Interview with Escape Dynamics on beamed microwave power SSTO spaceplanes

[Streetwind]

If you've not heard, a company called Escape Dynamics announced a few weeks ago that they've successfully completed the firing of a 100 kW beamed microwave thruster in the lab. They are developing this technology in order to build a fully ground-powered SSTO spaceplane.

There's now a lengthy interview with the CEO and CTO of Escape Dynamics on

. It has not only talk, but also computer animations and real video from development prototypes doing fancy things, and is well worth watching IMHO if you're at all interested in this kind of technology. I know that it is dear to the hearts of the devs and players of the KSP Interstellar mod, at minimum

(The TMRO people been out of town and have not been doing shows for two weeks, so the space news segment at the start has a lot of catching up to do. If you don't care about that and just want the interview, jump straight to 18:30.)

Here's some TL;DW info from said interview:

- Vertical takeoff, horizontal landing reusable lifting-body SSTO spaceplane with a 70/30 fuel-mass-fraction

- Initially aimed at 200 kg payload, then scaled up later to about 1000 kg

- Driven by 200 MW beamed microwave power via a heat exchanger on the belly of the plane, which drives a thermal aerospike rocket

- First thruster prototype already works at the 100 kilowatt level, next development milestone is a >1 megawatt model

- More than 500s sea level Isp with helium, more than 700s with hydrogen

- Rapid reusability enabled by simplicity of propulsion system on the plane (literally just a tank, a heat exchanger, a nozzle and some plumbing)

- The beam array will do some fancy precision targeting magic via phase-shifting the microwaves in specific patterns

- Prototype movement-tracking microwave emitter antenna is also already built and working at low power levels

- For LEO launches, just two array locations are required: one small one at the launch site, one large array 200 km downrange

- Aiming for first flight around 2020; company realizes that they have a huge amount of work left, does not want to rush

Please note: I'm making this new thread now because the existing one on the topic, from February this year, has been locked by moderation. Now I know that I'm asking a bit much from this here forum, but it would be great if people could express their opinions calmly and without getting personal. Please remember the THINK principle, remember that none of us amateurs here has all the right answers, and be excellent to each other!

[SomeGuy12]

The basic premise sounds solid. You can get ISPs and thrust to weight ratios far in advance of anything you can carry on a rocket without using nuclear energy. It's straightforward present tech to build phased-array antenna for the microwave transmitter so you can focus it without mirrors and lenses. Microwaves are a longer wavelength, though. What kind of energy losses do you face between the ground and the rocket?

I read the white paper. 55% energy loss at launch, 88% during the circularization burn.

Edited August 9, 2015 by SomeGuy12

[Streetwind]

Honestly, energy is reasonably cheap. 200 megawatts sounds like a lot of power, but if you only need it for 10 minutes to execute an entire mission, that's a surmountable obstacle even with major losses because the total energy will not be that large. And it's a fun thought, but because how rockets work, the power loss probably doesn't even have to be compensated. After all, the vehicle loses mass as it rises. If the power level reaching it goes down, its thrust will suffer, but that only means that the TWR is kept roughly stable along the way. Which you want anyway.

No, I'm wondering more how they plan to run the infrastructure. That's the one point that wasn't really addressed... they plan to have a whole square kilometer worth of microwave emitters. Land is cheap in New Mexico, but machines need maintenance. These are going to be very complex machines, and there will be a lot of them, and they'll have to finance the entire thing up front because they can't run with half an array.

Now that they're actually building hardware that shows the basic premise works, the key factor in this business proposal, I reckon, will be whether or not they save enough on the launch vehicle to pay for the transmitter infrastructure... and do so while lowering prices. I think the guy was pretty smart noting that he's not planning to compete with large rockets that cost $4k per kg to orbit, but rather with the smallsat launchers where even the ambitious startups currently under development run around $25k per kg to orbit. For all the talk of lowering prices to three digits, I think that's pure marketing spin, and the company will rely on feeding on that huge gap between the smallsat launchers and the heavy lifters.

And in a way, if they can manage to bring the price for smallsat launches down to almost paritywith heavy lifters, down to say $5k per kg to orbit, that's still an enormous gain for the market - an 80% price reduction would be a major enabler, one that companies like Rocket Labs or Firefly aren't going to manage. Or let it be $15k for the first generation vehicle, it would still be a big deal if it actually works.

If it works out for the same cost as other smallsat launchers, then well, I suppose it's still a really cool technology (I know I'd love to see launch footage of such a craft at least once), and good for them to have a viable if unexciting business, but to really move something forward it needs to actually keep those promises and be more than just competitive with traditional chemical rockets.

Edited August 9, 2015 by Streetwind

[Lukaszenko]

200 megawatts is nothing, considering how the space shuttle used like 12x that. I imagine that if they intended to launch larger payloads though, they would need similar if not greater power.

Either way, this really sounds like impressive technology. I didn't even know it was being worked on. I'm almost even more excited about this than about Space X's strides. I really hope it pans out.

[AngelLestat]

I would like to know more on the microwave choice vs laser.

With laser you will need high accuracy but you lose less energy, another drawback is that the sky needs to be clear of clouds.

Not sure what energy source can be easily converted into heat for the proppelent.

They use air as proppelent mass in the begining?

[Red Iron Crown]

- Vertical takeoff, horizontal landing reusable lifting-body SSTO spaceplane with a 70/30 fuel-mass-fraction

- More than 500s sea level Isp with helium, more than 700s with hydrogen

That mass fraction and 700s of Isp only yields 8,268m/s of delta-V, not quite enough to reach orbit. The helium Isp is a total no-go. I wonder how much more than 700s they actually get?

[Streetwind]

I don't think so - at least none of the animations or statements given in the interview show anything like that. They only mention that the vehicle runs on hydrogen.

It's probably a power constrained situation. The vehicle has a limited amount of battery power; it'll run a small turbopump to get enough liquid hydrogen to the heat exchanger, and its own computer systems, for a short while. It is supposed to release its payload and deorbit again within a single orbit, and be back on the runway before two hours have passed. It probably doesn't have much juice beyond that.

Meanwhile, an air-augmented system would increase complexity - it would need a closeable intake that doesn't interfere with aerodynamics, and the plumbing and valving necessary to switch from ambient air to a supercryogenic liquid without losing thrust for more than a second or so - as well as more power. Air is not partially self-pressurizing like liquid hydrogen is; the pump would need to be much larger to provide enough reaction mass for the first thirty seconds of flight. All that extra hardware will also eat up part of the gains. And the switchover is something that can go wrong, which is always something that rocket scientists seek to eliminate.

(Disclaimer: this is my own take on it. I wouldn't know what Escape Dynamics would say on the topic.)

[shynung]

That mass fraction and 700s of Isp only yields 8,268m/s of delta-V, not quite enough to reach orbit. The helium Isp is a total no-go. I wonder how much more than 700s they actually get?

700 was sea level I_sp. I'm guessing it goes a bit higher as altitude increases.

If that wasn't enough, a couple SRBs mounted alongside a la STS may be just enough to kick it up a little faster.

[Streetwind]

I would like to know more on the microwave choice vs laser.

With laser you will need high accuracy but you lose less energy, another drawback is that the sky needs to be clear of clouds.

Not sure what energy source can be easily converted into heat for the proppelent.

They use air as proppelent mass in the begining?

I don't think so - at least none of the animations or statements given in the interview show anything like that. They only mention that the vehicle runs on hydrogen.

It's probably a power constrained situation. The vehicle has a limited amount of battery power; it'll run a small turbopump to get enough liquid hydrogen to the heat exchanger, and its own computer systems, for a short while. It is supposed to release its payload and deorbit again within a single orbit, and be back on the runway before two hours have passed. It probably doesn't have much juice beyond that.

Meanwhile, an air-augmented system would increase complexity - it would need a closeable intake that doesn't interfere with aerodynamics, and the plumbing and valving necessary to switch from ambient air to a supercryogenic liquid without losing thrust for more than a second or so - as well as more power. Air is not partially self-pressurizing like liquid hydrogen is; the pump would need to be much larger to provide enough reaction mass for the first thirty seconds of flight. All that extra hardware will also eat up part of the gains. And the switchover is something that can go wrong, which is always something that rocket scientists seek to eliminate.

(Disclaimer: this is my own take on it. I wouldn't know what Escape Dynamics would say on the topic.)

That mass fraction and 700s of Isp only yields 8,268m/s of delta-V, not quite enough to reach orbit. The helium Isp is a total no-go. I wonder how much more than 700s they actually get?

Helium is used for development because it's easier to handle. They showed a graph from a test run that had the Isp oscillate constantly between 500 and 600, averaging about 550. The "over 700s with hydrogen" is extrapolated from the current prototype's performance with helium, but I can't say if it's a lower bound like the 500s is for helium, or an average. The "70/30" was a number the guy dropped while comparing their proposed plane to conventional rockets - and I'll mention that to my mild irritation, he kept talking about payload fraction and fuel-mass fraction as if they were the same thing It's likely that that number isn't to be taken entirely seriously, but then again that depends on the development success of the engine. And an 80/20 setup with 750s Isp can get into orbit just fine while still beating out a two-stage chemical rocket, so it's not like single-staging useful payload is physically impossible with this sort of performance.

Edited August 10, 2015 by Streetwind

[Kerbart]

Getting into orbit is easy. Take a container of oxidizer, a container of fuel, run them through a turbo pump, mix & ignite, and point your rocket up and then gradually to the horizon as it gains altitude.

Given that it's conceptually so easy really makes me wonder why not every country has a space station. What? Execution is hard? Ooooh.

So what does it really mean that this company has a "proof of concept" and can "transmit power through a microwave beam in a laboratory?"

It probably means they need money from inventors. Unless they're beaming 50MW from one mountain top to another 20 kilometers away, I'm not impressed. Yes, they have a concept. I can build a bottle rocket. Does that mean I'm running a spaceprogram, because I showed that conceptually my rockets work? Execution is the incredible, incredible hard part and they haven't showed anything close to it. I'll be impressed if they get it to work but I suspect that, after securing millions from their investors, this is the last we'll hear from them.

[Red Iron Crown]

700 was sea level I_sp. I'm guessing it goes a bit higher as altitude increases.

If that wasn't enough, a couple SRBs mounted alongside a la STS may be just enough to kick it up a little faster.

That's a good point I hadn't thought of, thank you.

[Streetwind]

It has an aerospike nozzle, so it should gain a good amount while rising out of the atmosphere without needing to stage, yes.

But: I don't know if the numbers quoted were from testing in a vacuum chamber or not... the closed compartment arund the test stand didn't precisely look like a typical vacuum chamber, but it does have a closed compartment in any case (for microwave shielding at minimum).

[KerikBalm]

700s Isp @ sea level seems awefully high... the basics of this are the same as a NTR... except instead of a reactor core, you have a microwave receiver....

How hot can you really get that microwave receiver? Enough to get 700s at sea level seems to imply much more in a vacuum... beyond what Nerva could get...

[Red Iron Crown]

NERVA used a vacuum optimized nozzle though, didn't it? And still delivered ~380s ASL Isp. An aerospike doing a good bit better is not unimaginable.

[Streetwind]

Additionally, the NERVA's reactor couldn't get arbitrarily hot without melting its constituent parts and/or fuel rods. Meanwhile the heat exchanger on this spaceplane uses a fancy-named modern carbide material which potentially might be able to get hotter, since it will be just a single part that can be rated for a certain operating temperature as a whole and is not limited by a "weakest link" like a reactor might be.

(Yes, this is speculation. I don't know how hot the heat exchanger is projected to get.)

[KerikBalm]

"NERVA used a vacuum optimized nozzle though, didn't it? And still delivered ~380s ASL Isp. An aerospike doing a good bit better is not unimaginable."

Yes, vacuum optimized... but lets not think that aerospikes work like the pre-1.0 aerospikes where they get vacuum level performance at sea level...

I'd expect something in the 400's or 500's, 700 is surprising to me...

But I don't have any math on that... just a guess based on various Isps for engines using the same fuel, but nozzles optimized for operating in a vacuum vs a first stage.

"Additionally, the NERVA's reactor couldn't get arbitrarily hot without melting its constituent parts and/or fuel rods. Meanwhile the heat exchanger on this spaceplane uses a fancy-named modern carbide material which potentially might be able to get hotter"

Well, its the same problem... how hot can the part get?

Nuclear reactors aren't actually that mechanically complicated... as nuclear lightbulb/liquid core/etc demonstrate.

Get enough Uranium that is enriched enough for U235 together, and you'll get a lot of heat produced.

The fuel rods would also be encased in some pretty fancy materials too (I'm pretty sure they didn't want the exhaust to make direct contact with the uranium fuel... for environmental concerns) that were supposed to have some pretty high melting points...

If they can substantially exceed those temperatures with this, that would suggest a next generation NERVA could do much better, without resorting to the radiation absurdity that is a liquid core design.

(Gas core would still be awesome)

[AngelLestat]

Well this old concept used the air (inside the atmosphere) as proppelent converted into plasma by the laser.

Not sure what happens with that idea, I imagine that should be many drawbacks, but the tests at low scale seems to work fine.

[Neil1993]

My first exposure to this idea was actually at the International Space Development Conference last May. By the time they rolled up, we had already heard the idea of using "Energy Beams" so much that it had become a running gag for my colleagues and I. The concept of beamed power is actually being slapped on to a lot of concept studies in a way that almost makes them seem like a Deus Ex Machina. This is a little different, however, seeing as the beamed power aspect is central to the craft. In the end, I have a feeling that by the time everything is developed for this craft to work, there will be more viable and practical technology available.

I guess we'll just have to see.

[kerbiloid]

Project cancelled in the end of 2015 due to high risks and constantly being reviewed price. This deterred its investors.

 

 

[Streetwind]

Yeah, I heard. It's a crying shame.   This really had me excited.

[Nibb31]

If you get excited by "new space" PR, you're signing up for a lot disappointment in life.

[SomeGuy123]

Aww.  It was a cool idea.  One nasty problem with something like this is that it costs a bunch of money in infrastructure.  (those massive microwave arrays).  So you need a large launch volume to make enough money to break even.

Except, supply and demand doesn't work that way.  Suppose you can break even if you launch 10 times global launch volume at $2000/kg.  Sounds good, right?  

The issue is that there just may not be enough demand for 10 times the current spaceflight volume at that still relatively high price.  $2000/kg is still very expensive, and so only delicate and light satellites are worth it, and you only need so many of those.

[wumpus]

2 hours ago, SomeGuy123 said:

Aww.  It was a cool idea.  One nasty problem with something like this is that it costs a bunch of money in infrastructure.  (those massive microwave arrays).  So you need a large launch volume to make enough money to break even.

Except, supply and demand doesn't work that way.  Suppose you can break even if you launch 10 times global launch volume at $2000/kg.  Sounds good, right?  

The issue is that there just may not be enough demand for 10 times the current spaceflight volume at that still relatively high price.  $2000/kg is still very expensive, and so only delicate and light satellites are worth it, and you only need so many of those.

A lot depends on passenger travel.  I suspect the value of high-speed China-US-EU travel to be pretty huge.  On the other hand, this is obviously optimized for orbital and beyond (no idea if you could lose less than 88% by doing an escape burn right after leaving the atmosphere but before circularization).  You need a huge percentage of the orbital velocity to get a significant suborbital flight (much beyond the Concorde's NYC-Paris range).

And people wonder why throwing a rockets makes sense.  This has to be the most workable means of getting into orbit I've seen. I wonder how much a 200WM maser really costs, anyway?  Too little for NASA, too much for private industry? 

[fredinno]

 

On August 10, 2015 at 6:31 AM, shynung said:

700 was sea level I_sp. I'm guessing it goes a bit higher as altitude increases.

If that wasn't enough, a couple SRBs mounted alongside a la STS may be just enough to kick it up a little faster.

...And also increase costs.