[ANSWERED] How to Execute Extremely Long Burns

[KerikBalm]

48 minutes ago, Plusck said:

But maybe I should have added an "indeed".

...

The second problem is you're totally ignoring the fact that with an ultra-low TWR, it is pointless getting into an orbit where you have 10 minutes max to do your burn at Oberth-effect speeds.

And that figure of 4131 m/s is the OP's ship. And you should know, without even thinking about it, that that 3800 m/s burn is impossibly large for Jool.

Perhaps I misinterpreted, but since your statement was proceeded by a "not quite", I interpreted it as pretty much an opposite of agreeing with an "indeed"

As to the 2nd part, I am not "totally ignoring the fact that with an ultra-low TWR,"

 

On 4/5/2016 at 4:32 PM, KerikBalm said:

Now you can easily throw away half the fuel(even more than half, because dV does not scale linearly with fuel amount, although linear approximations work for small dV values... 4100 vs 1800 is not small) on your transfer stage for a much better TWR

...

you could also add more engines, as you can afford the extra mass* because you've reduced the dV requirement.

If its too late and you've already attached the under powered overfueled transfer stage, ...

still not great at all... but what do you expect when you design a ship with barely better than a half meter per second burn time, knowing you'll need burns in the thousands of m/s?

You can perapsis kick the first burn to get your apoapsis past minmus, and your second burn will only need to be about 1050...

*I hope you interpreted this as extra mass due to more/bigger engines

Maybe I was too optimistic about when to start burning, but I do point out that if its too late to change his transfer stage, his current one has plenty of dV...

13 hours ago, KerikBalm said:

Yes, the acceleration is still horrible, and while the final burn only needs to be 1350*, the time to execute it is much worse. Considering he could have dV out the wazoo, he could start say... 7.5 minutes ahead of the node instead of 15 minutes, and take the penalty on the burn after the node... burning more to make up for it.

* as I pointed out in another post, an additional PE kick can reduce this 1350 to 1050, so thats a little error

10 minutes to do your burn at "Oberth effect speeds" is better than nothing, and I acknowledge that he won't be able to get close to optimum with that acceleration (again, assuming its too late to change the transfer stage), hence the phrase "take the penalty"... but his design for that acceleration also comes with a lot of excess dV. Total burn time, even taking into the burning done farther from PE, is still going to be much shorter.

I think my posts have made it clear that his acceleration is too low ("what do you expect when you design a ship with barely better than a half meter per second burn time, knowing you'll need burns in the thousands of m/s")...  I'm just trying to tell him a better way to do it.... more thrust, less fuel if he can change the transfer stage. If He can't change the transfer stage, the bi-ecliptic transfer is still going to be better, getting him there with less burning and more dV to spare.

I hope next time he remembers to plan for burns at PE that require less total dV but more TWR (Its why I use chemical ejectors for the final burn... and sometimes everything if I'm a bit impatient and don't want to do the PE kicking on nukes/do PE kicking past minmus/do PE kicking at all)

Edited April 7, 2016 by KerikBalm

[March Unto Torment]

4 minutes ago, KerikBalm said:

I hope next time he remembers to plan for burns at PE that require less total dV but more TWR (Its why I use chemical ejectors for the final burn... and sometimes everything if I'm a bit impatient and don't want to do the PE kicking on nukes/do PE kicking past minmus/do PE kicking at all)

Transfer stage is still in the design phase, so nothing's set in stone yet.

[KerikBalm]

42 minutes ago, Plusck said:

only actually enter Tylo orbit just before you want to leave the system (since burning to Kerbin from Tylo is much more efficient than burning from Tylo orbit out to Jool orbit then from there to Kerbin, for exactly the same reasons as you don't want to burn out to Kerbin SOI edge and then burn to Jool in the first place).

Oberth from burning near tylo orbit is pretty good, but isn't it better to drop PE down to just above Jool's atmosphere? IIRC, you'll be going about 10km/s at PE... If your last visit was Pol, and you just want to get back to kerbin, its certainly better to just drop PE down to Jool, rather than going to tylo. It may even work for departing from tylo.... oberth effect from a PE low over jool is pretty great I imagine... I haven't looked at the numbers yet though

Going to tylo first allows you to ditch a heavy tylo lander (assuming you plan on landing on all moons, or don't split your mission upon entering the jool system)

6 minutes ago, March Unto Torment said:

Transfer stage is still in the design phase, so nothing's set in stone yet.

based on the fuel fractions and burn times you listed, I'm guessing you're using nukes for the transfer.... less than one nuke per hundred tons.

Doubling the number of nukes will approximately double the acceleration...bringing the final 30 min burn down to a 15 minute burn, which is quite feasible. Assuming a 100 ton station with 1 nuke, if you replace the 1 nuke with a quad couple of 4 nukes, your final burn is now a mere 7.5 minutes, start burning 3 min 45s before the node, and you'll be fine. You'll have only increased the dry mass by 9 tons... not that much on a 100 ton station, and probably about 90 tons of fuel(assuming you don't change the tanks to smaller tanks because you need less dV)... making your wet mass somewhere around 250 tons (adding in engines, transfer stage fuel tank dry mass, etc etc) vs 240 tons with only 1 nuke

I don't know if this is sandbox or career, and how good you are at getting stuff to orbit cheap (sometimes I use those big KR-2L things because a) I can lift large payloads at 200 funds per ton (or less), b) I use ISRU to refuel them at no cost. Adding a few chemical rockets to help the acceleration, even if they only burn for a couple minutes, can reduce the burn time further.  As its a former station, you may have a problem like I had with wobble, limiting your top acceleration.... still 5m/s/s is way better than 0.5 m/s/s

Edited April 7, 2016 by KerikBalm

[March Unto Torment]

13 minutes ago, KerikBalm said:

Doubling the number of nukes will approximately double the acceleration...bringing the final 30 min burn down to a 15 minute burn, which is quite feasible

Doubling the number of nukes would be... difficult, to say the least. My craft is at the point where I basically can't fit any more nukes onto it. Hell, I probably have so many nukes mounted that the weight of the propulsion units alone outweighs the total tonnage of most Jool-5 missions.

Anyway, my mission profile involves parking my mothership, then splitting up the mission; each lander is taken out by a tug, lands, and then is returned to the mothership by the tug, which is then refuelled. After my entire Kerbal team is back at the ship, a secondary propulsion unit with about 4,000m/s of dV is broken off and returns to Kerbin, leaving the mothership in orbit to function as a space station. So where I park the mothership is mostly about which location will cost me the least in dV terms to travel back and forth from.

Edited April 7, 2016 by March Unto Torment

[Plusck]

40 minutes ago, KerikBalm said:

Perhaps I misinterpreted, but since your statement was proceeded by a "not quite", I interpreted it as pretty much an opposite of agreeing with an "indeed"

As to the 2nd part, I am not "totally ignoring the fact that with an ultra-low TWR,"

 

*I hope you interpreted this as extra mass due to more/bigger engines

Maybe I was too optimistic about when to start burning, but I do point out that if its too late to change his transfer stage, his current one has plenty of dV...

* as I pointed out in another post, an additional PE kick can reduce this 1350 to 1050, so thats a little error

10 minutes to do your burn at "Oberth effect speeds" is better than nothing, and I acknowledge that he won't be able to get close to optimum with that acceleration (again, assuming its too late to change the transfer stage), hence the phrase "take the penalty"... but his design for that acceleration also comes with a lot of excess dV. Total burn time, even taking into the burning done farther from PE, is still going to be much shorter.

I think my posts have made it clear that his acceleration is too low ("what do you expect when you design a ship with barely better than a half meter per second burn time, knowing you'll need burns in the thousands of m/s")...  I'm just trying to tell him a better way to do it.... more thrust, less fuel if he can change the transfer stage. If He can't change the transfer stage, the bi-ecliptic transfer is still going to be better, getting him there with less burning and more dV to spare.

I hope next time he remembers to plan for burns at PE that require less total dV but more TWR (Its why I use chemical ejectors for the final burn... and sometimes everything if I'm a bit impatient and don't want to do the PE kicking on nukes/do PE kicking past minmus/do PE kicking at all)

"Not quite": as in,

• yes lowering your Pe to burn at the bottom of a  70kmx3400km orbit can actually save fuel, but
• no, no and no again for the OP, because this maneuvre would be a complete waste of time, effort and fuel, would be impossible to do properly with OP's huge ship, and would very probably be wildly off target by the end of the burn.

So I wasn't disagreeing with the 1800 m/s total cost, I was disageeing with the rest of your suggestions which are unworkable, or directly contrary to what OP has said about the possibility of vastly increasing TWR.

 

And again, here: "10 minutes to do your burn at "Oberth effect speeds" is better than nothing". No, no and no again here. In theory that might be true, if you're planning to burn for a little more than 10 minutes. But if you're burning for far longer than that, your benefit from Oberth effect is going to number in tens of m/s, and the rest of the time your burn is going to be exactly what it would have been at those higher altitudes anyway. Remember, the maximum Oberth-effect benefit to get that 1350m/s burn is only at Pe, it is significantly less at any other time.

Take the OP's ship: if it takes 1h50m (110 minutes) to burn for 4000 m/s, that 450m/s burn down to Pe is going to take 12 minutes to start with. If it then starts burning for Jool at -5mins to Pe, then over the next ten minutes it'll accelerate for 360 m/s but only a certain percentage of that will reduce the counter (let's be generous and say 90%). So counter down by 330 m/s (amount spent: 450+360=810m/s; amount gained = 330/1350 = 25% of total burn to Jool). Now over the next 20 minutes the ship can accelerate by 720 m/s. Let's say that there is still some benefit from being lower than KEO, so if we'd started at the present alitude, it would have cost midway between 1350 and 2100, so 1725 m/s to go to Jool (total amount spent: 450+360+720=1530m/s; amount gained = 25% + (720/1725) = 25+42% = 67%). Now, however, we're back at something close to KEO, so we need to do that last 33% as if we'd started in KEO in the first place: 33%*2100=690 m/s. Total dv expenditure = 450+360+720+690 = 2220 m/s.

So those 10 minutes at greater efficiency are "better than nothing", but not if you have to make any significant expenditure to get them.

Of course the figures above are all approximations, but if anything I'm sure they are conservative. You simply cannot benefit from a highly eccentric orbit if you have a very low TWR. I'm sure that what you are proposing would end up more expensive than simply burning from KEO. I'm absolutely certain that it would severely complicate the whole process and multiply the inaccuracy of the burn.

[KerikBalm]

How big is this thing?

If its getting about 0.55 m/s/s, that's about 1 nuke per 110 tons.... if you had a quad of nukes, that means your mission is 440 tons...

Going from 4 to 8 nukes wouldn't be too hard... heck, even 8 to 16 nukes wouldn't be so hard... but at that point that means your craft is 880 tons how big is this thing?!

Are you excluding the use of ISRU in your career?

Don't be afraid to use some radially attached tanks to add extra places to mount LV-Ns

 

Plusk... the ship will be benefitting from oberth until its moving slower than it was at KEO... its going to be doing that for a long time, much more than the 30 minutes required to do the burn

Edited April 7, 2016 by KerikBalm

[March Unto Torment]

2 hours ago, KerikBalm said:

Going from 4 to 8 nukes wouldn't be too hard... heck, even 8 to 16 nukes wouldn't be so hard... but at that point that means your craft is 880 tons how big is this thing?!

More than 880 tonnes. A lot more. I haven't counted the total number of nukes, but, uh... yeah. This thing is mind-blowingly huge. Let's leave it at that.

And I've got ISRU on hand, but given the scale of this thing, mining enough ore at Jool to be useful is... impractical. Given any kind of sane timeframe, anyhow. I may end up using Minmus ore to help fuel it, though, once the transfer stage is docked (I feel that Minmus mining would be more practical than trying to lift insane amounts of LF into orbit).

(Before anyone asks me if I can downsize, the entire point is to see if I can pull off the highest-tonnage Jool-5 mission in history. But shhhhhh, that's a secret )

[Plusck]

1 hour ago, KerikBalm said:

Oberth from burning near tylo orbit is pretty good, but isn't it better to drop PE down to just above Jool's atmosphere? IIRC, you'll be going about 10km/s at PE... If your last visit was Pol, and you just want to get back to kerbin, its certainly better to just drop PE down to Jool, rather than going to tylo. It may even work for departing from tylo.... oberth effect from a PE low over jool is pretty great I imagine... I haven't looked at the numbers yet though

Going to tylo first allows you to ditch a heavy tylo lander (assuming you plan on landing on all moons, or don't split your mission upon entering the jool system)

Yes, it all depends on how much is being carried from one place to the next.

The reason I suggest going to Tylo last is because to get down to a low orbit on Tylo is quite expensive, to start with. Therefore you have an incompressible expense to get there, and another incompressible expense to leave. If you combine leaving Tylo with going back to Kerbin, you make all the same Oberth-effect gains we've been talking about here (re Kerbin) and can escape Jool relatively cheaply.

However, if the Tylo mission is, as you say, a heavy lander with a light re-orbiting craft , and if nothing else needs to go to Tylo to support it, then yes, by all means do that first.

 

7 minutes ago, KerikBalm said:

Plusk... the ship will be benefitting from oberth until its moving slower than it was at KEO... its going to be doing that for a long time, much more than the 30 minutes required to do the burn

Again, I don't think you're taking the dynamics of the situation into account. That increased velocity happens at all stages for any choice of strategy. The big difference is how much that changes as you start climbing out of the gravity well. 30 minutes after you start burning from 75x3400 Pe, you're back at KEO altitude, and because your orbit is highly eliptic, Kerbin's gravity is having a much greater effect in slowing you down.

I'm sure you know from experience that your burn counter starts slowing down enormously on a long burn, as you are climbing away from the planet.

So I decided to check. Put a satellite in KEO, and added successive burns of 360 m/s every ten minutes. With exactly six burns (2160 m/s) I intersected Jool's orbit.

Then reconfigured it for a 75x3400 orbit, first burn on Pe and then every 10 minutes: 5 burns total, 4x360 and 1x297 m/s= 1737 m/s to reach Jool.

So my original figures were actually pretty close: total cost of burn from KEO: 2160 m/s; Total cost by dropping to 75km Pe: 1737+450=2187 m/s.

[March Unto Torment]

11 minutes ago, Plusck said:

So I decided to check. Put a satellite in KEO, and added successive burns of 360 m/s every ten minutes. With exactly six burns (2160 m/s) I intersected Jool's orbit.

Then reconfigured it for a 75x3400 orbit, first burn on Pe and then every 10 minutes: 5 burns total, 4x360 and 1x297 m/s= 1737 m/s to reach Jool.

So my original figures were actually pretty close: total cost of burn from KEO: 2160 m/s; Total cost by dropping to 75km Pe: 1737+450=2187 m/s.

Huh, interesting. Thanks for testing this!

So, looks like they're roughly equal in terms of dV expenditure. However, I'll probably stick with the KEO burn, mostly because it means I can afford longer burns (I can split my main burn into a handful of larger burns instead of requiring numerous smaller burns) without losing too much precision.

Also, some alterations to mission objective and profile (long story) mean that I now need to park my mothership in a Laythe orbit. Which means that - ironically - I'm stuck with my original 4,130m/s stage, which has (allowing for some light modifications to pack on some extra fuel) just around enough dV to make the transfer, followed by a transition to Laythe orbit.

Does anyone know a more efficient method of getting into Laythe orbit? Swash's dV map is giving me 2,000m/s to transfer from Jool capture to Low Laythe Orbit, but I suspect that I can probably take some of that out with a gravity assist of some description.

Edited April 7, 2016 by March Unto Torment

[Plusck]

9 minutes ago, March Unto Torment said:

Also, some alterations to mission objective and profile (long story) mean that I now need to park my mothership in a Laythe orbit. Which means that - ironically - I'm stuck with my original 4,130m/s stage, which has (allowing for some light modifications to pack on some extra fuel) just around enough dV to make the transfer, followed by a transition to Laythe orbit.

Does anyone know a more efficient method of getting into Laythe orbit? Swash's dV map is giving me 2,000m/s to transfer from Jool capture to Low Laythe Orbit, but I suspect that I can probably take some of that out with a gravity assist of some description.

Do two passes - the first pass as a gravity assist.

The gravity assist pass from interplanetary speeds, passing Laythe just above the atmosphere, will put you into a sub-Laythe/Vall orbit. When you arrive at Pe by Jool, a retrograde burn of a hundred or so m/s (IIRC) will give a Laythe intercept one orbit later. When you arrive the second time, it'll cost very little to get into orbit around it.

Edited April 7, 2016 by Plusck

[KerikBalm]

The mission I'm doing now, I'm aiming for a laythe gravity assist to capture into Jool orbit, while simultaneously doing a laythe aerobrake.

You can use laythe to just barely grav capture with an Ap past pol, or with an Ap around Val, and aeorbrake at laythe will essentially make the resulting orbit more circular than it otherwise would have been, from there I plan to do small maeuvers to arrange for a 2nd laythe encounter with a lower perapsis for more aerobraking (taking into account the now lower velocity)... keeping in mind the relative velocity can't really get lower than about 3 km/s (roughly laythe escape velocity).

I'm guessing that the new inflatable heat shield will make me strongly favor pure laythe aerocapture, like I did before 1.0 came out.

Maybe I was wrong about KEO... I have only bothered to do a keosynchronous orbit a few times, and I'm a bit fuzzy on how high it is relative to say... Mun orbit...

The thing about a lot of these sort of things, is it doesn't really matter so much. Departing from LKO to duna vs departing from solar orbit (ina similar orbit to kerbin) takes about the same dV (making the dV you spent to get to solar orbit just a waste)... here much of the dV used to get to KEO goes to waste. You can get it back with a bi-elliptic transfer... but it seems you lack the TWR for such a transfer...

I still think it would be better that way because the test he did approximates 0.5 m/s/s, when your acceleration is about 10% higher.

Also he does all the burning at PE or after, ignoring you can feasibly get in 5-7 minutes of burning before PE in there (but in such a case, you don't neccessarily just follow the maneuver node, but somewhere between the node and prograde, I find picking a path that maintains the same PE to be a good compromise).

Also, for roughly 2100 m/s of dV with 800 Isp, your mass ratio will be about 1.32:1  meaning your end TWR will be roughly 32% higher

so 1.32* 1.1 (because he's getting about 0.55m/s, not 0.5)... ending acceleration should be 45% higher - about a whopping 0.7 m/s/s

My guess is that when these are taken into account, the bi eliptic transfer will win... but I guess the margins are small, and its simpler to do the transfer direct from KEO

March Unto Torment - curiosity has bit me... what is the part count on that station? what is the mass? are you running 1.1 pre-release which handles large ships better?

Edited April 7, 2016 by KerikBalm

[wumpus]

After reading this thread, the only thing I can be pretty sure about:  Once you leave kerbin's SOL, recompute your maneuver node.  Your KEO maneuver node won't begin to handle an hour of thrust, while one in Kerbol should.  This also lets you correct your mistakes early, where they cost the least to fix.

What I'm not at all sure about:  I'd think it would make sense to loop around Mun to get a hyperbolic escape trajectory (with multiple maneuver nodes repeatedly calculated), but most of that is to try to get the "circularization" delta-v back from the KEO orbit (it should be close to 400m/s) and very little from the Obereth effect.  Trying to match windows that allow a "loop around Mun" and "Jool transfer window" to match up is likely not worth it.

[March Unto Torment]

So, I think I've settled on the final transfer stage design. It's got a hair over 3,000m/s of dV (since I've broken it up into multiple pieces for the purposes of getting it into KEO, I don't have exact numbers). It's also only about 200 parts total, which is nice, and should keep my final part count at around 1,600.

@KerikBalm: I'm not willing to disclose mass - it's a surprise!  - but its part count is sitting on 900 right now, and I have yet to attach my refinery (80 parts), my four landers (around 75 parts each), my tug (50 parts) or my return and transfer stages (100 and 200 parts, respectively). I'm not playing  the 1.1 prerelease - hence, docking is currently a nightmare, due to my abysmal framerate - but I won't be starting the mission until the full release is out and all my mods (most importantly Near Future Construction) are updated, since 1.1 apparently features massive performance boosts (and I'm already in a good place for performance, seeing as I'm running an i5 4440).

EDIT: Did my numbers wrong; I've got 3,415m/s dV total. So, the question becomes - is that enough to get me from KEO to Low Laythe Orbit? That is, without requiring aerobraking or excessive numbers of difficult gravity assists, which (due to the sheer bulk of the ship in question) are difficult in the case of the latter and straight-up impossible in the former.

Edited April 8, 2016 by March Unto Torment

[Plusck]

2 hours ago, March Unto Torment said:

EDIT: Did my numbers wrong; I've got 3,415m/s dV total. So, the question becomes - is that enough to get me from KEO to Low Laythe Orbit? That is, without requiring aerobraking or excessive numbers of difficult gravity assists, which (due to the sheer bulk of the ship in question) are difficult in the case of the latter and straight-up impossible in the former.

That should be plenty enough. 2100m/s escape burn plus 50-150 m/s mid-transfer course correction should be all you need to get into a (dangerous) low-ish orbit, with Pe halfway between Laythe and Jool, and Ap just slightly above Vall's orbit. I just did this for a Laythe landing, but I can't remember what the subsequent burns were:

1. at Pe near Jool to get a Laythe capture the next time around - can't remember but I think it was low hundreds, maybe even less
2. at 60km or so above Laythe to turn that second flyby into capture - again, can't remember exactly but it was very low - maybe 50 m/s
3. again at around 60km to turn that orbit into a circular one - this is the most expensive part of the process (and makes me wonder whether you really want to put your mothership in low Laythe orbit: 590 m/s (you should take a look at the excellent Jool Delta-V Map for better details for the Jool system).

So that gives, say 2400 m/s (pessimistically) for all you need to do to get that first Laythe gravity assist, then maybe 900 m/s (again, somewhat pessimistic) to arrange Laythe capture and circulairsation.

Happily, it's the final circularisation that will be the most expensive bit at the end there - so you can choose to save some of that by not fully circularising in low orbit. Again, it's that cost of circularising at Laythe that makes me wonder whether it really is the best place to put your mothership...

For the burn from KEO outwards, I would highly recommend plotting it using the method I described earlier and which I used for comparison purposes, so I know that it works and is easy and accurate, and guarantees the best efficiency for the burn:

• plot a single burn to start with to get a Jool intercept. It should be about 2100 m/s. Note how long it will take (you may have to fire your engines for a second to get the numbers to show);
• drop a new maneuvre node that is more-or-less exactly this much time after the ejection burn, plus a couple of minutes of margin to be safe. Give it a certain prograde amount just to register. If all goes well, this will end up being the last of the series of burns you need to make to get to Jool;
• delete the first node, and correct the other one to give about 10 minutes of burn;
• now create a new node exactly 10 minutes before that final burn, give it 10 minutes' worth of burn;
• repeat, going 10 minutes earlier each time (and if ever it isn't quite 10 minutes earlier, make the burn for slightly less than 10 minutes...) until you get a Jool capture
• with 0.55m/s² acceleraton, you should have 6 burns plotted;
• check your ejection angle: since you gave a few minutes' margin at the end, it should be almost exactly the angle of the original single burn. If it isn't:

1. if the angle is too radially in with respect to the sun, reduce the amount of the first burn and increase the amount of the final one;
2. if too radially out, add another burn 10 minutes earlier and reduce or delete the last one

When you actually do the burns, each one should be exactly prograde (or close enough to make no difference), which is the most efficient. By plotting a series of prograde burns, you eliminate the error that creeps in to any long burn - both in ejection angle and in the actual fuel cost of the burn because of the off-prograde angle.

In fact, if your nodes have been accurately spaced 10 minutes apart with exactly 10 minutes of burn each time (and assuming that your TWR will not change much from start to finish) you could even forget about the nodes altogether: block off fuel tanks so that you have exactly the right total amount of fuel available for 2100 m/s (or whatever it is), have SAS align to prograde, start burning a couple of minutes before the first burn then go watch a movie. ; )

The only real concern I have is about running LV-Ns for an hour: I hope you have sufficient cooling because otherwise you might have to make breaks in the middle of the burn.

 

[March Unto Torment]

1 hour ago, Plusck said:

The only real concern I have is about running LV-Ns for an hour: I hope you have sufficient cooling because otherwise you might have to make breaks in the middle of the burn.

I've got six of the largest radiators possible, split between 80 LV-Ns; I'm not sure that it's enough, but combined with the sheer mass of the ship, it should be enough to keep me below critical temperature just long enough. Unfortunately, reliable information regarding LV-N heating is hard to come by.

Anyway, it sounds like I have just about enough dV to complete the Laythe capture; I may run a little short on Laythe circularisation, but if that's the case, I can fix that up post-mission by shipping out a few (dozen :P) tonnes of spare LF, since a non-circular Laythe orbit doesn't interfere with my mission profile much.

And I like your suggestion of letting things run themselves - I might just do that It'll save me some hassle, certainly. I wonder if there's a feature on MechJeb that'll let me tell it to automatically cut engines after a certain time...

[Starhawk]

4 hours ago, March Unto Torment said:

I wonder if there's a feature on MechJeb that'll let me tell it to automatically cut engines after a certain time...

MechJeb has a Utility called 'Prevent overheats' which will throttle the engines back as necessary before they get hot enough to explode.

Happy landings!

[March Unto Torment]

2 minutes ago, Starhawk said:

MechJeb has a Utility called 'Prevent overheats' which will throttle the engines back as necessary before they get hot enough to explode.

Happy landings!

Perfect! That saves me worrying about overheating, at least.

Wondering about other functions, though. Can I tell MechJeb to burn for, say, 30 minutes at full throttle, then cut engines? Or to expend 2,100m/s of dV, then cut?

[Starhawk]

Just now, March Unto Torment said:

Perfect! That saves me worrying about overheating, at least.

Wondering about other functions, though. Can I tell MechJeb to burn for, say, 30 minutes at full throttle, then cut engines? Or to expend 2,100m/s of dV, then cut?

Not as far as I know.  I've only used MJ a little bit, though.

As far as 'expend 2,100m/s of dV, then cut', why not just use a maneuver node and tell MJ to do the burn?  You can then make another node where/whenever for as much as you want and have MJ burn that one.

Or am I missing what you're getting at?

Happy landings!

[March Unto Torment]

13 minutes ago, Starhawk said:

As far as 'expend 2,100m/s of dV, then cut', why not just use a maneuver node and tell MJ to do the burn?  You can then make another node where/whenever for as much as you want and have MJ burn that one.

My problem is that (per the above explanation), I'm using multiple manoeuvre nodes in sequence for greater accuracy. However, if I'm remembering right, there's an 'execute all nodes' function on MJ, which basically solves my problem. I'll check tomorrow if I'm right.

EDIT: Checking the online manual backed me up - the function exists! Which means, once I finish assembly (and fuelling, which will likely consist of six or seven trips to Minmus and back to mine ore) I'll be able to sit back and get around to watching The Right Stuff.

Edited April 8, 2016 by March Unto Torment