Bussard Ram

[Rigel Stardin]

Could a bussard ram collect enough hydrogen from a solar system (or interstellar space for that matter), to provide a starship with the fuel to power the ship while collecting the necessary fuel required for the ship’s next jump?

The reason I’m asking this is would remove the need for a ship to carry an onboard tank for the power planet. It would a also allow for early space faring races with Jump 1 to cross Jump Gaps and allow them to colonize planet further out than simply confining them to Jump-1 routes?

 

[SpaceBadger]

I don't know the answer to your question, but I can tell you that Larry Niven was fond of Bussard ramjets for interstellar travel in the pre-hyperdrive years of his Known Space series. He postulated that early ones could not be used to carry living vertebrates (such as humans) due to some handwavicle from the magnetic fields, so robotic probes w ramjets checked out possible colonies, followed by "slow boats" carrying human colonists. Later versions of the ramjet had a safe pocket in the middle for human passengers.

I also remember reading in various places (pre-internet) that it wouldn't really work as he described.

I think Google is probably your friend here, or even Wikipedia (Bussard ramjet).

 

[SpaceBadger]

Thinking about it more, I think it is up to you as GM what you want to allow. The factors you need to keep in mind are how big a magnetic field you want to let the ramjet cast, and how long a period of travel through normal space you require to collect how much fuel.

Another issue that springs to mind is that using the magnetic field to collect fuel for storage on board is a bit different from using it just to concentrate the fuel, fuse it, and shoot it out the back of your ship. You would actually be "crashing into" all of those stray hydrogen molecules with your high speed ship - what is the effect of that?

 

[JimMarn]

I don't know the answer to your question, but I can tell you that Larry Niven was fond of Bussard ramjets for interstellar travel in the pre-hyperdrive years of his Known Space series. He postulated that early ones could not be used to carry living vertebrates (such as humans) due to some handwavicle from the magnetic fields, so robotic probes w ramjets checked out possible colonies, followed by "slow boats" carrying human colonists. Later versions of the ramjet had a safe pocket in the middle for human passengers.

I also remember reading in various places (pre-internet) that it wouldn't really work as he described.

I think Google is probably your friend here, or even Wikipedia (Bussard ramjet).

I remember the later ones having a very long monomolecule cable holding the engine to the passenger capsule to get it away from the radiation. If I remember correctly, this radiation was the magnetic field colliding with hydrogen atoms at high speed. I remember his mag fields being a cone several kilometers across at the opening and over a kilometer from the engine.

It has been years since I read his known Space books, so I may have bobbled there and got something wrong.

 

[Rigel Stardin]

You'd first have to disover jump drives before my idea would work. Second, the velocities would still range between 1-6 Gees. You'd also have the modifed ramjet discussed in Wikipedia article that collect carbon.

We know from Traveler, fuel scoops can collect hydrogen or water from planetary sources. In MTU, refuel can also take place if a close pass is made by a star. (Back to traveler) The only thing I haven't seen in print is how long it takes a starship to refuel off a gas gaint. I assume it is done by an air-braking manuver which allows the ship to pass through the upper atmosphere.

My thoughts on interstellar refuel at the moment is a ship is required to remain in normal space for at least 1d6 weeks to collect the fuel necessary for the next jump.

 

[Carlobrand]

... In MTU, refuel can also take place if a close pass is made by a star. ...

Umm, errr ...

(I don't think his starship insurance agent knows what he does on weekends. )

Could a bussard ram collect enough hydrogen from a solar system (or interstellar space for that matter), to provide a starship with the fuel to power the ship while collecting the necessary fuel required for the ship’s next jump? ...

Atomic Rockets is worth a look:

http://www.projectrho.com/public_html/rocket/slowerlight.php#Bussard

Gives you numbers you can work with.

And then this gives you a rough idea of what's in the "vacuum" of space.

http://deoxy.org/vacuum.htm
http://en.wikipedia.org/wiki/Interstellar_medium
http://en.wikipedia.org/wiki/Interplanetary_medium

What I get from this is that to get a dTon of fuel this way - one ton of hydrogen, 6.0221415×10²⁹ hydrogen atoms - you need something on the rough order of 10²⁹ cubic centimeters of interplanetary space, or 10¹⁴ cubic kilometers. A ship with a 10,000 square kilometer "net" has to move through ten billion kilometers to collect a single dTon. That's give or take a bit, depending on how dense the stuff is, but the magnitudes are very clear.

And, of course, you're burning fuel to create the net that you're casting. And, the hydrogen you're collecting is as subject to Newton's laws as anything else - when it gets caught in your net and accelerates to your speed, you slow down. You spend some energy overcoming that. Someone with better physics than me can tell you if you get more energy than you spend doing it that way, but my gut feeling is it'd be faster to fly out to the Oort and go mine a comet, and that's about the slowest way to find hydrogen there is.

Here's an odd thought maybe our physics people can answer: the interplanetary medium is a plasma. You are collecting a positively charged plasma with your fields - which is likely a lot easier than trying to collect something that's electrically neutral. However, you need electrons, don't you? Seems to me you're just one huge static discharge accident waiting to happen somewhere.

 

[McPerth]

I may well be wrong, but IIRC (or maybe I assumed) that was exactly how the generation ships in the background of the Islands Cluster Campaign, in CT:TCS worked, by collecting free hydrogen from the space, just they were not jump ships.

Also, again IIRC that was the way the ship in Kevin O'Donell's novel Mayflies worked (or was supposed to), though, again, it was not a jump ship.

 

[JimMarn]

I looked up a page of drawings of our local bubble, and found we are in a million degree area, part of the local stellar bubble.

http://www.solstation.com/x-objects/chimney.htm

This page shows two drawings of our local stellar bubble, with gas densities.

http://www.bibliotecapleyades.net/universo/cosmos15.htm

Looks like we could use hydrogen gas, but there isn't much near our solar system.

 

[Carlobrand]

I may well be wrong, but IIRC (or maybe I assumed) that was exactly how the generation ships in the background of the Islands Cluster Campaign, in CT:TCS worked, by collecting free hydrogen from the space, just they were not jump ships. ...

The Island Clusters ships crossed 400-500 light years in two thousand years, around 0.25C. I don't see anything in the writeup that suggested they were using ramscoops, and I don't know if 0.25C is consistent with ramscoop use.

 

[Vladika]

...The only thing I haven't seen in print is how long it takes a starship to refuel off a gas gaint...

Streamlined or partially streamlined ships are also capable of refueling from a gas giant during battle. The ship must be part of the reserve during the operation, and if interrupted is considered not refueled. One pass through the gas giant's atmosphere is sufficient to fill all tanks and takes 7 turns. Fuel may be transferred between ships in two turns. - TCS p39​