

NASA Ames’ Worden reveals DARPA-funded ‘Hundred Year Starship’ program - cwan
http://www.kurzweilai.net/nasa-ames-worden-reveals-darpa-funded-hundred-year-starship-program?utm_source=twitterfeed&utm_medium=twitter

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robin_reala
Interesting quote:

 _"Larry [Page] asked me a couple weeks ago how much it would cost to send
people one way to Mars and I told him $10 billion, and his response was, ‘Can
you get it down to 1 or 2 billion?’ So now we’re starting to get a little
argument over the price.”_

Larry is currently listed on Forbes as being worth $14b, so $1b really isn’t a
huge amount of his total cashpile.

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mbreese
But it was a one-way trip... I assume a trip there and back would be a tad bit
more (2-5X).

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JanezStupar
Unlikely...

IMHO designing a system that would enable a pretty good odds of coming back
would be at least an order of magnitude more expensive than a similarly
reliable one way system.

Think of all the additional R&D and engineering difficulties involved in
keeping a human alive long enough to get there, do something there come back
and survive.

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drats
More to the point, what's the cost of a Moon base - where a return and even a
rescue is feasible - AND a one-way extensive robotic exploration of Mars. It
just seems an overly dramatic waste (there will be no shortage of people
willing to go) to send people to die on Mars when we can get the same off-
Earth habitation expertise and Mars scientific data for the same price or
cheaper.

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gaius
The thing with Mars is, once you're on the surface, you can manufacture fuel
for the return trip in-situ. Dr Robert Zubrin covers this in his Mars Direct
mission blueprint.

<http://en.wikipedia.org/wiki/Sabatier_reaction>

And you get oxygen to breathe _for free!_ The Mars Direct plan calls for the
initial deployment of an unmanned mission to set up a fuel station on the
surface - then unmanned missions to cache supplies there - and only when you
have enough stuff pre-deployed for the return trip and/or a permanent
presence, send humans.

The moon may be closer, but until you have a working fusion reactor, there's
not much you can usefully do there in terms of resource extraction.

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jasonmorton
I find it somewhat astounding how much we are still reliant on blowing stuff
up whenever we want to go fast. At least this is being somewhat mitigated on
land with electric cars. I'll venture that we won't see any deep improvements
in space propulsion until we get a better (i.e. quantum) understanding of
gravity. However this beaming power idea is interesting.

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kiba
What's wrong with _blowing stuff up_?

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SkyMarshal
Inefficient.

[http://en.wikipedia.org/wiki/Spacecraft_propulsion#Power_use...](http://en.wikipedia.org/wiki/Spacecraft_propulsion#Power_use_and_propulsive_efficiency)

~~~
lutorm
I didn't think this through all the way, but something seems fishy about that
article:

 _... if the exhaust velocity can be made to vary so that at each instant it
is equal and opposite to the vehicle velocity then the absolute minimum energy
usage is achieved. When this is achieved, the exhaust stops in space [1] and
has no kinetic energy; and the propulsive efficiency is 100%_

This argument is not Galilean invariant, which makes it seem highly dubious to
me. There is no "stopping in space"; what absolute inertial frame defines what
"stopped" means?

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alphaBetaGamma
You are right, this is plain wrong.

You always want to have an exhaust velocity as high as possible. The energy
you have to impart to the exhaust is 1/2 _m_ v^2, but you get m*v momentum. So
small exhaust mass at very high speed will give you the same momentum, and
cost you much less energy than bigger mass and less speed.

~~~
alphaBetaGamma
Sorry, this I'm completely wron... I mean: I was testing if you read the
comments before upvoting.

The 1/2m _v^2 vs m_ v points to an exhaust speed as _low_ as possible, to get
as much momentum as possible from as little energy expenditure as possible.

Now, if your exhaust comes from the outside world then that makes perfect
sense. And this is why you have turboprop and turbofan engines: you slow down
the exhaust of the turbine, speed up outside air, and do a favorable
energy/momentum trade.

But in space you have to carry the mass you will exhaust. You don't have much
choice: all the energy you get from burning fuel will be transfer to kinetic
energy of your exhaust (in the reference frame of the rocket).

~~~
lutorm
Yeah, you're right. A bit of algebra reveals that your delta-V per MASS of
fuel (which is a frame-independent quantity) goes as the (propellant specific
chemical energy)^.5.

However, it is also true that if you calculate the delta-V per unit propellant
ENERGY used, it decreases with the propellant specific energy.

Since you don't really care about how much energy you carry but only about how
much fuel you need to use per delta-V, it's always better to have higher
exhaust energy. (As long as you are using a chemical propellant, i.e. the mass
carrying the energy and the reaction mass are the same.)

The statement in the article about "propulsive efficiency" is total bogus.
First: the relative kinetic energy of the rocket and the exhaust IS a frame-
dependent quantity, so it's meaningless. Second, any reasonable measure of
efficiency, like the delta-V per fuel energy, reveals that the "optimal" value
is an exhaust velocity of zero. (Optimal in the sense that it's more energy
efficient, but only because the delta-V goes to zero slower than the energy.
It's still a useless optimum, because it results in no delta-V at all...)

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VladRussian
somehow reading that, i'm more and more sure that i'll be Branson not Worden
who gets us to Mars. I'm not a "free market" zealot, and it isn't about how
Branson is good, it is more about how Worden is bad.

There is also Musk, whose drive to change things makes me awe in respect
(while his technical decisions may be debatable, the most important thing here
is that he actually DOES things). Google guys got the money, and if they still
have the same drive...

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charlesdm
Pretty interesting. I'm sure a lot of people would be interested in a one way
ticket to Mars if we could somehow make it livable over there.. I know I am!

~~~
protomyth
It's not like a one way trip is unprecedented in human history. Many of the
Europeans coming to North America did it one way to conditions that were very
much more primitive than the old world.

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athom
For those Europeans, there was still the option of turning it into a round
trip. Granted, it was probably an expensive and arduous option, and required a
ship in port ready and willing to take you, but it was there.

Right now, a one-way trip to Mars _really is_ a one-way trip. That is, until
we can put enough provisions up there to get a ship back out of that gravity
well.

And keep the occupants alive long enough to get back here.

~~~
protomyth
Some Europeans had the option. Many had a literal one way trip (no money /
resources or the whole go-to-new-world-or-go-to-jail thing).

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pshapiro
I wonder what kind of electric propulsion they're working on....

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rdj
Interesting ideas. I just can't get past the fact the a Director as NASA
actually said, "Anybody that watches the [Star Trek] Enterprise, you know you
don’t see huge plumes of fire". As if, instead of drawing from science fiction
as inspiration, he uses it as a blueprint.

You know what else we don't see, Director Worden? Human Teleportation. And
Klingons.

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neilc
I think he was just using it as an example that would be familiar to the
audience.

