reenter in earth with dgiv

[bemanos]

well i have tryied several times but always when the burn starts nose start going down(from 30-40o to-20 degrees) and i end up dead. why is this happening? must i dump the fuel to be lighter or something?



thanx in advance

 

[Urwumpe]

1. Lithobraking is not possible with manned vehicles.

2. Try it with two changes to what you currently do wrong: Lower reentry angle of more than -1.25° (Monitor Deorbit display during deorbit burn) and use the vehicle state check program to warn you if you have too much fuel onboard. If your vehicle mass exceeds the limit, you produce not enough lift to glide at lower atmospheric density - you will reenter too deep into the atmosphere in any case and thus get excessive aerodynamic heat flux. You burn up.

 

[bemanos]

ok i will try again thanx

 

[Urwumpe]

To make sure you understood it correctly: Make sure reentry angle is between -0.75° and -1.25°

 

[bemanos]

ok tryied to reentry at 0 ° but around 70 km above surface i just stoped falling and start to going up to space again :S(i didnt touch anything!)

 

[Urwumpe]

0° reentry angle is not 0° Angle of Attack (AOA).

Did you read (including understanding) the manual of the DGIV? There is a display which shows you, while you do the deorbit burn, at which angle you will pass the space/Atmosphere interface, if you cut the main engine now. This angle is called reentry angle.

Important also: You need to bank. If you fly at constant 40° AOA, you will raise again. for preventing this, bank to the side in the moment you reach level flight (vertical velocity zero)

 

[Sky Captain]

You can also turn on reentry autopilot and just watch the DGIV reenter itself so you get a clue how to do it properly. Check the DGIV manual for available autopilots.

 

[ar81]

[ame="http://www.orbithangar.com/searchid.php?ID=3428"]Tutorial: Concepts for atmospheric reentry[/ame]

 

[bemanos]

!! i did it.... well... by the time i reached 80 km my v\s was -117 angle of prediction 0.354 and reentry speed prediction 7, something km . by the time i reached 79 km my vs started to rising and then my angle started to falling and i endend up with angle 0 and speed prediction 0 telling me that there was no reenter but somehow i managed to do a nice burn and land to the ground..ok but the entire reenter mission was took lots of time i mean i was in 10x mode for some mins . what is wrong? should i decrease my vs more?

 

[Urwumpe]

bemanos: The angle and speed prediction is invalid once you fly below 120 km altitude - while it does display data, the data must be interpreted as "garbage in - garbage out". The display does just a free fall calculation, it does not include any aerodynamic effects.

 

[bemanos]

ok so is there a more fast procces for a reentry? or must i use the 10x time wrap tool if i dont want to wait for hour (maby)

 

[Urwumpe]

bemanos: Not if you want to stay intact. Each kg of your spacecraft has enormous amounts of kinetic and potential energy stored, which you have to shed before landing by slowing down and descending. The faster you slow down and descend, the more energy you shed per second and the hotter you get.

The trick of any good reentry is "riding on the red line": Shed as much energy as possible, while staying intact. For all gliding vehicles, you do so by controlling the vertical velocity. The heating is a function of velocity and altitude, the faster you are at a selected altitude, the more heat is produced there. Going lower at the same speed increases heat, going up at the same speed cools down. Drag will constantly slow you down, so you can keep a heat or deceleration limit by descending so fast, that the effects of slowing down are neutralized. If you regulate the vertical velocity by banking the spacecraft and do roll reversals (s-turns), you can reenter as fast as possible.

 

[MeDiCS]

bemanos: That depends on your reentry angle, the vessel heat (and possibly mechanical) resistance and, of course, your skill. It's been a long time since I last made a reentry, but I think you can make it in fifteen or maybe ten minutes, but I'm not very sure.

 

[bemanos]

ok thanx for help( by banking you mean the button 4 and 6 right?)

 

[MJR]

Yes.

 

[ar81]

When I reenter I use to set orbit at about 150 km, circular orbit, and then I start deorbit in the opposite side of the planet.

 

[MeDiCS]

When you're harcore, try a reentry with a 90º angle .
(Just for the record, I've done this more than once )

 

[IthyStPete]

How is that even survivable?

 

[Sky Captain]

The most extreme way how to do reentry is fly inverted the whole reentry. It can be done with craft like XR2 which have movable center of gravity. Basically when you are about to hit atmosphere roll inverted and pitch up towards the Earth and move COG aft a bit so you can keep AOA about 70 deg.
This way you can reenter faster because when peak heating is over you can pitch down to increase lift and pull yourself into thicker atmosphere to slow down faster.
This is how it looks like :speakcool:

 

[MeDiCS]

How is that even survivable?

Sure! Actually, it shouldn't be hard to figure out how to do it. I used the XR2 to literally drop into Wideawake International when I was trying the be the faster to fly from Cape Canaveral to Wideawake.