Am I doing the Wiki Campaign wrong?

[Tux1]

I have tried starting the wiki campaign, but I feel like I'm doing something wrong. I try to build the cheapest rockets I can according to the rules, but they turn out weird!

Mission 1: Solid Fuel Rocketry

My Rocket: Stayputnik with RT-10 booster and 8 fuel. It went up 1 kilometer.

My Second Rocket: OKTO with 4 Sepratrons, each with their fuel scraped down. There is a radially attached drough chute on top. I go up using the first 2 engines, then angle my craft 45 degrees and shoot the second engines. I get up about 50 meters.

I don't know about you, but this doesn't seem very realistic. Am I doing something wrong?

[Harry Rhodan]

1 hour ago, Tux1 said:

Am I doing something wrong?

Seperatrons are not boosters, they are meant to nudge heavy radially attached stages away from the rest of the rocket. And reducing the amount of fuel is also a bad idea. If you have trouble controlling a stage that mainly uses SRBs you could try reducing the thrust.

[Spricigo]

<scratches head>

exactly what you think is unrealistic? 

Your first rocket had a dry mass of 800kg, fuel mass 60kg (8 units). thrust 198kN, Isp 140.That results in 23 TWR and deltaV 99m/s. In simple terms: lots of power and a small autonomy. 

You secound rocket had dry mass 225kg, fuel mass ?? (for my calculations I will assume 1 unit so 7,5kg), thrust 27,58 (a pair of separtrons) Isp 118.  Result in 12TWR and 37m/s. Still a lot of power and small autonomy, however both are smaller.

So you second rocket have less power and less autonomy. Evidently it will build up less momentum(velocity) before the tanks run dry. Also by the time it run dry it had climbed to a much lesser height.

The max height of a projectile in ballistic trajectory,  given vertical velocity at initial height can be determined by: V² =   2gh.  Lets ignore exact number for an instant and focus on what this litte equation says: the max height is proportional to the square of  initial vertical velocity. That is: if the if the craft A have twice the speed of craft B at the time they run out of fuel the additional height it will climb will be four times, If the difference in velocity is three times the height difference will be nine! times.

 

There is an extra factor to be considered: Drag. How much drag is acting upon  each craft is probably not much different (for a given speed), however the fist craft have a much bigger thrust to counter it and after the engines run dry it still have four times more mass to resist it.

Edited August 4, 2017 by Spricigo

[Zhetaan]

@Tux1:

You're not following the intended campaign, true, but the rocket you designed is working exactly as it should.  I will not revisit the reasons why you generally should not use Seperatrons as boosters; simply accept based on your own experience that they are inadequate to the task.

The point of these two missions in the campaign is to show both the basics of how to fly and the advantage of staged rocket designs.  You're meant to keep a full fuel load for each but if you wish, you may turn down the thrust limiter to keep the thrust-to-weight ratio at about 2.  For your first rocket with just the Stayputnik and the RT-10, the mass is 3.61 tonnes.  The weight on Kerbin's surface is therefore 3.61 * 9.81 (this is the acceleration due to gravity at the surface) = 35.414 kilonewtons, or kN.  The thrust of the RT-10 at sea level is 197.90 kN, so the full thrust-to-weight is 197.90 / 35.414, or approximately 5.59.  To start with a thrust-to-weight ratio at around 2--and do keep in mind that this will change with altitude (gravitational acceleration decreases as you go higher), with air pressure (thrust increases as air gets thinner), and with the rocket's mass (weight decreases as you throw propellant out the back)--turn down the thrust limiter to about 36%.

For the second rocket, the idea is that you take your first rocket (or something close to it) and add a decoupler and second RT-10.  Since you'll be higher up when you light it, you may want to consider turning down the thrust limiter on the second stage (the original part of the rocket) even further, to about 30%, but for the first stage, the second RT-10 and decoupler add another 3.61 tonnes.  Forgetting the battery and parachute for now, the weight is 70.828 kN, but the thrust is the same, so the new thrust-to-weight ratio is 2.79.  To turn it down to 2, set the thrust limiter to 72% on the lower booster.

The reasons for turning down the thrust are several.  First, you have fewer drag problems in the lower atmosphere, whether they come from heating or from the air tearing off pieces of your rocket.  Second, the rocket is easier to control if the high relative wind speed is not forcing it into a particular orientation--efficient rockets need to turn.  Third, it is inefficient to burn so much fuel so low in the atmosphere; all rockets perform better in vacuum than they do at sea level, so while it is important to get out of the lowest part of the atmosphere quickly, there is also a diminishing return where you burn the fuel that you would otherwise save to make it happen faster than necessary.

What you will see for having done this is that turning down the thrust limiter makes your rocket go higher on the same load of fuel (to a point).

For the second mission, the idea is that your first stage will not go so high as your earlier rocket (because it's heavier), but because you have a second stage, you'll go far higher than you would any other way.  If you want to test this more thoroughly, you can do so with a rocket that uses two RT-10 boosters side-by-side and another that has them staged in sequence.  I will leave the problem of designing a balanced twin-booster rocket to you.

P.S.  I will say that inasmuch as this campaign is meant to re-enact historical space flight, you've done especially well:  your second rocket is your very own Four-Inch Flight! 

P.P.S.  Don't try to save money with solid rocket boosters.  They're already the cheapest rockets in the game.

Edited August 4, 2017 by Zhetaan

[James M]

On 8/4/2017 at 9:52 AM, Zhetaan said:

P.P.S.  Don't try to save money with solid rocket boosters.  They're already the cheapest rockets in the game.

Lol challenge accepted! Once console finally gets its update I plan on building the cheapest vanilla probe to orbit rocket  

[Zhetaan]

7 hours ago, James M said:

Lol challenge accepted! Once console finally gets its update I plan on building the cheapest vanilla probe to orbit rocket  

In that case ....

Get to Space with Only SRBs!

Roads to Duna: No Moar Boosters (Sub-challenge: A Solid Plan)

These are still actively updated as of this week.  There are many, many, many older versions of this challenge that you may consider resurrecting, as well.

[wumpus]

I hope you realize that the campaigns are a bit of an alternative to career mode in the game.  I really doubt they have been updated while drastic changes have happened in the game.  Some general principles:

• Be ready to skip anything that doesn't appeal to you.  This is one of the main advantages to the campaign over career mode.
• Don't take early rocketry too seriously.  Since you can't set a maneuver node on a pad, hitting a specific place with a missile is harder than it should be (especially for starting out)
• Rendezvous and docking are harder than landing on the Mun (and Minmus).  Since they are unneeded for these feats, they are included in the campaign due to historical events.  If you aren't playing with realism overhaul (and thus need Apollo-style missions to the moon), I'd skip them until after landing.

I'm glad the campaigns haven't been entirely forgotten, they gave me a great place to start before even "science career mode" and are better in many ways to the current career mode.  Just don't expect everything to play well with 1.3.0 (and no, you couldn't include maneuver nodes from the pad then.  I wouldn't be surprised if "kerbal rocketry", including hitting separate islands/continents, was written before maneuver nodes existed at all and has merely been copied ever since).