What are your ultimate commercial rocket designs?

[Hyperion5]

I was inspired after reading Spacex's page on the Falcon 9 and then seeing some interesting comments & claims by Spacex, Musk & ULA to create this thread. 

Spacex points out that their design for the Falcon 9 was shaped by a report on launch failures:
http://www.spacex.com/falcon9.php

"The vast majority of launch vehicle failures in the past two decades can be attributed to three causes: engine, stage separation and, to a much lesser degree, avionics failures. An analysis (p. 23) of launch failure history between 1980 and 1999 by Aerospace Corporation showed that 91% of known failures can be attributed to those subsystems."

To create the ultimate commercial rocket and counter those issues, Spacex brags about their design features:

Triple-redundant avionics with GPS overlay
Engine-out capability & reliability on SI
(They claim the Falcon 9 features "an improved" version of the design architecture of Saturn rocket series (Saturn I, IB, & V)
Same propellant tanks used in both stages (+ cost savings)
Road-transportable stages (only 3.66 meters in diameter)
Superior engine design eliminates hydraulic failures
Then there's the simple propellants to deal with, namely non-cryogenic RP-1 & modestly cryogenic Lox

Musk believes the Falcon 9 series is the best and cheapest commercial launcher on the market today.  He openly scoffs at one of his major competitor's rockets:  "Ariane 5 has no chance," he told BBC News.  "I don't say that with a sense of bravado but there's really no way for that vehicle to compete with Falcon 9 and Falcon Heavy. If I were in the position of Ariane, I would really push for an Ariane 6."
http://www.bbc.co.uk/news/science-environment-20389148

Of course ULA doesn't agree totally with Spacex' premise even if they aren't launching many commercial payloads: “Not to minimize SpaceX’s impressive achievements, but ULA’s customers want to see a track record of success, repeatably delivering complex payloads to orbit, safely and on time.  In the launch business, price is never the sole consideration for the buyer. That’s because launch price is a small percentage of the total program value (which can exceed replacement cost when there’s no money to replace, like the Glory spacecraft).” http://www.nasaspaceflight.com/2012/11/ula-customers-class-reliability-main-consideration/

Elon Musk clearly believes he's got the best commercial rocket design on the market today.  Some of his competitors would beg to differ.  I'm not convinced there is a really ideal commercial rocket design out there though.  All of the top contenders have some crucial flaws in their design that makes me hesitate to say, "this is as good as commercial rocket design gets".  So that brings me up to this question set and the ultimate challenge for everyone. 

1) What would your ideal commercial rocket designs look like?  Explain why your rocket designs would be superior to all competitors. 

There's a couple of markets I think you can divide this into.  Commercial launchers tend to send things to one of two areas currently. 
Low-earth orbit
Geosynchronous transfer orbit

There are several other places you might eventually send commercial payloads. 
Lunar orbit
Lunar surface
Earth-Moon Lagrange points
Beyond-Earth Orbit (probably to asteroids (Planetary Resources) or Mars) 

I would urge you to pick a couple of target markets or less & if possible, and refine the design by selecting a payload range or the amount of crew you hope to send there.   

The challenge is to create the absolute best, most competitive commercial rocket design possible that would be able to dethrone all current & near-future competitors (like possibly the Long March 5 & Angara series).  The best part is there are a huge number of design features to consider and plenty of different possible payload markets to target.  You can base your rocket company anywhere reasonable in the world (yes to Brazil, Russia, Europe, US, China, India, etc--no to places like Rwanda) in case that makes a key difference to your business case.

The categories to consider would include things like payload range, thrust range, target market, fairing sizes, engine number & type, number of stages, transportability/core size, man-rating (yes/no), propellants, modularity, engine-out capability, avionics, and so on.  This thread is flexible. 

Edit--Concern duly noted and acted upon. 

[Silmfeanor]

This topic is too broad, there are too many factors. You might want to add the word "current" in there somewhere. Or you're gonna get weird answers:

I'll go with a few examples:

fully reusable SSTO / TSTO.  High flight rate. Lifting body or with wings, aircraft like operations. Think Skylon. Doesn't work at all if you havent got the flight rate, or not enough money to finish design + building.

Hydrogen gun. Only works on propellant launches. can fire quite a few times per day. Not done before.

Simple RP-1 LOX 2 stage to orbit, common engine design. non-reusable. Basically falcon 9. Works in current environment, if it can be made reliably. RP can be changed to methane.
Perhaps it can be made reusable. Perhaps making it reusable is not economical, or not workable.

As I said - too many options, too many unknowns.

[Hyperion5]

 I thought about what my own ultimate commercial rocket design would look like.  Looking at what Musk & ULA have said, I think the two keys to success are low cost per kg to orbit & reliability. 

To get the cost per kg down, my design would be done in-house like Spacex does.  My initial choice of home country was the US, even if ITAR is not so helpful at times.  For the design, I wanted to choose a propellant mix that would be easy to handle, extremely cheap, and benefit the design.  My propellant choice was made when I saw Strangequark talking up the advantages of staged combustion methane engines.   

Centrifugal pumps are basically constant volumetric flow rate devices. A methox engine’s optimum O/F (~3) is pretty close to the equal volume ratio between O2 and CH4 (2.75). This means the pumps will have nearly identical requirements, and running them off a single spindle should be easy. In addition your turbine pressure drop will be low, so you have a simple 1-stage turbine. Then, your preburner is fuel-rich, running at the sweet spot temp for nickel superalloys (which might as well be brass in this industry), with a “non-coking” fuel. It could be a beautifully simple engine, with excellent sea-level and vacuum characteristics, a very respectable density Isp, and killer T/W.

After deciding on an entirely metholox rocket powered by Staged Combustion-cycle engines I made a few more choices to up reliability.  I wound up targeting my rocket at the large geosynchronous comsat market where it faces competition from the Ariane 5, Proton M, Zenit 3SL & soon from the Falcon Heavy, Long March 5 & Angara rocket families.  A lot of competition means there should also be quite a few payloads and my rocket will be able to prove itself against plenty of competitors. 

Here's what I came up with:

Rocket Name: Neptune V
Length: 60 meters
Diameter: 5.2 meters
Mass: 636 mt (1,400,000 lbs) (Imperial numbers rounded)
Thrust at liftoff: 909 mt (2,000,000 lbf)
Estimated LEO Payload: 19 mt (with margin to spare)
Estimated GTO Payload: 8 mt
SI: Five Triton I engines (400klbf, 2500 Psi, 35 expansion ratio, SC engines) arranged in Saturn V-like S-IC format
Estimated performance: 320 sec SL Isp
SII: Five Triton II engines: (50klbf, 2500 Psi, high expansion ratio, SC engines) arranged in Saturn V-like S-IC format
Estimated performance: 394 sec Vac Isp

The rocket has transportability issues, hence the factory has sea-side access and all launch sites would be sea-accessible.  This also is part of the reason for calling it "Neptune V" (the other being methane).  It's designed with blowout panels and kevlar lining to protect the other engines and propellant tank against bad engine failures.  Unlike current launchers, it would have engine-out capability on both stages at T+.1, giving potentially very good reliability.  Given how many times single-engine stages failed, I made sure this could handle an engine problem or two.  The rocket itself would be aluminum-lithium alloy, with common tanks for CH4 & Lox & also a common bulkhead between them to save weight and potentially expense. 

This launcher would be able to lift the biggest commercial comsats in existence.  It would be initially capable of 5 restarts with its SII engines and then 10 restarts on later versions for direct GEO insertion.  I'd equip it with fairings that would allow multiple missions for maximum flexibility.  It would be man-rated to enable potential future revenue from companies like Bigelow or their customers.  The eventual long-term goal would be reusability (hence the engine layout), and given the size of this thing, it'd be capable of carrying much more useful payloads to orbit than a fully reusable Falcon 9.  Eventually, I'd fly a Neptune V Heavy (3 cores) to compete against the Falcon Heavy straight on.  For anything heavier than that there's the 5-core version, the Neptune V Ultra. 

[neilh]

What's the ultimate commercial aircraft design?

[Rabidpanda]

Estimated performance: 394 sec Vac Isp

That seems way too high for methane.

[Hyperion5]

Estimated performance: 394 sec Vac Isp

That seems way too high for methane.

Well that's at 98% efficiency.  Anything lower and you'll be seeing your engine Isp dropping into the 380s. 

This topic is too broad, there are too many factors. You might want to add the word "current" in there somewhere. Or you're gonna get weird answers:

I'll go with a few examples:

fully reusable SSTO / TSTO.  High flight rate. Lifting body or with wings, aircraft like operations. Think Skylon. Doesn't work at all if you havent got the flight rate, or not enough money to finish design + building.

I've heard it repeated often that SSTOs are less than ideal launchers and really hard to pull off.  What are the odds you'd put on any fully reusable SSTO emerging as a commercial competitor in the launch market? 

Hydrogen gun. Only works on propellant launches. can fire quite a few times per day. Not done before.

You're right, that is a strange possibility.  Not something I'd ordinarily associate with being a possibility for a top commercial launcher. 

Simple RP-1 LOX 2 stage to orbit, common engine design. non-reusable. Basically falcon 9. Works in current environment, if it can be made reliably. RP can be changed to methane.
Perhaps it can be made reusable. Perhaps making it reusable is not economical, or not workable.

If you were designing something with today's tech, would you go this route with your launcher/launch vehicle? 

What's the ultimate commercial aircraft design?

I was busy driving for three hours and didn't get a chance to correct anything till now.  I've taken care of that issue.  It's now up to people to put forward what they think are the excellent designs meant to serve various payload markets (LEO, GTO/GEO, etc). 

[Tcommon]

Fully reusable, fast turnaround, lifting body. TSTO with identical stages - one carries extra tanks, the other carries payload +booster (if necessary). Propellant TBD. Something like this;

[Rabidpanda]

A rocket powered VTOL SSTO RLV fueled by liquid propane or LNG that can put 5-10 tons into LEO.

[Rabidpanda]

Estimated performance: 394 sec Vac Isp

That seems way too high for methane.

Well that's at 98% efficiency.  Anything lower and you'll be seeing your engine Isp dropping into the 380s. 

What's your source for that?  The highest number I've seen people give methane/lox is around 380 seconds.

[Hyperion5]

Estimated performance: 394 sec Vac Isp

That seems way too high for methane.

Well that's at 98% efficiency.  Anything lower and you'll be seeing your engine Isp dropping into the 380s. 

What's your source for that?  The highest number I've seen people give methane/lox is around 380 seconds.

The only reason you haven't seen better than 380 seconds vac Isp is the fact that you've never seen someone try out a metholox engine with 2500 Psi/172.37 Bar chamber pressure before.  380 seconds is on the low end of what staged combustion upper stages engines can do.  All you have to do is up the chamber pressure and have an adequate expansion ratio. 

http://www.astronautix.com/engines/rd160.htm

RD-160

Engine: 129 kg (284 lb). Chamber Pressure: 118.00 bar. Area Ratio: 352. Thrust to Weight Ratio: 15.5. Oxidizer to Fuel Ratio: 3.69.

Status: Developed 1993-.
Unfuelled mass: 129 kg (284 lb).
Height: 1.70 m (5.50 ft).
Diameter: 0.76 m (2.51 ft).
Thrust: 19.60 kN (4,406 lbf).
Specific impulse: 381 s.
Burn time: 900 s.
First Launch: 1993-.

The Russians hit 381 seconds of Vac Isp with this 1711 Psi metholox engine.  The ones I'd be using would have some 46% more chamber pressure than the RD-160.  I did the numbers on the jump in performance between the 2103 Psi NK-33 to the 3746 Psi RD-191, and they come out to a 16.5% chamber pressure increase per 1% jump in Isp.  Mind you, since we're coming up from an even lower pressure, the curve will actually be better than that. 

I figure a conservative estimate of 16% chamber pressure increase yielding a 1% Isp vac increase would see our engines' Isp jump 2.875%.  That yields 391 seconds of Isp, a number that stands right next to my figures.  If you use more realistic ratios of chamber pressure increase:Vac Isp increase, you should have no problems hitting that number.  I had modemeagle run over the numbers with his engine simulator to be sure, and the "Triton IIs" hit these figures with a lower expansion ratio than that featured on the RD-160.  I could have hit 400 seconds Vac Isp had I upped the pressure further. 

[Andrew_W]

If you'd asked me this twenty years ago I'd have shown you a sketch for a parallel burn LH2/LOX launcher, lift-off weight 360 tonnes, boosters and core 5 meters in diameter, the core stage powered by 1 SSME performance with each of 2 boosters powered by a pair of similar engines, I figured about 15-18 tonnes to LEO. The boosters lowered for recovery under paragliders, the core main engine housed in a up-side-down reentry capsule for recovery, the core stage tank going into orbit to be of future use.

Now I'd advocate subsonic air-launch with various orbital upper stages:
 1. A 140 tonne LH2/LOX space-plane with a 5 tonne, 8 person emergency re-enty capsule sitting semi-recessed into the LOX tank as with a fighter plane cockpit, powered by a pair of J2X or similar.
 2. An unmanned version to act as a fuel truck.
 3. An unmanned version with the capsule replaced with a PL fairing.

I see a natural progression to larger faster carrier aircraft, with the system evolving to using an orbital tether to catch the space-plane.

[Hyperion5]

If you'd asked me this twenty years ago I'd have shown you a sketch for a parallel burn LH2/LOX launcher, lift-off weight 360 tonnes, boosters and core 5 meters in diameter, the core stage powered by 1 SSME performance with each of 2 boosters powered by a pair of similar engines, I figured about 15-18 tonnes to LEO. The boosters lowered for recovery under paragliders, the core main engine housed in a up-side-down reentry capsule for recovery, the core stage tank going into orbit to be of future use.

Now I'd advocate subsonic air-launch with various orbital upper stages:
 1. A 140 tonne LH2/LOX space-plane with a 5 tonne, 8 person emergency re-enty capsule sitting semi-recessed into the LOX tank as with a fighter plane cockpit.
 2. An unmanned version to act as a fuel truck.
 3. An unmanned version with the capsule replaced with a PL fairing.

I see a natural progression to larger faster carrier aircraft, with the system evolving to using an orbital tether to catch the space-plane.

Ah, so a bit like the Raptor-powered spaceplane I once proposed but with liquid hydrogen.  This sounds sort of like a cross between the successor to the Lynx and a next-generation Virgin Galactic spaceplane.  XCOR I've heard is looking into a more powerful LH2/Lox engine for a possible follow-up to the Lynx.  Your design certainly would look interesting to the people at XCOR & Virgin Galactic. 

-----

I know my launcher looks rather conventional against everything else proposed so far, but it'd also be an unconventional LV.  No one, to my knowledge, has ever built an entirely metholox carrier rocket of truly commercial scale.  Also to my knowledge, no one's copied the engine number and layout of a 2-stage Saturn V since the original, nor had engine-out capability on all stages since then. 

Basically the Neptune V family would be like a cross between the Angara family, a 2-stage Saturn V, and the mini-Saturn V that results would burn methane. The Angara series inspired the overall family:

Neptune V
LEO: 19 mt (est.)
GTO: 8 mt (est.)

Neptune V Heavy (3 core)
LEO: 64.6 mt (est.)
GTO: 20 mt (est.)

Neptune V Super Heavy (4 core)
LEO: 84 mt (est.)
GTO: 28 mt (est.)

Neptune V Ultra (5 core)
LEO: 100 mt (est.)
GTO: 35 mt (est.)

Bear in mind my GTO numbers are very conservative. 

The family could compete with just about every major launcher bigger than a Vega.  The Neptune V would have multi-payload capability to take on the Soyuz and Falcon 9, while it could also compete with the Zenit 3SL, Proton M, the Angara A3, several Long March 5 variants, and the Ariane 5 for big geosynchronous satellites.  To compete with the Angara A7V & Falcon Heavy, the Neptune V Heavy would be more than adequate.  It should be able to put a Bigelow BA 330 into geosynchronous orbit, enabling the first GEO space station.  By the time you get to the 25-engine Neptune V Ultra, you could enable missions to the moon.  That's basically one launcher family capable of competing for payloads ranging from 8 mt to 100 mt.  Even the Angara family won't be that wide-ranging. 

[Robotbeat]

Reusable and cheap enough to fly every day. It'd become ultra reliable and cheap.

[sdsds]

I second Robotbeat's suggestion regarding the flight rate. At a minimum, it needs to be a question of "how many flights per month" rather than "how many months between flights."

I think that requires highly automated inspection between flights; perhaps running a "cold flow" diagnostics check and maybe taking a boroscopic peek at likely trouble spots such as engine throats. Reflight without disassembly should be the goal.

[strangequark]

Reusable and cheap enough to fly every day. It'd become ultra reliable and cheap.

Indeed, though I'd add a change to partially reusable. Give me a few billion, and I think I would pursue a TSTO with a reusable methane first stage that does as much of the delta V as is practical, and then a disposable, mass-produced pressure fed second stage.

[guckyfan]

Reusable and cheap enough to fly every day. It'd become ultra reliable and cheap.

Indeed, though I'd add a change to partially reusable. Give me a few billion, and I think I would pursue a TSTO with a reusable methane first stage that does as much of the delta V as is practical, and then a disposable, mass-produced pressure fed second stage.

I like that approach, as it seems certainly achieavable and can reduce cost a lot. But as higher ISP is very efficient on an upper stage, a turbo pump may be worth the extra cost and give less $/kg.

[beb]

I'm not a rocket scientist so my thoughts will have to remain vague.

The "ultimate commercial" rocket design would be one that gets you into space the cheapest so I think what you're seeing coming from SpaceX is about as close to the Ultimate Commercial rocket design as one can get. Still there is roo0m for some thought.

1.    I'd call for a single engine that can be used across a wide spectrum of applications. By that I mean one engine, kerolox, of, say, a half-million pounds thrust. A single engine would give you Delta II performance, two engines would equal EELV performance and four engines would get you into EELV-Heavy performance. Then forming a heavy version of this four engine rocket would get you a 12-engine, 6 million pound HLV launcher.  And I'd go with a gas generator engine sacrificing some ISP for a simpler, cheaper design.

2. I'd call for a moduler first stage tank design. I liked the ACES concept of adding babrrel sections to the tanks so that one line can produce small, medium or large stages. I'm not sure whether a common stage for 1 and 2 engine vehicles makes more sense or a common stage for 2 and 4 engine rockets. Maybe it's possible to remove enough  barrel sections to size the stage for 1, 2 and 4 engines. That would make the single engine version very stubby but I've often wondered how stubby a rocket could be before it becomes impractical to launch.

3. The upper stage would be an ACES hydrolox unit. As again it would use one engine in different numbers for the different mission needs and the same tankage, in different length.

4.    Standardized attachment points so that one could use the single engine version as a booster to the 2 or 4 engine launch vehicles to more closely match launch needs with launch capacities.

Most of this is just Atlas V Phase II. It always struck me as a very sound idea. The chief difference is replacing the Russian made engine with a domestic variant

[Jim]

What's the ultimate commercial aircraft design?

bingo

[simonbp]

What's the ultimate commercial aircraft design?

bingo

Long cylindrical fuselage, swept wings with complex control surfaces and winglets, high-bypass turbofan engines in nacelles either on the wing or tail, dense seating in the cabin, all facing forward, APU in the tail to provide ground power. Next time you are at the airport, I dare you to find a commercial passenger aircraft that doesn't follow this description.

So, the point is not "ultimate" as in final forever, but rather the style of design that many companies will converge on after many years of operation.

[Silmfeanor]

So, the point is not "ultimate" as in final forever, but rather the style of design that many companies will converge on after many years of operation.

I think that's the point to be made in that discussion. Rocketry is nowehere near this state.

Also, how about a F-22 raptor? An UAV? Weather/spying high altitude balloons? VTOLS? B-2?