Trying to make it into orbit

[AeroGav]

25 minutes ago, miki1234 said:

Secondly, I have installed the winglet and fins as suggested, but still the vessal spins out of control very early If i tilt it to the D direction from launch.

How do you think i should proceed? 

 

I suspect your CoL is in front of your Centre of Mass, or at least it will be until some of the lower stage fuel has gone.  Centre of lift needs to be below/behind CoM  or your rocket will want to flip out !

I am not seeing the Yellow or Blue ball in the VAB, means you have not turned the Centre of Mass and Centre of lift indicators on.   These are essential to make sure that each stage of the rocket has it's centre of lift behind its centre of mass.    Look at my post for more info on how to design a rocket with these tools.

Honestly, there's two mods that are "must haves" -  CorrectCoL  takes account of drag and lift from non-wing parts and gives you a more accurate CoL indicator.  It is often a lot further forward than the stock indicator shows, as the body of the rocket itself produces lift.

Also,  RCS build aid shows a Red ball which is your empty CoM.    This is more an issue for aircraft, rockets generally have fuel at the bottom so if its stable fully fuelled it will be more stable when empty,  but it's a great tool.

 

1 hour ago, Urses said:

I have only one point. If you begin to learn how to fly you can make your life a lot easier if you use at the begining steerable winglets or tail fins.

The steerable Tail Fins from the Aviation tech node have many advantages over the simple fixed ones

• Means you can use the Reliant instead of the Swivel for lower stage engine since you don't need gimbal.   The Reliant is cheaper, more powerful, lighter than the Swivel, it also has better ISP at low altitude, which is where you're gonna be using it.
• Means the rocket will point straight on ascent, but on re-entry you can steer it off prograde to slow down faster.   You can even make it fly level briefly, like an aeroplane, with body lift (won't glide as long as something with wings, but will give you a chance to open the parachutes).

 

Edited April 14, 2017 by AeroGav

[Alshain]

Your second stage doesn't need winglets.  By the time you stage away the first stage, the air should be thin enough that the rocket should be stable without them.  Having them there will destabilize the rocket by moving the CoL too far forward.

[Harry Rhodan]

53 minutes ago, miki1234 said:

Secondly, I have installed the winglet and fins as suggested, but still the vessal spins out of control very early If i tilt it to the D direction from launch.

Well, looking at the second picture with all those fins I guess you didn't quite follow why AeroGrav put them on the rocket in his last picture: He was trying to add them to his payload so the payload would stay stable when reentering nose first with a heatshield on the nose. In your case you added the upper fins only to the upper stage you would discard anyways, they serve no purpose and as they are above your CoM they are also counter productive and give the aerodynamic forces on the wrong end more surface area to push you around.

And contrary to what AeroGrav said: The CoL indicator even with the mods will only be a rough indicator of what is going wrong as the problem is not lift but pressure, which is a bit more complicated. Remember the golden rule: anything draggy above your CoM will work against you.

Also keeping the Boosters aligned with the north-south axis might reduce a bit of torque while turning.

[miki1234]

Ok.. Updated design! But it still I fall to ground with it while turning

 

9 hours ago, Harry Rhodan said:

Also keeping the Boosters aligned with the north-south axis might reduce a bit of torque while turning.

How do i do that?

[Spricigo]

 

11 hours ago, miki1234 said:

. . I have tried handling the trust first...

Notice:

A) the later stages will affect the performance of the early ones, the opposite don't happen.  Thus is much easier to design the stages in the opposite order of use. 

B) It's important to avoid over engineering, unused/unneeded resources will hinder the vessel.  Overengineering in later stages will be worse because of (A) 

So,  the first problem to solve is heat at reentry. Adding a service Bay below the command pod seems the ideal solution, when open it causes just enough drag to keep the vessel pointed retrograde and slowing down to reduce the time heat build up.  Unlike fins,  you don't need to make adjustments in lower stages. 

Next let's think about the stage used to circularize and deorbit.  Your payload is about 2,5t,  with a FL-T400 and a terrier it will be 5t with 1500m/s deltaV and TWR 1.2.  

For next stage a Reliant engine with 4 FL-T400 can provide 2000m/s with 1.3 initial TWR. It's enough deltaV,  but with this low TWR (which will not increase much)  gravity loss is a concern. A pair of hammers can help with the initial kick from the launchpad or you can add another fuel tank to increase the deltaV. Either way, 4 basic fins at the bottom tank to help stabilize. 

Since the steering power is so low (only the capsule has any)  consider to set a tiny inclination  toward west in the editor and use a launch clamp. Anyway, the idea is to launch the rocket in a curved trajectory and let it fly itself. Adjusting the angle and thrust will adjust the trajectory. 

 

 

 

[miki1234]

49 minutes ago, Spricigo said:

Since the steering power is so low (only the capsule has any)  consider to set a tiny inclination  toward west in the editor and use a launch clamp. Anyway, the idea is to launch the rocket in a curved trajectory and let it fly itself. Adjusting the angle and thrust will adjust the trajectory. 

 

 

 

Can you reference to a video/pic that shows how to perform this incline? I haven't succeeded

 

[Spricigo]

In the VAB/SPH top left there is four icons: place, move, rotate and reroot. 

With rotate active clicking in a part will make a mesh with 3 circles appear.  Drag those circles to rotate the part. Doing it in the root part will rotate the whole vessel. 

[Harry Rhodan]

5 hours ago, miki1234 said:

How do i do that?

You see that big door in the VAB leading to the launch pad? That is east, the direction you will generally launch to. So all you have to do is to attach boosters 90° perpendicular to it.

 

And when is your rocket flipping? What are you doing up to the point when it flips, what is happening?

[miki1234]

Hi! good news! I have managed to get a good orbit but still get burned at re entry. This is my updated configuration, includes some tilting... Thanks a lot so fat

What is next do you guys think?

 

[Spricigo]

Rearrange your reentry vehicle parts to move it's CoM and CoD so you can maintain it pointed retrograde in atmosphere. 

From top to bottom: command pod, service bay,  science Jr, crew cabin, heatshield. 

Also your trajectory when reentring matter.  For slight different reasons, too deep or too shallow may cause heat problems. For your craft lowering the periapsis to 10km and holding retrograde seems ok. 

Edited April 15, 2017 by Spricigo

[miki1234]

4 hours ago, Spricigo said:

Rearrange your reentry vehicle parts to move it's CoM and CoD so you can maintain it pointed retrograde in atmosphere. 

From top to bottom: command pod, service bay,  science Jr, crew cabin, heatshield. 

Also your trajectory when reentring matter.  For slight different reasons, too deep or too shallow may cause heat problems. For your craft lowering the periapsis to 10km and holding retrograde seems ok. 

Thanks. You don't think i need extra fuel to slow down rather it's the angle of entry?

[Lelitu]

8 minutes ago, miki1234 said:

Thanks. You don't think i need extra fuel to slow down rather it's the angle of entry?

Trying to slow down before entering the atmosphere is worse than useless.

The rocket equation means that the extra fuel to slow down enough to matter(2+kps) will completely cripple your rocket, by adding a *lot* of mass to the last stage used.
this means you need a vastly bigger rocket at every stage to achieve your mission. Re-entry doesn't require a periapsis anywhere near ground level on kerbin. Once you dip below 30KM(for most craft) you're committed to landing, even from interplanetary (except maybe jool). Atmospheric drag will see to it you slow down. If your re-entry vehicle is designed to be passively stable flying heatshield first, it'll even do it safely.

For your current design, it's neither passively stable heatshield first, nor close enough to it for SAS retrograde hold to keep it pointed the right way. @Spricigo is right. You need to rearrange the last stage, so that the COL is above COM, and heatshield right at the bottom. This will keep it stable flying heatshield first, or near enough for SAS retrograde hold to make it work.

[Spricigo]

I didn't tested it myself but I suppose it can handle the heat. 

In my experience coming from low orbit (70-100km) it's enough to lower the periapsis to 10-15km. If you have enough fuel and electricity may be worth to lower you orbit to something like 75 x 75 before re-entering. 

[Spricigo]

1 hour ago, Lelitu said:

Re-entry doesn't require a periapsis anywhere near ground level on kerbin. Once you dip below 30KM(for most craft) you're committed to landing

While Lelitu is correct, a word of advice about shallow trajectories:

Depending on you craft you may end in a layer of the atmosphere hot enough to increase the temperature but not dense enough to slow down the vessel. In this case the solution may be to dive deeper into atmosphere to slow down faster and give less time to heat up. 

[Lelitu]

41 minutes ago, Spricigo said:

I didn't tested it myself but I suppose it can handle the heat. 

In my experience coming from low orbit (70-100km) it's enough to lower the periapsis to 10-15km. If you have enough fuel and electricity may be worth to lower you orbit to something like 75 x 75 before re-entering. 

For this design, lowering orbit to 75x75 would be pointless. It won't take enough energy out of the orbit to matter. Either it can hold heatshield first, or it will burn (unless a barely suborbital hop at well under 2000m/s).

in general, it's only useful for designs that are overfuelled, and underprotected from heat. Nothing beats the efficiency of an atmosphere for stopping spaceships, except *maybe* magic. Even then, only by a little bit, and maybe.

Edited April 16, 2017 by Lelitu

[Spricigo]

Yes,  this design probably just need to drop periapsis into atmosphere and maintain retrograde. 

Nonetheless I often had a overfueled ship in a slight higher orbit. Rather than wonder if it would make any difference, I just lowered the orbit. It may not have mechanical effect but cause a psychological effect. 

 

[Harry Rhodan]

15 hours ago, miki1234 said:

This is my updated configuration,

Fins and winglets are the most efficient when they are as far as possible from the CoM. So you usually should put them close to the engine. You also need at least three so they actually give you stability and/or control in more than one axis.

And over the last few iterations of your ship you slowly but surely have transfered more and more fuel to the upper stage and now even use a stronger but less efficient and heavier engine in your upper stage. That will make you feel a bit more confident when you are using your last stage but the tyranny of the rocket equation will make your first stage suffer extremely.

[Reusables]

Try Pe of 38km, it takes some time to reenter but anything with heat tolerance over 2000K won't burn up.

Edited April 16, 2017 by Reusables

[AeroGav]

Try a re-entry stage with the following part order -

1. capsule (at top)

2. service bay

3. passenger cabin

4. heatshield

put the science junior on a decoupler or put it underneath the heatshield and just leave the doors open and let it explode.

on re-entry, open the service bay for extra drag, that should make it re-enter with heatshield facing the airflow.