Hard Light Productions Forums
Off-Topic Discussion => General Discussion => Topic started by: pyro-manic on December 14, 2005, 05:40:24 pm
-
New ion engine design developed by ESA works in initial tests: http://news.bbc.co.uk/1/hi/technology/4527696.stm
-
veeeeeery interesting...
-
Oh sweet...
-
Yup, Ion drives have been playing a small role in space exploration for while :)
They aren't actually more powerful than normal engines or anything, but stay functional for much much longer. They could be very useful for in-system exploration, however :)
-
Anything more efficient than rockets is better. :rolleyes:
-
I think conventional rocket boosters would still be needed to escape Earths atmosphere though. I'd say we could save around 90% of the money spent on Space Exploration if we could get over that one hurdle.
-
I think conventional rocket boosters would still be needed to escape Earths atmosphere though. I'd say we could save around 90% of the money spent on Space Exploration if we could get over that one hurdle.
We need orbital shipyards. Imagine an Orion built on Earth and launched using rockets :shaking:
-
There's still the small matter of getting either materials or just raw manpower up. Even with a system like a space elevator, that still takes a ton of energy.
Also, ion engines really shine in truely long-range exploration; because the exhaust is more energetic, a craft can accelerate to higher velocities (even if it takes longer to get up to speed) than one using conventional rocket engines. Not FTL by any means, but the fundamental limits of conventional rockets in terms of just raw speed are a lot lower than most people think.
-
rockets require mass to generate energy, with ion engines a majority of the thrust power comes from electricity generated by solar arrays, rather than fuel. you send out less mass but at a much higher velocity. if you can figure out how to convert electrical energy directly into motion, then you could pretty much explore space for free, minus the cost of leaving earth orbit and equipment obviously. we need to make probes that can be used for many missions rather than just one. ion engines get us closer to that goal. i really think solar sails need to be tested and used. last i recall the last time it was to be tested the rocket blew up. lets not let it ride a russian rocket next time. :D
-
There's still the small matter of getting either materials or just raw manpower up. Even with a system like a space elevator, that still takes a ton of energy.
Asteriod mining+self-sustaining habitat+orbital shipyard=exploration ;7
Almost seems like it's the tutorial level for some space-based RTS.
-
OK.
I usually don't bash anyone if I can help it, but this time.....CUT THE CRAP!
That said and done, I better go about giving a scientifically accurate description of what's great about an ion engine, and what's even better about this one.
In space any prolusion system other than a solar sail and its ilk has to rely on Newton's 3rd law to provide thrust:
You push thing out, meanwhile you're pushed in the opposite direction. No exceptions.
The rocket's motion equation:
FR = d(M*v) / dt = M * a
FE = d(mt * c) / dt
IF a || c THEN:
FT = c * mt
Legend:
FR : The force that is pushing the rocket
FE : The force that is pusching the exhaust
FT : The force of the Throttle
M : Full mass of the rocket, INCLUDING(!) the fuel onboard at the moment
mt: The mass of exhaust expelled under a unit of time (dm/dt)
v : velocity of the rocket
c : velocity of the exhaust
a : acceleration
t : time
d/dt : Derivating by time
underline : vector
For the less geek among us, the most important equation is the last one:
FT = c * mb
The force of the rocket engine is the ammount of exhaust it expells multiplied by the speed of the exhaust.
For getting into orbit you need a lot of force.
You need to defeat gravity and when your rocket is several hundred tons, accelerating all of that by more than 9.8 meter/second2, needs a damn lot of trust.
To get more thrust you either increase the exhause speed, or the exhaust ammount. The problem lies in the fact that to c - exthaust speed is constant for a given chemical reaction, so to gain more thrust you dump more and more fuel (= some flamable, lots of oxydiser) into the rocket engine.
c - is also often called specific impulse. It tells how much thrust a single unit of exthaust gives.
Since c is fixed for chemcial rockets, it dictates how much fuel you need to burn to achieve the desired thrust.
Hence it can be though of as the milage of the fuel. The higher the better.
Delta-v
However once in orbit, thrust isn't importnat. Delta-v is.
The easiest method how I can explain what delta-v is, is through Newton's second law:
dFdt = d(m * v) / dt
dv/dt = dF / dm
You're probably familiar with this law from Highschool in the following form:
F = m * a = m * v / t
F * t = m * v : This is the equation that's relevant here
Legend:
F : Force
m : mass
a : acceleration
v : velocity
t : time
F * t is the push the rocket gives over a period of time. m * v is the ammount of kinetic energy the ship gained.
No matter how strong the engine is, going from point A to point B in the solar system will need a given ammound of kinetic energy that equals the work of the Sun's gravity field over the same course.
When you actually take into account that rockets burn fuel (and ergo have less and less mass) you get the following equation for delta-v:
Rocket 101 Mass Basics
M = M0 + mb + mc
r = M / M - mb
p = M / M0
M : Full Mass
M0 : ordenance, payload mass
mb : mass of fuel
mc : structural mass or M - M0 - mb
p: useful mass rating
r : simple mass rating
The rocket's basic motion equation - Part 2:
(m-dm) * dv = - c * dm
- c since the rocket goes in the opposite direction than the exthaust
dv = - c *dm / (m - dm)
m >> dm
dv= - c * dm / m
Legend:
m : rocket's mass at the moment
v : rocket's velocity
c : exthauset velocity
The rocket's motion equation - Part 3:
v - v0 = - c * ln[m]mM = c * ln(M/m)
At burnout
v - v0 =c* ln(M/M-mb) = c * ln(r)
vmax = v0 + c * ln(r)
Legend:
v0 : starting velocity (For liftoff = 0, previous maxspeed for each further stage)
vmax : the rocket's maximum velocity at burnout
vmax = v0 + c * ln(r)
That's the most important equation for any mission design.
The maximum speed of the rocket we can impart onto the rocket is only dependant on the exthaust speed and the ammount of fuel it carries in relation to its own structural mass.
Max speed, translates to delta-v - the equivalent of mission range in the Solar system.
Ergo for long range, or just plain interplanetary missions you need either gigantic ammountof fuel or a high c.
FT = c * mt
max = v0 + c * ln(r)
Ion Engine
How does the ion engine fit into all of this?
In the ion engine you're accelerating ions in an electric field. (The only reason we use ions is that in order to use an electric field you need particles with charge, hence the ions. We usually use positive ions, and dangle an anode into the ionstream to get rid of the negative charge build up - if left unattended the charge differential between our rocket and the exhaust would eventually stop us. Since electrons carry the same charge as a proton but are a thousand times lighter, the loss of momentum is neligible.)
The field can accelerate ions close to lighspeed.
With c = 300.000.000 m / s the milage on an ion engine is pretty impressive.
So why don't we use it to lift our thousand ton spacebattleships off the ground?
Structural engineering limits: we can't dump enough fuel into the engine to create the necessary thrust for a liftoff.
Namely the ions in the acceleration array slowly nick at it - eating it from the inside out.
The wonderful thing about this plasma based ion engine is, that the acceleration array itself is made of plasma - no solid parts that the ions could destroy.
Granted our understanding of plamsa flow dynamics is still very limited, however this engine can output a lot more ions and as a result a greater thrust than.
So in the future, we may use ion engines for liftoff - however why do we bother with it on space probes and so on if its so weak in terms of thrust?
Remember this?
vmax = v0 + c * ln(r)
With c = 300.000.000 m/s it means we can employ probes with minimal ammount of fuel on long range missions.
Granted it still takes a chemical rocket to get it all in orbit, but once there, the ion engine is the choice of engine for high delta-v missions.
EDIT: miswrote an equation.
-
Very nice overview, and yeah it's definitely important to keep in mind that this isn't going to help us get off the planet, it'll just help us go further once we're already up there. Being a bit of a geek about these things myself, I've got to point out one thing you didn't mention: Energy efficiency.
As the fuel efficiency goes up with a higher delta-v, energy efficiency does the opposite; while an exhaust velocity of near light speed is theoretically possible, you'd need to haul a nuclear power plant along for the ride to provide the juice to run the thing. I'm not sure of the exact numbers without looking it up, but the energy requirement increases exponentially with the delta-v, not linearly.
This is why current ion drives are run at a relatively modest delta-v (for that technology at least) of 20.000ish, as this can be achieved by more feasible means like radioisotope generators or even solar cells like on the SMART-1 probe.
So what this advance can do for us with the power options available to us today is probably not a massive increase in thrust, though certainly some will come from the greater efficiency over regular ion thrusters, but a massive increase in lifespan and reliability as it's not continually destroying itself while operating :) We can just hope that power generation will one day allow these drives to truely come into their own and provide both high thrust and massive lifespan, after which we can be off for the stars :D
Ohh, and first post too! Such a geek am I it wasn't even in a freespace related topic :( Well, next time... next time
-
Very nice overview, and yeah it's definitely important to keep in mind that this isn't going to help us get off the planet, it'll just help us go further once we're already up there. Being a bit of a geek about these things myself, I've got to point out one thing you didn't mention: Energy efficiency.
As the fuel efficiency goes up with a higher delta-v, energy efficiency does the opposite; while an exhaust velocity of near light speed is theoretically possible, you'd need to haul a nuclear power plant along for the ride to provide the juice to run the thing. I'm not sure of the exact numbers without looking it up, but the energy requirement increases exponentially with the delta-v, not linearly.
This is why current ion drives are run at a relatively modest delta-v (for that technology at least) of 20.000ish, as this can be achieved by more feasible means like radioisotope generators or even solar cells like on the SMART-1 probe.
So what this advance can do for us with the power options available to us today is probably not a massive increase in thrust, though certainly some will come from the greater efficiency over regular ion thrusters, but a massive increase in lifespan and reliability as it's not continually destroying itself while operating :) We can just hope that power generation will one day allow these drives to truely come into their own and provide both high thrust and massive lifespan, after which we can be off for the stars :D
Ohh, and first post too! Such a geek am I it wasn't even in a freespace related topic :( Well, next time... next time
I'm afraid that you misunderstood the meaning of delta-v.
In space deployment, delta-v doesn't measures speed, it more like an equivalent of the distances we can cover.
If you substitute delta-v in your post though with c - specific impulse, it makes perfect sense.
With higher specific impulse fuel efficiency increases, though energy consumption goes through the rough....which is actually a good thing, as we take the most of the fuel.
The problem you mention isn't with the energy demand itself - it's once again an engineering problem - though truth be told IIRC NASA's new Jupite probe will have a fission reactor onboard.
You were definitly spot on though about lightspeed fast specific impulse - it's theoreticly possible, just not likely to happen due its engineering demands.
The bottomline is: the thing in constant critical demand on a rocket is always the propellant - hence the need to bring the most out of each gramm of it.
This translates to the need for high specific impulse engines.
The energy demand do is not that problematic, in Mars orbit and inside solarcells are sufficient while in deeper space mission isotope sources or maybe in the near future fission reactors can be used.
Nuclear engines are the other great stalwart in our search for better rockets. The basic technology is actually already researched and ready to deploy.
Their potential environment impact though prevents that, and they will most likely see their use only in pure-space missions.
There are several fission designs from the early solid core NERVA with realiably but short lifespan, through the numerous gas phased NERVA alteranatives, with a better long term usability, to exotic designs that use fissioning materail as their propellant.
The actual mechanics behind the nuclear engine are simple - swap out the reaction chamber and put in a reactor. Pass the propellant through the reactor and its heat will accelerate it just the same as an exotherm chemical reaction would.
Figuring out plamsa physics though could mean the end of the radioactive fission nightmare, as a fusion reactor could do the very same job, with a fraction of the nuclear concerns.
-
Heh, I remember when the height of our space exploration hopes was the Bussard Ramjet ;)
-
Heh, I remember when the height of our space exploration hopes was the Bussard Ramjet ;)
yea that would be cool :D
you could in theory circumnavigate the universe in 50 years, assuming einstein's equation was correct. of course you would come back and find the sun had gone nova.
-
Heh, I remember when the height of our space exploration hopes was the Bussard Ramjet ;)
Airbreathing Surface to Orbit Systems are a very likely and not to mention economic solution to the gravity of our situation.
You may want to check this out:
http://en.wikipedia.org/wiki/SABRE
-
Heh, I remember when the height of our space exploration hopes was the Bussard Ramjet ;)
Airbreathing Surface to Orbit Systems are a very likely and not to mention economic solution to the gravity of our situation.
You may want to check this out:
http://en.wikipedia.org/wiki/SABRE
somone hasnt seen cosmos :D
-
Heh, I find the odds of Flaser knowing as much as he does about space exploration and not having seen Cosmos infinitely small ;)
http://en.wikipedia.org/wiki/Bussard_ramjet
The basic theory is the same, and Air-fed Ramjet technology also has a good environmental promise as well, it puts out an absolutely minute amount of pollution when compared to the shuttle.
-
*yawn* wake me when we invent warp drive or hyperspace jump engines
-
*waves goodnight to Kosh... since he's going to be out for a while*
-
What, will nobody welcome Shade?
system tracking... target acquired... fire main batter!
:welcome:
Welcome to HLP!
Exits are to your right and left, and flamethrowers are under your seat. Be careful, though, as they are sometimes filled with water. If this is the case, try to club someone with the non-working shotguns in the weapon closet. Also, be careful while wandering the ventilation shafts, because sometimes Carl the Shivan lurks in there. If you happen to come across him, just toss him your lunch and hope that it satisfies him. If it doesn’t… pray. In the event of an emergency, you can and will be used as a flotation device. The Plasma rifles in the forward locker are released only under authorization of an Admin, [V] God, and/or hyperintelligent shade of the color blue. Finally, don't call Kalfireth Thunder. He doesn't like to be reminded of his former schizophrenic personalities.
-
I'm afraid that you misunderstood the meaning of delta-v.
In space deployment, delta-v doesn't measures speed, it more like an equivalent of the distances we can cover.
If you substitute delta-v in your post though with c - specific impulse, it makes perfect sense.
Thanks for setting that straight, I did confuse it with specific impulse. Consider me embarressed at making such a mistake... next time I will definitely look it up instead of going by memory :)
Nonetheless, the fact remains that the actual acceleration we can get out of these drives remains, for the time being, too small to make them useful for manned space flight. Or at least as the main engine for such a flight, I could see them being used for small course corrections or stationkeeping once in orbit around wherever you're going. It's probes that will benefit until we get vastly better options for power generation. Fusion reactors do sound promising if they ever get working properly, good thing there's been some effort in that area lately so hopefully some day...
[Edit] And thanks for the welcome :)