How to optimize a space plane - how to know where it is lacking?

[Pappus]

Pappus,

Sorry I missed this earlier.

Mach 2 is around 650 m/sec, so you're still over Mach 2 there.

Turbojet spaceplanes have a tighter margin than RAPIERs, so the balance point where your spaceplane will work is also tighter. This means that a TJ design is harder to pull off than a RAPIER design.

What I've found for TJ designs is that they don't respond well to overloading. A RAPIER can be loaded to where it needs to dive to break Mach 1 and still get plenty of speed and altitude for the closed cycle portion of the ascent.

Turbojets are different. They will lose top end speed and altitude long before they have any issues around Mach 1. This is crippling for turbojets because they run out of steam at a lower speed and altitude and it takes a lot of fuel to muscle out of the hole on rockets. 100 m/sec or 1 km altitude is a lot to make up in the region where turbojets crap out. But OTOH you *have* to have enough fuel on board and engine thrust to get you out of the hole and into orbit. If you don't have that, it doesn't matter how high and fast you're going when you kick in the rockets. You ain't making orbit, so there's no such thing as "better" or "worse".

So try this:

Start over on your spaceplane. Keep it around 30 tonnes total mass. 300 units of fuel for the jets, the rest LF&O for the Poodle. And here's the important part: Make the whole darn thing fuel tanks.

Get that into orbit and see how much LF&O you had left over.

The leftover fuel and oxidizer (minus the reserve for maneuvers in orbit) is how much of your design can be dedicated to payload instead of fuel.

This is where I always start when I'm designing an SSTO spaceplane, whatever the type.

Good luck!

-Slashy

Thanks for the help so far, I am still cycling through stuff and I mean I am not far off orbit just like maybe 10s of thrusting away and since most of my changes make no difference I am gonna wait until I have the wings with fuel, because I tried adding more fuel on the sides and that went worse because of the additional drag all around, I tried making the plane a bit longer to add fuel and it also didn't work because then I think the lift wasn't enough for that long plane anymore. So what I think I need for that design is wings that can hold fuel.

See I added like 2x spark with something like 5x of those miniscule tanks in a row and slapped that additionally on the wings. In total I added maybe a ton if even and I couldn't get the plane to 20k anymore with the rocket and could hardly steer so that led me to beleive that if I want to succeed I need to optimize my drag in terms of adding either more fuel without more drag or reduce drag somewhere, but the design choices are really slim for me to even go with less drag. There are only 2 wings, 2 intakes, 2 engines that are outside the "mainstream". I tried putting a air protective shell around those outer engines but it wouldn't let me for whatever reason.