Bussard Ramjets

[SpaceFace545]

These things are freaking awesome, like a space ramjet. seriously these need to be in the game. the technology is kinda wonky but darn they are awesome. if you don't know what they are a Bussard ramjet scoops up hydrogen from the vacuum and then fuses it shooting it out of the back. the whole thing basically collects hydrogen so you don't need a large fuel tank. thoughts?

Edited April 17, 2020 by SpaceFace545
I had to

[DStaal]

5 hours ago, SpaceFace545 said:

These things are freaking awesome, like a space ramjet. seriously these need to be in the game. the technology is kinda wonky but darn they are awesome. if you don't know what they are a Bussard ramjet scoops up hydrogen from the vacuum and then fuses it shooting it out of the back. the whole thing basically collects hydrogen so you don't need a large fuel tank. thoughts?

While I would love to see them - if we do, they'd have to have the drawbacks which make them impractical for most real uses.  (Basically that giant scoop creates drag, which limits how fast you can go.  For nearly all practical purposes you can go from star to star faster without a ramjet and just carrying your fuel.)

[SpaceFace545]

2 hours ago, DStaal said:

While I would love to see them - if we do, they'd have to have the drawbacks which make them impractical for most real uses.  (Basically that giant scoop creates drag, which limits how fast you can go.  For nearly all practical purposes you can go from star to star faster without a ramjet and just carrying your fuel.)

That Is completely true I was going to include that but they are awesome and pretty kerbal. 

[mcwaffles2003]

13 hours ago, DStaal said:

While I would love to see them - if we do, they'd have to have the drawbacks which make them impractical for most real uses.  (Basically that giant scoop creates drag, which limits how fast you can go.  For nearly all practical purposes you can go from star to star faster without a ramjet and just carrying your fuel.)

Any drag they experience would be from the fuel it is scooping so that being a drawback seems counter intuitive since more drag = more fuel..

On the other hand though, at lower velocities fuel flux would also be lower, and possibly unsustainable, similar to IRL atmospheric ramjets. (I'm guessing a bit here)

But IF that is the case then the limitation would be at lower velocities as opposed to upper velocities. Meaning they may not work when slowing down. Also, they shouldn't function well if they're facing off of prograde. This would create fun design constraints as the total vehicle would need a "low gear" set of engines to get to usable velocities, while performing maneuvers, and while slowing or cruising around in a solar system. Probably great for getting up to speed on a straightaway in interstellar/intergalactic transport though.

 

Overall calculating its performance, if my assumptions are true, shouldn't be hard to simulate. Have thrust be linearly proportional to the vessels current velocity relative to the interstellar/intergalactic medium it is in and multiply that thrust by the cos(angle off of prograde). This would be extra interesting if bow shock, heliosheaths, and termination shocks are modeled at solar system boundaries as crossing them would change the relative velocities of the interstellar medium. Modelling those as well shouldn't be difficult as a simple gradient over all space could be considered steady-state/static

Edited April 18, 2020 by mcwaffles2003

[SpaceFace545]

4 hours ago, mcwaffles2003 said:

Any drag they experience would be from the fuel it is scooping so that being a drawback seems counter intuitive since more drag = more fuel..

On the other hand though, at lower velocities fuel flux would also be lower, and possibly unsustainable, similar to IRL atmospheric ramjets. (I'm guessing a bit here)

But IF that is the case then the limitation would be at lower velocities as opposed to upper velocities. Meaning they may not work when slowing down. Also, they shouldn't function well if they're facing off of prograde. This would create fun design constraints as the total vehicle would need a "low gear" set of engines to get to usable velocities, while performing maneuvers, and while slowing or cruising around in a solar system. Probably great for getting up to speed on a straightaway in interstellar/intergalactic transport though.

 

Overall calculating its performance, if my assumptions are true, shouldn't be hard to simulate. Have thrust be linearly proportional to the vessels current velocity relative to the interstellar/intergalactic medium it is in and multiply that thrust by the cos(angle off of prograde). This would be extra interesting if bow shock, heliosheaths, and termination shocks are modeled at solar system boundaries as crossing them would change the relative velocities of the interstellar medium. Modelling those as well shouldn't be difficult as a simple gradient over all space could be considered steady-state/static

I like what you said a lot. They are kinda like sole sails what have restraints when using them cause the sun isn’t always relevant or at the desired angle.

To clarify Bussard ramjets are just like real ramjets, they are only good for going extremely fast in one direction like a dart once you start to turn the flow of matter will become insufficient for fusion requirements.

[DStaal]

5 hours ago, mcwaffles2003 said:

Any drag they experience would be from the fuel it is scooping so that being a drawback seems counter intuitive since more drag = more fuel..

On the other hand though, at lower velocities fuel flux would also be lower, and possibly unsustainable, similar to IRL atmospheric ramjets. (I'm guessing a bit here)

But IF that is the case then the limitation would be at lower velocities as opposed to upper velocities. Meaning they may not work when slowing down. Also, they shouldn't function well if they're facing off of prograde. This would create fun design constraints as the total vehicle would need a "low gear" set of engines to get to usable velocities, while performing maneuvers, and while slowing or cruising around in a solar system. Probably great for getting up to speed on a straightaway in interstellar/intergalactic transport though.

There's limitations on both lower and upper velocities.  At lower velocities as you said it isn't generating enough fuel through the scoop to resupply.  At high velocities it gets to the point where the fuel it's gathering isn't sufficient to accelerate all the fuel it's gathering to the velocity of the ship so it can be used.  There *is* a range in the middle where it's useful, but it's narrower than you'd think and total time star-to-star for nearly all voyages is actually lower with a ship that carries it's own fuel for the entire trip.  (As it can get to higher velocities.)  A ramjet is calculated to have trouble getting beyond 0.12c.  (And depending on the calculations, you may not be getting enough fuel to resupply until anywhere from 0.1c to 0.6c.  Assuming the lower of those is correct, you could cruse at 0.11c indefinately, with fuel in your tanks.)

[SpaceFace545]

1 hour ago, DStaal said:

There's limitations on both lower and upper velocities.  At lower velocities as you said it isn't generating enough fuel through the scoop to resupply.  At high velocities it gets to the point where the fuel it's gathering isn't sufficient to accelerate all the fuel it's gathering to the velocity of the ship so it can be used.  There *is* a range in the middle where it's useful, but it's narrower than you'd think and total time star-to-star for nearly all voyages is actually lower with a ship that carries it's own fuel for the entire trip.  (As it can get to higher velocities.)  A ramjet is calculated to have trouble getting beyond 0.12c.  (And depending on the calculations, you may not be getting enough fuel to resupply until anywhere from 0.1c to 0.6c.  Assuming the lower of those is correct, you could cruse at 0.11c indefinately, with fuel in your tanks.)

It’s cool that’s all I need to say

[Incarnation of Chaos]

Isn't proton-proton fusion that would proceed with the required intensity and rate exceptionally difficult to achieve in a controlled manner? Would you potentially need a more "Conventional" D-T or D-D fusion reactor to "bootstrap" the entire process?

I'm fine with the concept, but this is just a question I've had for a while.

[OOM]

I believe that the Bussard engine should be in the game. Even in spite of the fact that the scoop will be like a brake - he can still achieve decent speeds.
It does not require a ton of Helium-3 like Daedalus, for example.

As far as I know, the limitations for the Bussard engine are as much as 0.119 the speed of light.
This is decent for technology already available "now" so to speak.

According to my calculations, this will make it possible to make an interstellar flight to Alpha Centauri in 36-40 years!
True, the question of slowdown is of course open .... 
Scoop can not act in the opposite direction ???

And is there enough scoop itself if you use it as a “free” brake with 0.1 speed of light in that short period of time?

 

I doubt...

Edited April 19, 2020 by OOM

[mcwaffles2003]

18 hours ago, DStaal said:

At high velocities it gets to the point where the fuel it's gathering isn't sufficient to accelerate all the fuel it's gathering to the velocity of the ship so it can be used.

I'm having difficulties interpreting what you mean by this but my best guess is you mean the fuel gathered must be accelerated upon capture to become trapped within the ship for fusing? If so why do you think it must be? Similar to a scramjet the fuel could be used as it transits the reactor instead of being slowed down before being used, like a ramjet. I'm still reading the article on project rho, and am amazed at the number of variations this thing has.

A funny excerpt from the mentioned article:

Spoiler

Quote

Nyrath the nearly wise writes:

The question is: does anybody have a ballpark estimate of what this terminal velocity is likely to be?

I get 0.120c using a simple non-relativistic calculation, should be good to within a few percent. With such a limit, it is not worth the trouble of using a ramjet at all. A simple fusion rocket, with the fuel carried in tanks, can do the same job much easier.

Extra credit question: I understand that the terminal velocity constraint can be by-passed if the ramjet can use even more technomagic to somehow gather and fuse the hydrogen without affecting the hydrogen's vector.

Or if you can recover the energy associated with decelerating the incoming fuel, and pump it back into the exhaust stream.

For example, if one can collect the fuel without decelerating it, feeding the relativistic plasma jet through a suitable MHD generator would produce *enormous* ammounts of power. Add this to the power produced by fusing the hydrogen and use the combined total to accelerate the exhaust.

• Is this:
• [1] not even theoretically possible
• [2] not impossible, given about ten thousand years of research
• [3] possible with about 500 years of research

It is theoretically possible. Anyone who imagines they can predict the results of five hundred, much less ten thousand, years of research, is using a much higher grade of LSD than I have ever heard of. It would require an indeterminate ammount of research and an unknown number of theoretical breakthroughs, which means that it could take anywhere from ten years to forever.

 

 

[SpaceFace545]

10 hours ago, Incarnation of Chaos said:

Isn't proton-proton fusion that would proceed with the required intensity and rate exceptionally difficult to achieve in a controlled manner? Would you potentially need a more "Conventional" D-T or D-D fusion reactor to "bootstrap" the entire process?

I'm fine with the concept, but this is just a question I've had for a while.

These use hydrogen from the vacuum of space not protons.

[Incarnation of Chaos]

16 minutes ago, SpaceFace545 said:

These use hydrogen from the vacuum of space not protons.

Hydrogen is a proton and a electron; at the temperatures required for fusion the electrons have been ripped off the nucleus and only a proton effectively remains. Hense the term "proton-proton fusion".

In stars the fusion of hydrogen is a massive bottleneck; because the vast majority of the time after fusing the helium nucleus  (which is only two protons afterwards) flings itself apart. Only rarely does one decay into a neutron; forming "deuterium" which is an isotope of hydrogen containing a single neutron in addition to a proton. Which then can fuse with an additional Hydrogen to form stable helium-3. 

For context on why this is a problem it's estimated that it takes about 200 years on average within the sun for a hydrogen atom to become helium. Current work towards fusion on earth focuses almost exclusively on fusion of the mentioned deuterium isotope with another called tritium. Because they form stable helium on the first reaction, and are larger nuclei that are much easier to get to fuse.

And we still have to increase the rate of reaction with heat and compression well beyond the temperatures found within the sun to even attempt extracting usable energy! 

[SpaceFace545]

6 hours ago, Incarnation of Chaos said:

Hydrogen is a proton and a electron; at the temperatures required for fusion the electrons have been ripped off the nucleus and only a proton effectively remains. Hense the term "proton-proton fusion".

In stars the fusion of hydrogen is a massive bottleneck; because the vast majority of the time after fusing the helium nucleus  (which is only two protons afterwards) flings itself apart. Only rarely does one decay into a neutron; forming "deuterium" which is an isotope of hydrogen containing a single neutron in addition to a proton. Which then can fuse with an additional Hydrogen to form stable helium-3. 

For context on why this is a problem it's estimated that it takes about 200 years on average within the sun for a hydrogen atom to become helium. Current work towards fusion on earth focuses almost exclusively on fusion of the mentioned deuterium isotope with another called tritium. Because they form stable helium on the first reaction, and are larger nuclei that are much easier to get to fuse.

And we still have to increase the rate of reaction with heat and compression well beyond the temperatures found within the sun to even attempt extracting usable energy! 

I was thinking of photons lol

[έķ νίĻĻάίή]

A buzzard ramjet? Seems cool, totally agree

[OOM]

I wonder why in this concept there is no radiator to transfer heat into space?
When I tested the Bassard engine in the "interstellar" modification, a huge amount of heat was generated in the process, from which even a huge radiator could not save. I think the ship according to the scheme below will work for several seconds until it melts)))
 

Edited April 21, 2020 by OOM

[kerbiloid]

Also as probably any other (sub)relativistic starship, it should have something like a plasma cloud in front of, to vaporize everything on its way.
Otherwise the first stone will be fatal.

To dissipate the heat it should have enormous area of the radiator surface.

So, it probably should look not like on these classic pictures, but as a torus surrounded with many kilometers thick cloud of charged nano-dust orbiting around/through the torus in strong magnetic field and milling everything on its way.
At the same time this multi-kilometer nanodust cloud would have that enormous surface and work like a fuzzy radiator.

[SOXBLOX]

Bussard ramjets scoop up hydrogen from the interstellar medium. The medium is now known to be thinner than was thought back when this device was first proposed, and is not enough to sustain steady fusion. Also, it relies on the proton-proton chain fusion cycle, which has a huge Lawson criterion. This means it is one of the most difficult to ignite and keep going. 

I'm sure it could still work once your ship is moving fast enough to guzzle up the thin interstellar medium, but it's getting to that speed that's the problem.

[SpaceFace545]

On 4/24/2020 at 4:37 PM, SOXBLOX said:

Bussard ramjets scoop up hydrogen from the interstellar medium. The medium is now known to be thinner than was thought back when this device was first proposed, and is not enough to sustain steady fusion. Also, it relies on the proton-proton chain fusion cycle, which has a huge Lawson criterion. This means it is one of the most difficult to ignite and keep going. 

I'm sure it could still work once your ship is moving fast enough to guzzle up the thin interstellar medium, but it's getting to that speed that's the problem.

There cool so they can work

[Bill Phil]

Yeah. They're cool.

Realistically they have limitations - the assumptions made for the 0.12c answer may not hold true, and something like 0.2 or even 0.25c may be possible. Though 0.12c to 0.18c seem like the reasonable range.

On 4/19/2020 at 5:30 AM, mcwaffles2003 said:

I'm having difficulties interpreting what you mean by this but my best guess is you mean the fuel gathered must be accelerated upon capture to become trapped within the ship for fusing? If so why do you think it must be? Similar to a scramjet the fuel could be used as it transits the reactor instead of being slowed down before being used, like a ramjet. I'm still reading the article on project rho, and am amazed at the number of variations this thing has.

The classic Bussard ramjet does indeed accelerate the interstellar medium up to its speed. This takes energy, and eventually you're spending more energy accelerating hydrogen up to your speed than you get out of fusing it. What that speed is depends on your assumptions. 

What you describe could be called a Bussard "scramjet", and the possibility exists. But it's beyond our technology. Still, the possibility is interesting.

One interesting property of the "drag" of a Bussard ramjet is that you can actually slow down from high velocity (relative to some star). The drag would be higher at relativistic energies, but it loses effectiveness at lower velocities so you'll need some other method to slow down on top of the Bussard brake. Maybe some fusion drive could do it, or perhaps a powerful enough fission drive. Would be useful to maneuver in the target system anyways.

[SOXBLOX]

Perhaps one could design the ship so that the engine could fire prograde for the first 50% of the flight, and then point retrograde for deceleration while still maintaining the forward facing magnetic scoop. Worst-case, one could use cascade vanes...

[FreeThinker]

On 4/21/2020 at 1:00 PM, OOM said:

I wonder why in this concept there is no radiator to transfer heat into space?
When I tested the Bassard engine in the "interstellar" modification, a huge amount of heat was generated in the process, from which even a huge radiator could not save. I think the ship according to the scheme below will work for several seconds until it melts)))
 

Probably because of the rule of cool. Radiators are just ugly most of the time.

It could also that they assume they can minimize wasteheat by having acces to 99.9% efficient x-ray to direct energy converters.

On 4/19/2020 at 8:02 AM, OOM said:

I believe that the Bussard engine should be in the game. Even in spite of the fact that the scoop will be like a brake - he can still achieve decent speeds.
It does not require a ton of Helium-3 like Daedalus, for example.

As far as I know, the limitations for the Bussard engine are as much as 0.119 the speed of light.
This is decent for technology already available "now" so to speak.

According to my calculations, this will make it possible to make an interstellar flight to Alpha Centauri in 36-40 years!
True, the question of slowdown is of course open .... 
Scoop can not act in the opposite direction ???

And is there enough scoop itself if you use it as a “free” brake with 0.1 speed of light in that short period of time?

 

I doubt...

Idealy you combine the Bussard engine with  Beam Core Antimatter engine and use the bussard scoop mainly as a break and durring speedup between 0.01 and 0.1c. This would allow you to speed up to 0.8c and then speed down to 0.01c using the scoop. After that you reverse to slow down to interplanetary speed.

Edited April 30, 2020 by FreeThinker