"Direct" burn to planet?

[DrunkenKerbalnaut]

2 minutes ago, regex said:

"Pre-seeded trajectory" 

I'll take a look at the Wikipedia page in a moment, but this idea seems analogous to a train track through space. A subway track, in fact, and the rail powers the carriage/spaceship. 

What if the tracks "stretch"? If we are moving at ~.05c towards the nearest star system, it will have moved by the time we get to the terminus or turnaround point or apogee or whatever. Have you read anywhere where this is addressed?

As far as interplanetary cycling goes, I would imagine the Aldrin method would be cheaper in every way. Essentially the I.S.S. in a solar orbit. No need for 'static' infrastructure. 

[regex]

8 minutes ago, DrunkenKerbalnaut said:

What if the tracks "stretch"? If we are moving at ~.05c towards the nearest star system, it will have moved by the time we get to the terminus or turnaround point or apogee or whatever. Have you read anywhere where this is addressed?

On the time scales we're talking about I don't think that would make much of a difference. Certainly if routes last longer than, say, a few hundred years you'd have stars slipping in and out of the network, but I think the network engineers would be keeping that in mind. E: I also think the speeds could be much higher using that sort of system, on the order of 0.4 to 0.5c

E2: Also, isn't our Sun an outlier when it comes to stellar motion? Meaning that many stars move in clusters together, where a network would make more sense?

Quote

As far as interplanetary cycling goes, I would imagine the Aldrin method would be cheaper in every way. Essentially the I.S.S. in a solar orbit. No need for 'static' infrastructure. 

Yep. Large initial outlay, minor expenditure to keep it going, big benefit.

On the why of having a beam riding network:

You might use network ships to spin up a colony. Doing all that locally takes a very long time, maybe you send a pre-packaged "boost system" to orbit the star, which can decelerate logistics ships, which reinforce that boost system to support a proper beam rider. Then the beam riders start using that new star on the route to bring in heavier gear for much, much cheaper than boosting it alone. Sure, you could do it one-way, but the small craft can be much simpler if more of the requirements and amenities are offloaded to the beam rider. Once the colony has some infrastructure they can import more goods and begin exploiting the local resources, become more self-sufficient. But they also know they can communicate with the outside world, potentially get support, trade, even make a new colony of their own.

Edited January 24, 2017 by regex

[SpacedInvader]

4 minutes ago, regex said:

On the time scales we're talking about I don't think that would make much of a difference. Certainly if routes last longer than, say, a few hundred years you'd have stars slipping in and out of the network, but I think the network engineers would be keeping that in mind. E: I also think the speeds could be much higher using that sort of system, on the order of 0.4 to 0.5c

Yep. Large initial outlay, minor expenditure to keep it going, big benefit.

On the why of having a beam riding network:

You might use network ships to spin up a colony. Doing all that locally takes a very long time, maybe you send a pre-packaged "boost system" to orbit the star, which can decelerate logistics ships, which reinforce that boost system to support a proper beam rider. Then the beam riders start using that new star on the route to bring in heavier gear for much, much cheaper than boosting it alone. Sure, you could do it one-way, but the small craft can be much simpler if more of the requirements and amenities are offloaded to the beam rider. Once the colony has some infrastructure they can import more goods and begin exploiting the local resources, become more self-sufficient. But they also know they can communicate with the outside world, potentially get support, trade, even make a new colony of their own.

Kinda curious why such a system couldn't be set up in a more traditional accelerate / decelerate configuration. You'd still be able to offload most, if not all, of the propulsion requirements onto the fixed installation, but logistically you would have a beam shuttle instead of a circuitous route. On a related note, what sort of acceleration would this system provide?

Edited January 24, 2017 by SpacedInvader

[regex]

8 minutes ago, SpacedInvader said:

Kinda curious why such a system couldn't be set up in a more traditional accelerate / decelerate configuration. You'd still be able to offload most, if not all, of the propulsion requirements onto the fixed installation, but logistically you would have a beam shuttle instead of a circuitous route.

You could certainly do that but I imagine the network model would require fewer ships overall and/or allow the ships to be bigger overall, maybe makes better sense economically. The beam network systems could also be used in that manner for sure.

I haven't done the math, these are concepts out there on the internet from minds far more dedicated to the subject than mine. I find the network model paired with RAIR systems to be the most plausible, realistic way for humanity to "conquer the galaxy". Other systems may be better in practice E: or we might eventually generate negative mass and go for Alcubierre drives. vOv

Quote

On a related note, what sort of acceleration would this system provide?

That depends on what the static system is pushing the craft with AFAIK. If we're talking incredibly powerful lasers or mass drivers from low solar orbit you could probably get some fairly decent rates.

Edited January 24, 2017 by regex

[septemberWaves]

2 hours ago, regex said:

And might even be physically impossible.

I very much doubt it's completely impossible. Incredibly difficult, yes; probably not going to happen for centuries, also yes. But it's probably not impossible. It's probably in the same line of far-future high-energy technology as high-speed terraforming and Dyson spheres; we won't accomplish it until we've been a multiplanetary civilization for centuries and probably a multistellar civilization for quite a while too, but it's still scientifically plausible.

[SpacedInvader]

2 minutes ago, regex said:

You could certainly do that but I imagine the network model would require fewer ships overall and/or allow the ships to be bigger overall, maybe makes better sense economically. The beam network systems could also be used in that manner for sure.

I haven't done the math, these are concepts out there on the internet from minds far more dedicated to the subject than mine. I find the network model paired with RAIR systems to be the most plausible, realistic way for humanity to "conquer the galaxy". Other systems may be better in practice.

That depends on what the static system is pushing the craft with AFAIK. If we're talking incredibly powerful lasers or mass drivers from low solar orbit you could probably get some fairly decent rates.

The reason I ask is because, for the foreseeable future at least, it would seem that humanity would probably not expand at a rate that would justify having a full network instead of a hub-spoke setup with earth. As for the why question mentioned in an earlier post, we would leave because we can and we would have a trade network probably because initial colony development would be heavily supported by a stream of colonists and materials from earth, with the vessels either being cannibalized for materials or loaded with resources and sent back.

5 minutes ago, eloquentJane said:

I very much doubt it's completely impossible. Incredibly difficult, yes; probably not going to happen for centuries, also yes. But it's probably not impossible. It's probably in the same line of far-future high-energy technology as high-speed terraforming and Dyson spheres; we won't accomplish it until we've been a multiplanetary civilization for centuries and probably a multistellar civilization for quite a while too, but it's still scientifically plausible.

I think it would probably be nearer term than that, at least on a planetary scale, as I doubt serious colonization efforts will be made while interplanetary travel is still on the order of years. Draw that down to months or weeks with even low level continuous thrust (being able to produce even 0.01m/s² continuously would drop the travel time to within 2 months to Mars) and the task will become much more feasible.

[regex]

15 minutes ago, eloquentJane said:

I very much doubt it's completely impossible. Incredibly difficult, yes; probably not going to happen for centuries, also yes. But it's probably not impossible. It's probably in the same line of far-future high-energy technology as high-speed terraforming and Dyson spheres; we won't accomplish it until we've been a multiplanetary civilization for centuries and probably a multistellar civilization for quite a while too, but it's still scientifically plausible.

Is it scientifically plausible? vOv I think I'm a lot more skeptical than you regarding how we'll do things in the future. Don't get me wrong, I have high hopes, but I also don't have illusions of a Star Wars/Trek future, or even a Heinlein torchship future.

11 minutes ago, SpacedInvader said:

The reason I ask is because, for the foreseeable future at least, it would seem that humanity would probably not expand at a rate that would justify having a full network instead of a hub-spoke setup with earth.

Right. Our initial steps out of the solar system would probably look a lot like the "ISD Venture Star" ship from that one terrible cookie-cutter hero-journey movie I watched that one time. The network model would serve a more established civilization.

Edited January 24, 2017 by regex

[HebaruSan]

32 minutes ago, Nathair said:

I'm sorry, why are we burning the whole time? Once you hit that .12c why wouldn't you just turn it off and coast?

The scoop field also diverts relativistic-speed particles away from the crew module to keep them alive, which will induce drag, which needs to be compensated for with at least some thrust.

Did I say "full throttle?" If so, that was probably wrong. You could probably use a smaller field once you get acceptably close to 0.12c. But if you turn it off completely, you get a lethal dose of radiation.

[septemberWaves]

41 minutes ago, SpacedInvader said:

Draw that down to months or weeks with even low level continuous thrust (being able to produce even 0.01m/s² continuously would drop the travel time to within 2 months to Mars) and the task will become much more feasible.

Again, I was referring specifically to the high constant thrust required to simulate gravity during a journey. Constant low thrust systems are very much feasible in the near future.

[Carl]

You can;t get by without shielding period. That shielding isn't for day to day radiation. it's for the big completly unpredictable solar flares.

 

This is very worth reading IMO if your interested in the specifics of radiation and other hazards:

 

http://www.nss.org/settlement/ColoniesInSpace/colonies_chap12.html

[KerikBalm]

4 hours ago, DoctorDavinci said:

Yeah, acceleration couch ... is that something like an inertial dampener?

No such technology exists as of this post (and is not likely to exist in the forseeable future)

No, its nothing like an inertial dampener... its like a couch with a fancy name.

Just about anyone has experienced the feeling from suddenly standing up after resting and lying down -  caused by the blood draining from your head. Likewise, when blacking out from high G forces, its the blood leaving your head. Your heart has to suddenly start pumping a lot more to keep the blood circulating, and not just pooling at your feet.

Cardiac strain was specifically mentioned, and this strain is maximized when a persons body is aligned with the acceleration. The higher the G's, the more the heart has to work to keep blood flowing to the head. This is easily countered by lowering the head and raising the feet - just lie down.

F-16s, for example, in addition to G suits, simply have the pilot recline, reducing the difference in potential between the head and the feet.

Simply put, you can tolerate a lot more G's, and its easier on your heart if you lie down.

An acceleration couch is... a couch that is there to be used while accelerating. It is not technobabble nor future technology.

People could easily tolerate higher G's provided they can just lay down. If we're talking about a journey for a few days or hours, >1 G is fine (and for interplanetary travel, those would be the travel times)

[Nathair]

54 minutes ago, HebaruSan said:

The scoop field also diverts relativistic-speed particles away from the crew module to keep them alive, which will induce drag, which needs to be compensated for with at least some thrust.

Did I say "full throttle?" If so, that was probably wrong. You could probably use a smaller field once you get acceptably close to 0.12c. But if you turn it off completely, you get a lethal dose of radiation.

 

Sounds like a job for more traditional shielding.

[SpacedInvader]

2 minutes ago, Nathair said:

Sounds like a job for more traditional shielding.

The important part of that post is "reletivistic-speed particles"... At a high enough energy, even a single hydrogen atom carries enough force to do significant damage. Regular shielding just won't work in a situation like that.

[DrunkenKerbalnaut]

5 minutes ago, Nathair said:

Sounds like a job for more traditional shielding.

If this is an augmented design (RAIR), you just go into scoop-only mode (right click menu), and the drag can be mostly offset by the fuel your getting for free. Maybe some deceleration due to efficiency loss, but it's not using your augmentation fuel source. 

[SpacedInvader]

Just now, DrunkenKerbalnaut said:

If this is an augmented design (RAIR), you just go into scoop-only mode (right click menu), and the drag can be mostly offset by the fuel your getting for free. Maybe some deceleration due to efficiency loss, but it's not using your augmentation fuel source. 

Wait, is there a mod with this for KSP?

[regex]

Just now, DrunkenKerbalnaut said:

If this is an augmented design (RAIR), you just go into scoop-only mode (right click menu)

Confirming.

[DrunkenKerbalnaut]

1 minute ago, SpacedInvader said:

Wait, is there a mod with this for KSP?

Haha, sorry. Maybe? I was being sarcastic with that right click part. 

[Nathair]

3 minutes ago, SpacedInvader said:

The important part of that post is "reletivistic-speed particles"... At a high enough energy, even a single hydrogen atom carries enough force to do significant damage. Regular shielding just won't work in a situation like that.

 

0.2c is not "high enough energy" for that.

[Carl]

5 hours ago, KerikBalm said:

Well, assuming one lies down in an "acceleration couch", or something similar, there would be minimal strain on the heart and ciculatory systems.

People certainly wouldn't be up and about walking around on the ship for very long in those conditions.

In the past, on another forum, I participated in a forum sci fi game... my "ships" used constant thrust, but I was much more conservative: they were only capable of about 0.1 G acceleration - such a decrease in acceleration results in a decreased dV expenditure as well, and thus a truly massive decrease in required energy output relative to a 1 G acceleration. The other forum members more or less accepted the idea of fusion powered spacecraft accelerating at 0.1Gs (which were also capable of much higher accelerations at much lower Isps with simple impulse trajectories by good ol' NTR propulsion... but of course the long coast times meant travel would take months longer)

Yes, Impulse trajectories are more efficient than brachistichrone trajectories. The problem is that when you start to look at shorter and shorter travel times, that dV budget gets really high, so you need high Isps.

High Isp and high acceleration means ludicrous energy requirements. Most writers figured that this results in a power output limitation, and ships would simply operate at maximum reactor output throughout the journey.

Orion drives though... those are a case of high thrust and high Isp... the reactors being nuclear bombs... However, even those aren't really up to the task of a torchship drive... which are often matter-antimatter powered.

I suppose an orion drive with antimatter bombs could work- most writers assume the reactor is internal, but an external bomb reaction could work -> still the heat buildup from those bombs would be a problem - there are often 2 designs cited: with and without an ablative pusher plate. The ablative plate wouldn't work for a torchship because the ablator would be gone in short order. The non ablative one would quickly absorb too much heat, and couldn't sustain constant thrust either.

The main limitation of all torchships is the power output required, and the corresponding heat buildup from the slightest of inefficiencies.

When looking at those problems, the anatomical problems of humans at 2G constant acceleration seem trivial - besides, its so hard to get to even 1 G, why are we talking about 2 or 3?

One thing i've never seen discussed that applies to a lot of Sci-Fi concepts, (probably because no one has a bloody clue), is what really large drive cores, (in some cases i've seen them described in sizes you'd be best to use fractions or full km as a unit of measure, though one of my own lulzy fictional concepts i may write about a story some day goes to real extreme's with multi-km values for the biggest ships), could produce. At that size with hot gas you'd see thermal layering and boundary layer effects for sure. Magnetically bound plasma, i have no idea, but it would certainly help absorb radiation and neutrons from fusion type design, which would be a major positive to drive efficiency, and if you did get thermal layering it could make the whole "blow up the ship with waste heat" issue really fall off.

 

The concept of pre-seeded trajectories isn't bad either. You could actually use accelerator stations as a different way of achieving the same effect, they'd need a low thrust high ISP engine of their own to handle course corrections from newton's third law. but would be another way of achieving the same effect.

[DrunkenKerbalnaut]

Having danced through a few things online about pre-seeded trajectories, I'm not convinced it outshines other methods that much. If any. As this is a bit tangential to the original point of this thread, I've spoilered the rest. 

 

Spoiler

The logic is to offload the job of accelerating fuel from the ship to another vessel, a ground station, an orbiter, etc. Tsiolkovsky, eat your heart out! Now the ship can encounter these dense clouds of fuel en-route, and the clouds will be moving close to the ships velocity. Less energy expended scooping, potentially higher "octane" fuel supply because you made it in a controlled environment, and something about making brown dwarfs more visible. Did I get all that right? 

Ok, so we still need the energy to accelerate this fuel. And at considerable fractions of the speed of light. Newtons 3rd says this may be a problem. Whatever location is accelerating this mass is gonna be moving every time it fires a pod or capsule or whatever. If it's a ground station, it better be on a vacuum body so as to avoid atmo drag. But it's still moving along it's orbital path. which introduces a timing issue. If the gun is moving, we can still make successive shots line up along a path by means of timing and initial input, but that ship had better be on time. Every time. Or the cloud won't be there. 

If it's a space-borne fuel launcher, it's gotta correct it's own position between firings, in turn using fuel to deliver fuel so that the hero ship doesn't need to carry it. 

Doesn't this seem like a case of training 10 dogs to pull your 1 horse carriage? (I suck at these sort of analogies, but you know what I mean)

 

[Nathair]

34 minutes ago, DrunkenKerbalnaut said:

If it's a space-borne fuel launcher, it's gotta correct it's own position between firings, in turn using fuel to deliver fuel so that the hero ship doesn't need to carry it.

 

That's OK though because every bit of effort and energy that can be imparted by something other than your ship is a good thing. Doesn't matter if your launchers have to jump through hoops or expend energy, they're right at home where they can be tended to, maintained and refueled or replaced easily. Your ship, meanwhile, doesn't have to haul the fuel to accelerate the fuel used to accelerate the fuel used to haul the fuel used to accelerate the ship. 

[Carl]

30 minutes ago, Nathair said:

That's OK though because every bit of effort and energy that can be imparted by something other than your ship is a good thing. Doesn't matter if your launchers have to jump through hoops or expend energy, they're right at home where they can be tended to, maintained and refueled or replaced easily. Your ship, meanwhile, doesn't have to haul the fuel to accelerate the fuel used to accelerate the fuel used to haul the fuel used to accelerate the ship. 

This. Even in cases of say a magnetic accelerator setup along the predicted path the accelerator rings can use low thrust high ISP ions or similar because they only have to reposition in the span of hours, whilst the ship they're accelerating gets the benefit of a massless high acceleration rate from it's own perspective.

 

That the real advantage of pre-seeded trajectories. You can use high thrust low IS setups on the actual manned ship while the unnamed stuff that delivers it can use low thrust high ISP and just set off earlier.

 

The real issue with high speed transits is micrometeorites. Particles as small as a grain of sand will have the energy of nuclear bombs when they hit stuff at a modest fraction of C. Even talcum powder grain size ones will have the energy of many 100's of KG's of TNT.

Edited January 25, 2017 by Carl

[DrunkenKerbalnaut]

No, I understand that part. See my  bad Tsiolkovsky joke. I guess it just seems like a lot of possible failure modes. 

[Nathair]

3 hours ago, Carl said:

Particles as small as a grain of sand will have the energy of nuclear bombs when they hit stuff at a modest fraction of C. Even talcum powder grain size ones will have the energy of many 100's of KG's of TNT.

 

 

I think if you do the math it turns out that that "modest fraction of C" is pretty darn large for "nuclear bombs" to happen. Grain of sand (which is actually pretty big) weighs, say, 50 micrograms. At .2c and applying 1/2mv^2 we get (assuming my math isn't completely wrong) a "nuclear bomb" of 0.002kT. It's a boom and you definitely want to have some plan for dealing with it but it's not a "nuclear bombs" boom.

But check my math, seriously.

Edited January 25, 2017 by Nathair

[regex]

1 hour ago, DrunkenKerbalnaut said:

I guess it just seems like a lot of possible failure modes. 

Welcome to spaceflight.