November 30, 2013

Mouretsu Pirates -- thrusters

Our current rocket technology is, needless to say, quite primitive. Because of inherent problems with using a reaction drive, space launch is very expensive.

But it doesn't need to be. A reaction drive (that's any drive that is based on momentum change caused by high speed ejection of propellant) can be extremely efficient if the exhaust velocity is high enough. Our current problem is that the exhaust velocity of our rockets isn't all that high, so propellant efficiency is terrible.

In Mouretsu Pirates they have direct conversion of matter to energy, which is able to provide the kind of power that current rocket engineers could only dream of. And they also have inertia control and gravity control.

I was trying to think about how their thrusters work, and it suddenly occurred to me that it might be a form of gravity control. If the propellant is subjected to several hundred G's, and achieves an exhaust velocity of one or two percent of C, the propellant efficiency would be very high, and you've solved the major problem.

They have single-stage-to-orbit shuttles, and if they were powered the way I think they are, then it becomes very practical to build large structures in orbit, like the docking station orbiting Uminoakehoshi. Combined with efficient FTL drives (which they also have) then bulk interstellar trade becomes practical.

We can only dream of such technology, but it doesn't cost anything to dream.

UPDATE: Of course, they couldn't operate that way all the time. If they were firing 0.02*C while exiting from a space dock, they'd punch a hole in the side of the station with their exhaust.

Posted by: Steven Den Beste in Engineer's Disease at 09:55 AM | Comments (12) | Add Comment
Post contains 276 words, total size 2 kb.

1 Inertial dampers and artificial gravity often seem to get used as the magic wand of "mushy" sci-fi (everything from B5 to SG-1); but, it does make sense.  If you can somehow control those two forces, even in a small way, the game changes.  If you follow them to their logical conclusion, though, every engine becomes a WMD (Schlock in particular has covered this).

Have you seen the recent stories on the theoretical warp drive?  The Puppyblender just posted one today--the mathematical estimate for the required mass just dropped from Jupiter to a subcompact car.  I particularly liked the scientist's approach--the math says it's theoretically possible, but he makes no promises that it will actually work in the real world, and is building small-scale tests to find out.

Posted by: BigD at November 30, 2013 02:41 PM (VKO9N)


Have you seen the recent stories on the theoretical warp drive?

Yes, but I don't want to talk about it here. Please avoid topic drift.

Posted by: Steven Den Beste at November 30, 2013 04:29 PM (+rSRq)

3 The other problem with reaction drives is bulky, dangerous reactants, that frankly, don't have a lot of density. But if what you're spitting out of your thrusters isn't part of the reaction, it could be anything, and why not Lead, or waste material from your reactors (Although the environmentalists would pitch a fit)? It's gotta be better than being in the same ship with bottles of Hydrazine and Hydrogen Peroxide.

(I have some personal theories about the relationship between time and gravity that are irrelevant to the discussion of thrusters, but might come into play with Warp technology).

Posted by: Mauser at November 30, 2013 06:08 PM (TJ7ih)


I figure they're using water. There's no reason to use anything else. The density is reasonable, and it's easy to pump around, and it isn't very corrosive, and it isn't poisonous. And, of course, it's plentiful down on the planet.

Certainly they could be using something like lead, but why bother? Anything they could get by using something truly dense, they can also get by increasing the exhaust velocity. Assuming easy energy and gravity control, they don't have a problem doing that.

Posted by: Steven Den Beste at November 30, 2013 09:08 PM (+rSRq)

5 It needs to be noted that contemporary rockets can be made 100 or 1000 times cheaper just by engineering them differently, most importantly by making them truly reusable. Engineering for the economic efficiency in general would help too. By a point of comparison, the cost of fuel for an airliner is about half of the price of ticket nowadays (it varies; in some cases taxes and government fees come close to 1/2 (was way more 1/3 last time I flew to Australia), so fuel share falls to 1/3). The cost of fuel for a rocket, however, is only 0.2% of the price of the flight -- for the cheapest American rocket. It's even smaller for, e.g. Atlas V: probably less than 0.08%. If rockets were made just 10 times WORSE than airliners, their price would decreas 100-fold. Put it another way, if airlines purchased a Boeing 747 and threw it away after each flight, an economy ticket from San Francisco to Tokyo would cost $500,000. In actual fact it's 500 times cheaper than that, simply because airplane is not thrown away like a rocket. Note that in this second case like is compared to like, so the talk of rockets being "harder" does not apply (it's rubbish anyway -- a subject for another rant). Steven's second sentence is so wrong-headed that it always sets my teeth on edge when I see it repeated uncritically.

Posted by: Pete Zaitcev at November 30, 2013 09:09 PM (5aqkA)

6 Water is kind of valuable in space. but say, a nickel-iron asteroid, that's a ton of reaction mass in a fraction of the volume, and common as dirt.  It may also work better in some kind of linear accelerator type engine.

As for not throwing away rockets, one should take a good long look at what SpaceX is doing with their booster, once they're ready to re-ignite and stabilize on re-entry, they might be touching down on its tail at the launchpad the way God and Robert Heinlein intended.  Kerosene is cheap, they say.

Posted by: Mauser at December 01, 2013 04:44 AM (TJ7ih)


You're still thinking in terms of expensive lift. When you have the technology to lift material in thousand-ton lots, water isn't particularly any more valuable than anything else.

But water can be held in tanks, and run through pipes, which is a bit difficult for nickle-iron.

Posted by: Steven Den Beste at December 01, 2013 06:40 AM (+rSRq)

8 Depending on how they do matter/energy conversion, wouldn't one possibility be "do the m/e conversion in the rocket chamber"?  Convert, say, 1/100th the mass in the chamber to energy, which turns the rest of the mass in the chamber to extremely high energy exhaust.  No need to use any intermediary steps.

Granted, this depends on being able to do the m/e conversion in a rocket chamber.

Posted by: metaphysician at December 01, 2013 08:32 AM (3GCAl)


Well, probably not. The system seems to be set up like a diesel-electric engine is set up, with power being produced by the matter converters Ago and Ungo, and power then being fed to the thrusters.

Posted by: Steven Den Beste at December 01, 2013 09:30 AM (+rSRq)

10 Is that a cat-girl I hear crying in the distance? 

Posted by: Siergen at December 01, 2013 04:27 PM (c2+vA)

11 We haven't reached that level of nerdity yet. Wait until I start listing continuity errors in the show.

Posted by: Steven Den Beste at December 01, 2013 07:07 PM (+rSRq)

12 As long as Marika doesn't pull out a light saber, the cat-girls are safe.

Posted by: Mauser at December 01, 2013 08:21 PM (TJ7ih)

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