Author Topic: Interstellar Spaceflight: Is It Possible?  (Read 16784 times)

Offline IsaacKuo

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #40 on: 08/10/2011 08:47 PM »
By the way how do you get that cube anyway? Does the fields cross section increase with increased speed?

The diameter of the bow shock increases with speed.

Offline IsaacKuo

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #41 on: 08/10/2011 08:56 PM »
Hopefully the probe has JUST enough momentum to stop at the destination star system.  Any miscalculation in the ISM means that the probe either fails to reach the destination system or it goes sliding past the destination with the mag-brake powerless to stop it.  The risk of this isn't such a big deal if the probe has another propulsion system--but if such a potent propulsion system is available it should probably be used for braking in the first place.
The "Mag-Sail" shouldn't ever hit the point where it won't be able to accelerate or decellerate since it can ride the target stars solar wind as per the basic "Mag-Sail" concept. (It was proposed as an interplanetary "drive" originally after all)

The ISM mag-brake would have different characteristics than a mag-sail designed for stellar wind.  But that's not the point.  The point is that it can only provide a certain amount of braking.  If the probe enters the destination star system at 1% c (3000km/s), it doesn't really matter that the mag-brake can provide a small amount of braking all the way through the system and beyond.  What matters is that this small amount of braking simply isn't enough to stop it.  It might be able to provide on the order of 100km/s delta-v, which is inadequate.

Quote
"Better" would probably be to use the effect to swing the vehicle around and bring it back towards the target star from "behind"

Use what effect?  Zubrin's ISM mag-brake can't swing the vehicle around.

Offline KelvinZero

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #42 on: 08/10/2011 09:11 PM »
The holy grail of manned interstellar flight is imo 1 g acceleration and deceleration for most of the voyage.
Prepositioning propellant at correct velocity and/or beamed propulsion have always been a favorite of mine. Isaac‘s zillions of tiny sails sound like a good way of delivering intelligent beamed propulsion that remains on target across lightyears and can even dash ahead then slow down near the destination for braking.
perhaps some sort of cannon on the moon or in orbit could launch these at a significant fraction of light speed, or more conventional beamed propulsion could accelerate them before leaving our system.

Offline Downix

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #43 on: 08/10/2011 10:00 PM »
The most obvious answer is to use an Orion putt-putt.
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Offline Tass

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #44 on: 08/11/2011 04:47 PM »
By the way how do you get that cube anyway? Does the fields cross section increase with increased speed?

The diameter of the bow shock increases with speed.

Ah. I thought the medium would be so thin on the scale of an artificial sail that it was basically individual particles hitting a magnetic field, getting deflected and leaving. If you actually get significant plasma effects on the field then of course it changes things.

Offline mlorrey

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #45 on: 08/12/2011 02:38 AM »
The most obvious answer is to use an Orion putt-putt.

nuke pulse propulsion gets you to 5% of C at most.
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Offline Lampyridae

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #46 on: 08/12/2011 08:49 AM »
The most obvious answer is to use an Orion putt-putt.

nuke pulse propulsion gets you to 5% of C at most.

True but it gets you there in less than geological time. Use hibernation, extended lifespan or generation ship technology to get humans there alive. ISM does most of the deceleration; a combination of reserve nukes and sailing into the stellar wind slows the vehicle into orbit.

Nukes would most likely be those pellets for ICF, with the lasers running of an onoard nuke plant.

You'd probably want a nice big ship anyways. If it's a proper ORION with pusher plate, then the required yield is something like megatonnes and the pusher plate is 400 metres acros. When you get to the target star, at least you have a large enough ship to be self-sustaining and self-replicating with help from a few asteroids if for whatever reason surface colonisation doesn't pan out or is delayed.
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Offline strangequark

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #47 on: 08/12/2011 09:50 AM »
The holy grail of manned interstellar flight is imo 1 g acceleration and deceleration for most of the voyage.
Prepositioning propellant at correct velocity and/or beamed propulsion have always been a favorite of mine. Isaac‘s zillions of tiny sails sound like a good way of delivering intelligent beamed propulsion that remains on target across lightyears and can even dash ahead then slow down near the destination for braking.
perhaps some sort of cannon on the moon or in orbit could launch these at a significant fraction of light speed, or more conventional beamed propulsion could accelerate them before leaving our system.

No kidding! 1g constant acceleration will get you to anywhere in about 20 years with relativistic effects. Altair (18 ly) and Andromeda (2.5 million ly) are the same amount of ship time.

Offline DLR

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #48 on: 08/12/2011 11:23 AM »
The long deceleration time is a good argument for not using magsails as brakes, but we may have no other option if we want to put probes into other star systems.

What about deploying the mag-sail much closer to the target star than proposed by Zubrin, so rather than using drag from interaction with interstellar medium to slow down you utilize the more powerful solar wind and the denser particles in the target solar system? Would it make sense to use a magsail to brake from, say, 0.2c to 0.05c or so and use fusion or antimatter propulsion to complete deceleration, reducing the overall trip time?

Offline indaco1

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #49 on: 08/12/2011 08:16 PM »
Zubrin estimate is based on a "conventional" magsail?

Why not an M2P2? The plasma suppy to feed the magnetosphere will not sufficie?

I wonder if are possible other designs to improve mass/drag ratio, possibly steerable during deceleration to adjust trajectory.

A relatively good start for interstellar travel could be a M2P2 mission braked and steered beyond the heliopause to fly by one or more TNOs.


 
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Offline qraal

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #50 on: 09/07/2011 12:11 PM »
Zubrin estimate is based on a "conventional" magsail?

Why not an M2P2? The plasma suppy to feed the magnetosphere will not sufficie?

I wonder if are possible other designs to improve mass/drag ratio, possibly steerable during deceleration to adjust trajectory.

A relatively good start for interstellar travel could be a M2P2 mission braked and steered beyond the heliopause to fly by one or more TNOs.

Contrary to all the old material that Googles up when you do a search on M2P2, the more recent papers on the concept will tell you it doesn't work. Seems Winglee et.al. violated certain MHD assumptions that they had taken for granted. When the real plasma dynamics is computed, the thrust is much, much lower. M2P2 doesn't work as advertized. The Japanese are still working on a hybrid concept - mag-sail plus a plasma sail system - but the pure M2P2 is a dud.

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