The Cheap and Cheerful Rocket Payload Challenge 1.0.5

[Temstar]

Quote

No fuel may be drawn from the payload to feed engines in the lifter.

Okay fair enough, but it seems like that's encouraging designs that optimize payload delta-V expenditure to as close as to 500m/s as possible isn't it? Because whatever tankage that holds that 500m/s delta-V worth of fuel is payload for free, and that fuel spent is free delta-v as far as the launch vehicle is concerned.

Like say a payload made up almost entirely of ion engines and solar panels, plus a little bit of xenon to provide the last 500m/s to orbit. This last 500m/s would have extremely high Isp which then boost the average Isp across the whole launch?

Edited January 29, 2016 by Temstar

[Meithan]

2 hours ago, GoSlash27 said:

Meithan,

 Thus far, no LF&O engine can hope to compete with solid fuel for cost- effectiveness. There may be a true asparagus design that can keep up in terms of "bang for the buck", but if so it's likely to be a very large lifter.

Best,

-Slashy

Yeah, I didn't mean a full LFO-only asparagus design; it's clear that SRBs are needed in the lower stages due to their high TWR and low cost. I was thinking more along the lines of drop tanks. The central LFO core in maccolo's last entry is pretty big: at some point it's carrying two empty orange tanks. Would the increased drag and extra cost of decouplers/fuel lines outdo the mass saved by being able to drop those tanks as soon as they're empty?

[maccollo]

Well this wont do. But as Temstar said there is another way to game this which is to simply add as many engines of the high ISP kind as you need to get the TWR required at 500 m/s from orbit. If I got things right this is to allow us to simulate upper stages that fire before orbital insertion. However, what this does not take into account the cost effectiveness of that stage. Case in point:

https://www.youtube.com/watch?v=OjldySNQcJ8

Sorry about the blinding brightness. I forgot to turn down the ambient light I used on the nightside. Also forgot the sound.
Anyway, the launcher portion is exactly the same as before except for the decoupler, so the cost of the launcher is 61262+550, or 61812 funds.
However, the mass in orbit was increased to 110 tons.
Cost per tons: 561.9 funds

While using this many nukes allows me to get the best score I possibly can, it's probably not going to make for the most cost effective launcher since they are extremely expensive.

@Meithan
Having the two orange tanks as another set of drop tanks would only add 34 m/s, while the cost would increase by least 1584 + plus reducing the terminal velocity at launch from 700 to about 600.
So I would need to haul almost 3 more tons to orbit, while also having more drag. Having to go 34 m/s less on the upper stage nets about 0.4 tons, so I'm pretty sure it wont pay off.

Edited January 29, 2016 by maccollo
fixed video link. also a word

[Nich]

maccollo I am complimented that you stole my idea for drop tanks after I stole your idea for quad kickbacks

I am all for no explosive decoupling as if feels like xploity

I am also a believer that payload should arrive to orbit without any missing fuel how ever I feel my first entry should be allowed as a rhino makes sense as a thruster for a 136t transfer stage.  Depending on dv requirements it is a better selection then a nuke cluster.  If it was a lifter engine i.e. mamath it would be disqualified.

 

maccollo I think you might be able to break 500 if you take your original design and move 500 dv from the lifter stage to a nuke final.  First the nuke will get 500 dv for very little mass giving a greater final tonnage I was going to play around with that but ran out of time.

 

Meithan I tried to checkout your Optimal engine charts web app and it appears the link has gone dead?

 

 

Edited January 29, 2016 by Nich

[Meithan]

16 minutes ago, maccollo said:

Having the two orange tanks as another set of drop tanks would only add 34 m/s, while the cost would increase by least 1584 + plus reducing the terminal velocity at launch from 700 to about 600.
So I would need to haul almost more 3 tons to orbit, while also having more drag. Having to go 34 m/s less on the upper stage nets about 0.4 tons, so I'm pretty sure it wont pay off.

Alright, I'm sold.

And looks like your link is broken, I get a "This video does not exist" error.

[Nich]

I didn't even think of ions for a tug because you would probably need 50/100t just to get a bar minimum TWR and you cant IRU zenon gas  but it would be the best final stage for this comp without a doubt

Has anyone tried a SRB second stage to get cost down or are they just too heavy the first stage losses too much?  I was not able to get it to work for less then 1000/ton  SRBs to orbit was about 1800/ton but a lot of fun to play with no control lol

 

 

Edited January 29, 2016 by Nich

[Temstar]

18 minutes ago, Nich said:

I didn't even think of ions for a tug because you would probably need 50/100t just to get a bar minimum TWR

Nah it's not true. TWR depends only how how much of the craft is engine, not on the absolute amount of thrust. So you could just as well have a tiny craft where the ion engine + battery + xenon makes up most of the mass of the craft and you will get decent TWR (for an ion craft that is).

Yeah this 500m/s rule is messing with things, it's making us focus on payload instead of launch vehicle because we all know when you make the payload better that dramatically scales downwards towards the rocket due to the rocket equation. I still say we should go for 100% inert payload: no engine, no probe core, no reaction wheel, payload mass in VAB must match payload mass in orbit. Than way we can start to ignore the payload and really focus on the rocket.

[Nich]

I have no problems with 1 reaction wheel and probe core in the payload and I have never launched a payload without a reaction wheel.  2 or 3 is exploity  I as stated before have no problems with a deep space engine being used on the core stage as long as non of the payload fuel is touched and the final twr > .3

 

 

 

[maccollo]

Well I can see (I think) what this rule is meant for. Rockets often have an upper stage that fires before orbit is achieved.
However the relative performance of different rockets is not the same at different destinations.

What I would suggest if the rules were to be changed, is that the payload must be inert. To get a more nuanced picture of the performance the rockets would be graded on their ability to launch payloads to 3 destinations, for example LKO, Eve and Jool.
You wouldn't actually have to get an encounter, just propel the payload to a specified C3. An entry can attempt all 3 of these, but it must be unmodified. It could also get an overall performance score by taking some weighted average from it's performance to these 3 destinations to get an idea of it's versatility.

So a 1.5 stage entry might get great cost performance to LEO, but poor performance to Eve and very poor to Jool while a rocket with a big low TWR upper stage might have the inverse result.

[Norcalplanner]

I feel obliged to point out the text of the special rule, which hasn't changed since the third post or so of the thread several days ago:

"Special Rule: An LFO engine or engines which are part of the payload may be used for up to 500 m/s of an orbital insertion and/or circularization burn after the payload detaches from the lifter. If an engine on the payload is used, then the final payload mass is the mass after the orbital insertion burn is complete."

LV-Ns don't comply with the rule. Ions don't comply with the rule. 

Since nearly everyone appears to be using a single engine for orbital insertion or circularization, we could certainly amend the rules again and specify that only a single LFO engine can be used.  However, at this point I'd rather not make any more changes - I hate changing the rules after a challenge has begun, and I don't want to rely on something as subjective as the Wheaton Rule.

Just in case everyone hasn't read it, here's a little quote from the OP of the Cheap and Cheerful tutorial thread to keep in mind:

"C&C is about rockets - practical rockets that exist at the intersection of cost, capability, part count, ease of operation, and tech requirements. Building a rocket that has almost as much capability as an optimized design, while having a lower part count and costing a fraction of the funds - this is the C&C way."

Now let's get back to having fun playing KSP.

 

[Temstar]

5 minutes ago, maccollo said:

To get a more nuanced picture of the performance the rockets would be graded on their ability to launch payloads to 3 destinations

I disagree. We are now moving out of the area of rocket design into payload design. When faced with a problem of "I want to put payload to Jool", you can always divide up that problem into two halves of "KSC to LKO" and "LKO to Jool".

Of course the upper atmosphere being nearly a vacuum means most rocket's top stage naturally makes a decent injection stage, and conversely if you don't have a dedicated upper stage then payload engines are generally pretty good at getting the payload into a circular orbit from suborbital. But this overlap is more of a happy coincidence rather than hard requirement for rocket design in general. Getting out of LKO to places should always be the job of the payload, even if the payload is "borrowing" the upper stage to do part of its job.

[RA3236]

How about using Vens stock revamp? I also have Alternis Kerbol and some other mods, but I'll stick to Revamp. Is this ok?

[Norcalplanner]

As I see it, we have a few options.  I'd appreciate constructive feedback.  In no particular order, the options I see are:

1. Make no further changes to the rules and keep going with what we have.

2. Make a minor change or changes, like limiting the payload injection burn to a single LFO engine, or only allowing a single reaction wheel or manned capsule in the payload.

3. Either alone or in combination with #2, reduce the amount of delta V that the payload can contribute.  Slashy proposed something which was effectively less than 100 m/s (lifter must get payload to an Ap above 80 km and Pe above 1 meter before detaching).

4. We go with an oddball handicap system.  The one that seems to jump out at me is to start with 500 m/s, but your payload delta V allowance is reduced by 100 m/s for every dot you have beneath your forum avatar.

5. We scrap this challenge and start over with a new one which requires that the payload be completely inert.

Please give this some consideration, and then let me know what you think.

[GoSlash27]

2 hours ago, Temstar said:

Yeah this 500m/s rule is messing with things, it's making us focus on payload instead of launch vehicle because we all know when you make the payload better that dramatically scales downwards towards the rocket due to the rocket equation. I still say we should go for 100% inert payload: no engine, no probe core, no reaction wheel, payload mass in VAB must match payload mass in orbit. Than way we can start to ignore the payload and really focus on the rocket.

Yeah, I'm inclined to agree with this. A practical launcher wouldn't make such heavy use of the payload to help it get to orbit.

Best,
-Slashy

[Temstar]

I vote for inert payload, same additional requirements as the payload fraction challenge - no upside down decoupler or docking port on the bottom of the payload to cheat that little bit of weight. No using Ec from payload either.

[GoSlash27]

Yeah, I'd agree with Temstar. 100% inert payload, but 80km x 1m minimum. This would put the focus squarely on the lifter itself with the emphasis on "practical".
 This is how lifters are actually used in- game; the payload circularizes itself while the preceding stages deorbit.

Best,
-Slashy

[GoSlash27]

3 hours ago, Nich said:

Has anyone tried a SRB second stage to get cost down or are they just too heavy the first stage losses too much?  I was not able to get it to work for less then 1000/ton  SRBs to orbit was about 1800/ton but a lot of fun to play with no control lol

 

 

Nich,

 Yeah, they're too heavy and the Isp sucks. SRBs are a great "bang for the buck" solution so long as you don't have to actually pick them up. When used as a second stage, their inefficiency cascades and you wind up with a more expensive stack overall. At least... that's been my experience so far.

Best,
-Slashy

[Meithan]

Norcalplanner, I understand your reluctance to do fundamental changes to the rules with the challenge ongoing, but I'm afraid I have to side with Temstar and Slashy on this one: I vote for an inert payload.

That way the challenge can focus on the lifter exclusively, seeking designs that are practical because they will work for any payload that fits the mass bill.

Factoring in the "but the lifter usually separates just before orbit in practical designs" is still achieved by demanding the periapsis to be high but not all the way to 80 km. With an apoapsis of 80 km, circularizing a 1 km periapsis costs about 70 m/s (the current 500 m/s allowance corresponds to a periapsis of -300 km, by the way). Thus, demanding an inert payload but only a suborbital periapsis is effectively equivalent to having the payload finalize the circularization (as done in practice), but eliminates the lifter dependence on payload design.

While we're at it I'd also say that "inert" should include clear wording regarding reaction wheels on payload. I'd be OK with allowing one (but no more) reaction wheel in the payload to mimic practical conditions, but I don't know what you and the others feel about it. Having electric charge and guidance on the payload is fine IMO, since in practice this is almost always the case.

The point should be to encourage cheap and practical (cheerful, really) general-purpose lifters.

 

[Nich]

I missed the LFO requirement rule I like that it is a good call as the best isps are quite similar for all 3 sizes for circularization.  I do feel you should be limited to 1 circularization engine.  I am not opposed to 100m/s but I actually prefer the 500m/s as this feels more realistic.  We are at the point where the design has pretty much been worked out.  SRB first stage, efficient LFO to AP, Circularize.  At this point it is about tweaking the rocket to end with 0 usable dv left.

What have we learned?

LFO lifter engines are generally not worth it and if they are they need to be sustainers.

initial TWR of ~ 1.5

Low TWR in a mid stage is probably more efficient then flying on propagrade.

Drop tanks are quite viable from a cost perspective (quasi asparagus)

It appears nose cones are still worth there value although I am not sure if anyone has done nosecone less testing but has not possed it because it didn't work.

I originally thought I am fine with reaction wheels in payload but then I thought of someone using a 2.5m reaction wheel in a 10t payload has a definite advantage so I am leaning more to reaction wheels have to be on the launcher or limited to 5 torque in the payload

 

 

 

Edited January 29, 2016 by Nich

[GoSlash27]

Thinking about what the payload should or should not provide in this challenge...

Guidance: I'm okay with that. The end- user would have guidance in the payload.

Electricity: I'm kinda torn on this. I usually have enough batteries in the payload to keep the lifter alive, but I could picture a situation where it wouldn't be enough.

Reaction wheels: I'd say no reaction wheels in the payload. It's unrealistic to expect the end user to put enough torque in the payload to control the whole lifter.

Thrust: Definitely not. We know that the payload will circularize itself. Simulating that does nothing to develop the lifter.

Just my $0.02,

-Slashy

[Nich]

maccollo I attempted to make your first place entry and holy heck that is a tiny window to launch into.  Too low and you dont make it, too high and you dont make it.  Best I have been able to do is 78x71 and for some reason my rocket weights 90kg less and has 5 more dv  

 

 

[Norcalplanner]

I'm finally back at a computer and have had a chance to digest everyone's suggestions.  Here's what I'm going to do.

The initial ruleset and leaderboard will be rechristened the 1.0 version of the challenge.  No further entries will accepted under the old ruleset.  As a consequence of this, the asterisk section of the 1.0 leaderboard will be combined with the rest of that leaderboard.  The asterisks will stay, but the "subsequently prohibited" text will be removed.  Maccallo is officially the winner of the 1.0 version of the challenge.

The 2.0 version of the ruleset will have a new leaderboard, and will incorporate the following changes:

• Explosive staging will be prohibited.
• Payload may contain electricity and a probe core.
• 1.25 meter and 2.5 meter payloads may each have a single reaction wheel or manned capsule of that diameter. Because there is no stock 3.75 meter reaction wheel, 3.75 meter payloads may have two of the 2.5 meter reaction wheels.
• Score must be calculated when the payload Ap is a minimum of 80 km, Pe is a minimum of 1 m (i.e., you can see the Pe marker in map view), and altitude is at least 70 km.  In other words, you can detach from the lifter while still in atmosphere, so long as the payload still meets the Ap/Pe criteria after it exits the atmosphere.
• The payload may not contribute any thrust to meeting the above criteria, and the payload mass must remain constant from launch until after the lifter detaches.  While the payload may contain an engine, using that engine is outside the scope of the challenge.  In other words, if you can't bear to see your payload fall back into the atmosphere, you can include an engine in the payload, so long as you score your entry before firing up that engine. (This is intended to accommodate OCD/completionist/roleplaying types, and also allow people to enter existing craft they've used in a career save.)

If anyone has any further suggestions, please let me know in the next few hours.  I'd prefer not to make any changes after the 2.0 version of the challenge starts.

 

[Meithan]

21 minutes ago, Norcalplanner said:

The 2.0 version of the ruleset will have a new leaderboard, and will incorporate the following changes:

[snip]

If anyone has any further suggestions, please let me know in the next few hours.  I'd prefer not to make any changes after the 2.0 version of the challenge starts.

The new ruleset sounds great, I really wouldn't change anything. I liked the form of the reaction wheel rule. Hope the others agree with it so we can start (and I'll try to work out an entry this weekend).

[Temstar]

I know that the rules already say vertical launch only, but what about lifting surfaces? Are they allowed?

[Norcalplanner]

4 minutes ago, Temstar said:

I know that the rules already say vertical launch only, but what about lifting surfaces? Are they allowed?

Rules are currently silent on lifting surfaces. I'd say that they're allowed, so long as thrust is limited to LFO engines and SRBs.