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EarthWolf

Member

From: Missouri, U.S.A.

Registered: 2004-07-20

Posts: 59

Re: Plasma Rockets

Hello,

I read a paper detailing out a Mars mission using a VASIMR engine. Now usually these engines are supposed to reduce flight times to Mars from months to weeks. If this is true, would flight times to the outer planets be reduced from years to months?

Cordially,

EarthWolf

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" Man will not always stay on the Earth. "

Konstantin Tsiolkovsky

GCNRevenger

Member

From: Earth

Registered: 2003-10-14

Posts: 6,056

Re: Plasma Rockets

Well, I would say a Mars trip would go from six months to three without a revolutionary leap in nuclear reactor technology to power it.

Yes it would make a big difference for an outer-planet trip, but I don't think it would make enough of a difference without a new kind of nuclear reactor, like the Vapor Core reactor.

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[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]

[i]The glass is at 50% of capacity[/i]

srmeaney

Member

From: 18 tiwi gdns rd, TIWI NT 0810

Registered: 2005-03-18

Posts: 976

Re: Plasma Rockets

Considering the Nuclear propulsion systems have Impulse(specific) ratings of 800, (twice that of chemical drives) of course the journey is going to be reduced to a portion of the time it takes the chemical motors to make the same journey.

GCNRevenger

Member

From: Earth

Registered: 2003-10-14

Posts: 6,056

Re: Plasma Rockets

Although it is valid to say that, in general using nuclear as opposed to chemical energy has better performance for orbit-to-orbit transfers, there are lots of different kinds of nuclear-powerd systems with different performance.

The particular engine you mentioned, the 800-900sec NERVA type thermal engine, is the most primitive of nuclear engines. Although it offers good thrust and the possibility for medium/low power generation when not firing. 1000sec is possible with advanced fuel assembly materials, or switching to a graphite pebble-bed reactor, but the latter is only good for a few (maybe only one) firing. If there is a need for higher thrusts, a trick used in the LANTIR/TRITON engines, liquid oxygen can be added to the exhaust as an "afterburner," but this reduces the Isp by 20-25%.

These Isp figures are by no means the upper limit possible for "nuclear engines," but for thermal engines (that use the reactor to directly heat propellant), if you want to go higher the reactor would just melt because you have to raise the temperature to increase the efficency of engines that use expansion to push the exhaust out the nozzle. It is possible in theory to build an engine where the fuel intentionally melts and even boils, a beautiful concept really, called the Gas Core Nuclear Rocket. The secret is to hold the dense Uranium fuel in the center of a vortex of very low density liquid hydrogen (perhaps augmented with magnets), so you can run the temperature up really high... 50,000K high maybe. GCNR would yeild decent thrusts with Isp as high as 5,000sec, but the engine itself will be somewhat heavy... Not suitable for ground launch due to radioactive waste leaking into the exhaust and low thrust/weight ratio.

The engine you mentioned EW, plasma rockets like the VASIMR, instead use electricity generated by a seperate nuclear reactor to heat the propellant (hydrogen in this case) with microwaves up to a very high temperature, perhaps 1,000,000K with Isp up to 10,000sec. However, the enging is energy-limited, and it can produce only limited thrust without loads of power, which in turn the heavier reactor would weigh down the vehicle... hence the need for a new super reactor to power it to make it go really fast.

You can also use the electricity to power other types of engines, like an ion engine, which are great for their scaleability (big or small) and high reliability. Isp of up to 10,000sec are not unrealistic, but they produce very little thrust and are unsuitable for fast transits, only slow ones with very small amounts of fuel.

And lastly, the crazy "external ignition" engines, where you create a nuclear explosion intentionally behind your vehicle, and it pushes you. Several such concepts exsist (Orion, ACMF, and the NSWR "salt water" rockets) High thrust and high efficency, but presents big technical challenges and very high costs. Especially the former two will probobly never be practical for everyday flights.

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[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]

[i]The glass is at 50% of capacity[/i]

SpaceNut

Administrator

From: New Hampshire

Registered: 2004-07-22

Posts: 29,433

Re: Plasma Rockets

While this topic is well above my understanding for how it functions at the atomic level it creates a question as to whether Nasa is doing enough research with its army of engineers on Nuclear-powered rocket research could send astronauts to Mars?

Oregon State University (OSU) students work on plasma rocket

NASA is working on a plasma rocket for a Mars voyage, but the space craft needs a power source. That's where the OSU-WOU Microgravity Flight Team comes in.

"A plasma rocket relies on a nuclear-powered propulsion system, which requires a nuclear reactor," said Marci Whittaker-Fiamengo, team member and a senior in nuclear engineering at OSU. "We're designing an option for that reactor."

The five-member OSU contingent works closely with six students from WOU; WOU's group includes one high schooler.

Has Nasa really come down to not being able to do the research it needs and must search the universities and high schools to get the knownledge it seeks.

Read on for details of work..

GCNRevenger

Member

From: Earth

Registered: 2003-10-14

Posts: 6,056

Re: Plasma Rockets

Of course not. File this one under educational activities, not nuclear engineering.

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[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]

[i]The glass is at 50% of capacity[/i]

Fledi

Member

From: in my own little world (no,

Registered: 2003-09-14

Posts: 325

Re: Plasma Rockets

Can anyone tell what kind of trajectory such a faster-than-Hohmann transfer would go along? Also would like to know about the additional delta v requirements of such a mission.