Small Rocket Design

[Nik75]

I'm wondering how much design can vary for for a given set of limits, for example, a quick design experiment,

Make a rocket that lands on Minmus and then back with a surface sample home to Kerbin.

Limits:

* Must be based on Mk1 command pod
* Have real parachute/parachutes
* Have solar panel/panels

And the maximum part count is 14 . Maximum weight is 11 t.

Would be very interesting what you come up with! :-)

! UPDATE !

----> Kerbal Space Agency has rewarded Skystorm with a gold medal for
achievement in RRD (Rapid Rocket Development) and for the very cool
Minmus Rocket "Tiny Too II". KSA is still interested in some more rocket designs.
But development and budget concerns has suddenly emerged. For ease of
shipping and handling we would like to purchase 10 or more rocketships if the
following specifications are met:

* Must be based on Mk1 command pod   * Cost must be lower than 10.000
* Maximum height is 6 m.   * Maximum part count is 13.
* Weight must be lower than 10 t.   * Stock parts only
* Parachutes and solar panels are optional.
<----

Edited August 19, 2017 by Nik75
Update

[Rocket In My Pocket]

Neat idea!

Fortunately we have a whole area of the forum for just such things, the Challenge section. (No worries, a mod will move your thread in a bit I'm sure.)

You might want to consider making it more open ended though, and less restrictive, for example why force parachutes if someone can sort out a way to land safely without them?

[Nik75]

Ok. Maybe a challenge it is. Just was wondering how much design variation there could be with such limits.
And yes, maybe the parachutes could be replaced with something magic. Just makes it more intresting!

It was just a little curiosity from my side if maybe with such strict limits like 14 parts and 11t weight there just
cant be to many different designs.

[Rocket In My Pocket]

8 minutes ago, Nik75 said:

Ok. Maybe a challenge it is. Just was wondering how much design variation there could be with such limits.
And yes, maybe the parachutes could be replaced with something magic. Just makes it more intresting!

It was just a little curiosity from my side if maybe with such strict limits like 14 parts and 11t weight there just
cant be to many different designs.

I think you'll get more varied designs (and more submissions in general) if you just award points based on lowest weight/part count, instead of placing an arbitrary number on it.

Check out the Challenge submission guide for more ideas if you like:

Also if you have a design of your own that you've done this with, post some screenies of it! Screenies always get people excited about making their own. If I get some time later, I'll try my hand at designing my own minimal minmus ship!

[Nik75]

Thanks for the advice.

The specific restrictions was just an idea for me to see what people can come up with or if it comes just close to my design. And would like to see what others do before i post my screens. And one more plus would be a maximum height of 6 m. ;-)

I hope you agree that there can be some interesting design decisions based on very strict numbers too.

[DerekL1963]

4 hours ago, Nik75 said:

And the maximum part count is 14 . Maximum weight is 11 t.

For the lander/return vehicle in the VAB or for the whole vehicle at liftoff?

[Nik75]

Well, for the whole vehicle at liftoff...

[SpacedCowboy]

Wait a minute, REAL parachutes? What if you want to use fake ones?

Just messin' with you. Seriously, this is a very interesting challenge idea.

[NSEP]

Sounds cool! I dont have acces to KSP, so maybe later.

Edited August 18, 2017 by NSEP

[invision]

1 hour ago, SpacedCowboy said:

Wait a minute, REAL parachutes? What if you want to use fake ones?

Just messin' with you. Seriously, this is a very interesting challenge idea.

[Johnny Wishbone]

Stock parts only? If not, what mods are allowed?

you really only have 11 parts to work with after the mandatory 3. with mods, it could be very easy. stock only could be more of a challenge.

[Archgeek]

1 hour ago, invision said:

Spoiler

...Wait a minute.  I have never seen a trash bag that could take that kind of temperature.  In my experience, the things have trouble with 450 K.  

[Vanamonde]

Challenge-type thread moved to the challenge-type subforum. 

[Nik75]

Haha so funny comments

Let's say unreal parachutes are allowed.

But everything have to be stock only for a gold medal.

[Skystorm]

14 parts and weighs in at 9,040 kg (9.04 t).  You really have to nail the ascent profile or it won't make orbit.  Fortunately the fairings in 1.3 played nice and didn't explode or destroy my solar panels.

Still had around 1,900 m/s left on the ion engine.  I should have used that to bleed off some energy before re-entry.  Came within 2% of exploding the capsule.

So yeah.  It's possible.  Barely.

[Nik75]

4 hours ago, Skystorm said:

14 parts and weighs in at 9,040 kg (9.04 t).  You really have to nail the ascent profile or it won't make orbit.  Fortunately the fairings in 1.3 played nice and didn't explode or destroy my solar panels.

Still had around 1,900 m/s left on the ion engine.  I should have used that to bleed off some energy before re-entry.  Came within 2% of exploding the capsule.

So yeah.  It's possible.  Barely.

Very impressive! Did not think of using an ion engine. Very nice indeed!

So what about skipping the ion...? 
Would prefer the cost of the rocket to be about 10.000 Kerbal £ 

Edited August 19, 2017 by Nik75
Forgot last line.

[GDJ]

16 hours ago, invision said:

I love it!

[Skystorm]

@Nik75 I originally started the design with all liquid fuels.  The limits are so restrictive that I was running into problems with part count, mass, or the ability to reach orbit with every design.  I eventually came to the conclusion that the ion was capable, and probably the only, engine that could really power the upper stage and keep it light enough that the lower stage could get it into orbit.

 

Powering The Ion Engine

The ion needs about 55% - 60% thrust to have the TWR necessary to land or lift off from Minmus under power.  This created a bit of a conundrum because it requires around 6 EC/s or better to reach that thrust and there is only a limited selection of solar panels to choose from.

To keep the solar panel count down and always have full sun to power the ion they needed to be sun tracking panels which generate at least a 6 EC/s combined.  Ideally I would want closer to 10 EC/s combined for full power and to have some breathing room.  I would want a pair of solar panels to keep the ship balanced and the part count low.

• OX-4L, SP-L 1x6  Very lightweight but only 1.6 EC/s each.  A pair of these would only be enough to run the ion at 33%.
• OX-4W, SP-W 3x2  Very lightweight but only 1.6 EC/s each.  A pair of these would only be enough to run the ion at 33%.
• OX-STAT Very lightweight but only 0.3 EC/s each.  Not a sun tracking solar panel.
• OX-STAT-XL Very lightweight.  Improved at 2.8 EC/s but still not enough with a pair of them.  Also not a sun tracking panel.
• PN-NUK  Not a solar panel, but I considered it anyway.  Only 0.8 EC/s.  Doesn't need to be sun tracking, but it is rather expensive.
• Fuel Cell  Also not a solar panel.  Only 1.5 EC/s.  Same problem as the solar panels though; I would need too many of them.
• Fuel Cell Array  Again, not a solar panel but 18 EC/s.  Plenty of electric charge but 240 kg each and I would need two to balance the ship.  Also doesn't meet the challenge requirements.  They would work though and actually weight slightly less than the Gigantors but are very bulky which could be a problem.

That leaves me with the Gigantor XL Solar Array with 48 EC/s combined change rate with sun tracking capability and weighing in at 300 kg each.  A bit heavy for such a small rocket but there really wasn't much of a choice to stay within the part limits.  Also rather large compared to the rest of the upper stage.  I had to slide them upwards to so that they wouldn't hit the ground when landed.

Because of the concern that the solar panels might strike the ground when landing, I added a Z-1K Rechargeable Battery so that the panels could be retracted about 10 seconds before landing in case something went awry.  The panels were also retracted for the first 10 - 15 seconds during lift off to avoid damage from ground strikes.

Shame I couldn't use Near Future Solar's 5 EC/s or 7 EC/s panels because those would probably have been perfect for this.

 

Alternative Engines

There are a couple different possible engines I considered for the upper stage.  The upper stage needed to be as light and efficient as possible not only for the deltaV needed but also because it heavily affects the lower stage's ability to get it into orbit.  I ruled out radial engines because of part count and low efficiency.  I ended up with two possible candidates:

 

48-7S "Spark" Liquid Fuel Engine

This engine would normally be great for a small upper stage with a specific impulse of 320s, 20 kN of thrust, and weighing in at 100 kg.  This would need a much larger fuel tank to achieve the minimum delta V requirements for the mission.  Even with a FL-T400 tank the engine would fall about 500 m/s short of the 2,700+ m/s required.  Additionally it raised the overall weight of the rocket and upper stage by almost 1.5 tons!  The lower stage is already struggling to put the ion into orbit and the extra weight would likely kill it.

 

LV-909 "Terrier" Liquid Fuel Engine

I love this little engine but it is hard to afford 0.5 ton with only an 11 ton limit.  Very good specific impulse of 345s and even better thrust at 60 kN.  However it suffers from the same fuel requirements as the Spark requiring at least an FL-T400 to supply the delta V needed.  Unfortunately even with better Isp, the extra engine weight for the tiny upper stage causes it to fall over 600 m/s short of the delta V needed.  It would also bring the upper stage to 4.3 tons and the whole rocket to 10.85 tons.  It needs more fuel but there simply isn't enough of the weight limit left for it.

 

Other Considerations

I also tried all liquid fuel lower stage but they simply weren't efficient enough or couldn't bring enough fuel due to the weight or part limits.  I also considered solid rocket boosters but there are so few and are relatively heavy and have low efficiency.

 

Final Thoughts

I ended up going with a hybrid rocket / space plane concept to get the efficiency of the air breathing engines at low altitude while still being able to function as a rocket in the upper atmosphere with a single engine.  I chose the ion engine for the upper stage for the exceptional delta V and the light weight of the fuels and engine, and because anything heavier would simply have not made it to orbit.

Edited August 19, 2017 by Skystorm

[Nik75]

Thanks alot for all the explanation! Very interesting thoughts and good calculations!

But my second minmus rocket just now reached within these specs;

* Must be based on Mk1 command pod   * Cost must be lower than 10.000
* Maximum height is 6 m.   * Maximum part count is 13.
* Weight must be lower than 10 t.   * Stock parts only

What do you think about it? Can you figure out my design? :-)

[sevenperforce]

On 8/19/2017 at 1:10 PM, Nik75 said:

Thanks alot for all the explanation! Very interesting thoughts and good calculations!

But my second minmus rocket just now reached within these specs;

* Must be based on Mk1 command pod   * Cost must be lower than 10.000
* Maximum height is 6 m.   * Maximum part count is 13.
* Weight must be lower than 10 t.   * Stock parts only

What do you think about it? Can you figure out my design? :-)

Working on it. My current design doesn't quite have enough dV in the terminal stage.

[Nik75]

21 hours ago, sevenperforce said:

Working on it. My current design doesn't quite have enough dV in the terminal stage.

Great! Will be very interesting to see what you can do. I hope some more people here in this great forum would like to try! I admire Skystorms 9.04t rocket, as a beginner I would not have been able to build that one. It looks great and is a very nice solution to alot of problems with this type of low part, low weight design.

[sevenperforce]

4 hours ago, Nik75 said:

Great! Will be very interesting to see what you can do. I hope some more people here in this great forum would like to try! I admire Skystorms 9.04t rocket, as a beginner I would not have been able to build that one. It looks great and is a very nice solution to alot of problems with this type of low part, low weight design.

Aaaaand got it! Cost is 9038, height is 5.9 meters, it has 13 parts, and mass is a miniscule 5.815 tonnes. No part clipping.

Once I get a chance I'll do the full mission with all the screenshots.

Edited August 22, 2017 by sevenperforce

[Nik75]

1 minute ago, sevenperforce said:

Aaaaand got it! Cost is 9038, height is 5.9 meters, it has 13 parts, and mass is a miniscule 5.815 tonnes.

Once I get a chance I'll do the full mission with all the screenshots.

Amazing! How on Ear.. I mean, how on Kerbin did you get that low weight? 

[sevenperforce]

36 minutes ago, Nik75 said:

Amazing! How on Ear.. I mean, how on Kerbin did you get that low weight? 

I'll give you a hint: I get into Low Kerbin orbit with 1827.41 m/s of dV.

[Nik75]

Ok! Can't wait to see that spacecraft!

Anyway, here is mine;

Enters LKO with about 1900dV left for Minmus and back.