"Direct" burn to planet?

[SpacedInvader]

Over the years I've read in several science fiction franchises about a method of interplanetary travel in which a vehicle accelerates at 1g for half the transfer then flips and reverses the process, allowing for a sort of linear gravity simulation as well as an absolute minimal transfer time. First, I'd like to know what this maneuver is called and then I'd like to know if KSP is capable of simulating it. I am getting ready to start a new career after some time away and I'm debating installing KSP Interstellar which I believe has technology capable of giving enough dV to perform such a maneuver, but I would have no idea how to go about planning or executing it.

 

Thanks.

[DrunkenKerbalnaut]

Set your google gun to "Andy Weir" and "constant thrust". This burn method received recent notoriety due to it's use in the Book and Movie "The Martian". A apparently the writer Andy made a program to calculate this burn as it pertains to Earth<->Mars. There's a few good videos floating around YT where he talks in detail about. One is with him and Adam Savage, the other is him giving a presentation at a Google Android developers conference. 

EDIT: For the sake of those who skip around threads; attention was called to the fact that the fictitious ship from The Martian -Hermes- does not thrust at 1g. I offer it as a comparison because it does utilize a constant thrust flight plan. The author has stated that the Hermes was capable of 2mm/s^2 acceleration. 1 earth gravity is 9.8m/s^2. That's 4900 times more acceleration than the Hermes. 

Edited January 22, 2017 by DrunkenKerbalnaut

[Carl]

Oh it's been a thign for years. The problem is AFAIK until Vasimr came along the only drive concept ever seriously studied capable of it was fission/fusion drives. Before that it was just horribly impractical.

[DrunkenKerbalnaut]

Just now, Carl said:

Oh it's been a thign for years. 

Certainly. It's just become a great deal more visible since The Martian. 

Weren't the Soviets considering a manned Venus trip with constant thrust flight plan back in the day?

[SpacedInvader]

17 minutes ago, DrunkenKerbalnaut said:

Set your google gun to "Andy Weir" and "constant thrust". This burn method received recent notoriety due to it's use in the Book and Movie "The Martian". A apparently the writer Andy made a program to calculate this burn as it pertains to Earth<->Mars. There's a few good videos floating around YT where he talks in detail about. One is with him and Adam Savage, the other is him giving a presentation at a Google Android developers conference. 

 

Watching the Adam Savage interview right now.

 

Just now, DrunkenKerbalnaut said:

Certainly. It's just become a great deal more visible since The Martian. 

Weren't the Soviets considering a manned Venus trip with constant thrust flight plan back in the day?

 

I actually don't remember seeing it in The Martian (I admit I haven't found time to read the book sadly). The two sources I've gotten the idea from are the old tabletop RPG games Battletech, Mechwarrior, and Aerotech and then also newish Syfy show The Expanse.

[Carl]

I don't recall hearing about it, but then i don't think i've heard of any serious manned mission studies beyond the moon. A lot of wistful thinking and such like, but nothing like a real serious "we can do this" study. Closest that came that i've heard of was immediate post apollo when NASA expected to get funding for Mars and started looking at it before being told, nope, you don't matter anymore and we're not gonna fund you, (for all intents and purposes, the shuttle ended up such a massive debacle bcause it was so horribly underfunded, NASA tried to do too much with too little, though the US military sticking it;s oar in and stirring did not help).

[DrunkenKerbalnaut]

Here we go. 3 year flight. 1 year thrusting. So not constant thrust, but certainly not traditional Oberth maneuver:

 

http://www.astronautix.com/t/tmk-e.html

[SpacedInvader]

3 minutes ago, Carl said:

I don't recall hearing about it, but then i don't think i've heard of any serious manned mission studies beyond the moon. A lot of wistful thinking and such like, but nothing like a real serious "we can do this" study. Closest that came that i've heard of was immediate post apollo when NASA expected to get funding for Mars and started looking at it before being told, nope, you don't matter anymore and we're not gonna fund you, (for all intents and purposes, the shuttle ended up such a massive debacle bcause it was so horribly underfunded, NASA tried to do too much with too little, though the US military sticking it;s oar in and stirring did not help).

Its always saddened me that the only real reason we managed to put boots on the moon was because we wanted to "show the Reds" rather than really wanting to do it for the furtherance of scientific and technological understanding. That said, considering that we've had nearly 50 years of further development since then and still probably won't have another human on the surface of another orbital body for 20 more years, I can only imagine how far we'd be from that original goal without the cold war.

Edited January 22, 2017 by SpacedInvader

[DrunkenKerbalnaut]

16 hours ago, SpacedInvader said:

Its always saddened me that the only real reason we managed to put boots on the moon was because we wanted to "show the Reds" rather than really wanting to do it for the furtherance of scientific and technological understanding. That said, considering that we've had nearly 50 years of further development since then and still probably won't have another human on the surface of another orbital body for 20 more years, I can only imagine how far we'd be from that original goal without the cold war.

And it seems that I was confusing the TMK and TMK-E mission proposals, the former was the Venus flyby and it wasn't a constant thrust mission. The latter was Mars rover bonanza, and it was the 1 year ion burn mission. 

Edited January 22, 2017 by Frybert
2.2b

[HebaruSan]

1 hour ago, SpacedInvader said:

Over the years I've read in several science fiction franchises about a method of interplanetary travel in which a vehicle accelerates at 1g for half the transfer then flips and reverses the process, allowing for a sort of linear gravity simulation as well as an absolute minimal transfer time. First, I'd like to know what this maneuver is called

A vehicle capable of that is sometimes called a "torch ship," and its drive a "torch drive," but the only name I'm finding for the maneuver is "Brachistochrone trajectories."

http://www.projectrho.com/public_html/rocket/torchships.php

1 hour ago, SpacedInvader said:

then I'd like to know if KSP is capable of simulating it. I am getting ready to start a new career after some time away and I'm debating installing KSP Interstellar which I believe has technology capable of giving enough dV to perform such a maneuver, but I would have no idea how to go about planning or executing it.

In principle, yes, KSP's physics engine could do it; I think you would just target the destination body, aim at it, and burn. In practice, the burns would be mind-numbingly long, and you'd have to sit there and wait for them to complete. While you can time-warp through a Hohmann transfer at 100000x speed, you'll be limited to 4x while your engines are running. I don't want to attempt the math in my head, but I think it would take at least a few days, given that the corresponding Hohmann transfers would typically be a few hundred days. And of course you would definitely need a mod along the lines of the one you mentioned, because in both reality and stock KSP, you have to choose between 1g thrust and an ISP high enough to burn that long.

52 minutes ago, DrunkenKerbalnaut said:

Set your google gun to "Andy Weir" and "constant thrust". This burn method received recent notoriety due to it's use in the Book and Movie "The Martian". A apparently the writer Andy made a program to calculate this burn as it pertains to Earth<->Mars. There's a few good videos floating around YT where he talks in detail about. One is with him and Adam Savage, the other is him giving a presentation at a Google Android developers conference. 

Really? 1g thrust for the whole trip? I thought that book and movie were more near-term realistic, as in using technologies that are within or close to our current capabilities. At least in the movie I saw, the crew used a rotating habitat for gravity rather than constantly running the engines at 1g thrust.

[DrunkenKerbalnaut]

4 minutes ago, HebaruSan said:

Really? 1g thrust for the whole trip? I thought that book and movie were more near-term realistic, as in using technologies that are within or close to our current capabilities. At least in the movie I saw, the crew used a rotating habitat for gravity rather than constantly running the engines at 1g thrust.

No clue what the actual thrust level the writer used was. I would have to dig for that. I feel like I remember him basing it off of near future ion propulsion levels, but he may have fudged. 

Really, I don't think they spend too long talking about the propulsion in the movie (aside from the part where the hero uses a tarp for a rocket nose cone lol), but apparently the book gets a little down and dirty with it. Idk, haven't read it. Certainly wouldn't mind, though. 

Edited January 22, 2017 by DrunkenKerbalnaut
Trimming the quoted part

[SpacedInvader]

2 minutes ago, DrunkenKerbalnaut said:

No clue what the actual thrust level the writer used was. I would have to dig for that. I feel like I remember him basing it off of near future ion propulsion levels, but he may have fudged. 

Really, I don't think they spend too long talking about the propulsion in the movie (aside from the part where the hero uses a tarp for a rocket nose cone lol), but apparently the book gets a little down and dirty with it. Idk, haven't read it. Certainly wouldn't mind, though. 

In the video you suggested he says the Hermes can accelerate at 2mm/s/s.

[SpacedInvader]

1 hour ago, HebaruSan said:

A vehicle capable of that is sometimes called a "torch ship," and its drive a "torch drive," but the only name I'm finding for the maneuver is "Brachistochrone trajectories."

http://www.projectrho.com/public_html/rocket/torchships.php

In principle, yes, KSP's physics engine could do it; I think you would just target the destination body, aim at it, and burn. In practice, the burns would be mind-numbingly long, and you'd have to sit there and wait for them to complete. While you can time-warp through a Hohmann transfer at 100000x speed, you'll be limited to 4x while your engines are running. I don't want to attempt the math in my head, but I think it would take at least a few days, given that the corresponding Hohmann transfers would typically be a few hundred days. And of course you would definitely need a mod along the lines of the one you mentioned, because in both reality and stock KSP, you have to choose between 1g thrust and an ISP high enough to burn that long.

Really? 1g thrust for the whole trip? I thought that book and movie were more near-term realistic, as in using technologies that are within or close to our current capabilities. At least in the movie I saw, the crew used a rotating habitat for gravity rather than constantly running the engines at 1g thrust.

An admittedly very rough calculation using this displacement calculator resulted in a total travel time of about 41.5 hours with earth and mars at their closest positions and a constant acceleration / deceleration of 1g for the whole transfer. That's assuming straight line travel and doesn't take relative velocities of the planets into account, but I'm willing to assume that the only significant variation in time would result from different planet positions. Considering KSP interplanetary distances are far smaller than real life, the resulting travel time is only about 15 hours, something that might actually be possible with 4x acceleration.

Edited January 22, 2017 by SpacedInvader

[DrunkenKerbalnaut]

14 minutes ago, SpacedInvader said:

An admittedly very rough calculation using this displacement calculator resulted in a total travel time of about 41.5 hours with earth and mars at their closest positions and a constant acceleration / deceleration of 1g for the whole transfer. That's assuming straight line travel and doesn't take relative velocities of the planets into account, but I'm willing to assume that the only significant variation in time would result from different planet positions. Considering KSP interplanetary distances are far smaller than real life, the resulting travel time is only about 15 hours, something that might actually be possible with 4x acceleration.

Does this account for gravity? You said straight line, so I'm assuming were pretty much talking about slip stream or Alcubierre (sp?) drives. 

Its my [limited] understanding that unless you were roaring off towards mars at anything less than a considerable exponent of Solar escape velocity, your path would still be perturbed by it's gravity. So you would still fly a curve. 

Not trying to be a douchebag, just trying to wrap my head around what your path would look like. 

[Allocthonous]

2 hours ago, HebaruSan said:

A vehicle capable of that is sometimes called a "torch ship," and its drive a "torch drive,"

I remember reading about these in old Poul Anderson novels. I seem to recall applications of the idea that any engine powerful enough to be interesting is also powerful enough to be a WMD. Apply this to your game of KSP how you will.

[SpacedInvader]

12 minutes ago, DrunkenKerbalnaut said:

Does this account for gravity? You said straight line, so I'm assuming were pretty much talking about slip stream or Alcubierre (sp?) drives. 

Its my [limited] understanding that unless you were roaring off towards mars at anything less than a considerable exponent of Solar escape velocity, your path would still be perturbed by it's gravity. So you would still fly a curve. 

Not trying to be a douchebag, just trying to wrap my head around what your path would look like. 

I did said it was a rough calculation 

All I did was look up the straight-line distance between the planets at their closest pass and then use the calculator to determine the time it would take to cover half of that distance at an acceleration of 9.8m/s². I'm fairly certain this won't result in a 100% accurate calculation, just a rough estimate. I fully believe you that gravity would need to be accounted for, as would relative orbital velocities, but being able to sustain such significant acceleration would greatly diminish those effects.

As a side note, sustaining 1g acceleration for 24hrs would result in a velocity of 846,720m/s or 3,048,192km/h.

Edited January 22, 2017 by SpacedInvader

[DrunkenKerbalnaut]

1 minute ago, SpacedInvader said:

I did said it was a rough calculation 

All I did was look up the straight-line distance between the planets at their closest pass and then use the calculator to determine the  greatly diminish those effects.

Ok, gotcha. Sorry, you've piqued my interest.

The second video I recommended (Which was a google dev conference), Weir shows off his program in some detail - the one that plots these burns and routes.

skip to 13:30 if you're pressed for time

Now idk if he's a super cool guy because he figured this out with reasonable accuracy, or if he simply reinvented a wheel, but that is just BadS. 

[Carl]

Nah that sum probably isn't far off at all. The thing is at closest approach the vector will be directly away/towards the sun, and nothing else will apply enough gravity for long enough to distort things in a meaningful way. The thing is i'm pretty sure the suns gravity out at earth orbit and beyond is weak enough it shouldn;t radically alter things. The error is probably under an hour.

[SpacedInvader]

5 minutes ago, DrunkenKerbalnaut said:

Ok, gotcha. Sorry, you've piqued my interest.

The second video I recommended (Which was a google dev conference), Weir shows off his program in some detail - the one that plots these burns and routes.

skip to 13:30 if you're pressed for time

Now idk if he's a super cool guy because he figured this out with reasonable accuracy, or if he simply reinvented a wheel, but that is just BadS. 

Looks to me like he trial and errored the heck out of that, but that could just be the way he's presenting it. What surprises me is that the constant thrust calculations seem like that shouldn't be that complicated (beyond my capabilities currently for sure, but still, all of the variables are known so the math should be doable), though the fact that no one has bothered to figure it out with hard calculations could just be because we don't have the drive technology yet, so there isn't much reason to do the math.

[DrunkenKerbalnaut]

3 minutes ago, Carl said:

Nah that sum probably isn't far off at all. The thing is at closest approach the vector will be directly away/towards the sun, and nothing else will apply enough gravity for long enough to distort things in a meaningful way. The thing is i'm pretty sure the suns gravity out at earth orbit and beyond is weak enough it shouldn;t radically alter things. The error is probably under an hour.

I can get behind that, but with a caveat: You would have to leave earlier than closest approach, so that closest approach was actually at the moment you began reversing thrust. Now of course you would have to 'aim' ahead of Mars, but anyone who has done an orbital transfer in Kerbal knows that's a thing. In this case, however, you would only need lead it by 2 days or so. 

[SpacedInvader]

5 minutes ago, DrunkenKerbalnaut said:

I can get behind that, but with a caveat: You would have to leave earlier than closest approach, so that closest approach was actually at the moment you began reversing thrust. Now of course you would have to 'aim' ahead of Mars, but anyone who has done an orbital transfer in Kerbal knows that's a thing. In this case, however, you would only need lead it by 2 days or so. 

Even if the planets weren't in optimal position, the effect of gravity would only add a marginal amount of extra distance to the transfer, which with this sort of thrust should be handled by a few extra hours of acceleration. If you were to fully double the distance the vehicle would have to travel, you'd only add about 20 hours to the travel time. Basically, with so much dV at your disposal, you'd almost completely ignore the hohmann transfer and just thrust in a direction that would give you a straight line to the target while accounting for gravity since 2-4 days is not nearly enough time to have a real curving orbital trajectory.

Edited January 22, 2017 by SpacedInvader

[DrunkenKerbalnaut]

Just now, SpacedInvader said:

Even if the planets weren't in optimal position, the effect of gravity would only add a marginal amount of extra distance to the transfer, which with this sort of thrust should be handled by a few extra hours of acceleration. If you were to fully double the distance the vehicle would have to travel, you'd only add about 20 hours to the travel time.

I see what you mean. 

How do you plan to provide 1g thrust for ~15hrs in KSP? 

[SpacedInvader]

3 minutes ago, DrunkenKerbalnaut said:

I see what you mean. 

How do you plan to provide 1g thrust for ~15hrs in KSP? 

The only way would be to use something from one of the advanced tech mods like KSP Interstellar, though I've got no experience with those mods at all. Another option to simulate the same thing would be to use much higher than 1g acceleration (something I know some of those engines are capable of with large ships) for less than 15hrs and then fast forward to an opposing deceleration point to reverse the process.

Edited January 22, 2017 by SpacedInvader

[DrunkenKerbalnaut]

9 minutes ago, SpacedInvader said:

The only way would be to use something from one of the advanced tech mods like KSP Interstellar, though I've got no experience with those mods at all.

I don't have any experience with the mod, outside Manley vids, but you might have an issue with TWR. The highest ISP I see on the mod release page 

Is the DAEDALUS engine, @ 1,000,000 ISP.   but only 600kn for it's considerable 72t mass. Maybe I'm missing something, though. 

EDIT: you need a ram scoop haha. 

Edited January 22, 2017 by DrunkenKerbalnaut

[SpacedInvader]

1 minute ago, DrunkenKerbalnaut said:

I don't have any experience with the mod, outside Manley vids, but you might have an issue with TWR. The highest ISP I see on the mod release page 

Is the DAEDALUS engine, @ 1,000,000 ISP.   but only 600kn for it's considerable 72t mass. Maybe I'm missing something, though. 

 

Was actually thinking of the D-T Vista with its insane amount of thrust and respectable ISP.