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PostPosted: Sep 25, 2014 5:07 am 
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bensoon wrote:
But the tether sounds way less expensive than the 'ground to space' elevator
And three of them can be cheaper still, subsonic to hyper, hyper to LEO, and LEO up.

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PostPosted: Sep 25, 2014 7:20 am 
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Kirk Sorensen wrote:
Jim L. wrote:
I fear that I'd have to print out both Kirk's work and Jerry's work to see how they reach opposite conclusions,


My analysis is much more sophisticated than Pournelle's.

bensoon wrote:
Kirk, hope you don't mind me linking your report


Not at all. It just makes me sad to look at it and think of all the years wasted at NASA when I should have been working on LFTR.


Nothing is ever wasted Kirk, the things we learn all contribute to what we are today. I could say the same thing about my 13 years in the Airforce, but I know better than to discount the value of what I've learned and the people I've met :-)


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PostPosted: Sep 30, 2014 2:06 pm 
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Cyril R wrote:
So, could you tell us if the calculus changes if you have a low energy and variable cost way to launch and you have a relatively low frontal area (thin) cargo?


Assuming 9km/s to launch, and E=1/2mv^2, then E = about 10KWh/kg.

You could pay German electricity prices and still your energy only costs €2.50 per kg, compared to today's launch costs of about $10,000. Free electricity makes little difference.

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What if we shoot the cargo capsule at the right angle to get the required velocity (for geosynchronous orbit) and orbit altitude all in one go (with minor adjustment rockets on the cargo)?


You could launch straight up at 10km/s, but not much could survive that.

A more promising approach might be to aim for a Mach 5-10 launch from a mountain top, and then fire the rockets. A hybrid approach.

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Quote:
There's a good reason we use rockets to get things into space instead of things like big EM guns or whatever speculative device you wish to imagine.



The reasons might change with higher volumes. These speculative devices work best at a launch a day or so.


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PostPosted: Sep 30, 2014 4:30 pm 
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Quote:
Assuming 9km/s to launch, and E=1/2mv^2, then E = about 10KWh/kg.

You could pay German electricity prices and still your energy only costs €2.50 per kg, compared to today's launch costs of about $10,000. Free electricity makes little difference.


Yes I understand energy is a small fraction of space launch cost (even with conventional rockets). But if the propulsion hardware is all on the ground, the rocket becomes very light. That is where the main savings would be. The propulsion hardware on the ground would have low variable cost so it pays to have this system operate round the clock.

Might be some kind of cargo shooter that shoots little needle like rockets into roughly geosynchronous orbit.

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You could launch straight up at 10km/s, but not much could survive that.

A more promising approach might be to aim for a Mach 5-10 launch from a mountain top, and then fire the rockets. A hybrid approach.


Straight up is no good, we need over 3 km/s orbital speed. But if we start at a 6 km elevation maybe we can shoot stuff to geosynchronous orbit from there? A hybrid would work only if the rockets are really light. Otherwise don't bother the with the accellerator on the ground in the first place.


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PostPosted: Sep 30, 2014 7:45 pm 
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A MXER tether could provide half of the orbital energy needed for the trip to geosynchronous transfer orbit. A more speculative system based on stronger materials could conceivably provide three-quarters of the total orbital energy, all in a fully reusable system that involves accelerations on the order of 2 gees.

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PostPosted: Sep 30, 2014 8:02 pm 
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None of these technologies is likely to provide cheap enough orbital costs to actually significantly increase the use of spaceflight though.

Most of the businesses that the satellite industry was built on are being crushed by the proliferation of fibre and cellular networks.
About the only business likely to expand if launch costs drop are military adn civilian governmental missions like exploration.

Only a theoretical full tether could provide costs low enough to actually make a spacefaring civilisation.


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PostPosted: Jun 18, 2015 11:56 am 
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Cyril R wrote:
So we need an accellerator that can get to 8 km/s. Darn, there goes my idea of gentle G linear accellerators... 8 km/s is pretty serious. Either this becomes a circular accellerator or we have to design precision robots that can take serious G. What way to go?

3000 kg seems high to me though. If we can make 300 kg work it will be quite useful already.


From my limited knowledge and back-of-the-envelope study, the biggest problem with accelerators is "https://en.wikipedia.org/wiki/Max_Q". Man-rated launches have AFAIK always had a high initial launch acceleration, then reduced thrust to stay below the design loads (and leading edge temps) until atmospheric density is low enough, then back to fast acceleration. For these reasons, I could not come up with a complete replacement for a man-rated first stage using 10G. A 10G coilgun launcher with an exit at 18,000 feet and a track length of somewhere around 100 km was about the best you could do. But a somewhat larger "second stage" would probably still be cheaper than the standard 1st plus 2nd, with a lot more design options - flyable 2nd stage?

[edit]I should have mentioned that I like MXER but haven't looked at the potential of an accelerator + MXER.


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PostPosted: Jun 18, 2015 12:32 pm 
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E Ireland wrote:
None of these technologies is likely to provide cheap enough orbital costs to actually significantly increase the use of spaceflight though.

Most of the businesses that the satellite industry was built on are being crushed by the proliferation of fibre and cellular networks.
About the only business likely to expand if launch costs drop are military adn civilian governmental missions like exploration.

Only a theoretical full tether could provide costs low enough to actually make a spacefaring civilisation.


As someone involved in the "New Space" paradigm (I resist calling it a movement), I'll agree that those are issues but assert that you should not discount recent transformations in all aspects of space launch economics. The primary drivers will be new markets and technologies, not expansions of existing ones.

Space tourism looks to be the first big new suborbital space application, albeit initially mostly suborbital. Virgin Galactic has bookings with deposits sufficient to run full flights for at least seven years. XCOR has a similar booking status. Robert Bigelow (Budget Hotels) has committed a billion dollars to making orbital tourism a viable business - he has an interesting space-nut story, and now he's making his dream a reality.

(Notice that Ferrari, McLaren, BMW, Bugatti, several other companies and now Ford GT are all making supercars that cost as much as the projected cost of a trip to a Bigelow space hotel, and multi-year production schedules of those cars are sold out usually before the first one hits the street. The money is out there!)

Economic estimates of space business show an inverse geometric ratio between cost and market size, i.e. a reduction by 50% generates a 4X market size. Nearly all of this growth is new markets. A speculative example - using Atlas or Delta rockets, Planetary Resource's asteroid mining venture does not pencil out at all, but using the Falcon it does, especially once the first stage recovery system becomes viable. This market expansion matches that of the growth of electronics (and electronic engineers!) over the 20th century.

Today we are benefitting from a huge transformation in enabling technologies including launch technologies, nanosats, computing and electronics, ion thrusters, and 3D printing. Your smart phone has performance numbers comparable or exceeding that of supercomputers of the 1980s, using the power from a small battery. We now have high schools launching satellites, piggybacking on spare space in NASA launches. So a huge cadre of global entrepreneurs can now afford to do space-related experiments and engage in creative destruction. A friend of mine has a very good design for an orbiting computing node that is designed to 'live' in swarms in the Van Allen belt, and replace the huge facilities of Google and Facebook - today we have at least two ultra-high-speed computing technologies that are almost completely immune to cosmic rays and radiation of all kinds.


The Boeing 702SP, https://en.wikipedia.org/wiki/Boeing_702, has completely replaced rocket thrusters with ion thrusters. These satellites take a lot longer to accelerate up to their GEO locations, but once there are expected to last at least twice as long as their predecessors. The lifespace of commsats has been very much limited by their available fuel for station keeping. IntelSat makes IIRC revenue of over $100 million per quarter on each satellite. Launch costs are also being reduced by at least 1/2, which will also tend to extend this economic model for a while.

My group (Space Finance Group, http://spacefinancegroup.com - also see http://integratedspaceanalytics.com) is actively engaged with a number of New Space companies that have viable business models based on new space-based technologies.

Having said all that, despite the fact that one of my friends is one of the most active Space Elevator entrepreneurs, I don't think it's going to happen on Earth or the Moon in the next several decades if ever.


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