Flight Question Re-entry problem

[Lazers]

I cannot re-enter correctly. I follow all the steps, am on opposite side of the planet, but AS SOON as I hit the atmosphere, my orbit vanishes and I just fall.

I align planes, make sure I pass over the base, wait til i'm on the other side of the planet, and burn retrograde to lower my orbit into the atmosphere. Just as soon as I hit I get a massive speed reduction and the ballistic orbit fails and shrinks, so I don't have enough energy to reach the base, and fall far short.

What is going on?!!? I barely lower my periapsis into the atmosphere, it seems the only solution is direct descent.

Orbiters space-to-atmosphere modelling must be broken.

 

[Grover]

there is no space-atmosphere modelling, just no-atmosphere to negligible atmoshere to gradually thickening atmosphere

what do you set your PeA to after your de-orbit burn, what do you use to time your burn, and most importantly, what craft are you in?

we need far more information before we can help you out, and the "burn on the far side of the planet" is a rough guide, and only applys to certain craft (if you did that in a capsule, you would certainly land > 1Mm short

 

[Urwumpe]

Which spacecraft did you use?
Which flight path angle did you have at 120 km? (angle of the velocity vector below the horizon)

 

[Grover]

by the sound of it, they may just have set the PeA to negatives

 

[Poscik]

Also make sure you have proper Angle of Attack.

 

[garyw]

I always lower my oribt to around 60km. At this point it's not the altitude that matters so much as the attitude. Bank angles give you major changes in lift and this can easily be seen on the Aerobrake MFD.
I've used that MFD many times to get right over my target.

 

[Poscik]

Or you can use GlideslopeMFD to see If you are at the correct path. If you do everything correctly, you will land similar way as shuttle, without engines...

 

[Grover]

that also requires you to fly something with similar aerodynamics to the shuttle, im not sure how leniant it is, but testing Moach's G42 showed me how far off you can get just by using a new craft

 

[Lazers]

To be truthful, I tried several different ships, some that just spazzed out when they hit the atmosphere, so bad coding there. Literally, it just started swaying up and down and up and down.

I was using the TotalImmersion ShuttlePB for most attempts, and I managed to re-enter within about 500km, but I feel that's still too far away. I had to make a powered flight from my re-entry point to the landing site.

The way I see most people doing it is they come down almost on top of the base; at least close enough to not have to do a proper flight, so within 100 - 50km

 

[Grover]

Well, start with the DG IV, since it has its own autopilot programs. You should remember, that with and winged craft, you need to pitch up to around 40° so you dont get massive lift to throw you out of the atmosphere.

Ive written a tutorial on here, search for re-entry for dummies or something like that

 

[garyw]

To be truthful, I tried several different ships, some that just spazzed out when they hit the atmosphere, so bad coding there. Literally, it just started swaying up and down and up and down.

I was using the TotalImmersion ShuttlePB for most attempts, and I managed to re-enter within about 500km, but I feel that's still too far away. I had to make a powered flight from my re-entry point to the landing site.

The way I see most people doing it is they come down almost on top of the base; at least close enough to not have to do a proper flight, so within 100 - 50km

I deorbit around the other side of the planet then come in via S-Turns following aerobrake as a guide.

I haven't yet seen any 'bad coding' in entry dynamics just people who didn't understand what was going on.

 

[halcyon]

To be truthful, I tried several different ships, some that just spazzed out when they hit the atmosphere, so bad coding there.

You came to the forum asking for help, but now you make the conclusion yourself that "bad coding" is involved?

Several people asked for details you left out again.
People can't help you if you don't explain what the circumstances of your attempts are.

 

[agentgonzo]

Orbiters space-to-atmosphere modelling must be broken.
...
some that just spazzed out when they hit the atmosphere, so bad coding there

Firstly, there's nothing wrong with trying something new and asking for advice. However, if you can't do it and blame the coding when other people can do it fine it makes you look like an arrogant tool.

As for your problem. Here is some information:
"Just as soon as I hit I get a massive speed reduction and the ballistic orbit fails and shrinks, so I don't have enough energy to reach the base, and fall far short".
This is normal. The orbit MFD shows you what your current orbit is based on your current position and speed and not accounting for atmospheric drag. If you want something that shows you what your projected trajectory will be including drag, look at AerobrakeMFD. As you hit the atmosphere, the drag slows your speed (as you've noticed) and the ballistic orbit does indeed fall short and shrink as your speed decreases during reentry. This is normal. OrbitMFD does not assume that there will be atmospheric drag, so you will need to target a point ahead of your landing base. This is not an easy thing to do and there are lots of tutorials about it.

Literally, it just started swaying up and down and up and down

. This is what happens at hypersonic speeds with drag in the upper tenuous atmosphere.

Reentry is not a simple thing and getting it accurate on top of your base takes knowledge, practise and a bit of skill. It'll come. Take a look at some of the tutorials on this site, including the AerobrakeMFD tutorials. (see also http://orbiter.dansteph.com/?news=120)

 

[Urwumpe]

Yeah Lazer, you just invented the hypersonic waverider again.

The entry dynamics are all fine, what you do wrong is: You use the wrong distance between landing site and entry interface (EI) and the wrong reentry angle. Every spacecraft has its own demands there. Just "once around the planet" sounds easy, but is actually wrong. It is a coarse guideline, but practically, you need to aim better.

Once you pass entry interface in the right distance, the right altitude (usually 120 km) and the right reentry angle, you will be already on a good track, but your piloting is still needed. Best practice is to keep AOA constant (eg by using maximum trim, if other means are missing) and bank your spacecraft to one side, so you start flying s-curves. The more you bank, the faster you drop into the atmosphere, the more you slow down and the more heat you get. Start at positive lift (wings level, nose up), until you are reaching level flight during reentry. And then bank to increase your deceleration to the value you need for hitting the base.

If your EI is about 5000 km away from the base and you are using a DG like vehicle, 16 m/s² is a very good guideline for the deceleration - this will slow you down to Mach 3 in sight on the base.

 

[Lazers]

Yeah Lazer, you just invented the hypersonic waverider again.

The entry dynamics are all fine, what you do wrong is: You use the wrong distance between landing site and entry interface (EI) and the wrong reentry angle. Every spacecraft has its own demands there. Just "once around the planet" sounds easy, but is actually wrong. It is a coarse guideline, but practically, you need to aim better.

Once you pass entry interface in the right distance, the right altitude (usually 120 km) and the right reentry angle, you will be already on a good track, but your piloting is still needed. Best practice is to keep AOA constant (eg by using maximum trim, if other means are missing) and bank your spacecraft to one side, so you start flying s-curves. The more you bank, the faster you drop into the atmosphere, the more you slow down and the more heat you get. Start at positive lift (wings level, nose up), until you are reaching level flight during reentry. And then bank to increase your deceleration to the value you need for hitting the base.

If your EI is about 5000 km away from the base and you are using a DG like vehicle, 16 m/s² is a very good guideline for the deceleration - this will slow you down to Mach 3 in sight on the base.

No matter how I angle the PB shuttle thing, it always re-enters at the same rate. Similarly, banking does not move the velocity indicator.

Also, that up and down waving has never happened to me before, and seems to be limited to this one addon.

 

[agentgonzo]

No matter how I angle the PB shuttle thing, it always re-enters at the same rate. Similarly, banking does not move the velocity indicator.

Yes:

It produces little lift in atmospheric flight, and depends on its hover thrusters for takeoff and landing. Aerodynamic control surfaces are not supported in this version. Attitude control is performed via the RCS (reaction control system)

(source).
Basically, it has the aerodynamics of a brick, so will re-enter like one. So no matter what you do, it will always do pretty much the same thing - no matter how you orient a brick on re-entry, it's profile will be pretty much the same. It's not a lifting body like the shuttle or deltaglider/XR class.

Also, that up and down waving has never happened to me before, and seems to be limited to this one addon.

That's probably due to the aerodynamics of this addon rather than the other ones you were flying.

 

[Lazers]

Done, Orbiter bugged out, is why.

 

[Ripley]

Too many things look "broken"...Tried with a fresh Orbiter install?

 

[agentgonzo]

Done, Orbiter bugged out, is why.

PEBCAK?

 

[garyw]

all I can say is that Orbiter works for many people so if your copy is 'bugged' maybe you need to delete, download again and reinstall?

Certainly worth a go if you are having this many problems.