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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 60s 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 Bussards Ramjet in a different way. The ship would be simple: a small scoop Bussards 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 ships 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 dont 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 dont 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.
Impossibility of Intrastellar travel
[MisterQED, Oct 23 2007]
Bussard's Ramjet - wikipedia
[MisterQED, Oct 23 2007]
[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.
||I like the forced orbit part.
||//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.
||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 Neptunes 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. Plutos orbit gets to 30%C and less than 15 years, though now you are dealing with the Oort cloud which you definitely dont want to orbit in, it will be tough enough to get through an any case.
||//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
||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.
||//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...
||"The big problem is fuel."
||The big problem is increasing velocity per unit time.
||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
||//The big problem is time.//
Not if you have enough fuel.
||//The big problem is fuel.//
//The big problem is time.//
//The big problem is increasing velocity
per unit time.//
The big problem is distance.
||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.
||You could solve any four with unlimited amounts of one.
||We all know that space must mearly be folded like a blanket and stepped across.
||I prefer rolling it up like a newspaper, and using it to smack unfriendly aliens out of existence.
||I prefer rolling it up like a joint, and lighting it.
||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.