Spotted on http://hsf.nasa.gov/topics.php

"Jeff Findley" wrote:


"Derek Lyons" wrote in message
...
"Jeff Findley" wrote:

The depot would be on the critical path. Delivery of fuel to the depot by
nations other than the US would not be on the critical path.

That has to be among the top ten examples of double think ever posted
to these groups - making that shortlist given the amazing number of
high quality applicants is an achievement to be proud of.

Nations other than the US would not be on the critical path.

If you can affect whether the mission departs on time, you are one the
critical path.

I'm sorry you can't grasp the concept that the US could still provide its own
fuel launches using the lowest bidder. Unfortunately, doing so drives up the
cost to the US.

I can easily grasp the concept Jeff. I just refuse to indulge in the
handwaving and double think required to convince myself that someone
who can affect whether the mission departs or not, or by inaction
require additional work by the US isn't on the critical path...
Because either condition _is the very definition of being on the
critical path_.

The engineering necessary to build and fly a LEO fuel depot really isn't
beyond the current state of the art.

You keep trying to make this about the engineering, something
absolutely nobody is debating. There's a reason why Pat is
(humorously) lumping you in with Mook et al - because not only are you
utterly impervious to debate, but because you insist on trying to move
the goal posts.

D.
--
Touch-twice life. Eat. Drink. Laugh.

http://derekl1963.livejournal.com/

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

"Jeff Findley" wrote:


"Derek Lyons" wrote in message
...
"Jeff Findley" wrote:
"Derek Lyons" wrote in message
...
"Jeff Findley" wrote:

By far the biggest part of a Mars mission (mass wise) will be fuel.

So what? In terms of the cost of the program, it's nearly down in the
noise.

Launching and storing it is not.

So your solution is take launching and storing more complicated?

The really complicated part is cryogenic storage of LH2. LEO fuel depots
keep a large part of the complexity in earth orbit so that expensive
hardware can be used for multiple missions (e.g. large storage tanks along
with passive and active cooling systems). Reuse of expensive hardware
enables each individual mission to be cheaper, which means more missions are
possible for the same amount of money.

Yeah - building *two* sets of expensive hardware (one for the depot,
one for Mars bound craft) is cheaper than building one set. Not to
mention the added development and operational costs for the depot set
between missions *really* rack up the savings.

D.
--
Touch-twice life. Eat. Drink. Laugh.

http://derekl1963.livejournal.com/

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

Jeff Findley wrote:

LEO
fuel depots keep a large part of the complexity in earth orbit
so that expensive hardware can be used for multiple missions

The flip side of this is that the expensive hardware *must* be used
for multiple missions. In fact, it must be used for a large number of
missions. An orbital propellant depot is a scheme that assumes a high
traffic level beyond LEO - far higher than any level that anyone is
willing to fund.

The alternative is throwing away long term cryogenic storage
hardware for each and every Mars mission. That's going to get
expensive as the number of missions increases.

Unfortunately, outside of the space advocacy community there is
little interest in increasing the number of Mars missions to the
point where an orbital propellant depot makes economic sense. You're
falling into the old "Build it and they will come" paradigm.

Jim Davis

"Derek Lyons" wrote in message
...
"Jeff Findley" wrote:


"Derek Lyons" wrote in message
...
"Jeff Findley" wrote:

The depot would be on the critical path. Delivery of fuel to the depot
by
nations other than the US would not be on the critical path.

That has to be among the top ten examples of double think ever posted
to these groups - making that shortlist given the amazing number of
high quality applicants is an achievement to be proud of.

Nations other than the US would not be on the critical path.

If you can affect whether the mission departs on time, you are one the
critical path.

You size the depot to fuel up to two or more Mars missions at a time. The
whole idea of a depot is to make the fuel available to missions on demand.
Member nations don't get to fly their astronauts if they don't deliver, but
you simply make sure that the US keeps the tanks above the level needed to
fly a single mission.

The engineering necessary to build and fly a LEO fuel depot really isn't
beyond the current state of the art.

You keep trying to make this about the engineering, something
absolutely nobody is debating. There's a reason why Pat is
(humorously) lumping you in with Mook et al - because not only are you
utterly impervious to debate, but because you insist on trying to move
the goal posts.

Certainly it is a chicken and egg problem in terms of economics. That said,
there are historical precedents in the aerospace industry where the US
government has pushed technology forward when it was deemed in the best
interests of the country. This has happened in both the military and
civilian aviation markets.

Jeff
--
"Take heart amid the deepening gloom
that your dog is finally getting enough cheese" - Deteriorata - National
Lampoon

"Jim Davis" wrote in message
4.51...
Jeff Findley wrote:
LEO
fuel depots keep a large part of the complexity in earth orbit
so that expensive hardware can be used for multiple missions

The flip side of this is that the expensive hardware *must* be used
for multiple missions. In fact, it must be used for a large number of
missions. An orbital propellant depot is a scheme that assumes a high
traffic level beyond LEO - far higher than any level that anyone is
willing to fund.

The alternative is throwing away long term cryogenic storage
hardware for each and every Mars mission. That's going to get
expensive as the number of missions increases.

Unfortunately, outside of the space advocacy community there is
little interest in increasing the number of Mars missions to the
point where an orbital propellant depot makes economic sense. You're
falling into the old "Build it and they will come" paradigm.

I also happen to believe that NASA ought to be developing new technologies.
Ares I and Ares V don't. They are an application of existing technologies
supposedly because NASA must have heavy lift to go back to the moon and
supposedly because NASA can't build a heavy lift launch vehicle that is safe
enough to launch with a crew on top. I see this as a huge disadvantage in
the long run because it would saddle NASA with not one, but two low flight
rate launch systems. These are the very systems that help to force the very
low mission rate that you're talking about.

Jeff
--
"Take heart amid the deepening gloom
that your dog is finally getting enough cheese" - Deteriorata - National
Lampoon

Jeff Findley wrote:
I'm offended that you're lumping me in with these guys.

The engineering necessary to build and fly a LEO fuel depot really isn't
beyond the current state of the art.

No it's not. It's just that the idea doesn't make any sense, the same
way their ideas don't make any sense.
And you are just as fixated on this idea as they are on theirs.

Pat

Jeff Findley wrote:
Have you even read the testbed proposals from the Centaur guys? Here's one:

http://ntrs.nasa.gov/archive/nasa/ca...2006251226.pdf

Google "Centaur cryogenic testbed" and you'll find quite a bit of info on
the topic. Again, these proposals are from some of the world's leading
experts in cryogenic fluids in microgravity.


Again, the technology isn't the problem... it's the whole orbiting fuel
depot _concept_ that doesn't make any sense.
I'm going to killfile you now, as I'm getting sick and tired of reading
about this thing.

Pat

"Jeff Findley" wrote:


"Derek Lyons" wrote in message
...
"Jeff Findley" wrote:


"Derek Lyons" wrote in message
...
"Jeff Findley" wrote:

The depot would be on the critical path. Delivery of fuel to the depot
by
nations other than the US would not be on the critical path.

That has to be among the top ten examples of double think ever posted
to these groups - making that shortlist given the amazing number of
high quality applicants is an achievement to be proud of.

Nations other than the US would not be on the critical path.

If you can affect whether the mission departs on time, you are one the
critical path.

You size the depot to fuel up to two or more Mars missions at a time. The
whole idea of a depot is to make the fuel available to missions on demand.
Member nations don't get to fly their astronauts if they don't deliver, but
you simply make sure that the US keeps the tanks above the level needed to
fly a single mission.

Nice - once again you move the goal posts. (And increase, once again,
the complexity of planning and operations.)

The engineering necessary to build and fly a LEO fuel depot really isn't
beyond the current state of the art.

You keep trying to make this about the engineering, something
absolutely nobody is debating. There's a reason why Pat is
(humorously) lumping you in with Mook et al - because not only are you
utterly impervious to debate, but because you insist on trying to move
the goal posts.

Certainly it is a chicken and egg problem in terms of economics.

No, it's a solution in *search* of a problem.

That said, there are historical precedents in the aerospace industry where
the US government has pushed technology forward when it was deemed in the
best interests of the country. This has happened in both the military and
civilian aviation markets.

True, but it has not been demonstrated that orbital fuel depots
represent a capability in the best interests of the country.

D.
--
Touch-twice life. Eat. Drink. Laugh.

http://derekl1963.livejournal.com/

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

Jim Davis wrote:

Jeff Findley wrote:

LEO fuel depots keep a large part of the complexity in earth orbit
so that expensive hardware can be used for multiple missions

The flip side of this is that the expensive hardware *must* be used
for multiple missions. In fact, it must be used for a large number of
missions. An orbital propellant depot is a scheme that assumes a high
traffic level beyond LEO - far higher than any level that anyone is
willing to fund.

A point I had thought of, but didn't mention.

The alternative is throwing away long term cryogenic storage
hardware for each and every Mars mission. That's going to get
expensive as the number of missions increases.

Unfortunately, outside of the space advocacy community there is
little interest in increasing the number of Mars missions to the
point where an orbital propellant depot makes economic sense. You're
falling into the old "Build it and they will come" paradigm.

You're off target on that - his paradigm is to funnel money to
commercial operators without openly calling it a subsidy. But it
doesn't seem to have occurred to him that in order to be useful it
would require (as you correctly point out) a large number of Mars
flights.

D.
--
Touch-twice life. Eat. Drink. Laugh.

http://derekl1963.livejournal.com/

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

Derek Lyons wrote:
You're off target on that - his paradigm is to funnel money to
commercial operators without openly calling it a subsidy. But it
doesn't seem to have occurred to him that in order to be useful it
would require (as you correctly point out) a large number of Mars
flights.


I think he was mainly aiming this concept at the Moon, not Mars, in the
beginning.
The real killer though is orbit inclination.
It takes a _lot_ of fuel to change that very much, so everything taking
fuel to the depot must of necessity be launched into almost exactly the
same orbit.
You could do that with dedicated fuel tankers, but other countries
aren't going to start putting parasitic propellant payloads on their
rockets or the gear for docking and propellant transfer - as it weighs
so much that the total cost for launching a satellite with all the extra
stuff added goes right through the roof - particularly when they have to
shoot it into a non-optimal orbital inclination for their launch site,
and lose yet more payload that way.
If you were going to do this for a Mars flight, it behooves you to do it
with one or more giant rockets that could carry a lot of propellants at
a time rather than a whole pile of small rockets only carrying a little
propellant each, and still having to lug all the docking gear along.
Something along the lines of Sea Dragon would be needed, and carrying
large amounts of propellant into LEO was one proposed mission for it:
http://www.astronautix.com/lvs/searagon.htm

Pat