RSS Shuttle re-entry profile

[Vigelius]

I'm having trouble getting my Shuttle-type orbiter back into the atmosphere! Real Solar System, FAR, DRE, Real Fuels...

It's fundametally a B9 and Procedural Wings construction, using the Space Shuttle Engines mod for propulsion. It took a bit of balancing to make it aerodynamically stable with the massive load of engines at the back, but with a bit of careful juggling, extremely swept wings and carrying plenty of surplus RCS fuel in the nose I got it there in the end. Not given it payload yet, but the CoM is inside the payload bay so that should be fine. Sussed out the off-centre mass/thrust problem, got the thing into orbit, flexed the robotic arm, was feeling pretty happy with my efforts.

Then the time came to deorbit and everything fell to peices (literally ). First attempt, I did what I do with capsules - drop periapsis to about 60km and follow the path down. Trouble. Deceleration was not exceeding 1g. Things started blowing up, control surfaces first and shortly afterwards the rest of the craft (heated to about 1500/1600 degrees at the time. Ok, that didn't work. Try something else.

So I dropped to the same periapsis as normal, but this time resolved to hold the nose up at about 40 degrees as I went down. Sure enough, I got down to about 70km, lift and drag began to kick in and speed began to very very gradually bleed off. Trouble was, I started going up again! I travelled an entire half-orbit at between 70-100km altitude, but only dropped from Mach 27 to Mach 26. I then got a bit more positive about going down, and then as soon as I got below 60km the stability of my craft in this thicker air meant I could only get the nose up by about 5/10 degrees, deceleration still didn't hit 1g. Same end result as before.

Obvious answer seems to be that my craft is too stable and I need to bring the CoM and CoL closer together. Trouble is, I then wouldn't be able to hold the nose high at all without it flipping out altogether (as happened with a couple of prototypes).

How do you folk get your spaceplanes out of orbit???

[Hodo]

The trick is to do something that bleeds energy. Bringing a shuttle down is like bringing a fighter with the flight characteristics of a brick down. You have to do maneuvers like the real shuttle, large "S" turns to bleed off speed (energy) before you get down to a lower altitude. I used to try and hit 60-75km to do this. And make sure your CoL is closer to your CoM when empty, or have a fuel pump system that lets you shift your fuel to move the CoM.

[Vigelius]

The trick is to do something that bleeds energy. Bringing a shuttle down is like bringing a fighter with the flight characteristics of a brick down. You have to do maneuvers like the real shuttle, large "S" turns to bleed off speed (energy) before you get down to a lower altitude. I used to try and hit 60-75km to do this. And make sure your CoL is closer to your CoM when empty, or have a fuel pump system that lets you shift your fuel to move the CoM.

So just flare as much as possible 'sideways' essentially, keeping altitude around 60-70km until enough speed is gone to make a deeper dive safe. That makes sense!

So what does a safe speed look like? Also, how far ahead of the planned landing site do you generally place your periapsis?

[Hodo]

So just flare as much as possible 'sideways' essentially, keeping altitude around 60-70km until enough speed is gone to make a deeper dive safe. That makes sense!

So what does a safe speed look like? Also, how far ahead of the planned landing site do you generally place your periapsis?

That I can not tell you, I use powered space planes that have jet engines for in atmosphere flight. But I have had a few out of fuel landings where I have had to glide a lot further then I wanted. I usually set my PE target somewhere around 15-25km over the landing site and usually my slowdown through the atmosphere brings my landing down to with in a few kilometers of the runway. When it comes to gliding it is best to have targeted to far then not enough.

[Nicholander]

How do i accidently post something on the wrong thread!?!??!?!

Mods, please delete.

Edited June 26, 2014 by Nicholander
I aciddently posted this on the wrong thread. *Facepalm*

[Vigelius]

Wow, this is frustrating! I've just spent a good few hours running and re-running different approaches, and I reckon I'm going to need a complete redesign. I can get down to about 5.5km/s, then get sucked into an inevitable fiery death. Bleeding off all the fuel lets me hold the nose where I want it for maybe a minute or two more, but eventually the flaps blow up and its all over. One runthrough I was being more aggressive with manouevres and managed to get locked into a stable but completely uncontrolled belly-first descent which pulled enough g to get me down sub-mach, but then the whole thing was completely uncontrollable and came down short over the ocean anyway! Nightmare!

Anyway, this is the craft in various states:

Javascript is disabled. View full album

New wings perhaps? with more lift, and less stability.