Everyday Space Drives

[Zeiss Ikon]

9 hours ago, wumpus said:

"Beating a NASA launch from Earth to Mars" isn't hard (for equal launch windows) but requires an extreme amount of energy&reaction mass to do so.

A solar sail (which is what I stated that about) requires no reaction mass.  An electrostatic charge or a little spin can open the sail, lines finer than sewing thread can carry the thrust and steer the sail.  A sail big enough to take a Winnebago-sized hab from Earth to Mars faster than a Hohmann orbit ought to be about the size of two to eight football/soccer fields, and (once mass produced) cost less than the hab.  Coming back down, it's hard to beat a Hohmann transfer, because you can't thrust toward the Sun, but going out, you can get going like blazes if you time your departure to optimize the sailing.  You can beat a Hohmann orbit from Earth to Mars with a milligee, as long as you can keep it up the whole way.

I don't see solar sails as being worth much for moving people beyond the Belt -- too little thrust available with the light down to 1/4 or less of what Earth's orbit gets (1/100 when you get out to Saturn's neighborhood).  I bet they'll carry the heavy stuff to the Outer Colonies, though, possibly with some other means of braking down into orbit at the end (likely some combination of aerobraking and chemical or NTR).

I'm pretty sure we'll still be colonizing planets (or at least larger moons) for millennia to come; humans need gravity, and spin gravity has issues (you don't fall down if something fails, you fall away.  A structural failure won't be a search for survivors, so much as a race to catch up with survivors before they run out of air).

[DAL59]

2 hours ago, Zeiss Ikon said:

thrust toward the Sun

You can angle the sail to slow down and deorbit.  

What about pulsed plasmoids?  They have low thrust, though much more than ion drives, and have very high isps.  They work by turning propellant into ball lightning and shooting it out the engine.  

[Guest]

26 minutes ago, DAL59 said:

You can angle the sail to slow down and deorbit.

The nautical term is "tacking", IIRC.

Quote

What about pulsed plasmoids?  They have low thrust, though much more than ion drives, and have very high isps.  They work by turning propellant into ball lightning and shooting it out the engine.  

Do you mean like a pulsed MPD? MPDs are pretty simple insofar as I can see but they need a lot of energy to be useful. I'm pretty sure a PIT on argon gets better exhaust velocity (somewhere around 50km/s, have to check out the paper again) than a similar power MPD with argon. If you're talking about a PJMIF or something similar I would personally rule those out for small craft based on the complexity and power requirements even though I am enamoured with the possibilities. Those might drive outer system liners and haulers where transfer time needs to be quicker than a Hohmann.

Side note: Not sure why I'm hung up on argon but it's pretty common compared to other nobles, IIRC.

Edited September 30, 2017 by regex

[DAL59]

Pulsed plasmoids can use hydrogen and are unrelated to MPDs.  It was invented by Philip Eklund.  

[Guest]

You mean like an ELF thruster? Efficiency seems really nice and on skimming it seems like a relatively simple device.

[Nuke]

what we will run will be entirely dependent on what kind of power supplies are available. a fission reactor might be out of reach for a corporate entity due to government regulations and so your workhorse spacecraft are all going to be solar-electric or chemical. chemical will likely be dependent on a lot of isru bases, possibly with (government regulated and protected) nuclear powered bases producing the fuel, and a few nuclear powered tankers moving the fuel to various resupply bases and cycler ships. why carry the reactor everywhere you go, keep it on the ground (preferably low gravity ground) to improve efficiency. close to the sun many of those chemical engines would be augmented in an arcjet configuration. i get a lot done in ksp with an arcjet mod with about 600s isp, though irl arcjets would be slightly lower and distances larger.  mr-510s (a quarter newton thruster) use hydrazine and get about 585s with 2kw. lh2/lox arcjets would be a little better in performance if you could solve the boiloff problem. solar would provide sufficient power in the inner solar system. ion engines mostly get used for all the low mass satellites and space craft, we just dont have the power systems needed to push heavy things around with ion engines.

things might be better if space uses more of a libertarian model, where it would be considered ok for private entities to have mobile nuclear reactors. though this may pose security issues. we cant have space pirates sell radioactive material to terrorists now. we might also see next gen fission eliminate the non-proliferation issues with nuclear reactors. now if we get fusion reactors like the polywell or smaller, that changes everything. this gets you up to 100 megawatts so high power mpd thusters become viable for all vessels from the smallest to the largest. tea kettling might be the way to go in most cases, as its better to have an engine that can run on anything as opposed to require very high purity propellants that cost additional energy for production and can only be attained from certain places in the solar system. hydrogen based mpds might be the best bet, but it would be nice to have the option of also using nitrogen or argon in places where its hard to get. high cost and rare propellants like xenon might be used mostly for satellites and military use.

Edited September 30, 2017 by Nuke

[DDE]

13 hours ago, regex said:

Oh man, you totally reminded me of SAFE-400. IIRC it's a relatively simple mechanism, quite light, and puts out about 100kW of usable electricity. That's plenty for a small electric or two and for the mass it's worth it to carry a few for extra power or in backup (obviously the size and output would vary but I always like real world examples). Stopping at the fuel depot could also involve swapping out your reactor for a fresh one.

And you're totally right about the coolant flush, "solid state" reactors like RTGs or heat-pipe power systems would probably be favored by the outer-system. Hell, you could scavenge a lot of waste heat into an exchanger.

That's why I think a small fission reactor goes really well alongside the not-Epstein drive.

The Soviets eventually cast their lot in with thermionic power converters, and the Yenisei - which was later bought by the US SDI - featured integrated fuel rod-generator assemblies. High-end powerplants could use something more exotic, like the EU-610 gas-core reactor with MHD converter, but the lack of sunlight means you'd need a workhorse model.

And to the later issue, http://www.projectrho.com/public_html/rocket/enginelist.php#id--Electromagnetic_(Plasma)--Pulsed_Plasma_(PPT)

3 hours ago, Nuke said:

things might be better if space uses more of a libertarian model, where it would be considered ok for private entities to have mobile nuclear reactors.

So... exactly the way it is today? Like any piece of dangerous hardware, they are subject to government supervision, it's just there aren't many useful applications for them and there's a lot of anti-nuclear hysteria, so they haven't caught on.

https://en.wikipedia.org/wiki/NS_Savannah

https://en.wikipedia.org/wiki/Otto_Hahn_(ship)

https://en.wikipedia.org/wiki/Mutsu_(nuclear_ship)

"Dirty bombs" are absolutely worthless, and reactor-grade fuel needs extensive and highly specific equipment to process it into weapons-grade material... besides, I expect commercially-owned nuclear mining charges to be a thing, just of the "wet" variety, without easily portable lithium hydride fusion fuel.

Edited September 30, 2017 by DDE

[Zeiss Ikon]

22 minutes ago, DDE said:

... besides, I expect commercially-owned nuclear mining charges to be a thing, just of the "wet" variety, without easily portable lithium hydride fusion fuel.

Unless you're trying to completely break down some of the largest 1% of rocks in the Belt or the Trojans in a single shot, you don't need anything like the power of even a straight fission explosive, never mind a fusion-boosted type that would require lithium deuteride or tritium injection.  Liquid oxygen and any combustible material form a nice binary explosive that can be pumped into cracks or voids (or boreholes), diluted with liquid nitrogen if needed (for loading density control), and capable of breaking more rock than you'll want floating loose at any one time.  Don't forget that the vast bulk of asteroids are essentially gravel piles held together by (extremely weak) gravity and a little bit of vacuum welding.

The smallest practical fission device, as I recall, is around 2 kT yield, and while it's a lot more portable than 2000 T of TNT (or LOX/anything), it can't be divided up to provide controlled breaking -- it's like trying to mine when the only charge you have is a full truckload of loose ANFO, and you're can't pump or pour it into individual holes, but can only detonate it still in the trailer.

I hate to say it, but unless space has a more libertarian model than anything we've seen to date, there won't be any private space travel.  The weapon potential, based solely on kinetic energy, of a spaceship is something no government will ever willingly allow in individual hands (not even the equivalent of an airline pilot).  Never mind nuclear engines and high tech stuff, a Hohmann orbit from Mars to Earth with a ship big enough to carry a family on a nine-month orbit is a city-wrecker if you don't bother to brake into orbit at the end -- and even if you're suspicious, you won't be able to tell with confidence until it's inside the Moon's orbit (and only a few hours away) that it's not just a much more massive rock with a dummy comms unit and similar radar signature to the Winnebago.  And this goes equally for solar sails, VASIMR, or solar/ion as it does for a fantasy torchship capable of burn/flip/burn constant boost travel anywhere in the system.

[DDE]

1 hour ago, Zeiss Ikon said:

The smallest practical fission device, as I recall, is around 2 kT yield

Telkem-1 and Telkem-2 were pilot blasts for Project Taiga, a reversal of the Pechora river with 250 15 kt nuclear blasts that had to be canceled after the initial detonation irked off Sweden and US. 4 nuclear bombs in two blasts in late 1968, 0.24 kt each.

1 hour ago, Zeiss Ikon said:

I hate to say it, but unless space has a more libertarian model than anything we've seen to date, there won't be any private space travel.  The weapon potential, based solely on kinetic energy, of a spaceship is something no government will ever willingly allow in individual hands (not even the equivalent of an airline pilot).  Never mind nuclear engines and high tech stuff, a Hohmann orbit from Mars to Earth with a ship big enough to carry a family on a nine-month orbit is a city-wrecker if you don't bother to brake into orbit at the end -- and even if you're suspicious, you won't be able to tell with confidence until it's inside the Moon's orbit (and only a few hours away) that it's not just a much more massive rock with a dummy comms unit and similar radar signature to the Winnebago.  And this goes equally for solar sails, VASIMR, or solar/ion as it does for a fantasy torchship capable of burn/flip/burn constant boost travel anywhere in the system.

True, but then the technical and logistical realities of operating a spaceship also don't favour the libertarian worldview.

[Guest]

5 hours ago, Zeiss Ikon said:

I hate to say it, but unless space has a more libertarian model than anything we've seen to date, there won't be any private space travel.

I don't hold the same view by a long shot but this really isn't the place to discuss that. Not this thread and not these forums.

[Nuke]

On 9/30/2017 at 8:46 AM, regex said:

I don't hold the same view by a long shot but this really isn't the place to discuss that. Not this thread and not these forums.

didnt mean to get this thread too political. but if space is regulated by governments like what we have now, dangerous things like nuclear reactors wont be available to everyone. however if human populations in space are self governing, then they could justify anything on the grounds of efficiency and planet bound governments are going to have to tolerate them and maintain good relations. if i was on the ground i wouldn't want to go to war with a space faring nation. what kind of government we have at the time is going to dictate the kind of propulsion we will actually use. in fact this kind of thing is why i like the expanse.

Edited October 1, 2017 by Nuke

[Guest]

1 minute ago, Nuke said:

didnt mean to get this thread too political.

Nah, it's cool. The point of the thread, as I imagined it, is daydreaming about a "rocketpunk" future, thinking about what ordinary people will use to get around in a future where they can actually be leisurely in space (literally the kid turning out a Hall effect thruster on the school's CNC machine and sourcing a "vintage" hab for their ride). We already have tons of threads on why space is hard, and some even get hijacked to (rightfully) point that out. I kind of wanted to avoid that to some extent but it's somewhat relevant. Even I did it earlier, postulating that reactors would be need in the outer system; kind of hard to be leisurely when energy isn't nearly as free as the inner system.

Which kind of amuses me because the outer system is often seen in fiction as the lawless "periphery" where it would likely be a far more regimented society than the inner system even long after it was colonized.

As far as governments in space, that certainly does have some bearing on things like what drives are available, but if we're pontificating about things like laser-pumped thermal tugs boosting electric craft into Hohmann transfers we've already crossed the threshold of death rays in orbit. There's a lot of trust in those sorts of systems but they also provide a measure of defense from kinetic orbital terrorism, although one wonders what sort of power they hold over others in orbit.

Space requires a lot of energy. We've got to assume enough trust in people and their intentions to make space happen. On one side you trust the individual to act in the best interest of their fellow individuals, on the other side you have the hard experience of that not working out so well in the past and instead provide a framework within where people can act individually. How much of a framework we need will always cause contention, which is why I wanted to avoid the question here.

[tater]

You could borrow from Iain Banks, and imagine a post-scarcity future. You're specifying a near future, so imagine something like the benign AI explosion at the very beginning of Max Tegmark's book, Life 3.0.

The superintelligence is doing a millennia worth of intellectual work every week. It moves the technological ball forward rapidly. Better automation results in little human work being required. What if that intelligence is tasked with building a space infrastructure? Want a spacecraft? Have the bots make you one.

[Nuke]

5 hours ago, regex said:

Nah, it's cool. The point of the thread, as I imagined it, is daydreaming about a "rocketpunk" future, thinking about what ordinary people will use to get around in a future where they can actually be leisurely in space (literally the kid turning out a Hall effect thruster on the school's CNC machine and sourcing a "vintage" hab for their ride). We already have tons of threads on why space is hard, and some even get hijacked to (rightfully) point that out. I kind of wanted to avoid that to some extent but it's somewhat relevant. Even I did it earlier, postulating that reactors would be need in the outer system; kind of hard to be leisurely when energy isn't nearly as free as the inner system.

Which kind of amuses me because the outer system is often seen in fiction as the lawless "periphery" where it would likely be a far more regimented society than the inner system even long after it was colonized.

As far as governments in space, that certainly does have some bearing on things like what drives are available, but if we're pontificating about things like laser-pumped thermal tugs boosting electric craft into Hohmann transfers we've already crossed the threshold of death rays in orbit. There's a lot of trust in those sorts of systems but they also provide a measure of defense from kinetic orbital terrorism, although one wonders what sort of power they hold over others in orbit.

Space requires a lot of energy. We've got to assume enough trust in people and their intentions to make space happen. On one side you trust the individual to act in the best interest of their fellow individuals, on the other side you have the hard experience of that not working out so well in the past and instead provide a framework within where people can act individually. How much of a framework we need will always cause contention, which is why I wanted to avoid the question here.

im kind of a big fan of jon's law. "any interesting space drive is a weapon of mass destruction." it always disappointed me when in star trek every time 'ramming speed' was called for that it didnt result in a massive nuclear-like explosion. considering how powerful trek's impulse engines supposedly are, instead you get a bit of minor hull ripping as if it were an ocean going vessel running into another at a few knots. it seems like a massive bit of untapped potential you usually dont see in mainstream scifi.

[MatterBeam]

I see three types of propulsion for three types of ship:

-Network:
These ships rely on vast infrastructure to handle propulsion externally. Laser beams, kinetic streams and tether chains. The advantage is that the authority operating the infrastructure determines where the spaceship can go and when. Another advantage is that the spaceships are the cheapest possible and probably the easiest to buy. An example is the two-pulse laser ablative rocket. 

-Hauler:
These ships exceed the ability of the existing infrastructure to propel them, or operate outside of its reach. However, their commercial purpose prioritizes efficiency over speed. They will use small quantities of propellant paired with a high Isp reactor-powered electric rocket. An example is the electrodeless plasma rocket.

-Fast:
These ships can't wait around like haulers. They transport time-sensitive or precious cargo in addition to people on tight schedules. They must be authorized to use high-energy nuclear propulsion. Since cost is less of an issue, engine Isp is sacrificed to increase thrust, resulting in high mass ratios. Nuclear thermal rockets are an example. 

[Guest]

17 hours ago, tater said:

You could borrow from Iain Banks, and imagine a post-scarcity future. You're specifying a near future, so imagine something like the benign AI explosion at the very beginning of Max Tegmark's book, Life 3.0.

The superintelligence is doing a millennia worth of intellectual work every week. It moves the technological ball forward rapidly. Better automation results in little human work being required.

You know, that's interesting, what does life look like post-scarcity or post-singularity? Not that I subscribe to that singularity nonsense but apparently its an assumed trope in science fiction.

You really can't have a "rocketpunk" future without one or the other...

17 hours ago, tater said:

Want a spacecraft? Have the bots make you one.

I still prefer the kids turning out thrusters on a mill, but you have a point.

15 hours ago, Nuke said:

im kind of a big fan of jon's law. "any interesting space drive is a weapon of mass destruction."

I learned that as the Kzinti Lesson, and I agree that it's a massively underused fact of life.

[tater]

I'm fairly convinced that at the very least any achievement of human-level AGI will result in an "intelligence explosion" as Bostrom puts it. How destabilizing it will be, I cannot say, but it seems self-evidently true that under the assumption AI is possible at all, then achieving the level of a competent human programmer will result in rapid self-improvement by the system, for no other reason than clock speed vs our 200 Hz brains. The idea that it becomes a singleton in power, or otherwise takes over is a separate matter that is considerably less obvious to me. (and consciousness doesn't even matter)

Regardless, the "kids turning out thrusters" will be 3d printing them , and even current, narrow AI design systems come out with novel designs:

There is no turning back (unless it's a retro-history that then moved forward) that you'd at least expect people to use some linear improvement over current tech.

There are people printing mixed plastic and conductor, too (example was a printed quad-rotor where most all the wires were printed into the framework such that the motors, boards, servos, etc just snapped in, contact to contact.

The plus of this future is it makes some of the complexity much easier, and the people can mess around more, since the intelligent design software will take car of the mundane stuff (that keeps them alive, lol).

[mikegarrison]

On 9/28/2017 at 12:42 PM, Nibb31 said:

I don't think we will ever get to a point where people have individual spacecraft.

The amount of energy required to accelerate a couple of tons to orbital speeds is just huge. Even if you find a way to contain that energy in a compact and safe enough package, that sort of energy would be way too destructive to have people keep in their garage or fly around risking collisions or putting it into malevolent hands.

 

A truly "post-scarcity" world would necessarily involve little or no limits on energy. It is, of course, debatable whether humans will ever achieve a "post-scarcity" world.

[Guest]

19 minutes ago, mikegarrison said:

A truly "post-scarcity" world would necessarily involve little or no limits on energy. It is, of course, debatable whether humans will ever achieve a "post-scarcity" world.

Humans may not, but their software might make it possible.

[tater]

For a few million people living in space, energy is not really a problem.

[wumpus]

3 hours ago, mikegarrison said:

A truly "post-scarcity" world would necessarily involve little or no limits on energy. It is, of course, debatable whether humans will ever achieve a "post-scarcity" world.

Presumably any civilization without [instant] teleportation or similar tech (like the inside of the TARDIS) would have some sort of real estate scarcity (while the American Indians might not have accepted land "ownership", I suspect there were limits to sharing tribal hunting/fishing areas).  Not all areas will have equal value, and the time needed to travel will have value.

That said, it is scary how much of the global economy (and moreso the US) relies on the artificial scarcity of IP laws.  Very few products can't be counterfeited at equal quality at a fraction of the cost (and how many services rely on using such goods?).

[DAL59]

What about z-pinch fission- not z-pinch fusion- that is less plausible- but z-pinch fission, where subcritical mass pellets of uranium are compressed by magnets until they explode.  Estimates for specific impulses are over 9000s(no pun intended.)  It also has reasonable thrust.  The alternate name is Min-Mag Orion, though it bears little resemblance to Project Orion.

[wumpus]

5 minutes ago, DAL59 said:

What about z-pinch fission- not z-pinch fusion- that is less plausible- but z-pinch fission, where subcritical mass pellets of uranium are compressed by magnets until they explode.  Estimates for specific impulses are over 9000s(no pun intended.)  It also has reasonable thrust.  The alternate name is Min-Mag Orion, though it bears little resemblance to Project Orion.

Long term it might have a chance, but how do you manufacture the "uranium" such that it isn't easily set off by other means.  While I wouldn't expect weapons grade, having a meltdown thanks to a crash (and resulting high acceleration and compression of uranium) wouldn't  be great.

"Uranium" in quotes as I doubt that your typical fuel rod compresses well under magnetic pinching.  No idea how it works.

[DAL59]

It isn't in rods, but very small pellets.  

http://web.archive.org/web/20151005022120/http://ralph.open-aerospace.org/PDF/2003.01.23 - MMO Final Report Summary.pdf

[Guest]

1 hour ago, DAL59 said:

What about z-pinch fission- not z-pinch fusion- that is less plausible- but z-pinch fission, where subcritical mass pellets of uranium are compressed by magnets until they explode.  Estimates for specific impulses are over 9000s(no pun intended.)  It also has reasonable thrust.  The alternate name is Min-Mag Orion, though it bears little resemblance to Project Orion.

I can see this used by larger entities able to manage more stringent licensing and afford specialty fuel. There's a big difference between an argon PIT thruster and a z-pinch thruster in terms of the entire complexity of the system, not to mention the power requirements.

The point being, performance isn't everything.

PJMIF may be simpler than I think and gets good performance for a pinch system, and would be my preferred "high isp" fusion system given it doesn't require things like lithium liners.

Edited October 3, 2017 by regex