Heading Back to Rocketry School (Help Needed)

[Turk_WLF]

I HATE my Rocket Designs in 1.1.3, because I have to use way too large of rockets to do a simple task such as getting an Mk 1-2 Command Pod into a Low Kerbin Orbit (85 KM). The best way I can explain it is to use a real world example since I don’t have access to a 3^rd party hosting site for pictures.

I have a Mercury Capsule & a full Saturn V Rocket just to get it in a low Earth Orbit. (Crazy Design I know)

As I understand it I need 3400 Delta V just for an 80 KM Orbit, Therefore I would like to request some design suggestions with 5 requirements.

1. Using Stock Parts & MechJeb (the only Mod)

2. Please keep answers in Simple/Non-Scientific Terms

3. A Design for  a 1.25m,  2.5 m & payload rocket (hopefully I’ll get a design of each)

4. It must be reach at least an 80 km orbit

5. Pictures would be nice if possible

Thank you for your help & time,

To clarify Number 3:

What I meant by 1.25m would be the same size as the Mk 1 Command Pod & the 2.5m would be the same size as the Mk 1-2 Command Pod

Edited September 7, 2016 by Turk_WLF

[Aegolius13]

I put together a simple test launch rig as follows:

Booster stage: two Thumpers, radially attached to core stage with a decoupler in the middle and struts at top and bottom.  Advanced nose cones on top.  I left the Thumpers at full thrust but you could turn down a little if you wanted. 

Core stage: Skipper with orange tank.  Rockmax decoupler on top. 

Sustainer stage: Poodle with Rockomax 16 tank.  Rockmax decoupler on top. 

Payload: Mk 1-2 pod with XL parachute on the front.    

This thing worked fairly well, and got to 84km circular orbit with 2100+ delta-v left.  Launch TWR was a bit over 1.5.  My launch flying was not the greatest, probably owing to the amount of thrust from the boosters.  At least basic fins might help.  You'd probably want to add at least solar panels to the payload, and maybe batteries or science equipment or whatnot, but there's quite a bit of extra fuel here to worth with.  

You might be able to go lighter and use a Rockomax 8 tank and Terrier or Dart for the top stage, and maybe lose the radial boosters or replace with Hammers.  But it would be a little anemic, and not much cheaper (maybe more expensive with a Dart).  

 

 

Not sure what you mean on item 3 for a 1.25m design.  You mean to lift the smaller 1-kerbal capsule?  I would definitely not recommend trying to launch the Mk 1-2 with only 1.25m parts.  

How are you doing your maneuver to get to orbit (i.e., a gravity turn, go straight up until you hit space, something else?)  Often troubles getting to LKO can be maneuver related as well as design related.  

 

 

Edited September 7, 2016 by Aegolius13
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[Diche Bach]

I pay mostly modded, and haven't played vanilla for a long time. But I've been testing out mods, so it was a small thing to do a quick vanilla sandbox (so i had all the parts). Sorry too late here to fiddle with images, but if you look on Kerbal X you are sure to find a lot of stuff:

Stage 0----2 radial chutes on an Mk1 pod with heashield

Stage 1------2 radial drogues

Stage 2: one of the FLT 1.25m tanks (not shortest but slightly shorter than the middle length) and then a Reliant engine (the 1.25 t)

Stage 3: decoupler

Stage 4: Another FLT 1.25m tank longer + a "Vector" engine (says ~850 thrust, never used it before)

Stage 5: decoupler

Stage 6: Reaction wheel + FLT 1.25m to2.5m + Rockmax 2.5m tank, plus a Mainsail (overkill it seems, but it works)

              Four radial attached delta wings, with 4 radial decouplers midway between each wing

              Four kickback SRBs attached to the decouplers, with nose cones on the top.

              Run one section of light strut set to 4 point radial symmetry between the SRBs near the top.

That is pretty much it. Total overkill, and the technique for flying it up is probably more important than the craft itself.

 

1. Set Mainsail to ~5% thrust at launchpad

2. Engage SAS (if you wanted to add RCS to it you could, but it isn't really necessary) which means you need to use a "Pilot" Kerbal

3. Engage Stage 6, and keep the LqOx engine on low power (just for the maneuvering it affords)

4. Burn radial (straight up) until you are comfortable starting a gravity turn to eastish (can be done as early as 50m/s but 150 is "safer" from a manuverability standpoint and less risky of tumbling.

5. Once you are fast enough, begin to turn slowly and patiently to the east (just press lightly on D key to yaw to starboard . . . pause a half-second or so. . . press it lightly again . .  pause . . . press again . . . pause . . . press again . .. pause . . .do this until your craft is tilted at about a 10 to 20 degree angle. 10 is "safer" but 20 would be more "efficient."

6. Once you are flying east and radial and hit about 300m/s it is just a matter of keeping it from wobbling off course and keeping a nice stead rate of eastward yawing (toward horizon) as you continue to gain speed and altitude.

7. Very rough ballparks: 25 degrees yawed to east by about 250-300m/s and perhaps 15,000 to 25,000m alt

     35 to 40 degrees at about 350 to 450 m/s and  35,000 to 45,000 m

     55 to 65 degreees at about 750m/s and 65,000

8. When you get to 65,000 and are confident you are going to get higher than that (at least 70 which is edge of atmosphere) you can lay off the thrust and yaw your ship almost to 90 degrees. If you are not as confident at maneuvering, keep it in the 75-degree range until you begin your apoapsis burn.

9. Check flight planner and set a manuever node at apoapsis. You can take the time to actually set this up for your desired altitude but it that isn't necessary. Basically you just want to know when you are close to apoapsis, so you can start to burn prograde if not a bit anti-radial (if your prograde marker is still a good ways above the horizon). Basically just burn "at the horizon" (or its environs) till you raise the periapsis to above 70km. You are now in orbit.

It is of course easy to make a lot of various mistakes along the way, and wind up either crashing into the planet or wobbling around wasting fuel trying to keep it going in the right direction, else setting up a Kerbin escape trajectory. But the only real way to learn how not to do those things, and instead handle the craft well, is to practice. Use revert flight or F5-F9 to your advantage till you get the hang of it.

     

[Streetwind]

3 hours ago, Turk_WLF said:

I have a Mercury Capsule & a full Saturn V Rocket just to get it in a low Earth Orbit. (Crazy Design I know)

I once wrote a post about mass fractions that I keep linking to because it keeps being relevant When it comes to dV, the mass fraction is the number one thing to know about. If you understand this concept, you will have no problem getting exactly as much dV as you like. I know you said you don't want too much scientific stuff, so feel free to skip this if you feel so inclined, but I really tried to keep it simple over there. Basically, if you are able to perform multiplication and division, and are able to find the logarithm button on a calculator, you can get through this just fine. Give it a try, you might surprise yourself!

As an example of how much you can achieve with simple and efficient vehicles that have good mass fractions, here's your requested example vehicle for the 1.25m form factor:

- Mk16 Parachute
- Mk1 Command Pod
- TR-18A Stack Decoupler
- FL-T800 fuel tank
- FL-T800 fuel tank
- LV-T45 'Swivel'

The screenshot even has a heat shield in addition, but it doesn't actually need it to re-enter safely from low Kerbin orbit. Without the heatshield, dV is around 3700 m/s if I recall correctly.

As you may notice, that thing doesn't even stage. It is a SSTO rocket, capable of lifting the one-Kerbal capsule into an 80x80 km equatorial orbit and still having plenty of fuel left for a deorbit burn. You may even be able to get this thing into a polar orbit and return if you fly really well. (Beware too high a throttle when your tanks are nearly empty.)

Edited September 7, 2016 by Streetwind

[Aegolius13]

10 hours ago, Turk_WLF said:

To clarify Number 3:

What I meant by 1.25m would be the same size as the Mk 1 Command Pod & the 2.5m would be the same size as the Mk 1-2 Command Pod

Ah, that makes sense then.  This is my standard issue single-occupant Kerbin orbiter, for LKO rescues and tourists wanting to go to orbit.  Bottom engine is a Swivel, top is a Terrier.  Thrust is a little weak at launch but it gets the job done.   Don't recall the exact figure but I think it gets a least 1200 delta-v left in the tank after reaching orbit.

 

[Diche Bach]

So Aegolius13 and Streetwind have provided some more "bare bones" designs and I provided one that is "excessive" (should be MORE than enough d/V and main challenge might be going too fast in low atmosphere and experiencing loss manueverability)

Somewhere between those two extremes you may find your sweetspot.

Me personally, I like to design things that are capable of doing "more" than what they are designed for initialy. This way, an initial design can be reused and multi-purposed to future missions which may be more demanding. But then that motivation comes primarily from using Kerbal Construction Time and Stage Recovery mods which make career into a bit more of a "strategic" enterprise: reuse designs = more cost effective.