Future propultion systems for spacecraft

[Orc]

Hi all

 

Excuse a foolish Ork if he has missed this elsewhere in the thread but has anyone mentioned Solar Thermal Tugs / Boosters?

 

Almost all the benefits of Nuclear fission thermal with none of the problems, and if sensibly designed a reusable stage that can be refueled and used to send the next cargo trip to Duna ... sorry Mars.

 

Basically big ass (big, like very big, but not solar sail big) parabolic solar condenser focuses lots of sunlight on a heat exchanger. Heat exchanger exchanges heat with cryogenic reaction mass that goes out of rocket nozzle very fast. Every action has equal and opposite reaction, STB and its cargo go in opposite direction.

 

According to the smart people I first learned of the concept from the proposal is really only good for boosting cargoes out of LEO to the rest of the solar system. Their big plan was to design the system in such a way that the almost spent booster would do a hand-break turn on the Mun's (sorry Moon's) gravity well and come back to earth to be reused later. Over the course of a dozen missions or so it would pay for itself multiple times over.

 

I can not remember numbers off the top of my head but the ISP was supposed to be very impressive and the over all performance about 50% of a nuclear fission thermal booster designed for the same application. With the bonus of running on Magic Sunlight and not Nasty Atoms ;-) 

 

Further off for more distance goals:

Magnetic sails - huge (like multi-square-kilometer)  arrays of super-conducting cables charged up with ridiculously high amounts of electricity. Interacts with the solar wind converting the momentum of the charged particles coming from the sun. Equal and Opposite Reaction results. Said to be of marginal use for a Mars delivery system if you discount the potential benefit that the sail offers any crew in the event of solar storm. Yep, the sail is a SHIELD against some of the badness that will kill your kerbals (sorry humans) in the event of a solar storm. When the numbers are run for use going out to the outer solar system the mag-sail looks much more attractive.

 

More long term: the boosted Magnetic sail. When you absolutely have to get to Alpha Centauri in less than 999 life times. Get one big ass ship with an even much bigger big ass mag sail (or arrays of mag sails). Get several very big (and by big I mean very big) particle beam accelerators. These would probably be build on large asteroids, or even small moons. They would be supplied with power by stupendeously larger arrays of solar panels. These things are supposed to (in terms of charged particle release) OUTSHINE the Sun for suitable periods of time. Just on the tiny dot of space that is the target mag sail, but still.... Boost away. Thought to be able yield trip times to Alpha Centauri that are less than 6 decades. To slow down on the other end.... Well you might need to depend on the fact that the destination star is much bigger than Earth's. Or there are some complicated tricks you can do to 'tack' into AC's solar wind and whip your ship around for another decade or two of gravity-assisted slowing down. 

 

Another option is, if you can ignore silly things like test ban treaties is to use mini-nukes (0.1 kiloton wrapped up in lots of plasma producing material) to do an Orion-style engine with your Mag-sail. Might look pretty if observed from the other side of the solar system.

 

Anyway, 

regards

Ork

[wumpus]

On 1/23/2017 at 2:08 AM, Orc said:

Hi all

Excuse a foolish Ork if he has missed this elsewhere in the thread but has anyone mentioned Solar Thermal Tugs / Boosters?

The issue here is Isp.  If you use water as your reaction mass, your Isp is fundamentally limited to that of a hydrox rocket (which is pretty good, but hardly justifies something this exotic).  Using hydrogen is practically necessary, making a zero-boiloff system a necessity (I'd assume relatively low thrust, although that might not be true.  You'd still need a zero-boiloff system for Mars capture or similar burns).  Helium might be an option, but I have no idea of the Ve (and thus Isp) of He.

I'd be curious how big you could make such a reflector.  Presumably an impossibly thin mylar film would even work, although I'm not sure that this could possibly have any net thrust/m**2 benefits over a solar sail (thanks to basic conservation issues).

[WinkAllKerb'']

On 09/01/2017 at 2:22 PM, Nibb31 said:

Requirements would depend on the technology.

So far, we have to choose between chemical propulsion and electric propulsion, but in the end, the only way to obtain thrust is to throw stuff out the back, which requires an amount of energy proportional to the thrust that you want to get.

well, send me there xDr

also forgive *.jpeg irony, but well, why not after all at some point along the way could be handy // earth "energy stock"

Spoiler

 

Edited January 24, 2017 by WinkAllKerb''

[DDE]

7 hours ago, wumpus said:

The issue here is Isp.  If you use water as your reaction mass, your Isp is fundamentally limited to that of a hydrox rocket (which is pretty good, but hardly justifies something this exotic).  

In case of reasonable temperatures, yeah.

But apparently such a system is considered so simple that it's considered a viable backup drive.

http://www.projectrho.com/public_html/rocket/enginelist.php#solarmoth

[PB666]

11 hours ago, wumpus said:

The issue here is Isp.  If you use water as your reaction mass, your Isp is fundamentally limited to that of a hydrox rocket (which is pretty good, but hardly justifies something this exotic).  Using hydrogen is practically necessary, making a zero-boiloff system a necessity (I'd assume relatively low thrust, although that might not be true.  You'd still need a zero-boiloff system for Mars capture or similar burns).  Helium might be an option, but I have no idea of the Ve (and thus Isp) of He.

I'd be curious how big you could make such a reflector.  Presumably an impossibly thin mylar film would even work, although I'm not sure that this could possibly have any net thrust/m**2 benefits over a solar sail (thanks to basic conservation issues).

Well you could use dueterium instead of hydrogen, expensive but doubles the reaction mass. You could also use lithium, heat it up to its vapor point and react it with oxgen.

Thing about hydrogen, deuterium and tritium (later being generated in flight) is that these are the most productive fusion reactor fuels, the product ions once purified from starting materials could used as reaction mass.

I don't say hydrogen is absolutely neccesary. You can use magnesium metal for ion drives, this does not even require a container in space, just put a hole in the middle and store it in blocks or plates on a rod have a robot remove a plate when fuel is needed. What is needed is a source of power, far from the sun there is none, except nuclear.

 

[WinkAllKerb'']

on the other hand or forum entry this week chalenge is about spice so why not folding thread and ressource on various place that require low delta-v while finding somehting better ^^
 

 

[magnemoe]

16 hours ago, DDE said:

In case of reasonable temperatures, yeah.

But apparently such a system is considered so simple that it's considered a viable backup drive.

http://www.projectrho.com/public_html/rocket/enginelist.php#solarmoth

Solar thermal works mostly the same way as nuclear thermal. notice that the ISP is pretty much the same with liquid hydrogen.
You can go a bit higher than nuclear thermal as you should be able to reach an higher temperature. 

Now using an vasimr style drive you can get higher as you also accelerate your reaction in an magnetic field, downside is that it demand loads of electricity to run.  

[wumpus]

12 hours ago, PB666 said:

Well you could use dueterium instead of hydrogen, expensive but doubles the reaction mass. You could also use lithium, heat it up to its vapor point and react it with oxgen.

Thing about hydrogen, deuterium and tritium (later being generated in flight) is that these are the most productive fusion reactor fuels, the product ions once purified from starting materials could used as reaction mass.

I don't say hydrogen is absolutely neccesary. You can use magnesium metal for ion drives, this does not even require a container in space, just put a hole in the middle and store it in blocks or plates on a rod have a robot remove a plate when fuel is needed. What is needed is a source of power, far from the sun there is none, except nuclear.

Hydrogen, dueterium, and possibly even helium are needed for high Isp *thermal* systems (whether using combustion, solar heating, or nuclear heating).  I'd be fairly shocked if burning lithium gave better reaction mass than burning hydrogen (although I'd think that storing lithium would be easier, but I don't think it was even bothered with in Ignition!).  Once you accelerate your reaction mass by other means, mass often becomes a benefit.

[DDE]

@wumpus, Ignitions!'s final pages of the pre-conclusion chapter are dedicated to the 542 sec lithium-fluorine-hydrogen chemical rocket motor.

Quote

But somehow the Rocketdyne crew (H. A. Arbit, R. A. Dickerson, S. D. Clapp, and C. K. Nagai) managed to overcome them, and made their firings. They worked at 500 psi chamber pressure, with a high expansion nozzle (exit area/throat area = 60) designed for space work. Their main problem stemmed from the high surface tension of liquid lithium, orders of magnitude higher than that of ordinary propellants, which made it difficult to design an injector that would produce droplets of lithium small enough to burn completely before going out the nozzle. Once this problem was overcome, their results were spectacular. Using lithium and fluorine alone (no hydrogen) their maximum specific impulse was 458 seconds. But when they proportioned the lithium and fluorine to burn stoichiometrically to LiF, and injected hydrogen to make up 30 percent of the mass flow, they measured 542 seconds —probably the highest measured specific impulse ever attained by anything except a nuclear motor. And the chamber temperature was only 2200 K! Performance like that is worth fighting for. The beryllium-burning motor is probably a lost cause, but the lithium-fluorine-hydrogen system may well have a bright future.

 

Edited January 25, 2017 by DDE

[shynung]

@DDE Note that the Rocketdyne test crew depicted in Ignition! has to keep all of the propellants (lithium, fluorine, hydrogen) in liquid form. That means dealing with liquids that have wildly different boiling/freezing points (lithium melts at 453.7 K, hydrogen boils at 20.23 K). Add that to the problems of dealing with liquid fluorine (!), and difficulties of liquid hydrogen long-term storage, I wouldn't expect it to be a practical choice.

Also, there's a fusion rocket being worked on right now. 5000 s ISP. It basically uses electricity to induce fusion, and using that fusion energy to heat propellant (lithium) and blast it out the nozzle. Bear in mind that this isn't a reactor, so it needs electrical energy rather than producing it. The fusion was needed to obtain high exhaust temperatures, boosting ISP.

Edited January 28, 2017 by shynung

[WinkAllKerb'']

just asking a thing for fun, what's are we gonna find recursively and statistically in each/most system on the planet with the "farthest" from it's star , cold stuff probably

delta-v intersystem anyone ?

Edited February 2, 2017 by WinkAllKerb''

[ShotgunNinja]

It may be of interest: check out project starshot, that want to propel very small scale probes to fraction of the speed of light, using a light sail and giant 1.21 gigawatt lasers on the earth surface.

[Night_Wing_Zero]

[snip]

Should i request ro lock this forum thread?

Edited February 8, 2017 by Vanamonde

[Vanamonde]

On 2/6/2017 at 5:12 AM, Night_Wing_Zero said:

[snip]

Should i request ro lock this forum thread?

No need, though some posts have been trimmed or edited to get things back on-topic. 

[Night_Wing_Zero]

On 16/01/2017 at 10:23 AM, TheEpicSquared said:

It's a theoretical form of propulsion that involves warping space and time around the spacecraft, by contracting space in front of the spacecraft and expanding space behind it. Through some complex equations/concepts, this enables the craft to move at up to 10 times the speed of light (don't quote me on that, though), all without breaking the laws of physics! 

Thanks a lot! although they did brought me a smile and laugh though lol  

[Bill Phil]

On ‎1‎/‎28‎/‎2017 at 8:56 AM, shynung said:

Also, there's a fusion rocket being worked on right now. 5000 s ISP. It basically uses electricity to induce fusion, and using that fusion energy to heat propellant (lithium) and blast it out the nozzle. Bear in mind that this isn't a reactor, so it needs electrical energy rather than producing it. The fusion was needed to obtain high exhaust temperatures, boosting ISP.

Note that this is doable by using Orion. In any of its forms. The MiniMag variant is intriguing...

[Night_Wing_Zero]

On 16/01/2017 at 10:23 AM, TheEpicSquared said:

What if a ship had anti-matter engines?

Edited February 8, 2017 by Night_Wing_Zero

[wumpus]

23 hours ago, Night_Wing_Zero said:

What if a ship had anti-matter engines? (couldn't find original attribution)

Oddly enough, you would likely have very similar problems and results of the recently hyped metastable metalic hydrogen.

Simply banging matter into anti-matter to form a rocket would melt your engines, similarly metalic hydrogen would do the same.  Scott Manley recent had a science video claiming that a reasonable design would do no better than a nuclear thermal rocket in terms of Isp (although you could get huge advantages on later stages due to not needing to cool the engines after burning).  https://www.youtube.com/watch?v=nMfPNUZzG_Q  (note, much of the video deals with the unlikelyhood of this being the perfect fuel.  Not really sure where he lays out why metalic H Isp~=NTR Isp).

Or you could simply use an Orion-based design.  All Orion needed was a number of cans-of-boom to release energy on the pusher plate.  Anti-matter, metalic hydrogen, H-bombs, atomic bombs: they all could be used to push an Orion.  This would allow you to use the full force "uncut" with reaction mass and maintain much of your Isp (you actual thrust per Joule of energy might not be the same, and for sufficiently exotic materials that could be killer).

Don't forget about SCRAMJETS.  A SCRAMJET's big weakness is maintaining the combustion of fuel with the oxidizer rushing through the engine.  With either anti-matter or metalic hydrogen, you would no longer be concerned about combusting with the air.  The airflow suddenly becomes the "cooling/reaction mass" of the NTR-similar rocket, which doesn't really count against Isp (since you aren't carrying it).  Note I am assuming that the X-43's issues were not thermal and likely related to combustion (it could only technically be said to accelerate at mach 10), but I'd have to assume that such a SCRAMJET would work well.  Of course you would still need some sort of non-air-breathing rocket for circularization, but with 4-digit Isp available from the NTR-variation rocket, this shouldn't be much of a problem.  I'd also expect this to be an option for purely intercontinental flight, but both might have to wait while NTR-variants flew at first.

Finally, I'd wonder how much you could ignore Scott Manley's assumption that your reaction would happen roughly in a traditional "combustion chamber" and not out inside the nozzle.  I'd have to assume that you would want the nozzle with a roughly even thermal load, quite possibly almost spherical r with the energy release near the center.  Or possibly having the energy release quite close and letting the cooling/reaction mass slide down next to the nozzles and try to have the temperature cool down before reaching the nozzle.  Most of this assumes that high temperatures are ok as long as the density is low enough not to contain so much heat (while cooling mass circulates through the nozzle).

[Bill Phil]

There's also beamed propellant... which is frankly ridiculous, but who knows?

[hms_warrior]

6 hours ago, wumpus said:

Oddly enough, you would likely have very similar problems and results of the recently hyped metastable metalic hydrogen.

Simply banging matter into anti-matter to form a rocket would melt your engines, similarly metalic hydrogen would do the same.  Scott Manley recent had a science video claiming that a reasonable design would do no better than a nuclear thermal rocket in terms of Isp (although you could get huge advantages on later stages due to not needing to cool the engines after burning).  https://www.youtube.com/watch?v=nMfPNUZzG_Q  (note, much of the video deals with the unlikelyhood of this being the perfect fuel.  Not really sure where he lays out why metalic H Isp~=NTR Isp).

On the matter of metalic hydrogen: I am at work and can't watch the video right now so i don't know if the stuff i write here got addressed there but:

The main Isp increase of a metalic hydrogen rocket isn't in the high energy release but in the fact that the resulting gas would most likely be monoatomic hydrogen instead of the diatomic hydrogen a nuclear rocket use as propellant. that means each atom has roughly half the weight, and therefore, going with E = 0.5m*v² the exhaust velocity (Isp) would be 4 times as high for the same amount of energy per mass. So a metalic hydrogen rocket can run a lot colder than a nuclear rocket and still get higher Isp numbers. ( of course that is all highly theoretical)

[shynung]

16 hours ago, wumpus said:

Finally, I'd wonder how much you could ignore Scott Manley's assumption that your reaction would happen roughly in a traditional "combustion chamber" and not out inside the nozzle.  I'd have to assume that you would want the nozzle with a roughly even thermal load, quite possibly almost spherical r with the energy release near the center.  Or possibly having the energy release quite close and letting the cooling/reaction mass slide down next to the nozzles and try to have the temperature cool down before reaching the nozzle.  Most of this assumes that high temperatures are ok as long as the density is low enough not to contain so much heat (while cooling mass circulates through the nozzle).

Scott Manley's assumption is more-or-less the most efficient way to do it. Rocket nozzles are designed to convert pressure in a chamber into directed linear velocity. Having the propellant mass receive/release energy when it's well past the nozzle throat would lower specific impulse, because pressure generated after the throat is not as efficiently converted to thrust as when the same pressure is generated before the throat.

Diagram of typical rocket nozzle. Combustion chamber to the left.

[wumpus]

On 2/9/2017 at 3:05 AM, hms_warrior said:

On the matter of metalic hydrogen: I am at work and can't watch the video right now so i don't know if the stuff i write here got addressed there but:

The main Isp increase of a metalic hydrogen rocket isn't in the high energy release but in the fact that the resulting gas would most likely be monoatomic hydrogen instead of the diatomic hydrogen a nuclear rocket use as propellant. 

This only works if you somehow build a rocket that doesn't need to be diluted with reaction mass for cooling.  Works for Orion, but not so much on a NTR-variant system.

On 2/9/2017 at 0:54 PM, shynung said:

Scott Manley's assumption is more-or-less the most efficient way to do it. Rocket nozzles are designed to convert pressure in a chamber into directed linear velocity. Having the propellant mass receive/release energy when it's well past the nozzle throat would lower specific impulse, because pressure generated after the throat is not as efficiently converted to thrust as when the same pressure is generated before the throat.

This basically depends on the cost of manufacturing metallic hydrogen [and of course, anti-matter*].  "Pure" H_metal has a ~100ks Isp, the "efficient way" is less than 2ks.  Why it should be fairly obvious that you would get more thrust with the efficient method per gram of H_metal, the mass would be much higher.  No idea what the tradeoffs would be (as in, would you be willing to use twice as much metallic hydrogen to cut the mass by an order of magnitude?  We can't begin to tell yet).

Also I'd be fairly shocked if the SCRAMJET method wasn't roughly as efficient as the "thermal rocket" method (they're relatively similar, with the thermal method having wildly better compression at the expense of carrying much more mass).  It would likely come in handy for "dual use" as commercial aviation as well as space use.  Racking up more miles (or more literally flight-hours) with space-capable (or most of the way to orbital velocity) engines via commercial aviation would likely help human space migration more than any conceivable space program.

* unlike meta-stable metallic hydrogen, a [tiny, useless for any amount of energy] ring of positrons has been proven to have been created and captured (back in the 1980s, from memory).  But there isn't even a theoretical basis for an economical development of anti-matter.

[DDE]

On ‎09‎.‎02‎.‎2017 at 11:05 AM, hms_warrior said:

The main Isp increase of a metalic hydrogen rocket isn't in the high energy release but in the fact that the resulting gas would most likely be monoatomic hydrogen instead of the diatomic hydrogen a nuclear rocket use as propellant.

*sits up*

Source, please. I am sincerely intrigued.

Great, so it gets to explode twice.

[shynung]

19 hours ago, wumpus said:

This basically depends on the cost of manufacturing metallic hydrogen [and of course, anti-matter*].  "Pure" H_metal has a ~100ks Isp, the "efficient way" is less than 2ks.  Why it should be fairly obvious that you would get more thrust with the efficient method per gram of H_metal, the mass would be much higher.  No idea what the tradeoffs would be (as in, would you be willing to use twice as much metallic hydrogen to cut the mass by an order of magnitude?  We can't begin to tell yet).

I don't think we're on the same page here. I'm under the assumption that the metallic hydrogen is to be treated as propellant, injected into a combustion chamber, somehow make it release its stored energy, increasing pressure in the chamber, and then converting that pressure into velocity via a nozzle. How did you come to the conclusion that "pure" H_metal has 100ks Isp? Atomic Rocket's page on H_metal listed 1700 s Isp.

[wumpus]

On 2/12/2017 at 11:16 AM, shynung said:

I don't think we're on the same page here. 

I'm confused.  I think I multiplied by g instead of dividing.  I'm also confused by the need to dilute the exhaust gasses when the output appears "close" to the more efficient claims of more modern nuclear thermal rockets.  If the dilution is relatively minor, then my SCRAMJET idea is pretty pointless.