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PostPosted: Sep 23, 2014 11:54 am 
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There are two short term improvements to GEO launches cost wise:
1 - All electric satellites or ion thrusters instead of chemical ones. In this case the booster only needs to place the GEO bird on a LEO orbit, and the ion thruster takes the bird into GEO orbit (takes about 6 months). This allows the current Falcon 9 v1.1 rocket that has a GTO payload around 4.8 tons but can loft a 15 ton payload to LEO instead. So the same launch costs for a medium GEO bird into GTO (1800m/s DeltaV to GEO) would allow for a dual large bird (2x6 tons) with the ion thruster doing the balance of the work (and still some DeltaV left)
2 - Both SpaceX and Reaction Engines Skylon designs promise large reductions in payload to orbit costs:
Skylon is probably 10 years away, with a single-stage-to-LEO fully reusable launcher (using a hybrid air breathing / rocket engine capable of accelerating to Mach 5.5 in air breathing mode before transitioning to rocket mode, vastly reducing the mass of oxygen needed for the whole trip).
SpaceX Raptor MetaLox engine (Liquid Methane + Liquid Oxygen) is designed from the get go for full reusability, although a two stage rocket. The first stage reuse is already being tested on F9v1.1 (splashdown already demonstrated after a hover for a few seconds just above sea level). They are likely less than one year from landing the first stage in terra firma, and probably 2-3 years from demonstrating the second stage reentering and landing too. But the kicker with the Raptor based rockets is they will be designed for full reusability from the onset, using engines designed for 100 flights.
There are always more of science projects with novel ideas. Skylon claims to have no scientific innovations required to succeed, its just engineering challenges. Skylon goals are soo far from today's rockets that many don't think its possible.

Any kind of rail launcher system doesn't make much sense, unless you could accelerate a few hundred tons to Mach 3, otherwise the gain isn't enough the trouble. Even Mach 3 at sea level is still less than 10% of the total effort to reach orbit (7.8km/s or 28000km/h) considering altitudes of at least 200Km are also needed.

Nuclear thermal rockets would change the whole outlook, but if people are so afraid of a reactor firmly attached to land, I just don't think an operational nuclear reactor going up is a logical option. Even a NTR second stage is an unlikely proposition.

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PostPosted: Sep 23, 2014 1:27 pm 
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@Kirk Sorensen
Thanks Kirk for the demonstration of what is involved in actually getting something into orbit. At best, our magic EM gun might just save us some rocket fuel, and it's sounding like not all that much rocket fuel.


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PostPosted: Sep 23, 2014 1:34 pm 
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macpacheco wrote:
Nuclear thermal rockets would change the whole outlook, but if people are so afraid of a reactor firmly attached to land, I just don't think an operational nuclear reactor going up is a logical option. Even a NTR second stage is an unlikely proposition.


Forget anti-nuclear opinions. Nuclear thermal rockets are just a supremely bad idea:

SSTO is a bad idea, but NTR SSTO is worse


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PostPosted: Sep 23, 2014 2:06 pm 
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Kirk Sorensen wrote:
macpacheco wrote:
Nuclear thermal rockets would change the whole outlook, but if people are so afraid of a reactor firmly attached to land, I just don't think an operational nuclear reactor going up is a logical option. Even a NTR second stage is an unlikely proposition.


Forget anti-nuclear opinions. Nuclear thermal rockets are just a supremely bad idea:

SSTO is a bad idea, but NTR SSTO is worse

SSTO using normal rocket engines really doesn't work. But using Skylon hybrid Sabre engine, it's a completely different ball game.
HydroLox based rockets largest weight is the LOX (one oxygen atom for each two hydrogen, or about 8x heavier). With Skylon hybrid, far less LOX is needed, which permits carrying far more LH2. Like 2/3 less LOX. Mach 5.5 @ 80 thousand feet before transitioning from air breathing to rocket mode is a lot of oxygen saved.

If you want to criticize Skylon, read about it first. Don't generalize SSTO using conventional rockets with Skylon.

Plus Skylon is also a hybrid airplane / rocket. Takes off and land on a (very long) runway. Its design is optimized to make it very light on re-entry and landing, so its TPS is much lighter compared to the Shuttle, the lighter you are, the slower re-entry will be, hence lower temps to dissipate. Using wings to help climb instead of thrust only also saves lots of H2 too.

The question about Skylon isn't the basic premises they set out to accomplish, but instead if they can overcome all engineering challenges. Some very smart people have been working on this for years. It's been discussed at length on nasaspaceflight.com, and so for I'm yet to see an engineering argument why it won't work, but rather that the challenges are daunting.

The Sabre engine compress incoming air up to pressure high enough to match LOX pressure inlet on a rocket engine. They use an extremely advanced heat exchanger to cool down the high pressure air (using a helium loop and cold temps from the LH2). So in the end, they just inject enough air so there's enough O2 to combust the H2 in the rocket engine. The end of the Sabre engine looks much like a regular rocket engine, it's the precooler work that is the magical part of the design.

Its been over 6 months since I studied this stuff, so I won't try to explain the whole thing. Just enough its clear Skylon SSTO isn't a bad idea, it's a genious idea, if they can overcome all the engineering challenges. The SABRE engine is being tested for over a year on the stand.

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Last edited by macpacheco on Sep 23, 2014 2:19 pm, edited 2 times in total.

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PostPosted: Sep 23, 2014 2:12 pm 
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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.


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PostPosted: Sep 23, 2014 2:51 pm 
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The last time I looked, Skylon & etc. have issues with the mass-fraction associated with landing gear and wings. In Skylon's case, the leading-edge cooling is also an issue.

The laser launch people are pretty interesting these days. The efficiency of semiconductor lasers is now above their (optimistic) lower limits. Of course, this approach lets one leave the fuel at home, and still get a reasonable launch profile.


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PostPosted: Sep 23, 2014 3:07 pm 
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Cyril R wrote:
What way to go?


Air launched LH2/LOX reusable rocket followed by momentum-exchange tether. That is the way to go.


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PostPosted: Sep 23, 2014 6:17 pm 
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Kirk Sorensen wrote:
Use a momentum-exchange, electrodynamic-reboost (MXER) tether system to propel satellites from LEO to GTO. This will cut initial mass in LEO in half. It's fully reusable and uses solar power to restore orbital energy to the system after each use.
While you are at it, use KITE/HASTOL to launch to LEO. Maybe KITE/HSH would be better.

KITE: . . . . Kinetics Interchange TEther
HASTOL: . . Hypersonic Aircraft, Space (Spinning) Tether, Orbital launch
HSH: . . . . .Hypersonic Sky Hook

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PostPosted: Sep 23, 2014 10:00 pm 
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Kirk Sorensen wrote:
Cyril R wrote:
What way to go?


Air launched LH2/LOX reusable rocket followed by momentum-exchange tether. That is the way to go.


I read your work on MXER, nice job and it looks great on dramatically reducing the total fuel load you need to carry to get to GEO.

Just wondering though if Cyril's idea of using an EM launch system coupled by a boost from a pulse engine on the launch vehicle would get payloads to LEO even cheaper by reducing the amount of all up weight to begin with.

I don't think it's feasible to have an EM gun alone in anycase, but a multiple stage system all designed to reduce fuel load might be a good idea.

EM launcher (reduce zero to launch velocity) > onboard engine (reduce EM barrel exit velocity and reach LEO) > MXER (reduce fuel load to reach GEO)

The question is: roughly how much fuel-weight would be saved getting things to LEO vs getting things from LEO to GEO? I had imagined that the fuel requirements for ground to LEO would be pretty hefty given atmospheric resistance, but I have less of an idea of gravitational effects on objects between sea level to LEO and LEO to GEO.

If the fuel requirements for getting to LEO is just a fraction of LEO to GEO, then an EM launcher is simply not cost effective.


Last edited by bensoon on Sep 24, 2014 2:31 am, edited 1 time in total.

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PostPosted: Sep 24, 2014 1:03 am 
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After some more searching I have to concede Kirk is probably right. It looks like cost to LEO is a small fraction of cost to GEO. So, in terms of low hanging fruit first (cut launch cost the fastest), little is to be gained by shooting stuff to LEO and then using rockets to GEO.

This cannon ball approach would only make sense if we could shoot roughly to GEO and the only need modest power for fine positioning. (actually I like to think of it as a machine gun approach because we'd fire many smaller cargo packs in sequence).

If that isn't feasible, Kirk's approach of H2/LOX rockets to LEO and then innovative solution for GEO makes a lot more sense. Still have to make the tether which sounds really expensive?


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PostPosted: Sep 24, 2014 2:33 am 
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Cyril R wrote:
After some more searching I have to concede Kirk is probably right. It looks like cost to LEO is a small fraction of cost to GEO. So, in terms of low hanging fruit first (cut launch cost the fastest), little is to be gained by shooting stuff to LEO and then using rockets to GEO.

This cannon ball approach would only make sense if we could shoot roughly to GEO and the only need modest power for fine positioning. (actually I like to think of it as a machine gun approach because we'd fire many smaller cargo packs in sequence).

If that isn't feasible, Kirk's approach of H2/LOX rockets to LEO and then innovative solution for GEO makes a lot more sense. Still have to make the tether which sounds really expensive?


But the tether sounds way less expensive than the 'ground to space' elevator


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PostPosted: Sep 24, 2014 5:37 am 
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bensoon wrote:
Cyril R wrote:
After some more searching I have to concede Kirk is probably right. It looks like cost to LEO is a small fraction of cost to GEO. So, in terms of low hanging fruit first (cut launch cost the fastest), little is to be gained by shooting stuff to LEO and then using rockets to GEO.

This cannon ball approach would only make sense if we could shoot roughly to GEO and the only need modest power for fine positioning. (actually I like to think of it as a machine gun approach because we'd fire many smaller cargo packs in sequence).

If that isn't feasible, Kirk's approach of H2/LOX rockets to LEO and then innovative solution for GEO makes a lot more sense. Still have to make the tether which sounds really expensive?


But the tether sounds way less expensive than the 'ground to space' elevator


Also much safer - tether can be made to burn up upon entering the lower atmosphere if things go badly wrong somehow.

But, less expensive than a space elevator isn't saying much. We need a decent order of magnitude cost estimate, in $.


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PostPosted: Sep 24, 2014 6:05 am 
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For those who are interested

http://www.nasaspaceflight.com/_docs/MX ... Report.pdf

Kirk, hope you don't mind me linking your report ;-)


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PostPosted: Sep 24, 2014 11:40 am 
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For the pro SSTO (Single Stage To Orbit) folks: http://www.jerrypournelle.com/slowchange/SSX.html and somewhat related: http://www.jerrypournelle.com/reports/j ... space.html

The first link has the equations and numbers for those who enjoy plowing through them. I fear that I'd have to print out both Kirk's work and Jerry's work to see how they reach opposite conclusions, but it is easier to just watch SpaceX and the others actually accomplish it :lol:


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PostPosted: Sep 24, 2014 9:44 pm 
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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.


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