Super Atlas 1.5 Stage Delta-V Challenge

[sevenperforce]

Most of us are likely familiar with the staging approach used by the Mercury Atlas LV-3B, where three engines were lit at launch but two were dropped during the ascent on a jettisonable skirt:

Some of us are also probably familiar with the proposed Saturn S-1D SSTO, which would have repurposed a Saturn V first stage, with a modified thrust structure and jettisonable skirt, as an stage-and-a-half taxi to LEO carrying an Apollo crew capsule:

Your mission, should you choose to accept it, is to build a vertically-launched SSTO which reaches low Kerbin orbit with the maximum possible dV. All engines must fire at liftoff; no thrust limiter funny business. You can drop engines, but you cannot drop tanks. You can use any engines you like, including engines from the DLC. Airbreathing engines are fine if you want to try using them, but you still need to use a typical vertical takeoff and gravity turn. Fins for control are okay, but wings and aerodynamic lift are not allowed. 

To keep everything equal, your payload is a single Kerbal in a Mk1 command pod. Recovery is not necessary. You just need to be able to reach LKO with the  maximum amount of remaining dV *and* all of the tanks you launched with.

There are a lot of ways to tackle this challenge and I'm not sure what a straightforward path would be, so feel free to experiment. 

[Rutabaga22]

Love this! Are mods ok?

 

[QF9E]

This sounds like fun! I'm off work tomorrow and I might give this challenge a go.

Just to clarify (I guess the answer will be "no" as it would make the challenge trivial): Is a craft that uses engine parts that include propellant allowed to drop these parts? In particular, SRBs and the Twin Boar, can they be used and dropped?

[sevenperforce]

1 hour ago, Rutabaga22 said:

Love this! Are mods ok?

Visual mods and part mods that don't impact physics are fine. Mod tanks are fine as long as they have the same mass ratio as stock tanks. I don't think part clipping will be a significant issue simply because this is a vertical launch with a gravity turn and so aero exploits won't be particularly significant. Mod engines are fine as long as their TWR and specific impulse is in line with stock engines.

1 hour ago, QF9E said:

This sounds like fun! I'm off work tomorrow and I might give this challenge a go.

Just to clarify (I guess the answer will be "no" as it would make the challenge trivial): Is a craft that uses engine parts that include propellant allowed to drop these parts? In particular, SRBs and the Twin Boar, can they be used and dropped?

You're correct, the answer there is no; SRBs and Twin Boars would allow essentially ordinary staging and so that wouldn't work. You're welcome to use the Twin Boar or SRBs, of course, but they would have to go all the way to LKO. I suppose you could use the Twin Boar without any fuel onboard at launch, but that would be a waste since there are better engines.

I was able to reach LKO on a fairly inefficient trajectory with 6,550 m/s of dV off a 240-tonne launch vehicle but I'm sure improvements are possible. I worry that players may just start building larger and larger vehicles; I may eventually have to put in a launch mass limit or weight classes.

Also, it may be possible to hack the hell out of this challenge by spamming lots of xenon. If xenon makes the challenge trivial then I may have to ban Dawn engines altogether, or at least add a rule that nerfs them a little. So don't try that, haha. The spirit of the challenge is that you're supposed to light all the engines at launch like Atlas LV-3B or Saturn S-ID Super Atlas and drop them as they are not needed.

[Rutabaga22]

Version 1, the Moho Atlas!

Launch begins

Apoapsis Kick

Side boosters deployed

Booster deployed

Reentry!

Parachutes deployed

Full parachute deployment

Touchdown.

 

Didn't make it to orbit this time, but I'll get there. Could I make a single engine system, or does it have to be 1.5 stages?

[sevenperforce]

8 minutes ago, Rutabaga22 said:

Version 1, the Moho Atlas!

Launch begins

Apoapsis Kick

Side boosters deployed

Booster deployed

Reentry!

Parachutes deployed

Full parachute deployment

Touchdown.

 

Didn't make it to orbit this time, but I'll get there. Could I make a single engine system, or does it have to be 1.5 stages?

Loved those photos and whatever visual mods you have.

This doesn't have to be an Atlas LV-3B clone; you can make it as big or as small as you want, with as many or as few engines as you want. It's going to be to your advantage to drop engines, though. The goal is to reach LKO with as much remaining dV as possible.

[QF9E]

6 hours ago, sevenperforce said:

Also, it may be possible to hack the hell out of this challenge by spamming lots of xenon. If xenon makes the challenge trivial then I may have to ban Dawn engines altogether, or at least add a rule that nerfs them a little. So don't try that, haha. The spirit of the challenge is that you're supposed to light all the engines at launch like Atlas LV-3B or Saturn S-ID Super Atlas and drop them as they are not needed.

Yeah, I thought of (ab)using xenon as well. I might look into that, just to see how far you can go that way.

What is your stance on using a high ISP engine such as the NERV as sustainer and burn it at 1% thrust at liftoff? Since its efficiency at sea level is very low running it at full thrust would just be a waste of fuel.

[OJT]

Something I threw together in couple of minutes. Central stage with NERVA and 4 RAPIER engines on side. Elevons for control, no aerodynamic surfaces. RAPIERS are mounted on Structural Fuselages: these are not fuel tanks

Launch. RAPIERs take couple of seconds to spool up

Spoiler

NERVA gets decent performance numbers in higher atmosphere, but its low thrust means that I need to be going at considerable speed at first to not lose too much vertical speed once I jettison the RAPIERs. I figured that crucial factor would be to get as much prograde speed as early as possible. RAPIERs can generate thrust all the way to 25 kilometers, so ascent profile was quite aggressive to utilize them to the fullest. Infact, I think I kinda overkilled with RAPIERs since I didn't even go at full throttle due to immense TWR and fear of overheating

Spoiler

After jettisoning the RAPIERs, NERVA safely completes the rest of the climb and inserts into low Kerbin Orbit

Spoiler

5547 m/s of deltaV in what is essentially an oversized pencil

[Rutabaga22]

17 hours ago, sevenperforce said:

whatever visual mods you have.

I have so many visual mods, but here is the list I could concoct 

Environmental visual enhancements

Astronomer's visual pack

Parallax

Planetshine

Distant object enhancement 

Waterfall

Waterfall stock configs

realplume

I might have a few more, but this is what I know I have

 

[sevenperforce]

21 hours ago, QF9E said:

Yeah, I thought of (ab)using xenon as well. I might look into that, just to see how far you can go that way.

What is your stance on using a high ISP engine such as the NERV as sustainer and burn it at 1% thrust at liftoff? Since its efficiency at sea level is very low running it at full thrust would just be a waste of fuel.

I thought I said this before (apparently I didn't) but in the spirit of the challenge, no in-flight thrust limiter adjustments. If you wanna burn a NERV at 1% thrust, that's fine, but you can't change the thrust limiter later on. That's fairly true to life because real-world engines can't actually throttle that aggressively anyway so if you're going to build a sustainer architecture you'll probably use something that's altitude-compensating; if you're including a vacuum-only engine you'll just use ordinary staging.

I think you'll find that the NERV and the Dawn engines burn so little fuel anyway that burning them at full throttle from the ground up isn't that significant of a fuel waste. My 6.55 km/s test run burned two NERVs all the way from sea level to orbit. Since we are using a vertical ascent and gravity turn anyway, a decent TWR off the pad (which is essential to SSTO architectures anyway) will get you high quickly enough that the NERVs will be useful very soon.

21 hours ago, OJT said:

Something I threw together in couple of minutes. Central stage with NERVA and 4 RAPIER engines on side. Elevons for control, no aerodynamic surfaces. RAPIERS are mounted on Structural Fuselages: these are not fuel tanks

An all-LF design!! Very impressive. I honestly didn't expect anyone to start with an all LF design but it does make intuitive sense.

I think you could save significant weight by using fewer heavy shock cone intakes. I believe just one shock cone intake should be enough to power four RAPIERs all the way up.

8 hours ago, Rutabaga22 said:

I have so many visual mods, but here is the list I could concoct 

Environmental visual enhancements

Astronomer's visual pack

Parallax

Planetshine

Distant object enhancement 

Waterfall

Waterfall stock configs

realplume

I might have a few more, but this is what I know I have

All visual mods are fine. I just don't want someone with an unbalanced physics mod messing it up for everyone else.

21 hours ago, OJT said:

5547 m/s of deltaV in what is essentially an oversized pencil

Why did you use a fairing? I strongly -- STRONGLY -- suspect that just topping it with the Mk1 pod and the nose cone will have less weight and less aero incidence than the fairing. 

[OJT]

5 hours ago, sevenperforce said:

An all-LF design!! Very impressive. I honestly didn't expect anyone to start with an all LF design but it does make intuitive sense.

I think you could save significant weight by using fewer heavy shock cone intakes. I believe just one shock cone intake should be enough to power four RAPIERs all the way up.

5 hours ago, sevenperforce said:

Why did you use a fairing? I strongly -- STRONGLY -- suspect that just topping it with the Mk1 pod and the nose cone will have less weight and less aero incidence than the fairing.

Like I said, I didn't think about the design too hard. I basically went "haha roket go vroom" and slapped up some fuel tanks and RAPIERs together. And despite achieving my goal of reaching orbit and having pretty decent dV numbers in LKO, there's lots of room for optimization. For one, 4 RAPIERs provided way more TWR than I would need. Reducing amount of RAPIERs would save me lots of dry mass and still comfortably get me to orbit with roughly similar flight profile

As for the fairing, it is to protect the Command pod: due to accelerating quickly through lower atmosphere (another downside of having too many RAPIERs ) the nose cone overheated and exploded during my first attempt, so I put a small fairing to shield the payload from heating

[QF9E]

5 hours ago, sevenperforce said:

I thought I said this before (apparently I didn't) but in the spirit of the challenge, no in-flight thrust limiter adjustments.

Thanks for the clarification!

The only ruling on this that I could find was the following, from your top post: "All engines must fire at liftoff; no thrust limiter funny business. " Perhaps this is because I am not a native English speaker, but I wasn't quite sure how to interpret "funny business". I think that in some cases, adjusting the thrust limiter in flight should be allowed, such as to throttle down only the center engine in a Delta IV Heavy recreation.

 

[sevenperforce]

2 hours ago, QF9E said:

Thanks for the clarification!

The only ruling on this that I could find was the following, from your top post: "All engines must fire at liftoff; no thrust limiter funny business. " Perhaps this is because I am not a native English speaker, but I wasn't quite sure how to interpret "funny business".

Ah, yes, I thought it was in there. For non-English speakers, “funny business” colloquially would encompass anything that feels like cheating or abusing the rules to unbalance the challenge.

2 hours ago, QF9E said:

I think that in some cases, adjusting the thrust limiter in flight should be allowed, such as to throttle down only the center engine in a Delta IV Heavy recreation.

So, the reason the RS-68 on the DIVH is throttled down is to reduce prop consumption in the center core so that the side boosters run out of propellant faster and can be dropped at empty while the center core still has propellant. But in this challenge you can’t drop tanks, only engines, so there would be no reason to throttle down the center engine preferentially; if you need lower thrust you can either downthrottle all the engines or you can start dropping unnecessary engines. 

[camacju]

On 6/5/2022 at 11:25 PM, QF9E said:

What is your stance on using a high ISP engine such as the NERV as sustainer and burn it at 1% thrust at liftoff? Since its efficiency at sea level is very low running it at full thrust would just be a waste of fuel.

Actually, funny enough, the Nerv's Isp is just high enough that with a Nerv+Vector craft optimised for payload fraction it's beneficial to burn the Nerv right off the pad. Isp increases really quickly as you launch, and the extra thrust makes up for the Isp reduction.

[camacju]

Ok, I blatantly ripped off OJT's submission, except for optimizing the flight profile and drag characteristics.

Craft in VAB

Liftoff. Note the 2050 LF capacity

Once I get sufficient speed, the shock cone is now able to feed two rapiers, so the other intakes are dropped

Using body lift to pull up apoapsis (L/D is actually not that bad)

Running out the last of the rapiers

Rapiers detached

Circularizing

6783 m/s remaining

22 hours ago, sevenperforce said:

I believe just one shock cone intake should be enough to power four RAPIERs all the way up.

Shock cone actually doesn't have enough static suction for more than one rapier launched vertically, you need more intakes (basically what I did)

[OJT]

This is probably one of the weirdest crafts I've ever built

Two RAPIERs and one Dawn. I think you can kinda see where this is going

Spoiler

Ascent profile wasn't as steep as in my previous entry: superlow TWR of Dawn meant that I needed to get quite high so that I have enough free margin to raise my periapsis. At the same time, rocket engines didn't provide the necessary push for long enough. That's where RAPIERs come through: They burn in Airbreathing Mode for the first 25 km and then switch to Closed Cycle to get that extra push I need. Oxidizer amount in the tanks was accordingly reduced in VAB so that I don't carry too much unused oxidizer into orbit.

Spoiler

After using the last of liquid fuel, I jettison the RAPIERs and burn the rest of the way with Dawn. And yes, it was a long burn: 0.05 TWR certainly wasn't doing me many favors

Spoiler

Achieving stable orbit with 13057 m/s dV to spare

TL;DR: Ion engine OP, plz nerf

On a serious note though, I basically strapped this monstrosity together in 15 minutes without putting too much thought into its design and I already more than doubled camacju's numbers. I think it would be fair to either ban ion propulsion altogether or put ion engine submissions into separate category @sevenperforce

[sevenperforce]

21 minutes ago, OJT said:

On a serious note though, I basically strapped this monstrosity together in 15 minutes without putting too much thought into its design and I already more than doubled camacju's numbers. I think it would be fair to either ban ion propulsion altogether or put ion engine submissions into separate category @sevenperforce

Yes, it appears ions are too OP. I suppose I could make it a payload fraction challenge rather than a straight-up dV challenge; that would nerf the ions appropriately. Would that make this challenge better overall?

20 hours ago, camacju said:

Using body lift to pull up apoapsis (L/D is actually not that bad)

I am moderately concerned that what we are beginning to see is not a vertical launch with a gravity turn, but a vertical launch with an immediate tipover and airbreathing ascent. I'm not sure how to fix this. Maybe make airbreathers a separate category?

[jinnantonix]

This is not an SSTO, but it shows the staging used by the Atlas launch vehicle for the Gemini program: