Deep-space speed challenge

[numerobis]

KSC engineers want to send a probe out to interstellar space from their space factory in LKO. The only problem: government is about to shut down, and when it does, all guidance systems will have to be deactivated! Your mission, should you choose to attempt it, is to make a rocket that can get up to speed before the shutdown arrives.

You must send a probe body (any probe body), along with an RTG and an antenna. Make it go as fast as possible within four minutes.

Rules:

0. Highest delta V wins.

1. Stock main parts; autopilot & info mods are fine, but mention them. MechJeb is required for scoring.

2. At most 400t mass.

3. At most 300 parts.

4. At most 240 seconds burn time (4 minutes).

5. The final payload must include an RTG, antenna, and a probe body.

6. The spacecraft must be able to burn all its fuel and gain speed without destroying itself. Start from anywhere outside the atmosphere, and stay outside.

7. The deltaV, mass, part count, and burn time are based on what MechJeb reports when you're in the VAB. Burn time and delta V are based on the vacuum values.

Verification:

1. A picture in the VAB.

2. A picture just before your burn.

3. A picture just after your burn. It should be not much more than 4 minutes after you started.

Your score to beat:

1. 15264 by tavert, 399.97t and 298 parts designed by an optimization algorithm. Potentially beatable with SRBs!
   
2. 15096 by Nao, 399.90t and 299 parts -- a solid showing not quite topping tavert's design.
   
3. 13058 by Slugy, 399.59t and 159 parts.
   
4. 10720 by Nao, in a particularly simple spacecraft using 57.6t but just 19 parts.
   
5. 9740 by me, the demo entry, using 16.69t and 205 parts.
   

Edited October 14, 2013 by numerobis

[numerobis]

An example submission:

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Your score to beat: 9740 m/s.

[DisarmingBaton5]

An example submission:

Your score to beat: 9740 m/s.

Er... atmospheric drag will compromise some of that speed, yes? I think perhaps you need to fly it.

[numerobis]

Er... atmospheric drag will compromise some of that speed, yes? I think perhaps you need to fly it.

There's no atmosphere. You start from 100km altitude.

You do need to fly the thing, to make sure it doesn't fall apart in flight. My starting shot is over TWR of 3 at all time, so there's some substantial forces at play.

[Nao]

To get things going

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10720m/s in 3m 58s

19 parts and 57,6t in 3 stages of simplicity. Funny thing that launch stage ended up with <20 m/s Dv after reaching 100x100 orbit (41l of fuel left).

[Slugy]

As you have done a small one here's a big one!

399.99t (including launch clamps), 4m burn, 163 parts, 13058dV.

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Spins annoyingly, but does go straight.

[numerobis]

Nao: nice simple vessel there! Amazing how little you need to get the distance.

Slugy: excellent; you're now in the lead with over 13 km/s.

A bit of background might be in order -- a while back I was hacking at zarakon's 10-minute distance challenge. With a stupid number of jets, you can reach the top of the atmosphere in about a minute. After that, I wanted to get a top stage that could deliver as much oomph as possible, so that my entire burn was done in about five minutes, followed by coasting. That turned out to be challenging in itself, hence this thread.

The mass limit is based on the number of parts I would need on the jet stage. The part limit is based on keeping things from bogging down too much. I hope to take the winner of this thread and showcase it in a 10-minute flight to claim that throne

[numerobis]

Rules updates:

- No need for a 100km orbit; just stay outside the atmosphere.

- Use the VAB stats for verification. I'm taking prior submissions at face value, but the stats slightly differ.

[tavert]

Nicely put together challenge (figured it was related to zarakon's 10-minute one). One little quibble, the flight delta-V stats are more accurate than the VAB stats due to massless parts like struts.

I'm fiddling with a numerical optimizer for this... can't get mixed-integer multi-stage to work yet, but the continuous relaxation of the multi-stage problem is working, and I'm building up an approximation to it with some manual rounding and branching. According to the continuous relaxation, if we had infinitely divisible tanks and engines, 15 km/s could be achievable.

[tavert]

My by-hand approximation got surprisingly close to what the continuous optimization result was telling me:

VAB numbers say 399.97 tons, 15264 m/s delta-V, 298 parts, 240 second burn time.

Flight numbers say 399.87 tons, 15326 m/s delta-V, 298 parts, 240 second burn time.

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[Nao]

I was waiting for this , its ON!

[numerobis]

tavert: over 15km/s, nice! You've got a few places where you have strut-decoupler-strut; you could save a part each on some of those, or two parts each by switching to a slightly heavier radial decoupler, freeing you up to get another dozen or two parts on other endeavours. But you don't have any spare mass either, so it might not be useful.

I'm surprised there are no T30s involved, just 48-7S and mainsail.

Nao: show us how it's done!

[tavert]

Every one of my decouplers is strut-decoupler-strut, with the exception of the stages in the center stack. I initially used the small radial decouplers to save parts on the lower mainsail stages, but that made the stages too close together and they crashed into each other on decoupling. No mass to spare to use the larger radial decouplers. I could probably cut down on bracing struts too, the mass and burn time constraints were active but the part count constraint wasn't in the optimization result, so I filled in all the excess with struts.

To burn 15 km/s in 240 seconds, we're talking average acceleration of over 6 g's. At these TWR's, the Mainsail is optimum despite its poor Isp. 48-7S is the next best thing for stages too small for a Mainsail. If my result is beatable, it's either by slight tweaks to the engine/fuel counts, or possibly by incorporating SRB's. My optimization formulation wasn't considering them, since their fixed burn time is a little annoying to account for in combination with simultaneously burning liquid asparagus stages. I did try adding a pair of SRB's on the second stage (but starting to fire along with the first stage) and cutting down on fuel to get the same overall mass, but it wound up slightly decreasing total delta-V.

[numerobis]

Mainsail is best and 48-7s second-best, in terms of TWR. But I figured the combination of a mass limit and a part-count limit would allow the T30 to come into play. The 24-77 might also do well, given part count limits.

[tavert]

If the part count constraint were lower it would change things a bit. 24-77 has slightly better TWR than 48-7S and is easier to mount in large numbers without needing cubic struts, but its lower Isp removes it from contention here.

[Guest Capt_wheelchair]

is there a way to give this a go without "that" mod? can i just use the map view for weight and partcount; and MET for burn time?

[numerobis]

The whole "MechJeb gives you autism" thing is based on a fraudulent study by a disgraced doctor.

But if you insist, go ahead and post. You can't get an official score is all: I don't trust that you'll be able to compute a bug-for-bug compatible deltaV number.

[Slugy]

It looks like the power of science (or at least maths) has been shown!

I do like Nao's reminder of what simplicity can achieve too.

[Nao]

It turns out SRB's are quite on the edge for this. I thought they would give better performance but numerous problems with them cancel it out.

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Tavert done a great job making 13 stages out of 300parts. With the SRB idea and not so efficient design i could only fit 9. Still its above 15km/s so i'm happy.

Numbers:

VAB Dv: 15096m/s, VAB mass 399,90t, 299parts, 239s burn time.

In flight Dv: 15117m/s, mass 399,82t.

Edited October 13, 2013 by Nao

[numerobis]

A solid second-place showing there Nao. Seems you're limited by part count from making smaller stages?

For the intended application (the 10-minute challenge), SRBs have a substantial disadvantage: they have 50% more drag than liquids do.

[tavert]

Glad you investigated an SRB-heavy approach. Interesting to see them get within a couple hundred m/s. Seems to significantly increase the part count of the earliest, biggest stages, which ended up very light on part count in my (and Slugy's) all-liquid mainsail approach.

Edited October 14, 2013 by tavert

[numerobis]

I wonder if the bigger SRBs would work out better? Twice the burn time for the same part count. Except their Isp is worse than a mainsail's.

[tavert]

I doubt it... twice the amount of solid fuel for the same part count, but 3x the dry mass and only 26% more thrust, tiny bit better Isp than the RT-10. Guess it deserves at least trying through.

I did consider a few different sepratron-powered final stages, but found their lousy Isp and inability to asparagus-stage them cost more delta-V in all the lower stages than they could give in a final 3-second last stage.

[Nao]

BACC's are much much heavier without significant thrust increase over RT-10 so the overall performance is quite a bit worse for this challenge, much bigger empty mass does not help either.

From what i tested, when straight up compared in 30s of burn time RT-10 are better than mainsail stack but at this particular TWR (~6) the difference is quite small, and when we add the ability for mainsail to be staged twice (15s burns) or more, they give almost the same performance.

And on topic of drag, yes the RT-10 have 50% more, and terrible sea level ISP but they still are the best first stage for most crafts since their engine and tank weight is so small (including Eve ascent module). I imagine they are made of paper, and explosives .

Oh and I've found a fuel bug in my craft on the mainsail stage, repositioning one fuel line increased Dv by 8m/s and burn time to 240s haha .

[numerobis]

OK, now everybody go back and do this in 0.22 where the 48-7S is even more powerful.