DerekL1963

It's also a bit of making lemonade from lemons - the Merlin was originally designed for the much smaller Falcon I. (A booster that went nowhere because, despite it being an article of faith in the space community for decades, there turned out to not be much of a market down in that payload size.) Plus, engine-out capability has always struck me as a bit of red herring... modern engines fail very rarely indeed. It's also worth noting that smaller engines are somewhat cheaper to develop and build. Also one big engine simplifies the design of your thrust structure, makes your flight control software moderately simpler, etc... etc... So, one isn't really "better" than the other. As Bill said, it depends on your goals.

I'm not saying total program costs/flights isn't a useful metric - only that it's a one dimensional metric that doesn't take into account a number of variables (such as flight rate, and the time value of money). The latter program might turn out to be the more expensive when you take inflation into account if the costs of the former are front loaded. You also have to be careful of avoiding falling into the "subcompact vs. pickup truck" fallacy the Capsule Cabal indulged in throughout the late Shuttle era* and make sure you're comparing costs and capabilities like-to-like or you can end up with a right nasty mess trying to correct your figures so that you are. If your $200 billion program is a 200 ton launcher, while your $100 billion program is a 100 ton launcher - there's all kinds of side effects, tangible and intangible. And I'm not even going to get into the nasty mess that is the "broken window" fallacy and sunk costs. Spot on. Shuttle's total cost per annum was dominated by the "standing army". While the cost-per-launch (the marginal costs, the costs to add a launch to the manifest) remained more or less invariant regardless of the number of launches - the cost-per-flight (that is (fixed costs+marginal costs)/number of flights) drops radically the more you fly. Accounting is complicated, and it's something I wish more space fanbois studied as assiduously and treated as agnostically as they do physics and engineering - numbers matter, whether they're in the bean counter's ledger or the engineer's drawings. * Comparing the raw cost per seat of a Shuttle to Soyuz. Such a simple minded comparison does make Shuttle look more expensive, but when you add back in the costs of the boosters (even at Russian rates) required to carry the cargo that Shuttle also carried the picture becomes much murkier and nowhere near as clear a victory for Soyuz. (Especially when you consider the less tangible benefits such as the reduction in overall programmatic risk and the assured simultaneous arrival of installation crew and equipment.)

No, NASA could not have simply gone "ooh, shiny" for Curiosity and silenced the peeps, or at least it certainly did not work for any of the previous launches. For Curiosity, there were no lawsuits challenging the EIS or for repeating the EIS, or for cancelling the launch. There were no noticeable protesters at the gate (and I have sources on the ground and do not depend on the media for information on these). The blogosphere was essentially silent. Etc... etc... All of these thing characterized previous launches of spacecraft carrying RTG's.

If you don't care about the specifics of accounting, that's fine. You're free to believe that the world is flat if that's your thing. But please don't presume to lecture the rest of us when we treat the world as round.

That was before the Fukisima Meltdown. We launched Curiousity, with her two RTG's, four years after Fukishima and with essentially nary a peep from the usual protesters.

I really can't express how wrong you are without resorting to language that would get me banned, but really you are that wrong. If you're looking to cost out a new flight (that is, adding a flight to the manifest), then yes, only marginal* costs matter and fixed costs are completely irrelevant because you pay them whether you fly that mission or not. Total program cost/launches only matters when costing out the total program. This is Accounting 101 stuff. * Y'all have marginal backwards - marginal costs are the additional costs to add a flight, fixed costs are those that are fixed, that you pay regardless.

I know that, you know that... But Congress doesn't care because it's NASA that looks stupid rather than Congress. If NASA looks stupid (because of Congressional effups), then that's a chance for Congresscritters to grandstand about how wasteful and stupid NASA is. That's how NASA works in American politics - the great unwashed masses are neither particularly for it nor particularly against it, so it can be praised or pilloried at need.

There's nothing preventing a full checkout followed by immediate fueling and a swift departure thereafter. Apollo 11 was in parking orbit for two and a half hours. And the parking orbits were low not because of the Oberth effect, but to minimize the fuel spent reaching orbit and to maximize the fuel available for TLI. China isn't going anywhere fast. Despite the fever dreams of the space fanboi community, the reality is that they have just enough of a space program to be thought of as a Major Country and not a fen's worth more.

Nobody 'promised' anyone anything.

That's like your boss insisting you do 'x', but gives you no time to do 'x' and actually acts overtly to prevent you from doing 'x' - and then reaming you a new one for not having a plan for accomplishing 'x'. The Senate Launch System is a jobs-and-pork program, and these 'demands' are nothing more than a pair of Texas congresscritters (both of whom are up for re-election this year) grandstanding for the cameras. Note especially the Party the first Congresscritter, the one acting as though the Administration is at fault, belongs to.

Two reasons. First, it was an extremely expensive launcher. Second, it was a heavy launcher and heavy payloads are themselves expensive. (Note, this is the same dilemma the SLS is facing.) Also, they didn't "suddenly" pivot to the Shuttle. The Shuttle (or something much like it) was deeply embedded in NASA's DNA from the very start. You'll sometimes hear it referred to as the Von Braun Vision - Shuttle, Station, Mars. (Though the shuttle in the Vision was a passenger shuttle, cargo went up on heavy expendables. The historical Shuttle ended up being a pickup truck for complicated reasons.) Von Braun, and others at NASA, regarded the whole moon landing thing as something of a diversion from the Real True Path to space exploration. Anyhow, research on shuttle technology was underway by the early sixties in parallel with the lunar program.

There are three ways to reduce exposure: Time, Distance, Shielding. - Time is obviously not an option for a Mars journey, since it's years long. - Distance is a big part of exposure reduction, as can be seen in pretty much any NTR craft design they put the crew as far away as humanly possible. (Radiation follows the same inverse square law as visible light.) - Shielding, well you don't need as much as you might think. Not only does the vehicle's tankage and structure act as shielding, you only need a disk on the front of the reactor sufficient to put the rest of the vehicle into it's "shade".

*sigh* SLS lacks missions for two reasons, a) it wasn't designed to fulfill any mission in the first place other than channeling pork to key Congressional Districts, and b) it's not worth flying the thing unless you're flying huge multi-billion dollar battlestar class missions of the type we stopped doing back in the 90's. And frankly, anyone that thinks any Administration is going to do anything different is living in cloud cuckoo land. Space is nobodies priority other than the employees of a few government pork processors. It's not this Administration or that Administration, it's just the way the world works.

No they don't, not anymore at least. Over time the noise and activity of the usual protesters have markedly declined. (There was an especially noticeable drop after 9/11 and the start of Desert Storm II, the cynic in me wants to the said drop was due to the usual protesting types being distracted and busy elsewhere.)

It had the same payload - but a fraction of the capability.

Launch, and landing, and rendezvous, and planetary orbital insertion, and orbital maneuvering, and... the list goes on and on and on. People who care about real missions and real space care about TWR. Unlike people handwaving phantom spacecraft, they lack the luxury of picking propulsion systems based on a single dimension. NASA plans all kinds of things. Some of them even happen.

If the F9 was recoverable - that would be a valid question. But it's not. Only the first stage is recoverable, from much lower speeds and altitudes, and carrying zero payload or passengers. You're trying to compare apples and the thing least like apples you can possibly imagine.

Those are just the engineering problems. Looming much larger is the problem that an elevator renders large chunks of space below GEO essentially useless as they must be kept clear to prevent collisions and damage to the tower.

They don't - because ground based pumps and reasonable sized umbilical connection can't deliver sufficient flow. And, as far as weight goes, the bulk of the stage's weight is in the engines and thrust structure not tankage. A meter or two of extra tankage isn't quite lost in the noise, but close.

No. The F-1A wasn't throttleable. And large fins on the S-IC likely render it uncontrollable in a tail-first reentry and landing configuration anyhow. And you'd likely still need the fifth F-1A because while you've gotten rid of one upper stage, you've added a heavy Orbiter.

They have much better ISP, but they all have crap thrust and dodgy T/W ratios and are impractical for all but fairly small spacecraft. ISP isn't everything. That being said, there are no treaties preventing NERVA (no treaty prevents launching fissile material into space). We aren't using NERVA for one and only one reason - they're hideously expensive, and being very heavy they require large and hideously expensive boosters. The only reason they'd ever be useful is to power large and hideously expensive missions. And once we'd been to the Moon, Congress lost all remaining interest (of which wasn't much at that point) in paying for anything hideously expensive and space related. (And no, as such things go, Shuttle wasn't hideously expensive.)

Stephen Squyres book "Roving Mars" has all kinds of interesting tidbits about the trials and tribulations of the MER program.

Even more fun fact: The 'roving on Mars' software didn't even exist when they departed Earth orbit - it was written and tested during the cruise phase. (Because of their insanely tight schedule, they simply couldn't do it beforehand.)

The engines don't have to be inline with the center of mass - the thrust vector has to be through the center of mass. (Real life example: the Shuttle after SRB jettison, the SSME's gimbal to maintain thrust through the center of mass even though it's inside the ET for most of that period.)

Budgets and launch costs vary. The MRO spacecraft cost $720 billion, it's Atlas-V ride to space cost $100 million. It's operating budget runs around $30 million a year. So.... coming up on a decade in service, it's racked up a bill totaling about 1.1 billion - of which, the .1 represents the launch costs. To get up to $200 million you have to go to one of the really big launchers - and the probe costs go up too. (That's the reason we aren't tossing big heavy "battlestar" probes around the solar system anymore, they just cost too [censored] much for NASA's budget to stand.) 0.o No, that's not how these things work. The payload of a current Falcon 9 (currently $61 million a ticket) is 28klb to LEO. The payload of a Falcon 9 ($30-40 million with a reuseable first stage) is also 28klb to LEO. Probes must be light because the rocket equation is a stone cold [censored]. Significantly increasing the weight of a probe requires launchers size go up and their costs come down.