delta V needed to get to duna orbit from duna surface?

[gtrx]

I have a craft that weighs app. 12tons. It lands on duna fine. But then it has left just around 400delta V to get back to orbit and dock to big rocket. and 400 is not enough. the only engines are two mark radial 55 blah blah, so keep that in mind (using this info, you should be able to get a TWR at all altitudes.)

So can anyone tell me how much delta V is needed ? I need just enough to get back in orbit.

Or is there a way to dock vehicles on surface? my rover has a port right on top of it. If I can land a fuel carrying craft right on top of the rover and dock them, it could work. Has anyone here done that before?

Tell me if craft files are needed.

thanks.

[Pursuedtank]

The Delta V to Duna Orbit is around 1500 m/s. Do you use parachutes to land, and are you sure your lander has enough delat v in the first place. Try using some more efficient engines perhaps.

[gtrx]

The Delta V to Duna Orbit is around 1500 m/s. Do you use parachutes to land, and are you sure your lander has enough delat v in the first place. Try using some more efficient engines perhaps.

i use parachutes to slow down to around 30m/s and then the two engines to reduce speed to 5m/s and land. it takes i think less than 30 delta V to land. After that I'm left with ~400 or so delta V to get back in orbit, which is according to you, not enough. And I've tried it, with 400 delta V I can only get to around 40km straight up and then back. So I guess a velocity of about 800-1000m/s is needed for low duna orbit (less than 100km). which makes it 1500m/s total. 500 to get up to altitude and then 1000 prograde to get in orbit.

And how about the docking idea?

[Captain Sierra]

Definitlely land using parachutes. The less fuel you burn on the way down, the more you have for your ascent. I suggest using a skipper engine or a bunch of LV-909 engines mounted on radial tanks. That oughta give you a good TWR and efficiency to give you the delta V required. I also recomend using kerbal engineer or mechjeb to check your lander's delta V status in the VAB (you should have most of it left for takeoff assuming you land with mostly parachutes, lots and lots of parachutes).

[Landge]

I use 2 LV-N's mounted radially and, while slow at first, are able to achieve duna orbit and re-dock with the transfer stage. Then go and land on Ike and return to Kerbin.

Aerobraking in Duna's atmosphere:

Planting the flag ceremony:

Leaving Duna:

Landing on Ike:

Return to Kerbin's SOI:

Re-entry:

Safe at home:

[Cheebsta]

And how about the docking idea?

Yes, this will work, it's just not very easy to land right on top of something else, for me anyways. I have to use something dead stable or I end up just making big fireballs and Kerbal mist.

[Captain Sierra]

What I would suggest is abandoning that lander and sending a backup that can hold your stranded kerbals. Also, 30m/s with parachutes means you don't have a great lander. If you build it perfectly, you should be able to land with a sum total of 0 dV from your engines. Docking on top of an object (especially with a fuel can, which is heavy and may crush it), it extremely difficult. Unless you are an awesome VTOL lander pilot and can land on a dime, I suggest trying something else.

[capi3101]

1750 delta-V is what you need to get back into orbit from Duna according to the wiki's delta-V map.

I agree with most of the other folks here; landing on top of a stationary craft on the surface is possible, but you'd have to have some mad piloting skills to pull it off. Depending on the design, though, you might try tipping it over and trying to refuel it with something like a rover. Just a thought. Only other option is to send a rescue ship.

How much delta-V does your lander have fully fueled?

[arq]

Landing on the docking ports of vessels is very tough. Practice on Kerbin first, definitely. Also, Duna's atmosphere is thin enough that LVNs still have very high ISP even at sea level (at least 500, though IIRC it's over 700), so they are often a very good option for anything but the lightest landers. If the TWR is an issue with them, LV909's are rarely a bad choice.

As far as chutes go, it is *possible* to get to 5m/s on chutes for landing, but actually I would argue much less efficient. Parachutes are very very heavy. You lose a ton of dV just hauling them around. It's actually possible that, round-trip, it's cheaper to not use parachutes at all. Terminal velocity is ~150m/s near Duna's surface. I expect that for most ships the cost of getting 500kg (or much, much more) worth of parachutes from Kerbin to the Dunan surface is more expensive than that.

To get a ship near Duna's surface to land with chutes at 10m/s means that you need approximately 9% of the lander's mass to be parachutes. I find it hard to believe that getting an extra 10% of your lander's mass into orbit plus the 1000m/s from LKO to Duna (and possibly the 2000m/s back to Kerbin) is cheaper than using some rockets to assist the landing.

Approximate calculations below:

DragNeeded = (TerminalV/DesiredV)^2 * 0.2

ChuteMass/TotalVesselMass = DragNeeded/500

Edited July 23, 2013 by arq
formatting

[Xiphos]

If your lander for duna can make orbit around kerbin, you will have enough Dv to take off from duna and return to kerbin easily. With fuel to spare.

[mellojoe]

And I've tried it, with 400 delta V I can only get to around 40km straight up and then back. So I guess a velocity of about 800-1000m/s is needed for low duna orbit (less than 100km). which makes it 1500m/s total. 500 to get up to altitude and then 1000 prograde to get in orbit.

May I ask how you are going about achieving orbit? Because you may not be doing it very effeciently, which then leaves you at the end of your journey without enough to come home.

Are you just launching straight up until you hit deep space and then turning sideways to get oribt? This is not the most effecient way. It may be faster, time-wise, but you burn a ton of fuel. You really want a nice circular path upward, and depending on the atmosphere you are dealing with you want to start your circular turn fairly early. On Kerbin, most people do their gravity turn starting at about 10km. On Duna, you can start much, much earlier. Probably starting gravity turn around 3km, following a nice round path.

If you liftoff from Kerbin this way, you might find you end up on Duna with much more fuel.

[gtrx]

May I ask how you are going about achieving orbit? Because you may not be doing it very effeciently, which then leaves you at the end of your journey without enough to come home.

Are you just launching straight up until you hit deep space and then turning sideways to get oribt? This is not the most effecient way. It may be faster, time-wise, but you burn a ton of fuel. You really want a nice circular path upward, and depending on the atmosphere you are dealing with you want to start your circular turn fairly early. On Kerbin, most people do their gravity turn starting at about 10km. On Duna, you can start much, much earlier. Probably starting gravity turn around 3km, following a nice round path.

If you liftoff from Kerbin this way, you might find you end up on Duna with much more fuel.

the most efficient way to achieve orbit varies from rocket to rocket. rockets with lower TWR will have to go much higher in a straight vertical line before they can start turning. High TWR rockets can turn when ever they want. My rover is low TWR, about ~1.25 on kerbin surface. Thats a lot on Duna, but not enough that I could turn at 500m.

How I lift off doesn't make a difference, cuz the lander+orbiter refuels in kerbin orbit and goes to duna on full tanks.

btw, whats a good place to go after I've done moon, minmus and duna? (I've landed successfully on these three already)

minmus was quite boring. nothing challenging at all, easy to land, easy to take off.

[Francesco]

about 1400 m/s with a good ascent profile; you can start to pitch down at 5km instead of 10km as you would do on Kerbin, and complete a more aggressive gravity turn: on Duna, above 15km atmospheric drag becomes irrelevant.

[gtrx]

What I would suggest is abandoning that lander and sending a backup that can hold your stranded kerbals. Also, 30m/s with parachutes means you don't have a great lander. If you build it perfectly, you should be able to land with a sum total of 0 dV from your engines. Docking on top of an object (especially with a fuel can, which is heavy and may crush it), it extremely difficult. Unless you are an awesome VTOL lander pilot and can land on a dime, I suggest trying something else.

the lander is a rover. I dont make anything without wheels. Whats the point of going on to different planet when you cant move around on it?

I think 30m/s with parachutes is good enough. the red parachute itself weighs 0.2. And I need two of them to get to 30m/s or so.

here are some pics of the rover:

this is the earlier one:

And this is the later one, note I've replace inefficient orange thrusters with bigger, more efficient white engine and then added the orange ones, in case more thrust is needed(removed them in the latest one which I'll be landing soon). Also, added those ugly bars to avoid rolling over as happened with the first one (quicksave saved me lol)

And the additional fuel tank (which I forgot to connect to the small tanks and wondered where the extra fuel went lol):

[gtrx]

Landing on the docking ports of vessels is very tough. Practice on Kerbin first, definitely. Also, Duna's atmosphere is thin enough that LVNs still have very high ISP even at sea level (at least 500, though IIRC it's over 700), so they are often a very good option for anything but the lightest landers. If the TWR is an issue with them, LV909's are rarely a bad choice.

As far as chutes go, it is *possible* to get to 5m/s on chutes for landing, but actually I would argue much less efficient. Parachutes are very very heavy. You lose a ton of dV just hauling them around. It's actually possible that, round-trip, it's cheaper to not use parachutes at all. Terminal velocity is ~150m/s near Duna's surface. I expect that for most ships the cost of getting 500kg (or much, much more) worth of parachutes from Kerbin to the Dunan surface is more expensive than that.

To get a ship near Duna's surface to land with chutes at 10m/s means that you need approximately 9% of the lander's mass to be parachutes. I find it hard to believe that getting an extra 10% of your lander's mass into orbit plus the 1000m/s from LKO to Duna (and possibly the 2000m/s back to Kerbin) is cheaper than using some rockets to assist the landing.

Approximate calculations below:

DragNeeded = (TerminalV/DesiredV)^2 * 0.2

ChuteMass/TotalVesselMass = DragNeeded/500

absolutely correct. plus you gain weight with the adapters etc cuz you need round fuselage type structure to fit the red(the ones that work at 2500m) parachutes in. the red parachute weighs 200kg each, you can hardly fit two of them within 500kg. you probably need a ton or two of extra weight to land entirely on parachutes.