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Author Topic: [closed]Reentry tutorial for DGIV  (Read 15965 times)

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Offline DanSteph

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02 January 2007, 08:00:52
As this question come often, even if the DGIV is not finished I'll post here some tips:

-First deorbit with a a reentry around 1.2°-1.6° (D2 for reentry angle on computer)
-Then you can accelerate time w/o autopilot until 130-110 km altitude or a bit less.
-engage pro104spec40 and watch closely the vertical speed on mini hud or surface MFD.

Vertical speed will increase slowly from -190 m/s to -180 m/s until you arrive around 70km high.
Now decrease you AOA to 35° or 30° until Vertical speed increase to -30 -40 M/S
The goal now is to maintain more or less -30 -50 m/s vertical speed using INVERSE logic.


It work like this:
with more AOA the vessel stall and the vertical speed DECREASE (You fall more),
with less AOA you start to get some lift and the vertical speed INCREASE (You fall less).

The "neutral point" move as you descend at first it's around 40° (45° you fall, 35° you get lift)
then at lower altitude this point decrease (at 30° you fall, at 25° you get lift)

The goal is to stay the most time possible around 60km high to spend your speed.
The key is to manage vertical speed with AOA and watch your temp... higher temp lower vertical
speed... and don't let your vertical speed get out of control. Gently with AOA.

Some time the autopilot is a bit weak (I'll rework it) especially at lower AOA & Altitude , you can help it
a bit with joystick.

If you're good at this you can try to maintain a nose temp of around 1200C° all the time varying
your vertical speed beetween -30 m/s  -140 m/s with the AOA, this optimise the braking, it take less time.

I plan to write a new reentry autopilot for DGIV fully automated, it will not be a
"bring me to base" autopilot but will allow you to make full controlled reentry
100% of the time.

Hope this help ?

Dan



Message modifié ( 02-01-2007 08:10 )


Offline DanSteph

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Reply #1 - 02 January 2007, 08:04:15
:up:



Message modifié ( 02-01-2007 08:07 )


Offline skookum

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Reply #2 - 02 January 2007, 08:30:38
Dansteph,

Please see the DGIV Beta forum for an autopilot request.

Thanks


I'm a space cadet too!

Offline picto

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Reply #3 - 02 January 2007, 16:11:59
Pour quelqu'un qui ne voulait pas faire de " maintenance " sur plusieurs
threads à la fois, tu as fait très fort sur ce coup là :)


Pic

Offline Genesis

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Reply #4 - 02 January 2007, 18:07:39
After all my failed attempts at doing a proper reentry with the DG4, I think I'll just leave my crew up at the ISS for
awhile.  I feel guilty about killing them again and again, and again.

My one and only successful reentry was when I used the command: PRO104SPEC20 instead of 40.  It got me through the atmosphere
after a year of playing with the hover thrusters and watching the Vs like a hawk.  I still ended up over shooting my base by
a whole continent.

Don't get me wrong. The DG4 is a beautiful craft. This whole reentry thing is just a glitch or something.


Offline kwan3217

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Reply #5 - 02 January 2007, 19:49:59
What is the aerodynamic model of the DeltaGlider based on? How much is it supposed to be like the Space Shuttle? I've been
doing research on the Space Shuttle aero model, and at Mach >10, 40deg AoA, lift and drag are pretty close to equal. I tried
my space shuttle entry profile with the DeltaGlider IV and failed miserably of course. It seems that the drag in the
DeltaGlider is about 4-5 times higher than the lift at 40deg AoA.

Now up at high hypersonic, high in the atmosphere, the shape of the aircraft is almost irrelevant. Everything reasonably
plane-like acts like a flat plane. A barn door flies like a space shuttle flies like a DeltaGlider. This is because you are
up in the free molecular range where the airflow is more like a stream of ping pong balls than a flow of water. Maximum lift
is always achieved at near 45deg, since this deflects the ping pong balls out of stream the most.

If it doesn't screw up too much other stuff, consider changing the aero model of the glider for high mach numbers. The IK
shuttle (Source is on Orbiterhangar) uses a bunch of tables copied straight out of the space shuttle aero data book, but
since your model isn't exactly a space shuttle, maybe something simpler like the aero model for the Shuttle fleet (source
code for it is in the AutoFCS package) is in order. A warning with the AutoFCS model: it has a glitch at mach 5.0, that you
may want to smooth out.

I realize that this may be a large change, with the potential to break lots of other stuff, and I will understand if you
laugh in my face. Just consider it a humble suggestion from an otherwise-satisfied DeltaGlider pilot.


Offline DanSteph

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Reply #6 - 02 January 2007, 20:05:38
Quote
Genesis a écrit:
After all my failed attempts at doing a proper reentry with the DG4, I think I'll just leave my crew up at the ISS for
awhile.  I feel guilty about killing them again and again, and again.
[..]Don't get me wrong. The DG4 is a beautiful craft. This whole reentry thing is just a glitch or something.

Did you tried the procedure above ? what goes wrong ? did you let the vertical speed goes out of control ?
Something you didn't understand perhaps in my post ?

Quote
kwan3217 a écrit:
I realize that this may be a large change, with the potential to break lots of other stuff, and I will understand if you
laugh in my face. Just consider it a humble suggestion from an otherwise-satisfied DeltaGlider pilot.

Before doing the aerodynamic I had a look at a lot of ressources. I come to the conclusion that everything matter
at high speed and that even calculated shape with all actuall knowledge and modern computer have some surprise
when doing real test. It's a very complex things as the profile extent from supersonic high speed with low pressure to
high pressure low speed. Orbiter can't be accurate in this manner because you'll need the most powerful computer in
world to calculate a whole reentry and I doubt it can do it in real time.

Actual DGIV reentry is enough accurate (or reasonnably wrong if you preffer) to *look like* a real reentry
and give somes fun as any change can broke dozen other parameters and as I'm short in time I doubt
I'll rewrite it to simply get another "reasonnably wrong" reentry with simply other problems...

In brief you cannot do a real reentry profile with Orbiter yet, only cheat. I preffer to avoid hundred hour of
work to simply get another wrong profile.

Hope this answer ?

Dan


Offline zarb-dusk

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Reply #7 - 02 January 2007, 22:42:04
in your tutorial you will add the tutorial by  Michelle Megan in yours???


Offline kwan3217

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Reply #8 - 02 January 2007, 22:44:47
Quote
DanSteph wrote:
Actual DGIV reentry is enough accurate (or reasonnably wrong if you preffer) to *look like* a real reentry
and give somes fun as any change can broke dozen other parameters and as I'm short in time I doubt
I'll rewrite it to simply get another "reasonnably wrong" reentry with simply other problems...


Yeah, that makes sense. As long as there is some entry procedure that works, it doesn't matter if it doesn't match the
shuttle, since DeltaGlider is not the shuttle.



Post Edited ( 01-02-07 22:45 )


Offline KB9LAD

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Reply #9 - 03 January 2007, 04:10:03
Hey all,

I'm not sure what all the fuss is about on reentry. If anything, I'd say its even easier in the DGIV than it was in the
DGIII! I've been able to consistently land her at whatever base I want to without too much trouble. I use a similar
procedure to what Dan is describing except that I use a lower attack angle, about 25 to 35 degrees to start with,
and instead of changing the pitch to vary the vertical speed, I use banking maneuvers like what is done in real life
with the Space Shuttle. (To bank with the reentry autopilot use numpad keys 4 & 6) That is; if I want to
bleed off more speed and increase the vertical speed, I bank left or right until the numbers get to where I need them.
If I want to decrease vertical speed, I just put it back to 0 degrees of bank. Of course; you have to make sure to
alternate left & right banks to stay on course! To help with this, I use Aerobrake MFD
(http://www.orbithangar.com/searchid.php?ID=2139 ) on one screen & Reentry MFD
(http://www.orbitermars.co.uk/reentry.zip) on the other. I also keep a close eye on the reentry data display (D 3
) to see how hot the various areas of the ship are heating up. If it looks like its getting too hot, then put it back to
the middle and climb to some "cooler air". The vertical speed I aim for is between -60mps to -30mps, but it can get
down to -100 and as high as +30 or so if need be. Just don't stay at those numbers for very long! Don't be afraid to
bank all the way to 90 degrees if you have to either! Its a good way to burn off excess fat... er, speed.;) Also; do
most of your braking between 50km to 60km altitudes. Lower than that, you'll likely burn. Higher, you'll overshoot the
target or bounce back into space. Once you get down to less than around 1800 mps airspeed you can shut off the
reentry autopilot and fly her in using the joystick. You should be at around 40km to 45km altitude by this time. You
can use the airbrakes at this point (B key-- thanks for making that toggle on/off Dan! :top: ) to bleed off even
more speed if need be.

One more thing that can't be stressed enough... After the reentry burn & before you hit the atmosphere, make
sure to jettison fuel to 1/2 tank or less to get the weight low enough!
If you don't it won't matter how you fly it.

Using this technique, it is possible to keep the hull surfaces from getting any higher than 900 Celcius. Well within the
DGIV tolerances. I've even managed to keep it to less than 850 on a few runs.

Hope this helps!
Ken (KB9LAD) 8)



Offline DanSteph

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Reply #10 - 03 January 2007, 04:15:31
Glad to see that someone at least can manage DGIV reentry :)
Nice procedure KB9LAD (what a name? :trucdeouf: )

Thanks for posting :beer:

Dan


Offline KB9LAD

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Reply #11 - 03 January 2007, 04:21:50
Quote
DanSteph wrote:
Glad to see that someone at least can manage DGIV reentry :)
Nice procedure KB9LAD (what a name? :trucdeouf: )

That's my HAM radio callsign...

And You're welcome!

Ken



Offline DanSteph

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Reply #12 - 03 January 2007, 04:25:11
Quote
KB9LAD a écrit:
That's my HAM radio callsign...


Ooops :trucdeouf: deeply sorry... I should have tilted I made some CB and had a look at RA...well,
was last century... I'm only an OM in his SHACK :badsmile:

Dan



Message modifié ( 03-01-2007 04:50 )


Offline sunshine135

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Reply #13 - 03 January 2007, 04:59:35
Quote
I'm not sure what all the fuss is about on reentry. If anything, I'd say its even easier in the DGIV than it was in the
DGIII! I've been able to consistently land her at whatever base I want to without too much trouble. I use a similar
procedure to what Dan is describing except that I use a lower attack angle, about 25 to 35 degrees to start with,
and instead of changing the pitch to vary the vertical speed, I use banking maneuvers like what is done in real life
with the Space Shuttle.

Amen,

Dan and KB9LAD are correct. I use Dan's method in conjunction with Aerobrake MFD. I get a perfect reentry and landing at the
Cape just about anytime I please. As long as you deorbit around about Australia. That is the cool thing about Orbiter- you
can experiment with the type and method of reentry. One Aerobrake tutorial has you "skip" the DGIII (DGIV) in the atmosphere
for 2 orbits and has very little "burning" taking place. The rentry autopilot really lets you focus on "nailing the numbers"
and controlling the ship down to the final destination. If everything was "automated" where would the fun be in that?

Thanks again Dan for a great Add-on!

Sun Dog


"Sun Dog"

Offline reekchaa

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Reply #14 - 03 January 2007, 05:23:17
Damn... I should have used KB6PAL instead of this ever-sexy "reekchaa" handle.   :)

Yeah, I gotta agree that reentry for DGIV is tops.  Much more control, and just understanding the process of gaseous
heat-friction is the key.  Great fun, and always rewarding to watch the meteor shower when you're less than diligent.
:hot: On top of trying not to burn up... try surfing down hard to max-heat, then soaring back up to the top reaches of
atmospheric air (to the point where you almost break away back into space) and back again with increasingly higher
vertical velocities.  Makes for a fun surf... with sometimes rewarding 4th of july effects.


~ the Reekchaa

Offline n122vu

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Reply #15 - 03 January 2007, 06:30:47
FYI - Was able to bring her successfully back to SLF at the Cape using Dan's procedure above.  Worked like a charm,
although I began my reentry MUCH too soon and came up about 3,000M short.  I had to perform a powered flight
approach to the Cape, but I made it nonetheless.  

Thanks Dan!!  :applause:

n122vu



Offline sunshine135

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Reply #16 - 03 January 2007, 20:35:28
Quote
KB9LAD wrote:
One more thing that can't be stressed enough... After the reentry burn & before you hit the atmosphere, make
sure to jettison fuel to 1/2 tank or less to get the weight low enough

That is one more thing I wanted to point out. Weight will kill you in an environment that depends on friction to reduce
speed. A few more tips:

-Reduce your fuel load to about 20%- that will allow you to make any finite corrections on your final approach.
Remember, we do not have a team of rocket scientists mapping out our reentry progress with times and specific AoA
pitches to execute and line us up with the runway. Besides, I'm sure the real shuttle astronauts would love to have a little
extra "juice" to flatten out that approach angle (20 degrees nose down). It is neither unrealistic or absurd to think that
they wouldn't use some thrust were it available. Jovian Mining Corp. doesn't have enough $$$ to pay for your expert Orbitnaut
training anyhow. They need you to mine baby!!! You're behind on your quota.


- The sole purpose of the deorbit burn is to set the reentry angle
Dan stated above that between 1.2 and 1.6 degrees is good. I've had it very low .5 for farther distances (west of
Australia if you are aiming for the Cape). I certainly would not recommend any higher than 1.6 degrees. That goes with my
next point. If you thought the reentry burn was to slow the spacecraft down, you are mistaken, and you are likely becoming
fireworks a lot too. You are really going to pick up some speed before you interface with the atmosphere. Keep the powder
dry...you're coming in hot!!


-Reentry happens in a zone and better sooner than later.
Shuttle users know what I am talking about here. They use the GPCMFD and it has a reentry program that has a visual
representation of this zone. I have not used GPCMFD enough to speak eloquently enough about it though. I'm a
seat-of-the-pants, aerobrake kind of guy. Both of these programs though are excellent at helping you get to your final
destination. To hit the Cape, the envelope is about the longitudes of the country of Australia (that is in real life too, by
the way. The Shuttle OMS burn happens at the west coast of Australia usually.). If you do it sooner, you will have to
"bounce" the DGIV back into space a little by decreasing AoA past the balancing threshold (where the mini hud goes back into
positive territory in the verticle speed category). If you do it too late though, you will have to increase AoA, to try to
fall like a rock. You will likely end up as fireworks across the Eastern US with Atlantic fishermen taking pieces of you home
for souveniers.


-Engage your PRO104SPEC40 at about 100km altitude.
Before that time and you are wasting rcs fuel. If you must engage your reentry autopilot before then, keep a little
extra fuel in the main tank and crossfeed. Waste not, want not.


-The Map MFD is no way to make a reentry
It is not fine tuned enough to help you target anything. Burning until the orbit termination is over the Cape will
usually lead you to either become fireworks or cause you to land at Edwards instead. The point is that the MAP MFD is tuned
only to your current status, and it makes no prediction as to where you will end up when you hit the thicker atmosphere.
Hey, was that the Cape that just went by?


-Most importantly, it takes practice.
Rome wasn't built in a day (Just ask any of our Italian Orbitnauts). I'm sure that the astronauts who fly the shuttle
simulate like mad. You may want to first try flying the DGIV through the atmosphere without burning up. Then retry the
reentry with GPCMFD or Aerobrake MFD and see if you can hit your target. Then try and try and try and try again. After
awhile, it becomes an art and it is very addictive and satisfying.


Everyone has techniques and I hope these help.  I wrote these tips for new Orbitnauts and old ones alike. Many have flown
Orbiter for years and have never tried reentry and landing. Others have been around forever and know well how to reenter and
land. Still others are new and may be deterred from even trying by how "hard" it sounds. Nothing worth doing is ever too
easy. Now get out there and start your reentries. Experiment. Have fun!!!!  :badfinger:


"Sun Dog"

Offline Twilight

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Reply #17 - 03 January 2007, 23:24:23
If you want to do a de-orbit like mentioned by Dan, MAKE SURE YOU DROP FUEL UNTIL ABOUT 16 TON WEIGHT!




If you want to get on the ground, you could always do what I did on my first re-entry ^_^

Don't drop any fuel

About two squares away from where you want to land (Map MFD) turn retrograde, level horizon. Burn retrograde until
you make a VERY steep decent.

Use Hover engines to control your temp, and verticle speed, I was able to keep all of my tempatures under 1000

When at about 25k-50k altitude, cruise to your landing spot, you should have plenty of fuel to make it (if you didnt
jettison like I said)

Land!

It's kinda cheating though :P


Offline Travis Reed

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Reply #18 - 04 January 2007, 02:25:59
Quote
Twilight wrote:
If you want to do a de-orbit like mentioned by Dan, MAKE SURE YOU DROP FUEL UNTIL ABOUT 16 TON WEIGHT!




If you want to get on the ground, you could always do what I did on my first re-entry ^_^

Don't drop any fuel

About two squares away from where you want to land (Map MFD) turn retrograde, level horizon. Burn retrograde until
you make a VERY steep decent.

Use Hover engines to control your temp, and verticle speed, I was able to keep all of my tempatures under 1000

When at about 25k-50k altitude, cruise to your landing spot, you should have plenty of fuel to make it (if you didnt
jettison like I said)

Land!

It's kinda cheating though :P

This is a variant of a powered landing. I posted a similar variant in the beta thread (was it 2 or 3...). It's not as elegant
as gliding in the the shuttle and it's not terribly realistic unless you have (literally) tons of fuel to spare or very
powerful and efficient engines. It's cute to try once or twice, but gets old fast.


Offline DanSteph

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Reply #19 - 07 January 2007, 05:09:56
:bump:


Offline jer11

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Reply #20 - 07 January 2007, 19:27:33
too hard for me to make a good reentery, I jettison the fuel and i did a reentery  autopilot but it still fails. And it makes
the crew die :(:help:

Before reentery:



After


Jeramie Long.:Hello San Francisco.
San Francisco,CA: Hi whos this
Jeramie Long.: Its the pilot of DGIII
San Francisco: What is the problem pilot?
Jeramie Long: I going to make a reentery and i will die if it burns.
San Francisco: Are you going to land at the airport?
Jeramie Long.: Altitude 95km...90...Uh oh! im prepared.
San Francisco: I loated you, you are south of Florida. His Altitude is 87 km
Jeramie Long: Computer Reads Cockpit 500c.
Jeramie Long: Alt 80..75....70....65...[static]
San Francisco: he burned :hot: PILOT?? PILOT?? YOU THERE???
Jeramie Long.: uhhhh....buh...(cut off in mid word)




Post Edited ( 01-08-07 05:05 )



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Offline Cale

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Reply #21 - 08 January 2007, 17:02:37
Using Beta 4 and AFCS Version 2P1, I was able to make a safe re-entry and landing at KSC.  You need adjusted
trajectory numbers (See below) for the AFCS.ini file (rename the default one, don't overwrite!) and set your re-entry
distance for between 5.50 - 6.00M from landing site.

22 ; number of trajectory lines
100 7600 4500
93 7599 4000
87 7580 3500
80 7575 3000
75 7450 2500
70 7225 2000
65 7050 1750
61 6400 1500
59 6100 1250
57 5600 1000
55 4750 750
51 4200 500
47 3750 450
45 2800 380
40 2200 300
35 1500 200
32 1100 150
30 1000 110
25 750 75
20 600 50
15 500 20
10 300 0


A couple of caveats:

1.  Make sure that your weight is less than 16000 kg (less than 15000 is ideal).  Dump fuel in main tank until there's
approximately 10% left.  This should be more than enough fuel if you need to burn the main engines if you're short of
energy on the approach and landing

2.  You may need to disconnect the AFCS autopilot when you're about 50km from the landing site (make sure
you tune the landing site VOR).  I'm not 100% sure if this was due to specifics of the scenario I used, as Fort has said
that he was able to let AFCS fly the entire re-entry, approach and landing hands-off.   Anyhow, be prepared to fly the
HAC and landing manually.  To do this, bring up AFCS (CTRL-F4), and de-select PITCH, ROLL, YAW (leave only the
Flight Director enabled), and make sure that AF Control is set to ON (your altitude and speed at this point should
make this straightforward) on the main panel.

3.  Make sure you have HSI on the left MFD and GPCMFD (OPS 4 screen, tuned to appropriate landing site) on the right MFD.  If it looks like the flight director is steering you incorrectly (and it's happened a few times to me), with these 2 MFD's up, you should be able to manually fly the final approach and landing without too much of a problem.  AFCS should still lower your gear (provided you've turned on the gear hydraulics on the upper panel) at 200m altitude.  Try to keep your speed on landing above 150m/s or you'll fall too fast and possibly damage the gear.

Have fun!

Cale



Post Edited ( 01-08-07 17:35 )


Offline DanSteph

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Reply #22 - 08 January 2007, 17:21:45
Quote
jer11 a écrit:
too hard for me to make a good reentery, I jettison the fuel and i did a reentery  autopilot but it still fails. And it
makes the crew die :(:help:

You use the DGIII, it's outdated and this thread is dedicated to DGIV reentry.

Dan


Offline jer11

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Reply #23 - 09 January 2007, 01:30:16
Quote
DanSteph wrote:
Quote
jer11 a écrit:
too hard for me to make a good reentery, I jettison the fuel and i did a reentery  autopilot but it still fails. And it
makes the crew die :(:help:


You use the DGIII, it's outdated and this thread is dedicated to DGIV reentry.

Dan

Can i copy/paste the voice recording below the dead pictre?
(never mind)



Post Edited ( 01-10-07 01:39 )

« Last Edit: 09 January 2007, 01:30:16 by jer11 »


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