CEV PDQ

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 10 May 2005 12:35:13 GMT, in a place far, far away, Andrew Gray
made the phosphor on my monitor glow in
such a way as to indicate that:

On 2005-05-10, Neil Gerace wrote:
"Rand Simberg" wrote in message
...

Which is one of the several reasons that STS (to the surprise of many)
is not "human rated."

Well, it happens to airliners too. An abort (all engines out, no control
surfaces responding) is often not survivable. But they are still allowed to
fly.

The analogy isn't quite the same, though - 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?

Well, actually there is. If you lose all propulsion shortly after
rotation and takeoff, there's not a lot you can do.

On Tue, 10 May 2005 12:32:19 GMT, in a place far, far away, Reed
Snellenberger made the phosphor on my
monitor glow in such a way as to indicate that:

Rand Simberg wrote:

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

So I'm guessing you didn't buy a modular home?

No, I didn't, and if I had, it would have been much smaller. Also,
I'm not aware that they come with furniture and appliances installed.

Rand Simberg wrote:

Could be, but it's still better than losing an entire mission with a
single loss, and you can pay for a lot of lost pieces with the
development cost savings for the unneeded HLLV.


But in the case of the Shuttle-derived one, we already have most of the
cost covered in the development arena.
Building a new cargo pod would be around as difficult as building a new
third stage for the Saturn V, particularly now that we have the RS-68 to
use.


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?



If you put enough slack in the schedule. If not, launch windows to
Mars occur relatively frequently. This discussion presupposes much
more routine capability to get things into orbit (as well as doing
orbital assembly) than we have today. Developing that kind of
capability would have much greater long-term value for our prospects
in space than a heavy lifter.



But it also means an expanded civilian as well as military and
governmental demand to get the high volume of payload into orbit that
would justify a high launch rate capability for medium lift vehicles. So
far that hasn't happened, and if it does happen I wouldn't be surprised
to see a lot of those payloads going up on a Chinese-made rocket that
offers far lower cost than a U.S. one.
The obvious counter-argument is to launch the parts of the U.S. Mars
ship on the Chinese made booster; that presupposes that the Chinese
would launch our Mars ship on their boosters....rather than launch
_their_ Mars ship on their boosters. ;-)

Pat

Rand Simberg wrote:

Not necessarily. It's a lot easier to do a mission to Phobos for an
initial mission than it is to land on the planet, and a lot of good
science could still result.



After the amount of time it would take to get to Mars and back is
considered, getting that close and not landing would be pathetic.

Pat

On Tue, 10 May 2005 06:04:29 -0700, in a place far, far away, Dale
made the phosphor on my monitor glow in such a way as to
indicate that:

Well, it happens to airliners too. An abort (all engines out, no control
surfaces responding) is often not survivable. But they are still allowed to
fly.

Because, unlike a vehicle that has to be essentially rebuilt each
time, and only flies a few times a year (if that), they are reliable.

What does rebuilding/not rebuilding have to do with a possible
designed-in vulnerability to catastrophic failure?

Nothing, but there are other failure modes that aren't a function of
design. Most, in fact.

Rand Simberg wrote:

That's why it's important to build the infrastructure necessary to
make it affordable to privately fund it. Heavy lift definitely
doesn't do that.



Flyin' to Mars ain't like dusting crops, boy! :-)
Bill Gates could probably afford to finance the whole kit and kaboodle
right now if he felt like it... but he hasn't done it yet.
And I'm glad he hasn't...because when Windows crashes it's annoying-
but nowhere near as annoying as having a planet crash sometime. ;-)