Next-Generation launch technologies achievable with CURRENT technology

[sndrtj]

The closest thing on the list to being feasible with current technology is actually the magnetic launch-assist tube: which we've had the technology to build since at least the 1980's...

SpaceX's resuable vehicle has some problems with steep hypersonic re-entry on the lower stage, and even higher-energy re-entry on the upper stage from orbital velocity...

Nonetheless, both of these technologies (SpaxeX-style reusable launch vehicles, and magnetic launch-assist tubes) are perfectly doable with today's technology.

Sometimes you have to spend a lot of money (i.e. building a huge launch tube) in order to save a lot of money (i.e. drastically cutting the cost of getting things to orbit).

Obviously none of these things have actually been built yet, even if we already have the technology- or we wouldn't be talking about them as possible instead of existing launch systems. But just because something HASN'T been done with today's technology *doesn't* mean it CAN'T be done with today's technology...

Regards,

Northstar

That the technology exists doesn't mean it's practical. A SpaceTram would have to be launched out of a mountain at least 7km high. AFAIK, those only exist in the himalayas. Most certainly not in Europe. Try getting a mega-engineering project to work in the highly politically unstable himalayas. On top of that, the tube must be at least a 100 km in length, unless one utilizes truly extreme acceleration rates (which will then soupify any normal space probe designs).

[Northstar1989]

That the technology exists doesn't mean it's practical. A SpaceTram would have to be launched out of a mountain at least 7km high. AFAIK, those only exist in the himalayas. Most certainly not in Europe. Try getting a mega-engineering project to work in the highly politically unstable himalayas. On top of that, the tube must be at least a 100 km in length, unless one utilizes truly extreme acceleration rates (which will then soupify any normal space probe designs).

First of all, where did you get the figure "7 km high"? It doesn't say that on the article, I never said that, etc. The mountain would "only" need to be 6 km high for the standard design- and could be made to extend past the peak of a shorter mountain, such as some slopes in the Rockies that were deemed suitable...

30G for a 130 km track. That won't "soupify" all space probes. The design might have to be reinforced, but it's easily within the bounds of normal engineering...

Did you actually read the thread before commenting? Or the Wikipedia articles? All these concerns have been thoroughly addressed- including the ability to use shorter mountains with extensions past the peak (in fact, the 2nd-generation design extends 22 km up in the air- using electromagnetic forces to hold the end up), and the balance of track-length vs. acceleration...

Regards,

Northstar

[Northstar1989]

So... This is quite intentionally a bump of the thread. Does anyone have any ideas of any launch systems I've missed? (preferably rather than criticism of why they don't think these systems are unrealistic- though I'll keep discussing that too) I've only named a handful, so there certainly should be plenty more out there...

Regards,

Northstar

[NERVAfan]

Explanation:

We are entering the chicken and the egg problem. First of all, we don't have enough Space McGuffin^tm for we to seriously explore space. Because of that, no one wants to go to space. Then, no one develops cheaper launch techs. The sat guys that loves putting satellites into space are discouraged from putting it there, because of the costs. So, no one develops the necessary Space McGuffin^tm that will start massive amount of space exploration.

Yep. As I understand it, that's what SpaceX is trying to get around by building the cheaper launch system for higher launch rates and assuming "if you build it, they will come".

(Reaction Engines' Skylon project, too, but that's a lot less far along...)

[Northstar1989]

Yep. As I understand it, that's what SpaceX is trying to get around by building the cheaper launch system for higher launch rates and assuming "if you build it, they will come".

(Reaction Engines' Skylon project, too, but that's a lot less far along...)

Space-X's current pricing scheme is developed using current launch rates and ZERO re-usability, so I wouldn't be so sure about that... But it certainly does form the core of the R&D rationality- much like that followed for any other extremely innovative technology which doesn't yet have a market...

If nobody was willing to take risks like this, we wouldn't have made a lot of the progress that's been made in the past 2-3 centuries...

Regards,

Northstar

[Iskierka]

SpaceX are noticing issues with full reusability, such as if they actually reserve enough fuel to return both stages, they can't even launch an empty Dragon.

The electromagnetic launch tubes are quite infeasible, due to the sheer scale of the engineering required, where every part needs to withstand the counterforce of some silly-high acceleration on the payload. If you want a similar alternative that actually could be done with today's technology, look at launch loops - they require one very long cable (a few hundred to thousand km) and two base stations, but in terms of designing and making, that's a much more reasonable request.

In terms of power requirements, they're very modest, as they accelerate small payloads at much lower rates and longer distances, even to the point that passengers would be feasible. Stopping and starting the cable would be an impressive challenge, though there are some solutions, such as pylons that can support the cables electromagnetically at speed, and pulling the cable taut by moving the propulsive nodes in the base stations further apart. In the case of cable failure there might be some major concerns - but this is why you built it away from civilization, and didn't under-design the cable to allow that to happen, right?

[sojourner]

SpaceX are noticing issues with full reusability, such as if they actually reserve enough fuel to return both stages, they can't even launch an empty Dragon.

Citation needed.

[SargeRho]

SpaceX are noticing issues with full reusability, such as if they actually reserve enough fuel to return both stages, they can't even launch an empty Dragon.

No, they aren't.

[ThirdHorseman]

Laser launch can be done right now with off-the-shelf commercially available components:

http://www.niac.usra.edu/files/library/meetings/fellows/mar04/897Kare.pdf

That paper is 10 years old, and shows how you can build a modular laser thermal launch system using thousands of low-power modules. It estimates the cost of a 100MW system that can put 100kg into orbit at $2B...but you are looking at 30k launches per year!

A very large fraction of what you are putting into space can be done in small cheap launches. Fuel, water, oxygen, food, materials, etc. Imagine being able to get 3000 metric tons of this stuff into space each year!

30G for a 130 km track. That won't "soupify" all space probes. The design might have to be reinforced, but it's easily within the bounds of normal engineering...r

Agreed, and as I said above a large percentage of what you are putting into orbit is very good at withstanding very large Gs. For the laser launch system above, you can have several 100MW systems for putting metric tons of supplies into LEO, and then maybe two 500MW systems for crewed launches.

For a electromagnetic mass launch system, you can have multiple short-tube very highG launch systems to get supplies up and then maybe just one (or two) long-tube lowG systems for the squishy people.

All this can be done right now with commercially available systems and with low levels of capital. We just need the political will to move forward...

[Northstar1989]

Laser launch can be done right now with off-the-shelf commercially available components:

http://www.niac.usra.edu/files/library/meetings/fellows/mar04/897Kare.pdf

That paper is 10 years old, and shows how you can build a modular laser thermal launch system using thousands of low-power modules. It estimates the cost of a 100MW system that can put 100kg into orbit at $2B...but you are looking at 30k launches per year!

Awesome, I wasn't aware of that! I thought there were too many problems with atmospheric absorption of visible-light spectra photons for that to be feasible (sending the same photons as Microwaves, and using it to power a thermal rocket on the other hand, works perfectly fine...)

A very large fraction of what you are putting into space can be done in small cheap launches. Fuel, water, oxygen, food, materials, etc. Imagine being able to get 3000 metric tons of this stuff into space each year!

Bigger is better when it comes to launches- both because you don't need to lift a control/guidance system and cockpit (for manned launches) and a number of components as many times, and because larger rockets have better ballistic coefficients- and thus experience less drag relative to their mass (a rocket 10 times the mass might only experience 7 times the total drag, for instance). However, if lighter launches allow you to get by with a smaller/weaker launch-assist system, and with more cost-effective maintenance and vessel-recovery systems, then they're far superior to heavier launches...

Agreed, and as I said above a large percentage of what you are putting into orbit is very good at withstanding very large Gs. For the laser launch system above, you can have several 100MW systems for putting metric tons of supplies into LEO, and then maybe two 500MW systems for crewed launches.

No need for separate manned and unmanned launch-assist systems with lasers... Since I imagine construction/placement/maintenance of ground components (such as the lasers and their power supplies) would be a large part of the system cost, you'd be much better off building a single system powerful/robust to lift small manned vessels into orbit, and just using the same system for heavier launches of cargo/probes.

It's much like rocket launches in KSP- if your TWR is too high, you can either remove engines, or add fuel/cargo. Both methods accomplish the goal- and for reasons I described earlier, larger launches are more efficient in terms of Delta-V... (that is, you get more Delta-v due to relatively less dry mass, and less Delta-V losses to drag, with the same payload mass)

For a electromagnetic mass launch system, you can have multiple short-tube very highG launch systems to get supplies up and then maybe just one (or two) long-tube lowG systems for the squishy people.

Actually, like with the lasers, you'd just be better off with a single tube that can lift both. You simply build one long launch tube that is capable of manned launches, and simply use a lighter rocket for unmanned launches (assuming it would be more cost-efficient to exit the tube at higher speeds- if not, then it's just a matter of adding extra cargo to unmanned launches to replace the mass of the manned systems to get the same acceleration...) The main reason separate tubes have been proposed is because most people in the industry figure they'll be lucky just to get the funds for a short-tube version only capable of unmanned launches at first, before being able to proceed on to longer-tube variants also capable of unmanned launches.

All this can be done right now with commercially available systems and with low levels of capital. We just need the political will to move forward...

Indeed, but the problem is, most politicians (especially Americans) don't understand science. Many of them hardly understand basic physics, nevertheless orbital mechanics or the rationality behind assisted-launch systems. Even if they did have an elementary understanding of the principles, they certainly don't understand the science well enough to make an eloquent case for its benefits to the lobbyists and super-PAC's that are the real power in most democracies these days...

(And most lobbyists would rather have tax breaks for their respective corporations and stockholders anyways, so the rich can get richer and buy third and fourth-homes, rather than a real space program... The politicians/engineers would be best off making a case that it would allow the current space program to get by with a smaller annual budget after an initial investment, and make commercial launches cheaper, than that it would increase capabilities...)

Regards,

Northstar

[Northstar1989]

Laser launch

ACTUALLY, after looking through the article (I should have read it BEFORE commenting), it's just another variant of beamed-power thermal rocket- one that uses visible spectra light instead of microwaves. And it DOES have problems with laser absorption by clouds, etc- limiting launches to clear days.

Doing the exact same thing with Microwaves Beamed Power instead of lasers is vastly superior. You get a lot less absorption/refraction from the atmosphere at the relevant wavelengths (and even then, it's still a problem- you should see my Medium Reusable Microwave Thermal Launch Platform in my ongoing Career game and Mission Reports thread- less than 10% of the power gets through the atmosphere from a ground installation near the launchpad by the time you're 20 km up in the air...)

You can also lift a much heavier payload (albeit with higher complexity) to orbit with a spaceplane-style Microwave Beamed Power launch, using Thermal Turbojets, if you have a relay for the beamed power in geo/kerbostationary orbit overhead the launchpad (you actually lose LESS power to beaming the microwaves nearly straight up through the atmosphere to a geo/kerbostat relay and then back down through the upper atmosphere to a spaceplane at high altitude east of the runway, than you do by beaming the power on a longer path-length through the lower atmosphere directly to the craft...) And if you're willing to wait to time the launch right, you can get by with just a single relay at much lower altitude than geo/kerbostationary orbit (and get less power loss due to transmission path-length...)

Regards,

Northstar

Edited June 13, 2014 by Northstar1989

[ThirdHorseman]

No need for separate manned and unmanned launch-assist systems with lasers... Since I imagine construction/placement/maintenance of ground components (such as the lasers and their power supplies) would be a large part of the system cost, you'd be much better off building a single system powerful/robust to lift small manned vessels into orbit, and just using the same system for heavier launches of cargo/probes.

Actually, Kare has the facilities as a small fraction of the total cost...the majority being the lasers. So building multiple facitilities wouldn't add that much additional cost. But I agree that the lack of suitable launch sites might be a limiting factor to how many you can build.

The nice thing about Kare's modular laser system is that you can just start small and keep adding additional modules to increase the launch capacity of the site. In addition, as time goes by the costs of the modules decreases, so your capacity increases faster as time goes by and 1) you get better at building modules and 2) the components get smaller and cheaper as tech gets better.

I still think you might want multiple systems of varying scale. Power requirements for a large human-capable system will be pretty substantial, so it would be better to have a few small capacity systems that can get supplies into space rapidly and frequently. Granted, with a large capacity system you can just launch more of those supplies in each launch. But having rapid small capacity systems allows for things like spare-on-the-ground capability and rapid support response. One of your stations has just blown a circuit board? With a 100MW system you are launching 10 payloads per hour, you can just pop that circuit board on the next launch vehicle and they'll have it in hours, not days or weeks.

I guess it all comes down to the numbers. You'd have to calculate if it makes sense to have fewer large capacity launches or more frequent low capacity ones. If it's cheaper to have a single 1000MW system and ten 100MW systems, rather than two 1000MW systems, or the other way around.

[ThirdHorseman]

Doing the exact same thing with Microwaves Beamed Power instead of lasers is vastly superior.

From my understanding the big con for using microwaves in a propellant-based thermal system (where a propellant is heated using a heat exchanger) is the cost of the microwave generator. Granted I haven't looked at it in a while, but I remember gyrotrons being very expensive, highly complicated, and not exactly commercially available products. Kare was trying to design a system that would work with off-the-shelf components....something you could purchase from a catalog...and would be very easy for workers with minimal training to install and operate. Have gyrotrons advanced to that point yet?

You can also lift a much heavier payload (albeit with higher complexity) to orbit with a spaceplane-style Microwave Beamed Power launch, using Thermal Turbojets,

Yes, but don't thermal turbojets require an atmosphere to operate? It's the same issue I had with Myrabo's Lightcraft...it works fine with a nice dense atmosphere to detonate but you need a secondary propulsion system once you get high enough...or to circularize your orbit once in space. I'm also not sure how the power requirements scale...from what I remember you need a much higher power system to detonate the air than to just heat H2 propellant using a heat exchanger.

you actually lose LESS power to beaming the microwaves nearly straight up through the atmosphere to a geo/kerbostat relay and then back down through the upper atmosphere to a spaceplane at high altitude east of the runway, than you do by beaming the power on a longer path-length through the lower atmosphere directly to the craft...

Agreed, although it makes even more sense to have laser systems in GEO that would take over once the launch vehicle got far down range from the original launch facility. You'd need to redesign the launch vehicle a bit (either have upper and lower hear exchangers, or a single one that can be lit from both sides of the craft) or implement some kind of controlled roll to expose the heat exchanger to a new source, but that seems reasonably do-able.

[cantab]

IMHO one of the more promising approaches is air launch. That's how Scaled Composites did things for their suborbital craft, and Orbital Sciences have been launching their Pegasus rockets from carrier aircraft for a couple of decades and are now designing the much more capable Pegasus II.

Air launch to orbit could really benefit from a suitable supersonic carrier aircraft. There'd be new aerodynamic challenges of course, but it would shave yet more delta-V off the requirement for the rocket itself. Unfortunately aircraft development has shown no signs of going in this direction since Concorde. Some strategic bombers could be suitable, such as the B-1 or the Tu-160, but that would depend on considerably military co-operation.

[shynung]

Air launch to orbit could really benefit from a suitable supersonic carrier aircraft. There'd be new aerodynamic challenges of course, but it would shave yet more delta-V off the requirement for the rocket itself. Unfortunately aircraft development has shown no signs of going in this direction since Concorde. Some strategic bombers could be suitable, such as the B-1 or the Tu-160, but that would depend on considerably military co-operation.

Turning Reaction Engines' LAPCAT A2 supersonic airliner into a cargo version with a Shuttle-style cargo bay doors would be one solution.

[ThirdHorseman]

Been reading up on the laser vs microwave question. Very interesting stuff, I must say. Both systems look very similar...it seems to me that the big benefit the laser system has is the lower initial startup costs. By this I mean that you can build a very small kW laser system as a testbed because fiber laser systems can be built small, whereas microwave systems start at the MW level and can run a few million dollars. So it would be easier to build a small cheap laser test system and then increase the scale in small increments, whereas you have to make a large initial investment in a microwave system just to build a demo and then it could only be upgraded in large, expensive steps. But if you have tens of millions in startup funds then that doesn't really matter much.

I've skimmed through Kevin Parkin's 2006 thesis "THE MICROWAVE THERMAL THRUSTER AND ITS APPLICATION TO THE LAUNCH PROBLEM" and it is quite interesting. I need to really get into it in more detail, but he seems to make the same arguments that high-power microwave sources are cheaper than high-power laser sources, and atmospheric propagation is better for microwaves than lasers.

But you can see from this 2011 interview with Kevin Parkin that lasers have some advantages, where he says "Both microwave and lasers will lose some efficiency to atmospheric absorption. Microwave is currently more cost-effective than laser - one can buy a one megawatt millimeter wave source for $2 million dollars. The price for both laser and millimeter sources are steadily dropping, and should continue to fall for the foreseeable future. But at this point millimeter wave sources are cheaper. The lasers would be better suited to longer range activities, such as putting a payload into geosynchronous orbit, or putting a payload on the moon."

Again, while the cost issue might be true it just lends more weight to Kare's point of intentionally not using a small number of high-power sources and instead using a larger number of low-power sources to get 1) smaller initial system costs, 2) better failsafe, and 3) a modular system with small and cheap incremental increase rate.

I've also been looking into laser propagation in atmosphere, and it may not be as big a deal as many think. A 2004 Navy study Propagation of High-Energy Lasers in a Maritime Atmosphere showed that lasers operating in the 1μm wavelength fell right in a sweet spot of low scattering and absorption:

and normalized average power on the target vs power at the transmitter for the 1.045-μm wavelength was good at high power levels:

and a cross-sectional plot of average laser intensity on target for 1.045-μm wavelengths showed little distortion due to thermal blooming:

Turns out the 1.045-μm wavelength is right where you'd be with a Yb-doped double-core fiber laser from Kare's study. So the losses due to atmosphere might not be the showstopper it was made out to be.

You can hear Kare talk a lot about this and other issues during a webcast at TheSpaceShow where he explains:

1) microwave sources are just slightly cheaper, but they need much much bigger transmitters which adds a lot to the facility costs,

2) NASA has downplayed both of these systems, writing them off as too expensive. Kare criticizes them for overblowing their numbers, and not knowing what the system is designed for. The host also talks about how you can't trust NASA numbers, comparing what the cost of Falcon9 is and what it would have cost for NASA to do it. Basically, their numbers are way high and do not reflect what the actual costs would be,

3) fiber lasers are what they are focusing on, and wavelengths of 1micron propagate pretty nicely through the atmosphere.

You can also see that they downplay the atmospheric effects on his company's website, lasermotive.com, where in one of the FAQ questions they say "Power beamed near vertical suffers comparatively little energy loss because it quickly gets away from the ground effects. Scattering will depend on atmospheric conditions (e.g., dust, clouds). Absorption in the wavelengths we use is small" and "Power transferred from point to point near the ground can suffer significant energy losses due to turbulence and dust. We can reduce that effect by elevating the transmitter and receiver so that the beam remains a reasonable distance, perhaps 100 feet, above ground level." Granted this is from his commercial operation so take it as you will.

Lastly, to wrap up this TL;DR post, I've been slowly working my way through the 678-page 2012 NASA Beamed-Energy Propulsion (BEP) Study and it is a doozy, but there is a ton there about laser and microwave thermal systems and it even has a few reference missions which is pretty cool. It'll take me a pot or two of coffee to make it through the whole report though!

[Northstar1989]

Actually, Kare has the facilities as a small fraction of the total cost...the majority being the lasers.

WHAT DO YOU THINK THE GROUND-BASED COSTS I WAS REFERRING TO WERE, IF NOT THE LASERS?

I'm sorry for being dramatic and irritable, but I don't appreciate it when people don't use their heads (or their eyes to actually read what I wrote...)

My whole point was that you could use the same laser/microwave array for manned and unmanned launches, and thus avoid the need to buy a much more lasers to set up multiple launch sites... Sure, you *COULD* turn off some of the laser modules to lift a lighter cargo- but most of the time, why would you?

As I've pointed out, you'll get the same mass to orbit with less drag and fewer launches (and less extra mass in control systems) with a heavier rocket- and thus with less fuel. Unless the economies-of-scale were such that it was cheaper to launch ten 20-ton payloads instead of five 40-ton payloads to LEO, with the economics of laser/microwave-powered beamed-power arrays, I don't see why you WOULD turn off some of the array modules.

Even with a smaller payload, you could theoretically just work the heat-exchanger overtime (or make use of multiple heat-exchanges with relatively less fuel flow) to get higher exhaust-velocity and thus better ISP with the same beamed-power array, although I'd imagine you'd get diminishing returns on this the hotter you got the heat-exchangers...

So building multiple facitilities wouldn't add that much additional cost. But I agree that the lack of suitable launch sites might be a limiting factor to how many you can build.

Because of the cost of needing additional lasers (most of the cost of the plan you linked to- Kare is a consulting company that gave a presentation on the topic, by the way, not a company looking to actually manufacture this system...) you WOULD incur a MASSIVE additional cost from setting up additional launch facilities, rather than just re-using the same lasers for both manned and unmanned launches!

The nice thing about Kare's modular laser system is that you can just start small and keep adding additional modules to increase the launch capacity of the site. In addition, as time goes by the costs of the modules decreases, so your capacity increases faster as time goes by and 1) you get better at building modules and 2) the components get smaller and cheaper as tech gets better.

First of all, to make sure you get this, I'm going to write it again, in bold. Kare is a consulting company, not an engineering firm actually looking to build such a site.

Second, it's right in their presentation if you read it carefully: "There are no *cheap* (good) lasers" Lasers aren't going to get much cheaper just because you use a bunch of them for a space launch-system, *especially* when that would only make a *very small* contribution to the total global annual usage of lasers... (and a one-time contribution, at that- since after building the launch site, you'll only need to replace individual laser modules as they break down)

I still think you might want multiple systems of varying scale. Power requirements for a large human-capable system will be pretty substantial, so it would be better to have a few small capacity systems that can get supplies into space rapidly and frequently.

I'm convinced you didn't read the presentation you yourself linked to at all (I, on the other hand, did). The system is modular- thus by its very nature it is scalable without needing to build multiple launch sites. They themselves say that if you want to increase the power of the launch system, just add/turn on more lasers. The inverse easily follows- if for some strange reason you want to launch with LESS power, just turn off some of the modules and you're golden. No need to build an entirely separate launch facility with its own (very expensive) array of lasers...

You could build a small modular array, and then add more power as needed to bring it up to manned capabilities in the future (and assuming you're only rendezvousing with a space station or pre-assembled interplanetary mission in orbit, you don't NEED a very heavy lifting capacity to lift humans to orbit. You could easily lift them in small, 1-man capsules early on until you scaled up the system, by adding additional modules, to be able to handle heavier payloads).

I *REALLY* suggest you take a look at how I implemented my Microwave Beamed Power network. Currently, it's single-source to save on effort it setting it up from a player perspective, but I could easily add additional reactor carts to bring up the beamed power from its current 3 GW to 6, 12, or even 24+ GW if I wanted...

Technically, there's no limitation that a Microwave Beamed Power Array (as opposed to a laser-based array, which has trouble transmitting longer distances compared to microwaves) even need to be located entirely on the ground. I supplement my 3 GW power station near the KSC with a small 2.3 MW solar power satellite in orbit of Minmus, for instance...

Granted, with a large capacity system you can just launch more of those supplies in each launch. But having rapid small capacity systems allows for things like spare-on-the-ground capability and rapid support response. One of your stations has just blown a circuit board? With a 100MW system you are launching 10 payloads per hour, you can just pop that circuit board on the next launch vehicle and they'll have it in hours, not days or weeks.

There are certainly advantages to having a higher launch-frequency. I won't deny that. But the beauty of heavier launches is that they make better utilization of the existing infrastructure- you can lift more mass in a year with the same array lifting 500-ton rockets at a rate of 4 launches per hour, than you can lifting 200-ton rockets at a rate of 10 launches per hour, because (assuming there's 2.5 times the number of laser modules active for the 500-ton rocket) the heavier rocket would have a higher payload fraction.

So, while it makes sense to get by with the smallest ground-based array possible, and simply launch more rockets, to bring down total costs as much as possible- if you already have an array capable of lifting a 500-ton rocket, you shouldn't dial down the power to 40% to lift a 200-ton rocket... (if you can efficiently utilize the full production of the same array by simply heating the propellant gas hotter, and get 58% more ISP, on the other hand, then the lighter launches are definitely better as they will ahve higher payload-fraction despite their smaller size...)

I guess it all comes down to the numbers. You'd have to calculate if it makes sense to have fewer large capacity launches or more frequent low capacity ones. If it's cheaper to have a single 1000MW system and ten 100MW systems, rather than two 1000MW systems, or the other way around.

I *highly* doubt there's going to be enough buy-in to this idea early on to launch 10 rockets an hour, however optimistic the company may be, and however small the payloads and low the lifting-cost. More likely, even a single launch-facility will have trouble attracting sufficient launch volume at first, because of the novelty of the idea, and the much higher launch-insurance premiums for relatively untested launch systems...

The greater danger, then, is overbuilding the system so it has too high a maximum lifting-capacity-per-year (you'll get more launch purchases if the same customer has to launch their satellite or space station component or probe in 2 parts, and dock them in-orbit into one craft, than if they can lift it in just one launch- assuming the customer is willing to go through the extra hassle. Lower maximum payload sizes mean more launch purchases then, counter-intuitively...) and thus running cost, relative to its annual income...

A smaller array probably WILL NOT make any more income than a larger array (you'll have to charge the same rate per kg to orbit, and will simply lift the same payload in more launches), but it WILL have lower running/maintenance costs- and thus can be profitable from a smaller revenue stream.

You're right though- it *IS* a matter of numbers...

The numbers are, energy in, energy out. The energy in is the maximum amount of energy the lasers or microwave transmitters can fire off in a given year. The energy out is the energy it takes to get all those rockets to orbit. Since the same payload loses less energy to drag and to lifting redundant control systems on multiple launches with a heavier rocket than on multiple launches of lighter rockets, you end up expending less energy to get the same payload to orbit with heavier launches- and thus can get more payload to orbit in a year. The problem is, then, a matter of whether the array can handle the heavier launch vehicles, or whether you can beam more power to a lighter ship for higher ISP, instead of tuning-down the same array...

(Assume that a computer core for an unmanned rocket, and associated electrical systems, weighs 100 kilograms. If you have to lift two 250-ton rockets, each with a 100 kg control system, you expend more energy than if you lift a single 500-ton rocket with a 100 kg control system- or even one weighing a bit more at 150 or 180 kg...)

Regards,

Northstar

[Northstar1989]

From my understanding the big con for using microwaves in a propellant-based thermal system (where a propellant is heated using a heat exchanger) is the cost of the microwave generator. Granted I haven't looked at it in a while, but I remember gyrotrons being very expensive, highly complicated, and not exactly commercially available products. Kare was trying to design a system that would work with off-the-shelf components....something you could purchase from a catalog...and would be very easy for workers with minimal training to install and operate. Have gyrotrons advanced to that point yet?

Gyrotrons see common use in industrial and manufacturing systems, all the time. They're not exactly cheap- but as the *consulting firm* Kare points out, neither are lasers...

http://en.wikipedia.org/wiki/Gyrotron

You don't *HAVE TO* use gyrotrons either. Although the wavelengths gyrotrons produce are better-suited for beamed-power systems than lasers, due to reduced interference from the atmosphere, even a common Cavity Magnetron (the exact same device used to generate microwave-oven) is still superior to a laser in terms of the ability of the beam it produces to penetrate through the atmosphere (your microwave oven heats food several centimeters deep or more- now show me a laser that can do THAT!) - and due to their everyday usage in microwave-ovens and other devices, Cavity Magnetrons are a lot cheaper (and a lot less scary to the ignorant lay public) than gyrotrons too...

http://en.wikipedia.org/wiki/Cavity_magnetron

Yes, but don't thermal turbojets require an atmosphere to operate?

They do. But that's also where you need the most thrust (low to the ground, still on the launchpad). The beauty of a thermal turbojet is that it utilizes a lot of the same components as a thermal rocket- a heat exchanger, a working-mass feed, etc. So it's actually possible to develop a "Hybrid Turbojet" that proceeds to pass internal propellant through the nozzle once the surrounding atmosphere becomes too thin...

You'll still need a small store of internal propellant, though- and an air intake system and ducting (with all the associated extra weight) if you're going to use a Hybrid Turbojet or a Thermal Tubojet. The added complexity of the engine also adds a lot to cost- you're basically talking the difference between a turbofan engine, which is heavy and expensive to maintain- and a rocket engine, which is light and cheap. Thermal Turbojets would allow higher payload fractions on each launch, though, and are especially well-suited to spaceplane-style launches (though as I've repeatedly said, lasers don't work well for spaceplanes due to the long path-length through the atmosphere. For this purpose, microwaves are EVEN MORE superior...)

It's the same issue I had with Myrabo's Lightcraft...it works fine with a nice dense atmosphere to detonate but you need a secondary propulsion system once you get high enough...or to circularize your orbit once in space.

No atmosphere-based propulsion system will work all the way to circular orbit. But the nice thing is, you can drastically reduce the internal propellant load you need to carry this way, and thus significantly improve payload-fraction...

The lightcraft is also a beautiful system, because it utilizes the atmosphere for reactant/working mass- providing some of the same advantages as a Thermal Turbojet- but it's also a lot lighter and simpler to maintain than a turbojet, requiring nothing but a mirror-dish on the bottom in its simplest form. You probably would need some way to vent extra air to the dish as/after you break the sound barrier though, due to supersonic cavitation (I think that's what it's called) and the bubbles of extremely low pressure that would form under the lightcraft's tail at supersonic speeds- precisely where you need the air for propulsion...

I'm also not sure how the power requirements scale...from what I remember you need a much higher power system to detonate the air than to just heat H2 propellant using a heat exchanger.

You need a lot more power *at one point in space*, that's true. The amount of power you need depends on HOW MUCH air you detonate, however- so you would simply need to find a way to limit the amount of air that you detonate with less powerful laser-arrays...

A lightcraft, like a thermal rocket or thermal turbojet, can also be run off microwaves, however...

Agreed, although it makes even more sense to have laser systems in GEO that would take over once the launch vehicle got far down range from the original launch facility. You'd need to redesign the launch vehicle a bit (either have upper and lower hear exchangers, or a single one that can be lit from both sides of the craft) or implement some kind of controlled roll to expose the heat exchanger to a new source, but that seems reasonably do-able.

Lasers don't penetrate through the body of the craft, but Microwaves *DO* (Gyrotron-frequency microwaves will penetrate quite nicely through hundreds of meters of material, whereas Magnetron-frequency microwaves will only penetrate through a few centimeters of relatively low-density material, much like your household microwave-oven). That's one of Microwaves' many advantages- you don't have to design the launch platform and ascent profile to always have a clear line-of-sight to the beamed-power array if you use microwaves instead of lasers...

Stationing a separate beamed-power array in orbit creates its own problems- not the least of which is how to get the energy to run it in the first place (beamed-power isn't free energy by any means: it's just a way of leaving your generators on the ground, and beaming the power to your spacecraft without the extra mass). And, it's much more limited in power-sources...

Whereas a ground-based array can run off wind, biomass, tidal, geothermal, coal, oil, natural gas, solar, and nuclear power- among other options- a space-based array is solely limited to solar power; unless you can get the politicians to agree to allow a space-based nuclear power satellite, which is HIGHLY unlikely in the United States in the current (largely understandable) anti-nuclear climate... And a large nuclear power beamed-power satellite would require regular maintenance and refueling visits, making it VERY costly in the long run...

Regards,

Northstar

[Northstar1989]

IMHO one of the more promising approaches is air launch. That's how Scaled Composites did things for their suborbital craft, and Orbital Sciences have been launching their Pegasus rockets from carrier aircraft for a couple of decades and are now designing the much more capable Pegasus II.

Air launch to orbit could really benefit from a suitable supersonic carrier aircraft. There'd be new aerodynamic challenges of course, but it would shave yet more delta-V off the requirement for the rocket itself. Unfortunately aircraft development has shown no signs of going in this direction since Concorde. Some strategic bombers could be suitable, such as the B-1 or the Tu-160, but that would depend on considerably military co-operation.

Aircraft mothership-launches are never going to come ANYWHERE CLOSE to the economics of a beamed-power launch system, or a magnetic launch tube, or a Single-Stage-To-Tether design (although they could be combined with the last of these for even greater cost-savings if you weren't using a magnetic launch-assist system), so I don't get why you'd even bring it up here.

This is a *NEXT-GENERATION* launch technologies thread, and there's nothing next-generation on mothership-launches (as you said, it's already been done for several decades now). They're never going to provide the kind of cheap access to space the worlds needs if it is going to grow beyond the cradle of Earth, and as such, it's not really worth paying too much attention to here...

That reminds me of a GREAT quote, though:

"Earth is the cradle of the mind- but one cannot stay in the cradle forever."

- Konstantin Eduardovich Tsiolkovsky -

That comes from the same man who gave us the famous Rocket Equation we all know and love (and hate) so much...

Regards,

Northstar

[Northstar1989]

First off, let me skip to the end by saying I the end by saying, I think it's really goo you've been doing some in-depth reading on the topic. I was a bit critical of your posts earlier, because they didn't seem to show much understanding. But it looks like that's a problem you're aware of, and working very hard to rectify. I imagine you'll know a LOT more than me about the topic by the time you're done with that report...

I *DO* suggest you try out actually using a Microwave Power systems, with KSP-Interstellar, like in my Mission Reports thread which I've repeatedly linked to though... There's something to be said from gaining an intuitive understanding of a topic by actually seeing it and playing around with it, that you just can't get by reading up on it... Reminds me of a XKCD post I saw a while back (fat chance I'll find it now), with a plot of "My Understanding of Orbital Mechanics". There's a SMALL leap with "getting an actual job at NASA." (though who knows, maybe he was just a concept-artist or janitor...) There's a BIG leap with "started playing KSP"

Been reading up on the laser vs microwave question. Very interesting stuff, I must say. Both systems look very similar...it seems to me that the big benefit the laser system has is the lower initial startup costs. By this I mean that you can build a very small kW laser system as a testbed because fiber laser systems can be built small, whereas microwave systems start at the MW level and can run a few million dollars.

You're not going to launch *anything* significant to orbit with a few kW of power. In fact, you're probably not even going to make orbit at all that way, It takes 100 MW of beamed-power even to lift a tiny nanosatellite to orbit, according to the very first presentation you linked to, by Kare...

Even in KSP Interstellar, which uses pretty realistic/accurate numbers for its Microwave Beamed Power system, I can only get 17.5 metric tons (17500 kg) to orbit on a 100% reusable (Space-X style) rocket with 3 GW of beamed-power on Kerbin- where it only takes about 4.5 km/s of Delta-V to get to orbit. On Earth, where it takes 9-10 km/s, I'd be lucky to get 5000 kg to orbit... And THAT design was augmented with no fewer than eight "conventional" rocket engines (4 heavy-duty aerospike engines and 4 heavy-duty radial boosters from Novapunch2), and relied on Meth/LOX and LH2/LOX propellant in order to achieve additional thrust from the same propellant mass beyond the thermal energy imparted from beamed-power, due to the chemical reaction of the fuel components...

Of course, that was with a 100% reusable Space-X style rocket, which was limited to a "straight-up" initial ascent profile (which is PARTICULARLY bad for a Microwave Thermal Rocket, as it produces a VERY poor angle of incidence for the beamed power once it starts to climb in altitude...) With a 100% reusable spaceplane-style ascent (spaceplanes can stage too, if desired...), or better yet a disposable rocket, MUCH heavier payloads could easily be lifted to orbit...

As for demo systems- it's already been done. People have ALREADY built kW-scale beamed-power systems to demonstrate the technology behind beamed-power thermal rocketry... (I'll have to dig up some URL's on that...)

So it would be easier to build a small cheap laser test system and then increase the scale in small increments, whereas you have to make a large initial investment in a microwave system just to build a demo and then it could only be upgraded in large, expensive steps. But if you have tens of millions in startup funds then that doesn't really matter much.

A 1 MW microwave power-source *IS* a small increment. You'd need at least 100 of those to lift even a nanosatellite to orbit (at a cost of over $200 million just for the ground-system, but it would be reusable for potentially thousands of launches...) So, based on the evidence you yourself presented, Microwave Beamed Power *IS* available in small increments...

Beside, most space programs have not millions, but BILLIONS of dollars to play with anyways. NASA's 2011 budget was $20 Billion, for instance... So, in a single year, using only 1% of their 2011 budget expenditures, therefore, they could have built a 200 MW microwave beamed-power array, capable of beaming enough power to lift thousands of small satellites to orbit a year on specially-designed rockets...

What did NASA do instead? Some silly disposable conventional chemical rocket called Ares, which they only ended up abandoning in the end before it was finished...

I've skimmed through Kevin Parkin's 2006 thesis "THE MICROWAVE THERMAL THRUSTER AND ITS APPLICATION TO THE LAUNCH PROBLEM" and it is quite interesting. I need to really get into it in more detail, but he seems to make the same arguments that high-power microwave sources are cheaper than high-power laser sources, and atmospheric propagation is better for microwaves than lasers.

Great minds think alike, I guess.

Actually, I'm pretty sure I got some of my ideas from reading and digesting/analyzing mirrored/parroted versions of his arguments in the first place...

But you can see from this 2011 interview with Kevin Parkin that lasers have some advantages, where he says "Both microwave and lasers will lose some efficiency to atmospheric absorption. Microwave is currently more cost-effective than laser - one can buy a one megawatt millimeter wave source for $2 million dollars. The price for both laser and millimeter sources are steadily dropping, and should continue to fall for the foreseeable future. But at this point millimeter wave sources are cheaper. The lasers would be better suited to longer range activities, such as putting a payload into geosynchronous orbit, or putting a payload on the moon."

What he's referring to is that shorter wavelengths form tighter beams (and thus you lose less energy) over great distances, once you're in the vacuum of space (DOH! I don't know why I said it was the other way around before...)

But since lasers don't propagate well in-atmosphere, and the best/cheapest power sources are right here on Earth to begin with (wind power, for instance- which is MUCH cheaper than solar power, and not nearly as dirty as coal- and there's no reason you can't wait until a windy day for launch, assuming the winds aren't so strong as to endanger the launch...) it makes more sense to rely on surface-based Microwaves. ESPECIALLY since you can simply set up a relay-network in orbit to get the power from a single production site to anywhere it's needed (with manageable, but significant losses over distance, of course)

If you REALLY needed to carry out a long-range mission using beamed power, you might be best-off transmitting that power to a satellite in orbit using gyrotron-wavelength microwaves, and then converting those microwaves straight into electricity with a rectenna, and using a UV-wavelength laser to beam that power to a far-away spaceship (Ultraviolet Light doesn't do well crossing the Ozone in the atmosphere, but it's superior to a laser in terms of long-distance transmission in the vacuum of space...)

Or maybe just a near-IR beam- which would be inferior to visible light in terms of distance transmission, but would VASTLY simplify the process of converting that beamed power to heat for a thermal receiver, since IR light is quite efficiently converted directly into heat by most materials...

Again, while the cost issue might be true it just lends more weight to Kare's point of intentionally not using a small number of high-power sources and instead using a larger number of low-power sources to get 1) smaller initial system costs, 2) better failsafe, and 3) a modular system with small and cheap incremental increase rate.

Yeah, I agree with the advantages of a modular system. And with the ONE-HUNDRED modules in a 100 MW array- which would be VERY marginal for spacecraft launches, Microwave Beamed Power is more than fine-grained enough for the purposes...

In fact, while you do want SOME modularity, you don't want TOO MUCH modularity, as eventually it becomes inefficient when you have too many individual modules to maintain and keep track of. 100 module for a starter-sized array seems perfectly reasonable to me- and apparently is a reasonably economical unit-size with microwave-transmitters as it currently stands, once again according to the information you yourself posted...

I've also been looking into laser propagation in atmosphere, and it may not be as big a deal as many think. A 2004 Navy study Propagation of High-Energy Lasers in a Maritime Atmosphere showed that lasers operating in the 1μm wavelength fell right in a sweet spot of low scattering and absorption:

http://www.nrl.navy.mil/content_images/04FA2_Figure1.gif

and normalized average power on the target vs power at the transmitter for the 1.045-μm wavelength was good at high power levels:

http://www.nrl.navy.mil/content_images/04FA2_Figure5.gif

and a cross-sectional plot of average laser intensity on target for 1.045-μm wavelengths showed little distortion due to thermal blooming:

http://www.nrl.navy.mil/content_images/04FA2_Figure7.gif

Turns out the 1.045-μm wavelength is right where you'd be with a Yb-doped double-core fiber laser from Kare's study. So the losses due to atmosphere might not be the showstopper it was made out to be.

You have to realize that all that was developed for a Naval weapons-system designed to destroy speedboats over a range of only a dozen kilometers or so... That's small-change compared to the vast distances of atmosphere you have to transmit through to get to space- the Troposphere alone is up to 20 km deep near the equator- which is PRECISELY the best place to launch a rocket from... (it gets progressively thinner as you move towards the poles- but it's still rather thick at the latitudes of, say, Florida)

http://en.wikipedia.org/wiki/Troposphere

So, none of that even comes close to convincing me that lasers are a good idea for launch-assist systems. "With Aerosols" a 1 micrometer laser reaches an Extinction coefficient of close to 0.1 per km- do you have ANY IDEA how inefficient it would be to transmit that over 400 km of atmosphere? Even with rarification of the upper atmosphere, that's going to be the vast majority of your energy lost if you perform any sort of a gravity-turn... (which will increase your path-length even further- for instance to 800 km of atmosphere the laser must pass through at 400 km of altitude if you are 565 km downrange...)

You can hear Kare talk a lot about this and other issues during a webcast at TheSpaceShow where he explains:

I'll have to dig that up- but just addressing the points you bring up here...

1) microwave sources are just slightly cheaper, but they need much much bigger transmitters which adds a lot to the facility costs,

That sounds like pseudo-logic designed to confuse people to me. If they're cheaper per-MW, then they're cheaper. Scaling up the number of transmitters isn't going to change that equation- unless they're talking about the construction costs for the facility, and using 1-MW microwave transmitters vs kW-scale lasers. Even then, I'd have to see facts and figures that convinced me that the Microwave Transmitters would be bulkier/heavier to enough of a degree that the per-transmitter deployment cost would outweigh the cost-savings of not having to deploy as many transmitters in the first place...

2) NASA has downplayed both of these systems, writing them off as too expensive. Kare criticizes them for overblowing their numbers, and not knowing what the system is designed for. The host also talks about how you can't trust NASA numbers, comparing what the cost of Falcon9 is and what it would have cost for NASA to do it. Basically, their numbers are way high and do not reflect what the actual costs would be,

I agree with the consultants there- NASA is big and bloated, and makes everything 10 times more expensive. It's NOT because of any of that government-ruins-everything nonsense I hear so often though: it's mainly because NASA is controlled by politicians, and politicians are controlled by lobbyists and special interests... (like those from the United Launch Alliance, and Boeing)

Imagine if there was a corporation that was run by managers who were on the payroll of their suppliers- I strongly suspect that corporation would be a LOT more interested in their suppliers' well-being rather than their own, or that of their country, and would be big and bulky and much less subject to economic imperatives as a result...

3) fiber lasers are what they are focusing on, and wavelengths of 1micron propagate pretty nicely through the atmosphere.

Nicely is a relative term, in this case. It's a fact that lasers can approach 100% absorption with a simple layer of thick clouds overhead (microwaves, by contrast, will simply shrug the clouds off, and hardly be affected). I don't remember were I saw the link on that before, but it was actually posted by somebody else discussing this sam concept (laser-based launch-assist systems) earlier, and it's also somewhere on Wikipedia...

You can also see that they downplay the atmospheric effects on his company's website, lasermotive.com, where in one of the FAQ questions they say "Power beamed near vertical suffers comparatively little energy loss because it quickly gets away from the ground effects. Scattering will depend on atmospheric conditions (e.g., dust, clouds). Absorption in the wavelengths we use is small" and "Power transferred from point to point near the ground can suffer significant energy losses due to turbulence and dust. We can reduce that effect by elevating the transmitter and receiver so that the beam remains a reasonable distance, perhaps 100 feet, above ground level." Granted this is from his commercial operation so take it as you will.

Yes, on a clear, dry, non-dusty day, from the top of a 340-foot tower, lasers will work just fine. But do you REALLY, SERIOUSLY EXPECT to launch "10 rockets an hour" (like you quoted earlier) 365 days a year, if you're limited to these conditions?

Gyrotron-wavelength microwaves work much better- they cut through dust and turbulence and clouds like a diamond-edged knife through putty... Sure, microwaves still experience SOME losses, but they're not terrible...

(By the way, the reason my Medium Reusable Thermal Launch Platform experiences such enormous power-loss at high altitude is in large part due to the vertical Space-X style ascent profile, and low angle-of-incidence of the beamed power. With a standard gravity-climb, I could still easily expect to obtain more than 54% power from orbit with the same array- as I in fact did recently see when using the same technology to perform repeated trans-Munar maneuvers with an extra-atmospheric cargo ship I developed that relies on Microwave Beamed Power from the KSC for its propulsion system... For this reason, I've been looking at moving to a beamed-power spaceplane design: which would also allow me to carry a much heavier payload to orbit with the same amount of beamed-power...)

Lastly, to wrap up this TL;DR post, I've been slowly working my way through the 678-page 2012 NASA Beamed-Energy Propulsion (BEP) Study and it is a doozy, but there is a ton there about laser and microwave thermal systems and it even has a few reference missions which is pretty cool. It'll take me a pot or two of coffee to make it through the whole report though!

Best luck with reading that report! Try not to drink *too much* "Koffee", as I'm sure your Kerbals call it...

Like I said at the start of this post, I'm sure you'll understand a LOT more about this topic, when you're done with that report, than I do... In the meantime, I'll be continuing to play my game of KSP with the Interstellar mod installed, and *actually be putting microwave beamed-power to use in my (virtual) space program*, instead of just talking about it as a concept...

I appreciate the effort you're putting into your research though- it's certainly never a bad idea to be well-read on a subject.

Regards,

Northstar

[Rakaydos]

If you include systems that still need engineering probems resoved, I'm going to continue to shill for the ATO variation of the Airlaunch approach.

Some of the key optimizations seem to be oscillation-based active drag reduction, to maintain a turbulent free boundary layer that alows larger hull sizes without the drag usually associated with large objects moving at hypersonic speeds.

Another one seems to be using the bow shock as a plasma source for MHD thrusters, alowing the large (but low mass) craft to accelerate as long as the power holds out.

And thin-layer solar cells on the upper surface of the large body being used as a primary power source, both for the drag reduction and the engines as a lightweight power plant, supplimented by batteries at night.

If the efficencies of each of these can be brought to a certian high threshold, ATO goes instantly from unworkable nonsence to a launch system comparable in price to a space elevater "launch", with signficantly cheaper infrastructure. The concept either works or it doesnt, based on whether it can break even, and it it works, it's absurdly good.

[Northstar1989]

If you include systems that still need engineering probems resoved, I'm going to continue to shill for the ATO variation of the Airlaunch approach.

Some of the key optimizations seem to be oscillation-based active drag reduction, to maintain a turbulent free boundary layer that alows larger hull sizes without the drag usually associated with large objects moving at hypersonic speeds.

Another one seems to be using the bow shock as a plasma source for MHD thrusters, alowing the large (but low mass) craft to accelerate as long as the power holds out.

And thin-layer solar cells on the upper surface of the large body being used as a primary power source, both for the drag reduction and the engines as a lightweight power plant, supplimented by batteries at night.

If the efficencies of each of these can be brought to a certian high threshold, ATO goes instantly from unworkable nonsence to a launch system comparable in price to a space elevater "launch", with signficantly cheaper infrastructure. The concept either works or it doesnt, based on whether it can break even, and it it works, it's absurdly good.

I didn't realize before that ATO meant "Airship to Orbit". I thought you meant "Air Takeoff" or some other variety of mothership-launch platform, and was ready to dismiss your post the same way the one I did earlier about mothership launch platforms (don't get me wrong, mothership launch platforms are a GREAT use of current technology and resources, certainly an improvement over conventional launchpads at sea-level: but they're NEVER going to cut costs to the levels we need them to unless combined with something like Microwave Beamed Power and 100% reusable rockets...) This is why you REALLY need to always define your acronyms...

Yeah, Orbital Airships (or Airship-To-Orbit) are a pretty great technology. They're particularly good with Microwave Beamed Power, since the airships accelerate slowly and are thus easy to track. They also can get by with a much lower TWR than a spaceplane or a rocket, which means you could get a MUCH heavier payload to orbit with, say, 200 MW of beamed power for an Air-Augmented Thermal Rocket on an Orbital Airship, than you could with the same thermal rocket on a spaceplane or rocket...

200 MW of Microwave Beamed Power is enough to get a multi-stage thermal rocket carrying a couple nanosatellites to orbit. Or to keep an aircraft with low wing-loading in the sky using Thermal Turbojets with an altitude ceiling roughly comparable to a B-52 Stratofortress (though the Microwave Array alone would cost about $200-400 million using 1 MW units: as much as four to eight B-52H's...), as Thermal Turbojets can obtain much better thrust for a given amount of Thermal Power than a Thermal Rocket, due to their low exhaust velocity and high working-mass... (and an aircraft using them doesn't have to carry any fuel, only a thermal power source, such as a nuclear reactor or Microwave Receiver!)

I don't include any figures on spaceplanes, because there haven't been any built in real-life, aside from VTHL designs piggybacking or riding in the nose of disposable or semi-disposable rockets (like the Shuttle or X-37)

However, that same 200 MW of thermal power could provide consistent acceleration to an orbital airship, at an ISP of approximately 1000 seconds with hydrogen or 650 seconds with ammonia (which is more easily stored without boil-off on the high-altitude aerostat station than an Orbital Airship would depart from, and is also space-storable) on a pure thermal rocket, sufficient to eventually bring a MUCH larger payload to orbit in a single launch.

The ISP figures come from the Wikipedia articles on Solar Thermal and Laser Thermal propulsion:

http://en.wikipedia.org/wiki/Thermal_rocket

If you made use of an Air-Augmented Thermal Rocket, you could get EVEN HIGHER ISP: your exhaust velocity would go down, but only a portion of your working mass would actually come from internal fuel reserves (similar to how a turbofan engine has high ISP, but low exhaust velocity), so your "Effective Exhaust Velocity" would actually go UP...

http://en.wikipedia.org/wiki/Air-augmented_rocket

It's worth noting that you might be able to operate the Orbital Airship purely off Thermal Turbojets powered by Microwave Beamed Power, for essentially *UNLIMITED* ISP (as the propellant is the air around the ship) in the lower part of the ascent to orbit, before the airspeeds became too high and the atmosphere too thin for a Thermal Turbojet to any longer be effective, and you had to switch to Thermal Rockets...

In short, an Orbital Airship would GREATLY increase the payload you could lift to orbit in each individual launch using Microwave Beamed Power. The beamed power could additionally be augmented by thin-film solar cells sprayed over the envelope of the airship (all that surface area is generating drag- might as well also put it to good use generating electricity for the airship) used to power, in order of increasing altitude ceiling and decreasing TWR: electric propellers, solar Thermal Turbojets, solar Air-Augmented Thermal Rockets, solar Thermal Rockets (same ISP as Air-Augmented Thermal Rockets in vacuum conditions, but with better TWR), or solar-powered Ion Engines.

The cost of using this approach is that you wouldn't be able to launch as many payloads a year this way as with pure Microwave-Powered Thermal Rockets (no "3000 launches a year" using Microwave-Powered Orbital Airships- but the payload carried with each launch would be MUCH heavier).

So, it's a question of fewer, heavier launches vs. a larger number of lighter launches, for the same payload to orbit. The preferable method would have to depend on the payload you want to get to orbit each year, and how much Microwave Beamed Power you provide: there's an optimal balance between the greater-efficiency of heavier launches (better ballistic coefficients, less man-hours at the control center, less mass wasted on guidance/navigation and other control systems, better ISP of larger rocket nozzles near sea-level) vs. the economies of scale of smaller launches (smaller rocket nozzles also get better vacuum ISP- though you can achieve the same effect on larger rockets with engine-clusters of many smaller nozzles...)

OK, I've said enough for now. I'll have to remember to add Airship-to-Orbit to the Original Post, though...

Regards,

Northstar

[Northstar1989]

I hate to necro an old thread, but this is still an interesting topic to discuss, and I feel it would be a huge waste to start over with an entirely new thread...

So, any takers? Anyone have any more thoughts/ideas on this?

I want to take this opportunity to add in a few new thoughts/pieces of information.

First of all, not content to merely TALK about mass drivers, I went out and searched for a functional mod with them. Eventually, I was lucky enough to stumble across an old/outdated mod that had a working part (which wasn't broken by updates)- the Stanford Torus mod. I've went and re-released the Mass Accelerator parts from this mod in keeping with its open source/ open re-use license... (see the mod's pre-release thread for more details)

Second, I wanted to ask about Electrodynamic Tethers. Supposedly, these are devices that can push off Earth's magnetic field using an electric current running through a rotating wire to generate force (the Earth acts as the reaction mass- but is moved very little due to its enormous size). Are these credible? Has anyone else here ever heard of them before?

If they're real, I'd imagine maybe there would even be a way to exploit this on a smaller scale inside of a spacecraft to construct a vehicle that accelerated orbit purely by pushing off the Earth's magnetic field... It's not magic propulsion- there is still reaction mass (the planet itself), it's just not contained inside the spacecraft. Is there something I'm missing here. or would this actually be possible? I'd assume Microwave Beamed Power could be utilized to provide a sufficiently lightweight/dense power source to run such a propulsion system...

Regards,

Northstar

[78stonewobble]

Well, even IF miniaturization allows for all current satellite types to be launched by a laser launch system (an impossibility btw.) it would eat up what? 30 launches a year? For a complex designed to launch thousands of satellites / payloads a year.

That system would be an even bigger waste than the ares or SLS, could possibly be, especially considering that you would still have to have an assortment of other rockets, for payloads too big for the laser launch system.

Rockets are fine for now imho. and they will be fine enough for initial expansion into space, if mass produced on a scale necessary for expansion into space.

[KerikBalm]

There's nothing unrealistic or futuristic about scaling up existing magnetic technology to accomplish this- it simply would be a MASSIVE undertaking, in the same kind of manner as a space elevator would... (though not QUITE that large or expensive)

A space elevator is not just a matter of scaling up existing technology. We have no material with the requisite tensile strength - well, they've made some carbon nanotubes, bu they can't grow those to more than a milimeter or so. There is no technology to grow them bigger, and no way to peice the small bits together and maintaine the tensile strength.

For now, a space elevator on Earth requires unobtanium (though we're getting close to obtaining the needed material).

But it does seem that if it would be possible with current technology to make a massive maglev space gun to launch something nearly into orbit - but it would be a truly massive undertaking. I'm skeptical that the launch vehicle would be in thin enough atmosphere when leaving the tube - but ablative heat shields should be sufficient (but peak heating on reentry occurs before 6-7km I think, and this thing would be launching at orbital velocity already at that altitude...).

But if we're going to assume unlimited resources with current technology....

An orbital ring would be nice.

http://en.wikipedia.org/wiki/Orbital_ring

Its a way to make a space elevator with lower tensile strength material.

Instead of extending the tether out past geostationary orbit, you only extend it up to low earth orbit. At the top is a maglev train that "runs"on a track that completely encircles the planet and rotates at higher than orbital velocity.

"If built by launching the necessary materials from Earth, the estimated cost for the system in 1980s money was around $31 trillion if launched using Shuttle-derived hardware,[4] whereas it could fall to $15 billion with bootstrapping, assuming a large orbital manufacturing facility is available to provide the initial 18,000 tonnes of steel, aluminium, and slag at a low cost,[5] and even lower with orbital rings around the moon. The system's cost per kilogram to place payloads in orbit would be around $0.05."