variable specific impulse magnetoplasma rocket interstellar capabilities?

[noobsrtoast]

so i know that the VASIMR engine is being considered as a method of propulsion for taking humans to mars in the near future, however my question is does the vasimr engine have any potential use for an interstellar mission in reasonable time, i have seen them thinking about the use of ion drives and plasma rockets aside from this one so it cant be that far off

[-Velocity-]

No, the specific impulse, from what I've read, is only 5000s. Use the rocket equation-

vf = ve*ln(mi/mf) (vf = final velocity, ve = exhaust velocity, mi = initial mass, mf = final mass)

ve = 5000*9.81 = ~50000 m/s

Say you can put humans to sleep in cryo chambers, so you can get away with "only" a 1000 ton spacecraft payload.

You'll want vf of at least like 6e7 m/s so you can accelerate to 10% the speed of light (3e7 m/s) on the way out, and then slow back down at your destination. This is a one-way trip.

So,

6e7 m/s = 5e4 m/s *ln(mi/1e6 kg)

exp(6e7/5e4) = mi/1e6 kg

exp(6e7/5e4)*1e6 = mi

mi = 1.4e527 kg....

1.4x10^527... To put that in perspective, that's over 10^474 times MORE than the mass of the observable universe... which really fails to put it in perspective, honesty.

To deliver a 1000 ton spacecraft to Alpha Centauri within a reasonable time span, your spacecraft's initial mass would have to be 140 thousand million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million, million kg.

It's a number so large that the human mind cannot truly comprehend it.

Edited November 18, 2014 by |Velocity|

[-Velocity-]

So maybe you want to build a generation ship. And you're somehow still getting away with 1000 ton spacecraft. You're OK with getting to Alpha Centauri in 500 years time. That will require a top speed of like 2.6e6 m/s, so you'll need a total of 5.2e6 m/s of delta-V. Now your spacecraft's initial mass is "only" 1.5x10^51 kg. You'll need the combined mass of mass of like 400 million Milky Way galaxies to propel your spacecraft. No big deal, right?

[KerikBalm]

No, the specific impulse, from what I've read, is only 5000s.

It is variable, but can go much higher than 5,000s

http://www.adastrarocket.com/ISGLP_JPSquire2008.pdf

"As specific impulse increases, propellant usage decreases, with a minimum near 15,000 seconds. Accordingly, this results in increased cargo, with a maximum of approximately 75 metric tons, more than twice the mass delivered by the LOX-hydrogen chemical system. As specific impulse is raised beyond 15,000 seconds however, the power requirement grows so rapidly that the increasing mass of the array requires more propellant mass to be carried in the CDV, thus reducing the cargo delivered. With regard to cargo mass only, the optimum specific impulse is therefore 15,000 seconds. "

But, 5,000 is more reasonable for shorter trips, given it will get much better thrust, and operates at a higher efficiency.

"5. Lunar cargo application

As far back as the early years of the Apollo program, it was appreciated that electric propulsion could transfer payloads from low Earth orbit to low lunar orbit more economically than chemical propulsion [13]. We illustrate this here by comparing the performance of a hypothetical LOX-hydrogen chemical propulsion system operating at a specific impulse of 450 seconds with a solar-powered VASIMR propulsion system capable of operating over a wide range of specific impulse.

At present, the optimal specific impulse for a VASIMR based system appears to be approximately 5,000 seconds. "

[noobsrtoast]

fair enough, i guess i should have considered the rockets specific impulse before jumping to the conclusion that we may have just made an interstellar engine, chemical rockets are a failure, VASIMR is a complete failure, i sometimes wonder what we have left to turn to

[noobsrtoast]

im going to go look at a couple of other propulsion systems play around with the maths, then come back and see if i can find something reasonable just for the hell of it, also another question i have is, suppose we invent a cryo chamber or some sort of similar age halting technology, would the VASIMR engine then become practical?

[GregA]

im going to go look at a couple of other propulsion systems play around with the maths, then come back and see if i can find something reasonable just for the hell of it, also another question i have is, suppose we invent a cryo chamber or some sort of similar age halting technology, would the VASIMR engine then become practical?

It is NASA's position at the end of their Breakthrough Physics lab study that no propulsion method that requires reaction mass can feasibly travel interstellar distances in a single life time.

What that means to you, and this is a bitter pill for most space nerds to swallow, baring some near miraculous breakthrough in our understanding of physics, there will ~never~ be human interstellar travel.

There are several extremely exotic techniques that could possibly send tiny probes on flyby missions.

Humans are locked in the solar system forever.

[sndrtj]

Mwa, that's overly pessimistic. A human lifetime at current life span might not make it. Assuming generation ships, and increase in human life span (perhaps combined with cryogenic sleep periods) will mean that human interstellar flight might be in reach after all. Just the time spans on which this flight occurs will be on the order of several hundred years, if not more.

[magnemoe]

It is NASA's position at the end of their Breakthrough Physics lab study that no propulsion method that requires reaction mass can feasibly travel interstellar distances in a single life time.

What that means to you, and this is a bitter pill for most space nerds to swallow, baring some near miraculous breakthrough in our understanding of physics, there will ~never~ be human interstellar travel.

There are several extremely exotic techniques that could possibly send tiny probes on flyby missions.

Humans are locked in the solar system forever.

Some ways who will work but is pretty unpractical: anti matter and laser pumped solar sails should work but would be expensive require multiple breakthrough.

An good fusion engine might work but would run into the rocket equation pretty hard too.

None of the near future technology engines is closes, to put the requirements in perspective power demand would be more than global power production today.

And yes an manned mission is some magnitudes harder than a probe, requirements is more in the solar power who hit earth scale.

Seeing the starship in Avatar I thought it was pretty funny that they had pollution problems outside heat pollution.

[KerikBalm]

An orion drive could do it

As could a fusion reactor/Dense plasma focus.

Every propulsion method requires reaction mass*.

*Photons have zero rest mass, but they have relativistic mass. Thus a solar sail is similar to a bussard ramjet: you pick up your reaction mass "on the fly"

[-Velocity-]

It is NASA's position at the end of their Breakthrough Physics lab study that no propulsion method that requires reaction mass can feasibly travel interstellar distances in a single life time.

What that means to you, and this is a bitter pill for most space nerds to swallow, baring some near miraculous breakthrough in our understanding of physics, there will ~never~ be human interstellar travel.

There are several extremely exotic techniques that could possibly send tiny probes on flyby missions.

Humans are locked in the solar system forever.

A little pessimistic, at least the idea that "humans" will forever be locked in the solar system. Though forever is a long time, and not matter what happens, it won't be long before we are not what we would call humans anymore. Most people today have very limited imaginations when they think of people of the future- they only think of humans. Historically that would be right, but there are several expanding transformative and largely untapped technologies that could lead to the citizens of Earth being very much non-human in the not-so-distant future. So perhaps in a sense you could be right.

And on a longer time scale, millions of years, current "humans" are certain to cease to exist, even without technological intervention. We'll evolve into something else.

Anyway, I'm not terribly concerned about humans not being able to make the trip. That's a specieist viewpoint (discrimination based on species). Why is not enough to be able to send a being that represents our values and culture? Why should we care so much if this being is human or not? If a "non-human" mind respects morality and represents and appreciates our values, under what basis is it logical to discriminate against it? Such discrimination would be just as vile and unjustifiable as antisemitism or white supremacy. If it thinks like us and represents our values, then it IS one of us. There is no known reason such a thing cannot be realized in a machine intelligence , and such an intelligence may be able to make the trip, AND even grow humans (or whatever you want to call our descendants) when it arrives.

Oh and finally, given a long enough time span, the stars will come to us.. or at least, a bit closer. If our civilization is truly worthy of settling extrasolar systems, then it should be capable of surviving in our solar system for the requisite millions of years necessary for a close stellar encounter. According to this paper abstract, a star comes within a parsec about once every 430,000 years. So, scaling that probability by the inverse of the space volume, maybe once every 15 million years a star comes within 1 light-year and every 430 million years a star comes within 0.326 light-years.

And well... why does fusion pulse look like a dead-end for like 0.1c travel? What is a realistic Isp for it? And that black hole starship idea actually seemed like it might be remotely possible. A mini black hole is able to convert mass into Hawking radiation at a very high efficiency, and if you can keep it fed faster than it decays, AND if you can really practically form one with focused gamma rays, then that seems like it could be a real breakthrough in interstellar travel. It's a long-shot, but at least it may be within the laws of physics and possibly practical, unlike warp drives.

Edited November 18, 2014 by |Velocity|

[GoSlash27]

*snip* that's over 10^474 times MORE than the mass of the observable universe... which really fails to put it in perspective, honesty.

Mind= blown. I'll just be over here in the corner, gently weeping...

Best,

-Slashy

[Northstar1989]

If you're looking for something that could actually travel interstellar distances in a reasonable time period using current technology, look no further than Orion Nuclear-Pulse Rocketry:

http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29#Interstellar_missions

For "just" 10% of the U.S. 1968 GNP, you could get a 133 year voyage to Alpha Centauri (with a 50,000 ton payload). That's quite reasonable for a generation-ship, both in terms of mass and time, and the study was based on materials available in 1968 (modern materials are much lighter/stronger, and thus require less structural mass: 50,000 tons of structure were to complement the 50,000 tons of payload...)

Regards,

Northstar

[Nuke]

i have a feeling colonizing the universe will be through snowball hopping. we will start colonizing the solar system, and slowly move out into the oort cloud. this will push humans out a light year or more. if the nearest star has a similar cloud, then its only a 2ly trip to the next cloud, which is achievable with a generation ship.

[Northstar1989]

i have a feeling colonizing the universe will be through snowball hopping. we will start colonizing the solar system, and slowly move out into the oort cloud. this will push humans out a light year or more. if the nearest star has a similar cloud, then its only a 2ly trip to the next cloud, which is achievable with a generation ship.

If we can wait long enough (1.36 million years) without blowing ourselves up, the main sequence K-class star Gliese 710 is set to pass through the Oort cloud...

http://en.wikipedia.org/wiki/Gliese_710

Regards,

Northstar

[GregA]

If you're looking for something that could actually travel interstellar distances in a reasonable time period using current technology, look no further than Orion Nuclear-Pulse Rocketry:

http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29#Interstellar_missions

For "just" 10% of the U.S. 1968 GNP, you could get a 133 year voyage to Alpha Centauri (with a 50,000 ton payload). That's quite reasonable for a generation-ship, both in terms of mass and time, and the study was based on materials available in 1968 (modern materials are much lighter/stronger, and thus require less structural mass: 50,000 tons of structure were to complement the 50,000 tons of payload...)

Regards,

Northstar

Im just saying... I love this machine. However, concepts like Fermi Paradox, and the Great Filter come to mind when you starting talking about making nuclear bomb machine guns.

(wild speculation with a few facts thrown in) The legend is, Kennedy went to a presentation by the Pentagon for the Orion Program. Just a few days later he canceled the Orion Program, and funded Apollo. This is the specific device he was afraid that an arms race with the Russians would present as an existential threat.

Nasa to this day has a working group that does nothing but design state of the art Orion ships (they admitted this recently), in the event that one is needed.

The Character "Harry" in the book Footfall is how I have modeled my life, as the type of man I decided I wanted to be when I was a child.

It is an extreme ship, to be utilized in extreme circumstances.

- - - Updated - - -

i have a feeling colonizing the universe will be through snowball hopping. we will start colonizing the solar system, and slowly move out into the oort cloud. this will push humans out a light year or more. if the nearest star has a similar cloud, then its only a 2ly trip to the next cloud, which is achievable with a generation ship.

Carl Sagan wrote a fiction piece about this. I wish I could remember the title.

[magnemoe]

Im just saying... I love this machine. However, concepts like Fermi Paradox, and the Great Filter come to mind when you starting talking about making nuclear bomb machine guns.

(wild speculation with a few facts thrown in) The legend is, Kennedy went to a presentation by the Pentagon for the Orion Program. Just a few days later he canceled the Orion Program, and funded Apollo. This is the specific device he was afraid that an arms race with the Russians would present as an existential threat.

Nasa to this day has a working group that does nothing but design state of the art Orion ships (they admitted this recently), in the event that one is needed.

The Character "Harry" in the book Footfall is how I have modeled my life, as the type of man I decided I wanted to be when I was a child.

It is an extreme ship, to be utilized in extreme circumstances.

- - - Updated - - -

Carl Sagan wrote a fiction piece about this. I wish I could remember the title.

Footfall: sitting here waiting for an nuke to go off below my ass.

Main issue with Orion is cost, it only make sense if you need to move thousands of tons fast. For smaller cargoes its kind of overkill, and yes the fuel is expensive.

Think that is the reason the orion program was canceled, an space race with Soviet using orions would be very expensive and it would play on many of the Soviets strong sides.

However the interstellar orion has way better performance than I thought, might be smart to use as an acceleration stage, then turn it around and you has an good protection against interstellar dust. Now use something lighter to brake, Might be possible to do most of the braking using an magnetic sail.

You don't need a 1g acceleration either

[Northstar1989]

Footfall: sitting here waiting for an nuke to go off below my ass.

It sounds like a great book, that I only today became aware of for the first time (mere hours before your posts). I'll have to think about reading it some time...

Main issue with Orion is cost, it only make sense if you need to move thousands of tons fast. For smaller cargoes its kind of overkill, and yes the fuel is expensive.

Think that is the reason the orion program was canceled, an space race with Soviet using orions would be very expensive and it would play on many of the Soviets strong sides.

Expensive, yes. But the per-launch cost of an Orion was projected to be LESS than that of a Saturn V, while carrying thousands of times more cargo. Not a drastically lower cost mind you, but still slightly less, and with a much higher tonnage...

However the interstellar orion has way better performance than I thought, might be smart to use as an acceleration stage, then turn it around and you has an good protection against interstellar dust. Now use something lighter to brake, Might be possible to do most of the braking using an magnetic sail.

You don't need a 1g acceleration either

Yeah, magnetic sails would be a convenient way to brake. Also something I only read about today- but the thought concerns me: if you're pushing against the magnetic field of a star (and thus basically using the star as reaction mass), couldn't you significantly perturb its total trajectory if you're braking something on the order of a 100,000 ton vessel from 10% the speed of light? And if so, wouldn't that risk screwing up the orbits of the very extrasolar planets you probably came to investigate in the first place- possibly even causing apocalyptic changes to the orbit and magnetic fields of any inhabited planets that somehow existed? Maybe THAT is the reason for the Fermi Paradox... (other spacefaring races accidentally destroying each other using magnetic sails)

Of course, as a biologist with an incredibly deep understanding of history, I have my own answers to the Paradox. My belief is simply that very few planets have the correct setup to support intelligent life, and EVEN FEWER planets have the right circumstances to support an interplanetary (forget interstellar) civilization. I don't think we would even be considering traveling to Mars if we didn't have a Moon we were able to travel to first and prove technologies at, for instance...

Regards,

Northstar

[NERVAfan]

Yeah, nuclear pulse makes interstellar workable for humans.

And I do really think that it does matter that humans do things (OTOH, I do not at all believe in human-like AI - even if they were created that way, they would very rapidly become wildly nonhuman).

EDIT: And given interstellar dust/hydrogen, I don't think there's much point in sending unmanned probes - I'm pretty skeptical of the super-light laser-powered-sail probes people talk about surviving at even 1% of c. An interstellar craft should be armored so heavily -- and therefore so huge -- it might as well be a worldship/generation ship.

Edited November 19, 2014 by NERVAfan
grammar ("there for" -> "therefore")

[magnemoe]

It sounds like a great book, that I only today became aware of for the first time (mere hours before your posts). I'll have to think about reading it some time...

Expensive, yes. But the per-launch cost of an Orion was projected to be LESS than that of a Saturn V, while carrying thousands of times more cargo. Not a drastically lower cost mind you, but still slightly less, and with a much higher tonnage...

Yeah, magnetic sails would be a convenient way to brake. Also something I only read about today- but the thought concerns me: if you're pushing against the magnetic field of a star (and thus basically using the star as reaction mass), couldn't you significantly perturb its total trajectory if you're braking something on the order of a 100,000 ton vessel from 10% the speed of light? And if so, wouldn't that risk screwing up the orbits of the very extrasolar planets you probably came to investigate in the first place- possibly even causing apocalyptic changes to the orbit and magnetic fields of any inhabited planets that somehow existed? Maybe THAT is the reason for the Fermi Paradox... (other spacefaring races accidentally destroying each other using magnetic sails)

Of course, as a biologist with an incredibly deep understanding of history, I have my own answers to the Paradox. My belief is simply that very few planets have the correct setup to support intelligent life, and EVEN FEWER planets have the right circumstances to support an interplanetary (forget interstellar) civilization. I don't think we would even be considering traveling to Mars if we didn't have a Moon we were able to travel to first and prove technologies at, for instance...

Regards,

Northstar

You will not affect other orbits, remember the power you use, even the high order (sunlight who hit earth) is magnitudes less than orbital energies.

Secondly this will be done over time, say you start braking one lightyear away, the effect of the braking will go down as speeds drops too.

By the time you are in the inner solar system you are not moving relativistic anymore.

As for the Fermi Paradox, advanced life might be rare, more probably intelligence is rare.

A lot of roadblocks, everything from species who can be domesticated up able to do large scale organizations is required to become an technical civilization.

Also as we see here, interstellar travel is hard, manned interstellar missions will be expensive even for an rich interplanetary civilization.

[Streetwind]

There are better electric engines in the lab than the VF-200 VASIMR... granted, they're not as close to actual deployment, but that's mostly because the market for high powered electric propulsion is pretty much nonexistant (in other words, nobody is interested in buying something that consumes more than a few kW). We just don't have suitable power generation to really scale up electric propulsion in a sensible manner, especially for going away from the sun.

That said, ESA has been working on a dual-stage gridded ion thruster concept. An initial prototype with 4 grids (literally called the DS4G, dual-stage 4-grid ion thruster) entered subscale testing, and a prototype was verified to work in such a way that by extrapolation the fullscale version could be operated at 250 kW power, 2.5 N thrust, 19,300s Isp. Compare the VF-200's 200 kW power, 5 N thrust, ~5000s Isp. ESA scientists have since simplified the design to just three grids and refined everything a bit more, but no real prototypes have been built (again, nobody wants a 250 kW electric engine right now). So the performance of the refined dual-stage ion thruster can only be speculated about.

Meanwhile on the nuclear pulse propulsion side of things, NASA has been funding a serious fusion rocket project that will rely on the pulse propulsion principle. It will drop a deuterium/helium-3 fuel pellet out the back, then use a huge, short-duration magnetic field to collapse a set of lithium rings around the pellet, compressing it and igniting fusion. The result is expelled by a magnetic nozzle, propelling the spacecraft. Think of it as Project Orion, except with fusion bombs instead of fission bombs... and the fusion bombs are so small that no pusher plate is required. It also captures nearly all of the energy of the fusion, whereas Project Orion would only use a small part of each explosion's power. The aneutronic fusion also greatly reduces the required shielding on the spacecraft. The project started in 2011, and they're expecting to have a full-scale prototype by 2020 and fly a demonstration mission two or three years later. The development timeline is partially constrained by the technological progress in solar panels, which are required to generate power for the magnetic fields. The drive can technically work with today's solar panels - the Isp is independent, just overall thrust goes down a lot due to very long charge times between pulses and/or more mass dedicated to solar arrays - but to really exploit it to its fullest potential, at least a tripling in power output per kg is desired.

[noobsrtoast]

i dont like being pessimistic about it, i think that one day we will have a breakthrough in be it power production or propulsion systems, or even genetics for that matter. either that or we die a slow death on this planet, someone has to make the call eventually and i have hope that someone will

[noobsrtoast]

you know i knew one day that someone would find a use for all that fusion technology we have been seemingly needlessly producing for the past hundred years for nothing other than building nuclear bombs, which in my opinion is just a waste, the question remains though is: can it get us to another star?

[noobsrtoast]

this is a fair point you make, i really hope we find some kind of breakthrough in fusion propulsion, it seems like our best bet right now seeing as we love it so much (nukes), that is if we dont end up destroying ourselves before we have a chance to try, which with current world events seems likely. i wouldnt call his point pessimistic i would call it realistic, hope is a good thing to have but you must be realistic in your hope. lets be honest here do you really think anyone is going to pay for a huge starship that will not benefit them in any way, that they will never see again? the answer is no the only reason we ever went to the moon was because the united states wanted to beat the soviets there during their 50 year dispute. whether you like it or not until we change the way we think, until we can get over the fact that not everything we do were going to get something out of, we wont be traveling the stars anytime soon.

before we even consider an interstellar vessel a few things need to happen. for one we need to get over our greed and unwillingness to share our resources, we need to get over that maybe a few of us are different, and have different opinions than one another, we need to get over our hate for each other, our desire for power over one another, only then can we begin to consider building such a vessel. were already at a disadvantage considering how sparsely populated our local stellar neighborhood is, stars in our local cluster are extremely far apart, we cant put ourselves at more of a disadvantage by being selfish. however until we evolve more i fear that it might take a while for us to get over these traits, if we have time to do so.

[noobsrtoast]

we will start colonizing the universe when something that threatens our existence forces us to