Manual Reentry

[Dimkin]

Hello all!

I would like to learn how to perform manual reentry to Earth, by manual I mean only with the MDF that comes with Orbiter. Here are my questions:

1. How can I calculate when to make the burn to enter near the base I want to land?
2. How can I align myself with the base I want to land on?
3. How do I know how long should be my burn to enter correctly and not bounce from the atmosphere back to orbit?

Thanks!

 

[ar81]

1.Aerobrake MFD
2.baseSync MFD
3.Start from low orbit and deorbit when in the oposite side of planet.

 

[RisingFury]

1.Aerobrake MFD
2.baseSync MFD
3.Start from low orbit and deorbit when in the oposite side of planet.

Didn't Dimkin just say with stock MFD's only?


@ Dimkin: Well, the Map MFD and Orbit MFD would definitely be the ones I'd use... I use Map MFD to figure out my deorbit burn... I do my deorbit burn some 16 000 km from the base, and determining when the orbit will cross my target by the gut feeling...

Then I use AeroBreak MFD for the flight through the atmosphere, but without it, I'd hold some 38° AOA in DGIV and mainly keep an eye out on the slope. I'd be flying blind, but when I came withing 500 km of the target, that'd be a good time to decide what to do - if I had lower then 2 km/s, and somewhat low (20 km or less) I'd pitch down and start gliding to lose as little energy as possible. If I had too much energy, I'd keep on breaking till I lost some more...

In either case, it's gonna take you several tries to get it done.

 

[unknown_orbiter]

Jeeze good luck m8, I've only ever successfully completed one de-orbit to KSC...

 

[ar81]

I tried with stock MFDs in the past and I did lots of research with data.
The average distance from target base was about 1000km after entry.

 

[MeDiCS]

The average distance from target base was about 1000km after entry.

For me too, and I use the stock MFDs. Don't know why, but using 3rd party MFDs (specially AerobrakeMFD, BasesyncMFD and IMFD) seems like cheating to me, I don't want all data to magically appear so that I can do a perfectly aligned maneuver, or worse, let the AP do that for me :dry:...

 

[Bj]

For me too, and I use the stock MFDs. Don't know why, but using 3rd party MFDs (specially AerobrakeMFD, BasesyncMFD and IMFD) seems like cheating to me, I don't want all data to magically appear so that I can do a perfectly aligned maneuver, or worse, let the AP do that for me :dry:...

well, doesn't the Space Shuttle launch by AP? I know a lot of airplanes now can be controlled remotely or by AP. (UAV)

 

[ar81]

For me too, and I use the stock MFDs. Don't know why, but using 3rd party MFDs (specially AerobrakeMFD, BasesyncMFD and IMFD) seems like cheating to me, I don't want all data to magically appear so that I can do a perfectly aligned maneuver, or worse, let the AP do that for me :dry:...

The problem is that data dynamically changes in non linear ways, depending on eccentricity, position, altitude, orbit inclination, etc. So such MFDs compute for you. I already tried the exercise of trying to approach linear or wild guess solutions and failed.
I created many graphics to correlate variables and I always failed.
The highest level of precision I achieved was 1000km away from base with my estimates.

If you succeed then congratulations... until then you have a n intellectual challenge in your hands.

 

[Dimkin]

Ok, understood, I've tried 3 time:
1&2. The atmosphere pushed me back to orbit!
3. Guess I did a pretty big burn, ended up flying too fast and got burned in the atmosphere...

So, guess the mistake was with the burn length calculation.... ??

 

[Epsilon]

Keeping in mind that I'm absolute crap at reentry...
If I had to hazard a guess, I'd say that less than burn time, it's a problem with your AoA. Your angle of attack needs to be high enough that you don't generate (too much) lift, but low enough that you don't decelerate too quickly. I'm sure someone else can help out with the actual numbers based on the ship you're flying. :lol:

Also, start from a low circular orbit - 150km keeps you (mostly) out of the atmosphere, and it gives you a shallower glide angle. I think? <_<
I just know that's what I always read about re-entry. ^_^

 

[ar81]

If entry is too steep you will burn.
Braking involves creating drag and lift, and lift could make you go back to space.
S-turns could help you to dissipare energy to prevent the effect of lift.
AoA has a big impact on the rate of braking and AoA variations could mean a long distance once you reach surface. So not onlyyou need those MFDs but also a mechanism to keep constant AoA.

Basically you are riding a hypersonic bullet and you want it to land softly on a small ruler.

 

[MeDiCS]

I'm not playing Orbiter to let the computer do everything for me :compbash:. I'm playing Orbiter because it let me do what I can't in real life. I won't let the AP do something so that I can say 'well, nice. My ship went to Uranus and back on free-return trajectory, but I just watched it.' :weird:. 'I got to the Moon with not enought fuel for a safe return, and my orbit has a mean radius of 100m!' if far better, because I know I did it. Well, I have my pride...

I'm not saying to throw out of the window every piece of data, but how much is too much?. I'm happy to know where a certain body will be when I get to my escape-apoapsis, but I don't need (or don't want, still trying to decide) a MFD that'll tell me that exactly how to do my burns so that i can get exactly a hyperbolic orbit around the target body with it's vertice with a perfect alttitude for my orbit insertion, sing a song and cook me breakfeast at the same time. And an AP whitch'll do that alone while I passively watch...

 

[Epsilon]

Agreed, MeDiCS. The question is, how much is too much indeed? On one hand, I only have two extra MFDs: Basesync and TransX (the second is included with the base installation, although I have the new version). Sure, they both do stuff for me, but they do stuff that would be a royal pain in the to do manually. If you want to do re-entry fully manual, that's cool - but you've got to be prepared to miss the mark more often than not then. ^_^
Basesync does the hardest part for you - getting you in line with the base, assuming your orbit stays the same. In atmospheric flight, it will most certainly not.
When you're doing turns to burn off speed, as mentioned above, the farther away from the base you are, the farther off course those turns will take you.

Example:
Hold your fist in front of you on your chest. Turn 90 degrees left. It travels about a foot and a half (two and a half if you're a big guy like me.)
Now, hold your arm out, and make a 90 degree turn back to 'forward'. Your fist travels probably three feet (once again, four if you're big )

The farther away you are, the more the movement is magnified. A couple of moments of horizontal travel can be enough to toss you half a world away from your target (I exaggerate slightly). You -can- use the VOR transmitter (I think that's what it's called) to guide you in once you're within 500km, but I learned Basesync first - only discovered VOR after the fact.
Also, it seems that 112.70 (the VOR for KSC) is shared by a few transmitters that have overlapping ranges. This sucks, IMO. :lol:

 

[MeDiCS]

To get near the target base I usually use MapMFD, visual for crude alignment and VTOL/HTOL for finner adjustments. That generally works pretty well .

Actually, I do everything manually, using as little digested data as I can. This is simply beacause I want to succeed based on my skills, and still do it as realistically as possible. That's why I chose orbiter, and that's why I play Orbiter (and not the other way around). I'm not against those that prefer, let's say, less two-way interaction, this is just my opinion.

By the way, I'm thinking on buying a three-axis joystick, and maybe, maybe, I'll build a simple simpit (more realist, :lol.

 

[ar81]

If you want simple numbers, try ReentryMFD.

 

[eveningsky339]

Even the shuttle with its modest wing area will get shoved out of the atmosphere without perform 90 degree banks.

Orbiter comes with "Checklist" Flights in the "Checklist" Folder. The guides to the flights are there. Use the re-entry scenario to practice.

 

[Dimkin]

Ok, so Ive tried for the 4th time, this is what Ive done:
1. Ive made short retro-burn 15000M from the base. After descended to 150km made another short one.
2. While entering the atmosphere changed banks from -15deg to +15 deg while holding 40deg pitch.

The thing is that I made full successful reentry and my speed was mach 4 while the distance to the base 2000M, I didnt make it to the base

 

[RisingFury]

Ok, so Ive tried for the 4th time, this is what Ive done:
1. Ive made short retro-burn 15000M from the base. After descended to 150km made another short one.
2. While entering the atmosphere changed banks from -15deg to +15 deg while holding 40deg pitch.

The thing is that I made full successful reentry and my speed was mach 4 while the distance to the base 2000M, I didnt make it to the base

Watch the MapMFD that displays the distance to your target. If you see you're goinna fall short, pitch down and start gliding. You can glide for 100's of miles with 2 km/s at high altitude.

 

[Dimkin]

Agreed, but the idea is to make clean reentry and end it about 500-300km from the base.
Actually I made pretty accurate with only 1deg away from the target port. So the only problem is the distance.

 

[cbf]

Hi Dimkin, ar81 is right! During reentry the best "tools" are:
-Base Synchro MFD
-Aerobrake MFD
And the DeltaGlider IV

You must use Base synchro MFD in direct mode (E/D), target "Cape Canaveral" for example. Decrease Rinc at nodes using normal or antinormal.
In Aerobrake MFD, target "cape canaveral" as well.
To calculate at which distance to make your deorbit burn, it's quite simple. We consider a rentry angle of about 1.2°, roughly D(km) = Alt(km) / TAN 1.2°. That means D=12Mkm for an altitude of 250km for example. Reaching the computed distance, apply retrograde thrust until --+ grey ine is aligned with --+ yellow line on Aerobrake MFD.
If necessary and feasable, proceed to a last Rinc correction at node.
Afterward, if you fly the DGIV, engage ATT hold Autopilot (PRO104SPEC40) before Alt reaches 120k.
On Aerobrake MFD, press PG, then twice PRJ. On the top left of this MFD, you will find an indicator showing grey + & yellow --O
During reentry, you must have + and --O centered.
If --O is located after +, It means your slope is too weak. You have increase your ATT +5° a few seconds to increase your vertical velocity.
If --O is located before + it means your slope is too steep. You have to decrease your ATT -5° a few seconds to decrease your vertical velocity. In this case be carefull. T° increases and be carefull that your vertical speed remains negative.
You should reach Cape Canaveral at an altitude of 25km. Then you have to manage your total energy to perform perfect landing (lots of training...)