Why doees my craft's suborbital trajectory not degrade?

[Hoplite308]

I am currently playing Science Mode and launched my first science mission into space (not my first time in space in KSP overall). I mis-judged (noob mistake) and got Jeb caught in a sub-orbital trajectory (a: ~126,000, p: ~69,590) with no fuel. At first I thought "well, guess I'm baby-sitting this one until it crashes". Problem is, it never degraded significantly. I recorded the apoapsis and periapsis multiple times, and at first both go down, but then it pops back up again to (currently) (a: 123356, p: ~69536).

My ship is currently 2.03t, height 2.8m, width 1.4, length 1.6, and built as such:

1. Mk16 Parachute
2. Mk. 1 Command Pod
   1. Radial (EW) Mk2-R Radial-Mount Parachute x2
   2. Radial (N) Communotron 16
3. Service Bay x2
   1. Internal Modular Girder Segment
      1. Radial (NS) Goo Canister x4
      2. Radial (NE/NW/SE/SW) 2HOT Thermometer x4
      3. Radial (NE/NW/SE/SW) PresMat Barometer x4
   2. Radial (EW) Radiator Panel (small)
4. Heat Shield (1.25m)

It's orbiting with both service bays open to increase drag as much as possible. Is it possible that I just found a "skip" orbit? I read that those weren't supposed to be possible in KSP.

[Snark]

Hello, and welcome to the forums! 

1 hour ago, Hoplite308 said:

It's orbiting with both service bays open to increase drag as much as possible. Is it possible that I just found a "skip" orbit? I read that those weren't supposed to be possible in KSP.

Two things to understand:

First, there will be zero effect of drag on your ship unless you are actually flying the ship while it's in atmosphere.  That's because KSP runs every ship "on rails" other than the currently controlled vessel (and any other vessels within a few kilometers of it, a.k.a. the "physics bubble").  So for example, if you were to switch away from the ship and just watch it orbiting 'round and round from the tracking station or something, it will literally never degrade and orbit forever.

"Background drag" simply doesn't happen in KSP.  As long as your ship stays above an altitude of 1% Kerbin sea-level pressure (i.e. an altitude of about 23 km on Kerbin), then it will simply orbit forever with no drag happening, if you're not flying it.  (And if it goes below that altitude while you're not flying it, then it will simply be deleted as "lost", so beware).

Second, you mention that your Pe is 69,590 m.  That's just barely kissing the top of Kerbin's atmosphere, which is at 70,000 m exactly.  You're only dipping 410 meters into the atmosphere, and you're not going to be spending much time below 70 km.

That means even if you are flying the ship... drag forces are going to be only briefly applied for a moment right at Pe, and will be vanishingly tiny.  You're going to take for-gosh-darn-ever to noticeably degrade-- you could be continuously flying the ship and it would still probably take many hundreds of orbits to degrade and re-enter.  You really need to get your Pe a lot lower than 69,590 to start seeing significant drag.

My suggestion?  Get out and push.

...No, really, I'm not joking, I literally mean that.  Kerbal EVA thrusters are notoriously overpowered-- they're enough to give a lone kerbal something like 600 m/s of dV, and also you get a free refill of your EVA propellant every time you get back into the command capsule.

So in a situation like this, here's what you can do:

1. Wait until your ship has coasted up to Ap.
2. Go EVA, maneuver Jeb around until he's in front of the craft facing towards it in the orbital direction... and then thrust Jeb forwards so that he's pushing against the ship.  (It can be a little tricky not to spin the ship or slip off to the side while doing it-- will likely take some futzing around.)
3. This will give the ship a very gentle nudge in the direction.  Since you're doing it at Ap, this means it will lower your Pe.  The ship is a lot more massive than a kerbal, so you'll probably only be able to lower the Pe just a bit, but do what you can.
4. When Jeb starts to get low on EVA propellant, maneuver him back around and get back inside the command pod.

The above sequence of actions will lower your Pe by a bit.  Probably not enough in just one pass to reenter and come down... but as soon as Jeb clambers back inside in step 4, he gets a refill on his EVA propellant for free!  So if (as is likely) he hasn't lowered the Pe enough to be very helpful, you can just coast back up to Ap again and repeat the process.

[magnemoe]

As snark says, it might be better to have the ship pointing opposite of orbital direction and push toward the heat shield as its larger and flat. just treat jeb as an engine. Just getting down to 60 km will have an huge impact here.