Flight Question Re-entry

thumper235

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I spoke to soon in my last thread. Someone please take a wooden ruler and smack the back of my neck as hard as you can.

Ok, I used a tutorial in my last thread and I believe it was Grover who kindly created it. I used it 3 + times on a DG-IV to develop a basic set of steps in my head for re-entry that I could apply to just about any craft, orbiter or a big-boy burger sign that needed to re-enter.

Last night I took a Xr-2 Ravenstar down. I started the scenario where docked at the ISS. I basically used the steps in the tutorial presented and left the autopilot functions of it all to free hand since I have not taken the time to figure that out which I should do I know.. anyways, I applied the same principle from the DG-IV to the Ravenstar. Everything went "Swimmingly" until I hit roughly 50k in altitude where I end up floating back into space. The XR-2 and XR-5 behave in a similar fashion with this lets go back to space "attitude". By the time I *think* I have it saved its too late and im cruising by KSC at a mach over9000. with a very bright lightshow. Perhaps by the time I cross the atlantic I could attempt a long flight back, but thats just fail fail fail. So I did what any self respecting pilot would do. I open my hatch for some fresh air.

Does the problem lay with My angle of attack? Is 40 degrees to high? If you need more specifics, let me know and I will cough them up. Thanks guys. :)

EDIT :
http://orbiter-forum.com/showthread.php?t=18671
This is the tutorial I have used. I am going to try and ravenstar again and this time use the Pause button and double or even triple check everything. I know my issue lies within my entry angle because everytime I attempt it I have flown almost directly over my target. I have all the MFD's and areobrake is one of them. I must be doing something wrong... I must... This really cannot be THIS tough.
 
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fghjhfdfghj

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Something that would calculate the point where you end up after re entry could come in handy.
 

Urwumpe

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Your problem is that you don't understand the physics of reentry properly. Your AOA is perfectly right - and the behavior as it should be. Let me explain this part first and then tell you what you do wrong:

1. The lift of your spacecraft at 40° AOA points upward, which gives you the acceleration that reduces your descent velocity. That is all like you sure expected. But once you have reached level flight (vertical velocity = 0) this acceleration does not just go away. You need to reduce your vertical lift.

2. Now you could just reduce AOA. But you are still very fast and reducing your AOA into the needed slightly negative range (since effective gravity is still weak because of the centrifugal force) will make you burn up because the wind shield is not strong enough. You have only a small range for variations in AOA.

3. The better way is to bank to the side. Banking points your lift vector to the side and reduces the vertical component of your lift vector. You still have the same lift force, but now, instead of ascending again, you fly to the side, and make a turn.

4. if you invert your bank angle (from left to right for example), you turn in the other direction: You fly S-turns.

This is the most conservative way of reentry, so be sure: It works. It had been used by all spacecraft from Gemini on, including the Space Shuttle. The Space shuttle just uses more variables for calculating how much it should bank or reduce its AOA.

---------- Post added at 08:58 PM ---------- Previous post was at 08:58 PM ----------

Something that would calculate the point where you end up after re entry could come in handy.

Piloting is making sure your spacecraft ends up, where you want it. Not the other way around.
 

fghjhfdfghj

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Your problem is that you don't understand the physics of reentry properly. Your AOA is perfectly right - and the behavior as it should be. Let me explain this part first and then tell you what you do wrong:

1. The lift of your spacecraft at 40° AOA points upward, which gives you the acceleration that reduces your descent velocity. That is all like you sure expected. But once you have reached level flight (vertical velocity = 0) this acceleration does not just go away. You need to reduce your vertical lift.

2. Now you could just reduce AOA. But you are still very fast and reducing your AOA into the needed slightly negative range (since effective gravity is still weak because of the centrifugal force) will make you burn up because the wind shield is not strong enough. You have only a small range for variations in AOA.

3. The better way is to bank to the side. Banking points your lift vector to the side and reduces the vertical component of your lift vector. You still have the same lift force, but now, instead of ascending again, you fly to the side, and make a turn.

4. if you invert your bank angle (from left to right for example), you turn in the other direction: You fly S-turns.

This is the most conservative way of reentry, so be sure: It works. It had been used by all spacecraft from Gemini on, including the Space Shuttle. The Space shuttle just uses more variables for calculating how much it should bank or reduce its AOA.

---------- Post added at 08:58 PM ---------- Previous post was at 08:58 PM ----------



Piloting is making sure your spacecraft ends up, where you want it. Not the other way around.

I don't have all day to fly. I landed in South America because of good luck. I was crashed because I had to fly for half a hour over the Indian Ocean. That is a no, with a single stage to orbit.
 

Urwumpe

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I don't have all day to fly. I landed in South America because of good luck. I was crashed because I had to fly for half a hour over the Indian Ocean. That is a no, with a single stage to orbit.

The Shuttle needs 1 hour from deorbit burn to landing. Do you think your time schedule is stronger than the laws of physics?

if you miss your landing site because your entry interface was too close to the landing site, do your deorbit sooner.
 

fghjhfdfghj

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How soon is soon? If I want to land in Russia, is soon in Argentina, Brazil, the Atlantic Ocean or even Spain?

It is so hard to see when I should do re entry.
 

Urwumpe

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How soon is soon? If I want to land in Russia, is soon in Argentina, Brazil, the Atlantic Ocean or even Spain?

It is so hard to see when I should do re entry.

Depends on the spacecraft that you use and the target deceleration (how fast you lose speed without burning up) of it.

For all Deltaglider-Type vehicles, I fly well with 45° great circle distance between landing site and entry interface in 120 km altitude. Important is passing entry interface at the right angle, the angle, altitude and the distance from landing site to EI is only valid for one kind of spacecraft.

Practically, this means about 18000 kilometers from low Earth orbit to landing site, of course, this distance gets longer the higher your orbit before deorbit is.

Target deceleration for Deltaglider type vehicles is about 16 m/s². You can increase this a bit for a short time, but I don't recommend it, because it also takes a moment to reduce the heating again.
 

Urwumpe

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AerobrakeMFD! Don't reenter without it...

I still prefer Reentry MFD, but it does not work in 2010... I should maybe do something similar for 2010...
 

Aeadar

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How soon is soon? If I want to land in Russia, is soon in Argentina, Brazil, the Atlantic Ocean or even Spain?

It is so hard to see when I should do re entry.


In my experience, with AerobrakeMFD, and given a circular orbit of approx. 200-250km, it's not so much a question of when to burn, but how long to burn. I usually do my deorbit burn somewhat less than halfway around the planet, say between a third of the way and halfway around. Burn to lower your PeA to 45-60km, check AerobrakeMFD to make sure your G-forces will not be going into the red, adjust pitch and bank to keep the end of the flightpath on or near your destination, while monitoring your altitude and temps.

And give yourself time to practice. I've been doing this for about 6 years now, and I couldn't re-enter with a DGIV or XR vessel without AerobrakeMFD.

Good Luck!
 

Tommy

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1. The lift of your spacecraft at 40° AOA points upward, which gives you the acceleration that reduces your descent velocity. That is all like you sure expected. But once you have reached level flight (vertical velocity = 0) this acceleration does not just go away. You need to reduce your vertical lift.

2. Now you could just reduce AOA. But you are still very fast and reducing your AOA into the needed slightly negative range (since effective gravity is still weak because of the centrifugal force) will make you burn up because the wind shield is not strong enough. You have only a small range for variations in AOA.
I have to correct you on point 2. At high AoA, you need to INCREASE the AoA to reduce vertical lift. Reducing the lift will increase the lift. On a glider type vessel, consider 20 degrees or higher to be "High AoA" - max lift is at around 17 -18 degrees.
 

Cras

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Orbiter does simulate that well enough. I recall doing it in the DGIV, where things were getting a little out of hand during the re-entry, I was too fast and too high as I came over the west coast of Florida, that I pulled the nose almost straight up to get the speed to drop and increase the v/s.
 

Urwumpe

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Hmmm. I have been using reentry MFD for all my re-entries, even with 2010. Seems to work fine for me. ??:shrug:

It failed for me... OK, then it is just a local problem. Good to know :)
 

thumper235

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I am going to quote a step from the from the tutorial. I THINK this is what is giving me such a rough time as well... I kinda just... err... ignored it.

"13) once your orbit on the orbit MFD hits the atmosphere, the entry angle on the central display will rapidly count upwards, stop as close as you can to 0.7, then use lin thrusters (RCS- press numpad /, then numpad 6 or 9) to fine tune it, use CTRL-[direction] for ultra fine tuning. it doesn't matter if you're a little out, but its best to be exactly on it to reduce your total error margin.
turn off the De-orbit display (press DEO) again and time warp until you approach the final node before landing, this is the node 90* from your target, usually ~90* from your de-orbit position. then you should re-align your flightpath, turning to orbit normal or anti-normal (as required) and burning until the DIST readout on the highlighted line (MUST BE THE TOP LINE AT THIS STAGE) is close to 0."

The " the entry angle on the central display will rapidly count upwards, stop as close as you can to 0.7," . This part. I do not understand what he is talking about in the DG-iv craft as I do not see it. Where besides the DGIV can I find this so I may utilize it? Or better yet what is he talking about? Where in, and which MFD's will show me this?

Being my entry angle is off, this I think is where alot of my problems are coming from with floating back up or riding the redline to excessive heat.
 
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Tommy

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He's talking about the DGIV's FCS computer, which has several screens. Seems to me that the de-orbit display is page 2, so hit the "d" key, then the "2" key on your keyboard. Your ReA will be shown on the top. Fter the burn, hit the "d" key, then the "3" key to bring up the re-entry display so you can monitor the hull temps.

As an alternative, from LEO, you can just lower your PeA to about 50k.
 

Ripley

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Yes, it's the same computer monitor that tells you about your reentry configuration when you press "d65".

PDF manual is "hidden" in:
YOUR ORBITER FOLDER\Doc\DeltaGliderIV\res\DGIV_Documentation_en.pdf
 

thumper235

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Yes, it's the same computer monitor that tells you about your reentry configuration when you press "d65".

PDF manual is "hidden" in:
YOUR ORBITER FOLDER\Doc\DeltaGliderIV\res\DGIV_Documentation_en.pdf

You did not need to respond to me in such a condescending tone. If it truly is that bothersome then just dont reply good sir. I realize I may not be the sharpest crayon in the box, but I maintain politeness at all times while on these forums.

I am well aware of the "hidden" pdf. Since I was let in on that secret long ago, I use them frequently as I am now part of the "secret" club. There was some-type of issue with my installation. A simple download, followed by installing it again has resolved the problem.

EDIT: Ok, figured it out. Ran a scenario with the vanguard docked to the ISS. Heck, I learned how to use the Autopilot on her and how to fine tune everything. Now all I have to do is stop picking my landing times smack in the dead of night. It really stinks trying to see everything in darkness. :)

I will now step off the forums and give everyone a break. I cant thank you all for the help! This has been a tough learning experience, but this simulator is so much FUN! Im addicted. Server space and bandwidth is not cheap. I will make arrangements to get a donation made ASAP to help out.


Thanks Everyone. :)
 
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Ripley

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Just a web-misunderstanding...

You did not need to respond to me in such a condescending tone. If it truly is that bothersome then just dont reply good sir. I realize I may not be the sharpest crayon in the box, but I maintain politeness at all times while on these forums.
What?
I really don't see where I have not maintained politeness in all this.
Please, excuse me if I just wanted to help...I'll stop to.
 
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