Optimal Delta V in orbit

[Jestersage]

Okay, we have the delta V map from one place to another. But what the the optimal delta V when staying within a SoI, such as "only working in Kerbin orbit" and etc?

[Zeiss Ikon]

Still depends on what you're planning to do in orbit.  If all you want is a Gagarin or Glenn mission, you need enough dV to deorbit when done (if you're just launching a Sputnik or Vanguard, zero is the correct dV to reserve).

For anything else, look at the subway map, and add an appropriate figure for on-orbit maneuvers that might be needed at either end (which will often depend on your level of skill and experience; I recently made three different rendezvous in LKO for under 300 m/s total -- six months ago, that would likely have required three times that dV or more).

Generally, every time you change your orbit it costs you some dV, and if you raise or lower your apoapsis, then circularize, the second maneuver will cost nearly the same as the first.  Change plane, you spend some dV (and the faster your orbit when you do it, the more you'll spend per degree of change).  In the end, unless you want to leave your spacecraft as orbiting junk when you're done, you'll need to reserve enough dV to bring your Pe down in to the atmosphere (and then follow your craft down to burn-up or crash, else it'll just continue to orbit even with a 10 km Pe).

[Gargamel]

I recently discovered, the hard way, that going to repair my telescope at 5500km takes as much (or more) fuel as going to the Mun.    Once you leave LKO, the fuel costs go up significantly. 

[Lisias]

41 minutes ago, Gargamel said:

I recently discovered, the hard way, that going to repair my telescope at 5500km takes as much (or more) fuel as going to the Mun.

It makes sense... When going to Mun, Mun's gravity well helps a lot.

[Jestersage]

As a sidenote, What is the optimal amount of monoprop for docking/rendezvous?

[Gargamel]

21 minutes ago, Jestersage said:

As a sidenote, What is the optimal amount of monoprop for docking/rendezvous?

I'd really think that is a "that depends" answer.  If you have a huge ship, it's gonna take a lot of MP to maneuver that behemoth.  If you are really really skilled, I'd think a rendezvous and docking is possible with no MP at all on a small, reactive ship, all main engine use.   So I guess it depends on mission requirements and personal play style.

[Jestersage]

Oops. Let's be more specific. The total DeltaV for RCS according to KER -- what would be consider optimal?

Say an Orion style mission; for both its Moon (Mun) and Mars (Duna mission), it seems to be the main shuttle, so have to do the intialization for all the docking...

[bewing]

5 hours ago, Jestersage said:

As a sidenote, What is the optimal amount of monoprop for docking/rendezvous?

Zero. Get rid of all those silly/heavy/draggy/useless thrusters.

 

[Zeiss Ikon]

I think @bewing's point is that, especially with a small, easily rotated ship, it's quite possible to dock without RCS.  I haven't done it, but I've seen video of the feat.

[Jestersage]

On 5/10/2018 at 4:32 PM, Zeiss Ikon said:

I think @bewing's point is that, especially with a small, easily rotated ship, it's quite possible to dock without RCS.  I haven't done it, but I've seen video of the feat.

Agree. I am testing my Orion clone, which "only" have 120 Monoprop. Yet so far for EOR docking to the Orion, it seems fine.

However, unlike in the past, I did install a docking indicator.

[NSEP]

The optimal amount for a rendezvous is 120m/s, on a direct path to your destination. 30m/s for raising your orbit and 30m/s for slowing down. I recommend an extra 60m/s for docking.

But that number may very likely vary, it really depends on the size and path of the orbit, and your docking skills.

[AVaughan]

@NSEP  That depends at least a bit on player skill, and a lot on patience.  Other requirements, like max time in orbit because of a life support mod, can also be a factor.  (And all of this assumes you have managed to launch into the plane of your target.  If you need to do a plane change then the cost of that is extra).   With enough time in orbit, then yes a small increase/decrease in apoapsis/periapsis will allow rendezvous, but depending on the phase angle separating the vessels, it might take a lot of orbits.  Often it is easier to just use a design with 800 or so excess dV, and increase apoapsis enough to force a rendezvous in an orbit or two.

 

The amount of monoprop/dV you need for docking depends a lot on your experience with docking and your patience.  (A slow approach at 0.1m/s tends to require less monoprop for corrections than a faster/less patient approach at 1 m/s).   I find the Docking Port Alignment Indicator mod to be very useful.  With it I can often dock 20 ton ships using 5 monoprop, or 5 ton landers with 2.5 monoprop.  Without it I use much more.

A tip I find useful is to set your rcs to just translation, thrust limit your rcs thrusters and use fine controls, and let your reaction wheels control rotation.  Having rcs centered around your CoM is also useful, but not required if you have enough reaction wheels and limit rcs to just translation.

Edited May 13, 2018 by AVaughan