CEV PDQ

Rand Simberg wrote:

So? We end up with a lot of launches (assuming we can't get
propellant from the moon). Big deal.

Last time I had a house built, I don't recall demanding that it be
delivered assembled on a giant truck.



Assuming that your component parts go up on rockets that have around 95%
reliability (which is around what most have, particularly the larger
ones) and you've got to assemble something from say 20 or more
parts...then you can be pretty sure of losing a part of it along the
way....and that means building back-up parts for all the parts if you
want to be fairly sure that you have all the components you need to
assemble it, which won't be cheap.
The cost of building a lunar base to extract propellant for the ship
would be far more than any savings accrued from not bringing it up from
Earth, at least if only a flight or two to Mars is intended. The Moon
propellant extraction base option only makes sense if you intend to
start doing a permanent Mars base, which is going to be one hell of a
way down the road compared to what we are planning now.

Pat

"Jorge R. Frank" wrote in message
...
"Neil Gerace" wrote in
:

" wrote in
message ups.com...

the DIV has to fly an odd trajectory (due to structural
concerns) that means that there are points in the ascent when abort is
*not* survivable.

Is that bad? Seems to me that it happens to STS as well.

No. That's due to not being able to terminate the SRBs safely, not due to
trajectory as is the case with the D-IV.

Well, I was only referring to the second part of the sentence: "there are
points in the ascent when abort is *not* survivable."

Andrew Gray wrote:

this would be equivalent to
saying that there's a dead-zone during takeoff where you can't try to
do an emergency landing of the airliner, surely?



Stop calling me Shirley. :-)

The Ottopilot

On Mon, 09 May 2005 21:35:49 -0500, in a place far, far away, Pat
Flannery made the phosphor on my monitor glow in
such a way as to indicate that:

If we actually intend to do a manned Mars mission we are going to need
a heavy lift vehicle of some sort,



Many believe this. That doesn't render it a fact.



You are going to end up with a lot of launches if you try to do it with
anything smaller than some of the proposed souped-up Delta IV heavy
variants from the viewpoint of crew life support requirements alone.

So? We end up with a lot of launches (assuming we can't get
propellant from the moon). Big deal.

Last time I had a house built, I don't recall demanding that it be
delivered assembled on a giant truck.

On Mon, 09 May 2005 21:47:38 -0500, in a place far, far away, Pat
Flannery made the phosphor on my monitor glow in
such a way as to indicate that:

Which cuts into your payload weight, and therefore ups your
launch price per pound for large numbers of launches.



That's an interesting theoretical argument, but in practice, what do
you think that Thiokol would do differently in manufacturing a motor
for an unmanned launch that they do for a manned one?



The recovered SRB segments wouldn't have to meet the strict inspection
requirements they now do. After Challenger, Thiokol is probably
extremely paranoid about the recovered booster segments it fills and
ships. I'll bet any scratches or small dents get the segment rejected,
even though they shouldn't really compromise its structural integrity in
any significant way. But they'd be far more likely to use something that
isn't all bright and gleaming on a unmanned launch.
If fact, for warm weather launches, you could use the old style
pre-Challenger booster segments without any real problem.

You could do all those things for manned launches as well. If you
were sensible, anyway.

On 2005-05-10, Pat Flannery wrote:

Assuming that your component parts go up on rockets that have around 95%
reliability (which is around what most have, particularly the larger
ones) and you've got to assemble something from say 20 or more
parts...then you can be pretty sure of losing a part of it along the
way....and that means building back-up parts for all the parts if you
want to be fairly sure that you have all the components you need to
assemble it, which won't be cheap.

So, what you do, is you build one flight's worth of hardware in advance,
so there's always a spare of each part "in stock" (this also protects
you against manufacturing accidents, or the like)... which then gets
used for the next flight, anyway. A little more sunk cost at the
beginning, trivial increases for storage through the life of the
program, and (possibly) some non-trivial savings on your final flight.

--
-Andrew Gray

Rand Simberg wrote:


Not if a replacement part can go up on another cheap (something that
heavy lift will never be at planned usage rates) ) launch. There's an
old saying about eggs and baskets...



I was concerned about the cost of the parts themselves- which could be
more than the rocket that carries them.
The big problem is needing replacements for ones that may get lost
during launch.
With our unmanned planetary missions we have many times used dual
spacecraft in case one was lost for some reason.
If you have to build a complete back-up modular Mars ship that will be
expensive; the other concern is the launch window- can you get the
replacement component for the lost one up and docked while the launch
window is still open?

Pat

Rand Simberg wrote:

Of course you should have backups for all the parts. It's not like
you're only going to go once.



To Mars? With all that entails? There'll be a very long time interval
between the first manned flight for the prestige factor and the second
one...for whatever reason it is done.




It would be nutty to go to Mars at all if only a flight or two is
intended.



Remember the Bush administration suggested a manned flyby flight of Mars
with no manned landing- which is about the nuttiest, most pointless
thing I ever heard suggested in the field of spaceflight outside of the
Soviet Voskhod test EVA by a dog. :-)


Pat

Andrew Gray wrote:

So, what you do, is you build one flight's worth of hardware in advance,
so there's always a spare of each part "in stock" (this also protects
you against manufacturing accidents, or the like)... which then gets
used for the next flight, anyway. A little more sunk cost at the
beginning, trivial increases for storage through the life of the
program, and (possibly) some non-trivial savings on your final flight.



If we are talking Lunar flights, that makes sense.
But if you think that the Apollo flights got truncated due to lack of
public interest and the perceived high cost, wait till you see how fast
manned Mars missions get ditched after the first one... especially
considering the time factor involved for each flight.
About the only thing one could do is build the component parts for the
first mission in duplicate, so that you could be pretty sure that you
could get at least one fully assembled ship in orbit for the first
mission, and two if you are lucky.
The journey to and from Mars will be about as exciting as the astronauts
living on the ISS to the general public- and to tell you the truth, I
sometimes forget there is even a crew on the ISS, or an ISS itself for
that matter.
Can you name the current ISS crew off of the top of your head? I sure
can't. :-)

Pat

On Tue, 10 May 2005 18:49:56 GMT, h (Rand
Simberg) wrote:

If it's going to be flags and footprints, as you imply, then we
shouldn't do it at all.

....Gosh, then I guess scaling Everest shouldn't be done, either. Much
less crossing the street.

Coward.

OM

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