Air-Launched Mun SSTO Help

[Astr0Guy5]

Hello all you experienced SSTO flyers!

I'm currently trying to get to the Mun in KSP2, but I wanted to do it in style as opposed to using another mundane rocket.  I thought I'd attempt the challenge of air-launching an SSTO instead (which I've never done before).  However, after many failed launches, I can't seem to reach orbit.  Here's the order of events for my current flights:

1) The carrier aircraft takes the SSTO up to 7-8k km and decreases throttle to ~35%, the SSTO lights its rapiers, and then the carrier pulls away and drops the payload

2) The SSTO switches rapiers to closed cycle and increases its ascent profile to ~45 degrees to gain altitude

3) At this point I just guess at when to start gradually pitching down (typically around 30k km mark) and light the nerv (I've no clue when to do this).

After these maneuvers, I get an apoapsis of 70k km, but feel like I've wasted a lot of fuel being inefficient. Plus, sometimes the maneuver planner won't let me plan a circularization because I run out of fuel, even though I've got ~1300m/s of dv left.  Obviously I need more dv than that to get to the Mun.  Anyway, any tips on a better ascent profile or just better SSTO design is greatly appreciated!

The carrier and SSTO as they stand currently.  I will add that they both fly like a dream, but fuel management might still be an issue.

 

[Socraticat]

That's definitely flying with style!

If this was my build, this would be my next steps:

I usually try to get my SSTOs to use airbreathing mode as long as possible- usually up to 20k.  Whiplash engines are my preference, paired with enough air intake for high speed high altitude flight. Gotta scoop up the little bits of air like an atmospheric whale up to 1,000 m/s.

I'd cruise to just before AP with the lauch vessel before letting the "SSTO" go (Although the decoupling seems like a second stage) and keep the ascent profile at 10-20*. The air above 20k is too thin, so oxidizer is necessary. If you choose this profile the "SSTO" Doesn't need Rapiers to switch modes, which may reduce how much Liquid Fuel you need to pack on the SSTO.

I wouldn't light the NERV until your Ox is burned out. The higher you can go before lighting it, the more DV you'll have for extraplanetary moves.

Landing with less than 1.0 TWR on the Mun is another story. You can land on the Mun with a NERV, but it's easier if you can get into a super low orbit first and zero out your lateral velocity. Unfortunately there's a bug that makes that... difficult.

Disclaimer, I have yet to get an SSTO to the Mun on it's own. I'm close to a Flyby.

I'm excited for thermals to be added to the game- The airbreathing portion of the SSTO profile can get quite hot; I'd like to see just how fast we can go in atmo before burning up. Good fun.

 

Edited August 4, 2023 by Socraticat
Added some words for clarity

[Astr0Guy5]

Thanks for the advice, @Socraticat!  As you can tell by my new profile picture, I successfully made it to orbit and beyond with the spaceplane.  In fact, I was able to land on the Mun (albeit with extreme caution) and return home.  There's still some modifications to be made, however, as I didn't have enough fuel to land to re-circularize at Kerbin.  Tim and Val survived the crash landing though! Thanks again for the help 

Spoiler

[Socraticat]

2 hours ago, Astr0Guy5 said:

In fact, I was able to land on the Mun

AWE! YEAH!

I keep shooting myself in the foot for that achievement. I keep putting restraints on myself like payload capacity or fuel type. An SSTO that can carry a payload to the Mun and return to Kerbin would be an awesome achievement. I should really just try for the basic accomplishment.

Great work!