"Direct" burn to planet?

[DrunkenKerbalnaut]

1 minute ago, HebaruSan said:

Drag from the interstellar medium.

Which would become worse as you approached the center of a galaxy, right?

[HebaruSan]

2 minutes ago, DrunkenKerbalnaut said:

Which would become worse as you approached the center of a galaxy, right?

I'm not qualified to give an authoritative answer, but my best guess is that as the interstellar medium gets denser, both the drag and the thrust are increased, since you would have more fuel to burn per unit time, and they'd cancel out, so you can still go 0.12c. But please be sure consult a real physicist before beginning construction of your ramjet or laying in courses for it.

[DrunkenKerbalnaut]

Just now, HebaruSan said:

I'm not qualified to give an authoritative answer, but my best guess is that as the interstellar medium gets denser, both the drag and the thrust are increased, since you would have more fuel to burn per unit time, and they'd cancel out, so you can still go 0.12c. But please be sure consult a real physicist before beginning construction of your ramjet or laying in courses for it.

BRB, canceling Amazon order. 

[Nathair]

Just now, HebaruSan said:

As much as I love that book, we should note that it was later proved that such a craft has a speed limit of 0.12c due to drag from the interstellar medium. If I'm doing the math right, that means your 1g would run out after about 42 days (maybe longer if it winds down gradually).

 

IRL ramjets (and RAIR systems) have a whole raft of issues to overcome but ignoring them... 0.12c is almost respectable. That's Alpha Centauri in under forty years...

9 minutes ago, DrunkenKerbalnaut said:

Which would become worse as you approached the center of a galaxy, right?

In the book they thrust laterally in order to spend most of the trip well above the galactic plane to minimize density then when they actually got close to the core other things became more significant.

[regex]

2 minutes ago, Nathair said:

IRL ramjets (and RAIR systems) have a whole raft of issues to overcome but ignoring them... 0.12c is almost respectable. That's Alpha Centauri in under forty years...

A RAIR system would function much better than 0.12c methinks, since it carries a lot of its own fuel and at the target can use the scoop to brake (and refuel). tbh I think that will eventually be humanity's road to the stars.

[Nathair]

Just now, regex said:

A RAIR system would function much better than 0.12c methinks, since it carries a lot of its own fuel and at the target can use the scoop to brake (and refuel). tbh I think that will eventually be humanity's road to the stars.

 

I'm with you that far but (sadly) I don't think 1g all the way to the core is going to happen.

[regex]

Just now, Nathair said:

I'm with you that far but (sadly) I don't think 1g all the way to the core is going to happen.

Oh, I'm already way beyond that discussion.

[SpacedInvader]

4 minutes ago, Nathair said:

I'm with you that far but (sadly) I don't think 1g all the way to the core is going to happen.

I would tend to agree that 1g for that kind of duration would be impossible. This whole discussion was more intended for intrasystem travel rather than intersystem travel. It might be outside of our current technological prowess, but I don't think it truly impossible to sustain 1g for the relatively short duration required to travel among the planets in system.

[DrunkenKerbalnaut]

6 minutes ago, Nathair said:

I'm with you that far but (sadly) I don't think 1g all the way to the core is going to happen.

6 minutes ago, regex said:

Oh, I'm already way beyond that discussion.

It's all well and good. Just means we (humanity, not us) might see some of those fantastic "generation starships" one day. I clearly don't read as much as some of you folks, but I'm a music nut. The required "reading" is Planet Caravan, Black Sabbath   

2 minutes ago, SpacedInvader said:

I would tend to agree that 1g for that kind of duration would be impossible. This whole discussion was more intended for intrasystem travel rather than intersystem travel. It might be outside of our current technological prowess, but I don't think it truly impossible to sustain 1g for the relatively short duration required to travel among the planets in system.

What kind of velocity were you coming up with for your Earth-Mars, or Kerbin-Duna transits? 

[SpacedInvader]

3 minutes ago, DrunkenKerbalnaut said:

What kind of velocity were you coming up with for your Earth-Mars, or Kerbin-Duna transits? 

For Earth-Mars around 700Km/s and for Kerbin-Duna around 370Km/s.

[regex]

3 minutes ago, DrunkenKerbalnaut said:

It's all well and good. Just means we (humanity, not us) might see some of those fantastic "generation starships" one day.

I don't really see "generation ships" ever being a thing, at least not in the conventional sense. I think the most likely way we'll get around the galaxy is with RAIR or antimatter drives supplemented by local "beamrider networks".

[Nathair]

2 minutes ago, DrunkenKerbalnaut said:

It's all well and good. Just means we (humanity, not us) might see some of those fantastic "generation starships" one day.

 

 

Is 40 years a generation ship? If we could achieve, say, .2c then we'd have Lalande 21185 within reach in about that time.

[SpacedInvader]

3 minutes ago, regex said:

I don't really see "generation ships" ever being a thing, at least not in the conventional sense. I think the most likely way we'll get around the galaxy is with RAIR or antimatter drives supplemented by local "beamrider networks".

Beamrider networks sounds much more like hand-waving sci-fi than anything we've discussed here so far... "self-maneuvering smart pellets"? On a separate note, can please provide a link for a description of RAIR, all I'm coming up with in google is some compliance management companies and I'm not familiar with the term.

[Nathair]

1 minute ago, SpacedInvader said:

Beamrider networks sounds much more like hand-waving sci-fi than anything we've discussed here so far... "self-maneuvering smart pellets"? On a separate note, can please provide a link for a description of RAIR, all I'm coming up with in google is some compliance management companies and I'm not familiar with the term.

 

Try Googling "RAIR rocket".

[regex]

6 minutes ago, SpacedInvader said:

Beamrider networks sounds much more like hand-waving sci-fi than anything we've discussed here so far... "self-maneuvering smart pellets"?

It's more the basic concept, that being beamed power. It could involve arrays of lasers and lightsails, and be slightly slower, that sort of thing.

Quote

On a separate note, can please provide a link for a description of RAIR, all I'm coming up with in google is some compliance management companies and I'm not familiar with the term.

https://en.wikipedia.org/wiki/Bussard_ramjet#Ram_Augmented_Interstellar_Rocket_.28RAIR.29

E: Also, check in that link, "Pre-Seeded Trajectory". That is exactly the concept that a beamrider network takes advantage of. The methods can vary based on the technology available, the idea is more that the heavy carrier craft gets its fuel from external sources and provides the means for smaller craft and cargo to get where they need to go.

Edited January 24, 2017 by regex

[SpacedInvader]

5 minutes ago, regex said:

It's more the basic concept, that being beamed power. It could involve arrays of lasers and lightsails, and be slightly slower, that sort of thing.

https://en.wikipedia.org/wiki/Bussard_ramjet#Ram_Augmented_Interstellar_Rocket_.28RAIR.29

Thank you for the link. So RAIR is to chemical rockets as a propeller is to throwing rocks out of the back of a boat to get it to go forward. I can see how that would be a much better way of doing things.

[Tyko]

5 minutes ago, regex said:

It's more the basic concept, that being beamed power. It could involve arrays of lasers and lightsails, and be slightly slower, that sort of thing.

https://en.wikipedia.org/wiki/Bussard_ramjet#Ram_Augmented_Interstellar_Rocket_.28RAIR.29

E: Also, check in that link, "Pre-Seeded Trajectory". That is exactly the concept that a beamrider network takes advantage of. The methods can vary based on the technology available.

The problem with beam riding is slowing back down at your destination. Unless you've already gotten there another way to install a beam to decelerate...

[regex]

Just now, Tyko said:

The problem with beam riding is slowing back down at your destination. Unless you've already gotten there another way to install a beam to decelerate...

The beam riding ship never slows down. It may change crew and/or become obsolete (in which case you just take everything not nailed down and let the husk float off) but it is a carrier for smaller ships and cargo making large, circuitous routes. I imagine this would work very well on the "local" level of a few tens of light years (depending on the speed of the craft) and you'd have many of these craft making their loops, keeping trade going between worlds. When a smaller craft disembarks from the beam rider it may use whatever means to brake, including the "fuel" that the beam riding ship uses (lasers, particulates, a RAIR system, etc...) RAIR or antimatter ships would provide the more direct means of getting to a place, setting up a new network, investigating new worlds, that sort of thing.

[SpacedInvader]

4 minutes ago, regex said:

The beam riding ship never slows down. It may change crew and/or become obsolete (in which case you just take everything not nailed down and let the husk float off) but it is a carrier for smaller ships and cargo making large, circuitous routes. I imagine this would work very well on the "local" level of a few tens of light years (depending on the speed of the craft) and you'd have many of these craft making their loops, keeping trade going between worlds. When a smaller craft disembarks from the beam rider it may use whatever means to brake, including the "fuel" that the beam riding ship uses (lasers, particulates, a RAIR system, etc...) RAIR or antimatter ships would provide the more direct means of getting to a place, setting up a new network, investigating new worlds, that sort of thing.

Seems to me that this would actually be incredibly inefficient. If the ship never slows down, then anything that is going to be carried within must, by default, catch up to it to get on board, meaning they will require the same energy expenditure as if they were to make the journey on their own.

[regex]

1 minute ago, SpacedInvader said:

Seems to me that this would actually be incredibly inefficient. If the ship never slows down, then anything that is going to be carried within must, by default, catch up to it to get on board, meaning they will require the same energy expenditure as if they were to make the journey on their own.

Less, actually, since it will be smaller than the beam riding ship. I'm not read up on the inefficiencies of such a system but it seems fairly plausible and workable since all the energy required to keep the system going is in orbit around a star in the network and not carried by the ship. In fact, the cargo and small craft can take advantage of those systems as well.

Those systems also provide a formidable in-system defense, come to think of it...

[DrunkenKerbalnaut]

15 minutes ago, regex said:

The beam riding ship never slows down. It may change crew and/or become obsolete (in which case you just take everything not nailed down and let the husk float off) but it is a carrier for smaller ships and cargo making large, circuitous routes. I imagine this would work very well on the "local" level of a few tens of light years (depending on the speed of the craft) and you'd have many of these craft making their loops, keeping trade going between worlds. When a smaller craft disembarks from the beam rider it may use whatever means to brake, including the "fuel" that the beam riding ship uses (lasers, particulates, a RAIR system, etc...) RAIR or antimatter ships would provide the more direct means of getting to a place, setting up a new network, investigating new worlds, that sort of thing.

A similar concept was discussed a few days back in these forums, in the form of a Earth-Mars cycler - a craft that serves as living quarters for the extended journey between the two locales. It's advantages are that a smaller craft can rendezvous with flat packed resources, unload them to the cycler, and then live there for the trip. When the cycler approaches the target, they offload all the waste materials into their shuttle and slow down to meet the target. 

The DV needs are nearly identical to if the shuttle were to make the trip itself. But if the cycler houses certain amenities that can be reused (rad shields, solar arrays, air handlers, larger berthing, recreation, etc...) then you leave them circling. 

 

EDIT: it pays for itself after so many uses. It is expensive to get there, but cheap to "station-keep". 

Edited January 24, 2017 by DrunkenKerbalnaut

[Nathair]

11 minutes ago, SpacedInvader said:

Seems to me that this would actually be incredibly inefficient. If the ship never slows down, then anything that is going to be carried within must, by default, catch up to it to get on board, meaning they will require the same energy expenditure as if they were to make the journey on their own.

 

 

It's like the Aldrin Cycler. The ship itself carries all the massive engines, shielding, etc. Just add a few passengers and consumables on each cycle, much easier to accelerate to board and then the accelerate again at the other end.

Edited January 24, 2017 by Nathair
He may be Drunken, but he posts like a ninja.

[HebaruSan]

40 minutes ago, Nathair said:

IRL ramjets (and RAIR systems) have a whole raft of issues to overcome but ignoring them... 0.12c is almost respectable. That's Alpha Centauri in under forty years...

... 39 years and 281 days of which would be spent burning at full throttle just to stay in free fall, unless the ship can spin up.

(Assuming a ramjet, of course. RAIR looks neat.)

19 minutes ago, regex said:

I don't really see "generation ships" ever being a thing, at least not in the conventional sense. I think the most likely way we'll get around the galaxy is with RAIR or antimatter drives supplemented by local "beamrider networks".

Why would we need to "get around the galaxy" as a routine thing? It takes a great expenditure of energy to accelerate even a speck of dust dust to these velocities, which is a big hurdle for interstellar trade to overcome before it can be competitive with interplanetary or intraplanetary trade. We can't even come up with economically viable reasons to build things at the Moon, for Fermi's sake, because it's the same minerals we already have here but for a few extra billion dollars in transport costs (helium-3 notwithstanding). What do the local systems get out of operating their beam transmitters that they couldn't get much more cheaply by building solar panels, mining stations, and factories nearby?

[regex]

8 minutes ago, DrunkenKerbalnaut said:

A similar concept was discussed a few days back in these forums, in the form of a Earth-Mars cycler - a craft that serves as living quarters for the extended journey between the two locales. It's advantages are that a smaller craft can rendezvous with flat packed resources, unload them to the cycler, and then live there for the trip. When the cycler approaches the target, they offload all the waste materials into their shuttle and slow down to meet the target. 

The DV needs are nearly identical to if the shuttle were to make the trip itself. But if the cycler houses certain amenities that can be reused (rad shields, solar arrays, air handlers, larger berthing, recreation, etc...) then you leave them circling. 

Totally, which means the small craft can be ... smaller.

It's also worth noting that the beam rider network concept is a logical outgrowth of the "Pre-seeded trajectory" concept in the Ramjet Wikipedia link. Basically you offload the entirety of the propulsion demands to static systems so that the travelling craft can be larger and have more amenities, removing the bulky fuel requirements from interstellar travel. Those propulsion systems can also serve the smaller craft.

3 minutes ago, HebaruSan said:

Why would we need to "get around the galaxy" as a routine thing? It takes a great expenditure of energy to accelerate even a speck of dust dust to these velocities, which is a big hurdle for interstellar trade to overcome before it can be competitive with interplanetary or intraplanetary trade. We can't even come up with economically viable reasons to build things at the Moon, for Fermi's sake, because it's the same minerals we already have here but for a few extra billion dollars in transport costs (helium-3 notwithstanding). What do the local systems get out of operating their beam transmitters that they couldn't get much more cheaply by building solar panels, mining stations, and factories nearby?

vOv I have no idea why people in the future would need to get around, or why they might want to trade, or stay connected. Why would people even want to leave Earth? I mean, if they can do it relatively cheaply and at fairly quick relativistic speeds they may have a reason we don't.

Edited January 24, 2017 by regex

[Nathair]

1 minute ago, HebaruSan said:

... 39 years and 281 days of which would be spent burning at full throttle just to stay in free fall

 

 

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?

4 minutes ago, HebaruSan said:

economically viable reasons

 

Economically viable is not the only metric to apply.