+2500 m/s (redux)

[MrChris]

Hi all. As a newcomer, I'm struggling to achieve the early "Set speed record of 2,500 m/s" contract in Career Mode. I note the earlier thread on this same topic, but it doesn't really address the problem I'm facing, as the proposed solution is not possible to me at present.

My resources are not great. I have the following parts available:

Fuel tank

• FL-T100
  

Engine

• Liquid fueled:
  
  • LV-T30
    

  [*]Solid fuel:

  • RT-10 Hammer booster
    
  • RT-5 Flea booster
    

Structural

• TR-18A stack decoupler
  

Plus parachute, Mk1 command pod, and a few other elements I don't think are of use to me here.

I've mostly tried a three-stage design with a pair of the RT-10 boosters, a liquid engine and a couple of fuel tanks so that boosters and liquid engine run out together and are jettisoned. The other two stages are liquid engines.

Yet, try as I might, I cannot reach the 2500 m/s achievement. My best was 2340, and that was orbit speed. I suspect my ground speed was lower.

Any advice on how to pass this?

Edited October 11, 2015 by MrChris

[DeMatt]

Higher orbit.

Increase your apoapsis, leave your periapsis around 70 km. All orbits in KSP are Keplerian; higher apoapsis = faster speed at (fixed) periapsis. 2.5km/s isn't going to kick you out of Kerbin sphere of influence (that takes more like 3.4km/s).

[MrChris]

Thanks for the lightning-quick response. My problem is in achieving an orbit at all given my weight limit of 18 tonnes. Generally I have been aiming for an initial (suborbital) apoapsis of about 50 km, and then try burning prograde at that to achieve orbital velocity. But I run out of fuel long before I can achieve 2500 m/s.

[Mastikator]

A mun flyby will break that record, and will get you a mun flyby.

[MrChris]

Unfortunately I don't have access to more parts than I listed in my first post, and I can't reach even orbit with those.

[ForScience6686]

Start off with boosters to get altitude for better efficiency of your rocket engines. You'll make orbit at that speed, so make sure you have enough left over to de orbit.

[Laie]

Rephrasing DeMatt's answer:

if you are in a low circular orbit, you will already be going ~2200m/s. Adding 300m/s to that isn't that hard, really, and you will still be in a pretty low orbit around kerbin.

(that said, why don't you unlock a few tech nodes? It can be done with the stuff you have, but more & better stuff will make the task easier.)

Edited October 6, 2015 by Laie

[Chaos_Klaus]

Why don't you just get more science and get better engines?

Don't use SRBs when you are on a weight limit. Use liquid fuel only.

[Invader Jim]

I just did it to see if I could. My ship:

Mk1 command pod Plus parachute, TR-18A +

• FL-T100 (10)
  
• T30
  
• TR-18A
  
• RT-10 Hammer booster
  
• TR-18A
  
• RT-10 Hammer booster
  
• 
  

It wasn't pretty and I bet there are better ways but this rocket exceeded 2500 m/s and the pilot could return home safely. I shut off the top 4 T100s before liftoff to help keep it top heavy and the turned them back on when the lower tanks were empty.

[GoSlash27]

Mr. Chris,

Orbit is totally do-able within the part restriction and pad limit you outlined.

In fact, the LV-T30 can do it in a single stage.

If you balance it properly, you should need 18 FL-T100 tanks and a single T-30 engine.

*edit*

Proof of concept.

And since the T-30 can lift more than this, it's simply a matter of stacking in more tanks. You'll run out of part count before you exceed this engine's lifting capacity.

Best,

-Slashy

Edited October 6, 2015 by GoSlash27

[MrChris]

Made it! And landed! Just! Thanks for the suggestions. One big error I was making was using the boosters in a side-by-side strap-on configuration. Without aerodynamic caps, they add considerable drag.

One problem, I should have said, is that I'm to be gaining very little science through my launches. Otherwise I would have been putting more effort into 'levelling up' and gaining more powerful engines and larger fuel tanks.

My final vehicle had three RT-10 stages, and one LV-T30 with 8 FL-T100 tanks. I pitched to a heading of 270, initial periapsis of 75km and then burned all my remaining fuel at that. This was just enough (like, by about 5 m/s) to hit 2500 m/s and I completed about 2-3 orbits before drag brought me down.

[Ripper2900]

You should pitch to 90 degrees. That will give you a bonus of Kerbin's rotation, instead of the penalty.

[Kryxal]

Of course, launches going over water's a good idea in the first place, so stuff isn't liable to hit anything much ... but that's probably why they placed the launch facility on the east coast in the first place.

[tbarcello]

Problem solving would take 24hours less than it did should you take 1 minute to post the damn screenshot.