Solar-pumped laser power transmission, a way to dramatically decrease launch costs?
in [Physics]
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From: Scott M. Kozel on 15 Feb 2010 22:52 OM <o...(a)sci.space.history> wrote: > > "Scott M. Kozel" <koze...(a)comcast.net> wrote: > > >I can see that you have put a lot of thought into this > > ...Most of it the result of years of substance abuse, especially > sniffing paint fumes from a paper bag while high on really poorly made > acid. I asked about the temperature at 2 million miles from the Sun, because I wonder if there is any substance that would not melt if that close. Mercury at 35 million miles is 800 F ... at 2 million miles it might be hot enough to melt tungsten ... i.e. a satellite would melt or maybe even vaporize long before it got that close. "The metal with the highest melting point is tungsten (W) at 3410 degrees Celcius (6170 degrees Fahrenheit). However, technically Carbon has a higher melting point, though not under normal atmospheric conditions. This is because it sublimates (turns directly from a solid to a gas) at 6740 degrees Fahrenheit under normal circumstances." http://wiki.answers.com/Q/What_metal_element_has_the_highest_melting_point ....... "The Sun is the most prominent feature in our solar system. It is the largest object and contains approximately 98% of the total solar system mass. One hundred and nine Earths would be required to fit across the Sun's disk, and its interior could hold over 1.3 million Earths. The Sun's outer visible layer is called the photosphere and has a temperature of 6,000°C (11,000°F). This layer has a mottled appearance due to the turbulent eruptions of energy at the surface." http://www.solarviews.com/eng/sun.htm The Sun itself has a diameter of 0.84 million miles.
From: Pat Flannery on 16 Feb 2010 03:12 Scott M. Kozel wrote: > > Mercury at 35 million miles is 800 F ... at 2 million miles it might > be hot enough to melt tungsten ... i.e. a satellite would melt or > maybe even vaporize long before it got that close. The radiation flux at that distance is going to be ferocious also. You would be well inside the Sun's corona, and the first time a major flare erupted underneath it it would be like sticking it inside of a nuclear reactor. At least as of 2008, JPL was planning to send a spacecraft to 4.1 million miles from the Sun's surface, and just designing that was driving them nuts: http://www.astronomy.com/asy/default.aspx?c=a&id=6917 > "The metal with the highest melting point is tungsten (W) at 3410 > degrees Celcius (6170 degrees Fahrenheit). However, technically Carbon > has a higher melting point, though not under normal atmospheric > conditions. This is because it sublimates (turns directly from a solid > to a gas) at 6740 degrees Fahrenheit under normal circumstances." Temperature at 4.1 million miles is 2,160F according to the above article, so assuming halving the distance increases the temperature four times over (I think that's how it works, though the large solar radius may screw this up; it's going to at least double) that makes the temp it could be facing over 8,000 F. So unless you are building it out of Larry Niven's Puppeteer Hull Metal... another problem at this distance is that you aren't going to be orbiting it in vacuum, but rather in the very thin superheated gas of its outer atmosphere. That's going to generate drag on the solar array, and given its extremely high orbital velocity it's probably going to end up falling into the Sun in fairly short order. Pat
From: Pat Flannery on 16 Feb 2010 06:55 Fred J. McCall wrote: > : > > No. You've engineered a vehicle when you can take your data package, > hand it to a bunch of metal benders, and get back a working vehicle > that performs approximately as you claimed it would. > > You're not even close. Consider the plumbing on all those tiny engines at the base of its three stages sometime; that's going to probably weigh a bit, isn't it? :-D When Henry Spencer was discussing his 100+ RL-10 engined SSTO design, I tried to figure out how to do the plumbing to all of those also, and it was no treat from the weight point of view either. Where exactly are the turbopumps on Mook's design? You sure can't see them in the drawings. Pat
From: Pat Flannery on 16 Feb 2010 07:55 Pat Flannery wrote: > Consider the plumbing on all those tiny engines at the base of its three > stages sometime; that's going to probably weigh a bit, isn't it? :-D > When Henry Spencer was discussing his 100+ RL-10 engined SSTO design, I > tried to figure out how to do the plumbing to all of those also, and it > was no treat from the weight point of view either. I maybe shouldn't have described it as "his" design, as it was a design that came out of the post Challenger loss years; but he thought it was a good one. When you think about it, there's only one way you can do the propellant feed system for all those engines, each with its own turbopumps, to keep weight minamized. You have to mount them in a concentric series of rings, each ring having fewer engines in it. Outside the outer ring sits a toroidal pipe that feeds LOX to the outer engines, inside of them sits a another toroidal pipe that feeds LH2 to both that ring and the next ring in; then another LOX feed pipe ring that feeds the LOX outwards to ring two of the engines and inwards to ring three, and so on till you reach the center. Each RL-10 sits between two propellant rings, getting fuel from one side and oxidizer from the other. There's no other way of doing it that's lighter in weight. Although this is workable from a structural point of view, one has to ask oneself if you really want to be using over one hundred individual turbopumps on a single booster from both a weight and reliability point of view, when a few larger ones could provide propellants to all of the combustion chambers - making them each far cheaper to build and far lighter in weight, as well as individually less prone to malfunction during operation. That, and his argument that what a individual rocket engine consisted of was one combustion chamber, no matter if several combustion chambers were connected to a single turbopump (by that standard, my 1969 Dodge Charger was powered by eight individual engines, as it had eight individual cylinders...combustion chambers...hooked up to one fuel pump...fuel feed...and carburetor...oxidizer feed) was when I started to drift away from the concept of "Spencer Infallibility". :-) Pat
From: Pat Flannery on 17 Feb 2010 01:28
Alain Fournier wrote: > Yes the large solar radius does screw this up. The correct way to compute > this is to measure the solid angle that the sun covers at a given distance. > For something far away, when you double the distance the solid angle > is divided by four. But when you are close to the sun the the squaring > law no longer applies. Very close to the surface of the sun, the > temperature > will basically be constant, because whether you are 100 km from the surface > or 200 km makes little difference, the sun basically fills half the sky > in both cases. What makes it tricky to figure out is that this isn't just a case of the object in orbit being bombarded by the sunlight and heating up that way, but it actually being in the tenuous outer atmosphere of the Sun. At its hottest points the corona can get up to between 8 and 20 million degrees Kelvin. Pat |