Author Topic: Vasimr: A true game changer? Role of Vasimir in future programs  (Read 35604 times)

Offline baldusi

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The thrust is pretty easy to calculate, but it WILL have a lot lower efficiency because it has to ionize the gas (which penalizes efficiency at lower Isp). At the same power, thrust will be 5 times for one-fifth the Isp (which is proportional to Isp) at the same efficiency (which is a naive assumption).

I was under the impression that VASIMR was particular because it allowed to trade thrust for isp at a given efficiency (particularly because it already works with ionized gas). I thought the reason to test the hish isp mode was a limitation of the vacuum chamber.
« Last Edit: 01/21/2011 07:12 PM by baldusi »

Offline Rhyshaelkan

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Does VASIMR scale well with more power?

If x power and y reaction-mass = z thrust

what about b power and y reaction-mass

Will more power yield higher thrust if reaction-mass stays the same. Diminishing returns that limit the reaction-mass/ power ratio?
I am not a professional. Just a rational amateur dreaming of mankind exploiting the universe.

Offline alexterrell

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The thrust is pretty easy to calculate, but it WILL have a lot lower efficiency because it has to ionize the gas (which penalizes efficiency at lower Isp). At the same power, thrust will be 5 times for one-fifth the Isp (which is proportional to Isp) at the same efficiency (which is a naive assumption).

I was under the impression that VASIMR was particular because it allowed to trade thrust for isp at a given efficiency (particularly because it already works with ionized gas). I thought the reason to test the hish isp mode was a limitation of the vacuum chamber.
Not quite, it can trade thrust for Isp, but higher Isp leads to higher efficiency.

Offline sanman

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But weight savings doesn't come from Isp alone. For instance, if VASIMR's thrust flexibility allowed you to save an extra stage, then this too could reduce overall vehicle weight.

Offline baldusi

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But weight savings doesn't come from Isp alone. For instance, if VASIMR's thrust flexibility allowed you to save an extra stage, then this too could reduce overall vehicle weight.
We are talking about 5N to 20N out of an engine of 300kg + energy source. This is only good for interplanetary drive. It's even questionable if it can cross the Allen Belt fast enough (for itself or it's payload).

Offline RobLynn

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Vasimr really does change things because it enables atmospheric scoop mining.

Vasimr means we can build a propellant depot/space station with a megawatt or two (@~5000kg/MW) of solar power and a few VASIMR engines on it (~1500kg/MW), stick it at 200km altitude and drop a tethered collector down to maybe 100-120km to scoop up and compress atmosphere.

1MW VASIMR with 65% efficiency at 3000Isp gives about 45N thrust, enough to overcome about 45N/7200m/s=.006kg/s = 540kg/day, 180 tonnes per year.

huge turbomolecular pump, feeding secondary compressors, partially powered by 7km/s gas impact on the oblique inlet blades as well as solar, power down tether or perhaps other beamed power from above.

20 tonnes in LEO would go a long way towards getting this all working.
Ditch any gases you don’t want. Use about 25% of Nitrogen collected to fuel the VASIMR scoop drive, pull tether up every few weeks to offload collected atmosphere.  Basically this can enable and feed all propulsion requirements for beyond LEO operations.

With CO2, N2 and H2O there are also quite a few useful materials that can be made, as well as fuels for Moon or Mars Landings etc.

Using the CO2 scoop mined from mars could make a CO+O2 or hybrid C+O2 rocket for landing and lauch
I'm a "glass is twice as big as it needs to be" kinda guy

Offline MP99

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Offline Patchouli

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But weight savings doesn't come from Isp alone. For instance, if VASIMR's thrust flexibility allowed you to save an extra stage, then this too could reduce overall vehicle weight.
We are talking about 5N to 20N out of an engine of 300kg + energy source. This is only good for interplanetary drive. It's even questionable if it can cross the Allen Belt fast enough (for itself or it's payload).

For ops near Earth not all the power generation equipment needs to be on the vehicle.

The required power could be beamed as microwaves to the vehicle.

The power source could located on Earth's surface,a solar power sat in LEO or GEO, or even a solar collector array on the surface of the moon.
This could be a killer application for HAARP
http://www.haarp.alaska.edu/
A demo of wireless power transmission from 1975 and they achieved 82% efficiency.
« Last Edit: 01/27/2011 11:52 PM by Patchouli »

Offline bolun

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http://www.asi.it/en/news_en/vasimir_a_propulsion_system_for_the_future

Quote
Franklin Chang-Diaz creator of the project, will host a conference at the headquarters of the Italian Space Agency on April 5

An opportunity to learn new technology and assess the opportunities for cooperation in the field. This is the leitmotif of the event dedicated to the project VASIMIR, an innovative space plasma propulsion concept developed by former NASA astronaut and chief of the Ad Astra Rocket Company, Franklin Chang-Diaz. The meeting will be held on April 5 at 2.30 pm at the headquarters of the Italian Space Agency Viale di Villa Grazioli.

Offline Blackjax

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Could someone with a better science background than I have weigh in on whether this might have useful implications for VASIMIR?

http://www.gizmag.com/discovery-paves-way-for-optical-battery/18410/

What I am looking at is this:
Quote
"In solar cells, the light goes into a material, gets absorbed and creates heat. Here, we expect to have a very low heat load. Instead of the light being absorbed, energy is stored in the magnetic moment. Intense magnetization can be induced by intense light"

If I understand VASIMIR properly, doesn't a lot of its power requirement come from the need to generate intense magnetic fields?  If you could go more directly from sunlight to magnetism might it make things more practical?

Offline neutrino78x

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So could vasimr theoretically be used to accelerate to say 90% c (at 9.81 m/s^2 acceleration or less), if you had a sufficiently powerful nuclear reactor?? Let's say we had a spacecraft the mass of a Trident nuclear submarine, which is about 16.7 metric tonnes. Actually the back 1/3 of a Trident is the engine room, so we will assume that holds the reactor and the vasimr drive. Propellent is assumed to be hydrogen. Anybody who knows calculus, what do you think?

I mention the trident because I was a USN submariner and I have lived at sea on a Trident submarine. They have more room than a 688 but they are still small (people dont' realize, most of the missile compartment is missiles; we sleep in between the tubes, 9 men to a bunkroom).

--Brian

Offline IsaacKuo

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So could vasimr theoretically be used to accelerate to say 90% c (at 9.81 m/s^2 acceleration or less), if you had a sufficiently powerful nuclear reactor??

No, it can't.  The maximum exhaust velocity is on the order of 100km/s, which means even 1% of c is out of the question.

Offline fatjohn1408

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It could also be used as a space tug from LEO to geostationary orbit or high inclination orbits.
This would be very good in combination with future reusable launchers such as skylon.

Offline docmordrid

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Paper presented at the Space, Propulsion and Energy Sciences Forum, March 15-17 2011 at the University of Maryland

VASIMR Human Mission to Mars (PDF)....

This one is nothing we haven't read before, but a VASIMR article is on the Voice Of America site -

http://www.voanews.com/english/news/science-technology/Former-Astronaut-Develops-Powerful-Rocket-123960664.html
« Last Edit: 07/03/2011 08:34 AM by docmordrid »
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Offline tnphysics

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Why does VASIMIR have a low T/W?

Offline pathfinder_01

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Why does VASIMIR have a low T/W?

Vasmir and all forms of electric propulsion have low thrust. Basically ISP and thrust are rather opposites.  It is difficult to get both high isp and high thrust in the same system.  VASMIR as plasma propulsion has more thrust than ion propulsion and has a great ability to trade thrust for ISP but it will never have as much thrust as a chemical system.

Basically in terms of thrust

Chemical>Nuculear thermal>Electric propulsion

In terms of ISP

Electric propulsion>Nuclear thermal>Chemical propulsion

Offline tnphysics

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Okay let me put it this way: why is the power/weight of VASIMIR bad vs. an arcjet?

Offline docmordrid

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Robert Zubrin launched into a rant about VASIMR on July 11, 2011 calling it a "hoax" -

http://www.marssociety.org/home/press/tms-in-the-news/thevasimrhoax

PhysOrg story from July 13, 2011 -

http://www.physorg.com/news/2011-07-zubrin-vasimr-hoax.html

and Ad Astra posted this on July 15, 2011 -

http://www.adastrarocket.com/VASIMR_development_AdAstra_15July2011.pdf

I found several problems with Zubrin's article including his contention that high temperature superconducting magnets it would find useful do not exist.  Ad Astra countered that assertion in their reply -

Quote
>
The technology of advanced high-temperature superconductors has also matured significantly in the last decade with the development of commercially available high current density BSCCO and YBCO conductors by companies such as Superpower Inc. and American Superconductor. These developments have made lightweight, high-field magnets for VASIMR® applications feasible. Moreover, miniaturized cryocooler technology, such as the Sunpower M series model, has already flown in space and are being considered by Ad Astra as part of the cryogenic system for the flight magnet. Ad Astra’s VX-200 test engine features the largest cryogen-free, high-field, low-temperature superconducting magnet in existence today. This magnet was developed to meet Ad Astra’s specifications and has operated quite successfully in the VX-200 engine since its integration in May of 2009. The company is currently designing a high-temperature flight version of this system.
>
« Last Edit: 07/21/2011 08:09 AM by docmordrid »
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Offline alexterrell

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Okay let me put it this way: why is the power/weight of VASIMIR bad vs. an arcjet?
Mainly because VASIMR's exhaust velocity is much faster than an Arc Jet.

Assume it's 5 times faster (25km/s v 5km/s).

That means every gram thrown out produces 5 times the thrust. But it needs 25 times the energy. So with the same power supply, you can only throw the stuff out at 1/25th the rate.

So your thrust is 5 x 1/25. i.e you have one fifth the thrust. But the same fuel lasts 25 times longer.

Hence VASIMR is suited to long duration missions.

Offline alexterrell

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Robert Zubrin launched into a rant about VASIMR on July 11, 2011 calling it a "hoax" -

http://www.marssociety.org/home/press/tms-in-the-news/thevasimrhoax

PhysOrg story from July 13, 2011 -

http://www.physorg.com/news/2011-07-zubrin-vasimr-hoax.html

and Ad Astra posted this on July 15, 2011 -

http://www.adastrarocket.com/VASIMR_development_AdAstra_15July2011.pdf

I found several problems with Zubrin's article including his contention that high temperature superconducting magnets it would find useful do not exist.  Ad Astra countered that assertion in their reply -

Zubrin himself did some work on magsails and in his chapter on it (written 10 years ago) stated that existing superconductors could operate with no cooling, just insulation.

Zubrin always goes over the top to try and make a point and then discredits himself. That said, both his arguments and the counter points are valid.

VASIMR is a useful electric thruster and could be useful for shipping cargos to Mars orbit in 1 year. However, chemical rockets have the Oberth effect advantage, so I don't see a significant benefit. More useful is a Low Earth Orbit to L1 tug, especially with a fuel depot at L1.

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