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Old July 3 2012, 08:20 PM   #158
Crazy Eddie
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Re: SpaceX is a go for April 30th: 1st commercial launch to space stat

publiusr wrote: View Post
newtype_alpha wrote: View Post


]Since "Faster better cheaper" is the cornerstone if affordable manned space flight, their resistance to the idea should tell you something.
It tells me that folks are fed up with the Dan Golden era stagnation of endless also-ran Delta II missions of the Goldin era.
Hard to be fed up with something that is no longer occurring, don't you think? That's like going to a political rally next Tuesday and saying "I'm sure we're all really fed up with Osama bin Laden."

And six or seven Delta IV heavies will easily cost as much as a single production SLS
Then it's a good thing it only takes four of them to outperform the SLS' initial payload mass.

overcomplicated ISS style assembly methods...
Have been employed and proven to work on two different space stations now. The one and only time we used an HLV to throw an entire station into orbit in one sitting... guess what? It arrived in orbit barely functional and had to be rescued by an astronaut crew anyway. Interestingly, the Soviets tried the same thing with the Energia rocket, attempting to toss an entire unmanned space station in a single sitting, resulting in epic fail and the epitaph of Energia.

Ultimately, avoiding in-space assembly doesn't save you any money, it only saves you TIME, which in the context of space flight is about the ONLY thing we have in abundance. Unless we're building a space station with the intention of fighting off a Klingon invasion next month, we can afford to take the time and split the construction up into multiple launches, which ultimately saves money AND leads to a more robust launch system that can be used to do other things.

Take the skycrane for Curiosity. That work-around is the direct result of EELV contraints.
LOL not by a longshot. It's a result of the fact that what they're essentially trying to do is a propulsive landing on mars with a robotic vehicle the size of a jeep, without having the time or the money to develop a totally new space capsule for it to ride in (which would be neccesary if you want a propulsive landing all the way to the surface without screwing up the rover's sensors). If they waited a few years they could get Elon Musk to loan them a man-rated Dragon and launch it on a Falcon Heavy. If they waited a few years longer, they could launch it on a regular Falcon 9, and then use a second Falcon 9 to lift an ion-powered transfer stage: the entire curiosity mission at one tenth the budget.

On the second bit, SLS is directly necessary for what we want to do in space
Only if we want to do it really quickly on a ridiculously huge budget. Either of which necessarily implies TEMPORARILY, which is exactly what we have always gotten with HLVs: very short-lived, very temporary space missions with absurdly high price tags.

That's the problem with HLVs: with a non-infinite budget, you can't use them very often and you can't use alot of them. Your weight restrictions are actually made WORSE, because you have to fit everything you need into a single launch and if something goes wrong you won't get another chance for AT LEAST six months. Smaller launch systems can tolerate a higher flight rate, which means more on-orbit support, which means you can launch longer missions more often for less money.

The first Delta IV flight won't be a flyby but a simple test to a high Earth orbit to test the heatshield.
The first FLYBY probably will be as well, which is what I actually said.

Boil-off problems are not solved
Hydrazine doesn't boil off.

and any depots are likely to be SLS launched anyway
And my grandmother is likely to grow wheels and become a wagon.

Also remember that the larger an LV is, the greater the internal volume growth--External surface area grows with the square with volume increasing by the cube--so having large diameters, especially for hydrogen--should be encouraged
Using hydrogen for orbital propellant, however, should not. On long term missions you need a storable propellant that doesn't need babysitting; the extra isp you get from LOX/LH2 isn't all that useful in the context of orbit changes and stationkeeping (for most spacecraft, it's a difference of like 200m/s BEFORE it gets eaten up by the extra weight of the tankage). Hydrazine takes a smaller tank and less complicated engines, and you can store it for years; twenty tons of that stuff in an orbital depot could meet the needs of a hundred space probes or a thousand Hubble telescopes.

From this you get mission flexibility: Curiosity rides up in a Falcon-9 and an astronaut crew checks it out in orbit BEFORE it leaves to make sure nothing got damaged during liftoff. And therein lies the rub: what if something DID get damaged during liftoff? Are you gonna pack up replacements and wait six months for NASA to prepare the next SLS, or are you gonna toss a repair package into orbit with the other Falcon 9 you already contracted to launch an unfueled Earth Departure Stage?

In terms of a down select--it would actually be better if Dream Chaser and Musk got the contracts, perhaps allowing them to work together and pool money, instead of Dream Chaser being a junior partner to ULA
Actually, I'm pretty sure ULA is going to wind up being the Junior Partner to Sierra Nevada; the way things are working out, NASA's mainly focussing on getting a manned spacecraft developed, not so much a man-rated ROCKET, which they see as a secondary need for commercial crew development.
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