Speculation thread: intermediate-lift Raptor-derived RLV

[sevenperforce]

A 6 Raptor booster would slightly more powerful than New Glenn. A 9 Raptor version considerably more so.

I do think that mini-ITS on FH is feasible, though, since I believe the biggest structural issue with Falcon Heavy is how fast it goes in the dense lower atmosphere. A heavier upper stage means Max-Q and trans-sonic regions are higher up in thinner atmosphere with less dynamic stress, and the rocket goes through high altitude wind shear much slower. It also means that staging is lower and slower so it's easier to get the boosters back.

Agreed, both are feasible. Perhaps a logical development path would be half scale BFS on FH first, then half scale BFS on half scale BFR, and once they are making money from that system, full scale of both.

Yeah, I definitely like this idea. Build a fully-reusable methalox upper stage that can be tested on Falcon Heavy as a flying testbed for Raptor and ITS, then either go straight to ITS or go to a single-stick methalox first stage.

My concept, posted earlier, could be dropped in on FH easily. It would need a custom interstage but it would still have pretty solid performance.

I think the reason for vertical us the load structure. During EDL, the load is distributed over the entire surface which is not so problematic as landing on discrete points like legs.

With the wing extensions, the load is distributed across most of the stage.

Another option is a second stage for FH as a half scaled ITS. 6m diameter, 24m long, 1 raptor and 3 flavours:
1- Cargo version with integrated fairing (crocodile style) to deploy satellites
2- Mini crewed ITS launched as FH: minibus of 20 PAX to LEO, 10 PAX to moon vicinity and 5 to asteroids or even Phobos. Crewed part is 6m diameter, 9m long with around 180m3. Could copy-paste beefed up ECLSS systems from Dragon and become a very polyvalent spaceship.
3 - Tanker version

That would be the spaceship that NASA needs for BLEO and would match beautifully with the SLS. But I guess reminds too much the shuttle. Would delay too much the bigger brother, but a very good exploration spaceship.

It would be similar in size to NASA's Mid-L/D Mars lander design for the Evolvable Mars Campaign. Although I guess some of the tanking (and Raptor) would have to be removed to make room for the payload. It would be "landing only".

I bet Blue Origin has plans for something like that.

Oh, neat -- that looks a lot like my reusable second stage (though without the whole "single use" thing).

[dror]

The second stage re-enters on its belly using split flaps for attitude control, like the ITS Spaceship and Tanker. However, it has no landing legs near its tail, and no tail auxiliary thrusters. Instead, panels on the underside open up, both serving as landing skids and exposing auxiliary landing thrusters for a propulsive belly-first landing:



I've worked out all the specs...filled up about three Excel spreadsheets doing so, too.

First stage dry mass: 17 tonnes
First stage propellant: 421 tonnes
First stage mass ratio: 24:1
Thrust at launch: 6,266 kN

Second stage dry mass: 6.6 tonnes
Second stage propellant: 141 tonnes
Total vacuum thrust: 2,292 kN

Reusable payload to LEO: 24 tonnes
Reusable payload to GTO: 6.8 tonnes
Downmass from LEO: 22 tonnes

 

Upper stage landing would look like something out of Star Wars, because it drops straight down, winglets open, and it lands on the wingtips with rocket propulsion.

Know what else is great? Due to the vertically-oriented thrusters, the upper stage could both land on and take off from the Moon or from the surface of Mars without needing a launch pad.
 

To see that thing land, it would be mindblowing. Very cool stuff indeed. The ultimate space shuttle.
I hope some SpaceXer is reading this.
They could also arrange to show this launch technique on earth if they can manage to fly with ~ 2/3 empty tanks.

I do want to ask:
how and why did you opt for 4 meter diameter for both stages?
With this diameter you put a harder constraint on the payloads' diameter and volume than F9.
It also seems that most posters think that more performance is needed.
A three-engine version would be too big for most payloads, but will be big enogh for all.

[sevenperforce]

To see that thing land, it would be mindblowing. Very cool stuff indeed. The ultimate space shuttle.
I hope some SpaceXer is reading this.
They could also arrange to show this launch technique on earth if they can manage to fly with ~ 2/3 empty tanks.

Yeah, they could easily do manned or unmanned hypersonic flight tests using the VTOL mechanism with the vacuum engines swapped out for SL-expanded mini-Raptors. Would also be a fantastic antipodal high-speed transport.

I do want to ask:
how and why did you opt for 4 meter diameter for both stages?
With this diameter you put a harder constraint on the payloads' diameter and volume than F9.
It also seems that most posters think that more performance is needed.
A three-engine version would be too big for most payloads, but will be big enogh for all.

The four-meter diameter is just seven inches wider in every direction than F9, which is all I need to make the first stage identical in height to the Falcon 9 first stage. That's a 19% increase in volume while the stage remains entirely road-transportable and still capable of using many of the systems already in place for Falcon 9. Might even be able to use the same grid fins and landing legs.

The upper stage could also drop in to the Falcon Heavy using only a small modification to the interstage.

If we were sticking with an aluminum first stage, then you'd need three Raptors to get decent performance. But with a composite first stage and the auxiliary landing thrusters, two Raptors is plenty.

[dror]

The four-meter diameter is just seven inches wider in every direction than F9, which is all I need to make the first stage identical in height to the Falcon 9 first stage. That's a 19% increase in volume while the stage remains entirely road-transportable and still capable of using many of the systems already in place for Falcon 9. Might even be able to use the same grid fins and landing legs.

The upper stage could also drop in to the Falcon Heavy using only a small modification to the interstage.

So you went for 4 meters based on booster road-transportability and kept it to the upper stage, thus making a 4 meter faring.
Wouldn't you be able to make a 5.4 meter upper stage  like the Falcon fairing?

[GWH]

The upper stage could also drop in to the Falcon Heavy using only a small modification to the interstage.

Could it not drop onto a Block 5 F9 as well?  At a glance it looks like full stage mass is only a hair over F9, and therefore within acceptable TWR. 

Curious as well what the performance of this mini ITS would be with either F9 or FH booster rather than the methalox single stick.

[sevenperforce]

The four-meter diameter is just seven inches wider in every direction than F9, which is all I need to make the first stage identical in height to the Falcon 9 first stage. That's a 19% increase in volume while the stage remains entirely road-transportable and still capable of using many of the systems already in place for Falcon 9. Might even be able to use the same grid fins and landing legs.

The upper stage could also drop in to the Falcon Heavy using only a small modification to the interstage.

So you went for 4 meters based on booster road-transportability and kept it to the upper stage, thus making a 4 meter faring.
Wouldn't you be able to make a 5.4 meter upper stage  like the Falcon fairing?

Upper-stage dimensions are more flexible. It could be 4 meters, or it could be 5.4 meters with a taper to 4 meters at the rear. I prefer 4 meters because it allows some commonality with the first stage, just like Falcon 9 has. I didn't set a specific height limit. The whole front end would probably need to come in several variants depending on whether it was crewed or not.

Note that the upper stage has 165% the dry mass of the Falcon 9 upper stage, while the first stage has only 77% the dry mass of the Falcon 9 first stage. So it is even more balanced toward the upper stage than the Falcon 9.

With the mini-vacuum-Raptors swapped out for SL raptors, the upper stage would have the following specs:

Dry mass: 6.4 tonnes
Propellant capacity: 141 tonnes
Total vacuum thrust: 2,166 kN
Vacuum isp: 360 s

It could make orbit as an SSTO with about 700 kg of payload and enough margin for recovery. That's if it launches vertically, with full fuel tanks. Obviously the landing thrusters don't have enough umph to get it off the ground with full tanks.

The upper stage could also drop in to the Falcon Heavy using only a small modification to the interstage.

Could it not drop onto a Block 5 F9 as well?  At a glance it looks like full stage mass is only a hair over F9, and therefore within acceptable TWR. 

Curious as well what the performance of this mini ITS would be with either F9 or FH booster rather than the methalox single stick.

Full second-stage mass at liftoff is 149.4 tonnes without payload, which is rather high compared to Falcon 9's 111.5 tonnes. F9 FT has 775 tonnes thrust, so TWR is lower but acceptable.

Based on this calculator and assuming 21.6 tonnes of residuals for first stage recovery, I get 22.6 tonnes to LEO, fully reusable. That's with the second stage delivering 6.1 km/s, which allows staging to occur at less than 2 km/s.

Looks like they wouldn't need Falcon Heavy to test it after all. They could fly every Falcon Heavy mission with full reuse and first-stage RTLS, single-stick.

[GWH]

Looks like they wouldn't need Falcon Heavy to test it after all. They could fly every Falcon Heavy mission with full reuse and first-stage RTLS, single-stick.

I'm thinking that while it may have lower refurbishment costs the methalox booster would have pretty slim margins of cost reduction vs. Block 5 F9's & FH's.

[sevenperforce]

Looks like they wouldn't need Falcon Heavy to test it after all. They could fly every Falcon Heavy mission with full reuse and first-stage RTLS, single-stick.

I'm thinking that while it may have lower refurbishment costs the methalox booster would have pretty slim margins of cost reduction vs. Block 5 F9's & FH's.

I think you're right. The methalox booster is higher-performing, but clearly not needed. Not when F9FT + methalox upper stage can already do as much as FH.

[GWH]

One huge advantage of this architecture that I can think of is Lunar or Mars missions could be performed quite economically through reuse without any use of ISRU tech and actually getting the stage back.
If each upper stage could be used as little as several times before performing a one way trip and landing the hardware cost for those missions should be very low. 

[sevenperforce]

One huge advantage of this architecture that I can think of is Lunar or Mars missions could be performed quite economically through reuse without any use of ISRU tech and actually getting the stage back.
If each upper stage could be used as little as several times before performing a one way trip and landing the hardware cost for those missions should be very low.

SpaceX could build a tanker variant to be sent up on Falcon Heavy easily enough, for refueling on-orbit. I get 41.2 tonnes of fuel to LEO with full reuse, off Falcon Heavy with booster RTLS and center-core recovery. No crossfeed necessary.

I can't remember if I already said this here, but with full fuel tanks in LEO, the methalox upper stage would be able to burn from LEO to the moon, land on the moon, and return to lunar orbit, all without refueling. It would need to refuel in cislunar space to get back home, though. Of course it could take off fully fueled from the lunar surface on its side thrusters easily.

[Bynaus]

I like your idea, sevenperforce, but aren't you forgetting something? Namely, the payload. To first order, a rocket must launch satellites. How would you deploy them with that upper stage? Does your upper stage have an internal compartment with cargo bay doors? How would the satellites then be deployed? Using a robotic arm? Or rather "crocodile"-style? But then what about the joints being exposed to re-entry heating? Or does it have a front adapter onto which the satellite and normal fairings could be mounted? (but your drawing suggests otherwise)

[gospacex]

The four-meter diameter is just seven inches wider in every direction than F9, which is all I need to make the first stage identical in height to the Falcon 9 first stage. That's a 19% increase in volume while the stage remains entirely road-transportable and still capable of using many of the systems already in place for Falcon 9.

Even though it is only +30 cm, it is likely to cause all sorts of headache at the existing F9 factory. All those 3.7m fixtures need to be remade.
Welding machines need to be readjusted - if you are lucky. If you are not, you need different welding machines.
And if there is a door frame which is just a bit too narrow for 4m? Need to change that too. Let's hope that wouldn't require walls to be moved...
And if you want to continue building F9s, you need to support both at once.

At which point you ask yourself, "maybe it's easier to just build a separate factory and don't mess with the existing one". "And while we are at it, why not build this new factory in a location where road transport is not a limitation".

IOW: a small diameter change probably is not worth it. If you go for a diameter change, got for a big one.

[sevenperforce]

I like your idea, sevenperforce, but aren't you forgetting something? Namely, the payload. To first order, a rocket must launch satellites. How would you deploy them with that upper stage? Does your upper stage have an internal compartment with cargo bay doors? How would the satellites then be deployed? Using a robotic arm? Or rather "crocodile"-style? But then what about the joints being exposed to re-entry heating? Or does it have a front adapter onto which the satellite and normal fairings could be mounted? (but your drawing suggests otherwise)

Originally, I was thinking that the single bay door shown in the drawings could hinge up (or, if that was difficult to achieve, it could be split and open like the cargo bay doors on the shuttle) and the payload would be deployed perpendicular to the long axis of the satellite.



As you can see, the payload adapter would need to wrap about the body to some degree in order to transfer force to the main axis. This design would keep seams outside of the re-entry plasma stream. Of course, that's not necessarily a huge concern; there will need to be seams in the TPS anyway for the landing skids/landing engine ports, but there were seams in the Shuttle's TPS for its landing gear, and the seams in the ITS Spaceship (for landing legs) are not entirely out of the plasma stream.

If seams turn out to be nonproblematic, it can also open up at the nose, like this:



There are a few ways it can work. I have some structural concerns about the difference between the crewed and uncrewed versions. Because this configuration (low forward cross-section for launch, high belly cross-section for re-entry, perpendicular thrusters for propulsive landing) is highly advantageous for landing on Mars or on the Moon, we definitely want manned capability.

But then the differences between manned and unmanned flights become tricky. Ideally, you could manufacture the entire back end of the spacecraft exactly the same 100% of the time, and fit the front end with either the payload deployment/recovery module or a crew cabin. In theory you could even swap out the front module between flights. But getting the structure to work with this is tricky, particularly if you have landing propulsion on the front end, as I've depicted.

[guckyfan]

At which point you ask yourself, "maybe it's easier to just build a separate factory and don't mess with the existing one". "And while we are at it, why not build this new factory in a location where road transport is not a limitation".
............
IOW: a small diameter change probably is not worth it. If you go for a diameter change, got for a big one.

That would be true for a new booster stage. If you want a new upper stage that can be launched on mostly existing ground support hardware you go for the diameter that can be supported on a TEL. 4m is exactly what I was thinking about. Enough volume increase to have at least the same propellant weight, making good use of methalox propellant. Prove a lot of technology by using carbon composite, Raptor, self pressurization, even refuelling in orbit. As was shown in this thread the system would be very capable. keeping the existing payload capability or even increasing it slightly and have full reusability of the system. They may use a conventional fairing. No problem with reusing the fairing too.

[sevenperforce]

At which point you ask yourself, "maybe it's easier to just build a separate factory and don't mess with the existing one". "And while we are at it, why not build this new factory in a location where road transport is not a limitation".
............
IOW: a small diameter change probably is not worth it. If you go for a diameter change, got for a big one.

That would be true for a new booster stage. If you want a new upper stage that can be launched on mostly existing ground support hardware you go for the diameter that can be supported on a TEL. 4m is exactly what I was thinking about. Enough volume increase to have at least the same propellant weight, making good use of methalox propellant. Prove a lot of technology by using carbon composite, Raptor, self pressurization, even refuelling in orbit. As was shown in this thread the system would be very capable. keeping the existing payload capability or even increasing it slightly and have full reusability of the system. They may use a conventional fairing. No problem with reusing the fairing too.

Yeah, after seeing how capable a double-dev-Raptor US would be, there is absolutely no reason to add a new booster. Falcon 9 would be able to lift a double-dev-Raptor composite upper stage with no trouble whatsoever.

[GWH]

How much payload to LEO would this be upper stage MITS (mini-ITS) be capable of with a fully expendable Falcon Heavy, and the more pertinent number what mass to TMI, (and maybe TLI for fun).
I suspect this FH-MITS number would be well above SLS block 1.

Now I know what you are thinking "But why expendable? This system is reusable!" However I think there is SOME merit to a single lift straight from pad to Mars, and there is no reason whatsoever why this type of mission would be flown with brand new cores.  I also suspect that there would be "maintenance intervals", where after say 9* flights the Merlins may need to be stripped down for a complete refurbishment.  At this point the cost of building new cores amortized over 10 flights may be less than the operating cost of distributed lift**, and the economical choice would be to fly those used cores expendable for max payload.

*The 9 flight number is just pulled out thin air as an example.  Could be anything.
**Another strategy could be to ALWAYS fly the FH-MITS variant when launching sats to GTO and transfer over excess prop to awaiting MITS in circular LEO orbit before making the GTO burn and returning.  Launch costs generally go down on a per-kg basis with larger launch vehicles and this averages out those costs considerably. Could be a future optimization. 

[envy887]

How much payload to LEO would this be upper stage MITS (mini-ITS) be capable of with a fully expendable Falcon Heavy, and the more pertinent number what mass to TMI, (and maybe TLI for fun).
I suspect this FH-MITS number would be well above SLS block 1.

Now I know what you are thinking "But why expendable? This system is reusable!"...

I am thinking that, and I am right. FH is never going to match even SLS Block 1A without LEO refueling. With LEO refueling, it easily beats SLS Block 2 to any BLEO orbit. The only way LEO refueling makes sense is with reuse.

With LEO refueling, a 5 to 6 meter mini-ITS on reusable FH could send about 50t all the way to the surface of Mars or the Moon. Refueled on Mars via ISRU (or a combination of ISRU and delivered fuel), it could send at least 30t back to land on Earth.

[sevenperforce]

How much payload to LEO would this be upper stage MITS (mini-ITS) be capable of with a fully expendable Falcon Heavy, and the more pertinent number what mass to TMI, (and maybe TLI for fun).
I suspect this FH-MITS number would be well above SLS block 1.

Now I know what you are thinking "But why expendable? This system is reusable!" However I think there is SOME merit to a single lift straight from pad to Mars, and there is no reason whatsoever why this type of mission would be flown with brand new cores.  I also suspect that there would be "maintenance intervals", where after say 9* flights the Merlins may need to be stripped down for a complete refurbishment.  At this point the cost of building new cores amortized over 10 flights may be less than the operating cost of distributed lift**, and the economical choice would be to fly those used cores expendable for max payload.

Flying expendable doesn't make much sense for this system, as envy points out, because you've got the dry mass of the recovery system tacked on there, which hurts it quite a bit.

But I'll go ahead and crunch the numbers for a few things. How's this: current Falcon 9 upper stage, a hypothetical one-dev-Raptor flying with the exact same current Falcon 9 upper stage (other than a shifted common bulkhead), and my proposed mini-ITS; to be flown on F9 and FH in each possible configuration?

[GWH]

Flying expendable doesn't make much sense for this system, as envy points out, because you've got the dry mass of the recovery system tacked on there, which hurts it quite a bit.

But I'll go ahead and crunch the numbers for a few things. How's this: current Falcon 9 upper stage, a hypothetical one-dev-Raptor flying with the exact same current Falcon 9 upper stage (other than a shifted common bulkhead), and my proposed mini-ITS; to be flown on F9 and FH in each possible configuration?

Payload to LEO with expendable Falcon Heavy boosters is just a "what-if" measuring stick since most rockets are compared by LEO payload. 

More interested in just the TMI number for the expendable FH scenario, as if one were trying to land volume+mass on Mars as soon as possible it would probably be the fastest path forward.
The scenario where expendable booster 3-cores of Falcon Heavy might launch this mini-ITS direct to Mars would be where: in space prop transfer isn't developed yet, but one really wants to get a test of the system to land on Mars with at least some meaningful payload, so you expend some used FH cores. 

Its a matter of phased development, with in space cryo fluid transfer being one of the low TRL sticking points for people when discussing feasibility of the ITS.  From spreadsheets I've done on re-use its actually quite sound economically on a $/kg basis if there is a concern of high periodic refurbishment costs.  That's not to say reuse doesn't make sense and go off on THAT tangent, just that if you actually look at the cost vs capability it is a non-trivial improvement if refurb costs are high and stage life limited.

[envy887]

Flying expendable doesn't make much sense for this system, as envy points out, because you've got the dry mass of the recovery system tacked on there, which hurts it quite a bit.

But I'll go ahead and crunch the numbers for a few things. How's this: current Falcon 9 upper stage, a hypothetical one-dev-Raptor flying with the exact same current Falcon 9 upper stage (other than a shifted common bulkhead), and my proposed mini-ITS; to be flown on F9 and FH in each possible configuration?

Payload to LEO with expendable Falcon Heavy boosters is just a "what-if" measuring stick since most rockets are compared by LEO payload. 

More interested in just the TMI number for the expendable FH scenario, as if one were trying to land volume+mass on Mars as soon as possible it would probably be the fastest path forward.
The scenario where expendable booster 3-cores of Falcon Heavy might launch this mini-ITS direct to Mars would be where: in space prop transfer isn't developed yet, but one really wants to get a test of the system to land on Mars with at least some meaningful payload, so you expend some used FH cores. 

Its a matter of phased development, with in space cryo fluid transfer being one of the low TRL sticking points for people when discussing feasibility of the ITS.  From spreadsheets I've done on re-use its actually quite sound economically on a $/kg basis if there is a concern of high periodic refurbishment costs.  That's not to say reuse doesn't make sense and go off on THAT tangent, just that if you actually look at the cost vs capability it is a non-trivial improvement if refurb costs are high and stage life limited.

Mars is 6,000 m/s past LEO; if you bring the upper stage tanks and propulsion along all the way to the surface the payload drops to about what Red Dragon can do with a fully expendable FH - roughly 2,000 kg.

Cryo prop transfer is really, really important if we want to go to Mars or anywhere else. It's not that hard, compared to landing on Mars and making fuel there. It's something that could easily be flight-ready before the rest of a mini-ITS system.