Flight Question I cant re-enter the atmosphere.

[Phillips]

On the deltaglider, I undock from some space station, then I turn around into earths direction, so the deltaglider is looking towards it, then I cntrl+num+ I click t to speed up, but im stuck in earths orbit!

 

[Grover]

you need to read up on orbital mechanics a little.

burning facing towards the earth will EVENTUALLY get you to go sub-orbital, but it is far more efficient to burn RETROGRADE, lowering your PeA below 70KM such that you hit the upper atmosphere before reaching your PeA.

and once you get there, its best that you read up on how to perform a re-entry without getting burned to a crisp, it will take some practice.

good luck!
-=Grover=-

 

[marooder86]

... I turn around into earths direction, so the deltaglider is looking towards it, then I cntrl+num+ I click t to speed up, ...

Haha:lol:. This is almost the same thing I did when I lunched Orbiter after downloading it for the first time:thumbup:. I had no idea then that this is a capital "S" simulator. I thought it was more like "space shooter":facepalm: and had this evil idea to burn DG during re-entry, cause what I knew about returning from space was: when you do it wrong, you should end up like chickens in KFC:lol:. I was quite surprised when I bounced off of the atmosphere. This was the moment I've decided to start reading manuals and I advise you to do the same:thumbup:.

 

[Urwumpe]

For reentering, you want to reduce your orbit energy a bit, so you get to a lower place, as you are now... that always means retrograde burns.

Pointing at Earth is extremely ineffective, not only you actually increase your orbit energy and reenter faster as good, also you waste a lot fuel for getting even faster without need, by pointing at Earth (this means you gain energy from the gravity field of Earth during the burn, which again, means more energy).

Of course, there is a thing that has to be mentioned: sometimes you want exactly that bad reentry by burning approx towards Earth. I often do high speed reentries for tests.

 

[Grover]

i can explain the basics of it, it took me a week or two to get the hang of it.

to re-enter- your goal it to get your speed down to aircraft levels, so you have to lose ~7 Km/s of speed. the problem is that if you have this sort of speed in the lower atmosphere you will generate too much heat through friction, and melt. your airframe.

so you need to descend as you slow down, keeping your speed close to what it should be at your altitude. go too fast and you melt, go too slow and you fall too fast and will then MELT.

@ marooder, you bounced off because you went nose first into the atmosphere, making your wings generate a HUGE amount of lift. the massive G forces would have killed your crew, so they wouldnt have felt the heat later on.

to fix this, you need to approach the amosphere pointing up by about 40* (this changes as you descend, its a balancing game).

so you need to balance your "nose down" and "nose up" configuration to descend at a constant, slow rate, proportional to your horizontal deceleration. i find that an easy way to do this is to hold a certain vertical speed. if you are descending from ISS-altitude LEO, you should hold between 70M/s and 90M/s VERTICAL speed. too slow and you will bounce out if you arent careful, and too fast and youve had it.

to alter your speed, you have to alter the lift that your wings generate. you achieve this by pitching up or down, changing your Angle of Attack (AoA). higher AOA (nose up) gives less lift and more drag, lower AOA (nose down) gives more lift and less drag. 40* is a good place to start, if you are using the DGIV you can use the Autopilot to hold your angle of attack (40* is a good place to start).

for a good idea what to do, check my re-entry tutorial, its all there

good luck guys!
-=Grover=-

 

[Urwumpe]

The rule is: The higher your orbit is, the higher has to be your periapsis for reentry. at hyperbolic orbits, you even just try to skim on the outer edge of the atmosphere.

 

[Grover]

all thit talk of re-entry is making me want to do an aero capture on mars... time to get orbiter out again!

 

[marooder86]

... @ marooder, you bounced off because you went nose first into the atmosphere, making your wings generate a HUGE amount of lift.

I know that now, I just didin't know that back then at my first Orbiter's space flight.

... the massive G forces would have killed your crew, so they wouldnt have felt the heat later on.

In the way I was trying to do this, probably yes, but not if I would try to make re-entry quite properly, but with some AoA and speed differences which would cause heat-shield to overheat and therefore produce nice fireball falling down the sky. I failed to do that because of lack of knowlege, and frankly speeking I've never attempted to do such nasty thing again.

 

[Carmen A]

I've been flying the XR2 almost exclusively and while it's not terribly realistic in today's spaceplane technology I love doing "powered" re-entries to actively control descent rate and re-entry speed.

I found that doing a Shuttle style re-entry does not work very well due to the flight parameters for the XR2 (or the way I fly it in orbit). I re-enter at 85 degrees AoA using the hover thrusters to shave off as much speed as I can (as fuel permits) while a bit of main engines are used to maintain a constant descent rate.

At a certain velocity and attitude the ship tends to buffet a bit in a sort of small scale S turn bleeding off speed tremendously without heating the hull much.

This method allows me to keep hull temperatures manageable and transition to scramjet flight ASAP to the landing destination. So to me it's one huge Cobra maneuver and since I'm still not fully skilled at orbital maneuvers, "powered" or "semi powered" re entry profiles at reduced speed means I can get familiar to this toasty region of the flight envelope without blowing up

Of course, sometimes I can't resist and setup a "Firefly style" ballistic re-entry on the Shuttle A that my multiplayer ground observers report pull more than 50Gs

The fun thing is that my powered entry profiles get a lot of raised eyebrows:

"Are you sure you'll survive that 33G re-entry in your XR2?"
"Ever watched Firefly?"

 

[Wishbone]

Re: 33G re-entries - the first thing to _structurally_ break in one's body is one's nose, at 30G. Lower jaw - 40G, cheekbones - up to 50G, teeth - 100G, forehead up to 200G... By that time pretty much inside has already been destroyed...

 

[Carmen A]

I just love keeping the "projected" 33G re-entry until the last moment then I activate the powered re-entry procedure and it becomes a smooth not-toasty descent

 

[Urwumpe]

Strange... I never have seen any spaceplane in orbiter, not even the Shuttle, that is so precise in unpowered reentry as the XR2. program the deorbit in IMFD, regulate deceleration to constant 16 m/s² and arrive right in front of your target base at low super sonic speed, when you drop your nose. Never needed any propulsion there, except for kidding around..."I have never landed on such a short runway...but wide is it."