Reentry question

[Spricigo]

1 hour ago, jonpfl said:

Thanks, but I don't think that will help me as I still have problems getting into orbit and back with delta V 3.4k.

That is no problem with this design.  Just press space and it will steer itself in the right direction,  no SAS or control input required. If anything be careful to not raise the apoapsis too much (the Reliant,  chosen for being low tech,  is more powerful than the rocket needs). It also is stable at reentry with command pod forward and SAS off. 

[Spricigo]

@Abastro the heatshield is not for heat tolerance,  but for drag.  For what it's worth one can put a aerodynamic nose cone and make it draggier then a Mk1 command pod topped by a parachute 

[FullMetalMachinist]

59 minutes ago, jonpfl said:

In regards to parachutes, should I release it when the icon is grey (I assume it provides some drag) and then use it higher than 1k?  Lately I have not been able to get to the grey icon though (like I said, I usually crash and sometimes burn up).

Thx
jonpfl

So it breaks down like this. Parachutes have 4 modes. 
1. Unarmed.  This is how they are when you first launch your ship. They're just sitting there, waiting for something.
2. Armed.  This is when they have been staged (activated with the space bar through staging) or if you have right clicked them and clicked "arm". At this point they're ready to deploy, but haven't yet. If you armed them accidentally, then you can right click and disarm them.
3. Semi-deployed. This is when they first deploy, but they aren't generating their full drag yet, but they do give some.
4. Fully deployed. This is when they are completely open and making the most drag. 

In addition, they have several colors.  (I'm going from memory here so this might not be 100% accurate)
Unarmed and safe to deploy is a grey icon on a grey background.
Unarmed and risky to deploy is a grey icon on a yellow background.
Unarmed and unsafe to deploy is a grey icon on a red background.
Semi-deployed is a yellow (I think?) icon on a grey background.
Fully deployed is a green icon on a grey background.
Damaged/deployed-then-cut is a red icon on a grey background. This needs an engineer kerbal to fix it / re-pack the parachute before it can be used again.

The default behavior for parachutes is that when you arm them they will wait until you are falling down in the presence of an atmosphere and it is safe, before they deploy. So you could stage them in space, and they won't deploy until you've gone mostly through reentry and are going slow enough so that it's safe to deploy.

In regards to you not being able to slow down enough to get the grey 'safe' icon: are you able to keep pointed retrograde? I didn't have any problems with that when I tried it last night. Make sure that your reentry isn't too steep. My Ap of 85 km and Pe of 25 km reentry profile worked perfectly. I slowed down enough to deploy my chute at around 8 km. Could you be more specific about exactly what is going wrong? Ideally a screenshot during one of your failed reentries where you are going too fast would help the most. 

Do note that for the parachutes to go from semi-deployed to fully deployed does take some time. So if you're worried about not slowing down quick enough (meaning you hit the ground before they are finished being fully deployed) then you can raise the fully deploy altitude in the right click menu of the chute. Note that this value is meters above the ground below you, not meters above sea level, so if you come in over a mountain you should still be okay.

[Reusables]

1 hour ago, Spricigo said:

@Abastro the heatshield is not for heat tolerance,  but for drag.  For what it's worth one can put a aerodynamic nose cone and make it draggier then a Mk1 command pod topped by a parachute 

Hmm, it could be the case.

I think mk1 pod + crew cabin topped by a parachute won't have heating problem, though.

[Spricigo]

47 minutes ago, Abastro said:

Hmm, it could be the case.

I think mk1 pod + crew cabin topped by a parachute won't have heating problem, though.

Well,  I tested.  Going at 2km/s it exploded at 23km. Periapsis set at 20km from 80km orbit. 

Enough to convince me that a safe trajectory is very narrow if possible at all. 

 

Edited May 24, 2017 by Spricigo

[Reusables]

7 hours ago, Spricigo said:

Well,  I tested.  Going at 2km/s it exploded at 23km. Periapsis set at 20km from 80km orbit. 

Enough to convince me that a safe trajectory is very narrow if possible at all. 

 

Then I need to test with 38km, where it decelerates well while not heating up too fast.

[Spricigo]

23 minutes ago, Abastro said:

Then I need to test with 38km, where it decelerates well while not heating up too fast.

That would fit "too narrow" by my standards.  Mostly because I'd rather take the performance hit during lift off than the increased reentry time. (As my posted craft shows) 

I still think it may not slow down enough,  but will be happy if you prove me wrong. 

[jonpfl]

Here is my ship.

This thing takes off and spins around, how do I stop that?  I put fins on it but it still spins.

 

Thx
jonpfl

[jonpfl]

All,

So I changed the ship and added more fins and it still is very hard to control (and I am fighting it to stop spinning).  I don't have any pilots left, they are all stuck in space :-(

Any advice?  This is getting frustrating.

 

Thx
jonpfl

[jonpfl]

All,

Still blowing up, if I add stuff as requested, I cannot control the ship so I took it off.

I guess I need to add that radial thing, sucks not having a pilot!!

 

Thx
jonpfl

[bewing]

The stayputnik that you are trying to use is worse than a level 1 pilot. It has no SAS control at all. The OKTO is equal to a level 1 pilot. The HECS is equivalent to a level 2 pilot. The OKTO2 is equivalent to a level 3 pilot. And so on.

And to make a rocket like that stable with no SAS, you need to be very careful about drag. You want very low drag at the front of your rocket. And plenty of drag at the very back end of your rocket. And as much mass as possible at the front end of your rocket. It's a very tricky balancing act.

 

[Spricigo]

1 hour ago, jonpfl said:

Here is my ship.

This thing takes off and spins around, how do I stop that?  I put fins on it but it still spins.

 

Thx
jonpfl

You have CoD in front of CoM.  Your rocket want to fly tail first.

The solution it's to move the CoM upward or the CoD rearward. 

My suggestions: change a Swivel for  a Reliant get rid of the 2nd (-1,75t at launchpad),  put only 4 basic fins at the bottom fuel tank,  put the cabin on top of the pod (for stability at reentry),  remove 2 hammers. Tilt the rocket 5° in the editor and use a Launch Stability Enhancer to hold it before launch. 

Launch it (unkerbaled)  and let it go.  Just stage when SRBs burn out.  DONT TRY TO STEER IT.

Depending on the result of the test flight you will adjust the initial tilt:

Started to fall before reaching space? Tilt up (more vertical) 

Reached space but run out of fuel before orbit? Tilt down (more horizontal)  

Once you get the correct angle you may archive a 75x75km orbit with 200-300m/s for return.  

 

Edit: notice I didn't tested it myself,  maybe it still flip (drag from exposed parts of the cabin).  Also settings fuel priority so lower tanks empty first help to maintain the CoM forward. 

 

Edited May 25, 2017 by Spricigo

[FullMetalMachinist]

1 hour ago, jonpfl said:

All,

So I changed the ship and added more fins and it still is very hard to control (and I am fighting it to stop spinning).  I don't have any pilots left, they are all stuck in space :-(

Any advice?  This is getting frustrating.

I'm going to expand on @Spricigo's excellent advice above.

The reason that you're having such a hard time, is two-fold. When you first launch that rocket, the only control authority it has is from the reaction wheels in the command pod, which is not very much. The other reason is that (as was said above) you're essentially trying to throw a dart backwards. It naturally wants to flip around, and you have no way of countering that natural tendency. 

Another thing is that you have way too much thrust in your first stage from those four boosters. I also agree that you should get rid of two of them, and ignite the main engine at the same time. You could also probably add a little fuel tank to the first stage to give you back some of that dV that you lost from not using those two solid boosters. I also concur with using a swivel instead of the reliant. It might seem like the reliant is better, but trust me, you really need the gimbal that the swivel gives you. Also, make sure that second liquid fuel engine is a swivel as well (and when you unlock it, you're going to want to use a terrier there instead). That way you can get rid of those basic fins near the top which are almost certainly causing you some drag problems.

I also agree with @bewing that the Stayputnik is doing you more harm than good.

[jonpfl]

23 minutes ago, Spricigo said:

You have CoD in front of CoM.  Your rocket want to fly tail first.

The solution it's to move the CoM upward or the CoD rearward. 

My suggestions: change a Swivel for  a Reliant get rid of the 2nd (-1,75t at launchpad),  put only 4 basic fins at the bottom fuel tank,  put the cabin on top of the pod (for stability at reentry),  remove 2 hammers. Tilt the rocket 5° in the editor and use a Launch Stability Enhancer to hold it before launch. 

Launch it (unkerbaled)  and let it go.  Just stage when SRBs burn out.  DONT TRY TO STEER IT.

Depending on the result of the test flight you will adjust the initial tilt:

Started to fall before reaching space? Tilt up (more vertical) 

Reached space but run out of fuel before orbit? Tilt down (more horizontal)  

Once you get the correct angle you may archive a 75x75km orbit with 200-300m/s for return.  

 

Edit: notice I didn't tested it myself,  maybe it still flip (drag from exposed parts of the cabin).  Also settings fuel priority so lower tanks empty first help to maintain the CoM forward. 

 

Ok, sorry for all the dumb questions

1) What is CoD (center of drag?  If so, how do you know where that is?)?  I assume CoM is center of mass.
2) How do you move either up or down?
3) What does -1.75t mean?
4) How do you tilt the rocket in the editor?

Thx
jonpfl
 

9 minutes ago, FullMetalMachinist said:

I'm going to expand on @Spricigo's excellent advice above.

The reason that you're having such a hard time, is two-fold. When you first launch that rocket, the only control authority it has is from the reaction wheels in the command pod, which is not very much. The other reason is that (as was said above) you're essentially trying to throw a dart backwards. It naturally wants to flip around, and you have no way of countering that natural tendency. 

Another thing is that you have way too much thrust in your first stage from those four boosters. I also agree that you should get rid of two of them, and ignite the main engine at the same time. You could also probably add a little fuel tank to the first stage to give you back some of that dV that you lost from not using those two solid boosters. I also concur with using a swivel instead of the reliant. It might seem like the reliant is better, but trust me, you really need the gimbal that the swivel gives you. Also, make sure that second liquid fuel engine is a swivel as well (and when you unlock it, you're going to want to use a terrier there instead). That way you can get rid of those basic fins near the top which are almost certainly causing you some drag problems.

I also agree with @bewing that the Stayputnik is doing you more harm than good.

1) What do you mean by "control authority"?  What are reaction wheels?

Thx
jonpfl

Edited May 25, 2017 by jonpfl

[FullMetalMachinist]

2 minutes ago, jonpfl said:

What do you mean by "control authority"?

It's just a catch-all term for any way of providing positive, active (as opposed to passive) control for your ship. For example: fins that move to steer your rocket (only works in an atmosphere), RCS thrusters that rotate your ship using compressed gas (basically little tiny rocket engines), rocket engines that gimbal (change the direction they thrust to push the ship in the opposite direction), and reaction wheels. 

6 minutes ago, jonpfl said:

What are reaction wheels?

Reaction wheels are basically flywheels that, when spun, provide torque to the ship around it. There's a pretty lengthy discussion here about how and why they work:

 

[Spricigo]

@FullMetalMachinist he is using the Swivel. And I suggested to use the Reliant instead.  

Notice that I did it because I also suggest to design the rocket to be aerodynamic stable and capable to do a gravity turn, hands free, from the launchpad.  (Also provided a working example a few posts before and again in this one) 

@jonpfl there is no dumb questions. 

1.yes. center of drag and center of mass. I flipped enough rockets to learn how to eyeball it with some accuracy.  In the editor,  bottom left,  there is 3 circular icons ,  the one with a weight symbol toggles the CoM indicator. Drag need to be estimated based on the exposed area (and some perks of KSP's drag model) 

2.the only way to move it around its by moving around the mass/draggy parts. (e.g. fins at the rear,  using less/lighter engines) 

3. Lighter by 1750 kilograms.  One way to increase deltaV it's to reduce dry weight (everything except fuel) . 

4.using the rotate toll,  the globe icon at top left.  The four icons are for place,  translate,  rotate and reroot. You will need a Launch Stability Enhancer (Also known as Launch clamps, technology node General Construction required)to keep it in position until launch.  Otherwise you will need to do the initial tilt manually (which is not as reliable as launch clamps) 

I will again offer 

kerbalx.com/Spricigo/Orbiter-Zero It fly itself to space.  You just need a astronaut (a scientist or engineer will do) to point prograde near apoapsis.  Also cheaper and carry more passengers than your current design.  Also stable at reentry. 

[FullMetalMachinist]

10 minutes ago, Spricigo said:

@FullMetalMachinist he is using the Swivel. And I suggested to use the Reliant instead.  

Notice that I did it because I also suggest to design the rocket to be aerodynamic stable and capable to do a gravity turn, hands free, from the launchpad.  (Also provided a working example a few posts before and again in this one) 

Ah, my mistake. Hard to tell the difference from just a screenshot (for me at least). 

[Reusables]

3 hours ago, Spricigo said:

That would fit "too narrow" by my standards.  Mostly because I'd rather take the performance hit during lift off than the increased reentry time. (As my posted craft shows) 

I still think it may not slow down enough,  but will be happy if you prove me wrong. 

Dang, you're right, it explodes. Crew cabin is weaker than I thought.. 

So it seems that couple of elevon 1 saved my crews' lives. I didn't know this..;

EDIT: It also allows control of my craft, so I was happily using it with aerodynamic rockets.

Besides, I've been actually putting a radial parachute in front of the ml16 one. Which helps heating problem even more.

Edited May 25, 2017 by Reusables

[Spricigo]

Just now, FullMetalMachinist said:

Ah, my mistake. Hard to tell the difference from just a screenshot (for me at least). 

Also don't have eyes sharp like that,  but KER says 215kN. That's how I know.  

[jonpfl]

9 hours ago, Spricigo said:

@FullMetalMachinist he is using the Swivel. And I suggested to use the Reliant instead.  

Notice that I did it because I also suggest to design the rocket to be aerodynamic stable and capable to do a gravity turn, hands free, from the launchpad.  (Also provided a working example a few posts before and again in this one) 

@jonpfl there is no dumb questions. 

1.yes. center of drag and center of mass. I flipped enough rockets to learn how to eyeball it with some accuracy.  In the editor,  bottom left,  there is 3 circular icons ,  the one with a weight symbol toggles the CoM indicator. Drag need to be estimated based on the exposed area (and some perks of KSP's drag model) 

2.the only way to move it around its by moving around the mass/draggy parts. (e.g. fins at the rear,  using less/lighter engines) 

3. Lighter by 1750 kilograms.  One way to increase deltaV it's to reduce dry weight (everything except fuel) . 

4.using the rotate toll,  the globe icon at top left.  The four icons are for place,  translate,  rotate and reroot. You will need a Launch Stability Enhancer (Also known as Launch clamps, technology node General Construction required)to keep it in position until launch.  Otherwise you will need to do the initial tilt manually (which is not as reliable as launch clamps) 

I will again offer 

kerbalx.com/Spricigo/Orbiter-Zero It fly itself to space.  You just need a astronaut (a scientist or engineer will do) to point prograde near apoapsis.  Also cheaper and carry more passengers than your current design.  Also stable at reentry. 

Ok, I will download this tonight and try it, thanks for the link!!!

I guess, at the very least, I can use your design, feel comfortable with it and then start tinkering with it.  I hope the parts on it have been unlocked (what happens if they have not, will it not allow me to fly it?).  

I might go start a new game in science mode so I can better understand things, I am the type who usually likes to just right in but this game seems to have a massive learning curve (which is good).

Thx
jonpfl

[Kryxal]

To quickly fix that rocket, I'd dial the SRBs down by half and lose stage #4's decoupler and engine.  There's little point going from a reliant and some fuel, to a second reliant and some fuel.  If you have the terrier (I think, the 909 anyway) unlocked, that would be a reasonable engine for that stage if you want to keep it.  Also, move the fins down on to stage 5, they're too high.

[jonpfl]

All,

I started a new game in v1.3 in science mode and am hoping to get to the moon soon, what do you suggest I research next?

Thx
jonpfl

[bewing]

Electricity for solar panels, and the OKTO.

[Spricigo]

Personally I unlock Electricity,  Precision Propulsion, Miniaturisation,  Advanced Flight Control and Heavy Rocketry in that order.