Solar-pumped laser power transmission, a way to dramatically decrease launch costs?
in [Physics]
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From: Brad Guth on 9 Mar 2010 16:10 On Mar 8, 1:46 pm, OM <o...(a)sci.space.history> wrote: > On Mon, 08 Mar 2010 11:43:08 -0600, Marvin the Martian > > <mar...(a)ontomars.org> wrote: > >McCall is a first class idiot. > > >The only way you don't win is if you don't killfile that jackass. > > ...Fred's the longest-standing resident in my killfile, having been > thrown in there *before* .history came into being. With the exception > of a few months where I'd given him a second chance at the urgings of > one other .history regular - a second chance he blew right out of the > starting gate as I predicted - that's a period spanning almost 20 > years, from the days when his lover's feud with Eric Chumpko derailed > .policy into the morass it's been ever since. > > Then again, I will point out that Mookie's got the same rep with a lot > of other people, and he's been sentenced to Killfile Hell for almost > as long... > OM > > -- > > ]=====================================[ > ] OMBlog -http://www.io.com/~o_m/omworld [ > ] Let's face it: Sometimes you *need* [ > ] an obnoxious opinion in your day! [ > ]=====================================[ You killfiled your own mother, so what's the big deal. ~ BG
From: Brad Guth on 9 Mar 2010 16:22 On Mar 8, 8:43 pm, Fred J. McCall <fjmcc...(a)gmail.com> wrote: > "J. Clarke" <jclarke.use...(a)cox.net> wrote: > > : > :Still nothing about costs. > : > :Show us the numbers, Marvin. > : > :All you've shown us is that you can improve gas mileage. You haven't > :shown that that is going to reduce costs significantly. > : > > He keeps dodging the fact that it is *NOT* the fuel costs that are > driving the cost to orbit (and beyond). Fuel costs are just a tiny > part of cost to orbit. The bulk of the cost is vehicle processing and > the vehicle itself. Those both drop with more launches. > > This rather explodes the 'plan' to spend preposterous amounts of money > to come up with a launch system that is cheaper by some amount of > fuel. > > -- > "Ordinarily he is insane. But he has lucid moments when he is > only stupid." > -- Heinrich Heine In other words, with you it's all or nothing gets improved. ~ BG
From: Brad Guth on 9 Mar 2010 16:27 On Mar 9, 12:16 am, OM <o...(a)sci.space.history> wrote: > On Mon, 08 Mar 2010 23:05:01 -0500, "J. Clarke" > > <jclarke.use...(a)cox.net> wrote: > >Still nothing about costs. > > ...This is a Mookie project. He expects costs to be nonexistent > because it's such a great project, people will volunteer labor and > materials for free, and even throw money into it just to be a part of > it. The only guy who's managed to even vaguely accomplish that kind of > financing is Jerry Lewis, and for all his insanity and ineptitude, > Mookie's no Jerry Lewis. > > OM > > -- > > ]=====================================[ > ] OMBlog -http://www.io.com/~o_m/omworld [ > ] Let's face it: Sometimes you *need* [ > ] an obnoxious opinion in your day! [ > ]=====================================[ That as a bad analogy, because Jerry Lewis still doesn't know how a toilet works. ~ BG
From: William Mook on 10 Mar 2010 11:54 On Mar 8, 5:50 pm, "J. Clarke" <jclarke.use...(a)cox.net> wrote: > On 3/8/2010 1:08 PM, Marvin the Martian wrote: > > > > > On Sun, 07 Mar 2010 12:50:27 -0500, J. Clarke wrote: > > >> On 3/7/2010 11:53 AM, Marvin the Martian wrote: > > >>> NASA has been looking into laser transfer of energy for propulsion > >>> since at least 1976. > > >>>http://hdl.handle.net/2060/19760014427 > > >> Yep, and it doesn't address the main driver in launch costs. > > >> All these schemes aimed at saving gas are worthless until gas is the > >> major cost driver. > > > Gas is the major cost driver? This isn't like driving a car, it has to do > > with the rocket equation, specific impulse of the fuel, and the > > percentage of the mass that can be driven to a given delta V. > > > Specific impulse being the change in impulse for a given weight of fuel, > > and it turns out to be the exhaust velocity of the gases out of the > > rocket. > > > The thrust, T = v * dm/dt, where v = g * I_sp and dm/dt is the rate at > > which mass leaves the rocket engine. However, the energy of dm at > > velocity v is dE = dm * v^2 /2 or power P = 1/2 v^2 dm/dt. That energy > > has to be in the fuel itself for conventional rockets. This limits the > > percentage of the mass of the rocket. Chemical fueled rockets top out at > > about an Isp =<450. > > > (Note the ratio T/P = 2/v) > > > IF you can get large amounts of power to the rocket from an external > > source, then: > > 1) You are not limited to reactive masses with a high I_sp. Any mass will > > do. > > 2) You can achieve a much higher exhaust velocity out of the rocket, > > which increases the payload to total mass of the rocket ratio. > > > So, this laser idea has some merit, and that's why NASA has been looking > > at it for some time. > > > It isn't about 'saving gas'. It is about physics. > > Seven paragraphs, not one of which addresses its actual effect on launch > costs. Nice try at a straw man. Dude, http://ocw.mit.edu/OcwWeb/Aeronautics-and-Astronautics/16-885JFall-2005/CourseHome/ Call the CO-OP and ask to get a copy of the textbook and notes, and then take a look at the open courseware. You will see that the cost of flight hardware is a function of structural mass, and the cost of launch infrastructure is a function of take off weight. Let's do an example calculation. Lets say we want to send payloads to the moon and back on a regular basis. This means we've got to carry our payloads through a delta vee of 18 km/sec. Let's say we do this with six stages. Lets also say structural fraction is 10% of total weight. We have two systems A hypergolic system with a 3.0 km/sec exhaust speed A jetfuel lox system with a 3.5 km/sec exhaust speed A liquid hydrogen lox system with a 4.0 km/sec exhaust speed. Six stages and 18 km/sec per stage, is 3 km/sec per stage. Propellant fractions 0.632120558828558 0.57562715432305 0.527633447258985 Add 10% structural fraction 0.732120558828558 0.67562715432305 0.627633447258985 Subtract to get payload fraction per stage 0.267879441171442 0.32437284567695 0.372366552741015 Invert to get multiplier per stage 3.73302257025391 3.08287211253164 2.68552584177858 Raise to the sixth power to get ratio between payload and launch weights 2,706.22370781451 858.485679409479 375.125005394878 Multiply by the payload weight (60 tonnes in this case) to get total take off weight 162,373.422468871 51,509.1407645687 22,507.5003236927 Multiply by 10% to get structure 16,237.3422468871 5,150.91407645687 2,250.75003236927 So, our vehicle will cost $160 billion if we use the less efficient fuel, and $22.5 billion if we use the more efficient fuel in the list. The cost of the launch center will be equal to about twice the cost of one of the vehicles. A fleet of five vehicles and launch center will cost about 7x the cost of one vehicle - and you're right, the cost of propellant is nil compared to this. Reuse the vehicles 10,000x - the same as airplanes - we we have a cost of $2.2 million to $16.0 million per launch. At 60 tonnes payload, this gives the cost of carrying out this mission. See how that works? Its not the fuel per se, but the cost of building a structure to handle it and use it. THATS WHY we want to reduce the amount of fuel used.
From: William Mook on 10 Mar 2010 14:57
The three propellant combinations I used in the example above indicate the importance of exhaust speed. Six stages to get from Earth to Moon and back are problematical if we leave some stages on or around the moon - which means they're only used once, or refueled and flown back. It would be nice to have them all come back to be reused. A minimum energy transfer orbit takes 3 to 4 days - so a round trip takes a week or more. This limits the number of flights to 50 per year. So, 1,000 flights would take 20 years or more to fly off. 10,000 flights would take 200 years - all of which means more has to be charged per flight cycle since dollars earned in later years are worth less than dollars earned today - showing how costs and flight rate are related in one way. There are others. Increasing flight speed just a little lowers flight time to the moon to 18 hours. Which makes a round trip of two days possible. Which means 150 flights per year - which means 1,500 in 10 years and 10,000 in 60 years. Contrast this set of vehicles with a really improved vehicle system. Something like a nuclear pulse rocket, or perhaps a laser pulse rocket, that operates with an exhaust velocity of 20 km/sec. We still have the same 18 km/sec delta vee requirement but we use only one stage because we have an exhaust speed far higher than the delta vee. Propellant fraction is 0.593430340259401 Propellant plus structural fraction of 10% is 0.693430340259401 Payload fraction is 0.306569659740599 Which makes take off weight divided by payload weight equal to 3.26190139248007 So, for a payload of 60.0 tonnes we have a take off weight of 195.714083548804 And with a structural fraction of 10% we have an empty vehicle weight of 19.5714083548804 Which means a vehicle cost of $200 million a launch center cost of $400 million and a fleet of five combined with a launch center of $1.4 billion. Clearly, an R&D effort to develop laser propelled vehicles or nuclear pulse vehicles of this size if it cost substantially less than $20 billion would be better than building bigger systems. In fact, if we could develop laser pulse or nuclear pulse for $10 billion and spend $10 billion on vehicles and infrastructure, we could take the $8.6 billion and build a fleet of 43 ships, or alternatively, build LARGER ships - say ones with a 300 tonne payload for $1 billion each - and a launch center to handle them. |