Author Topic: VASIMR Engine  (Read 156453 times)

Offline Stormbringer

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Re: VASIMR Engine
« Reply #140 on: 01/21/2015 08:35 PM »
1. It will work
2. yes.








3. The critics are full of... stuff.
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Offline Raj2014

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Re: VASIMR Engine
« Reply #141 on: 01/21/2015 10:47 PM »
1. It will work
2. yes.








3. The critics are full of... stuff.

What Stormbringer said. Has there been an update from Ad Astra or Franklin Chang Diaz on VASIMR? What I know so far is that they are low on money, which they need to continue. They were planning to test VASIMR on ISS called VF-200 with a battery pack attached called Aurora.     

Online abaddon

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Re: VASIMR Engine
« Reply #142 on: 02/27/2015 09:13 PM »
Noticed these recent tweets today, linked from Wayne Hale's blog:

https://twitter.com/waynehale/statuses/570399963919704064
Quote
At the JSC-NAL dinner listening to Dr Franklin Chang Diaz discuss advanced space propulsion and his VASIMR rocket

https://twitter.com/waynehale/statuses/570415042874601472
Quote
Ad Astra ready to test fire their 200KW electric VASIMR rocket for 100 hours continuously. Planning to install it on ISS in a few years
« Last Edit: 02/27/2015 09:14 PM by abaddon »

Offline A_M_Swallow

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Re: VASIMR Engine
« Reply #143 on: 02/27/2015 09:21 PM »
Instead of putting the VASIMR on the ISS could it be added to a Dragonlab? Large solar panels will also be needed.

As a derivative of the Dragon space capsule the Dragonlab would come with RCS and navigation equipment.

Offline ChrisWilson68

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Re: VASIMR Engine
« Reply #144 on: 02/27/2015 09:31 PM »
Instead of putting the VASIMR on the ISS could it be added to a Dragonlab? Large solar panels will also be needed.

As a derivative of the Dragon space capsule the Dragonlab would come with RCS and navigation equipment.

SpaceX likes to talk about DragonLab as if it's a done deal, but really it will only happen if they find paying customers for it.  So far, there's no evidence to indicate even a single paying customer.  So DragonLab keeps getting postponed indefinitely.

And ISS also has far larger solar panels.  I don't see any advantage to sending it on DragonLab versus ISS and lots of disadvantages.

Offline Stormbringer

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Re: VASIMR Engine
« Reply #145 on: 02/28/2015 12:33 AM »
also if comments in the electric propulsion thread are true other electric thrusters have evolved to surpass VASIMR's projected specs. If those comments are true then Dr Diaz will need to significantly improve the technology in order to be competitive. This could be good for VASIMR if it is improved or catastrophic if it cannot be improved.
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Offline Hop_David

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Re: VASIMR Engine
« Reply #146 on: 03/01/2015 05:35 PM »
2) ignoring power demands (nuclear, solar, fusion) will VASIMR be able to propel a manned spacecraft to Mars in record time or not?
Please answer using the KISS method.

Ignoring power demands? Well okay, since you're assuming the use of Harry Potter's wand, 39 day trips to Mars are no problem.

But if you live in this world, the need for a 2kWe/kg power source is a definite show stopper.
« Last Edit: 03/01/2015 06:03 PM by Hop_David »

Offline A_M_Swallow

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Re: VASIMR Engine
« Reply #147 on: 03/01/2015 07:35 PM »
Instead of putting the VASIMR on the ISS could it be added to a Dragonlab? Large solar panels will also be needed.

As a derivative of the Dragon space capsule the Dragonlab would come with RCS and navigation equipment.

SpaceX likes to talk about DragonLab as if it's a done deal, but really it will only happen if they find paying customers for it.  So far, there's no evidence to indicate even a single paying customer.  So DragonLab keeps getting postponed indefinitely.

And ISS also has far larger solar panels.  I don't see any advantage to sending it on DragonLab versus ISS and lots of disadvantages.


A DragonLab with a VASIMR is a space ship rather than a spacestation - it can go places like a higher orbit. The ISS has other uses for the power from its so only occasional use will be permitted.

Offline Robotbeat

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Re: VASIMR Engine
« Reply #148 on: 03/01/2015 07:41 PM »
I think anything that poops anything out one end (even if it's just blue glowy stuff) produces thrust.
You would be thinking wrong then. Plasma "poop" is made up of charged particles. If you just shoot out positive ions then a massive electric field will form that will be strong enough to pull those ions back to the rocket, thereby cancelling all thrust. That's why ion thrusters also have electron guns, to neutralize the ions, allowing them to leave the rocket system as neutral atoms.
Vasimr doesn't use such a neutralizing mechanism. In fact, I've never quite understood how the ions were to be neutralized efficiently. That's what will define how well the ions detach and whether their blue glowy stuff has any kick to it.
How is this still in question??

VASIMR has lots of problems, but this isn't one of them.

VASIMR is a big, expensive, complicated, heavy electric thruster. That is its main problem. I have no doubt that technically it could be made to work with enough money (I took a plasma physics course, and magnetic bottles is one of the things we studied). I am not, however, sure that it's worth it. Other electric thrusters may have less mass for the same power.
« Last Edit: 03/01/2015 07:49 PM by Robotbeat »
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Offline Impaler

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Re: VASIMR Engine
« Reply #149 on: 03/02/2015 01:44 AM »
2) ignoring power demands (nuclear, solar, fusion) will VASIMR be able to propel a manned spacecraft to Mars in record time or not?
Please answer using the KISS method.

Ignoring power demands? Well okay, since you're assuming the use of Harry Potter's wand, 39 day trips to Mars are no problem.

But if you live in this world, the need for a 2kWe/kg power source is a definite show stopper.

Lets remember that anything <6 months is 'record time' because Chemical systems are running into brutal rocket-equation induced propellent fractions above that point and no one considers it practical to push Chemical that far.  For any Electric propulsion the power needs for 4-6 month transfers are well within reason both in total power and power density.

Ad-Astra has always presented the whole portfolio of how their engine produces different flight times when combined with a variety of power-systems over a range of power-densities.  These range from currently operational solar arrays to complete fantasy fusion reactors.  Claiming the system NEEDS a fantasy reactor is intellectually dishonest *cough Zubrin cough*  simply because they show what COULD be done if such a reactor existed.

No reasonable person claims 39 days is a bar we need to aim for now or ever.  Personally I think anything shorter then 3 months is complete overkill and very likely 6 months will be preferable as we will prefer the payload mass over the short transit time.

And lastly an alpha value (kW/kg) of 2 for the TOTAL propulsion system is actually quite reasonable, so long as you use thin-film solar and some thruster OTHER then VASIMR because it's so heavy.

Offline Robotbeat

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Re: VASIMR Engine
« Reply #150 on: 03/02/2015 02:25 AM »
Nah, you can do WELL under 6 months with chemical rockets, especially if you fuel up at near C3=0 (like EML1/2 or something like that). Down to below 120 days transit, even. Doesn't mean it's ideal, but it IS definitely doable.
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Offline Hop_David

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Re: VASIMR Engine
« Reply #151 on: 03/02/2015 03:10 AM »
Claiming the system NEEDS a fantasy reactor is intellectually dishonest *cough Zubrin cough*  simply because they show what COULD be done if such a reactor existed.

*cough Sorensen cough*

When the 39 day Mars trip story first came out I didn't notice the caveat it relied on a fantasy power source. Maybe it was in the fine print.
« Last Edit: 03/02/2015 03:13 AM by Hop_David »

Offline Robotbeat

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Re: VASIMR Engine
« Reply #152 on: 03/02/2015 03:16 AM »
Solar could actually do that level of performance, with the right structural concept. As Impaler said.
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Offline Hop_David

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Re: VASIMR Engine
« Reply #153 on: 03/02/2015 03:35 AM »
Solar could actually do that level of performance, with the right structural concept. As Impaler said.

You have an example? I seem to recall you saying some film on the solar sails of a venus probe achieved 1 kWe/kg.

I sounds to me these 2kWe/kg solar arrays are acres of Seran wrap or maybe Cellophane with little supporting structure.

Offline Hop_David

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Re: VASIMR Engine
« Reply #154 on: 03/02/2015 03:38 AM »
Nah, you can do WELL under 6 months with chemical rockets, especially if you fuel up at near C3=0 (like EML1/2 or something like that). Down to below 120 days transit, even. Doesn't mean it's ideal, but it IS definitely doable.

Indeed. Assuming a propellent source at EML2, chemical can do transfers a lot faster than Hohmann.



« Last Edit: 03/02/2015 03:43 AM by Hop_David »

Offline Nilof

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Re: VASIMR Engine
« Reply #155 on: 03/02/2015 09:25 AM »
Though to be fair, 7 km/s is a pretty huge delta-v for a chemical rocket. Compared to the 5.7 month option, you'd be roughly tripling the mass ratio of the spacecraft for a 25% decrease in travel time. I think it's more or less fair to say that chemical can do a 5 month transfer, but pushing it beyond that really isn't worth it.
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.

Online clongton

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Re: VASIMR Engine
« Reply #156 on: 03/02/2015 11:48 AM »
I think it's more or less fair to say that chemical can do a 5 month transfer, but pushing it beyond that really isn't worth it.

Depends entirely on whether the cargo is toilet paper or people.
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Offline Stormbringer

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Re: VASIMR Engine
« Reply #157 on: 03/02/2015 12:47 PM »
If its toilet paper it's got to be faster. The colonists would revolt if they had to wait in the bathroom for 5 months.
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Offline Hop_David

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Re: VASIMR Engine
« Reply #158 on: 03/02/2015 01:43 PM »
Though to be fair, 7 km/s is a pretty huge delta-v for a chemical rocket. Compared to the 5.7 month option, you'd be roughly tripling the mass ratio of the spacecraft for a 25% decrease in travel time. I think it's more or less fair to say that chemical can do a 5 month transfer, but pushing it beyond that really isn't worth it.

I'd like to see a combination of ion and chemical. Most ion Mars trips already assume use of chemical to haul humans to the edge of earth's sphere of influence and rendezvous with the ion MTV. This is to avoid subjecting human astronauts to a slow spiral through the Van Allen Belts.

A chemical reusable Earth Departure Stage (EDS) could provide a hefty boost into a heliocentric transfer orbit and thus eliminate the slow spiral out of earth's gravity well and leave more reaction mass for the ion rocket.

Given a boost by a chemical EDS, large solar arrays with a good alpha become more plausible. Low earth orbit with it's high debris density and Van Allen belts would be tough on a solar array with a big cross section. It would be better if the ion space craft could unfurl it's solar arrays after leaving the tough neighborhood of low earth orbit.

Offline Impaler

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Re: VASIMR Engine
« Reply #159 on: 03/02/2015 04:49 PM »
7 km/s Burns from EML1 are crazy high on their face but get even worse when you remember that it is 4 km/s just to get up to EML1 so your cumulative total is 11 km/s if your moving everything chemically, that is Earth launch level of DeltaV and is going to result in propellent fractions in the 90's (92% for HydroLox, 96% MethoLox).  That is completely untenable in my opinion as we would need thousands of tons IMLEO just to send small vehicles to Mars (or the even more unlikely massive Asteroid/Lunar based propellent production process).


Boosting a SEP stage with chemical is pointless, I do not see why anyone thinks this is a good idea.  First off mixing two different propulsion techs means we have to carry the mass of two completely separate engines which clobbers the efficiency of both.  We also have the combined risk of failure of both engines (the chemical is by far the more failure prone of the two).

The argument that we don't want to spiral out from Earth is only applicable for CREW and even then only for the first few Radii of the Earth where the Belt is.  We would send the bulk of the mission mass up to a high orbit and then after the crew arrives we just Spiral out some more for the Earth-Escape.  The initial escape velocity from Earth will be low but that is fine, we are going to be building velocity over months.  The speed that the Chemical departure from Earth would have gotten us (1 km/s which still costs a hefty 20% propellent fraction) will be obtained in mere 11 days at an acceleration of 1 mm/s^2.  We would much rather have 20% of our mass devoted to more EP dry-mass (power system) or propellent then to get a measly 1 km/s escape velocity, devoting that mass to EP will always get you to Mars faster.

Thus any in-space propulsion, unless it must be high thrust (such as an attempt to propulsive capture around a planet when your coming on a hyperbolic trajectory at high velocity) it is never a reason to hybridize EP and Chemical, they will just drag each other down.

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