Reentry not slowing down enough

[Zappt]

This is my Space-Travel ship to transport four people into an orbit. Works realy well but I have trouble to get that ship safe to the ground. Often it isn't just slowing down enough because it isn't coming back on the side with its heatshield, it's coming down with it's nose because SAS is running out of battery. I don't loose enough speed and I can't open the parachutes -> crash.

Any suggestions? I'm early in the game.

http://imgur.com/T2SrzYX

Edited March 14, 2017 by Zappt

[Jarin]

You need to move more weight close to the heat shield, so you aren't trying to re-enter nose first. Also try a shallower re-entry. What are you setting your PE at to deorbit?

[Streetwind]

The golden rule of rocketry says: "heavy bits at the front, draggy bits at the back". Guess what's the heaviest part of your reentry vehicle? The mk1 command pod. Guess what's the draggiest part? The flat underside of your heatshield. This is why it wants to flip. And once the pointy, low-drag end faces forward, you don't get enough air resistance to slow down in time. (Your reentry profile has nothing to do with it, by the way.)

Many different solutions exist.
- For example, you could include batteries so that your reaction wheels can keep your craft stable.
- Or you could change the design of your spacecraft to be more symmetric, so the reaction wheels don't have to fight as hard to keep it stable, thus using up less energy.
- Or you could add radial drogue parachutes, which can open at speeds of more than two times that at which normal parachutes are safe.
- Or you could make the command pod end of your spacecraft more draggy by mounting fins on it - but careful while launching into space, because unshielded nose fins will make your rocket want to flip on ascent. To avoid this, you could employ a fairing.
- Or you could just place the heashield above the pod, in place of where the nosecone is. You don't need any ablator to return from an orbit around Kerbin; the heatshield itself has enormous heat tolerances, so you don't need to worry about ablator burning off during launch. Just remove all ablator and save weight and money. In order to avoid creating massive drag on ascent, place an upside-down decoupler over the heatshield and put a nosecone on top. That way you can stage away the nosecone once in space.
 

Edited March 14, 2017 by Streetwind

[Zappt]

23 minutes ago, Jarin said:

You need to move more weight close to the heat shield, so you aren't trying to re-enter nose first. Also try a shallower re-entry. What are you setting your PE at to deorbit?

Good to know but more weight to my heat shield is extremly difficult. My spacerocket looked kind of funny with that and not like sometthing you would see in the real world
 

15 minutes ago, Streetwind said:

The golden rule of rocketry says: "heavy bits at the front, draggy bits at the back". Guess what's the heaviest part of your reentry vehicle? The mk1 command pod. Guess what's the draggiest part? The flat underside of your heatshield. This is why it wants to flip. And once the pointy, low-drag end faces forward, you don't get enough air resistance to slow down in time. (Your reentry profile has nothing to do with it, by the way.)

Many different solutions exist. [...] In order to avoid creating massive drag on ascent, place an upside-down decoupler over the heatshield and put a nosecone on top. That way you can stage away the nosecone once in space.

The last option sounds like the best for me. I don't want to be dependent of batteries. I had the idea of MK1-Pot - heatshield - decoupler- nose but the decoupler wasn't shooting away with the nose instead it stuck to my mk1-Pot-heatshield.

Long story short: How do I place an upside-down decoupler? 

Edited March 14, 2017 by Zappt

[Foxster]

You may accidentally be doing yourself a slight favour with that nosecone on the top. 

It is not helping with reducing drag on the way up, parts need to be the same size in KSP for them to occlude each other. 

However, it will be nice and draggy on the way down where you do need more drag at the back to keep it retrograde. 

[Kryxal]

Maybe the inline cockpit would work better, and some batteries wouldn't go amiss so you can hold your nose up.  Body lift can do wonders around 15 km.

[bewing]

48 minutes ago, Zappt said:

Long story short: How do I place an upside-down decoupler? 

Before you attach it to your ship, hit S twice. (Or A or D or W.)

 

[Spricigo]

 

try an empty service bay just below the command pod, it will move the center of mass toward the botton and you if you open it increase the drag in the top.

A further modification its to change the command pod for a probecore+antenna +2 OX-STAT solar cell (I'm supposing this is a tourist ship). It will make the upper stage a bit more expensive but lighter so you may be able to compensate with cost reducition of lower stages.

 

Unrelated to the question: seems you can benefit from some optimization of your launch vehicle. Looks like there is too much TWR at launch Pad. for starts, I would consider dropping 2 SRBs and adding a fuel tank (do about the same job but with less hassle)

[Snark]

Some other options, @Zappt, to add to the nice list that @Streetwind has already provided:

• Or airbrakes (if you've unlocked them).  Not helpful for reentry from orbital speed (they burn up), but once you're past the "hot" part of reentry, they're excellent at stopping you from slamming into the ground.
• Or ditch the heat shield entirely, put some stubby wings amidships and some stubby pitch-control surfaces at the back, and you can reenter "airplane style" instead of "capsule style":  like the space shuttle does, nose-up, using the aero surfaces both to generate extra drag to slow down, and also to generate lift so that you can slow down while still high up.  And also allows slowing down to a reasonable speed before you hit the ground, so regular chutes can work.

 

[Zappt]

Thx all for your kind help and good tips! =)

 

Quote

Unrelated to the question: seems you can benefit from some optimization of your launch vehicle. Looks like there is too much TWR at launch Pad. for starts, I would consider dropping 2 SRBs and adding a fuel tank (do about the same job but with less hassle)

I always have the problem if my rocket get's "longer" it's very difficult for me to navigate it. It often flips down if it's to long. So i try to kepp my rockets always as short as possible. 

Edited March 15, 2017 by Zappt

[Loren Pechtel]

15 hours ago, Snark said:

Some other options, @Zappt, to add to the nice list that @Streetwind has already provided:

• Or airbrakes (if you've unlocked them).  Not helpful for reentry from orbital speed (they burn up), but once you're past the "hot" part of reentry, they're excellent at stopping you from slamming into the ground.
• Or ditch the heat shield entirely, put some stubby wings amidships and some stubby pitch-control surfaces at the back, and you can reenter "airplane style" instead of "capsule style":  like the space shuttle does, nose-up, using the aero surfaces both to generate extra drag to slow down, and also to generate lift so that you can slow down while still high up.  And also allows slowing down to a reasonable speed before you hit the ground, so regular chutes can work.

 

I forget what mod but one had Space-X style grid fins.  Fold for flight, deploy on the way down.  They've never gotten dangerously hot even when deployed at near orbital speeds.

[Spricigo]

6 hours ago, Zappt said:

I always have the problem if my rocket get's "longer" it's very difficult for me to navigate it. It often flips down if it's to long. So i try to kepp my rockets always as short as possible. 

 

The rocket flips because you have too much weigth at the rear and too much drag in the front. The solution its to increase the drag in the rear and increase the mass in the front. A pair of tail fins can make a hug difference, same for adjusting the fuel priorities so the lower tanks get used first.