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Use a plane to carry up a rocket -- but what next?


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I have this special plane with a rocket attached onto it. When the plane is high enough, I detach the rocket and it flies straight up while the plane is in stable flight.

My issue: the plane soon disappears from the map. I'm almost sure that it doesn't crash. I believe that it's because here's a distance limit to two probes flying in real time simultaneously. I've never done that before.

Therefore, two questions:

 1) Is my statement about some maximum distance correct? 2) How do you proceed? (would Mechjeb fix the issue?)

 

Edited by jeancallisti
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1) Partially.  There is a distance limit to any craft flying in the atmosphere that you are not focused on that causes the craft to be deleted and assumed lost.  In space, it doesn't exist, the craft will unload but not be deleted.  This is because of physics calculation limitations.  The physics change so much in the atmosphere that too many craft (or debris) would really pull your computer down.  In space they go "on rails" which means only minimal calculations for orbit, but not physical interactions.  However in the atmosphere they cannot go on rails.

2) There are mods, there is one that freezes the craft so you can come back to it later.  I can't remember the name.  Another one is StageRecovery which looks at the craft at the time of deletion and determines if it could have been possibly been landed safely.  If so, it refunds the cash and puts the Kerbals back in the astronaut complex... but the craft is still deleted.

EDIT Found it!

 

Edited by Alshain
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12 minutes ago, Alshain said:

2) There are mods, there is one that freezes the craft so you can come back to it later.  I can't remember the name.  Another one is StageRecovery which looks at the craft at the time of deletion and determines if it could have been possibly been landed safely.  If so, it refunds the cash and puts the Kerbals back in the astronaut complex... but the craft is still deleted.

Thanks a lot. That first mod suits me much better. If anyone remembers the name...

Also what's the best mod to fly my plane while I'm away? Does Mechjeb have an altitude autopilot for planes?

Edited by jeancallisti
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1 hour ago, jeancallisti said:

How do you proceed?

It's also possible to do this without mods, if you're willing to alter your mission profile to work around the game's limitations.

It requires having your "airplane" stage have enough oomph to send it on a suborbital (or close-to-suborbital) trajectory.  The magic number here is 23 km:  that's the altitude below which an unattended craft will get automatically deleted by the game.  So, with a little bit of creative switching around, it's doable.

To put a satellite in low orbit:

  1. Launch.
  2. Airplane stage takes it to a trajectory that's got it going close to leaving the atmosphere.
  3. When the airplane conks out, and when it's HIGHER than 23 km (very important!), separate the rocket stage and switch to the rocket, leaving your airplane coasting on its upward path.
  4. Give the rocket a small boost if needed to lift its Ap out of atmosphere.
  5. When the rocket reaches Ap, do a burn to circularize.
  6. Immediately switch back to your airplane.  It's still there because you left it on a high, upward-coasting path, and it hasn't yet fallen below 23 km.
  7. Fly your airplane back to land.

It also works for a satellite in high orbit where it's going to take a long time to coast to Ap, but you need to change the order of operations slightly:

  1. Launch.
  2. Airplane stage takes it to a trajectory that's got it going close to leaving the atmosphere.
  3. When the airplane conks out, and when it's HIGHER than 23 km (very important!), separate the rocket stage and switch to the rocket, leaving your airplane coasting on its upward path.
  4. Give the rocket a large boost to lift its Ap to whatever way-up-high altitude you want.
  5. Immediately switch back to your airplane, leaving your rocket coasting up to Ap.  The airplane is still there because you left it on a high, upward-coasting path, and it hasn't yet fallen below 23 km.
  6. Fly your airplane back to land.
  7. Immediately switch back to your rocket, which hasn't reached Ap yet.
  8. Coast up to Ap, then burn to circularize.

Anyway, I've tried it and it works reasonably well.

 

(By the way:  If you're wondering, "what's so special about 23 km?":  the actual "ship deletion limit" programmed into the game is "1% of Kerbin sea-level atmospheric pressure."  On Kerbin, that happens to be 23 km.  On other planets with atmospheres, it would be a different altitude.)

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It's worth noting that at 23km and 1% of sea level pressure, you're essentially in vacuum. Your nuke and terrier engines will work great. You won't need any special aero designs or fairings. 

Also interesting that you can get to 23km with whiplash jets alone, though you'll need to time your rate of climb right. Can be much, much simpler than dialing in a fully orbit capable SSTO.

Thanks for that post!

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13 hours ago, Snark said:

 

It's also possible to do this without mods, if you're willing to alter your mission profile to work around the game's limitations.

It requires having your "airplane" stage have enough oomph to send it on a suborbital (or close-to-suborbital) trajectory.  The magic number here is 23 km

I'm planning on doing that when my planes are powerful enough. For now they aren't. Far from it. They barely go above 15km. But trust me. as soon as I unlock the proper engines....

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5 hours ago, jeancallisti said:

I'm planning on doing that when my planes are powerful enough. For now they aren't. Far from it. They barely go above 15km. But trust me. as soon as I unlock the proper engines....

You also need to get comfortable with a type of maneuver known as a "zoom climb." This is where you go high and fast on jet power, and pull up sharply to convert forward speed into vertical speed, letting you glide above the flameout altitude (and the magic 23km cutoff) on a ballistic trajectory. This is, of course, easier with some engines than with others. There's a lot of meters between 15k and…let's face it, something way higher than 23.

You also might consider a rocket assist to hump you over the critical altitude. I'm currently working on a design that uses thuds and wheesleys to pop up high enough to do high-altitude surveys, which is conceptually pretty similar to what you're trying to do, so I thought I'd mention it.

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6 hours ago, jeancallisti said:

I'm planning on doing that when my planes are powerful enough. For now they aren't. Far from it. They barely go above 15km. But trust me. as soon as I unlock the proper engines....

It's doable with Whiplash, you don't need the Rapier to do it.

Haven't tried it with Panthers.

I'm really not an airplane guy myself.  When I tried this technique with Whiplashes, my air-breathing recoverable first stage was a vertical take-off that had a bunch of Whiplashes around a center 2.5m core.  That core had some (just a small amount) LFO and a Skipper.  I used a brief burst from the Skipper at takeoff to help build up speed so the Whiplashes could gain thrust, and then another brief "sustainer" burst when the Whiplashes conked out.

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