NASA Ames’ Worden reveals DARPA-funded ‘Hundred Year Starship’ program
kurzweilai.net
kurzweilai.net
"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.
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.
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.
Each launch enables a one-way trip to or from Mars.
... 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?
On the other hand, this doesn't make blowing stuff up efficient. An explosion, unless it's lensed properly, will push mass equally in all directions.
But I linked that mainly for the table just down the page a little comparing various efficiency measures of different propulsion systems. I'm pretty sure that chemical rockets are the least efficient we've ever implemented or imagined, barely sufficient for travel within the solar system, and certainly not efficient enough for any trips, round or one-way, beyond our solar system.
You always want to have an exhaust velocity as high as possible. The energy you have to impart to the exhaust is 1/2 mv^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.
The 1/2mv^2 vs mv 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).
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...)
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...
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.
You know what else we don't see, Director Worden? Human Teleportation. And Klingons.