Science: Spacecraft: Propulsion
Bussard Centrifuge   (+1, -3)  [vote for, against]
Use close orbit solar wind to feed ramjet to reach light speed

Combine Bussard's Ramjet with backup solar sail to take small ship to near light speed. This is in response to an article I read by some sci-fi writer who claimed the impossibility of interstellar travel. (See link.) The big problem is fuel. It takes a lot of energy to accelerate to near the speed of light and the more fuel you have the more you need, because you have to accelerate all the extra mass. Bussard's Ramjet (See link) is an idea from the 60’s were a ship would scoop up fuel along the way and feed it into a fusion reactor.. The idea died away when they found that interstellar matter was too thin to feed a reactor, and gathering it in with a giant scoop would cause more drag than thrust.

My idea, which I am trying to turn into a sci-fi story, is to build a small ship which uses a Bussard’s Ramjet in a different way. The ship would be simple: a small scoop Bussard’s Ramjet feeding into a fusion reactor, a solar sail, a survival pod and inflatable living quarters. 1. The ship would leave earth and use the solar sail and planetary slingshot maneuvers to dive as fast as possible into a close orbit inside Mercury. 2. When the speed reaches high enough, use the combination of the ship’s speed and the higher speed and density of the solar to ignite the Ramjet. 3. Angle the thrust of the ramjet to keep an artificially small orbit around the Sun that keeps accelerating. 4. As G-forces become unworkable, increase the orbital radius. 5. Once the required fraction of the speed of light is reached, shut the engine off and coast to another solar system use the solar sail for minor corrections. Inflate the living quarters and climb out of the pod. 6. At the other end reverse the process or deploy a massive magnetic scoop to slow the ship to reach a rational orbit of the other star. The idea relies on the fact that the solar wind density drops by the square of the distance from the sun and the solar wind slows as it travels. An ideal Ramjet will produce thrust based on the mass of matter that enters the fusion reactor. The mass is based on three quantities, density of matter to be scooped, size of the scoop and speed of the craft. The other advantage this system has over the standard approach is that solar wind near the sun starts out ionized, so magnetic scoops don’t need a forward facing laser to ionize the matter to be scooped. As speed increases the radius increases, which lowers the density, but should be compensated for by the increased speed. The questions are: 1. Could a fall into the sun plus some crazy slingshot maneuvers create enough speed to ignite the ramjet? 2. How much thrust could this system produce? 3. Can the max thrust exceed the centripetal force enough to allow a near light speed exit from the solar system? (and an tense four year trip hoping you don’t run into an asteroid or even a big piece of dust.) 4. Assuming a human in a liquid breathing pod, how many Gs could they survive and how much food would needed to be stored to feed them intravenously for the spin up and spin down.
-- MisterQED, Oct 23 2007

Impossibility of Intrastellar travel http://www.antipope...frontier_redux.html
[MisterQED, Oct 23 2007]

Bussard's Ramjet - wikipedia
[MisterQED, Oct 23 2007]

Liquid Breathing
[MisterQED, Oct 23 2007]

We may just have to face the fact that we are not destined for interstellary travel. It may be nature's way of keeping solar system civilizations apart...if there are more than one. We can dream about going to the stars and perhaps even some day, send probes. But, ten thousand year trips may be rather hard for Earth bound civilizations so far in the future to remember by the time they arrive at destination.

To accellerate to speeds to make such trips plausible, there are some even less fantastic things we might do...for example, shrinking people via genetic engineering to the size of mice, thus making the ship able to be infinetly more capable...or perhpas we would merely launch a few dozen frozen human embryos and allow them to mature when they near the destination star...say thirty years before arrival and let automated systems raise them and give them an education so they would be valuable observers ....Now, there is a fantastic Sci-fi story in itself!

But, practical interstellar travel may be so many centuries away in time, we might as well be satisfied exploring this solar system until then.
-- Blisterbob, Oct 23 2007

I like the forced orbit part.
-- baconbrain, Oct 23 2007

//a super strong magnet on board that exerts an cancelling force on the human body via diamagnetism. // That is an intriguing idea - has it been proposed before? If you could apply force directly to every atom in the body, you could survive just about any acceleration. I would guess that the diamagnetic force would differ for different body components (eg, proteins v water), but it should still be possible to apply pretty big accelerations if diamagnetic forces were high enough.
-- MaxwellBuchanan, Oct 24 2007

Magnetic force to cancel G forces may be possible, but problematic because the scoop for the ramjet is magnetic as is the accelerator that will raise the speed of the scooped atoms up to near light speed in preparation for fusion. Also I think it is unnecessary as fish live at the bottom of the Marianas trench which is at 1000 atm pressure, so I think that means a liquid breathing apparatus should work to 1000Gs. So assuming you could gather enough solar wind to power the engine to develop the 1000+G of acceleration you will be traveling "about" (need to recalculate for relativity) 25% of the speed of light by the time you increase to Neptune’s orbit. This drops the trip to Alpha Centauri to 18.6 years, but due to relativistic effects, it would seem much shorter. If there is enough matter that can be scooped in the space in between to exceed the needs of life support and add acceleration the trip could be shorter. Pluto’s orbit gets to 30%C and less than 15 years, though now you are dealing with the Oort cloud which you definitely don’t want to orbit in, it will be tough enough to get through an any case.
-- MisterQED, Oct 25 2007

//I think that means a liquid breathing apparatus should work to 1000Gs.//

No no. Very much no, and it's a false analogy. Bones are denser than water, for a start. The density of compact bone is about 1.9 grams per cubic centimetre, whereas water is 1.0. Your soft tissues are pretty close to 1.0. If you have no gas in your body, your overall density is something like 1.1 or 1.2.

So, suppose you're breathing liquid and floating neutrally in a tank filled with saline (density 1.1 or 1.2). Suppose also that you're on the surface of the earth, at 1g. Your femur (which is mostly compact bone, with spongy ends and a meaty filling) weighs maybe 1 or 2kg (say 2 for argument's sake). Of this 2kg, about half is "excess weight" (ie, weight in excess of the weight of the water it displaces) - this 1kg is supported by your soft tissues.

Now apply an acceleration of 1000g. Your femur now "weighs" 2000kg, but the volume of water it displaces now "weighs" 1000kg. The difference, 1000kg, has to be supported by your soft tissues. Soft tissues will not handle that load, hence the term "soft".

In other words, at 1000g your bones are going to exit your body by the most direct available route, whether you're floating like a goldfish or not.
-- MaxwellBuchanan, Oct 25 2007

//at 1000g your bones are going to exit your body by the most direct available route//

Of course, exactly what happen in any centrifuge, the heavy bits settle to the bottom. Ouch, so how about those magnets...
-- MisterQED, Oct 26 2007

"The big problem is fuel."

The big problem is time.
-- phoenix, Oct 26 2007

The big problem is increasing velocity per unit time.
-- 4whom, Oct 27 2007

For your science fiction book, it might be appropriate to investigate the option of allowing the space travellers to remain stationary (relative to some point outside of our visible universe) and allow the rest of space to wizz by. Which it does every <measurement of time> at an alarming pace. The Romanian Drive
-- 4whom, Oct 27 2007

//The big problem is time.//

Not if you have enough fuel.
-- ldischler, Oct 27 2007

//The big problem is fuel.// //The big problem is time.// //The big problem is increasing velocity per unit time.// The big problem is distance.
-- MaxwellBuchanan, Oct 28 2007

Remember the 'fast-cheap-good' triangle where you get to pick any two? I think this is one where you've got five problems - fuel, time, acceleration, range, cost - and you can solve any one assuming you have unlimited amounts of the other four. Maybe it's solve two with three, I haven't checked all the permutations yet.
-- lurch, Oct 28 2007

You could solve any four with unlimited amounts of one.
-- 4whom, Oct 28 2007

We all know that space must mearly be folded like a blanket and stepped across.
-- 2 fries shy of a happy meal, Oct 28 2007

I prefer rolling it up like a newspaper, and using it to smack unfriendly aliens out of existence.
-- ye_river_xiv, Oct 28 2007

I prefer rolling it up like a joint, and lighting it.
-- jtp, Oct 30 2007

Actually, the thing is, space is already all folded up. Basingstoke is actually 183 light-years away from Reading, but spacetime pleating makes them appear only a few tens of miles apart. By the same token, the M25 actually describes a very tortuous and approximately toroidal route between no fewer than three different galaxies in our local cluster but, because of the way space is folded up, it's possible to drive around it in 48 hours. Belgium (to pick an example at random) is actually a pastiche of landmasses on four distinct planets - we just don't notice the joins.

This is as good as it gets, unfortunately.
-- MaxwellBuchanan, Oct 30 2007

I have liked this idea since I first read it. The difficulties with the acceleration get a lot easier if you only use it for missions that do not carry intact animal bodies.
-- notexactly, Mar 11 2019

//shrinking people via genetic engineering to the size of mice//

I think you'll find issues with retaining sufficient intelligence in your mouse-sized gene-engineered "humans" for them to maintain any sort of society that could plausibly be called "civilization" [bob].

Perhaps a more productive avenue of research would be to engineer humans with the physiological responses of hibernation found in dormice & some other mammals together with temperature induced production of organic anti-freezes so they can more easily be "cryogenically frozen" for the trip, journey-time becomes much less of an issue then.

It seems like it might even be possible to back-engineer that sort of thing into an adult organism with gene-therapy before too much longer.
-- Skewed, Mar 11 2019

//engineer humans with the physiological responses of hibernation found in dormice// Have you met the Intercalary? He slept through a large part of the 1990s.
-- MaxwellBuchanan, Mar 11 2019

A drug induced coma isn't the same thing at all, which reminds me, can you pass on my apologies for that last tab I gave him back then?
-- Skewed, Mar 11 2019

He's already asked me to ask you if you can get any more.
-- MaxwellBuchanan, Mar 11 2019

TIL that MisterQED agrees with my previous annotation, according to his profile.
-- notexactly, Mar 11 2019

random, halfbakery