Author Topic: Why the VASIMR hype?  (Read 289884 times)

Offline mlorrey

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Re: Why the VASIMR hype?
« Reply #480 on: 12/04/2009 10:23 pm »
It is simpler if the port and starboard solar arrays use the same design but it is not necessary.  Keeping the ISS in orbit until 2020 would allow a 6 - 7 year soak test of rival designs.


From the above figures

20 metres per day for 7 years = 20 * 365.25 * 7 = 51,135 metres

A 15 minute VASIMR burn uses 0.085 kg of propellant and 3.4 hours per day are needed.  15 minutes = 0.25 hours
Total propellant = (0.085/0.25) * 3.4 * 365.25 * 7 = 2,956 kg

Assume solar array is 150 W per kg UltraFlex BOL and 300 kW is needed
300,000/150 = 2,000 kg

Allocate mass of VASIMR thrusters, power converters, cables and cooling system to the experiment.  Extra mass is 2,956 kg + 2,000 kg = 4,956 kg.
With 10% mass reserve 5.5 mT.

It will be interesting to know the mass and cost difference of using chemical fuel for the station keeping.

I'd like to see what the fuel requirements are to change the orbital inclination from 56 degrees to 23 degrees to be in line with lunar orbital plane, using VF-200.
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Offline Robotbeat

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Re: Why the VASIMR hype?
« Reply #481 on: 12/04/2009 10:47 pm »
It is simpler if the port and starboard solar arrays use the same design but it is not necessary.  Keeping the ISS in orbit until 2020 would allow a 6 - 7 year soak test of rival designs.


From the above figures

20 metres per day for 7 years = 20 * 365.25 * 7 = 51,135 metres

A 15 minute VASIMR burn uses 0.085 kg of propellant and 3.4 hours per day are needed.  15 minutes = 0.25 hours
Total propellant = (0.085/0.25) * 3.4 * 365.25 * 7 = 2,956 kg

Assume solar array is 150 W per kg UltraFlex BOL and 300 kW is needed
300,000/150 = 2,000 kg

Allocate mass of VASIMR thrusters, power converters, cables and cooling system to the experiment.  Extra mass is 2,956 kg + 2,000 kg = 4,956 kg.
With 10% mass reserve 5.5 mT.

It will be interesting to know the mass and cost difference of using chemical fuel for the station keeping.

I'd like to see what the fuel requirements are to change the orbital inclination from 56 degrees to 23 degrees to be in line with lunar orbital plane, using VF-200.

I wonder if such an orbital inclination change could be improved via taking into account the attitude of the station (with its giant solar arrays) and its affect on drag.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline Stephan

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Re: Why the VASIMR hype?
« Reply #482 on: 12/05/2009 08:20 am »
I'd like to see what the fuel requirements are to change the orbital inclination from 56 degrees to 23 degrees to be in line with lunar orbital plane, using VF-200.
I don't think it would be useful, because nodal regression will rotate your orbit plane out of moon plane.
Best regards, Stephan

Offline mlorrey

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Re: Why the VASIMR hype?
« Reply #483 on: 12/05/2009 10:02 am »
I'd like to see what the fuel requirements are to change the orbital inclination from 56 degrees to 23 degrees to be in line with lunar orbital plane, using VF-200.
I don't think it would be useful, because nodal regression will rotate your orbit plane out of moon plane.

It will be useful at least once per day even with regression.
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Offline A_M_Swallow

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Re: Why the VASIMR hype?
« Reply #484 on: 12/05/2009 08:29 pm »

I'd like to see what the fuel requirements are to change the orbital inclination from 56 degrees to 23 degrees to be in line with lunar orbital plane, using VF-200.

Assuming

ISS mass = 350 mT
Average velocity = 27,743 km/h = 7,706.6 m/s
VASIMR VF-200 force is 5 newtons at Isp 5000 seconds
Propellant = 0.085 kg per quarter hour = 0.340 kg/hour
Inclination change (Delta-I) is 56 degrees to 23 degrees
Start and finish orbits are circular

Delta_V = 2 v sin( delta_I / 2)
* = 2 * 7706 * sin( (56-23) / 2) = 4377 m/s

a = F/m
t = Delta_V / a = Delta_V * m / F
* = 7706 * 350000 / 5 = 306,390,000 seconds or 85,108 hours

Real time.  A SEP does not work when in the Earth's shadow and 4.3 hours a day are needed to handle drag.  So burn hours per day
is 24/2 - 4.3 = 7.7 hours per day (controversial)

Time to change orbit is 85,108 / 7.7 = 11,053 days or 30.26 years

Mass of propellant is 85,108 * 0.34 = 28,937 kg

So using a single VF-200 to move the ISS to 23 degree orbit will take over 30 years and 29 mT of propellant.

Offline A_M_Swallow

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Re: Why the VASIMR hype?
« Reply #485 on: 12/05/2009 08:42 pm »
I'd like to see what the fuel requirements are to change the orbital inclination from 56 degrees to 23 degrees to be in line with lunar orbital plane, using VF-200.
I don't think it would be useful, because nodal regression will rotate your orbit plane out of moon plane.

It will be useful at least once per day even with regression.

An alternative to launching 29 metric tons of propellant to move the ISS to 23 degrees is to launch a Bigelow Transhab space station.

Call it the Earth Tropical Inter-planetary Space Station.

Facilities

4 docking ports (Earth, inter-planetary, emergency return and spare).
Sleeping quarters for crew and passengers.
Robot arm to transfer cargo.
Control room.
Station keeping thrusters.
Propellant depot.

Offline alexterrell

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Re: Why the VASIMR hype?
« Reply #486 on: 12/06/2009 01:10 pm »
For changing the inclination of the ISS orbit an electrodynamic tether with energy store is far and way the most effective method. Virtually no additional energy is required (just battery and system losses) as the final orbit has similar energy to the initial orbit.

I can't find the study but I think the time frame was of the order of a year. The battery needs to charge/discharge every orbit so about 6,000 cylces, with high Power / Energy rates. This suits some of the new Li-ion automotive batteries.

Offline mlorrey

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Re: Why the VASIMR hype?
« Reply #487 on: 12/06/2009 05:42 pm »
I'd like to see what the fuel requirements are to change the orbital inclination from 56 degrees to 23 degrees to be in line with lunar orbital plane, using VF-200.
I don't think it would be useful, because nodal regression will rotate your orbit plane out of moon plane.

It will be useful at least once per day even with regression.

An alternative to launching 29 metric tons of propellant to move the ISS to 23 degrees is to launch a Bigelow Transhab space station.

Call it the Earth Tropical Inter-planetary Space Station.

Facilities

4 docking ports (Earth, inter-planetary, emergency return and spare).
Sleeping quarters for crew and passengers.
Robot arm to transfer cargo.
Control room.
Station keeping thrusters.
Propellant depot.

I agree. It's no wonder NASA was interested in abandoning it in 2015. Other than more cumbaya moments of international carebear love and rockets, and some orbital science on long duration human missions, its about useless for lunar or martian missions.
« Last Edit: 12/06/2009 05:43 pm by mlorrey »
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Offline Robotbeat

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Re: Why the VASIMR hype?
« Reply #488 on: 12/06/2009 06:04 pm »
For changing the inclination of the ISS orbit an electrodynamic tether with energy store is far and way the most effective method. Virtually no additional energy is required (just battery and system losses) as the final orbit has similar energy to the initial orbit.

I can't find the study but I think the time frame was of the order of a year. The battery needs to charge/discharge every orbit so about 6,000 cylces, with high Power / Energy rates. This suits some of the new Li-ion automotive batteries.
Although they currently have lower energy density, supercapacitors have much higher specific power and lower recharge/discharge losses as any kind of battery, besides having longer lifetimes. It's quite likely they would be preferable to lithium ion batteries for this application.
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Offline MickQ

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Re: Why the VASIMR hype?
« Reply #489 on: 12/11/2009 01:23 am »
For changing the inclination of the ISS orbit an electrodynamic tether with energy store is far and way the most effective method. Virtually no additional energy is required (just battery and system losses) as the final orbit has similar energy to the initial orbit.

I can't find the study but I think the time frame was of the order of a year. The battery needs to charge/discharge every orbit so about 6,000 cylces, with high Power / Energy rates. This suits some of the new Li-ion automotive batteries.
Although they currently have lower energy density, supercapacitors have much higher specific power and lower recharge/discharge losses as any kind of battery, besides having longer lifetimes. It's quite likely they would be preferable to lithium ion batteries for this application.

Could this be used for a lunar "Hopper" type vehicle, instead of a wheeled rover ?

Mick.

Offline Cinder

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Re: Why the VASIMR hype?
« Reply #490 on: 12/14/2009 08:23 pm »
How hot can a liquid sodium heat pump get?  If you could get the radiators up to 1200 K, you could do more than 400 MW with a couple of square radiator panels 30 metres on a side.

Just make sure the rest of the spacecraft is real shiny.

...and, of course, you have to have a reactor hot-side temperature pushing 2800°F to get 200 MW of useful power out of it with a cold side that hot...

You'd have to do a tradeoff between radiator compactness and combined power cycle efficiency, maybe with practical considerations thrown in just for the heck of it.  I don't have actual experience in this area (and I'm super busy right now), so I'll bow out for the moment...

Really, just build the VASIMR engine with a cooling loop.  There's nothing 35% of 200 MWe will do to your radiator problems that 67% of 600 MWth won't.
What's the convention for radiator mass estimation in such a hypothetical VASIMR craft?
« Last Edit: 12/14/2009 08:39 pm by Cinder »
NEC ULTIMA SI PRIOR

Offline glemieux

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Re: Why the VASIMR hype?
« Reply #491 on: 02/09/2010 03:20 pm »
What makes VASIMR superior to other forms of electric propulsion, for example MPD-Thrusters?

I searched through all the pages on this topic and didn't see one of the other major selling points for VASIMR beside variability: no cathode, arrays, or grids to degrade since it uses a helicon to heat the plasma (major drawback of MPD).  I believe the only other thruster that compares to VASIMR is the HDLT being developed at ANU.

Offline Robotbeat

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Re: Why the VASIMR hype?
« Reply #492 on: 02/09/2010 03:30 pm »
What makes VASIMR superior to other forms of electric propulsion, for example MPD-Thrusters?

I searched through all the pages on this topic and didn't see one of the other major selling points for VASIMR beside variability: no cathode, arrays, or grids to degrade since it uses a helicon to heat the plasma (major drawback of MPD).  I believe the only other thruster that compares to VASIMR is the HDLT being developed at ANU.
Right. In my book, that's VASIMR's biggest strength compared to other electric thrusters. I mean, the Dawn spacecraft is bringing THREE ion thrusters because one won't last long enough for the whole mission. That's not to say there aren't ways to make the other electric thrusters last longer.
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Offline isa_guy

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Re: Why the VASIMR hype?
« Reply #493 on: 02/09/2010 05:14 pm »
And what about the Pulsed inductive thrusters such as in this nasa study http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930023164_1993023164.pdf , which also offers multi-mw thrusters (without the cathode erosion problem like vasimr) .

Offline William Barton

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Re: Why the VASIMR hype?
« Reply #494 on: 02/09/2010 05:18 pm »

I'd like to see what the fuel requirements are to change the orbital inclination from 56 degrees to 23 degrees to be in line with lunar orbital plane, using VF-200.

Assuming

ISS mass = 350 mT
Average velocity = 27,743 km/h = 7,706.6 m/s
VASIMR VF-200 force is 5 newtons at Isp 5000 seconds
Propellant = 0.085 kg per quarter hour = 0.340 kg/hour
Inclination change (Delta-I) is 56 degrees to 23 degrees
Start and finish orbits are circular

Delta_V = 2 v sin( delta_I / 2)
* = 2 * 7706 * sin( (56-23) / 2) = 4377 m/s

a = F/m
t = Delta_V / a = Delta_V * m / F
* = 7706 * 350000 / 5 = 306,390,000 seconds or 85,108 hours

Real time.  A SEP does not work when in the Earth's shadow and 4.3 hours a day are needed to handle drag.  So burn hours per day
is 24/2 - 4.3 = 7.7 hours per day (controversial)

Time to change orbit is 85,108 / 7.7 = 11,053 days or 30.26 years

Mass of propellant is 85,108 * 0.34 = 28,937 kg

So using a single VF-200 to move the ISS to 23 degree orbit will take over 30 years and 29 mT of propellant.

Maybe Ad Astra is planning to steal ISS, but do it so slowly no one will notice?

Offline Star-Drive

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Re: Why the VASIMR hype?
« Reply #495 on: 02/10/2010 01:34 am »
And what about the Pulsed inductive thrusters such as in this nasa study http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930023164_1993023164.pdf , which also offers multi-mw thrusters (without the cathode erosion problem like vasimr).

What cathode in the VASIMR are you referring to?  Last time I looked, the propellant ionization process was accomplished by the contactless first stage helicon antenna.
Star-Drive

Offline Robotbeat

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Re: Why the VASIMR hype?
« Reply #496 on: 02/10/2010 02:12 am »
And what about the Pulsed inductive thrusters such as in this nasa study http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930023164_1993023164.pdf , which also offers multi-mw thrusters (without the cathode erosion problem like vasimr).

What cathode in the VASIMR are you referring to?  Last time I looked, the propellant ionization process was accomplished by the contactless first stage helicon antenna.
What he meant to say was that it is electrodeless like VASIMR.
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Offline glemieux

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Re: Why the VASIMR hype?
« Reply #497 on: 02/10/2010 05:57 pm »
And what about the Pulsed inductive thrusters such as in this nasa study http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930023164_1993023164.pdf , which also offers multi-mw thrusters (without the cathode erosion problem like vasimr) .

From the little bit that I read of the paper you provided, some of the initial ionization is done via a coil.  The paper pointed out that the erosion problem is greatly reduced compared to cathodes, but I wonder how it compares to general wear and tear of other components in VASIMR and HDLT.

Offline Rhyshaelkan

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Re: Why the VASIMR hype?
« Reply #498 on: 02/15/2010 12:54 pm »
From Wiki

"The helicon discharge uses 30 kWe of radio waves to turn argon gas into plasma. "

So I can assume you can use other fuels than hydrogen? Why not an O2 rocket? O2 is more plentiful, and a large byproduct of Lunar mining.
I am not a professional. Just a rational amateur dreaming of mankind exploiting the universe.

Offline tamarack

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Re: Why the VASIMR hype?
« Reply #499 on: 02/16/2010 12:43 am »
...So I can assume you can use other fuels than hydrogen? Why not an O2 rocket? O2 is more plentiful, and a large byproduct of Lunar mining.
Technically, any element could be used as propellant but only a few work as VASIMR is designed.
A few factors include: Diamagnetism
http://www.periodictable.com/Properties/A/MagneticType.html
Ionization energy
http://www.periodictable.com/Properties/A/IonizationEnergies.html
Boiling point, liquid density, conductivity and reactivity.

It should also be noted that higher atomic weights have higher thrust, but lower Isp. Given that; Krypton could be a good high-thrust and Nitrogen a mid-use propellant to accompany Hydrogen and Argon. Not sure about Xenon.
« Last Edit: 02/16/2010 12:44 am by tamarack »

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