Atmospheric Reentry

From Rise: The Vieneo Province

Atmospheric reentry is the process by which spacecraft from orbit of a planet or moon enter the atmosphere and reach the planetary surface intact. Typically this process requires special methods to protect against aerodynamic heating. Various advanced technologies have been developed to enable atmospheric reentry and flight at extreme velocities.

Methods

The preferrable method for atmospheric reentry is the drag method. The drag method (not to be confused with aerobraking) saves fuel, compared to the direct use of thrust (see TVM).

For this methodology, the following assumptions are made...

  • You are flying between 100-120 km MSL
  • You are travelling at roughly 5.6km/s
  • You are not carrying cargo (which changes the distance at which you start to slow down dramatically)

Deciding when to drop

First you must understand that the atmosphere has no effect on your vessel until you descend below about 70km MSL assuming normal orbital speeds. Since you are not yet in the atmosphere you can not use the air to brake.

If you are travelling at the specified speed and altitude, you will start to descend at around 1500km from your target. Aim to be hitting the atmosphere at between 850-1000km from your target.

The best way to descend in a controlled fashion is to first zero out your trim and use your vertical thrusters (F8/F9). In order to do this starting using your roof mounted thrusters to push yourself into a descent. A sensible descent speed when going down to meet the atmosphere is about 300m/s

If you sense you are going to overshoot your target because you are too high think about increasing that rate of descent to about 500m/s.

It is important that you do not let that descent rate increase above 600m/s or you are at high risk of burning up the atmosphere.

REMEMBER it is NOT your FORWARD speed that will kill you IT IS your RATE OF DESCENT

Meeting the atmosphere

At about 850-1000km, you are just starting enter the atmosphere and you are now starting to pick up airspeed. You will notice your speed both velocity and ground speed will start to decrease ever rapidly as you descend.

At this point you need to make sure your wings are level with the horizon and your pitch is no more than -5°. When you are more confident and want to slow down faster feel free to go in nose first. But it is dangerous and I don't recommend it until you know what you are doing. You are aiming to go in "belly first" so-to-speak.

The two main instruments you need to pay close attention to now are your VSI and your J which is on the left MFD.

Slowing down

You will also notice that as you descend and slow your rate of descent will start to decrease and head towards a positive rate of climb. This means that you are now picking up lift from the oncoming air, and at your current speed that lift is so powerful it is pushing you right back up!

There is a way to combat this and keep your rate of descent constant or to your desire... by rolling 90° left or right you can maintain the descent rate that you wish to hold. I suggest that you alternate your roll left and right at intervals so that you do not drift too far off course.

It is IMPORTANT that you DO NOT roll inverted, this will cause your rate of descent to increase VERY rapidly and you are very likely to burn up!

All the while during your rolls and manuvers keep watching that J number on the left MFD, this is how many Gs of acceleration/decceleration your are pulling from below your vessel. I advise that you do not allow this to get further than ±5km/s or your will be injured and parts of your ship will begin to break away. The same goes for K which is the force in Gs from the front of your vessel although you can let this get up to about 12G I DON'T advise it unless you know what you are doing.

As you reach about 3km/s ground speed look at your distance from you target... if you sense you are falling short, roll level and point your vessel at the horizon, this will reduce the level of slowing that is being placed on your ship, do not be concerned if you start to gain altitude due to lift, and do not try to fight where the air is taking you with pitch too much. Y ou can then glide a bit further a then try to lose some more altitude when you feel you are at a good distance... I would say you want to aim to be about 350-450km away from your target before continuing a descent and brake from 3km/s.

Once you are down to about 1km/s you can start thinking about using your ptch controls to gently ease the velocity vector down towards your target vector. Your ship will continue to slow gently from here and you can apply power as and when you feel it is neccesary.

If you made it down safely WELL DONE and CONGRATULATIONS! You just completed your first safe operational reentry!! Go and get a drink and celebrate!!!

Points to remember

Caution.png
  • Do NOT fight the lift being placed on your vessel with pitch or thrusters you will risk overstressing the airframe and losing bits from it, and causing injury or death. However if you need to help slow your descent rate, thrust downwards and use a little positive pitch to reduce your rate of descent.
  • Do NOT roll inverted!
  • If you are going to overshoot, no problem. Stop manuvering and level out, ride the lift and begin your descent again when you are ready.
  • Do NOT scramble to get on target in your first few attempts if you overshoot or come short SO WHAT?!?! The main thing is you need to be in one piece to be pleased with what you just acheived, you can work on getting on target with practice... safely!! Getting on target is not to promote expansion of your e-genitals!
  • Your instruments are your friends, they will show you when danger is approaching, not the window.
  • STAY CALM AND DO NOT PANIC!

Need further help just ask!