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Comment: Re:Hype pain (Score 1) 75

by brambus (#49517889) Attached to: Rocket Lab Unveils "Electric" Rocket Engine
Their design trades chamber pressure and engine Isp for lower pumping power requirements. They have 9 engines with pumps in the 50HP range, so around 350kW of pumping power. That really isn't able to give much more than 3-4MPa, which also roughly meshes with their claimed Isp figures (~270s at SL). The required power for self-feeding of fuel to the turbine engine is comparatively tiny, perhaps less than 1% of the overall output power requirement. As for cooling, they said they're using regenerative.

Comment: Re:DAB or DAB+? (Score 1) 293

by brambus (#49512523) Attached to: Norway Will Switch Off FM Radio In 2017

112k mono

Is perfectly workable. The lack of a second channel almost cuts bitrate requirements in half. Then again, it's mono, so yuck!

99% of DAB radio is in mono

That's just f'ing atrocious.

The other stereo station on DAB reduced from 192k to 128k

If it's MP2, then yuck again! AAC at 128k is near transparent. MP2 is definitely not!

in no way is that an FM replacement, the dropping bitrate makes even the mono stations sound bad

It would be an FM replacement, *if* they were to use it right. Unfortunately, it seems most stations are hell-bent on crapping all over sound quality to save a few bucks on bandwidth.

Comment: Re:Hype pain (Score 1) 75

by brambus (#49507289) Attached to: Rocket Lab Unveils "Electric" Rocket Engine

You can in fact just "dunk" the rotor in LOX.

Have you see this demonstrated on 1000HP-scale motors? Again, scale is the big question here.

Using AC Induction

They're using DC motors. The additional weight of inverters would be quite a cost. And an AC motor would heat up internally as well, away from the cooling liquid. You just can't get around it, as soon as you induce any current, you get losses and heat production. At your 5HP, it may be a non-issue. At >1000HP maybe not so much any more.

They have made the motor. It performs to their specifications.

Yes, and in other posts I have also calculated their specifications. OK performance for a modern hydrocarbon engine, but certainly not amazing. Very power limited (9 engines for only a 10 ton rocket?!) Less efficient than a much larger Merlin 1D and far less efficient than a staged cycle engine. So yeah, compromises, exactly like I said.

The next hardest part is controlling the rocket, which is going to be a damn sight easier with electric fuel pumps (Think fuel injection for your car, same principle).

Eeh, what? Rocket control (by which I presume you mean flight control) has almost nothing to do with engine cycle and everything to do with aerodynamics. Car control also has dick-all to do with fuel injection. A car is equally controllable whether it's fuel injected, carburated, naturally or forced-induction aspirated, etc. Moreover, my point wasn't that they didn't have a working engine. Of course I knew they had. But there's an awful lot of engineering that goes into rocket design besides the engines. It isn't "just a bunch of tubes around the engine". It takes an enormous amount of effort to take an engine which runs on a test stand and building a flyable piece of hardware using it. Take airplanes for instance. Yeah, 25% of the cost is in the engines, but that doesn't mean the remaining 75% doesn't exist. It just means that it's subdivided into millions of other parts, which together mean you've still got a lot of work ahead of yourself. And that's before we get to the regulatory and red-tape stuff that everything with the label "aerospace" is totally swamped with.

They are not using *rechargeable* batteries.

That's what I've been saying all along and I used it in my calculations. See about 4 posts back.

Comment: Re:Hype pain (Score 1) 75

by brambus (#49503673) Attached to: Rocket Lab Unveils "Electric" Rocket Engine
Thanks, all of those I already read. Like I said, it's a compromise between cost/complexity and performance. Because their turbopump is so small (50HP really isn't much), they're running 9 engines on the 1st stage. Let that sink in. 9 engines on a 10-ton rocket. 450HP total will also give you quite low chamber pressure (probably in the 3-4MPa range), which pretty much meshes with the Isp I calculated for their first stage (272s at sea level). That's less than a much larger Merlin-1D can manage (282s at SL) and a far cry from what large staged combustion engines can do (RD-180, 311s at SL).
Also, their statement that they can build a Rutherford in 3 days is somewhat dishonest. First of all, they need to build 9 of them (so 27 days) for the 1st stage and one of the main reasons why building rocket engines takes so long is because large engines need custom machining, fitting, welding and subsequent assembly testing. These guys are 3D-printing their parts, so it's a lot simpler. It's really significantly a function of size. If they tried building something the size of a Merlin 1D, I can guarantee you they wouldn't be doing it in 3 days.

Comment: Re:Hype pain (Score 1) 75

by brambus (#49503649) Attached to: Rocket Lab Unveils "Electric" Rocket Engine

There is no cryo equipment.

I meant the piping and pumping and internal structure required inside of the motor to get the heat exchange. You can't just dunk the motor inside of a pool of LOX and expect it to work, because the LOX will add friction, reducing power, and surface-to-volume means internal parts not in contact with it will overheat regardless. In engineering, scaling from 50HP to 1000HP isn't as simple as multiplication.

No, I mean a kerosene Fuel Cell

What's the efficiency of that? If it's comparable to hydrogen, it's probably not even worth it. Also can you point to a kerosene-hydrogen fuel cell capable of delivering 1MW continuously and that's also aerospace-grade?

At the end of the day, These folks have *made* an electric pump driven rocket

They have not made the rocket. They have made some prototypes of the engines and have nice drawings on their website. But as far as flying hardware, it's a pipe dream so far.

I suspect its an offshoot of the idiotic public bias against electric drive vs ICE for passenger vehicles.

You suspect wrong. The reason I'm skeptical is because a system with lots of intermediate energy conversion steps tends to be a lot less efficient and more complex. Now if we had batteries with an order of magnitude more energy density, it'd be an open and shut case. But until such time, it's simply a compromise between performance and cost.

Comment: Re:Hype pain (Score 1) 75

by brambus (#49502043) Attached to: Rocket Lab Unveils "Electric" Rocket Engine
You forgot the pump/compressor assembly. The engine itself is only a part of the weight I considered. I was also quite conservative, you could probably get it closer to 40kg for a purpose-built 1MW unit.

End of the day, I would be surprised if the motors they have are not producing close to 50 HP / Kg.

Which at 1MW would come to 27kg just for the motor. Then add on the cryo equipment, fuel pump and everything and you'd be at a lot more than that. Also, let's see that scaled up, because surface-to-volume can really mess these assumptions up. Just the electrical wiring needed to carry MW-type powers is no joke.

I have personally seen a 5 HP cryogenic motor that weighed about 300 grams.

I hope you meant 50HP, otherwise it'd be just silly (>260kg at 1MW assuming linear scaling). Also, let's see it productized and available commercially. In a lab for a few seconds you can get away with almost anything.

Also, you'd be crazy to use Li-ion batteries.

I said lithium, not lithium-ion. Rechargeable batteries have even worse specific energy and there's no need for recharging in a use-once scenario.

You already have an awesome fuel supply it would make far more sense to use a fuel cell.

If by "fuel cell" you mean hydrogen fuel cell, hydrogen is used on very few lift stages. So add the complexity of another fuel supply and dedicated tankage. Also, fuel cell efficiency is in the 50% range, with the rest emerging as heat (and possibly even less efficiency at the extremely high power densities you propose). Combine with a 80-90% efficient motor and you're back to turbopump levels of efficiency. So all you've done is made the rocket engine much more complicated and expensive for no gain. Honestly, if efficiency at all cost was your motto, just use a staged cycle engine.

Comment: Re:Hype pain (Score 4, Informative) 75

by brambus (#49501323) Attached to: Rocket Lab Unveils "Electric" Rocket Engine
Turbine engines typically achieve around 33%-34% efficiency. Going off of Wikipedia, non-rechargeable lithium batteries are around 1.8MJ/kg, whereas kerosene is around 46MJ/kg. Now with kerosene, you need to carry around another 2.5 parts of oxygen, so gram-for-gram, the split is around 13 MJ/kg for RP-1/LOX. Accounting for engine efficiency, it comes to around 1.6MJ/kg for non-rechargeable lithium batteries driving an electric motor pump vs. 4.5MJ/kg for an RP-1/LOX turbopump. IOW, the turbopump version is around 3x more efficient. Now the dry weight of the assembly. A 1MW turbopump can be built in as little as 50kg (in fact, the Merlin 1C turbopump weights around 70kg and produces 1.86MW). A comparable DC electric motor would probably weigh in at close 2x than that. Not to mention, the dry weight of the turbopump is just the pump plus about 4-5% of the fuel weight for the tank to hold it, whereas for the electric motor pump + batteries, dry weight is essentially unchanged throughout the entire burn.
Overall for a 1MW pump system for a 120s burn, the numbers would stack up roughly like this:
  • wet turbopump: 50kg + 8kg of fuel + 20kg of oxidizer + 2kg tank, total: 80kg.
  • dry turbopump: 50kg + 2kg tank = 52kg
  • wet & dry motor + batteries: 100kg motor with pump, 74kg batteries, total: 174kg.

From a pure performance perspective, electrically driven pumps in rocket engines are simply worse. However, considering the cost and complexity of turbopumps and the relatively small part that fuel pumping overhead contributes to overall efficiency, it may be a cost worth paying, especially on a smaller launch vehicle, where the electrical equipment is relatively cheap. I'm not convinced ti scales to multi-MN engines, though, as there the electrical requirements would be enormous (100MW+ electric motors are somewhat impractical, as is the supporting electrical equipment).

Comment: Re:Sensors wrong (Score 5, Insightful) 460

by brambus (#49422359) Attached to: Planes Without Pilots
This is such an ignorant post I can't believe it. It appears you've never actually had an airplane's controls in your hands.
1) Fly-by-wire isn't what you think it is. It simply means there are no mechanical linkages.
2) Airbus' computer-over-human approach is no panacea and it has resulted in numerous near-disasters, one of the most recent ones.
3) Even Airbus isn't religious about this approach. Read up on Alternate Law and Direct Law.
4) Had Sully not maneuvered USAirways 1549, it'd have landed in the middle of housing.
5) Water landings require you to do a flare & float to stall just feet above the water level to minimize airspeed. If he had not done this, the airplane could have easily smashed itself apart, since an A320 power-off glide rate of descent is around 1500 fpm. Water isn't soft at these kinds of speeds you know.

Comment: Re:15 minutes buffer ? (Score 3, Interesting) 447

by brambus (#49364851) Attached to: Why the Final Moments Inside a Cockpit Are Heard But Not Seen
Agreed, and this is already how the cockpit voice recorder (CVR) works, but it records for a lot longer (around 24 hours, IIRC). Personally, as a pilot I wouldn't mind a 24-hour circular video buffer that's stored on the airplane and not automatically archived unless there's an incident - in that situation, I'd wanna have as much data available as possible, as that improves the chance of preventing a future occurrence. Preferably not just a wide-angle lens inside of the cockpit, but also perhaps a closeup of the instrument panel so that indications displayed to pilots are clearly visible.
ATC operators are already being filmed left and right (in addition to voice recorded) when they're at their stations and the footage is archived as well, so why should pilots not be similarly scrutinized is beyond me.

Comment: Re:Photosynthesis thumbs up! (Score 1) 65

by brambus (#49224735) Attached to: Solar Impulse Plane Begins Epic Global Flight
Fully agree here, a solar-powered blimp might actually not be such a bad idea, especially when your goal is primarily loitering for hours on end over something like a race track, or conducting traffic surveillance. However, for transport, especially mid- to long-distance transport, it's a horrible idea. It's akin to placing solar panels on roofs of cars and expecting to be able to use it practically, except much worse due to the much higher drag and power requirements of airplanes.

Comment: Re:Five months? (Score 1) 65

by brambus (#49219539) Attached to: Solar Impulse Plane Begins Epic Global Flight

Just as well not everyone is as limited in their imagination as you.

Please do give me a call when your imagination figures out a way to break the laws of physics. There's no problem with having your head in the clouds, as long as your feet are firmly on the ground. No amount of inventive imagination is going to let you circumvent things like conservation of energy.

Comment: Re:Photosynthesis thumbs up! (Score 1) 65

by brambus (#49219451) Attached to: Solar Impulse Plane Begins Epic Global Flight

A Boeing 777 is designed for speed. If you're not in a hurry, solar power might just be a reasonable option very soon.

No, a Boeing 777 is built for efficiency and "good enough" speed. High speed rail is already killing short-haul aviation in many places around the world.
Anyway, let's play this game. How slow is slow enough? The Solar Impulse cruises at 35 knots true airspeed - given upper altitude winds, your actual ground speed might in fact be negative on many days. Just to give you a taster of the energy requirements of "slow" flight (I have the actual manufacturer perf tables): at the lightest loadout (10000 lbs) and lowest and most economical cruise power setting, a 19-passenger Beechcraft 1900D airliner cruises at 25000 feet at 209 KTAS and requires 502 kW of power to do so (2 x 1400 rpm x 1266 lbft). It's surface area is probably less than 1/10 of that of the Solar Impulse. So even assuming 100% efficient power conversion, you're more than an order of magnitude removed. And that's assuming huge concessions to the lightness of the airplane (~3t empty airplane to carry 19 passengers - totally unrealistic), which given current electrical component & battery weight is just pure science fiction.

Comment: Re:Five months? (Score 1) 65

by brambus (#49218971) Attached to: Solar Impulse Plane Begins Epic Global Flight
Oh yeah, the safety is a whole other matter :) The reason I took it from a physics angle is that if the basic physics isn't there, we don't even need to consider the question of safety and risks (which are, to a much larger degree, qualitative). It'd be like discussing the safety implications of intergalactic wormhole transportation technology.

Comment: Re:Five months? (Score 1) 65

by brambus (#49217057) Attached to: Solar Impulse Plane Begins Epic Global Flight
I know they charge during the day and use that to run during the night, however, that's not really addressing the basic power requirement problem.
I'm glad to see you acknowledge that this is probably not realistic to power an airliner and I'm sorry to put a dampening on your hopes for this being used to power on-board systems. The electrical draw in an airplane is minuscule compared to the mechanical load of just moving the airplane through the air. As I've calculated, the 777 requires about 100 MW of power to cruise. I'd be surprised if the electrical load was anything more than 1/1000 of that (100 kW) - pretty much a drop in a bucket when it comes to the engines. A much higher load, in fact, are things like bleed air (used to pressurize the cabin, among other things) and anti-ice systems. The electrical load is in fact so small, that modern commercial airliners have a thing called a RAT (Ram Air Turbine), a miniature windmill electrical generator, that serves as a backup should all on-board power generation fail (which is triple-redundant in the 777) and is capable of providing several kW worth of last-resort backup power for things like avionics, electrical hydraulic pumps and emergency lighting.

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