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SSTO Losing Thrust Early in Ascent. Please help.


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I've made this kick-ass SSTO that could get up to 20 people to Laythe. In previous tests, I managed to get to LKO (and Minmus' surface for refueling) and re-enter with no problem.

  • However, after I was done with the ALT-12 Laythe tests, for some reason the Poseidon started to fail.
    • More specifically, it lost thrust and speed as it got to Mach 1 and never got past 400 m/s during the initial ascent.

 

For more details regarding the previous Poseidon tests, read my "Neptune Mission Files" post about them.

 

nVWnJq1.png

  • SPH image of the latest variant

 

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  • CORRECTION ATTEMPT 1
    • Tried the "low-angle" approach to get to a high enough velocity so that the engines can't stop working

 

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  • CORRECTION ATTEMPT 2
    • Tried to ascend as fast as possible at a 30-degree angle. Backfired miserably

 

How do I fix this? This plane used to be awesome, and now for some reason it's a "massive flop."

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16 minutes ago, Mars-Bound Hokie said:

How do I fix this?

You're not losing thrust. Getting from 330 m/s to 400 m/s is the game's Mach 1 barrier, and that is where drag is highest. Your problem is drag, not thrust.

Somehow, either you've made a little tweak to your craft that increased drag a little bit, or there has been a slight change in the version of the game and the aero calculations have changed a little bit. It does not take much of a change to make a working spaceplane suddenly not get past Mach 1 anymore.

You have a hell of a lot of little goodies radially attached to the outside of your craft. It looks like you also have a cargo bay. You need to take most of the radially attached thingies (radiator panels, gigantors, science experiments, antennas) and move them into your cargo bay. Yes, it'll be a little tricky making it so they still serve their functions and deploy properly after putting them in a cargo bay, but that's definitely the easiest way to cut your drag by a lot.

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23 minutes ago, bewing said:

You have a hell of a lot of little goodies radially attached to the outside of your craft. It looks like you also have a cargo bay

Correction: I have TWO cargo bays: a downward one in the front, an upward one in the back. Both of these contain the drills and the ISRU unit, respectively, so that I can refuel this bad boy.

  • For further details, read the Neptune Mission Files post I put up earlier.

 

You're right, I probably should put the scientific instruments in the cargo bay; specifically, the front one, where a scientist can reach the goo from the ground. I'm not sure about the Atmospheric Fluid Spectro-Variometer, though, since I don't know if it will work stowed. As for the antenna, I can probably afford to downgrade to an RA-2 since I have extensive relay coverage (pretty much) everywhere.

 

The rear cargo bay has a Convert-O-Tron 250 in it - along with two small ore tanks (enough for 150 capacity). Is it possible for me to place the radiator panels directly on the unit itself and not risk damage from overheating while it and the drill are in operation?

  • If not, then can I just reduce drag by having small TCS panels in a line?
    • Or is one medium TCS enough?

 

There's no way in hell I'm taking the Gigantors off. Aside from the fact that they worked just fine in all the previous tests - and they caused minimal to no drag interference in other SSTO models of mine - I need that kind of power generation (combined with a large capacity) to refuel this plane. For that matter, you think I need to do anything with the aerobrakes?

  • And no, I'm not stupid enough to fly with them out while not landing.

 

"or there has been a slight change in the version of the game and the aero calculations have changed a little bit"

  • Actually, I noticed this weird anomaly in the plane BEFORE I updated to 1.8 today. I thought it would fix the issue, but it either did nothing or screwed me up worse.
Edited by Mars-Bound Hokie
Forgot something
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52 minutes ago, Mars-Bound Hokie said:

Is it possible for me to place the radiator panels directly on the unit itself and not risk damage from overheating while it and the drill are in operation?

Retractable radiators cool your entire ship. It doesn't matter where you place them. But no, you can't attach anything directly to a converter -- you'd have to attach all your stuff to the little ore tanks.

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36 minutes ago, bewing said:

But no, you can't attach anything directly to a converter -- you'd have to attach all your stuff to the little ore tanks.

Actually, if an end attach node is available, they can get stuck on there the offset/rotated to a more desirable position.  I have a refueling base design that has a vertical mounted convert-o-tron with a tcs panel mounted on top. 

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Actually there are plenty of things that go nice inside bays:

Parachutes, you can not deploy them anyway at speeds where doors should be closed. Maybe you can even get rid of some airbrakes if you get used to open bays for braking.

Gigantor: in space you can fly with doors open and arrays extended as well landed. Just like parachutes: only safe to use when opening doors is less of a problem.

A small service bay at front will serve to balance parachutes.

In general bays are important to stay closed exactly at atmospheric ascend in order to decresse drag. Anything you do not need during this ascend can go inside. All the other time it is only aesthetic to keep closed.

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1 hour ago, CBase said:

Parachutes, you can not deploy them anyway at speeds where doors should be closed. Maybe you can even get rid of some airbrakes if you get used to open bays for braking.

Why would I put parachutes in cargo bays? I probably should get rid of some of the parachutes surrounding the cabin, though.

  • They're only to be use after I use the abortion sequence, which detaches the cabin from the rest of the plane. That many parachutes seems like overkill, so I'll have to cut back.
    • I'm definitely keeping the rear parachutes, which brings me to this.

 

1 hour ago, CBase said:

Maybe you can even get rid of some airbrakes if you get used to open bays for braking.

I may remove one or two sets of brakes, but there's no way I'm using open cargo bays for braking. I need something more powerful to slow down a plane that big, especially on the surface of Laythe.

 

1 hour ago, CBase said:

Gigantor: in space you can fly with doors open and arrays extended as well landed. Just like parachutes: only safe to use when opening doors is less of a problem.

With my plane's current design, how am I going to fit and deploy the panels from the cargo bays? Even if I could, I'll be significantly reducing my solar panel intake.

lvmeyIv.jpg

To sum it up: NO WAY!

 

After reading @bewing's answer, I took his advice and kept the science in the downward-facing front cargo bay; I also installed a ladder so that the scientist can reach the goo. I then switched antennae and reduced my number of medium TCS units to 1. 

 

For the next test, I launched as normal. I then noticed I started to lose speed at around 370 m/s before leveling out my plane. As soon as I got to 400 m/s, I knew I was back in action.

  • I don't know if I actually did better, or just got lucky.

 

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  • I used the thermal overlay on this image because the plane looked like it was covered in a white shock-wave-shaped blanket.

 

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  • Don't you just love the smell of burnt titanium in the morning?

 

If you all want to read more about the Neptune IV, feel free to read the attached Mission Report in the original post.

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