility of suborbital flights as a service as well as for testing. Mentions possibility of at least tanker being single stage to orbit.

I didn't see mention of a shorter block 0. Were you just referring to what is being discussed on this thread?

I had been discounting the SSTO, especially due to the mention of not being able to bring it down, but I guess there is one reasonable use if you can just get the non-tanker version to orbit: You could avoid developing the tanker or booster at all until flight rate is high. Instead you launch SSTO with no cargo and use many launches of you F9R to refuel it. You could also use F9R to get 6 crew to orbit, plenty for an early mission. Maybe the safety would be the most important factor. The booster does sound pretty simple once you have the space ship and the  F9R very likely would still not be fully reusable.

Offline HMXHMX

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Re: Full diameter shorted ITS as FH replacement?
« Reply #14 on: 10/09/2016 03:43 pm »
They intend to build and sub-orbitally test the Ship first.
Does ship mean upper stage? Where can I read about this?
Well yes it would mean that, if it were a standard launch system. It's an upper stage of a launch vehicle, a trans-planetary habitat, a planetary lander, and a single-stage-to-orbit (from Mars at least) ascent vehicle. You can hear more about it in ... the speech Musk gave announcing the ITS. Look particularly at the timeline graphic which shows which systems are developed when....
I just meant the top bit (as distinguished from the bottom bit)  :)

Ok, I found the timeline inside the speech.
https://www.youtube.com/watch?v=IFA6DLT1jBA?t=3157

It is saying top bit first, possibly in 4 years, mentions vague possibility of suborbital flights as a service as well as for testing. Mentions possibility of at least tanker being single stage to orbit.

I didn't see mention of a shorter block 0. Were you just referring to what is being discussed on this thread?

I had been discounting the SSTO, especially due to the mention of not being able to bring it down, but I guess there is one reasonable use if you can just get the non-tanker version to orbit: You could avoid developing the tanker or booster at all until flight rate is high. Instead you launch SSTO with no cargo and use many launches of you F9R to refuel it. You could also use F9R to get 6 crew to orbit, plenty for an early mission. Maybe the safety would be the most important factor. The booster does sound pretty simple once you have the space ship and the  F9R very likely would still not be fully reusable.

Yes, someone should think about a refuelable SSTO excursion vehicle for interplanetary missions.  :)

Offline DOCinCT

Re: Full diameter shorted ITS as FH replacement?
« Reply #15 on: 10/09/2016 09:08 pm »
What kind of performance would you get out of a 9+1 Raptor, 12m diameter, TSTO launcher?
FH triples the booster thrust, but with a standard 2nd stage barely doubles the LEO performance of a F9, gets better to Mars (triple). 
With 9 raptors you get 6M+ lbf at launch vs. 5.1M lbf  a 20% boost.  Vacuum 787K vs 210K about 4x.
So maybe triple the overall performance?   (I think the 2nd stage is more important than booster - a F9 is 80% of a Delta IV Heavy to LEO with less booster thrust but a 2nd stage engine 8-9 time the thrust of a RL-10)
But I'm no rocket scientist/space engineer.

Offline sdsds

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Re: Full diameter shorted ITS as FH replacement?
« Reply #16 on: 10/09/2016 11:06 pm »
I didn't see mention of a shorter block 0. Were you just referring to what is being discussed on this thread?

Yes, I should have been clearer on that. Neither the "block 0" terminology nor the concept come from anything SpaceX has said. It's only a thought experiment!

But what if the first Ship they build doesn't have quite the performance capability they currently say the final version will have? Wouldn't it then be interesting to supplement its capabilities with a minimalist, reusable version of the Booster? That would allow them to fly fully reusable missions to Earth-orbit....

Then they could develop and fly a Tanker to validate their plan for on-orbit "refilling."
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Offline Robotbeat

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Re: Full diameter shorted ITS as FH replacement?
« Reply #17 on: 10/09/2016 11:19 pm »
I could see this as a possible SpaceX development timeline:

1) F9R-Dev1-like version of ITS with just 3 Raptors initially mounted for suborbital testing in 2018, maybe without TPS at first.
2) later, extra engines are added to get closer to the flight vehicle. Let's say they're Vacuum-optimized ones. Still just suborbital tests, but they test operation of the Vacuum Raptors this time. TPS needed for these tests. 2019-2020. 2021 sees the tanker version doing tests and Mars-entry-like tests for spaceship.
3) Booster testing, initially just 7 Raptors, could be even fewer. 2020. Mainly to test launch cradle concept.
4) Add 14 more engines. 2021
5) 21 more engines 2022. They put the ITS on top, do refueling tests and go to Mars uncrewed.

To be continued...
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Offline KelvinZero

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Re: Full diameter shorted ITS as FH replacement?
« Reply #18 on: 10/09/2016 11:25 pm »
Yes, someone should think about a refuelable SSTO excursion vehicle for interplanetary missions.  :)
Well I did hear about something like that somewhere :) I just meant there is an example where SSTO from earth is not totally useless even if it can manage no cargo, no crew, and has used up every drop of fuel so can't return to earth by itself.

Offline KelvinZero

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Re: Full diameter shorted ITS as FH replacement?
« Reply #19 on: 10/09/2016 11:47 pm »
But what if the first Ship they build doesn't have quite the performance capability they currently say the final version will have? Wouldn't it then be interesting to supplement its capabilities with a minimalist, reusable version of the Booster? That would allow them to fly fully reusable missions to Earth-orbit....
For a while I thought the OP of this thread was thrown out by this test vehicle concept. I think this is reasonable though. The test vehicle is going to test this new sideways glide and flip for landing. Maybe there will be just a grasshopper version first but I think this gliding (or sideways falling) is a big new thing.

I think given you have tested all the hard stuff, a short booster would be easy to whip out towards the end. It is almost a subset of the problems, except that it needs attachments for more engines.
« Last Edit: 10/09/2016 11:49 pm by KelvinZero »

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