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How do i get 27 tons into orbit?


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vZR3ZcD.jpg

This is the core of an inter-planetary spacecraft, other parts will be docked with it in orbit. It is also the heaviest part of my planned spacecraft so if i can get this into a safe orbit the other pieces should be easy but i just can't seem to make it happen. The rockets either do not have enough thrust or are too unstable and crash. I looked at the rocket equations on the wiki but since i am not a physics or mathematics major, they are kinda confusing.

Any suggestions?

(If you are wondering how a Rockomax 64 only weighs 26.8 tons its because its only carrying liquid fuel, this is going to be an atomic rocket when it is finished.)

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I have a few concerns with the payload before we even get to lifting it into orbit:

1. I realize that the stock LF only tanks are limited, but stringing a bunch of those together may be better than lifting up a larger tank that's not even half full.

2. Get the solar panels away from those docking ports.  If they're deployed while docking, you're gonna have a bad time, and if part clipping bothers you at all, it's not gonna look pretty when you have other pieces attached there.  It's also going to be really easy for them to be blocked if you have stuff docked next door.

3. Do you have any interest in modding?  A couple informational mods (Like KER) and some mods that let you either switch the stock large tanks to LF only or add large LF only tanks would really help if you're going nuclear.

 

Pictures of the entire craft you're launching would help as well.  You may not have to change much.

Edited by Geonovast
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1 hour ago, Geonovast said:

2. Get the solar panels away from those docking ports.  If they're deployed while docking, you're gonna have a bad time, and if part clipping bothers you at all, it's not gonna look pretty when you have other pieces attached there.  It's also going to be really easy for them to be blocked if you have stuff docked next door.

Will it even dock?  Those panels will hit the craft way before it gets close enough to actually mate up.  I foresee a RUD with this design. 

 

Have you "dry fit" the pieces together as a whole?  Those docking ports right next to each other may cause the modules to interfere with each other, especially during docking (see above).  Even if they do fit, It will still be a tight fit and take a steady hand to dock.  

 

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2 minutes ago, Gargamel said:

Will it even dock?  Those panels will hit the craft way before it gets close enough to actually mate up.  I foresee a RUD with this design.

It should, solar panels are rather fragile.  The solar panel would disintegrate before anything too terrible would happen.  Would just have to make sure it's retracted when docking.  Personally, the inevitable clipping would be the biggest hassle, and you'd still have the blockage problem.

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6 minutes ago, Geonovast said:

It should, solar panels are rather fragile.  The solar panel would disintegrate before anything too terrible would happen.  Would just have to make sure it's retracted when docking.  Personally, the inevitable clipping would be the biggest hassle, and you'd still have the blockage problem.

Ha, didn't even consider retracting them, as I try to design away from this scenario.  I always try to give the docking part a clear corridor. 

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1 hour ago, Geonovast said:

1. I realize that the stock LF only tanks are limited, but stringing a bunch of those together may be better than lifting up a larger tank that's not even half full.

For an optimal LF-only design you should build your transfer stage exclusively out of Mk 1 LF fuselages. They have the best wet mass to dry mass ratio of all LF-only parts, at 10 to 1. Lf/Ox tanks just aren't worth using for this kind of thing-their wet mass/dry mass ratio is terrible when you're only using them to carry Lf. Also, that RCS tank is probably excessive. Monoprop is really heavy, and carrying that much of it around is not good for dV.

But, yes, a Mainsail-based core with either solid or liquid boosters (and maybe a Skipper/Poodle upper stage) should do just fine for getting 27 tons into orbit.

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Quick & dirty liquid fuel lifter for 27 tonnes:

1st stage: Twin Boar + Jumbo 64

2nd stage: Skipper+ X200-32+X200-16.

Launch cost $35,000 not including payload.

Best,
-Slashy

Edited by GoSlash27
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I'd put a nose cone on it and launch it on a Twin-Boar SSTO - Just a Twin-Boar and 2x Orange Tank. Eyeballing it the Twin-Boar should have enough power, but you can always add some SRBs on the side - from past experiments, I know that with optimal trajectory a Twin-Boar Rocket SSTO can launch ~31t to orbit so definitely it can do your payload, the SRBs would just be to add margin for non-optimality or reaching a higher orbit.

The Twin-Boar offers 33% more thrust than a Mainsail and is cheaper (taking into account the integrated Orange Tank) so it's rarely a good idea to use a Mainsail.

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1 hour ago, IncongruousGoat said:

Mk 1 LF fuselages. They have the best wet mass to dry mass ratio of all LF-only parts, at 10 to 1.

Sorry for nitpicking, but I want to point out that mk0 LF fuselage has better wet to dry ratio of 11 to 1. Also the ratio of Mk1 fuselage is 9 to 1.

16 minutes ago, blakemw said:

Twin-Boar

Just a note, it's way draggy for a 2.5m part.

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Wow, there is a lot to consider here. There are a couple things i want to make note of...

1. I chose the big orange tank more for structural stability more than anything else. Being one large piece it would be more stable, i've had problems with ships falling apart because there were too many parts fitted together, and the large size meant i could easily fit multiple docking ports and not worry about modules running into each other. This is also why i chose such a large RCS tank because it is the only one that would fit onto a large tank without an adapter, which i am trying to avoid.

2. As for the rest of the ship, it is still being designed. There will be an engine module of course, probably 4 atomic motors fitted radially onto one of these and possibly mounted on the front of the ship to pull it rather then push it. I was thinking about a science module, a mobile processing lab with its own solar panels and experiments, perhaps left in orbit around duna as the start of a space station there.

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11 hours ago, phantom000 said:

Wow, there is a lot to consider here. There are a couple things i want to make note of...

1. I chose the big orange tank more for structural stability more than anything else. Being one large piece it would be more stable, i've had problems with ships falling apart because there were too many parts fitted together, and the large size meant i could easily fit multiple docking ports and not worry about modules running into each other. This is also why i chose such a large RCS tank because it is the only one that would fit onto a large tank without an adapter, which i am trying to avoid.

5

have you considered to enable autostruts in the advanced setting? I can assure you that a ship of those dimensions won't wobble

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12 hours ago, Reusables said:

Just a note, it's way draggy for a 2.5m part.

This is inconsequential. In practice, for a Twin-Boar SSTO using an aggressive gravity turn the drag losses peak at about 30kN - 1.5% of the Thrust, and that peak (Max Q) is very brief because when the rocket is still traveling slowly in the lower atmosphere drag is very low, and then the air quickly thins out so much the drag becomes negligible. In total you might expect to lose about 0.5% of the total thrust to drag on the Twin-Boar. For reference, the Mainsail drag peaks out at about 1.1% of the thrust at Max Q - and the Mainsail doesn't have a built-in fuel tank (to be completely fair, you should deduct out the drag of an Orange Tank from the Twin-Boar - I haven't done that here and I think if you did the Twin-Boar would be about exactly as draggy in proportion to it's thrust as the Mainsail).

The Twin-Boar is brilliant at catching air when going in reverse though, making it by far the best engine at slowing down and not burning up on reentry.

Edited by blakemw
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13 hours ago, blakemw said:

I'd put a nose cone on it and launch it on a Twin-Boar SSTO - Just a Twin-Boar and 2x Orange Tank. Eyeballing it the Twin-Boar should have enough power, but you can always add some SRBs on the side - from past experiments, I know that with optimal trajectory a Twin-Boar Rocket SSTO can launch ~31t to orbit so definitely it can do your payload, the SRBs would just be to add margin for non-optimality or reaching a higher orbit.

The Twin-Boar offers 33% more thrust than a Mainsail and is cheaper (taking into account the integrated Orange Tank) so it's rarely a good idea to use a Mainsail.

Isp. Bottom node. I don't play much stock but it I did I would use it in preference to twin boar a lot.

 

And for the OP. I'd probably use a skipper with less than 1 TWR and SRBs to get it off the ground

Edited by Antstar
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1 hour ago, Antstar said:

Isp. Bottom node. I don't play much stock but it I did I would use it in preference to twin boar a lot.

The ISP is pretty much balanced by the absurdly good TWR of the Twin-Boar (being lighter per unit of thrust can lift more payload or fuel per unit of thrust which is a good advantage). There isn't usually a good reason to use the bottom node on the Mainsail basically because except in the rarest of cases the Skipper will be a better choice for a second stage engine, since for the second stage gravity losses are almost non-existent so 3t lighter is 3t more payload (also the Skipper has +10 Vac ISP and is waaay cheaper just to make sure). And the Mainsail also has to compete with the Rhino which eliminates further cases it might be worth using - though the Mainsail is at least a lot cheaper than the Rhino.

 

1 hour ago, Antstar said:

And for the OP. I'd probably use a skipper with less than 1 TWR and SRBs to get it off the ground

This is a solid choice (no pun intended). A while back on reddit there was a challenge to launch a full orange tank as cheaply as possible (in this challenge recovery was not allowed). The cheapest was a Poodle core with lots of Kickbacks at just under 30K, similar designs with a Skipper also performed very well, and a Skipper is much less tedious than a Poodle. Twin-Boar SSTO (cheating a little with some SRBs to get off the pad) came in at about 40K. So SRBs can be extremely economical and will be the most cost-effective option if you don't care for recovery and are happy to revert in case of staging mishaps.

Edited by blakemw
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9 hours ago, blakemw said:

In practice, for a Twin-Boar SSTO using an aggressive gravity turn the drag losses peak at about 30kN - 1.5% of the Thrust

It was just for a note. And also drag depends on the TWR, and sometimes high TWR is better for efficiency. (Especially as gravity drag tends to be huge)

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On 2/26/2018 at 11:56 AM, phantom000 said:

I looked at the rocket equations on the wiki but since i am not a physics or mathematics major, they are kinda confusing.

phantom000,

 Those equations are your best friend. All successful players utilize them, either directly or indirectly through mods. I would encourage you to become familiar with them. Feel free to hit me up with whatever parts you find confusing.

Best,
-Slashy

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On 2/26/2018 at 1:11 PM, Marschig said:

Vb9ZCpC.png

 

This actually worked! Very well in fact, i had to change it a little, using 2 sets of 4 kickbacks with one set at 75% but it worked!

Thanks to everyone, this is a lot to consider for future missions.

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I'd say NOT to launch it empty, but if you're willing to refuel it, go ahead and use the fuel to get into orbit.  Better to have the weight there at the front than something that will let your CoM go backwards.

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Don't use the orange tank without oxidizer. Either use Interstellar Fuel Switch or Configurable Containers to change it to an LF only tank or stick to spaceplane tanks, like the MK3 line, which come in LF only variants. You're wasting an insane amount of dV with your current setup.

I usually rely on rtgs for electric generation, as you don't need to worry about the ship alignment with the sun, the night or about accidentally breaking them while maneuvering. 2-4 rtgs with a good battery are more than good enough.

Also, the 2.5 RCS tank is too heavy and has too much RCS. You typically don't need that much, not even in a large ship. You can use radial tanks. I usually use Procedural Parts to create a very short 2.5m RCS tank.

Edited by juanml82
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