Trying to make it into orbit

[miki1234]

Hi guys!

 

I'm trying to reach orbit using this vessal i designed

https://ufile.io/2e4f8

 

Any ideas on how to make it better? Right now I barely make it into orbit or get burned in on re entry..

Pics:

https://ibb.co/dcFDd5
https://ibb.co/emwarQ
https://ibb.co/dmWmy5

 

There is a solid state stage and two engines (Outlined)

Thanks:-)

 

Edited April 11, 2017 by miki1234
Added pics

[Vanamonde]

Pictures are more attractive to viewers than downloads, since we wouldn't know what we'd be downloading. How about some screenshots? 

[Harry Rhodan]

The most obvious proble is that you launch with 6 SRBs that are absolutely unsteerable because your winglets clip right into them. You basically have to go straight up until they are burned down at which point you have an AP slightly above 70km but next to no horizontal speed. That means you have to build up the orbital speed of more than 2000m/s with two stages that have so much fuel that the anemic engines that push them need forever.

My solution would be LESS BOOSTAZ: You really only need them to push you anemic Swivel stage the first few kilometers before it can push itself. Also less fuel on the upper stage to have enough acceleration for the second half of the flight:

This version still has to much initial TWR for my liking. Limiting the thrust of the SRBs will cost you a bit of efficiency but will make the flight more controllable (and slightly more boring).

Also minor nitpicks: There's a useless second Heatshield between the science jr and the crew thing. There are also a few useless struts and decouplers on the upper part of the rocket. And I don't know why you need that giant ugly 2.5m decoupler btween your upper and lower stages. The payload is still too top heavy and will probably tumble and burn on reentry.

[bewing]

Well, the first basic answer is Get rid of the heatshield!! Heatshields make your ship much less draggy on reentry, and you need drag on reentry in order to slow down and not die. So what a heatshield does is make you face a lot more heat, and then it gives you the capability of facing a lot more heat. But it's a race and sometimes you lose. If you replace the heatshield with some other part -- for example a service bay -- then it will have a lot of drag (especially if you open the doors!) and will slow your craft down very quickly, and can easily handle the amount of heat you will experience reentering from orbit. Make sure you use all that extra fuel in this ship to brake before you reenter.

There are other little quibbles -- you do not need to strut your launch clamps, for one ... I don't think any of these struts are doing you any good. Those radiator panels aren't doing you any good. The rocket is so stable it won't do a gravity turn. I assume that you are trying to fill a bunch of contracts with this launch? Because you have a lot of stuff stuck to this ship that looks like it's for part test contracts.

 

Edited April 12, 2017 by bewing

[Aegolius13]

I would suggest turning your Swivel on at least a bit at launch, especially if you remove some of the SRBs.   This can allow you to steer without needing control surfaces or the like. 

Long, thin craft like your top stage are inherently hard to reenter with,  since they naturally tend to knife through the air rather than slowing down.  Agree an open service bay might help.   You could try drogue chutes too, but they don't open that much earlier than regular chutes these days. 

 

[bewing]

BTW, I made it to orbit with your ship, with a huuuuuge amount of fuel left, and I didn't even launch it very efficiently. So if you are barely making it to orbit with this thing, then there are a few tips we need to teach you about gravity turns and when to burn, and how much.

 

[Reusables]

Replace the rockomax(2.5m) decoupler with 1.25m one, it's too draggy for the purpose. Otherwise it looks okay albeit overpowered for its purpose.

As you have a lot of thrust, you should perform gravity turn early. Try hard to turn 5 degrees just after engine ignites, and hold prograde after that.

+ I think you can land on minmus several times with the lifter.

[Alshain]

When you are designing 2 stage lifters (that is 2 stages not counting boosters), remember that the more fuel you add, the more mass you have and therefore your engine becomes quickly insufficient at the upper stage.  The biggest problem I see is the overly large amount of boosters, but the second biggest problem I see is a mother load of fuel tanks on the upper stage.  Your first stage should get you through the thickest parts of the atmosphere, after that you shouldn't need a lot of fuel because the upper stage engine is more efficient at that point.  If you make the upper stage too big, not only does the upper stage engine need more power, but then you have to lift the upper stage which takes more power in the lower stage... the problem feeds on itself.

This of course means you need to know where your engine is best used.  In the case of the Terrier, it's a vacuum engine. Of course upper atmosphere is almost the same as vacuum so it works perfect for that, as long as it isn't over worked.

@Harry Rhodan's lifter looks pretty much like mine would.  Notice how little his upper stage is.  If you are launching a well maneuvered gravity turn, that lifter should have you at about 30-40km (maybe a bit more depending on your piloting) before discarding the first stage.  That is far enough out of the atmosphere to take advantage of the Terrier's efficiency.

[bewing]

I'm still pretty confident that most of these design issues you guys are pointing out were put there deliberately to fill contract requirements.

 

[miki1234]

Many thanks for all the replies ! I will try and test it later when I get home.

 

My main problems were the module heating up and exploding,  and inefficient gravity turning. I tried adding more and more fuel which fed the problem..

 

What is the height / angle you recommend to turn at?

[Kryxal]

That design?  5 degrees right off the pad.  2.76 TWR is way overkill.

[miki1234]

Hi! I've tried modifying using some of the advices given here to the best of my attempts. I didn't make it entirely to orbit and got re burned on entry.. see photos attached

 

Any more notes?

p.s

How do I adjust the TWR?

 

Many thanks

 

[Spricigo]

2 hours ago, miki1234 said:

What is the height / angle you recommend to turn at?

 

My suggestion its to adjust the angle right off the editor and hold it with a launch clamp, start with about 5° and adjust if you notice it go too step(more angle and/or less thrust) or to shallow(less angle and/or more thrust).  Fine tune until it does a gravity turn with minimal effort from your part and it have 'just enough' deltaV to reach a stable low orbit, the result will be a reliable Launch Vehicle that will serve you well for that particular payload mass.

As a rule of thumbs if you reach about 45° at 10km its a good trajectory.  (just notice: make a slow and constant turn(if possible following prograde), an abrupt change of direction will probably make you flip). Another trick its to hover your mouse over the Apoapsis marker in map mode  and see if the time to apoapsis is slowly increasing.

Finally, either learning to calculate by hand (or just estimate) deltaV and TWR or using a mod that gives a readout will be handy to design better crafts.

[bewing]

You are staging your rocket when the first stage runs out of fuel, and lighting the second stage with the terrier engine, right? The first stage won't make it all the way to orbit just by itself in your design.

 

[Ten Key]

 

I am certainly not an expert when it comes to this sort of thing, and I'm sure the other folks posting here will be able to help you out more, but I had a couple of questions based on the above picture. . .

Is there a reason your throttle is not all the way forward? You're pretty much out of the atmosphere at this point, so drag losses aren't a problem. Unless you're having attitude control (steering) issues at a higher throttle setting, there's really no reason to not "stand on the gas".

I'm running an older version of the game at the moment, back when the atmosphere of Kerbin had a lot more drag to it. And even in that environment, I have almost always pitched all the way over to 90 degrees by about 30 - 35 km. In this picture you're at 55 km and still only pitched over to about 45 degrees. For the purposes of getting to orbit, your rocket's velocity can be neatly split into two components-- horizontal and vertical. Any energy you spend in the vertical direction is only temporary. . .Kerbin's gravity will eventually "eat" it. The only velocity you get to keep is your horizontal velocity. The only reason rockets launch vertically is because of atmospheric drag. If Kerbin did not have an atmosphere, and there were no mountains in your way, you could launch a rocket horizontally right off the pad. In this picture, your rocket is more or less halfway between horizontal and vertical, which means fully half of your energy is going to vertical velocity. And you don't get to keep that, so in effect you're wasting half of your delta-v at this point in your flight. 

According to your navball, your rocket's heading in this picture is currently 63 degrees. Unless you're trying to reach an inclined (non-equatorial) orbit, you should try to stay as close to 90 degrees (due east) as possible. The reason for this is that your rocket is not sitting still on the pad. . .it already has an eastward velocity due to Kerbin's rotation. By launching due east, you pick up some extra delta-v for free. 

 

1 hour ago, miki1234 said:

How do I adjust the TWR?

Thrust-to-weight ratio can be found with the following equation. . .

TWR = Thrust / (mass * gravity)

Thrust is the total thrust of your engines. Mass is the current mass of your rocket. Since rockets are mostly fuel, this number changes wildly during flight. Gravity is the local gravity field. Kerbin's gravity is right around 9.81 m/s².

If your TWR is less than one, your rocket will not lift off the pad. If your thrust to weight ratio is barely above one, it will crawl off the pad. If your TWR is too high, you will experience greater drag losses down in Kerbin's lower atmosphere. If your TWR is way too high, you might start to have control problems. 

Aside from redesigning your rocket (too much TWR means too much engine, and engines are heavy) you can use thrust limiters (right click on the engine, its in the menu) to keep your thrust under control. If you can't redesign your rocket for whatever reason, you could also try stagger firing your solid rockets. . .if your have six SRBs in your first stage for example, you could try starting with only four, and then fire the other two once the first four have burnt out. 

[bewing]

Agree with Ten Key -- at that altitude your rocket should be pointed at the horizon, due east  And the nose direction should almost always be pointing at or "below" the prograde marker during ascent. Almost never above.

Edited April 12, 2017 by bewing

[Spricigo]

1 hour ago, miki1234 said:

Hi! I've tried modifying using some of the advices given here to the best of my attempts. I didn't make it entirely to orbit and got re burned on entry.. see photos attached

Any more notes?

Well, there is several ways to improve a design and several design philosophy. Mine is about as good as the other guys (or worse). I usually design my launch vehicles following this procedure:

1.Define a Payload mass/size and orbit height. I build a 'test weight' on top a decoupler as stage 0.

2.Design stage 1: vacuum engine, TWR > .5, deltaV ~500m/s

3. Design Stage 2: liquid fuel engine, TWR > 1, deltaV ~ 500-1000m/s

4.Design Stage 3:

      4a. 2x radial decouplers with crossfeed enabled, SRBs with Fuel tanks on top, 1.5 < initial TWR <2.5 (depends also on final TWR, stage burn time and considerations about drag/heat), deltaV = whatever is missing in upper stages. The fuel tanks are to feed the liquid fuel engine of stage 2 for just about SRB's burn time

      4b. (For smaller payloads) Single SRB, 1.4 < initial TWR < 2 (same consideration as 4a). DeltaV = whatever is missing in upper stages.

      4c (Bigger payloads), Same as 4a but with more than 2x radial SRBs.

5.  Basic fins (4-8) to help stability.

6. Set incination in editor between 1° and 10°. Hold in place with launch clamp.

7. Add gizmos from smart parts mod for staging.

8. Test flight, adjust steps 4 and 6 until the launch vehicle is able to put the payload in the target orbit with minimal input, reducing the cost as possible(/convenient).

My launch vehicles either reach the desired apoapsis with SAS off and no input or with SAS set to prograde when I reach a specific speed (varies between 50m/s and 200m/s). The throttle is always at 100% during the ascent  and the circularization is manual.

That said you craft seems to have enough deltaV to reach a low orbit with some margin. You only need to adjust your trajectory, which may require some TWR adjustment to avoid control/heat/drag issues.

2 hours ago, miki1234 said:

How do I adjust the TWR?

As pointed by @Ten Key: Its important to notice that the value varies in flight. By engine choice, thrust limit and throttle you change the Thrust part; by adding or removing parts and resources you change the mass part. If it is too low you will not make orbit in time, if too high may cause loss of control, drag and heat.

Particularly relevant for pure SRBs stages since you cant turn down your throttle to keep TWR in check.

 

 

[Regor]

I only have one question for you. How does the SciJr even survive?! I put it on top of a heat shield and it still blows up in my face.

[bewing]

There needs to be one part between the scijr and the heatshield. And if you burn your engines to get your reentry speed below 1800 m/s they don't blow up no matter what you do.

[Alshain]

18 hours ago, miki1234 said:

My main problems were the module heating up and exploding,  and inefficient gravity turning. I tried adding more and more fuel which fed the problem..

The best gravity turn is a real gravity turn, but it takes practice to get it right.  If you can get your Launchpad Atmospheric TWR to around 1.5, then launch and tip over about 5 degrees just a bit off the pad.  Wait for the rocket to center (the SAS will stop making adjustments as seen in the lower left on the HUD), turn off SAS, and take your hands off the keyboard.  The rocket should fly it's own gravity turn, at least most of the way.  Minor adjustments may be needed.

[Regor]

7 hours ago, bewing said:

There needs to be one part between the scijr and the heatshield. And if you burn your engines to get your reentry speed below 1800 m/s they don't blow up no matter what you do.

Thanks!

[phoenixr]

Regarding your burnup issue:

- Make sure the Science Junior is closed if you used it - it doesn't like heat and explodes very easily if it's open. Right click and Close.

- Your return section is long and top heavy (the Mk1 capsule is quite heavy). This will cause it to tumble or invert completely. You can try to put some fins on the Mk1 to generate some aero drag and guide it so it comes down on it's own bottom first - where the heatshield is. This can cause some stability issues during your ascent, so you might want to put bigger fins on your boosters/lower stage to counter balance the aero drag on front that will want to invert your rocket. Airbrakes would be best because you can open them only for the return, but they are unlocked later in the techtree

- Heatshield are not always necessary if you can make a gentle reentry - You can use another heat tolerant part too - engines for example or some aero caps (black parts are often more heat tolerant, but you can right click and check).

Edited April 13, 2017 by phoenixr

[AeroGav]

On 12/04/2017 at 6:16 PM, miki1234 said:

Hi! I've tried modifying using some of the advices given here to the best of my attempts. I didn't make it entirely to orbit and got re burned on entry.. see photos attached

The problem is that on the way up, you want your rocket pointing forwards.   However, because your heat shield is on the back of the re-entry stage, you want it to go backwards on the way back down.  This also is a high drag config, that helps you slow down.

To show you what's going on , take your complete rocket and temporarily remove everything but the re-entry stage -

You can see the CoL is behind CoM, so it's going to want to fly forwards.  Like I say, good for going up, not so good for re-entry if the heat shield is on the back.     The best solution is steerable fins,  but I'm guessing you don't have those because they're in the Aviation tech node and you're into building rockets, right?

One workaround is to put fins on the re-entry stage to make CoL in front of CoM.   This makes it fly backwards

Now, we don't want our rocket flying backwards or we will not go to space today.   So, reattach stages one at a time and add fins to get CoL where it should be for forward flight.   Starting with the upper stage, 6 way fins keep CoL going where it should -

For the lower stage, four way fins are needed to bring CoL down far enough -

A pair of fins on each booster ensures the rocket is stable from liftoff, even with that pineapple tree on top.

Now, that is a lot of fins.  9 of them get carried all the way to orbit, and another 8 leave the pad.  Still , at 37kg each the weight isn't too bad.    The fact your rocket is so tall makes this approach harder.

Copy of the "finspam" version here https://www.dropbox.com/s/vvm9tzkzvkcjtl1/basic3.craft?dl=0

A more elegant solution is to have your rocket re-enter the same way it takes off.  For this you need an inline crew pod.   Since you're rocket centric i'm assuming you are more likely to have the mk1 lander can, so built something around this.      The Lander can and Crew cabin are at the bottom/back  of the re-entry stage.   Ahead of them is the heat shield.   In front of the heat shield is a science jnr. then an aero nose cone.   On re-entry, the science jr. explodes, detaching the nose cone and exposing the heat shield.  The vessel becomes high drag and slows down fast.    If you think exploding science jnr.s are too chancey,  then perhaps a decoupler to remove the nose cone from the heat shield before re-entry is the way to go.

I stripped a bit too much fuel and boosters out of this.  It took me a few attempts to get to orbit (gravity turn), but i eventually made it with 300dv to spare.

This is a copy of the "inline" version -

https://www.dropbox.com/s/1hrud23ucwoqoji/basic5.craft?dl=0

Edited April 14, 2017 by AeroGav

[Urses]

Many wise man had a word.

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. For exercise they are realy helpful. Your only stearing ability on start is the pod all the way up and SRB's push you all the way up without realy control ability. 2 fins on SRB 1 for each and 4 steerable winglets or Tailfins on your first liquide fuel stage (downwards) and try out if you have it easier this way.

Funny Kabooms 

Urses 

PS: try, evaluate, try again. It is not rocketscience... ohhh

Edited April 14, 2017 by Urses

[miki1234]

Thanks again for all the replies. I have tried handling the trust first. I have calculated a mass of 24t approx. That means that two RT-10 engines with the capacity of about 90% will do the optimal job?

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?