[QUOTE=Loopydude]
The sheer mass of the fuel is a cost in itself. The larger the spacecraft, the more fuel required, the more fuel required to lift the more fuel required, the larger the craft. The relationship isn’t linear, and eventually becomes insurmountable. This has been known for decades.
[/QUOTE]
The cost of liquid fuel and oxidizer for a Shuttle launch is a few million dollars, compared to between $600M-$1500M per launch, so figure that fuel is on the order of 1% of actual refurb, maintainence, and launch costs. This doesn’t include the cost of the SRBs owing to the fact that they are simultaneously “fuel” and “motor”, but the cost of the actual material–essentially aluminum flakes, ammonium perchlorate and rubber–is negligable compared to the cost of manufacture of the entire booster (~$25M per).
The scaling problem you refer to isn’t a fiscal one, but rather a physical one; with chemical propulsion systems you asymptotically approach the limit to which additing additional propellent mass doesn’t increase net payload capability; in essense, your extra fuel only serves to lift itself. In fact, there is no operational booster system that can launch a significant payload directly to orbit (referred to as Single Stage To Orbit or SSTO), hence all orbital boosters utilize multiple stages and/or external boosters. (The original Atlas rocket was technically a single stage but dumped two of the three engines after achiving a given altitude, and is often informally referred to as being a “1.5 stage rocket”.) However, credible fully reusable single stage orbital boosters have been proposed and even developed to a limited degree (the McDonnell Douglas DC-X and the Chrysler Aerospace SERV proposal for the STS among them) using more efficient propulsion technology, and the use of an air-breathing flyback booster with a spaceplane ascent stage (similar to the Soviet Spiral system or the Scaled Composites White Knight/Space Ship One) could reduce launch costs and fuel requirements dramatically. (Indeed, this was the original plan for many early STS concepts, but the development costs and timeframe were considered to be too extensive for the allotted budget.) In any case, we’re nowhere maximum efficiency for chemical propulsion.
The real cost, again, is labor. The STS requires a team of ~2500 people (technicians, engineers, managers, et cetera) working a minimum of 2 months (more typically 4-6) to return a Shuttle to flight status and integrate it with the SRBs. A more mature and less complex system (along with a more streamlined bureaucracy) could reduce that expense to a modest fraction. While it seems unlikely that orbital travel using chemical propulsion will ever be as inexpensive as an intercontinental aircraft flight, it certainly shouldn’t be seen as infeasible to reduce launch costs to on the order of $100/lb payload, or a few tens of millions a flight, with an incidence of catastrophic failure as a fraction of a percent.
[QUOTE=Loopydude]
What’s this all about?
From here.
[/QUOTE]
That’s about the difference between a press release and a Prime Item Development Specification. There is absolutely nothing in the Stage I spec that addresses in any but the most superficial detail the requirements for an interplanetary mission. There was brief reference to Mars in the Spiral 4 and 5 developments (back when NASA was still talking about spiral develoment), but they were treated as merely extensions to the system rather than addressing some of the fundamental developments of radiation shielding, long duration interplanetary hazards, propulsion, risk abatement in a non-rescue scenerio, landing and extended habitation on Mars, et cetera. If such a mission were going to occur on a, say, twenty five year timeframe, NASA should be developing the specifications and allocating future funding for research and development right now. All the talk about going to Mars using Orion (that is, the CEV Orion, not the Project Orion rocket concept) is so much hot air without a single definitive step.
And even this was being established as a serious goal for NASA, by the time the technology is there, the CEV should be obsoleted out and replaced with the next generation of system. One of the nearly fatal flaws about the STS was that NASA was so wedded to the Shuttle (by budget restrictions, political impetus, bureaucratic complacency, and the failure of aerospace contractors to be held accountable for failures to demonstrate progress for the billions of dollars spent on potential successors and development programs) and until the failure of Columbia, did not seriously push forward with a replacement for the Shuttle which used lessons learned to reduce complexity and launch costs while extending propulsion and spaceflight technology. The STS is a pastiche of Sixties- and Seventies-era technology, cobbled together on the (relative) cheap to keep NASA in the manned spaceflight business and meet unrealistic combined expectations of the manned program, the military, and commercial spaceflight interests. There was never a good reason for building Endeavor (the last of the Shuttles to be built) rather than pushing forward with the development of a new–or at least, dramatically improved–system, other than the unwillingness by many parties to admit to and learn from the problems of STS.
CEV is a quick and cheap solution to replace critical aspects of the STS with Shuttle-derived hardware (hence the name for ATK’s campaign of Safe, Simple, Soon), but it shouldn’t be considered anything but a stopgap while advancing spaceflight technology. The Lunar objective seems to be little more than nationalistic flag-waving, proving that we can get (back) to the Moon before the Chinese do, and any proposals for using this system as a Mars vehicle fail to account for many required developments. Even Zubrin’s childishly optimistic Mars Direct proposal presumes more development and offers greater detail than the Exploration Systems Architecture Study (which mostly focuses on extracting methane from Mars for fuel).
Stranger
