Delta-v for Vall ascent?

[Mitchz95]

How much delta-v does it take to get into a low orbit (say 20km) of Vall from the surface? My lander has about 1,500 m/s, not sure if that will be enough for the landing and ascent.

[Pecan]

According to the deltaV maps (google one, they're terrific!) Val needs 860m/s for landing/ascent - so 1,720m/s for both.

[Alchemist]

The orbital velocity itself is about 800 m/s, so your lander definitely is insufficient. About 2 km/s should be enough for landing and ascent (depending on your skill and craft's TWR, of course). Also mind the terrain - it's several km between the mountain ridges and the valleys

[Dkmdlb]

1,500 m/s should... be... enough... to... get... to... orbit.

Landing and getting back? Not so much.

[Mitchz95]

Crap. Well, maybe if I use the transfer stage to slow down most of the way, then push it back to orbit and finish the landing...

Thanks for the responses. If nothing else, I can use the extra fuel to visit the whole Joolean system. I brought a lab with me, so that should come in handy.

[Alymon]

1,500 m/s should... be... enough... to... get... to... orbit.

Landing and getting back? Not so much.

Love the links here. Thanks!

[Captain Sierra]

Thanks Dkmdlb! That last link is the first Joolian system dV map I've ever found and I've been looking quite a while for one.

[XiXLLAMAXiX]

General equation for dv needed to take off from a body and reach a circular orbit of height H above the surface is:

sqrt(G/(R+H))*(1-sqrt(2R/(2R+H)))+sqrt(G/R)*(sqrt(2(H+R)/(2R+H)))+sqrt(G/R)

where G is the gravitational parameter of the body, R is the body's equatorial radius, H is the height you are trying to get to. Assumes no atmosphere, and that you took off from an altitude of 0.

Plugging in the values for Vall, we get that an ascent takes 858.03m/s, thus with a perfect ascent and descent, your lander will need 1716.06m/s. If you want to land and take off to a minimum safe orbit (~8km), that will require 1685m/s, so no matter what, you're going to need to get out and push (the last time I checked, kerbal eva's have 600m/s dv, so your lander might work if all you need is the kerbal in orbit).

Also, note that landings tend to take up a not insignificant amount more dv then they should, because a perfect landing requires a "suicide burn" which are hard to pull off properly, I normally give myself an extra 20% on landings to make up for this (more specifically, 60*(surface gravity)).

[Mitchz95]

I've decided to forgo the Vall landing in favor of a "grand tour" of the system, collecting science from flybys of all the moons, before making a landing on either Bop or Pol.

Or maybe both. I have a fuel tanker entering Jool orbit as we speak; once I rendezvous, I might be able to make an extra stop before heading home.

Here's an awesome screenshot I got during my Laythe flyby:

Edited April 24, 2014 by Mitchz95

[FREEFALL1984]

I tend to use my transfer craft a lot to land on none atmospheric and atmospheric bodies, in fact I've become quite proficient at landing with an FL-T800 and a LV909 or LV-T45 attached to the bottom of my lander, then decoupling and flying a few yards clear before touching down without using more than perhaps 5m/s DV from my actual lander.

[Pecan]

I've decided to forgo the Vall landing in favor of a "grand tour" of the system, collecting science from flybys of all the moons, before making a landing on either Bop or Pol.

Landing/Ascent requirements (both): 'A' indicates atmosphere

Gilly 30 (60)

Pol 130 (260)

Minmus 180 (360)

Bop 220 (440)

Ike 390 (780)

Dres 430 (860)

Mun 580 (1,160)

Eeloo 620 (1,240)

Vall 860 (1,720)

Moho 870 (1,740)

Duna 1,300 (2,600) A

Tylo 2,270 (4,540)

Laythe 3,200 (6,400) A

Eve 12,000 (24,000) A

If you're considering Bop though I assume you haven't looked at any of those deltaV maps yet? There's a 2,440m/s requirement just to change planes from Jool before you can think of landing!

[Mitchz95]

Landing/Ascent requirements (both): 'A' indicates atmosphere

Gilly 30 (60)

Pol 130 (260)

Minmus 180 (360)

Bop 220 (440)

Ike 390 (780)

Dres 430 (860)

Mun 580 (1,160)

Eeloo 620 (1,240)

Vall 860 (1,720)

Moho 870 (1,740)

Duna 1,300 (2,600) A

Tylo 2,270 (4,540)

Laythe 3,200 (6,400) A

Eve 12,000 (24,000) A

If you're considering Bop though I assume you haven't looked at any of those deltaV maps yet? There's a 2,440m/s requirement just to change planes from Jool before you can think of landing!

Thanks for that list. I'm going to use my transfer stage to match inclination and burn into orbit; it has a lot of spare delta-v, and since my refueller just entered Jool orbit I should be able to rendezvous with it no problem. I can use gravity assists as well, if needed.

[NERVAfan]

Minmus 180 (360)

...

Mun 580 (1,160)

Wow, my landings must be pretty sub-optimal...

[Pecan]

Well yes, those are 'best case' figures AFAIK. They are taken from this deltaV map, as are all the others.

While we're at it - "How hard is it to get to and orbit (from Kerbin)?" table:

Mun 1,170

Minmus 1,430

Ike 1,550

Duna 1,700

Eve 2,880

Gilly 2,950

Dres 3,860

Tylo 3,860

Vall 3,890

Pol 4,040

Laythe 4,360 <- Kerbin orbit 4,500m/s "Halfway to anywhere"

Eeloo 4,790

Jool 5,170

Bop 5,920

Moho 6,640

Kerbol 33,680

I use these tables to plan missions within projects, within programmes, within overall space-travel strategy so everything I design and fly fits into an overall structure that progresses 'logically'. Current one is 'exploring the system'; i) SCANSat mapping satellites around Kerbin, ii) manned orbital follow satellites, satellites move on to lunar (Mun & Minmus) mapping, iii) manned lunar landings, interplanetary mapping satellites, iv) launch <-> Kerbin station infrastructure, visit all Kerbin 'anomalies' found by the satellites, v) Kerbin station <-> tractor <-> Mun station <-> landers infrastructure to visit the anomalies there, vi) interplanetary manned.

Next up: RT2 and Kethane-mining (possibly. Not excited about Kethane itself but looking for something that gives an excuse for bases)

Edited April 25, 2014 by Pecan

[NERVAfan]

Wait, why is the Kerbol number so huge? I don't think that can be right... the wiki says "While Kerbol can be reached from Kerbin's orbit by using a Hohmann transfer orbit, doing so requires a ÃŽâ€v of about 8 km/s. The most efficient way to reach Kerbol from Kerbin orbit is to use a bi-elliptic transfer. With a sufficiently-distant apoapsis, the required ÃŽâ€V to "sundive" can be reduced to under 4 km/s at the expense of drastically-increased flight time"

So why is that delta-v map showing 68 km/s?

I've done it with a simple ion probe and there's no way that had THAT much delta-v?

[Alchemist]

Wait, why is the Kerbol number so huge? I don't think that can be right... the wiki says "While Kerbol can be reached from Kerbin's orbit by using a Hohmann transfer orbit, doing so requires a ÃŽâ€v of about 8 km/s. The most efficient way to reach Kerbol from Kerbin orbit is to use a bi-elliptic transfer. With a sufficiently-distant apoapsis, the required ÃŽâ€V to "sundive" can be reduced to under 4 km/s at the expense of drastically-increased flight time"

So why is that delta-v map showing 68 km/s?

I've done it with a simple ion probe and there's no way that had THAT much delta-v?

4-8 km/s is for crashing. If you want to enter ultra low orbit it would require much more, and even more to stop your orbital movement and attempt landing

[tavert]

Delta-V maps are oversimplified for the costs of landing and takeoff. The actual values depend on your craft's TWR, staging, Isp (since that determines how quickly TWR changes), and your landing trajectory. Here is the math for best-case single-stage numbers as function of TWR and Isp http://forum.kerbalspaceprogram.com/threads/39812-Landing-and-Takeoff-Delta-V-vs-TWR-and-specific-impulse

[Pecan]

Delta-V maps are oversimplified for the costs of landing and takeoff. The actual values depend on your craft's TWR, staging, Isp (since that determines how quickly TWR changes), and your landing trajectory. Here is the math for best-case single-stage numbers as function of TWR and Isp http://forum.kerbalspaceprogram.com/threads/39812-Landing-and-Takeoff-Delta-V-vs-TWR-and-specific-impulse

This. And for the best engines to use for your various vehicles the absolute best resource is also by tavert.