What are pros and cons of the...

[hachiman]

Space Shuttle.

Saturn V.

Soyuz.

Shenzhou.

The N1.

If you want to talk about your opinions on other rockets that I've not mentioned, do so.

[icefire]

Space Shuttle:

Pros: It's manned and reusable

Cons: Everything else

Saturn V:

Pros: Payload capacity

Cons: Price

Soyuz:

Pros: Its dependable

Cons: It's not dependable anymore lolol

Shenzhou:

Pros: It's a Soyuz ripoff

Cons: It's a Soyuz ripoff

N1:

Pros: It's big

Cons: It has a 100% failure rate.

[Johno]

I'll do one of these at a time. That way I'll be able to give each a more thorough analysis.

Space Shuttle:

Pros:

Reusability. This allowed for a larger and more capable spacecraft, since it was not going to be thrown away at the end of each mission. The shuttle system was a far more versatile spacecraft than anything before or since, and the only systems which could have matched it for versatility were those which were pretty much direct copies of the concept (for example the Russian Buran).

Capacity. The Shuttle's payload bay was truly prodigious in size, and whilst the shuttle was operational, the USA had an enviable heavy-lift ability (and note that whilst other systems could lift heavy loads, only the Shuttle could actually bring crews to actually install and activate payloads such as the Space Station or the Hubble Telescope).

Crew size. A command crew of two with a mission crew of up to five meant that the Shuttle could operate impressively as a space work platform - the ISS assembly missions definitely proved the worth of the concept there. In a sense, the early missions where it was used to launch satellites and probes were a waste of the capability of the spacecraft.

Cons:

Complexity. In one sense, the Shuttle's weaknesses all stem from this. The system was probably the most complex vehicle ever devised by humankind. Whilst this complexity resulted in the versatile and capable system that it was, it ALSO massively increased cost, decreased safety and resulted in long delays in launching.

Safety. The Shuttle stands as the most dangerous man-rated spacecraft in history, with two catastrophic failures leading to fourteen deaths. Now there are plenty of mitigating factors to this - it is possible to argue that ultimately both failures would never have occurred without reckless management of the program as a whole - but in any case, neither failure would have occurred if a simpler design philosophy had been followed (in that both failures involved the parallel staging architecture in some way). Also, in retrospect, having a spacecraft with no safe abort modes during certain phases of the flight has to be seen as insanity.

Cost. Ironically, given that the Shuttle was designed to lower costs by being reusable, the cost of the system ended up being immense. Mainly this was because the turnaround cycle turned out to be much more complicated than envisaged (for example, the three engines of each orbiter needed to be basically rebuilt between flights, eliminating most of the advantage of keeping them).

[Johno]

Saturn V

Pros

Capacity. Good grief, and how. The Saturn V was certainly a muscular rocket. Lifting 119 tonnes to LEO is an impressive achievement in anyone's language.

TLI. The Saturn V was designed specifically to inject massive payloads into Lunar orbit, which it did handsomely. The Apollo spacecraft was overpowered and oversized (owing to its direct ascent roots), and yet it was injected into a Free-Return trajectory with plenty of propellant for any amount of orbital maneuvering that would be necessary.

Safety. No serious failures were suffered during the 11 launches of this rocket. The five-engine architecture made it comparatively simple for it to survive engine shutdowns without significant changes to mission parameters, which happened a few times.

Cons

Cost. When inflation is taken into account, a single launch of the system works out to about 4.2 BILLION dollars. It's hard to know if the system would have been more cost-effective had more units been constructed, but however you slice it, those are nasty numbers.

Inflexibility. The rocket was designed to fly people to the moon; it really wasn't well suited for any other role, simply because there were very few payloads that could take full advantage of such a lifting capacity to LEO (with the obvious exception of a FULLY EQUIPPED LARGE SINGLE MODULE SPACE STATION! ).

Unwieldiness. A staggering amount of infrastructure had to be built to enable this massive lump of metal to be stacked and launched. A Vehicle Assembly Building so large that it contains its own weather system had to be built. The largest crawler-transporter in history had to be constructed to inch its prodigious bulk to the launch complex, compared to the comparatively straightforward process of moving a Soyuz to the pad by train (lying down). Talking of the Crawler-transporters, there needed to be a road that could carry them.

Ultimately all this proved beneficial, since the infrastructure has been used by subsequent programs (and will presumably be used by the new SLS as well); but it was still difficult and expensive to create.

[rdfox]

As a side note, according to Wikipedia, the incremental cost (i.e., the price to build one unit, NOT including all R&D and infrastructure costs, just the cost to build and launch a single flight) for the Saturn V, adjusted for inflation, was about $1.1 billion, which is pretty comparable to the Space Shuttle's per-flight incremental cost (~$600 million), and is about $10,000 per kilogram to LEO. That's on the high side of the range for expendables, but it's still in the ballpark of the heavy-lift Titans, for example.

Development plans *were* in place to try and reduce its cost, too; most notable were the various studies towards recovering and at least partially reusing the first stage.

And yes, it is confirmed that SLS is to use LC-39, too.

[DoctorEvo]

PROS

Shuttle: Semi-reusable, fast-turnaround, EXTREMELY large crew capacity, heavy-lift capability, potential to be very cost-effective for frequent launches. Gentle reentry with wide crossrange capability.

Saturn V: Super-heavy lift capacity, solid safety record. Minimal primary development costs.

Soyuz: Proven R-7 rocket, simple and cheap horizontal assembly, well-evolved spacecraft with extremely low-weight construction, very low per-launch costs.

Shenzou: Similar to Soyuz spacecraft in many respects. Low cost.

N1: Heavy-lift capability. Horizontal assembly.

CONS

Shuttle: High initial development and production costs. Lack of comprehensive launch-abort modes; labor-intensive post-Challenger safety measures crippled the program in nearly every respect. Requires considerable (but mostly pre-existing from Apollo) infrastructure to launch. Difficult to fill its payload capacity given its restricted launch inclinations.

Saturn V: Very high production costs for an expendable vehicle. Difficult vertical assembly required. Considerable new infrastructure (VAB, cryogenic fuel production) required. Difficult to make use of its superheavy payload capacity.

Soyuz: Fairly low lift capacity. (Can be seen as a good thing in some ways, given the extremely-low per-launch costs).

Shenzou: Long March rocket uses slow vertical-assembly and has a questionable safety record. Low payload.

N1: Abysmal launch record. Complex design.

Is this for manned rockets only?

[icefire]

I would love to see you list out some pros and cons (perhaps comparatively) of rockets like the Proton, Atlas, or Titan rockets.

[sneakeypete]

How long was the turn around times on the shuttle pre accident era?

[DoctorEvo]

How long was the turn around times on the shuttle pre accident era?

DoD specified two weeks. The fastest they actually performed was eight weeks. The fastest achieved post-Challenger was thirteen weeks, and the idea of deferring any inspections for one turnaround was considered unacceptable - they just flipped and decided that all the sudden they had to check absolutely everything, absolutely every time.

Note that turnaround time is not a sustained launch rate (well, at least not in the initial pre-Challenger case). The sustained launch rate was somewhat slower, initially limited by external tank production to 24 per year for the entire fleet. Of course, even with a four-orbiter fleet, the slow turnaround rate caused by the expanded post-Challenger safety measures easily drowned this limitation. IF they somehow sustained that thirteen-week turnaround for the entire four-orbiter fleet (not possible given that the Orbiter Processing Facility isn't capable of handling four orbiters at once), they'd still only manage 16 launches per year.

[rdfox]

In NASA's defense, they *did* discover that parts that should have been replaced and/or refurbished were flying again after falling outside the specified tolerance bands, and that would be in violation of all practices in the aviation industry. Frankly, the shuttle was *far* too complex a vehicle to acheive a sustainable turnaround rate of less than roughly 20 weeks, I expect.

Really, the only way you're going to make a sustainable turnaround rate for a reusable spacecraft that's less than about 16 weeks would be if you made most of the systems be sealed 'black boxes' that, after each flight, you just pulled out of the spacecraft for inspection and refurb, then installed new/refurbished ones off the shelf for the next flight. If you can do sealed-box system unit swapouts with some sort of simple, standard connection--which military aircraft have been doing since about 1980--you *might* be able to actually meet DoD's spec for Shuttle turnaround, if you have a huge amount of manpower to do it. But those sorts of modular systems are heavier than ones directly integrated into the vehicle, and since dead weight is a killer for any spacecraft...

[DoctorEvo]

In NASA's defense, they *did* discover that parts that should have been replaced and/or refurbished were flying again after falling outside the specified tolerance bands, and that would be in violation of all practices in the aviation industry. Frankly, the shuttle was *far* too complex a vehicle to acheive a sustainable turnaround rate of less than roughly 20 weeks, I expect.

Yes, but I'm not talking about 'sustained turnaround rates.' I'm talking about maybe checking some of the more reliable or less-critical parts maybe, every third or fifth launch. Of course, certain parts will need to be swapped or inspected every flight, but many components can be trusted to survive multiple launches, especially if they aren't critical. And if you DO find parts that are wearing well past tolerance during the inspection intervals, you can shorten those respective inspection intervals, and lengthen intervals for components which are not wearing as fast as expected.

If you stay rational about such issues instead of completely flipping out when something goes wrong (or, on the other hand, being complacent and ignoring problems outright), you can actually maintain a healthy balance between safety and utility.

Really, the only way you're going to make a sustainable turnaround rate for a reusable spacecraft that's less than about 16 weeks would be if you made most of the systems be sealed 'black boxes' that, after each flight, you just pulled out of the spacecraft for inspection and refurb, then installed new/refurbished ones off the shelf for the next flight.

Why every flight? You don't trust an APU or a hydraulic pump to work for more than a single flight in a row? If you distrust your hardware THAT much, then you have no place in such a high-stakes endeavor in the first place.

It's worth noting that many catastrophic mechanical failures in the aerospace industry are human error, caused by careless or hurried maintenance. Sometimes there are actual SAFETY-ORIENTED reasons for choosing the less-frequent, more-deliberate inspection and maintenance schedules, lest someone slip up and leave a rag in your turbopump after their hundredth time disassembling and inspecting it.

If you can do sealed-box system unit swapouts with some sort of simple, standard connection--which military aircraft have been doing since about 1980--you *might* be able to actually meet DoD's spec for Shuttle turnaround, if you have a huge amount of manpower to do it. But those sorts of modular systems are heavier than ones directly integrated into the vehicle, and since dead weight is a killer for any spacecraft...

I don't think so. Replacing stuff takes time. I'm pretty sure the 2-week turnaround consisted of just replacing the components that were actually broken, assembling the stack, rolling it out, and launching. Like I said, there was no illusion of being able to sustain such ludicrous launch rates. Extensive inspections WOULD be required at some point, resulting in a sustained launch rate MUCH lower than this shortest-possible turnaround time.

[rdfox]

OK, I think we were talking at cross purposes there. I thought that the DoD spec was a requirement that they be able to maintain a turnaround time of two weeks per orbiter indefinitely, not that they just be able to give it a quick 'pit stop'-style servicing and launch again for one or two flights.

Given that situation, where you're just doing a quickie turnaround for a small number of flights before a more detailed turnaround, *that* I could see being feasible, the same way that it is for airliners and military airplanes, particularly if you work out a reliable MTBF figure for all the quick-change sealed-black-box systems and use that minus one mission to schedule their being swapped out with a new/refurb unit. (For example, 'OK, the APUs have an MTBF of about 20 hours. They're usually on for four hours per flight, so just to be safe, we'll swap them out every fourth flight even if there haven't been any problems.')

Still, I think the big problem is that really, there's only been one manned spacecraft that's ever been flown enough times that the aviation industry would classify it as an 'operational' vehicle, instead of an experimental one, and that's Soyuz. Shuttle *might* have qualified, too, after about STS-100, but by then, the rapid-turnaround goal had been pretty much dropped. Declaring any vehicle 'operational' after only four tests is ludicrous, and experimental aircraft (by which I mean prototypes and true experiments, not homebuilts) tend to be hangar queens *because* they need to be inspected in detail after every flight, since nobody yet knows just how good their reliability is...

[Johno]

rdfox: Shuttle was in an awkward half-way house between experimental and operational. It was what it was. Without it, we lose a capability that I fear will not return during my lifetime; but that said, it was a capability which perhaps over-reached what the American space program was equipped to support, which is why for all its sophistication Shuttle remained hard to maintain and, yes, dangerous.

Soyuz

Pros

Cost. Over a thousand of the R-7 series of rockets have been flown, and the corresponding economies of scale have made the Soyuz very cheap as space vehicles go. Throughout its long life[1], Soyuz has been the most cost-effective way of getting people into and out of space.

Reliability. Despite a few catastrophic failures early in the program (largely due to political interference rather than any genuine fault with the spacecraft - the earliest spacecraft were flown before their creators believed them to be ready!), the Soyuz has gone on to be the poster child for rugged and reliable spacecraft.

Specialization. Soyuz is an excellent space taxi, since that is exactly what it is - no more, no less. But see below.

Cons

Specialization. Because the Soyuz is so specialized, it can't really do much more than act as a ferry for crews to and from the Space Station (even though Soyuz was designed with a lunar mission in mind, it would have taken a specially redesigned version of the craft to do it). It is not able to launch anything other than cosmonauts and [a very small amount of] personal gear, and it can't act as a work platform.

Mediocrity. Don't let its good points fool you - though it's cheap and reliable, the Soyuz hardly represents the best of spacecraft. It's a good working concept, but let's be blunt- the Russians could do a lot better than Soyuz (and they're trying to; but lack of cash for the program remains a problem).

Antiquated technology. Part of the abovementioned mediocrity comes from the fact that, despite incremental improvements to Soyuz capsules over the years (see footnote below), the Soyuz is no longer representative of state-of-the-art. The basic design of the spacecraft comes from an earlier era, one in which we knew much less about how to make a spacecraft than we do today.

[1] It has to be pointed out, in fairness, that Soyuz has seen much development over the years, and it is probably a fairly good analogy to compare the difference between current model Soyuz spacecraft and the initial models as being similar to the differences between, say, a 1970 Holden Kingswood and the latest model Holden Commodore - the two are similar vehicles, of a broadly similar configuration, and the later model is clearly developed from the earlier; but the technology used to build the later is greatly advanced on the earlier models.

[DoctorEvo]

Given that situation, where you're just doing a quickie turnaround for a small number of flights before a more detailed turnaround, *that* I could see being feasible, the same way that it is for airliners and military airplanes, particularly if you work out a reliable MTBF figure for all the quick-change sealed-black-box systems and use that minus one mission to schedule their being swapped out with a new/refurb unit. (For example, 'OK, the APUs have an MTBF of about 20 hours. They're usually on for four hours per flight, so just to be safe, we'll swap them out every fourth flight even if there haven't been any problems.')

Yes, that was pretty much the idea. However, MTBF is usually not used to define replacement intervals, but rather inspection intervals, with parts being replaced as needed - that is, whenever they fail, or whenever they pass certain margins, depending on how critical they are. After Challenger, though, they refused to take ANY chances - even though the vast majority of their measures were completely unrelated to the cause of the disaster.

[AstroAndrew]

This rocket wasn't mentioned but I'm curious what the pros/cons of the early ATLAS series, since my grandfather on dad's side of the family made the rocketnozzles for it after getting out from the Marines post-WW2. Dad remembered watching him machining the nozzles on a freakin' shop 'lathe' in a shed out back middle of nowhere Missouri, guess subcontracting is nothing new LOL.

[DoctorEvo]

Atlas is very comparable to R-7 (the rocket that Soyuz is launched by) in many ways. The Mercury spacecraft was obviously quite a bit smaller and more primitive than Soyuz, but the rockets are similar in terms of performance, cost, growth, etc.

Cons

Specialization. Because the Soyuz is so specialized, it can't really do much more than act as a ferry for crews to and from the Space Station (even though Soyuz was designed with a lunar mission in mind, it would have taken a specially redesigned version of the craft to do it). It is not able to launch anything other than cosmonauts and [a very small amount of] personal gear, and it can't act as a work platform.

Dude, have you NEVER heard of Progress or Fregat?

[icefire]

I think he was speaking with a crewed launch in mind...

[rdfox]

Yes, that was pretty much the idea. However, MTBF is usually not used to define replacement intervals, but rather inspection intervals, with parts being replaced as needed - that is, whenever they fail, or whenever they pass certain margins, depending on how critical they are. After Challenger, though, they refused to take ANY chances - even though the vast majority of their measures were completely unrelated to the cause of the disaster.

Well, yes, but I was also assuming the use of 'sealed-box' components that are designed to just be swapped out with a new one and sent to the appropriate shop for inspection and servicing. Allows for much faster line maintenance ('It's still working and it hasn't come up on the swap schedule yet, so I can ignore it; this one's due for a swapout, so I'll just pull it and send it to the avionics shop.') at the cost of... well, higher cost (from having to maintain a larger stockpile of spares to swap instead of inspecting in place), and slightly higher weight (from it being a modular 'sealed box' component instead of something integrated into the vehicle).

Basically, it's similar to the old 'QEC' Quick Engine Change units developed for piston-engine military aircraft and airliners by the late 30s, where you'd have a complete engine, propeller, and all ancillaries and accessories completely assembled and on a wheeled engine stand, so that if an engine had a problem or reached TBO, you'd just pull the old one off as a complete unit, mount the new one, and the plane could be flying again in a few hours instead of being grounded for days or weeks.

This rocket wasn't mentioned but I'm curious what the pros/cons of the early ATLAS series, since my grandfather on dad's side of the family made the rocketnozzles for it after getting out from the Marines post-WW2. Dad remembered watching him machining the nozzles on a freakin' shop 'lathe' in a shed out back middle of nowhere Missouri, guess subcontracting is nothing new LOL.

Major pros:

Quickness -- Atlas's simple staging design (see below) made it so that it could be ready for service much sooner than its competition, the Titan series. Due to the fears of a 'missile gap' after Sputnik, this was a HUGE issue for the US military, and that alone guaranteed that Atlas would be built and enter service.

Simplicity -- While it was still a massively complex booster, the Atlas had one major advantage over other ICBM designs of the era: All its engines were fired while still safely on the ground, where you had ample ground power to start them, and holddown clamps just in case one engine failed to light. This was possible thanks to the stage-and-a-half design and the use of balloon tanks, which allowed a high specific impulse after the early stages of flight, and reduced the vehicle's deadweight considerably, respectively. All other designs required multiple stages, and at the time, reliability in rockets was low enough that the airstart was considered dicey at best.

Cons:

Difficulty of handling -- The very balloon tanks that allowed the Atlas to complete its mission made it extremely difficult to work with, because if it was vertical and the tanks were not pressurized, the whole booster would crumple over like it was made out of tinfoil. (I can't find it right now, but I've seen video of just that happening to one that was being prepped for a test launch from Vandenberg in the 60s.) Most variants escaped that by being based in 'coffin' shelters, where they were stored horizontally before being erected for launch, but that just exacerbated the next issue.

Slow response time -- This was probably the single biggest flaw of the Atlas as an ICBM. Even the final versions that were intended to be stored vertically in silos could not be launched rapidly; they had to be winched up out of the silo(!) to the surface, then they had to be fueled before they could launch. The entire procedure took about five hours, one hour to raise the missile and then four to fuel it. Unlike Titan, with its 'storable' hypergolic propellants, the Atlas could not be stored ready-to-fire; the kerosene fuel could be left onboard, but the liquid oxygen oxidizer had to be stored elsewhere so that it wouldn't boil off. At best, an Atlas could be kept on 'hair-trigger' alert, fully fueled and ready to go, for about 24 hours before the LOX boiled off to the point of needing replenishment. (Ironically, this same flaw as a weapon made it excellently suited for a space launch vehicle, since the semi-cryogenic propellant mix had a better specific impulse than either the Titan-style hypergols, or the Minuteman-style solid fuels.)

Poor mass fraction -- Despite the use of jettisonable 'half-stage' boosters to provide most of the thrust at launch, and the use of balloon tankage to reduce structural weight, the fundamental reason that the Atlas ended up being eventually supplanted by Titan in both missile and space launch roles (Atlas I, that is--Atlas II was a major redesign, and Atlas IV and V are completely different vehicles) was that the lack of true staging meant that the booster had to lug a lot of extra weight all the way to the end of the flight. Once Titan had demonstrated that staging and airstart of liquid-fuel engines was feasible, that allowed a much better percentage of fuel versus total weight compared to the stage-and-a-half design, resulting in better payload from a given engine.

[DoctorEvo]

Major pros:

Quickness -- Atlas's simple staging design (see below) made it so that it could be ready for service much sooner than its competition, the Titan series. Due to the fears of a 'missile gap' after Sputnik, this was a HUGE issue for the US military, and that alone guaranteed that Atlas would be built and enter service.

That, and Convair was much better-versed with rocketry than their competitors were, having designed a true ICBM as early as 1946, but not having built it since warheads were not yet small enough to be launched by one.

Difficulty of handling -- The very balloon tanks that allowed the Atlas to complete its mission made it extremely difficult to work with, because if it was vertical and the tanks were not pressurized, the whole booster would crumple over like it was made out of tinfoil. (I can't find it right now, but I've seen video of just that happening to one that was being prepped for a test launch from Vandenberg in the 60s.) Most variants escaped that by being based in 'coffin' shelters, where they were stored horizontally before being erected for launch, but that just exacerbated the next issue.

It's still immensely easier to handle than something that needs to be assembled and transported vertically.

Slow response time -- This was probably the single biggest flaw of the Atlas as an ICBM. Even the final versions that were intended to be stored vertically in silos could not be launched rapidly; they had to be winched up out of the silo(!) to the surface, then they had to be fueled before they could launch.

The same was true of Titan I. Atlas F was, for all intents and purposes, equivalent to Titan I in terms of response and survivability. Earlier, horizontally-stored Atlases were only marginally slower, but their coffins had lower survivability and fuelling had to be done outside of the coffin with no protection whatsoever.

The entire procedure took about five hours, one hour to raise the missile and then four to fuel it. Unlike Titan, with its 'storable' hypergolic propellants, the Atlas could not be stored ready-to-fire; the kerosene fuel could be left onboard, but the liquid oxygen oxidizer had to be stored elsewhere so that it wouldn't boil off. At best, an Atlas could be kept on 'hair-trigger' alert, fully fueled and ready to go, for about 24 hours before the LOX boiled off to the point of needing replenishment. (Ironically, this same flaw as a weapon made it excellently suited for a space launch vehicle, since the semi-cryogenic propellant mix had a better specific impulse than either the Titan-style hypergols, or the Minuteman-style solid fuels.)

Atlas F could be kept on alert in-silo for prolonged periods with the kerosene tank full. From this point, it could be fuelled with LOX (in-silo to enhance survivability), elevated out and fired in the span of ten minutes. That's every bit as good as Titan I.

Poor mass fraction -- Despite the use of jettisonable 'half-stage' boosters to provide most of the thrust at launch, and the use of balloon tankage to reduce structural weight, the fundamental reason that the Atlas ended up being eventually supplanted by Titan in both missile and space launch roles (Atlas I, that is--Atlas II was a major redesign, and Atlas IV and V are completely different vehicles) was that the lack of true staging meant that the booster had to lug a lot of extra weight all the way to the end of the flight. Once Titan had demonstrated that staging and airstart of liquid-fuel engines was feasible, that allowed a much better percentage of fuel versus total weight compared to the stage-and-a-half design, resulting in better payload from a given engine.

Oddly enough, they concluded that attempting to divide Atlas, with its lightweight balloon tanks, into two separate stages without stretching would actually negatively effect performance due to the added dead weight - it was actually better to carry all that tankage with you than to bother figuring out how to leave some of it behind. In fact, they later went EVEN FURTHER with the stretched Atlas H. You gotta admit, those balloon tanks were LIGHT.

When it comes down to it, the Titan's biggest advantage over Atlas was raw muscle - bigger, taller, heavier... Atlas really never stood a chance.

[Johno]

Dude, have you NEVER heard of Progress or Fregat?

I actually debated whether or not to mention Progress (I wasn't aware of Fregat, but I am now! ) in my comment. In the end, I decided that the brief was to discuss the pros and cons of the Soyuz itself, so I stuck with that. However, the comment I was going to make was that one way to get around a specialization problem is to create different versions for different specializations - this is what they have done in creating the dedicated Progress cargo ship. This is actually in some ways a more cost-effective technique than making the one multi-purpose craft (although such an approach does bring its own set of problems).

In a similar vein, when SAAB were given the task of designing the generation of fighter aircraft before the current Gripen, they created one aircraft (the Viggen) and built it in five different versions for the five different missions it would face. It allowed them to build an aircraft that was excellent for every role - but it also meant that squadrons would not be able to be reconfigured for different missions. I think this illustrates the basic drawback well. If you build two variants, one each for crew and cargo, you necessarily will have more challenges meeting unpredictable mission requirements.

[rdfox]

That, and Convair was much better-versed with rocketry than their competitors were, having designed a true ICBM as early as 1946, but not having built it since warheads were not yet small enough to be launched by one.

Fair point, though I expect that Convair would have had serious trouble with the guidance system before at least '53 or so, and the B-36's rather horrific engineering demands probably would have made it very hard for them to take that design study to a fully realized, buildable design before then, too, even if lightweight warheads were available.

It's still immensely easier to handle than something that needs to be assembled and transported vertically.

I'll grant you that. I just meant that, at least as a *missile*, the balloon tanks got to be somewhat awkward; I wish I could find the YouTube video of one that was undergoing pre-fueling checks on the pad at Vandenberg, when one of the tanks sprung a leak and, in about 15 seconds, the whole thing had just sort of flopped over with the thrust structure still rigid on the pad, but the rest of the fuselage having banana'd. Very interesting footage, actually, and since they hadn't fueled it yet, there was no fire or explosion, just a crumpled and ruined booster.

The same was true of Titan I. Atlas F was, for all intents and purposes, equivalent to Titan I in terms of response and survivability. Earlier, horizontally-stored Atlases were only marginally slower, but their coffins had lower survivability and fuelling had to be done outside of the coffin with no protection whatsoever.

Wasn't Titan I all-hypergolic like Titan II? If so, that'd reduce the response time once a missile was put on alert.

Atlas F could be kept on alert in-silo for prolonged periods with the kerosene tank full. From this point, it could be fuelled with LOX (in-silo to enhance survivability), elevated out and fired in the span of ten minutes. That's every bit as good as Titan I.

Huh, for some reason, I had always heard it took about four hours to prep an Atlas for launch. Must have been Atlas D and Atlas E, not Atlas F. (Of course, ten minutes just isn't fast enough--given the flight time of ICBMs, the amount of time it takes to detect and confirm their launch, the amount of time it takes to inform the President, the amount of time it takes him to make a decision to launch on warning, and the amount of time it takes to send the orders down the chain, I believe the Air Force worked out that they would have about seven minutes from the time the launch order was received until incoming warheads arrived, so they felt they needed the missiles in the air within five to six minutes of the order being received. But that remained a problem until Minuteman arrived, really...)

Oddly enough, they concluded that attempting to divide Atlas, with its lightweight balloon tanks, into two separate stages without stretching would actually negatively effect performance due to the added dead weight - it was actually better to carry all that tankage with you than to bother figuring out how to leave some of it behind. In fact, they later went EVEN FURTHER with the stretched Atlas H. You gotta admit, those balloon tanks were LIGHT.

Wow, never knew that. VERY light; I'd always thought that one of Titan's big advantages was the use of staging to let you drop the now-superfluous launch tankage. Still, stage-and-a-half is a concept that basically exists as an option when you're not sure you can build engines that can be airstarted reliably (the big reason that the 'Saturn-Shuttle' concept of using the S-IC to loft the Space Shuttle out of the lower atmosphere and avoid the SRBs entirely was nixed--we weren't confident enough in the SSME design's reliability at startup to commit to a mode requiring it to airstart), and thus need to have them all firing before you let it go. (Or where you want to try and recover engines for reuse, but that's another story...)

When it comes down to it, the Titan's biggest advantage over Atlas was raw muscle - bigger, taller, heavier... Atlas really never stood a chance.

True. Atlas was, I think, always seen as an interim vehicle until they could get Titan working reliably, and a 'safe' fallback option should Titan's technical problems have been unsolvable. A surprisingly good and capable interim vehicle that ended up being excellently suited as a satellite/space probe launcher, but still an interim solution.

[DoctorEvo]

Fair point, though I expect that Convair would have had serious trouble with the guidance system before at least '53 or so, and the B-36's rather horrific engineering demands probably would have made it very hard for them to take that design study to a fully realized, buildable design before then, too, even if lightweight warheads were available.

It depends on your standards. A continent is a pretty big target. Obviously, V-2-level inertial guidance was available. With the thermonuclear warheads that WERE eventually developed, they could've caused plenty of devastation even with a poorly-guided missile.

I'll grant you that. I just meant that, at least as a *missile*, the balloon tanks got to be somewhat awkward; I wish I could find the YouTube video of one that was undergoing pre-fueling checks on the pad at Vandenberg, when one of the tanks sprung a leak and, in about 15 seconds, the whole thing had just sort of flopped over with the thrust structure still rigid on the pad, but the rest of the fuselage having banana'd. Very interesting footage, actually, and since they hadn't fueled it yet, there was no fire or explosion, just a crumpled and ruined booster.

I know the incident you're talking about. And I don't believe there is any motion footage of it, but the photo sequences I've seen do the job just fine. They were defuelling, and someone forgot to open a pressure valve. There was no leak. The balloon tanks were actually incredibly durable when pressurized - Bossart invited ABMA (including the very-skeptical Von Braun, who was known to had said of Mercury-Atlas astronauts that they deserve a medal just for having the bravery to SIT on top of one of Bossart's 'flimsy' rockets) to come and hit one of his fuel tanks with a sledgehammer. ABMA obliged, and the sledgehammer simply bounced back with such violence that it nearly maimed the technician who had taken the swing. The tank was completely unharmed.

Wasn't Titan I all-hypergolic like Titan II? If so, that'd reduce the response time once a missile was put on alert.

Ahahah. No. Titan I was semi-cryogenic. In fact, the LR-87 developed for the Titan is one of the few engines capable of burning RP-1, hypergolic, or liquid hydrogen propellants interchangeably with just a few modifications.

Huh, for some reason, I had always heard it took about four hours to prep an Atlas for launch. Must have been Atlas D and Atlas E, not Atlas F.

Atlas D and E both only took about fifteen minutes to elevate, fuel and fire from an alert state. Four hours may be the response time when not on-alert, though I have no idea what would take four hours to do. Then again, they say that the R-7 could take as much as twenty hours to prepare to launch...

Wow, never knew that. VERY light; I'd always thought that one of Titan's big advantages was the use of staging to let you drop the now-superfluous launch tankage.

Yeah. I never understood why they gave up on it with Atlas III - the performance is simply astounding. The original Atlas was in fact capable of performing true SSTO with a reduced payload. SpaceX seems to think it's a good idea, as the Falcon I uses a partially pressure-supported structure. And of course, Centaur sees continued usage as one of the best high-energy upper stages out there, and ACES will carry on the balloon-tank structure into the next generation of high-energy transfer stages.

[rdfox]

It depends on your standards. A continent is a pretty big target. Obviously, V-2-level inertial guidance was available. With the thermonuclear warheads that WERE eventually developed, they could've caused plenty of devastation even with a poorly-guided missile.

Granted, but V-2 guidance wouldn't have let you hit a specific city at that range. Be pretty embarassing if Ike had decided to order a massive attack, only to have all the weapons land out in farmland or uninhabited mountains or something, y'know?

I know the incident you're talking about. And I don't believe there is any motion footage of it, but the photo sequences I've seen do the job just fine. They were defuelling, and someone forgot to open a pressure valve. There was no leak.

No, I've seen actual motion picture footage of this one. It might be the same incident, though. I *will* say that the final result looked very similar to when the Air Force Museum's original Atlas sprang a leak and crumpled back in the 80s. (The one they have now is apparently modified for display with, essentially, a steel telephone pole up the middle to support it, so that it won't collapse no matter what.)

The balloon tanks were actually incredibly durable when pressurized - Bossart invited ABMA (including the very-skeptical Von Braun, who was known to had said of Mercury-Atlas astronauts that they deserve a medal just for having the bravery to SIT on top of one of Bossart's 'flimsy' rockets) to come and hit one of his fuel tanks with a sledgehammer. ABMA obliged, and the sledgehammer simply bounced back with such violence that it nearly maimed the technician who had taken the swing. The tank was completely unharmed.

THIS, I hadn't heard. It doesn't surprise me--I know how much force pressurization can exert--but that's one tale I hadn't heard. (At the same time, I can understand von Braun's skepticism--it was, at the time, a *very* radical concept, after all, and von Braun had an engineer's conservatism, taken to a bit of an extreme. as seen with his attitude towards LH2 as fuel...)

Ahahah. No. Titan I was semi-cryogenic. In fact, the LR-87 developed for the Titan is one of the few engines capable of burning RP-1, hypergolic, or liquid hydrogen propellants interchangeably with just a few modifications.

Ahhhh, OK. That explains it. I knew that the 'storable' hypergolics were considered one of Titan's best features; I just didn't realize that they weren't introduced until the Titan II.

Atlas D and E both only took about fifteen minutes to elevate, fuel and fire from an alert state. Four hours may be the response time when not on-alert, though I have no idea what would take four hours to do. Then again, they say that the R-7 could take as much as twenty hours to prepare to launch...

Oh, I bet I can guess what it was, now that I think of it. Atlas did use an early inertial/celestial guidance system. (In fact, I'm not sure it even used celestial at all.) It might well be that the IMU took four hours to align initially, though while the booster was still hooked up to ground power, it could be *kept* spun up and aligned for an extended period. (One of the reasons the Honeywell ring laser gyro was such an advance is that it brought INS alignment times down into periods measured in seconds, not minutes or hours.) Add in the checkout procedures that had to go on while powering up the missile, and you've got a pretty slow response time from a non-alert status.

Yeah. I never understood why they gave up on it with Atlas III - the performance is simply astounding. The original Atlas was in fact capable of performing true SSTO with a reduced payload. SpaceX seems to think it's a good idea, as the Falcon I uses a partially pressure-supported structure. And of course, Centaur sees continued usage as one of the best high-energy upper stages out there, and ACES will carry on the balloon-tank structure into the next generation of high-energy transfer stages.

I suspect that they gave up on it with Atlas III simply because they felt that for a space launch booster that spends days or weeks vertical on the pad, the pressure-supported first stage was simply more potential trouble than it's worth, since there would be the requirement to keep it pressurized before--and during--fueling operations, which requires specialized (and expensive) ground equipment, etc. With the performance of the RD-170, they could get pretty much the same net performance with a non-pressure-supported structure.

SpaceX is right, though; if you can find some way to prevent the first stage from collapsing if pressure is lost (maybe some lightweight rigidizing elements that would allow the tanks to remain stable under 1G with partial pressure, or even ambient, but not enough for flight?), the weight reduction is dramatic. And, of course, using it on your top stage makes perfect sense, because the structural loads are probably about as low there as anywhere (less mass to support on top of it), and every pound shaved out of an upper stage trickles down to several pounds saved in the lower stages...

[DoctorEvo]

Granted, but V-2 guidance wouldn\'t have let you hit a specific city at that range. Be pretty embarassing if Ike had decided to order a massive attack, only to have all the weapons land out in farmland or uninhabited mountains or something, y\'know?

Ah, here we are...

It looks like the initial test articles for MX-774 used the simple gyroscopic guidance system similar to the V-2\'s, but Convair set out to develop the very same Azusa radar-tracking command guidance system that was eventually used on Atlas-D. So yes, it looks like they probably could\'ve had an intercontinental missile with a CEP on the order of five miles by 1950 - but still no warhead small enough to launch with it.

No, I\'ve seen actual motion picture footage of this one. It might be the same incident, though. I *will* say that the final result looked very similar to when the Air Force Museum\'s original Atlas sprang a leak and crumpled back in the 80s. (The one they have now is apparently modified for display with, essentially, a steel telephone pole up the middle to support it, so that it won\'t collapse no matter what.)

Ah, here it is: http://www.thespacereview.com/article/1326/1

Looks like this one\'s where it finally bursts...

Apparently there was a video, but it got pulled. In any case, the pictures tell the story pretty clearly.

THIS, I hadn\'t heard. It doesn\'t surprise me--I know how much force pressurization can exert--but that\'s one tale I hadn\'t heard. (At the same time, I can understand von Braun\'s skepticism--it was, at the time, a *very* radical concept, after all, and von Braun had an engineer\'s conservatism, taken to a bit of an extreme. as seen with his attitude towards LH2 as fuel...)

Yes, by Von Braun\'s standards, Bossart was clinically insane in more ways than one. He was, after all, one of the first proponents of LH2 propellants as well...

Oh, I bet I can guess what it was, now that I think of it. Atlas did use an early inertial/celestial guidance system. (In fact, I\'m not sure it even used celestial at all.)

Inertial/command. A interferometric radar ground station would track the rocket during launch and send updates to the rocket to make corrections. The military pushed for an independent fully-inertial system which was implemented in Atlas E and onwards, but the technology developed for the Azusa system saw continued usage in the spaceflight industry, with related ground-based tracking and command systems being the favored system right up to the Shuttle era, and even today to some extent (complimented by GPS and TDRS).

I suspect that they gave up on it with Atlas III simply because they felt that for a space launch booster that spends days or weeks vertical on the pad, the pressure-supported first stage was simply more potential trouble than it\'s worth, since there would be the requirement to keep it pressurized before--and during--fueling operations, which requires specialized (and expensive) ground equipment, etc. With the performance of the RD-170, they could get pretty much the same net performance with a non-pressure-supported structure.

They used an RD-180, not a 170. And performance is performance; adding extra weight that doesn\'t otherwise help performance is a performance penalty no matter what engine you have underneath.

As for the logistics, I think transportation and assembly are by far the more difficult aspect of handling balloon tanks than fueling is. For fueling, the fuel hoses are pressurized by pumps anyways, and I\'m sure pressure CAN be reduced on an Atlas even during on-pad fueling (maybe not down to the 5 PSI that they were stored at, but somewhere significantly less than the 25-30 PSI they launched with) if need be. Atlas already had all the systems for regulating pressure internally after fueling, so I can\'t see all that much extra external infrastructure being required to maintain pressure during fueling, aside from a pressure fitting on the nozzle-end of the fueling hoses. During transportation or assembly, on the other hand, the rocket\'s own pressure regulation systems are disabled and the rocket must be kept pressurized to 5+ PSI with nitrogen at all times. Now it\'s not terribly difficult to keep a steel balloon from leaking, but care must be taken not to open the wrong valve at the wrong time, and the pressure should probably be monitored during transportation.

SpaceX is right, though; if you can find some way to prevent the first stage from collapsing if pressure is lost (maybe some lightweight rigidizing elements that would allow the tanks to remain stable under 1G with partial pressure, or even ambient, but not enough for flight?), the weight reduction is dramatic. And, of course, using it on your top stage makes perfect sense, because the structural loads are probably about as low there as anywhere (less mass to support on top of it), and every pound shaved out of an upper stage trickles down to several pounds saved in the lower stages...

Oddly enough, the Falcon 1\'s second stage is not considered pressure-supported at all. Of course, being a pressure-fed stage rated for more than 135 PSI, the fuel tank itself is built heavily enough to completely eliminate any need for dedicated structural members at all anyways - pressurized or not. I sometimes wonder if this may be the answer - to simply increase the pressure rating of your fuel tanks so they can handle all assembly and pad loads unpressurized, and then re-assess your engine choice to see if the weight of the turbomachinery is really worth the ISP increase. (I mean, heck, the Kestrel, with a mere 135 PSI chamber pressure, achieves a vacuum ISP even better than Merlin does with its turbopump and 1000 PSI combustion pressure, just due to turbopump and nozzle losses!)

[Designer225]

Ah, here we are...

It looks like the initial test articles for MX-774 used the simple gyroscopic guidance system similar to the V-2\'s, but Convair set out to develop the very same Azusa radar-tracking command guidance system that was eventually used on Atlas-D. So yes, it looks like they probably could\'ve had an intercontinental missile with a CEP on the order of five miles by 1950 - but still no warhead small enough to launch with it.

Ah, here it is: http://www.thespacereview.com/article/1326/1

Looks like this one\'s where it finally bursts...

Apparently there was a video, but it got pulled. In any case, the pictures tell the story pretty clearly.

Yes, by Von Braun\'s standards, Bossart was clinically insane in more ways than one. He was, after all, one of the first proponents of LH2 propellants as well...

Inertial/command. A interferometric radar ground station would track the rocket during launch and send updates to the rocket to make corrections. The military pushed for an independent fully-inertial system which was implemented in Atlas E and onwards, but the technology developed for the Azusa system saw continued usage in the spaceflight industry, with related ground-based tracking and command systems being the favored system right up to the Shuttle era, and even today to some extent (complimented by GPS and TDRS).

They used an RD-180, not a 170. And performance is performance; adding extra weight that doesn\'t otherwise help performance is a performance penalty no matter what engine you have underneath.

As for the logistics, I think transportation and assembly are by far the more difficult aspect of handling balloon tanks than fueling is. For fueling, the fuel hoses are pressurized by pumps anyways, and I\'m sure pressure CAN be reduced on an Atlas even during on-pad fueling (maybe not down to the 5 PSI that they were stored at, but somewhere significantly less than the 25-30 PSI they launched with) if need be. Atlas already had all the systems for regulating pressure internally after fueling, so I can\'t see all that much extra external infrastructure being required to maintain pressure during fueling, aside from a pressure fitting on the nozzle-end of the fueling hoses. During transportation or assembly, on the other hand, the rocket\'s own pressure regulation systems are disabled and the rocket must be kept pressurized to 5+ PSI with nitrogen at all times. Now it\'s not terribly difficult to keep a steel balloon from leaking, but care must be taken not to open the wrong valve at the wrong time, and the pressure should probably be monitored during transportation.

Oddly enough, the Falcon 1\'s second stage is not considered pressure-supported at all. Of course, being a pressure-fed stage rated for more than 135 PSI, the fuel tank itself is built heavily enough to completely eliminate any need for dedicated structural members at all anyways - pressurized or not. I sometimes wonder if this may be the answer - to simply increase the pressure rating of your fuel tanks so they can handle all assembly and pad loads unpressurized, and then re-assess your engine choice to see if the weight of the turbomachinery is really worth the ISP increase. (I mean, heck, the Kestrel, with a mere 135 PSI chamber pressure, achieves a vacuum ISP even better than Merlin does with its turbopump and 1000 PSI combustion pressure, just due to turbopump and nozzle losses!)

Few days ago I checked about the Falcon 9 rocket engines. The Falcon 9 first stage engines (Which are 9 Merlin 1C's) also works on vacumms, but no better than Merlin 1C Vacumm, which is the engine for Falcon 9 second stage. (So technically, you are right --- partialy.)