Escape Dynamics and the Microwave Thermal Spaceplane

[Northstar1989]

This is a thread for discussion of Microwave Thermal Spaceplanes, as are *CURRENTLY* being developed by the company "Escape Dynamics". Read more about them here:

http://escapedynamics.com/

After you've introduced yourself a little to the concept, I suggest doing some more reading about Microwave Beamed Power:

http://en.wikipedia.org/wiki/Beam-powered_propulsion

http://www.cnet.com/news/rocket-scientist-aims-to-relaunch-propulsion-technology/

Only AFTER you're sure you know what this is about, feel free to discuss...

Regards,

Northstar

Edited February 11, 2015 by Northstar1989

[Nibb31]

I think it's way too early to consider beamed powered rockets as the propulsion technology of the future. The real-world engineering of the power station(s) and vehicles, the economical feasibility studies, the ecological impact studies, put it decades away in the future, and as we all know, anything can happen in 20 or 30 years, including better potential power sources, new materials, and a different economical and social environment.

The best that has been done was to make a 50g vehicle hover at 71m by heating ambient air with a laser. That is very far from accelerating several tons to orbital speed while carrying your own propellant. You would really need to scale things up to gargantuan proportions to make this worthwhile, and the investment would be considerable. Divide that investment by the number of expected flights and you get your launch cost.

The wikipedia article quotes "Such a system would use just about 20 dollars' worth of electricity, placing launch costs per kilogram to many times less than current launch costs (which are measured in thousands of dollars)", which is just as stupid as quoting the cost of rocket fuel as if it represented the entire launch cost. It ignores the cost of building what would be the largest laser(s) in the World and developing a whole new infrastructure around the system.

There are plenty of problems to solve before you can even consider it technically possible, let alone viable or beneficial. We don't even have any experience of large scale, long duration, long distance, atmospheric microwave or laser power beaming and there are many problems with the idea. The further you are from a laser, the harder it is to focalize the energy on a specific spot. Maintaining a concentrated beam over 100 km will be extremely difficult. The square law rule means that you lose energy as your distance from the power source increases. We also don't know anything about the environmental impact on wildlife or on the ionization of the upper atmosphere. As for reusability, fast turnaround, or economical viability, those are totally premature considerations when you don't even know how to combine the shape and material constraints of a beam-powered vehicle with hypersonic flight, orbital operations, and reentry conditions. We also don't know the maintenance requirements for the laser. It's going to get seriously hot, so maybe it will need a total stripdown with replacement of crucial parts between each firing.

All of those points might or might not be permanent roadblocks, but at this point, we simply don't know enough about how it would work. At this point, it's just as unfeasible as a space elevator or a launch loop.

Edited February 11, 2015 by Nibb31

[Northstar1989]

I think it's way too early to consider beamed powered rockets as the propulsion technology of the future. The real-world engineering of the power station(s) and vehicles, the economical feasibility studies, the ecological impact studies, put it decades away in the future, and as we all know, anything can happen in 20 or 30 years, including better potential power sources, new materials, and a different economical and social environment.

Any new launch vehicle is at least 10-20 years away from when it's begun. That's not exactly a long time...

The best that has been done was to make a 50g vehicle hover at 71m by heating ambient air with a laser. That is very far from accelerating several tons to orbital speed while carrying your own propellant. You would really need to scale things up to gargantuan proportions to make this worthwhile, and the investment would be considerable. Divide that investment by the number of expected flights and you get your launch cost.

That's a very narrow definition of "best that's been done". We've already built and tested plenty of Microwave Thermal thrusters on the ground, for instance. Why are you bringing up lightcraft anyways? The thread is titled "The Microwave Thermal Spaceplane". Please don't change the subject just to beat up on completely different technologies...

The wikipedia article quotes "Such a system would use just about 20 dollars' worth of electricity, placing launch costs per kilogram to many times less than current launch costs (which are measured in thousands of dollars)", which is just as stupid as quoting the cost of rocket fuel as if it represented the entire launch cost. It ignores the cost of building what would be the largest laser(s) in the World and developing a whole new infrastructure around the system.

It's Wikipedia, what do you expect? But it's an easily-accessible introduction to the subject for many who don't know much about it...

Which clearly includes you, by the way. "World's largest laser"? Did you even bother to read the recommended introduction articles? Nobody in their right mind has ever talked about a single-source beamed-power craft. Every single proposal calls for an ARRAY of a much larger number of lower-powered sources... (which is much more reliable and affordable)

There are plenty of problems to solve before you can even consider it technically possible, let alone viable or beneficial. We don't even have any experience of large scale, long duration, long distance, atmospheric microwave or laser power beaming and there are many problems with the idea.

I'm going to stop you right there, because that's not true. Even Wikipedia is full of articles about long-distance power-beaming technology (used for everything from weapons development to beamed-power research).

Read the introductory articles, and then do some research of your own. The rest of your post smacks of having not actually done anything as simple as a Google search on the subject as well. Most to all of these issues have already been thoroughly researched, and in many cases already solved. It's true, some issues remain- but based on the way you're talking about them, we wouldn't be able to have an intelligent conversation about the subject because, no offense, you haven't done your homework on the subject. Go do some reading. I've read literally dozens of articles, reports, studies, etc. on the subject... (and my brain hurts from doing so more than enough that I don't want to put up with your unwillingness to educate yourself as well...)

I'm not going to put up with you continuing to troll my threads (this isn't the first, or second, or even third time you've shown up with this kind of irritating commentary on one of my threads) so you can talk negatively about things you haven't bothered to do your homework on...

Regards,

Northstar

[Nibb31]

Any new launch vehicle is at least 10-20 years away from when it's begun. That's not exactly a long time...

It takes about 10 years to design and build a new launch vehicle based on well-understood technology, yes.

Rockets are TRL-9, operational and flight proven. Beam-powered launch systems are TRL-2 or 3 at best. I don't see how you could get an operational vehicule up the TRL tree in less than 30 years.

We've already built and tested plenty of Microwave Thermal thrusters on the ground, for instance. Why are you bringing up lightcraft anyways? The thread is titled "The Microwave Thermal Spaceplane". Please don't change the subject just to beat up on completely different technologies...

Lightcraft is the only practical experiment that was mentioned in the links that *you* provided. The Escape Dynamics web page is, well, just a web page. It's on the same level as Golden Spike, Planetary Resources, Kistler, Almaz, or even Skylon. Nice PR, nice vaporware, but no real financial backing or business model for something that would seem to require a multi-billion dollar investment

Besides, why use a spaceplane? In this system, the expensive part is going to be the laser stations, not the vehicle. So why not just make it disposable, at least as a first step? Adding wings, wheels, hydraulics, and a large-surface heatshield is only going to make it heavier and more complicated for no good reason.

And again, you don't even know what shape a beam-powered vehicle would be. Giving it a spaceplane shape only adds a whole lot of engineering constraints that are simply unnecessary at this stage of the concept. Building a microwave thermal thruster that is capable of subsonic, supersonic, hypersonic atmospheric and exoatmospheric propulsion, combined with some sort of rectenna device or heat exchanger and a propellant tank, is going to be the major constraint before you even get into the aerodynamic problems.

First, try getting something into orbit with the system. Only then can you start thinking about reentry, reusability, and fast turnaround.

It's Wikipedia, what do you expect? But it's an easily-accessible introduction to the subject for many who don't know much about it...

Which clearly includes you, by the way. "World's largest laser"? Did you even bother to read the recommended introduction articles? Nobody in their right mind has ever talked about a single-source beamed-power craft. Every single proposal calls for an ARRAY of a much larger number of lower-powered sources... (which is much more reliable and affordable)

Then show us those proposals instead of linking. Give us something to discuss if you want to have a discussion. Nobody here is going to spend a whole day on Google just to qualify to engage with you.

I'm going to stop you right there, because that's not true. Even Wikipedia is full of articles about long-distance power-beaming technology (used for everything from weapons development to beamed-power research).

Can you provide an example of something heavier than a few grams that has actually flown using beamed power? Wake me up when they get a demonstrator vehicle to Mach 1 or Mach 2.

Read the introductory articles, and then do some research of your own. The rest of your post smacks of having not actually done anything as simple as a Google search on the subject as well. Most to all of these issues have already been thoroughly researched, and in many cases already solved. It's true, some issues remain- but based on the way you're talking about them, we wouldn't be able to have an intelligent conversation about the subject because, no offense, you haven't done your homework on the subject. Go do some reading. I've read literally dozens of articles, reports, studies, etc. on the subject... (and my brain hurts from doing so more than enough that I don't want to put up with your unwillingness to educate yourself as well...)

I'm not going to put up with you continuing to troll my threads (this isn't the first, or second, or even third time you've shown up with this kind of irritating commentary on one of my threads) so you can talk negatively about things you haven't bothered to do your homework on..

Yes, I confess. I didn't spend hours researching the subject. The common trend in internet forums is for the OP to bring some content to the table and then have a discussion. The only content you brought were a venture-capital-milking web site, a general news article, and a link to wikipedia that you don't want us to discuss. If you have better sources, then you should be sharing those.

I don't get what's irritating or trollish, except that I question the feasibility of beam-powered orbital flight when nobody has even demonstrated low speed/low altitude flight.

I'm sorry if I don't qualify to the level required to discuss something with you. However, from your tone, I suspect that the only decent qualification in your mind will be to agree that beam-powered propulsion is the only possible path to cheap access to space. Anyone who is going to criticize your pet idea is apparently going to be shot down for not having done their homework.

Edited February 11, 2015 by Nibb31

[LordFerret]

Interesting stuff. Reminds me of tests NASA did not too long ago with pulsed lasers launching a small rocket/cone. If I recall correctly, in years prior, the concerns with beaming microwave energy down to Earth for power systems regarded 'splash'... and that the solution was to base the receivers out in remote unpopulated areas, which defeated the purpose because of the cost/loss of power over long distance transmission lines. I've bookmarked your links for later reading. Thanks.

Edited February 12, 2015 by LordFerret
made not personal

[KSK]

I'm afraid I'm siding with Nibb31 on this one, certainly from the links provided so far.

The Escape Dynamics website is pure puffery. Lots of grand ideas and hand-waving, almost no tangible details. Heck, the cnet article was more informative. Concrete points for discussion:

From the cnet article - "According to Parkin, who is an Escape Dynamics adviser and who wrote his own Ph.D. thesis on microwave thermal propulsion, a beamed energy propulsion system is capable of producing 2.5 times as much thrust as a traditional chemical-based system. He said that the standard system tops out at an energetic reaction of 16 megajoules per kilogram, while the beamed energy approach can reach 40 megajoules per kilogram."

That's good but doesn't sound groundbreaking. A beam powered launch vehicle would still require a substantial amount of propellant, which takes you right back to the good old rocket equation. And at 1MW per Kg (as per the Wikipedia article) for the duration of the flight to orbit, that's a lot of power for any sort of reasonable payload. Put a cubesat in a light-as-possible disposable shell and it might work. Might. A spaceplane would be significantly more challenging.

Also from the cnet article - "Further, he said, there are those who are critical of the very concept of beamed energy propulsion, mainly because they worry that the technology is not really capable of producing enough of an increase in propulsion efficiency to make investing time and money in it worthwhile."

I would say that's an entirely justified concern if you're only looking at a 2.5 x better propulsion system. It is better but it's also untried and going to be expensive.

Pet peeve - "But to Diamandis, bringing high technology into the equation means that for the first time, Moore's Law could be applied to the science of propulsion, and that could mean that the cost of putting payloads in space could very well drop rapidly as does the price of computer components."

What the blue stripey blazers does Moore's Law have to do with anything? Rapid advances in one field of technology don't necessarily have any sort of bearing on advances in another field. We have totally sci-fi phones, but we have a notable lack of flying cars for example. "High technology" isn't some magic wand that automatically makes everything possible.

If anyone could link to a more detailed paper on any of this, I'd be grateful. I'm curious about a lot of the technical details, most notable vehicle steering and giving it sufficient velocity on the right direction to get to orbit. I presume this has already been thought about, so I bring this up as a genuine 'enlighten me' request.

[Vanamonde]

As always, guys, please don't make the science discussions personal.

[Northstar1989]

It takes about 10 years to design and build a new launch vehicle based on well-understood technology, yes.

Rockets are TRL-9, operational and flight proven. Beam-powered launch systems are TRL-2 or 3 at best. I don't see how you could get an operational vehicule up the TRL tree in less than 30 years.

That was my point, which you completely mis-read. 30-40 years isn't all that long a time when it takes 10-20 years just to get something like SLS, Falcon Heavy, or Elon Musk's Mars Colonial Transport Vehicle up and ready even when we have all the requisite technology thoroughly-prepared.

Microwave Thermal Rockets are indeed currently at a low tech-readiness level (to the point were Escape Dynamics' first project is trying to determine how to cheaply mass-produce 100 kW transmitters so they can affordably build an array large enough to get a spaceplane to orbit, which will take at least 30 or 40 MW- apparently the decided to abandon 1 MW gyrotrons which are the current state-of-the-art...), but there are no major scientific barriers that have to be overcome, no laws of physics (or economics) that have to broken. It's just a simple matter of putting in the 20-30 years of hard work to make it a mature, TRL8-9 technology, like chemical rockets already are... Keep in mind that Microwave Thermal Rockets *ARE* a subset of rocket, though- and they still do benefit from a lot of the work already put into chemical rockets like turbopump, materials, and engine-nozzle design...

Lightcraft is the only practical experiment that was mentioned in the links that *you* provided. The Escape Dynamics web page is, well, just a web page. It's on the same level as Golden Spike, Planetary Resources, Kistler, Almaz, or even Skylon. Nice PR, nice vaporware, but no real financial backing or business model for something that would seem to require a multi-billion dollar investment

It's just an introduction. The point was to whet your appetite to learn more. I can easily provide you with more links with more detailed information on Microwave Thermal Rockets. Despite your (arrogant) assumptions, lightcraft are actually much LESS practical experiments than Microwave Thermal Thrusters... Whereas a Microwave Thermal Rockets is really just an extension of the chemical rocket concept, and re-uses a LOT of the same technology (the only new components are the Heat Exchanger and the ground-based transmitters, actually), a Lightcraft is an ENTIRELY different class of vessel that is MUCH further from application than Microwave Thermal Rockets... Don't confuse early results with long-term practicality...

Besides, why use a spaceplane? In this system, the expensive part is going to be the laser stations, not the vehicle. So why not just make it disposable, at least as a first step? Adding wings, wheels, hydraulics, and a large-surface heatshield is only going to make it heavier and more complicated for no good reason.

You clearly didn't read the articles or OP carefully enough (although I might not have done a good enough job explaining it). It's PRECISELY for the reason that the transmitters are the most expensive component that you want to use a spaceplane. A spaceplane can get off the ground with a lot LESS Thrust thanks to its wings (optimal rocket TWR is >2, optimal spaceplane runway TWR is between 0.8 and 0.4), and can rely on Microwave Thermal Turbojets for a large part of its ascent- which get a *MUCH* better Thrust:MW of beamed-power ratio than Microwave Thermal Rockets, due to their much higher working-mass and lower Exhaust Velocity... If you do a spaceplane-ascent right, you don't ever even need a TWR much higher than 1 (if ever)- and you can use Methane instead of Hydrogen as a short "kicker" for a large amount of Thrust at a better Thrust:MW ratio (but a lower ISP) to get out of the atmosphere as quickly as possible once the L/D ratio declines to the point where atmospheric flight is no longer profitable... (you can also deploy a rocket on a suborbital-trajectory once you have kicked your spaceplane out of the atmosphere, if you want, and use most of the beamed-power to circularize that smaller and lighter craft, while the spaceplane glides back down to the surface using its wings and Thermal Turbojets to perform a descent with very little engine-power...)

And again, you don't even know what shape a beam-powered vehicle would be. Giving it a spaceplane shape only adds a whole lot of engineering constraints that are simply unnecessary at this stage of the concept. Building a microwave thermal thruster that is capable of subsonic, supersonic, hypersonic atmospheric and exoatmospheric propulsion, combined with some sort of rectenna device or heat exchanger and a propellant tank, is going to be the major constraint before you even get into the aerodynamic problems.

The aerodynamic challenges aren't easy, and are by far the most involved part of the process- but it's not like we haven't solved for them before. The STS proposal that led to the Shuttle saw the proposal of a large number of saceplanes, some of them capable of relatively good hypersonic performance (even if they didn't make it to space that way- but instead mostly relied on drop-tanks of external tanks and a vertical ascent like the Shuttle...)

The secret is, you DON'T need a spaceplane that flies well at "subsonic, supersonic, hypersonic, and exoatmospheric" conditions- you just need something that is capable of getting off the runway... You design for optimal-performance in hypersonic conditions, and as long as the plane is capable of ascending to the necessary speed+altitude at all, it really doesn't matter how long it takes or how efficiently it gets there. This is because you can use Microwave Thermal Turbojets (which should be designed with optimal hypersonic performance in mind) for your initial propulsion, and the time it takes you to get to the hypersonic regime comes at essentially no mass-penalty because the ATMOSPHERE is your propellant up through this point, and you don't have to carry extra fuel if your plane requires a slower initial ascent due to having highly-swept wings and a high wing-load...

As for the heat exchanger (you don't need, or use, rectenna devices, unless you want a small one for auxiliary electrical power- even though usable aircraft rectennas have been around since the 1960's, where their first demonstrated use was to fly around a toy Microwave-Powered RC helicopter more than 50 years ago...), it's not a particularly difficult engineering-challenge: a scientist was able to build one in his lab using surplus components, a small gyrotron built for laser research, and surplus *GARDENING* equipment from the local hardware store that had an ISP that nearly matched the Space Shuttle Main Engines- which actually isn't particularly good performance for a propulsion system than can achieve 800+ second ISP's (the story of this was in the CNET article I linked, I believe- although if it wasn't I'll definitely have to get you the correct article, as it's quite amusing...) Microwave Thermal Thrusters aren't particularly challenging- it's the Microwave Transmitters that present the real technological hurdle...

First, try getting something into orbit with the system. Only then can you start thinking about reentry, reusability, and fast turnaround.

They're hoping to have a sub scale-demonstration out in 20 years, that can fly around in the atmosphere, and maybe fly itself to orbit (without any payload) without any help. Re-entry and reusability isn't something that they plan to demonstrate with the early model, though- just getting something like this to orbit should be enough to convince people that it's viable...

Reusability is trivially-easy for the Microwave Thermal thruster component of such a spaceplane, though- there are virtually no moving parts outside of the tubopump, and the operating temperatures are MUCH lower than comparable chemical rockets (it relies on the low Molecular Mass of Hydrogen for its high Cacuum Specific Impulse). The turbopump is the only real barrier to reusability- but it's not like that's something Space-X and others aren't already working on...

Then show us those proposals instead of linking. Give us something to discuss if you want to have a discussion. Nobody here is going to spend a whole day on Google just to qualify to engage with you.

I'm not going to post a 12-pge PDF on the thread, obviously. But what I *CAN* do is get you some additional links to the articles so you can read them yourself. If you can't be bothered to click on a simple URL address and read what's on the other side, you probably can't be bothered to have a serious discussion about this anyways...

Can you provide an example of something heavier than a few grams that has actually flown using beamed power? Wake me up when they get a demonstrator vehicle to Mach 1 or Mach 2.

A toy helicopter- which weighed at least a couple kg, was flown around via Microwave Transmitter and rectenna back in the 1960's when this technology was first presented (although it wasn't nearly viable back then like it is today). Microwave Beamed Power has a MUCH longer history in aerospace science/engineering than most people are aware of... Konstantin Tsiolkovsky himself was the first to propose beamed-power as a way to fly spacecraft to orbit- although at the time much of the necessary physics of photons wasn't adequately understood to make this a serious proposal. It's not exactly something new under the sun by ANY stretch of the imagination, it's just that for the first time in world history, we've reached a point where Gyrotron and semiconductor technology is well-developed enough to make a cost-effective proposal for a Microwave Thermal Rocket/Spaceplane a reality...

Yes, I confess. I didn't spend hours researching the subject. The common trend in internet forums is for the OP to bring some content to the table and then have a discussion. The only content you brought were a venture-capital-milking web site, a general news article, and a link to wikipedia that you don't want us to discuss. If you have better sources, then you should be sharing those.

Some of the articles are fairly involved. I thought it would be a good start to give you guys some low-level stuff to digest. I'll post some incrementally more challenging stuff in a second, although I'm going to save some of the really heavyweight stuff until a little later in the discussion... (I could link you to some other forum threads where some of it has been brought up, though- for instance a particularly interesting article on long-distance atmospheric transmission of Microwaves by the Navy- which was looking at using this stuff as a weapon against small speedboats trying to suicide-bomb battleships...)

I don't get what's irritating or trollish, except that I question the feasibility of beam-powered orbital flight when nobody has even demonstrated low speed/low altitude flight.

I'm sorry if I don't qualify to the level required to discuss something with you. However, from your tone, I suspect that the only decent qualification in your mind will be to agree that beam-powered propulsion is the only possible path to cheap access to space. Anyone who is going to criticize your pet idea is apparently going to be shot down for not having done their homework.

I'm open to criticism- but you need to do your homework. I've had some very high-level discussions about this topic before- but those threads focused mainly on rockets. I started this thread to transfer the discussion over more to the advantages of spaceplanes as a better usage of Microwave Power on a MW-for-kN basis...

Regards,

Northstar

- - - Updated - - -

Pet peeve - "But to Diamandis, bringing high technology into the equation means that for the first time, Moore's Law could be applied to the science of propulsion, and that could mean that the cost of putting payloads in space could very well drop rapidly as does the price of computer components."

What the blue stripey blazers does Moore's Law have to do with anything? Rapid advances in one field of technology don't necessarily have any sort of bearing on advances in another field. We have totally sci-fi phones, but we have a notable lack of flying cars for example. "High technology" isn't some magic wand that automatically makes everything possible.

I'll start off by answering this question, because I have to go AFK for a bit, and the CNET article doesn't do a very good job of explaining it...

Microwave Thermal Rocketry benefits from Moore's Law because the technology is inherently one of semiconductor-based electronics. Both the gyrotron/magnetron used to generate the microwaves, and the Microwave Thermal Receiver/ Heat Exchanger itself, are built out of semiconductors.

The Thermal Receiver utilizes semiconductors because, when built to the right layer-thicknesses, they have some of the best pound-for-pound Microwave-absorptivity of any known material. The gytotrons or magnetrons, on the other hand, include a large number of semiconductor components that are necessary to make the transmitter work in the first place. Both are expected (predicted?) to follow Moore's Law with regards to their cost-over-time as the technology needed for manufacturing them matures...

It's roughly-equivalent to saying solar panel technology should follow Moore's Law, because solar panels are also built out of semiconductors. So it's not a perfect assertation, but there is *SOME* evidence to support what he's saying...

Regards,

Northstar

Edited February 11, 2015 by Northstar1989

[magnemoe]

Nice idea, liked the idea too combine heat shield and energy antenna, yes you must be able to run your engine dry, this is that happens then you reenter.

has one benefit in that you can scale down it pretty well, here is also on skeptic point, why not an small test of concept UAV, nothing fancy might well be subsonic, pull it up like an sailplane or drop it and use an small version of the array to power it to prove that it work. Then an slightly larger version who also contain the rocket part, this should be able to test all parts of the system except reentry.

An full scale model would require an full scale array even for ground testing as I see so it would be pretty expensive.

One question how do you launch? You need some attitude before the array can lock on to you? Actually pulling it up like a glider should work even for the full scale model, this has the benefit that you can put the array pretty far away from the runway.

[KerikBalm]

Essentially, this is the same concept as a NTR, but your remove the nuke from the craft, and beam power to it.

Escape Dynamics has nothing tangible, and Skylon is much closer to being a reality than this.

[PB666]

As always, guys, please don't make the science discussions personal.

Oh, damn, I was getting a warm cozy feeling from the conversation, but you provided the perfect seq-way for a couple of comments.

"If A and If B and If C then D" styled conversations are never good and that's why I going to make one.

Suppose one builds a space craft and one needs a huge spike of power, say every 30 minutes for science and communication, but the rest of the time electrical power is hardly being used. Therefore there is an excess of electrical power say 30% of the time that is not being used.

Suppose that craft has alot of science equipment, and say after 2 years at a particular station that science is saturated and there is diminishing returns. Lets also say that its science can be done effectively at a range of orbits, from low earth to translunar.

Suppose that the crafts energy gathering and EM drives where infinitely durable.

Suppose that the electromagnetic drive was relatively lightweight then:

1. It could be used for station keeping

2. It could be used to slowly elevate orbit

3. It could be used during science complete cycle to transit the craft to a new location, for example and Lagrangian point where it can transfer to other planets.

The drive would be ideal since one does not need to plan for the next experiment other than raising orbit. The would be like mars rovers in space, 6 months of planned operation and years of unplanned operation. Alternatively they could be like the philae lander . . . . . .

Extending this logic one step further, the problem with ION drives as we know it is that their gases eventually expire and the charge grids eventually degrade (Or they are going to be huge things (like VASIMR) that consume lots of power. Still VASIMRs ISP is not great, and gas recharging is a problem. So if we are using ION drives as shuttles, and as long as they are shuttling back to low earth orbit then ION drives are just fine, but if not, eventually fuel limits the mission.

An EM drive that picks up stable fuels from high earth orbits and shuttles it between distal sites with low thermodynamic energies (e.g. Lagrangian points of other satellite celestials) might also be a suitable mission.

Sets of purely space problems can be divided along three lines IMO.

1. Transports that need to go to way far off destinations (pluto, alpha centauri, that hot new star with an ancestral-earth like planet)

-Need lots of acceleration C = gravity(earths-surface) * year - for nearest star in a lifetime

-Need a source of energy (like mass energy conversion close to 90%, and hv -> dV conversion of similar efficiency) for a nearest star venture

- ----or------

- very patient. Waiting 10,000s of years for a star to make the right approach and the sending another 10,000 year mission to intercept. with patients you need some very good electronics and power supplies.

2. Transports that need huge bursts of power for very short intervals entering or breaking orbit for some short duration mission, and of course landing or simply carrying the fuel or supplies for landed missions. I should add to this one moving large asteroids.

So EM drives are not suitable for the above.

3. Transports that can use a long slow steady source of thrust, that do not need to create huge dV and that drop their supplies off to 'the big boys' and then return back for more'

Just to state, I have no complaint against 'renewable' low thrust engines, the problem is that any thruster cannot be applied to every problem. We do not see ION drives on cars or launches yet so . . . . . .

And the third issue is this, the concept of IR spectrum and dispersed gases. Space is not devoid of inertia, for example solar winds have very diffuse gas but with high inertia/particle. Said particles have both absorption and emission spectrum. There is actually no particular need to go with complete em drive, one gets a bigger bang if one leverages the impulse against particles that that can be turned to move other directions, the efficiency over time may improve by finding mass for the massless drive.

The key relationship that I observe is that the more mass one ejects, the more thrust force that is available, and the more energy that can be derived from the ejecta (like LF and Ox). The less mass one ejects per unit of engine mass the less force that is available, the higher ISP one can potentially generate, and the higher need for 'arm-stretched out' electrical power. The observation I make is that there is a need for drive with ISP in the 5000s to 15000s range, but that uses power more efficiently. Beyond 15,000s and given both the lack of electrical power is not really necessary since it does not greatly reduce vehicle weight in fuel. Most of the targets are limited to the inner solar system until more reliable power can be obtained. If one can come up with a cheaper source of power - say converts 10% of an atoms weight into electrical energy, then very high ISPs will be more useful, in theory, but in practice, the ability to convert electrical energy into that high of a directional 'impulse' in a confined space may have issues.

The second observation is that without a more efficient solar panel of lower mass, the power equation starts to flatten out, when the weight of the craft exceeds 50% in solar cells, acceleration is reaching its saturation point. This is limiting anyway, so there needs to be a different power source.

[Duxwing]

@KSK We have flying cars; we just also have densely-settled areas full of bad drivers with no autopilot. If the cars flew themselves well-enough not to require FAA babysitting, then we could use them.

-Duxwing

[KSK]

First of all, thanks to Northstar for the reply to my Moore's Law question. That makes more sense now.

Taking another look at the cnet article, I'm still wondering about the tradeoffs with the proposed beamed power engine.

As far as I can see we're still looking at a fairly complex and heavy piece of machinery that's basically half a conventional rocket engine. We've got a supply of cryogenic hydrogen, which isn't the easiest or cheapest stuff to work with, we've got a turbopump and we've got some kind of closed loop to drive that turbopump. It's obviously not as complex as a full hydrolox engine but neither is it a trivial piece of engineering, especially if it also needs to be reliably reusable.

Then on top of that, we've got the added complexity and cost of the microwave transmitter station and the need to keep the beam on-target throughout the launch. Technically it might be feasible, but there seems to be a lot of added complications to stack against the touted performance increase. Or in other words, unless the 2.5x performance increase of your engine can translate into a 2.5x reduction in launch costs then it's not going to be worth it. Reusability will certainly help but then you're facing competition from SpaceX style reusable systems and (far more speculatively) Skylon or other airbreathing reusable launchers.

Of course, we won't know for sure until somebody takes the plunge and tries it, but I can see why the idea hasn't gained a lot of traction yet, and I don't believe that's entirely down to vested interests and scientific conservatism, as the cnet article suggests.

[magnemoe]

First of all, thanks to Northstar for the reply to my Moore's Law question. That makes more sense now.

Taking another look at the cnet article, I'm still wondering about the tradeoffs with the proposed beamed power engine.

As far as I can see we're still looking at a fairly complex and heavy piece of machinery that's basically half a conventional rocket engine. We've got a supply of cryogenic hydrogen, which isn't the easiest or cheapest stuff to work with, we've got a turbopump and we've got some kind of closed loop to drive that turbopump. It's obviously not as complex as a full hydrolox engine but neither is it a trivial piece of engineering, especially if it also needs to be reliably reusable.

Then on top of that, we've got the added complexity and cost of the microwave transmitter station and the need to keep the beam on-target throughout the launch. Technically it might be feasible, but there seems to be a lot of added complications to stack against the touted performance increase. Or in other words, unless the 2.5x performance increase of your engine can translate into a 2.5x reduction in launch costs then it's not going to be worth it. Reusability will certainly help but then you're facing competition from SpaceX style reusable systems and (far more speculatively) Skylon or other airbreathing reusable launchers.

Of course, we won't know for sure until somebody takes the plunge and tries it, but I can see why the idea hasn't gained a lot of traction yet, and I don't believe that's entirely down to vested interests and scientific conservatism, as the cnet article suggests.

Somebody with more data and knowledge know how much power an small subsonic test drone would require, say 100 kg, towed or dropped over the array who then fly for say 30 minutes gaining attitude. That would be something who would draw media interest and investors.

Target lock is not so hard I think, weapons are able to lock on targets, yes you have to aim all the emitters at the heat shield an not much outside.

[Northstar1989]

Somebody with more data and knowledge know how much power an small subsonic test drone would require, say 100 kg, towed or dropped over the array who then fly for say 30 minutes gaining attitude. That would be something who would draw media interest and investors.

Not much, actually. A small UAV with a very low wingload could *EASILY* be driven by a few hundred kW of beamed-power (Escape Dynamics just built a 200 kW prototype unit with Side Lobe Suppression, and 1 MW units are currently available at a market-price of $2 million) to a Thermal Turbojet or even to an electric propeller. Since you're not needing to actually haul around any fuel for an initial low-altitude test, and TTJ's and (especially) electric propellers (powered by a rectenna converting the microwaves to electrical power in the latter case) have a VERY good conversion-rate of kW of beamed-power to Newtons of Thrust compared to a Thermal Rocket (due to the much higher working-mass and lower Exhaust Velocity), you can easily keep an aircraft aloft with a trivial amount of power.

Not that it hasn't already been done before- back in thee 1960's when rectenna technology was first developed, one of the early demonstrations of the technology was to fly around a small (toy-sized) electric helicopter driven by a few kW of beamed microwave power...

Target lock is not so hard I think, weapons are able to lock on targets, yes you have to aim all the emitters at the heat shield an not much outside.

Target-lock can be difficult when you're trying to target something like an ICBM that has been intentionally designed to *AVOID* being locked onto, but it's really not that difficult when you're targeting something like a spaceplane that has an onboard signal-transmitter and onboard telemetry to tell you how accurate your targeting is...

It should be TRIVIAL to target the spaceplane with today's technology: the greater obstacle is actually keeping the beam sufficiently focused to be useful for a vessel of that size at those distances (which is a reason larger spacecraft actually work BETTER with Microwave Beamed Power- you have a larger receiver area, and so your beam doesn't need to be nearly as focused- which leads to EXPONENTIAL decreases in transmitter dish size with progressively larger targets...)

Regards,

Northstar

[Beowolf]

Interesting, Northstar. I never heard of Escape Dynamics before, and appreciate you pointing them out.

The big thing that stuck out for me was mention of getting their power from the grid. I've encountered beamed propulsion several times in hard SF, but think this is the only time they didn't have a dedicated power plant to handle most of the load. I've seen nuclear, stored hydrogen, and even MHD power from a static rocket engine, but never just loading the grid.

How much power are we actually talking about? I didn't see that in either of the places you linked. Seems like it'd need hundreds of MW, and can one really buy that from the grid in 20-minute chunks?

/If so, then can you also buy 1.21 Gigawatts for a couple of seconds? Doc Brown wants to know.

[magnemoe]

Interesting, Northstar. I never heard of Escape Dynamics before, and appreciate you pointing them out.

The big thing that stuck out for me was mention of getting their power from the grid. I've encountered beamed propulsion several times in hard SF, but think this is the only time they didn't have a dedicated power plant to handle most of the load. I've seen nuclear, stored hydrogen, and even MHD power from a static rocket engine, but never just loading the grid.

How much power are we actually talking about? I didn't see that in either of the places you linked. Seems like it'd need hundreds of MW, and can one really buy that from the grid in 20-minute chunks?

/If so, then can you also buy 1.21 Gigawatts for a couple of seconds? Doc Brown wants to know.

As I understand they will not launch this like an rocket, more like an KSP space plane, gaining attitude and speed until you reach supersonic.

However at this point you become an rocket and would want high TWR, this is also the time you move fast away from the emitters.

You might be able to do deals, gas and hydro is pretty fast to ramp up and down, as an fallback you get your own peak load gas plant and store gas for burn.

[KSK]

Not much, actually. A small UAV with a very low wingload could *EASILY* be driven by a few hundred kW of beamed-power (Escape Dynamics just built a 200 kW prototype unit with Side Lobe Suppression, and 1 MW units are currently available at a market-price of $2 million) to a Thermal Turbojet or even to an electric propeller. Since you're not needing to actually haul around any fuel for an initial low-altitude test, and TTJ's and (especially) electric propellers (powered by a rectenna converting the microwaves to electrical power in the latter case) have a VERY good conversion-rate of kW of beamed-power to Newtons of Thrust compared to a Thermal Rocket (due to the much higher working-mass and lower Exhaust Velocity), you can easily keep an aircraft aloft with a trivial amount of power.

Not that it hasn't already been done before- back in thee 1960's when rectenna technology was first developed, one of the early demonstrations of the technology was to fly around a small (toy-sized) electric helicopter driven by a few kW of beamed microwave power...

Oh I'm sure it could work at the UAV scale, I'm just less convinced about it working economically for orbital flight, for the reasons I mentioned before.

Target-lock can be difficult when you're trying to target something like an ICBM that has been intentionally designed to *AVOID* being locked onto, but it's really not that difficult when you're targeting something like a spaceplane that has an onboard signal-transmitter and onboard telemetry to tell you how accurate your targeting is...

It should be TRIVIAL to target the spaceplane with today's technology: the greater obstacle is actually keeping the beam sufficiently focused to be useful for a vessel of that size at those distances (which is a reason larger spacecraft actually work BETTER with Microwave Beamed Power- you have a larger receiver area, and so your beam doesn't need to be nearly as focused- which leads to EXPONENTIAL decreases in transmitter dish size with progressively larger targets...)

Sorry - I didn't put this very well. Targeting the spaceplane - I can see that working, at least until it flies over the horizon. I was just wondering how easy it is to target the right part of the spaceplane throughout its climb? How easy will it be to position the rectenna(s) or microwave absorbing heater or whatever, so that they work reliably at different angles of attack and orientations relative to the emitter array?

[magnemoe]

Sorry - I didn't put this very well. Targeting the spaceplane - I can see that working, at least until it flies over the horizon. I was just wondering how easy it is to target the right part of the spaceplane throughout its climb? How easy will it be to position the rectenna(s) or microwave absorbing heater or whatever, so that they work reliably at different angles of attack and orientations relative to the emitter array?

Yes, you might need 2-3 arrays, the takeoff would be an problem anyway.

[PB666]

Yes, you might need 2-3 arrays, the takeoff would be an problem anyway.

Design your ship like a ray-fish, there is lots of surface area.

Orbital velocity is 17800 you get a boost of about 500 from the turn of the earth plus altitude, that leaves 17200.

Then Mach 3 at high altitude roughly 1000 m/s leaves 16200 dV. Its not worth the extra weight.

In addition you are microwaving a ship that is already as hot as be-jezzuz cause of frictional heating of super-mach speed.

Don't see this working.

[Northstar1989]

Design your ship like a ray-fish, there is lots of surface area.

That's the plan Excape Dynamics is going with, actually- turning the entire belly of the spaceplane into a Microwave Thermal Receiver...

Orbital velocity is 17800 you get a boost of about 500 from the turn of the earth plus altitude, that leaves 17200.

Then Mach 3 at high altitude roughly 1000 m/s leaves 16200 dV. Its not worth the extra weight.

*Cough* it takes 10 km/s for a ROCKET to get to orbit (that includes atmospheric drag and gravity-losses). Orbital velocity is NOT 17.2 km/s. Orbital velocity is about 7.8 km/s.

As I've pointed out repeatedly, Microwave Thermal Thrusters get more than twice the Specific Impulse (ISP) of Hydro/LOX. And, they're much lighter than chemical engines (for 2-3x the TWR, due mostly to lower mass rather than higher Thrust). So it's more like you can't afford *NOT* to carry a Microwave Thermal Thruster- in that it will MASSIVELY reduce your mass-requirements (pun intended).

In addition you are microwaving a ship that is already as hot as be-jezzuz cause of frictional heating of super-mach speed.

The heat you pour into the Microwave Thermal Receiver doesn't remain in the ship. It is used to heat Liquid Hydrogen (which is colder than cold), which then exits the ship. It actually acts to COOL the ship, because the exhaust gasses STILL don't get heated as hot as the frictional heating could potentially get- and will pick up more heat on the way out. Which brings up an interesting point- you could actually use the frictional heating of the spaceplane's skin (especially the belly) to help heat the propellant (at high enough Thrust levels, you would still need more heat-energy than the skin of the spaceplane could provide...), using the Liquid Hydrogen as a coolant. This would help solve two problems (frictional heating, and the need to heat the propellant) with one system!

Don't see this working.

The Microwave Thermal Thrusters have already been proven to work (on the ground). Gyrotrons, the main component of a Microwave Transmitter, are already routinely used in metallurgy. The necessary targeting technologies are already well-developed from warfare. What's NOT to work about it?

Regards,

Northstar

[Kibble]

So it's more like you can't afford *NOT* to carry a Microwave Thermal Thruster- in that it will MASSIVELY reduce your mass-requirements (pun intended).

What's NOT to work about it?

So why has no one flown a microwave-thermal space vehicle ever? I don't know enough about the intricacies of aerospace design to answer that question, but there must be an answer otherwise we wouldn't of been flying only "inefficient chemical rocket engines" since the invention of human spaceflight, with no real flight-worthy microwave-thermal hardware even being considered, much less designed, tested, or flown.

My guess is that the expected returns on the investment in such complex hardware and extensive infrastructure simply aren't high enough to justify replacing the already-sufficient convention of expendable multiple-stage chemical-thermal space vehicles. Especially considering that most of the payloads that go into space at all, are to geosynchronous altitude.

[Northstar1989]

Yes, you might need 2-3 arrays, the takeoff would be an problem anyway.

The most sensible plan (to me) seems to be to have 2 transmitter arrays.

A very SMALL one North-Northeast or South-Southeast of the runway. This would provide the Thrust needed for takeoff. You actually don't need a lot of beamed-power for takeoff, in fact it's the point in your ascent where you need the LEAST beamed-power. This is because you don't have to be traveling as fast to generate enough Lift to get airborne (ESPECIALLY with the Ground-Effect) as you do to stay aloft at higher altitude...

The most energy-efficient Exhaust Velocity in-atmosphere is always the one where your Exhaust Velocity equals your plane's velocity, and you can achieve this at a lower Exhaust Velocity near the ground than at higher altitude. The lower your Exhaust Velocity, the more Thrust/MW you will generate, as:

Thrust = Mass Flow Rate * Exhaust Velocity

Energy = Mass * Velocity^2

Thus, for a fixed Mass Flow Rate (where Mass = Mass Flow Rate) and where your Exhaust Velocity = Spacecraft Velocity, you get...

Thrust = (Energy/ Velocity^2) * Velocity --> Thrust = Energy/Velocity

Which proves, when you are traveling lower in the atmosphere, you can get more Thrust/MW...

What this actually looks like from a engine-design standpoint is that you concentrate the same amount of beamed-power into an increasingly small Working Mass by doing things like switching from high-bypass to low-bypass turbofans to turbojets to rockets, shutting down engines (and concentrating the available beamed-power into a smaller number of engines operating at higher temperature), and possibly even using Electric Propellers (operating off Microwave Beamed-Power via rectennas) to get off the runway in the first place...

Given the different optimal engine designs for different speeds/altitude, an argument could be made for a multiple-stage spaceplane design (such as a Microwave Thermal Tubojet lower-stage that releases an orbiter at max cruising altitude which operates entirely off Microwave Thermal Rockets), although for the smaller-scale payloads that will probably compose most of the launch-diet with this technology early on (until people trust it enough to use it to launch astronauts!) it probably just makes more sense to design for high altitudes and speeds, as you only *just barely* need to be able to make it off the Runway with your Thermal Turbojets...

Anyways, so you use a small transmitter-array near the runway due to the MUCH higher Thrust/MW you get from Thermal Turbojets than Thermal Rockets, and the complete lack of any need for internal reaction-mass when using them. You ascend in slow, lazy circles to stay in range of the transmitter, and then only head East when you're near maximum cruising altitude/speed using Thermal Turbojets... You then switch over to Thermal Rockets as you come in range of the second transmitter array, which should be located a good deal East of the runway...

This ascent-profile is actually the Escape Dynamics plan- although they just rely on a single transmitter-array instead of two!

Regards,

Northstar

- - - Updated - - -

So why has no one flown a microwave-thermal space vehicle ever? I don't know enough about the intricacies of aerospace design to answer that question, but there must be an answer otherwise we wouldn't of been flying only "inefficient chemical rocket engines" since the invention of human spaceflight, with no real flight-worthy microwave-thermal hardware even being considered, much less designed, tested, or flown.

My guess is that the expected returns on the investment in such complex hardware and extensive infrastructure simply aren't high enough to justify replacing the already-sufficient convention of expendable multiple-stage chemical-thermal space vehicles. Especially considering that most of the payloads that go into space at all, are to geosynchronous altitude.

Simple answer: The cost/kg of Microwave Thermal Rocketry has come down *DRAMATICALLY* over the 50+ years since the discovery of Microwave-Beamed Power as a means of wireless power-transmission (in the 1960's with the invention/refinement of the rectenna). It would now cost only around $6000/kg to LEO using a purely ROCKET driven approach with expendable launch-vehicles, but with 1970's technology it could have EASILY cost $60,000/kg or more (for comparison, chemical rockets are about $10,000-$8,000/kg to LEO).

Microwave Thermal Spaceplanes are MUCH cheaper per kg of payload-capacity than Microwave Thermal Rockets, however, due to being reusable AND being able to carry *MUCH, MUCH* more payload to orbit per MW of beamed-power... The same relationship actually exists between MW of Thermal Energy and payload-capacity with chemical spaceplanes vs. rockets, at least in theory- but it's not really limits on the available MW of Thermal Energy that drives up the costs of chemical rockets...

Long Answer: The technology behind Microwave Transmitters, in the form of gyrotrons, has only reached the appropriate stage of maturity (and cost-effectiveness) in the past 10 years or so to make it worthwhile (THIS is the main reason a Microwave Thermal Rocket would be $6,000/kg now, and perhaps $4,000/kg in 2030, but $60,000/kg in 1970). If the space program had started in 2010, it very well *MIGHT* have used Microwave Thermal Rocketry from the start. But the gyrotron technology simply wasn't mature enough back in 1960 to make it worthwhile to use Microwave Beamed-Power for things like the Apollo Program...

Perhaps not surprisingly, maturing gyrotron technology further is one of the TOP priorities for Escape Dynamics, as Microwave Transmitters represent something like 95% of the cost of a Microwave Thermal Rocket (this is also why a Microwave Thermal Spaceplane is worthwhile- even if it costs 10x as much as a Microwave Thermal Rocket per mission for the vehicle itself, it it gets to orbit on half the beamed-power it will actually by CHEAPER than a Microwave Thermal Rocket...)

This has reached the point where Escape Dynamics (which wants to build a SSTO Microwave Thermal Spaceplane!) has hardly even bothered messing around with Microwave Thermal Thrusters yet (which are, by comparison to Microwave Transmitters, relatively cheap and easy), and has instead focused on developing better gyrotrons and Microwave Transmitters- because this will save them more money in the long run... Their most recent breakthrough, a 200 kW Microwave Transmitter with Side Lobe Suppression and a lower cost/kW than existing transmitters, is actually one of their most important- because it means that they will be able to execute their entire launch-architecture *MUCH* more inexpensively than if they had focused on developing better Microwave Thermal Thrusters right off the bat...

There *ARE* labs focusing on Microwave Thermal Thrusters, at *several* universities across the country, though (for instance, check out the webpage of this PhD project at Stanford). So it's not a topic that is being ignored by ANY means...

Regards,

Northstar

Edited February 18, 2015 by Northstar1989

[Nibb31]

Yeah, but again... Let's see a subscale demonstrator that can fly subsonic before dreaming of hypersonic SSTO spaceplanes and extrapolating costs for which you have absolutely no idea.

[shynung]

Seconded. ED should at least be tinkering with microwave-beam R/C planes right now.