IF i use parachutes what is the delta-v required for a Laytrhe Landing?

[Rockhem]

Title says it all, what is the delta-v requirements. (not including de-orbit, got that covered)

[RocketPilot573]

None, as long as you have enough chutes.

[Rockhem]

None, as long as you have enough chutes.

Im planning to have a small probe land with 1 drogue and 2 main chutes. the probe will probably be about 3 tons.

[Specialist290]

You probably don't even need the drogue, honestly. Laythe's atmosphere is almost as dense as Kerbin's, though it doesn't reach quite as high.

[RocketPilot573]

The probe is only 3 tons? Then all you need is one of the smallest chutes you can find. If it works on Kerbin, then it will work on Laythe.

[tavert]

If it works on Kerbin, then it will work on Laythe.

Yep, and here's why: at sea level, Laythe's gravity and atmospheric pressure are both 80% of Kerbin's. Terminal velocity is therefore the same at sea level on both planets. Chutes are modeled in KSP as parts with very high drag coefficients, lowering your terminal velocity.

[Rockhem]

Yep, and here's why: at sea level, Laythe's gravity and atmospheric pressure are both 80% of Kerbin's. Terminal velocity is therefore the same at sea level on both planets. Chutes are modeled in KSP as parts with very high drag coefficients, lowering your terminal velocity.

Could I get away with one chute?

[Specialist290]

Most likely, yes. Three tons is lighter than the three-kerbal capsule, I think.

[tavert]

Depends on what kind of landing speeds your design can stand. 3 tons total mass including one small chute (0.1 tons) should have a landing speed of 7.71 m/s at sea level on either Kerbin or Laythe.

Here's how to calculate the landing speed in general:

Let g be the acceleration due to gravity at your landing altitude (this is G*M_planet/r^2)

Let rho be the atmospheric density at your landing altitude (this is 1.223 times the pressure)

Let m_total be your total craft mass

Let m_chute be the total mass of conventional chutes

Let m_drogue be the total mass of drogue chutes

Landing speed = sqrt(g * m_total / (0.008 * rho * (0.2 * (m_total - m_chute - m_drogue) + 500 * m_chute + 170 * m_drogue)))

This assumes that every part of your craft besides the parachutes has the common 0.2 drag coefficient. If a significant portion of the mass of your craft is composed of parts with higher or lower drag coefficients, replace 0.2 with the mass-weighted-average drag coefficient of everything except the chutes.

I'm getting the formula here from https://github.com/numerobis/KSP-scripts, which I highly recommend if you're comfortable using Python code. Note his landingspeed function takes vehicle mass not including chute mass, and I think his drogue drag coefficient is wrong.

[Joe_Bender]

or add a tiny motor/tank on the bottom just to help in slowing down the descent if it gets too fast with chutes alone....just crank it up before you land, no sense in wasting fuel when you still have ten thousand feet before landing.

[Fractal_UK]

Do you plan on landing the probe on land or just splashing down? If you're splashing down, then yes, just test it on Kerbin and it should work the same. If you want to land on land then you'll either have to pick your landing spot carefully or pack an extra chute or two in case you land on higher ground, Laythe is fairly hilly. I damaged my first colony module on Laythe by landing at too great an elevation but that was much much bigger than 3 tonnes.