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I’ve rediscovered asparagus staging! And have officially given up on SSTO rockets.


Brainlord Mesomorph
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Recovery is a good idea and IRL the recovery of lower stages is cost effective and definitely helps a space program get more bang for its buck.

In KSP however, we have the physics bubble, which makes lower stage recovery impossible.  The only way around this is the SSTO rocket, carry the whole rocket into space, and deorbit it later hopefully to the KSC.  If you get to the KSC Peninsula you can get 90% value back, and all it costs is fuel.

It makes sense.  At least on paper.  But somehow, I kept coming in over budget.  So I had to take second look at how this actually works.

To make a rocket SSTO and recoverable you have to add a lot to it.  A probe core, parachutes, RCS, SAS, additional fins, heat shield, landing gear the list goes on, it can cost up to 20,000 funds just in additional parts.  (“That’s OK,” you say, “I’m going to get all that money back when I recover the rocket.” In theory yes, but we’ll get back to that in a moment.) it also takes additional fuel to get all the way to orbit and still have enough fuel left for a deorbit maneuver, and you don’t get any of that money back.  Plus all the extra equipment and fuel is costing you payload capacity, my guess is that a stripped down version of the same booster (fuel tank, engine and fins only) designed for suborbit, easily lifts 10 to 15% more payload than its SSTO counterpart.

But still it’s OK assuming you get back to the KSC and nothing goes wrong.  (But this is KSP and that’s a ridiculous assumption.) What can go wrong?  I’ve been using as SSTO rockets for over a year now, and a lot can go wrong.

1.       What if you miss the KSC?  You might come down on the water, can your rocket survive that?  Or in the black mountains to the west, and you’ll lose it.

2.       It tumbles during reentry and the probe core overheats, you lose it.

3.       They are often so large that they block their own solar panels, so they go dead in orbit and become a large expensive piece of orbital debris.  Or go dead during reentry.  You lose it again.

4.       You overload it, and it barely gets the payload into orbit and comes down on the far side of the planet: 30% recovery, you lose money.

Because recoverable boosters are so much more expensive to build and take so much more fuel, by my guestimate, if you lose one out of seven SSTO rockets, you give back all the profit you made recovering the other six! (and I certainly was losing 1 out of 7)

So (in KSP’s physics/economics model) disposable boosters are actually cost-competitive, a lot easier to build and fly (just jettison and forget) and take a huge variable out of your budget. (IMHO: SSTO rockets just aren’t worth the extra trouble)

And since we’re throwing the rocket away, there is no reason not to go for multi-staging, its cheaper, and since asparagus staging is the more advanced form of multi-staging, my rocket designs have now come full circle.


I’ve rediscovered asparagus staging!  :D

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I could be wrong about this, but it seemed to me that the decline in use of asparagus staging here didn't coincide with an increase of use of SSTO, but rather the introduction of the SLS parts into stock (Rhino, Mammoth, the big SRB, and the associated fuel tanks). Once we had stock parts with that kind of power and fuel capacity, asparagus staging quickly became a thing of the past. The new parts made lifter designs a lot simpler and reduced part count.

I don't recall SSTOs becoming a big thing here until the new spaceplane parts (primarily the MK3 parts) got added into stock, which was after the SLS rocket parts were added.

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So you're saying that, because SSTO rockets are difficult to recover and engineer and can be inefficient, you have switched to the most inefficient way of staging a rocket (cost- and mass-wise): asparagus ?

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It mostly comes down to calculating what kind of weight you want to send into what kind of orbit... In my gaming experience, I ferry Kerbin SOI orbits up to 25tons by spaceplane, a bit heavier loads by a recoverable first stage (which, only does a sub-orbital trip to keep costs down) and all heavy craft or high dV craft either by assembling them in low kerbin orbit, or just use disposable boosters... There just isn't a one size fits all solution!

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8 minutes ago, Gaarst said:

So you're saying that, because SSTO rockets are difficult to recover and engineer and can be inefficient, you have switched to the most inefficient way of staging a rocket (cost- and mass-wise): asparagus ?

please explain.

Isn't asparagus better than stacked stages?
(seems logically better, all engines on from liftoff, all stages fully fueled after separation) 

what would be better?

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Just now, Brainlord Mesomorph said:

please explain.

Isn't asparagus better than stacked stages?
(seems logically better, all engines on from liftoff, all stages fully fueled after separation) 

what would be better?

Asparagus uses a lot of rocket engines and fuel tanks as boosters that, while allowing greater payloads with a given diameter, are very heavy and expensive. That is not that much of a problem, but since 1.0 and the aerodynamics overhaul, people realised that asparagus had become very draggy reducing its efficiency further down. Asparagus is not useless, but it is no longer the magical way to do things in KSP as it was before 1.0 and career mode.
If you're really looking for the most efficient way to launch a given payload, you have to test which designs are better. Design a SSTO rocket, an asparagus, and a conventional rocket (with boosters or no, solid or liquid) for a given payload mass, and compare their masses, costs, tech...

If you're looking for:

  • Cost efficiency: reusable SSTO spaceplane or rocket, or all SRB if you're looking for design simplicity (hard to fly)
  • Mass efficiency: linear staging or liquid fueled strap-on boosters
  • More payload without using larger parts: asparagus
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@Brainlord Mesomorph I made a couple of recoverable launch rocket stages, so you can make them. Not because it has no budget purpose in KSP, just because of the "Cool" and "proof of concept" factor.

The trick to making it work is to make sure that your first stage can get its apoapsis out of the atmosphere (70km+)

Once it reaches that, stage fire the heck out of your 2nd stage and switch to map view from time to time. Make sure you manage to get your time to apoapsis on your 2nd stage atleast to 1 minute and 30 seconds before your first stage is dropping. Before your 1st stage loses its altitude it will reach its apoapsis at 70km+.

You can now switch back to it since it is out of the atmosphere. Fire 270degrees and make sure the trajector hits in between the abandoned airstrip and the main shore (because of Kerbins ridiculous fast rotation) it will not land in the water but on land. After your burn, switch back to the 2nd stage if you can, as long as you have enough time to switch back to the 1st stage (only do this if you didn't manage to get enough velocity on your 2nd stage)
Try to avoid it at all imho.

You can now switch back to your first stage that's on a KSC recovery trajectory and you'll have your full fledged stock recoverable rocket my friend.

Edited by Vaporized Steel
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1 hour ago, Brainlord Mesomorph said:

In KSP however, we have the physics bubble, which makes lower stage recovery impossible.

It makes it tricky, maybe even awkward, but definitely not impossible. People do SpaceX style booster landings in KSP, and I have seen more than one way of doing that (if you like KSP streams I can give you two examples: EJ_SA style, ghost riding the second stage to PE while you land the booster, or like MatoroIgnika does it, let the booster fall by itself after the boostback burn while you fly the 2nd stage to circularization, and then switch to the booster and land)

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54 minutes ago, Dedjal said:

The sls parts just made me build bigger asparagus rockets :D

Oh so very true when in the sandbox... Look at what was on my launchpad yesterday...

Spoiler

Oq9dXRE.png

 

Edited by LaytheDragon
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19 minutes ago, Vaporized Steel said:

@Dafni

2 people trying to say the same each in their own way at exactly the same time. Lol:lol:

hehehe, yes, that was nice. You have an advantage that I obviously dont have though: native English... I'm glad you could make sense of my post, and explain it much better too.

cheers

 

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My main problem with staging rockets is that big boosters don't sod off Kerbinwards quickly enough. Sepratrons are too big to brake boosters the size of medium rockets, and the smallest SRBs just break them and the core stage, and blast their aero caps into the payload. I could use fairings, but they'd basically be shrapnel. And they separate too high for chutes.

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You could always install stage recovery and not really worry too much.  Slap on a parachute, two ,or ten and/or have a probe core on your recoverable debris with some fuel, and stage recovery will determine if it's plausible to save.  It can even recover science and kerbals!!

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24 minutes ago, mrclucks said:

You could always install stage recovery and not really worry too much.  Slap on a parachute, two ,or ten and/or have a probe core on your recoverable debris with some fuel, and stage recovery will determine if it's plausible to save.  It can even recover science and kerbals!!

I use stage recovery all the time, I've never trusted it enough to recover kerbals though.  Science experiments like atmosphere sensor  on the boosters when I unlock them. works just fine.

Currently my designs are lots of boosters to get above 70km, then fire the main stack. Separate the payload in a stable orbit and carry on the mission. I then rdv with an orbital tug called Vampir, drain the booster of fuel for the refuelling station and nudge the spent stack back into the atmosphere, Following the stack back down after I've re-circularized Vampir. 

 

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Thanks @Basto, SSTO rocket are now harder to use because engines don't resist as well as before. They tend to burn now. My launchers were very efficient ans easy to use in 1.0.4 and even 1.0.5. But since 1.1, the reentry profile maybe kind of awkward (or Kerbal).

I'm not sad, before after using them in my last career, I felt thos SSTO are largely OP. They are very easy to build, very easy to fly and easy to land (to get 97%) when you know what to do. Building a regular staged rocket was more complex (you have to deal with flipping risks on each stage.

As for asparagus, since dV went down from 4500 to 3200m/s, I find them useless. Sure it's more efficient, but not much and the building of the launch stage takes more time. In the end it's largely more expensive than SSTO.

In my current career, I just do regular 2 stage rockets which I rebuild each time. I don't really care much as I focus on my LKO vehicle.

 

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1 minute ago, Warzouz said:

Thanks @Basto, SSTO rocket are now harder to use because engines don't resist as well as before. They tend to burn now. My launchers were very efficient ans easy to use in 1.0.4 and even 1.0.5. But since 1.1, the reentry profile maybe kind of awkward (or Kerbal).

I'm not sad, before after using them in my last career, I felt thos SSTO are largely OP. They are very easy to build, very easy to fly and easy to land (to get 97%) when you know what to do. Building a regular staged rocket was more complex (you have to deal with flipping risks on each stage.

As for asparagus, since dV went down from 4500 to 3200m/s, I find them useless. Sure it's more efficient, but not much and the building of the launch stage takes more time. In the end it's largely more expensive than SSTO.

In my current career, I just do regular 2 stage rockets which I rebuild each time. I don't really care much as I focus on my LKO vehicle.

 

While it's a little cheaty coming in with a high periapsis (45k) and rotating the craft along its axis seems to mitigate the overheating issues. I usually lose the air breaks but the engines survive and the increase in parachute survivability in 1.1 has helped. Still using them and loving them in 1.1.3 

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It's been discussed that there are plenty of ways to make recoverable or semi-recoverable launchers in KSP. Falcon 9 style landable boosters can be done. Shuttles are partly recoverable, as are spaceplanes that use drop tanks or boosters. SSTO spaceplanes and SSTO rockets are fully recoverable. Perhaps you could make a rocket with a big core that makes orbit and then lands, and cheap boosters to help it into orbit.

As far as disposable rockets go, the drawback to asparagus designs is you're often using relatively expensive liquid engines and tanks as boosters, plus the cost of lots of decouplers and fuel lines. It might be cheaper to use solid boosters.

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I use solid-fueled boosters in my first stage, generally with some fuel tanks stacked on top of them so that the remaining stage(s) are more or less at full fuel when the slid boosters burn out.

Depending on how heavy my payload is, I may or may not have a set of liquid fueled boosters as well.

This is around the lunch-core that takes the payload vessel to orbit and will often help with the initial departure burn.

 

not really asparagus, but SRB+drop-tanks->Liquid boosters -> liquid fueled core -> payload vessel(usually nuke powered)

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14 minutes ago, Terwin said:

I use solid-fueled boosters in my first stage, generally with some fuel tanks stacked on top of them so that the remaining stage(s) are more or less at full fuel when the slid boosters burn out.

Depending on how heavy my payload is, I may or may not have a set of liquid fueled boosters as well.

This is around the lunch-core that takes the payload vessel to orbit and will often help with the initial departure burn.

 

not really asparagus, but SRB+drop-tanks->Liquid boosters -> liquid fueled core -> payload vessel(usually nuke powered)

Hauling up some snacks, are we? :sticktongue:

I've been using something that's not quite Asparagus staging, but similar. I believe the term is "tri-feed"? Something like that; it's named on Atomic Rockets somewhere. Three liquid-fuel booster stages, feeding fuel into the main stage and jettisoned simultaneously.

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Just now, SingABrightSong said:

Hauling up some snacks, are we? :sticktongue:

I've been using something that's not quite Asparagus staging, but similar. I believe the term is "tri-feed"? Something like that; it's named on Atomic Rockets somewhere. Three liquid-fuel booster stages, feeding fuel into the main stage and jettisoned simultaneously.

I think that's called "onion staging".

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Back in 0.90 I made a cost comparison in career for what was required to get a modest satellite to LKO. I built a Mk2 sized spaceplane that could launch a satellite to LKO to fill a typical satellite launch contract. I made a note of the net cost of that mission, that is the total launch cost minus the funds recovered when I landed safely. I then set about building the absolute cheapest fully disposable rocket I could that would get the same payload to the same orbit. The total cost of the disposable rocket came out as about 10% more than the net cost of the "fuel only" SSTO net cost, because the space plane actually burned through quite a lot of fuel.  The more important element, though, was the much shallower space plane launch profile and the time taken to recover it on the runway meant completing a satellite launch contract took about three times the gameplay time as it took to complete the same contract with a disposable rocket. If my objective was farming money, the profit I could make by completing two additional satellite launches with disposable launchers massively dwarfed any savings from a cheaper launch.

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