Keep having problem with glide re-entry

[Jestersage]

I have been playing with the Mk-II bodies using a wingless lifting body design, and so far, I still have occasional overheating, exploding nuclear battery, and always coming in too fast in a ballistic manner (angle > -30) ... long story short, I am unable to produce some kind of glide landing.

My glide entry are usually done as follow:
-Drop the PA altitude to around 43000m (NOT negative... I am not that dumb to have it disappear)
-Once it start heating, angle up to +20~+30 degrees
-Once the atmosphere burn is complete, point the nose down close to prograde, as long as it's <-20 degree. Otheriwse I tried to bring it up to -20

Not sure what i did wrong. I decided to actually put in a pair of structural wing A (which actually makes it resembles dyna-soar), but have not test it yet. Anyone got some pointers before I test it out??

[Rhedd]

Wow. Negative 43km? Is that honestly what you meant to say?? That's not a glide reentry, that's reentering like a BULLET, man! Seriously, that has GOT to be a typo.

The steepest reentry (from a circular orbit of 72km) that I've been able to consistently use with a spaceplane is a Pe of 0. Zero. And that's super-steep compared to a 20-30km Pe for ballistic pod reentries.

My shuttle is a Mk3 size, but I let it follow its prograde until it hits an altitude of 50km, then I make it hold its rotation, which makes it tilt up gradually as it descends. I start manual piloting at subsonic speeds. Works consistently, even using airbrakes which have a surprisingly low heat tolerance. Nothing explodes.

[A Fat, Angry Serval]

Unless you're already in atmo or you're simply making a suborbital hop, your Periapse should NEVER be negative on reentry. That is a balistic reentry, not a glide.

I'm currently using a completely stock MKII SSTO (I'm probably going to upgrade to a B9 SSTO after that). I tend to go for a very steep angle of attack and a very high periapse on reentry, and I prefer to get my speed down as much as I can in the upper atmosphere. Otherwise the vessel experiences some nasty heat issues.

[Rhedd]

Yep, VestedGamr. I would usually reenter the same way you do. Unfortunately, that shallow path kept overheating my fragile airbrakes, so I tried the crazy (to me) experiment of going in much steeper. That was hotter but for a shorter period of time, so nothing explodes. I was surprised.

[Azunai]

proper "gliding" with just the bodylift of mk2 parts is difficult. it's more like "controlled falling". if you want to glide, you should add some wings and control surfaces. also helps with the aerobraking, so they might help with the overheating issues.

don't see a problem with a steep reentry. a periaps below ground work fine. actually i find it much easier to reenter that steeply (helps with getting a somewhat accurate reentry near KSC)

the only problematic parts during reentry are low heat resistance parts. mk2 cockpits are a bit risky (the inline cockpit or a passenger cabin with an adapter tank in front of it is *much* safer). stuff like batteries or solar panels should be on the "cold" upper side of the plane - or better - inside a service bay (which also helps with lowered drag during ascent). i've noticed that cargo bays are somewhat unreliable. i often get heat bars from items inside an mk2 cargo bay. not sure what's going on with that. i rarely use them, though. use the 1.25m service bays instead - they work fine and protect the stuff you put inside

[Jestersage]

Oops. Typo. I meant my Pe was around 43000 above sea level.

What I need to do are two things:
1) Glide rentry AND Landing. Landing is the difficult part for me, since I always ended up with a prograde of -30 degree once burn in completed.
2) Trying to land on the runway. I usually ended up landing on the large patch of desert to the west of KSC.

Or should I just get MechJeb?

[Syd Khaos]

Originally posted by Jestersage:

Oops. Typo. I meant my Pe was around 43000 above sea level.

What I need to do are two things:
1) Glide rentry AND Landing. Landing is the difficult part for me, since I always ended up with a prograde of -30 degree once burn in completed.
2) Trying to land on the runway. I usually ended up landing on the large patch of desert to the west of KSC.

Or should I just get MechJeb?

If your hitting the desert your starting your re-entry WAY to soon.
And, as mkunz2 said, you will NOT get a proper glide-plane with just Mk2 body parts. Yes, they do provide some lift due to lifting body design, but its not nearly enough, not for this purpose at any rate.

Think about the distance between KSC runway and where you typicaly touch down in the desert. Adjust your deorbit point back by at least this much. When in doubt overshoot and pack a drag-cgute onto the craft.

[Jestersage]

Also, is mechJeb is bad idea?

Doing one final test using ONLY the cockpit. for testing purpose, of course, but I also start to come to the conclusion that it needs some wings.

[Rhedd]

Originally posted by Jestersage:

Oops. Typo. I meant my Pe was around 43000 above sea level.

What I need to do are two things:
1) Glide rentry AND Landing. Landing is the difficult part for me, since I always ended up with a prograde of -30 degree once burn in completed.
2) Trying to land on the runway. I usually ended up landing on the large patch of desert to the west of KSC.

Or should I just get MechJeb?

Oooh, okay! A Pe of +43km, then! Yeah, now you're burning up because of the OPPOSITE problem, sorry!

43km Pe is way too shallow. It gives too much time for the ship to build up heat without ever having a break to get rid of it again. It just gets hotter and hotter for minute after minute and then BOOM.

Like I said in an earlier post, I usually do Apollo-style pod reentries at 20-30km, but I found that with a spaceplane/shuttle that kept burning things off. Try it with the same plane you've been using but fly it like I described in post #1. It will probably work far better.

As for using MechJeb, no, it's a great idea, but in this case only for navigating and holding a heading. (I love that it will hold a heading prograde and level to the ground. Great for planes!)
Do your kerbals a favor and don't ask MJ to land the thing for you! It does a fine job putting landers on the Mun, but asking it to land anything with wings in an atmosphere is asking for an opportunity to take "funny" screenshots of the catastrophe. Spaceplanes need to be flown by hand a lot more than most things.

Anyway, try Ap=72km, Pe=0. Use MJ to hold prograde level to the ground until 50km (about when flames start), then set MJ to hold rotation so that your nose slowly tilts up. See how it goes.

[Jestersage]

@Rhedd: About how much ahead the 0 Pe should be compare to runway? Say I am going counter clockwise; should the PE be close to the closest desert, or to the larger desert further to the west?

[Rhedd]

Originally posted by Jestersage:

@Rhedd: About how much ahead the 0 Pe should be compare to runway? Say I am going counter clockwise; should the PE be close to the closest desert, or to the larger desert further to the west?

Unfortunately, I can't tell you that. It's VERY different for every vessel. The drag characteristics aren't even close for two different vessels.

I have two different shuttle-type designs I use regularly, and I had to figure out when to reenter seperately for each. Heck, even if I forget to open the airbrakes on my big shuttle before hitting the atmosphere, it throws my landing point way off.

Here's how I do it, though. (Trial and error, yay!)
I use Hyperedit to put my ship in an orbit at the height I intend to always do my reentry from (usually 72km). Make certain your vessel is in the same configuration you expect it to be in during a real reentry (fuel depleted, airbrakes open, etc.)

I then create a maneuver node to drop my Pe to the desired height (zero, in this case) and I let MechJeb do the burn for me so I know the timing is exact. When the burn starts I note down the longitude (MechJeb and a number of other mods will tell you that).

Then just follow whatever plan you have for a normal reentry. When the vessel finally touches down, note the longitude. (This process will be more accurate if you land in the ocean or within about 100m of sea level.)

Now compare the two longitudes you recorded and you'll know how many degrees it takes for your shuttle to land. Subtract that (or add it, if you're orbiting the WRONG WAY) from the longitude of your intended landing site (presumably the KSC landing pad) and then in future flights, start your deorbit burn at that longitude.

If all goes well you should come down within gliding distance of the landing strip!

You can do this wihout "cheating" with Hyperedit, if you prefer. You just have to be willing to set a shuttle or two down God-knows-where. I don't look at it as cheating. I look at it as running simulations like actual NASA does.

Also, ScanSat and a decently mapped planet are pretty helpful when doing accurate landings.

[Jestersage]

Hey Rhedd, thanks for the ideas.

With my vessel going counterclockwise, what I did was about a few distance away from KSP (1/8 of Kerbin circumference), and go with AP of 72k, Pe of 0, using the launchpad as 0,0 What i did different is that I go to manual mode once the arc started to end at the sea, and tap it lightly so the plane always point up at 30 degrees, and then once that is done, at around 20k, I have enough momentum to coast through and glide parallel to the runway; manually adjust until I am at 55m/s.

And it was with my wingless lifting body, composs only of a mk-2 rocket fuselage, the mk-2 cockpit, and the mk-2 inline dock, and 2 wings mounted vertically for yaw. Granted, I have emptied the mk2 fuel tank, but I did it nonetheless.

Thanks for the suggestions. Will tests other designs now.

[Rhedd]

So it didn't burn up? That's progress!!
Happy to help. Let me know how it goes.

[Bubba Fett]

I've played with a similar ship as what you're using for my crew transport. I usually have a negative pe that intersects the ground about a quarter orbit from my reentry burn. I try to make the impact zone just east of the mountains near the KSC.

I use the AV-R8 winglets on my design. They provide a bit of lift which gives me mroe control over my final landing spot.
After a rapid fall through the upper atmosphere I hit the lower atmosphere and rapidly slow down before before the heat explodes anything. I'm usually subsonic by the time I get to 12km and my descent path has flattened out a lot. I then point the nose down to keep my airspeed up as well as keep from overshooting my target.
http://steamcommunity.com/sharedfiles/filedetails/?id=700712820

On an ideal landing I end up over the KSC about 100m off the ground where I pitch up to stall the craft. As it stalls I deploy the parachutes on the roof and float to a soft landing.

The lift and COM are properly balanced at 1/8 tank of fuel, but I've got vernor engines on the bottom at the nose and tail to help with pitch control on the final parachute descent if the amount of fuel remaining is wrong.

I also had a problem with yaw stability till I added one of the winglets as a vertical stabalizer.
This meant I had to turn the entire rocket in the VAB to make my gravity turn by pitching forward rather than yawing right. Any attempt to yaw or roll was a problem because of the single vertical stabalizer.

Due to the drag that the winglets cause at the top of the rocket I also had to use a tall skinny launch rocket. A short rocket with flip because of the drag while a long one will have enough leverage for the tailfins and engine gimbal to keep it under control.
http://steamcommunity.com/sharedfiles/filedetails/?id=700708864
While I've done a number of trips to my station and back, I'm still refining the design so I've found that quicksaving before the retro burn to be a lifesaver.