How do I get more delta v without expanding outwards?

[Voyageur]

Just crafted a simple 3-stage rocket that gets my comm-sat payloads to Duna, and I've still got a whole bunch of leftover Delta-V. So if I was feeling really frugal, I could probably strip some of the fuel tanks I've got on the upper stage but I like having the extra margin for error. It's all about efficient flying my man. 

[Kryxal]

2 hours ago, TDplay said:

Yes, with 10k dV I could probably brute force it out to Duna (no gravity assists, I usually use Mun as a cheap way to escape Kerbin)

Never mind no gravity assists, that would get you there playing fast and loose with transfer windows!

[HebaruSan]

I strongly suspect that @skendzie figured out the answer to this question in the nearly 4 years since it was asked, plus many more.

[The_Rocketeer]

I think dV is confusing because change-in-velocity isn't a very meaningful term to our Earth-bound experience. It isn't a distance you can cover or a speed you can reach, but just an amount of powered (thrust) accelerating you can do. We're wired to think of dV like it's the same as the distance a car can drive on a full tank, but the thing is we forget that the distance the car can go is not only determined by its fuel efficiency or size of its fuel tank, but also by the parameters of the environment of the surface of Earth, where the effect of resisting gravity is (nearly) nulled out by rolling along the surface, and where (barring wind) atmospheric drag is very consistently correlated to the vehicle's speed, but doesn't otherwise change very much.

Take the same vehicle and put it on Mars and (assuming it could still run without an oxygen-rich atmosphere) you would discover it would go much further on the same tank of fuel. This isn't because it's gained dV, but because driving on Mars uses less dV per mile. This is mostly down to reductions in atmospheric drag, but also partly down to lower gravity reducing bearing friction etc. Now take the car and put it on the moon, and (again assuming it didn't need oxygen) it would go even further, because now there is effectively no atmospheric resistance, and even lower gravity-related friction. Again, the car hasn't gained any dV just because there's no atmosphere, it's just capable of going further with the same amount. Importantly tho, the car still doesn't really use very much of the fuel to resist gravity in the way that a manoeuvre in space does, because it's still just rolling along the ground. What is useful, though, is that the lower gravity of Mars or the moon shows us what it would be like to drive along a surface at a higher altitude 'on Earth' if one existed - in other words, by being higher, we can go further on the same fuel.

This is as true, and even more important, for a rocket moving against gravity and much greater variance of altitude than a vehicle bumbling over a few hills. It means that the dV used to get up the first meter post launch could come from the same amount of fuel as it takes to climb the last several million meters as your trajectory approaches the altitude of a planned rendezvous.

Edited March 4, 2017 by The_Rocketeer

[eddiew]

Necrophilia abounds...

(Indeed I believe the the dV to LKO was higher when this thread was started )

[GoSlash27]

Quick 'n dirty design for 1t payload and stock parts:

T3 stage: 1 Ant, 6x FL-T100.         2,840 m/sec @ .47g
T2 stage: 1 NERV, 2xMk.1.           3,090 m/sec @ .5g
T1 stage: 1 Poodle, 8xX200-8.       3,400 m/sec @ .5g
OTS      : 1 Skipper, 9xX200-8.      1,420 m/sec @ .7g
Boost    : 1 Mammoth, 8xS3-3600. 2,120 m/sec @ 1.4g

This is enough DV to impact the sun or escape the solar system entirely.

Best,
-Slashy


 

15 minutes ago, HebaruSan said:

I strongly suspect that @skendzie figured out the answer to this question in the nearly 4 years since it was asked, plus many more.

I hate when this happens. There's got to be a more effective way to signal people that they're commenting in a necro thread...

Best,
-Slashy

[Captain Vlad]

Eh, necromancy isn't so bad.  I found some of this useful.

[Tex_NL]

2 hours ago, GoSlash27 said:

I hate when this happens. There's got to be a more effective way to signal people that they're commenting in a necro thread...

Well at least nowadays there is a line mentioning a thread is 'rather old'. Obviously this is still not enough. Instead it should be A BIG BOLD OBNOXIOUS POP-UP slamming you in the face.
Unfortunately this still won't stop the second person from replying. Since the thread is 'alive' again he won't get the reminder.

Another possible option would be to auto-report a necro thread as soon as it gets revived so it will alert a moderator to take action if required.

Edited March 4, 2017 by Tex_NL

[Vanamonde]

Okay, so it's an old thread. Calm down, guys. 

[Loren Pechtel]

On 5/2/2013 at 11:29 PM, sadron said:

I feel stupid, because I don't completely understand the concept of Delta-V and how to efficiently construct my rockets and other things to plan for. Anyone have a "KSP Delta-V for Dummies" guide or something that can open up the synapses in my brain to let me understand the mathematics behind this stuff?

Delta-V, sometimes expressed as Δv (the Greek letter delta) is how much velocity change your rocket is capable of.  With a car you measure miles per gallon because the fuel weight is basically unimportant.  Your first gallon of gas and your last gallon of gas give basically the same performance.  With a rocket, though, the fuel weight is very important, as is the weight of engines and fuel tanks you discard on the way.  Thus we are forced to use the far more complex Δv way of measuring how far we can go.  You can either do some messy math to figure it out or you can use one of the mods (MechJeb, KER etc) that can figure it out for you.

Now take a map that shows the requirements: http://wiki.kerbalspaceprogram.com/wiki/Cheat_sheet#Maps and you can figure out what it will take to get a rocket somewhere.  Follow the lines, adding up all numbers that lack arrows and you'll know the minimum fuel for a mission.  So long as your craft can survive the fire numbers with arrows need only a small amount of fuel. 

Note that going sideways on this chart will greatly overstate the fuel:  Look at Mun -> Minmus.  580 to launch, 310 to the SOI and on the Minmus side 160 to low orbit, 180 to land.  These costs are incurred entirely within their own SOIs and are accurate.  However, going between them we have 860 and 930.  That would imply a big detour to low Kerbin orbit.  In practice the required burn is no more than a few hundred m/s.  While I have never flown the path I would expect to do it for something like 1500 m/s.

Note, also, that the price to add Δv to a rocket is exponential, not linear.  That's why NASA will jump through more hoops than you would find at a circus in order to save a little bit of Δv.  Getting 10k in Δv out of chemical rockets is going to take a pretty impressive bird.  If you actually need to go that far you need to look at the Nerva engine.  (Note that you will find this a pain to use unless you install a fuel tank switching mod as the game lacks decent fuel-only tanks for spacecraft.)  I've got one on my screen as I write this, it launched with nearly 15,000 m/s.  I used the engine to capture at Eve and spent a few hours with thoughts of being an airplane in the very upper atmosphere of Eve, I'm now in a fairly low orbit and still have almost half my Δv remaining.  Once I've gathered as much science as I can I'm going to head over to Gilly and grab science and then go home  I hope the guy in the external command seat (gathering EVA reports) hasn't gone star-crazy by the time I head for home!

[Kryxal]

In fact, your burn from Mun to Minmus will take less delta-v than you have listed, as will your Minmus capture burn.  You'll probably want a plane change in the middle, but that's no big deal in this case, maybe 20-30 m/s at most.