Author Topic: Advancements in Electric Thrusters  (Read 104499 times)

Offline Raj2014

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Re: Advancements in Electric Thrusters
« Reply #20 on: 02/16/2015 03:00 pm »
What is the most ideal space reactor used or planned and If they used that on a electric thruster, which has the highest thrust, what will the speed be? Will it be enough for human deep space travel?   

Offline Robotbeat

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Re: Advancements in Electric Thrusters
« Reply #21 on: 02/16/2015 05:08 pm »
What is the most ideal space reactor used or planned and If they used that on a electric thruster, which has the highest thrust, what will the speed be? Will it be enough for human deep space travel?
The Sun is the ideal space reactor in the inner solar system, and yes, solar-electric propulsion is enough for human deep space travel.

And the speed depends on how fast you need to go.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Impaler

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Re: Advancements in Electric Thrusters
« Reply #22 on: 02/16/2015 07:55 pm »
Wouldn't the charged particles from the van allen belts drastically reduce the efficiency of the thin film cells by the time you are in EML2?

No, because you use Amorphous silicon, which is very resistant to degradation under the space-radiation environment.  The other parts of the craft like electronics we already know how to make resistant to radiation as well.  And their is even a natural 'annealing' effect that restores the cells back to near original performance as they warm in the sun.

Offline Raj2014

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Re: Advancements in Electric Thrusters
« Reply #23 on: 02/16/2015 08:11 pm »
What is the most ideal space reactor used or planned and If they used that on a electric thruster, which has the highest thrust, what will the speed be? Will it be enough for human deep space travel?
The Sun is the ideal space reactor in the inner solar system, and yes, solar-electric propulsion is enough for human deep space travel.

And the speed depends on how fast you need to go.

Could I have numbers please. To get to Mars it is ideal to get there as quick as possible because of radiation but we also know there are ways to reduce or stop radiation harming the crew and technology plus the orbit of Mars could make the journey shorter or longer.  I just want to know with the most power space reactor powering the most highest thrust produced on a electric thruster, what will the maximum speed be? Also has there been any advancements on the EM-Drive? 
« Last Edit: 02/16/2015 10:03 pm by Raj2014 »

Offline Impaler

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Re: Advancements in Electric Thrusters
« Reply #24 on: 02/16/2015 10:02 pm »
Power and thrust are not directly related, you need to know ISP to finish the equation.

It's best to look at the acceleration needed to do a Heliocentric transfer from Earth-Escape to achieve a given transfer time assuming ideal departure timing.

Some rough numbers from AdAstra trajectories using the average distance between Earth-Mars and 5k ISP and constant power availability.

About 1 mm/s (1 N force per 1000 kg vehicle mass) will get you to Mars in 180 day.  If you can crank up thrust to 10 mm/s then you get to Mars in ~50 days.  Lower the thrust to 0.5 mm/s and the transit takes 250 days. 

Rough equation is  (Transit Days^2) * Thrust in mm/s = ~30,000

The lower the ISP the more mass you will lose and this will tend to help because you gain acceleration as you lose mass.  But the effect is modest because SEP vehicle designs for Mars transits are rarely more then 1/3 propellent.  A Solar systems reduced power and thrust at Mars increases transit time ~10% over this baseline, which in my opinion is not sufficient to justify nuclear systems of even equal specific power.  The general consensus seems to be 5k ISP is ideal but a denser power source will change that.

Note that if your concerned about radiation you need to have a strategy IN ADDITION to fast transit, because Mars surface has half the daily dosage of space.  Either you need to do a sprint mission and get headed back towards Earth in a month or so, or you need a deeply buried habitat on Mars and minimal EVA's over a long stay.  Their is simply no point to going to and from Mars in 100 day sprints and then spending 500 days on surface getting the equivalent of 250 days of transit dosage.

Offline Robotbeat

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Re: Advancements in Electric Thrusters
« Reply #25 on: 02/17/2015 04:52 pm »
...
About 1 mm/s (1 N force per 1000 kg vehicle mass) will get you to Mars in 180 day.  If you can crank up thrust to 10 mm/s then you get to Mars in ~50 days.  Lower the thrust to 0.5 mm/s and the transit takes 250 days.  ...
Minor quibble: Don't you mean mm/s^2 instead of mm/s?
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Impaler

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Re: Advancements in Electric Thrusters
« Reply #26 on: 02/17/2015 09:26 pm »
Yes, same as any acceleration rate it would be in units of s^2.

I found http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0CC8QFjAC&url=http%3A%2F%2Fwww.dtic.mil%2Fcgi-bin%2FGetTRDoc%3FAD%3DADA513936&ei=LbTjVIPDL4HsoASN6oC4Dw&usg=AFQjCNHxL-4st7lrzUUJ8ryVdkY7mrtXKw&sig2=Ff5jujM1ebpyCb6YuCd71w&bvm=bv.85970519,d.cGU

Paper from the Airforce with a nice summary of HALL, VASIMIR and ELF thrusters

Nested HALL (X3)    0.5 kg/kw (thrusters)  1.4 kg/kw (Thruster and PPU)
VASIMIR                  1.5 kg/kw (thrusters)  Ad-Astra estimates 10MW device would be 4 kg/kw
ELF                        0.25 kg/kw (thrusters)  0.7 kg/kw (Thrusters and PPU)

I think this shows rather clearly why VASIMIR has fallen out of favor vs HALL and why ELF and similar Reverse-Field-configuration designs are attractive as the next follow-on technology.  ELF + 1kw/kg solar is an 'alpha' value of near 2, look at any of the VASIMIR papers and that's near the Alpha value they were needing for some of the insanely short 40 days to Mars ideas (anything under 3 months is total overkill in my opinion).

Offline Raj2014

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Re: Advancements in Electric Thrusters
« Reply #27 on: 02/17/2015 10:40 pm »
Yes, same as any acceleration rate it would be in units of s^2.

I found http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0CC8QFjAC&url=http%3A%2F%2Fwww.dtic.mil%2Fcgi-bin%2FGetTRDoc%3FAD%3DADA513936&ei=LbTjVIPDL4HsoASN6oC4Dw&usg=AFQjCNHxL-4st7lrzUUJ8ryVdkY7mrtXKw&sig2=Ff5jujM1ebpyCb6YuCd71w&bvm=bv.85970519,d.cGU

Paper from the Airforce with a nice summary of HALL, VASIMIR and ELF thrusters

Nested HALL (X3)    0.5 kg/kw (thrusters)  1.4 kg/kw (Thruster and PPU)
VASIMIR                  1.5 kg/kw (thrusters)  Ad-Astra estimates 10MW device would be 4 kg/kw
ELF                        0.25 kg/kw (thrusters)  0.7 kg/kw (Thrusters and PPU)

I think this shows rather clearly why VASIMIR has fallen out of favor vs HALL and why ELF and similar Reverse-Field-configuration designs are attractive as the next follow-on technology.  ELF + 1kw/kg solar is an 'alpha' value of near 2, look at any of the VASIMIR papers and that's near the Alpha value they were needing for some of the insanely short 40 days to Mars ideas (anything under 3 months is total overkill in my opinion).

On page 8, it shows that ELF thrusters have the highest thrust produce and it has less mass. When will they test ELF thruster or thrusters in space?

Offline Impaler

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Re: Advancements in Electric Thrusters
« Reply #28 on: 02/18/2015 12:47 am »
Probably not for a long time, they are still in VERY early testing in vacuum chambers at University of Michigan.  I don't even know if NASA is interested in ELF yet.   I expect large (200 kw) SEP vehicles using Nested HALLs will happen first because that's the low risk tech and we won't see ELF in space until we start to feel the ceiling of HALL performance.

Offline Paul451

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Re: Advancements in Electric Thrusters
« Reply #29 on: 02/18/2015 12:09 pm »
DS4G   19,000s

Sweet Jesus. Unless I dropped a few decimal places, a vehicle with a fuel MR of 3 could reach more than 200km/s. At an (arbitrarily chosen) acceleration of 1/10,000 g's, that means you'd reach the solar gravitational focal distance (550AU) in 16 years, and the more desirable 1000AU in about 26 years. (Pluto orbit (not flyby) in about 7 years with a fuel MR of 2.)

This thing may have an order of magnitude too high exhaust velocity for a trip to Mars, but it's something magical for the edge of the solar system.

Offline tea monster

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Re: Advancements in Electric Thrusters
« Reply #30 on: 02/18/2015 12:38 pm »
At first, I thought it would never work. I mean, can you imagine Darth Vader turning to his lackeys and saying "Launch the Twin Elf Fighters?" No, me neither.

Then, I thought of a time in the far, far flung future when Congress decides to finally get its finger out of it's fundament and pay to go to Mars. I can just see the nation's foremost rocket expert being called onto the Hill to tell them how the deed will be done. The  distinguished expert represents the pinnacle of America's space and science acumen. All eyes are upon him as he slowly takes the podium. The normal hub-bub of the chamber falls to silence as every ear and eye is upon him. He coughs authoritatively, straightens his papers, and in a calm and measured voice, tells them that elves will take them to Mars.

It has to be done.
« Last Edit: 02/18/2015 12:39 pm by tea monster »

Offline Nilof

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Re: Advancements in Electric Thrusters
« Reply #31 on: 02/18/2015 12:47 pm »
I found this paper on the X3 to be a fascinating read(also attached): http://pepl.engin.umich.edu/pdf/2014_Florenz_Thesis.pdf
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline Impaler

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Re: Advancements in Electric Thrusters
« Reply #32 on: 02/18/2015 05:12 pm »
Follow up on earlier testing question: 

It appears that 100 kw and above class thruster development is running into a problem, their are hardly any vacuum chambers that are large enough and can draw a vacuum rapidly enough to accommodate the propellent flow rates these things are capable of.  The upper end of the power range of the X3 could only be tested at Glenn, which is the NASA epicenter of Electric Thruster R&D.  This testing bottle-neck may slow down the development of EP unless more/large chambers are built.

Paul451:  The DS4G would indeed be ideal for that kind of long duration, high ISP mission.  The power source would certainly need to be nuclear which is likely a much bigger technical challenge then the DS4G itself.  Throwing in some gravitational-sling-shots wouldn't hurt either.  Basically the further out in the solar-system you go the higher the idea ISP is because your trip time is going to be long and building up speed is the way to go.

It would be interesting to try to create a graph of how this ideal ISP rises as your mission objective moves outward from Earth.

Nilof:  Good find, though it is packed with details I found it kind of rambling at times.  Overall I think the X3 and the concentric-nested-HALL concept are real breakthroughs and are THE advanced propulsion that has been need for manned trips to Mars, we just need a bit of an improvement in power-density and we would be ready to make a vehicle out of off the shelf components.

Offline KelvinZero

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Re: Advancements in Electric Thrusters
« Reply #33 on: 02/18/2015 08:28 pm »
It has to be done.
Trying to come up with a spaceflight term beginning with Y.. I want to perform a Gravitational Assist something ELF insertion..
Aaaaanyway..

This idea is too hand wavey for its own thread, but I was thinking there might be the possibility to beat the rocket equation entirely with electric thrust in deep deep space. For example I remember some experiment that ejected a persistent plasma loop. If this could grow to an absurd size, experience drag and eventually come to rest wrt to the interstellar medium, then if your next loop could push against the previous, then ultimately you would be pushing against a fixed frame of reference and could get a velocity^2 instead of exponential relationship... or something like that. It is also inspired by the claim that you could create massive artificial magnetospheres for braking wrt to the interstellar medium. They can just grow arbitrarily in size.

 

Offline Robotbeat

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Re: Advancements in Electric Thrusters
« Reply #34 on: 02/18/2015 10:43 pm »
Follow up on earlier testing question: 

It appears that 100 kw and above class thruster development is running into a problem, their are hardly any vacuum chambers that are large enough and can draw a vacuum rapidly enough to accommodate the propellent flow rates these things are capable of.  The upper end of the power range of the X3 could only be tested at Glenn, which is the NASA epicenter of Electric Thruster R&D.  ...
Yeah, I was just going to suggest Glenn (I was an intern there). They have several that are very large and with high pumping capacity. Especially if you include the (also in Ohio) Plum Brook facility (which isn't normally used for electric propulsion, but they have the biggest thermal vacuum chamber in the world with high pumping capacity and also another very large one... the biggest one was originally built for testing space nuclear power).
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline TrevorMonty

Re: Advancements in Electric Thrusters
« Reply #35 on: 02/19/2015 12:38 am »


Follow up on earlier testing question: 

It appears that 100 kw and above class thruster development is running into a problem, their are hardly any vacuum chambers that are large enough and can draw a vacuum rapidly enough to accommodate the propellent flow rates these things are capable of.  The upper end of the power range of the X3 could only be tested at Glenn, which is the NASA epicenter of Electric Thruster R&D.  ...
Yeah, I was just going to suggest Glenn (I was an intern there). They have several that are very large and with high pumping capacity. Especially if you include the (also in Ohio) Plum Brook facility (which isn't normally used for electric propulsion, but they have the biggest thermal vacuum chamber in the world with high pumping capacity and also another very large one... the biggest one was originally built for testing space nuclear power).

NASA has access to a huge vacuum chamber, its attached to ISS.

Offline Impaler

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Re: Advancements in Electric Thrusters
« Reply #36 on: 02/19/2015 02:26 am »
NASA has access to a huge vacuum chamber, its attached to ISS.

Hugely expensive to use and power limited, being dependent on that was part of what stalled VASIMR for decades.  If your device can only be tested in space it's really DOA.

Offline Paul451

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Re: Advancements in Electric Thrusters
« Reply #37 on: 02/19/2015 06:10 am »
Re: Using ISS...
If your device can only be tested in space it's really DOA.

{sigh} Speaking of creating a vacuum, we really suck at doing space.

This came up in the rotating-station thread. What do we have a multi-billion dollar per year permanently manned space station for if not to use it to develop advanced technology for next-gen systems? Precisely things like centrifuges and experimental ion drives that are hard/impossible to test on Earth. Not crystals and student contests and half-hearted "commercialisation" of research.

Offline Krevsin

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Re: Advancements in Electric Thrusters
« Reply #38 on: 02/19/2015 11:35 am »
Well, if I've learned anything about spaceflight, it's that whenever a "Why don't we do X?" question is raised, the answer is probably either "the budget", or "politics".  :P

On a less facetious note, are there any reliable thrust figures for hall thrusters using alternative propellants, such as hydrogen, water and the like? Not noble gases, in any case.

Offline llanitedave

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Re: Advancements in Electric Thrusters
« Reply #39 on: 02/19/2015 05:37 pm »
Re: Using ISS...
If your device can only be tested in space it's really DOA.

{sigh} Speaking of creating a vacuum, we really suck at doing space.

This came up in the rotating-station thread. What do we have a multi-billion dollar per year permanently manned space station for if not to use it to develop advanced technology for next-gen systems? Precisely things like centrifuges and experimental ion drives that are hard/impossible to test on Earth. Not crystals and student contests and half-hearted "commercialisation" of research.


(cough-cough, uhem...)  Dragonrider?
"I've just abducted an alien -- now what?"

 

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