Cant slow down in Kerbel rentry

[Emperoreddy]

Realize this is a noob question but I am trying to do some missions that require sub orbital flight. 

Problem is I keep coming down like a bullet and Cant get my chutes. 

What are solutions to slowing down when you are deep enoigh in the atmosthere to use the chutes. 

Have not seen usual info in a tutorial and i don't recall this issue in older builds

[Flavio hc16]

Having a picture of your craft (or the craft file) would be very helpful, you can upload it on imgur and the give us the link. However 9/10 you have made a reentry stage that is too pointy and aerodynamic, so you butter through the atmosphere and crash. If reentry vehicle are usually ugly and as aerodynamic as a brick, there is a reason for it 

[Harry Rhodan]

Launch at a shallow angle or do a gravity turn like in a regular launch to orbit. If you just go straight up you will drop like a rock.

[Hupf]

• Try to keep a horizontal flight profile instead of a vertical one (by not slowing down too much): you'll spend more time in the atmosphere, giving it more time to slow you down. Fine-tune your Periapsis between blowing up (too low, heating up too quickly) and blowing up (too high, too much time building up heat)
• Make your craft lighter. Light craft are more easily slowed down by the same amount of drag. Do this e.g. by appropriately burning fuel during descent
• Increase drag: use Airbrakes or try to steer such that larger surfaces are exposed to the airstream (if you don't go spinning wildly or exposing temperature-sensitive parts doing this)

[GuyWithGlasses]

46 minutes ago, Hupf said:

• Try to keep a horizontal flight profile instead of a vertical one (by not slowing down too much): you'll spend more time in the atmosphere, giving it more time to slow you down. Fine-tune your Periapsis between blowing up (too low, heating up too quickly) and blowing up (too high, too much time building up heat)
• Make your craft lighter. Light craft are more easily slowed down by the same amount of drag. Do this e.g. by appropriately burning fuel during descent
• Increase drag: use Airbrakes or try to steer such that larger surfaces are exposed to the airstream (if you don't go spinning wildly or exposing temperature-sensitive parts doing this)

+1 and I'll suggest burning retrogade (It's the obvious answer but if its a noob-question...).

 

 

[Gurkonier]

• Put your Apoapsis only slightly above the atmosphere
• And pointing the capsule retrograde on reentry, otherwise you have way too less drag.

[bewing]

The other answer that all these rocket guys always seem to miss is aerodynamics. If you put control surfaces at the front or back and some little fins radially at your empty CoM, your rocket will have aerodynamic lift and control. It will be able to pull out of a dive, it will be able to pull up, it will be able to turn, it will be able to stall. You will be able to stop it on a dime.

[Hupf]

48 minutes ago, bewing said:

You will be able to stop it on a dime.

At mach 6.8

One other related point: if you do have trouble with uncontrolled spinning or the craft not pointing in the desired direction (usually with a heat-resistant part in front, like a heat shield or in some cases an engine): put aerodymanic surfaces (tail fins etc) on the end you want pointing retrograde (i.e. opposite of the heat shield) and make sure mass is concentrated at the front (e.g. by pumping remaining fuel to the front-facing tanks). You will get a "shuttlecock" effect and the vessel will have a stable orientation.

[Snark]

6 hours ago, Emperoreddy said:

Problem is I keep coming down like a bullet and Cant get my chutes. 

What are solutions to slowing down when you are deep enoigh in the atmosthere to use the chutes. 

As @bewing points out, aerodynamics is key.  It would really help if you could post a screenshot of your ship-- that way we could help with concrete suggestions.  Without seeing what your ship looks like, we can only talk in general terms.  Also, just how fast are you going when you faceplant?  If you're going under 600 m/s, you could solve the whole problem just by putting some drogue chutes on your craft.

Lengthy explanation below, but what it boils down to is that doing any of the following will help you:

• Make your craft lighter
• Make your craft less long-and-skinny-and-pointy
• Give your craft the ability to steer itself (either via reaction wheels, or controllable aero surfaces) so that it's not pointing perfectly
• Give your craft some way to slow itself down when it's going faster than standard chutes can handle.  Drogue chutes are one option; airbrakes are another.

^ All of the above will help you, and of course there's nothing stopping you from doing more than one. 

 

Okay, let's talk about this in a bit more detail.  "How to slow down my craft below parachute speed before face-planting."  Three main options, discussed below.  Note that these options aren't mutually exclusive-- you could do all three, if you want.  But depending on your design, just doing one of them might be sufficient.

 

Option #1:  Design the ship to have a low ballistic coefficient.

"Ballistic coefficient", loosely paraphrased, is basically the ratio of mass to drag.

• A craft with a high ballistic coefficient (i.e. something dense and massive and long and skinny and pointy, like a dart) will have a very high terminal velocity, and will tend to faceplant at high speed.
• A craft with a low ballistic coefficient (i.e. something lightweight and draggy, like a badminton birdie) will have a low terminal velocity, and will come down slowly enough that it has no problems popping its chutes well above ground level.

If you're hitting the ground still going faster than parachutes can deploy, it sounds like you've built something like a dart.  It's too aerodynamic.  So... don't do that. 

I realize that the above recommendation is a bit vague, but it's hard to get more specific without seeing your ship.  In general, what I mean is, some combination of "reduce the weight", and making it more short-squat-pancake rather than long-pointy-skinny-javelin.

 

Option #2:  Design the ship to be steerable, and point it above while reentering.

Suppose you do have a ship that's long and skinny and shaped like a javelin.  Well, yes, that's very very aerodynamic (which is bad for you)... but only if it's pointing prograde during entry.  If you steer the ship so that it has another orientation, you can really help yourself a lot.

Steering helps you in two ways.

First, drag.  If you have your ship pointing sideways (e.g. with the nose of the ship pointing skywards, instead of ), then you drastically increase the drag and you should have no problem at all slowing down.

Second, body lift.  Suppose you don't point the craft completely sideways, but instead just angle it a bit above , say by 30 degrees or so.  What happens then is that the incoming airstream deflects off the underbelly (i.e. the side of the ship that's facing the ground), and generates lift and drag.  That's absolutely golden, because not only does the drag slow you down, but the lift helps maintain your altitude so that you have a lot more time to slow down.

Note that body lift works even if you don't have any actual "wings" on the plane.  Even if your ship is just a big long cylinder, it works just fine.

Now... when you try to do what I just suggested above... well, depending on your ship design, you might find that you can't.  "Hey," I hear you cry, "I tried to do that, but it didn't let me!  I pushed the 'pitch up' button, and my ship simply won't budge, it's locked hard onto and won't let me move it!"

Well, if you do find yourself in that position, what it means is that your craft is too aerodynamically stable, lie an arrow in flight.  Its aerodynamics really strongly want to keep it pointed forward.  If that's the case, you have a few options.  One would be to redesign your ship so it's not so "over-stable".  Another option would be to put some steerable fins on the back, such as the AV-R8 Winglet.  Having those fins will allow you to use aerodynamic control to pitch your nose up, which should solve the problem nicely.

 

Option 3:  Add hardware that can add drag at higher speeds than a standard parachute can handle.

This can be the easiest option, since it's simply a matter of adding a few parts onto your ship.

Just how fast are you going when you're faceplanting?  Obviously it must be faster than 250-300 m/s, otherwise you wouldn't be having this problem and your standard parachutes would work just fine.

But are you going faster than, for example, 500-600 m/s?  If you're going less than that, the solution is easy:  Just add drogue chutes.  You don't need many-- even just one or two will do, even for a big ship.  Drogue chutes are great.  They're tiny, you can put them pretty much anywhere, and they really work.  They can deploy at twice the speed that regular chutes can, and they will very quickly slow you down to speeds that your regular chutes can then open.

If you're on Kerbin, I strongly suspect that drogue chutes will be plenty enough to handle the job.  It's pretty rare, in my experience, to design a reentry ship that's going faster than 600 m/s when it hits the ground.

But, just on the off chance that you're somehow seriously hypersonic when you hit the ground... well then, you can consider airbrakes.  Those work great, and they have no max deployment speed-- you can be going at well over 1000 m/s and they still work fine.  (However, don't deploy them until you get through the "hot" part of reentry, because they have a max temperature tolerance of 1200 K when deployed, and have a tendency to melt.  So wait until the flames die down before you deploy them.)

[Vanamonde]

No law says you have to eject the engines before entering atmo. How about simply retaining the last stage long enough to do a braking burn? 

[GrouchyDevotee]

Drogue chutes might help, but if you are too steep you still might not slow down enough for the main chutes.