On Saturday I posted a review of Stephen Baxter's brilliant hard-science Alternate History novel, "Voyage." In that book, he came up with the very clever idea of attaching Shuttle-styled Solid Rocket Boosters to the old Saturn V moon rockets, so as to get more bang for their buck. Baxter avoids specifics when discussing the superattenuated Saturn Vs, but makes some offhand comments about them being able to carry twice as much cargo as a 'real' Saturn.
He never actually gives these rockets a name beyond "Modified Saturns" or "The New Saturns," but that's clunky, so since a Saturn V had five engines, and we're adding four Solid Rocket Engines to it, let's just call it a "Saturn Nine" for ease of reference, ok? Anyway, I got to wondering exaclty what the performance on these hypothetical "Saturn IXs" would be like, and so I stayed up all night doing some sloppy calculations for comparison. Since theyr'e kind of interesting, and kind of useless (Like everything else I do), I thought I'd share 'em with you.
A little background before we get in to the numbers, though: The Saturn series was the largest, most reliable family of rockets ever devised by man, with far-and-away the largest cargo capacity. There were two basic variants - the early "Saturn I" and the "Saturn V." The "I" was later improved to the Saturn 1B 'production line' model, of which 12 were built and 9 were launched. The monsterous Saturn V saw 20 models built, and 19 were used. In fact, there was an even larger Saturn that was designed - the "Saturn VIII." The "VIII" began its design phase in the late 1950s, and was originally called the "Nova," but after the more popular Saturn/Apollo nomenclature was adopted they changed the name of the project. The VIII used the same basic technology as the Saturn V, just different ammounts of it. As the Apollo program proceeded and the flight plan evolved, it was realized that the VIII was actually more powerful, and complicated than they actually needed, so they started thinking smaller, which resulted in the Saturn V. In essence, a Saturn V is a scaled down version of the designed-but-never-built VIII/Nova.
Which is handier than it sounds because by the time that project was abandoned, they had all the performance specs worked out, excepting the wind tunnel testing. We know what the VIII *should* have been able to do on paper, but there's always a difference between theory and actual practice when you're talking about hypersonic high-stress machines on this scale.
Now, in the latter days of the Apollo progam, NASA funded a number of studies ot modify the Saturn 1 and V series for various applications which resulted in a bewildering arraoy of variations and configurations, none of which were ever built (Fascinating reading about these here http://www.friends-partners.org/partners/mwade/lvfam/saturnv.htm and here http://www.friends-partners.org/partners/mwade/lvfam/saturnii.htm and some more of the plucky little guys here http://www.friends-partners.org/partners/mwade/lvfam/saturni.htm ) Since the Saturn Family was incredibly successful, and never suffered a loss or failure, lets revisit the idea of using it as a Heavy Lift Launch Vehicle for putting various large cargos in orbit. Unlike the inital battery of modification proposals from the early '70s, I'm just going to go the same rout Baxter did in his novel, and see how it stacks up. In essence we'll be using Shuttle SRBs as "Performance Enhancers."
First, let's see how the actual existing equipment compares:
SATURN 1B - Weight: 1,300,000 lbs; Thrust: 1,600,000 lbs; Payload to orbit: 30,000 lbs.
SATURN V - Weight: 6,423m000 lbs; Thrust: 7,650,000 lbs; Payload to orbit: 201,000 lbs; Payload to Lunar Orbit: 100,000 lbs; Payload to the moon: 33,000 lbs.
SATURN VIII - Weight: 10,494,572 lbs; Thrust: 12,109,900 lbs; Payload to Orbit: 462,971 lbs; Payload to Lunar Orbit: 163,142 lbs; Payload to Moon: 53,842 lbs
SPACE SHUTTLE: - Weight: 4,500,000 lbs; Thrust: 6,710,000 lbs; Payload to orbit: 60,000 lbs.
All numbers are based on as factual information as I could come by: The basic Saturn 1B, V, SRB, and Shuttle information I used is unaltered from the actual real-world equipment. The Saturn VIII information was never actually tested, but is taken from official publications about it's anticipated capabilities. In the ficticious rockets below, I've only extrapolated based on how a Saturn's weight, thrust, and payload would be improved by adding X number of SRBs.
So how would Baxter's own imaginary super-rocket compare?
SATURN IX - Weight: 11,595,984 lbs; thrust: 18,250,000 lbs; Payload to orbit: 392,000 lbs; Payload to lunar orbit: 200,000 lbs; payload to moon: 66,000
This is pretty encouraging and suggests that Baxter and I are on the same page here, since the numbers I came up with completely jibe with his "Twice as much" comments. This got me thinking, how can we come this far to only go this far? Let's attach one more SRB on to the stack:
SATURN X - Weight: 12,889,230 lbs; Thrust: 20,900,000 lbs; Payload to Orbit: 419,075 lbs.
That's about as far as we can take a Saturn V - there's simply no more space to strap on additional boosters. Converting the first stage from kerosine to hydrogen fuel would probably add another 5% to 9% in thrust, but that would require a massive redesign of the engines, and of course the math is beyond me. But...what about our old buddy the Saturn VIII Nova? What if we attached some SRBs to that?
SATURN XII "Supernova" - Weight: 15,667,556; Thrust: 22,709,900; Payload to orbit: 600,010 lbs - this is more than the full payload of the hypothetical "Sea Dragon" rocket!
SATURN XIII - Weight: 16,960,802; Thrust: 25,359,900; Payload to Orbit: 622,233
Of course there are some gaps in these numbers. Also, this doesn't take in to account things like wind resistance, increased G-forces on launch, and even the difficulty of moving a Saturn V that weighs twice as much as usual to the pad. Hell, you couldn't even fit a Saturn VIII *INSIDE* the Vertical Assembly builting, it's vastly taller than a V! Even though all these numbers have to be taken with a grain of salt, they're probably *fairly* accurage ballpark figures for the performance we could reasonably expect, all things being equal.
Complaining about the shuttle these days is like beating a dead horse, but it's not hard to see that we were sold a load of magic beans when we traded in our big rockets for this crappy space plane: Two cheap Saturn 1B launches more than equal the cargo of a shuttle launch. One Saturn V launch is the cargo equivalent of THREE shuttle launches (At $500 million per Saturn V launch, as opposed to $1 Billion per Shuttle launch, it's quite a bargain, actually). A hypothetical "Nova/VIII" Launch equals almost 8 shuttle launches.
Of course not all of that weight is cargo - some of it is the actual third stage structure itself, but it's still vastly more than the shuttle is capable of, and despite the fact that Saturns are not reusable, their reliability and massive payload capacity more than offset the complexity and inefficience and lengthy turnaround times rquired for our shuttle fleet. An additional economic consideration is that the larger, more complete cargo we can place in orbit, the less on-site construction is required. For example, the Skylap space station (1973-1979) weighed about 90 tons, and was sent up in one piece with just one Saturn V launch. A comparable station built with our present-day technology would take at least three shuttle flights to put in orbit, and at least some ammount of work to assemble the station. Our International Space Station took more than half a decade and a dozen Shuttle flights to get up to that size. And of course the SRBs themselves are semi-reusable anyway, which further offsets the cost, though it's hard to figure out by how much since accounting in NASA has always been a black art.