Why are parachutes so useless?

Question

It seems that in one of the last few version the physics have been tweaked to make re-entry and landing much more dangerous.

In particular, parachutes now (1.0.5) seem absolutely useless. I've been able to get by with a little trickery where capsules are concerned, but I recently decided to put parachutes on my stages so they touch down softly instead of exploding, instead of blowing up. I know that in vanilla KSP stages beyond a few km just vanish anyway, but I'd still like to design a stage that in principle could land in one piece.

I decided to test it by building only the individual part of my bottom stage as its own rocket, and trying to launch and then parachute down with it. My rocket was made up of:

• Stayputnik (only for the test, so I can control it, should have negligible effect on mechanics)
• 2x FL-T800 liquid fuel tanks (only 10% full for the test)
• LV-T45 "Swivel" engine
• Variable number of Mk2-R radial parachutes

All these components are stacked like a tower, except the parachutes. With these, I tried several different configurations:

• One parachute on the side of the fuel tanks, above dry CoM (located by looking at CoM with tanks 0% full)
• One parachute on the side just below the CoM, a second parachute above the CoM on the same axis as the first one
• One parachute above the CoM, cluster of 3-5 parachutes below CoM
• I have also tried RealChute Radial Chute from the RealChutes mod (I did all applicable tests with and without the mod, seems to make no difference)

Settings on the parachutes were always default, and they definitely opened way ahead of the critical moment (speed was constant for the last several seconds in each case).

So the idea is I launch this "rocket", get it to about 1 km before fuel runs out, activate parachute and see how well it lands. Since it's difficult to control this, most landings have been on the ground, not water. You should be able to reproduce my experiment if you want to.

The rocket has dry mass of about 3.5 t. According to the calculator, 2 radials should be enough to land with 8 m/s and 5 should be enough for 5 m/s. However, 2 chutes result in a very rough (~18 m/s) crash. 6 chutes result in about 8 m/s and the engine and tank explode on ground contact.

Surely I can just attach 100 chutes to this stage and it will land very gently. But the idea here is that I want expensive stages to land intact to be more economical (again, leave aside how the game handles stage recovery for a second). The point is that this rocket costs about 2.5k and the radial chutes are 300 each. If I need to deploy more than 1-2 chutes, a large fraction of the money starts going to the chutes, which seems silly to me.

Are parachutes supposed to be this useless, or am I doing something wrong? I noticed, for instance, that the chutes overlap when deployed - I never noticed this being important before, but if two chutes overlap does that somehow decrease their effectiveness? Is there some sort of trick to correct chute placement? It seems like I should have more than enough chutes to land safely, but with few chutes I get 10+ m/s, and even 6 chutes only gets me to 8 m/s which still explodes the rocket.

Answer 1

TL:DR: chutes are not magical balloons, especially since update 1.0.5

Chutes will only slow you down from terminal velocity in thick lower atmosphere (~250ms) to landing speed (~10ms). Rest is up to landing legs, engines and clever engineering.

Do not land on engine, just don't.

For Career, you want some kind of Stage Recovery Mod

For example this one.

Parachutes are not intended for soft landing, both in real life and in KSP

There is a (lot of) reason why SpaceX uses powered landing instead of chutes.

Apollo capsules landed at ~9m/s. That's ~32km/h. Ouch.

And do not even think about Space Shuttle boosters. Their impact velocity was 23m/s... 83km/h. I wouldn't dare to call it landing.

KSP follow up on that. In arcade manner, that is.

Do not bother slowing below 6m/s with chutes

There is a lot of fake math involved (KSP aerodynamics are weird) but 6m/s is pretty much practical limit for chutes on Kerbin so you can just accept it as a "law of pfysics".

Impact Tolerance > moar chutes

Impact Tolerance works as you could guess, it tells you how hard you can smash into ground and survive.

Empty fuel tank is just a can. (Liquid fuel) Engine is quite precise machinery, lithobraking is not advised. And KSP simulates it, somehow, partially... (well, its a game ;)

If you want to survive landing lithobrake with structural parts, not engine.

For example:

1. Mk1 Command Pod: 14m/s - safe to chute down
2. Science Jr.: 6m/s - don't bother landing on it
3. Heatshields: 9m/s -it can save Science Jr. just by being below it. Sometimes. Other times Science Jr. will score collision with heatshield and explode anyway.
4. Fuel tanks and (lower tech) engines: below 10m/s. Higher tiers have higher values (spiky Aerospike have 20m/s because magic).
5. Service Bay's: 14m/s - very good thing to place on bottom of lander
6. Landing Legs: 10ms/12ms - Note: it can get damaged under heavy payload or harder collision.
7. Girders and I-Beams: 80m/s - build a cage out of them around sensitive parts and you are (relatively) safe.

Answer 2

You aren't supposed to be landing entire ships with chutes. Like in real life only the manned capsule can be landed using only chutes. Still I'm surprised that the ship can't handle the landing.

You have a few options:

1. Try not using the mod "Realchutes" - that's probably the problem.

2. Make sure you're not using drogue chutes (they're the orange chutes.). The regular chutes are blue.

3. Use some landing legs to take some of the landing impact.

4. Try water landings. They're softer IRL and KSP.

5. I use the mod "StageRecovery" which automatically trys to land parts that are out of "physics range".

Answer 3

In your staging diagram, which is on the left side of the screen during flight, the parachute icons will have a particular color. If they are all red, then the parachute is destroyed, either from impact damage from another part/ship, or that it was deployed when the craft was going way too fast. You can set the altitude of deployment (or something to that effect, I'm not where I can look at the moment) but I usually deploy them manually via staging. The simple fact of the matter is, they will slow down a craft, but not enough to land entirely. I usually try to save some fuel to land upright (the same way I launched) but use the parachutes to slow my descent so I don't need as much fuel.

Drogue chutes are made to be deployed at a much faster velocity, but won't slow you down for landing, but rather just decreases your speed for the purposes of allowing you to open your primary chute. (Taken from the wiki page for drogue chutes).

So if you find that your chutes are getting destroyed just as you deploy them, then you are going too fast, and either burn retrograde to slow down, or try using drogue chutes to slow your vessel enough to safely deploy the regular chutes.