Atmospheric Reentry: Difference between revisions

Latest revision as of 22:11, 25 November 2019

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

Aerobraking --- Example of NASA using Aerobraking to enter Mars orbit

None of the E, W,or P-series aerospace vehicles are designed for true areobraking. In the case of MRO (Mars Reconnaissance Orbiter) It took 6 months to decelerate to orbital velocity.

Thrust/Lift/Drag (Modified Aerobraking)

The ships in Rise use Iagreous fuel, For all practical purposes a pilot at orbital speed could use TVM set it to 0.5km/sec and let the ship use the engines to try and maintain that 0.5km/sec total speed all the way down to about 30km altitude and then transition over to normal flight.

TVM

TVM will get you down safe but it will literally fight lift, drag, gravity all the way down trying to get and maintain the set speed you put in.

Normal re-entry attitude

This entire discussion is based on the assumption that you are wings level, nose pointed in the direction of travel, and all of this is lined up with your desired destination.

Deciding When To Drop

A heavy ship takes more time and distance to decelerate. This entire lesson is based on an acceleration of 1.2 G in the vacuum of space.
First you must understand that the atmosphere has no measurable effect on your vessel until you descend below about 95-85km MSL assuming normal orbital speeds. Since you are not yet in the atmosphere you can not use the air to slow or generate lift.
If you are traveling at the orbital speed, or just under, and at 100-120 km altitude, you will start to using reverse thrust at around 1500-1300 km from your target. Use the up thrust (F9) to hold your ship above 100km till your ground speed is about 3km/sec.
With luck and or practice you will end up at about 2.5-3 km/sec as the target get to about 12-15 degrees nose down. Lower your nose to 15 degrees down. KEEP the engines in reverse but use the F8/F9 to help keep your direction of travel lined up with your nose. You will see some aerodynamic heating and plasma effects. As you generate more and more lift you will stop using the up and down thrust and start pitching the nose up and down to adjust your rate of descent.

REMEMBER it is NOT your FORWARD speed that will kill you IT IS your RATE OF DESCENT
The faster you change the outside air pressure the faster the drag changes. Higher drag, higher deceleration rate. 5km/sec at 100km altitude no problem. 5Km/sec at 70km you might as well drive in to a brick wall.

Slowing Down

If you kept close to your ideal 15 degree down you will end up close to 30km and at 0.5 km a sec. If you made it down safely to where you are now flying like an airplane. WELL DONE and CONGRATULATIONS! You just completed your first safe operational reentry!! Go and get a drink and celebrate!!!

Points to Remember

Do NOT fight the lift being placed on your vessel with pitch or thrusters you will risk over-stressing the air frame and losing bits from it, and causing injury or death. However if you need to help slow your descent rate, thrust downwards (F9) 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 maneuvering 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!

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 ==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]]).
+* [https://en.wikipedia.org/wiki/Aerobraking Aerobraking] ---  [https://mars.nasa.gov/mro/mission/timeline/mtaerobraking/ Example of NASA using Aerobraking to enter Mars orbit]
+None of the E, W,or P-series aerospace vehicles are designed for true areobraking. In the case of MRO (Mars Reconnaissance Orbiter) It took 6 months to decelerate to orbital velocity.
-For this methodology, the following assumptions are made...
+*Thrust/Lift/Drag (Modified Aerobraking)
+The ships in Rise use [[Refined_Fuel|Iagreous]] fuel, For all practical purposes a pilot at orbital speed could use [[TVM]] set it to 0.5km/sec and let the ship use the engines to try and maintain that 0.5km/sec total speed all the way down to about 30km altitude and then transition over to normal flight.
-*You are flying between 100-120 [[kilometer|km]] [[MSL]]
+*[[TVM]]
-*You are travelling at roughly 5.6km/s
+TVM will get you down safe but it will literally fight lift, drag, gravity all the way down trying to get and maintain the set speed you put in.
-*You are not carrying cargo (which changes the distance at which you start to slow down dramatically)
+===Normal re-entry attitude===
+This entire discussion is based on the assumption that you are wings level, nose pointed in the direction of travel, and all of this is lined up with your desired destination.
 ===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.
+A heavy ship takes more time and distance to decelerate. This entire lesson is based on an acceleration of 1.2 [[G]] in the vacuum of space.
+<br />
-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.
+First you must understand that the [[atmosphere]] has no measurable effect on your vessel until you descend below about 95-85km [[MSL]] assuming normal orbital speeds.  Since you are not yet in the [[atmosphere]] you can not use the air to slow or generate lift.
+<br />
-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 are traveling at the orbital speed, or just under, and at 100-120 km altitude, you will start to using reverse thrust at around 1500-1300 km from your target. Use the up thrust (F9) to hold your ship above 100km till your ground speed is about 3km/sec.
+<br />
-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.
+With luck and or practice you will end up at about 2.5-3 km/sec as the target get to about 12-15 degrees nose down. Lower your nose to 15 degrees down. KEEP the engines in reverse but use the F8/F9 to help keep your direction of travel lined up with your nose. You will see some aerodynamic heating and plasma effects. As you generate more and more lift you will stop using the up and down thrust and start pitching the nose up and down to adjust your rate of descent.
+<br />
-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]].
+<br />
+REMEMBER it is NOT your FORWARD speed that will kill you IT IS your RATE OF DESCENT
- REMEMBER it is NOT your FORWARD speed that will kill you IT IS your RATE OF DESCENT
+<br />
+The faster you change the outside air pressure the faster the drag changes. Higher drag, higher deceleration rate. 5km/sec at 100km altitude no problem. 5Km/sec at 70km you might as well drive in to a brick wall.
-===Meeting the Atmosphere===
+<br />
-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 [[artificial horizon|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 [[acceleration|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!
+If you kept close to your ideal 15 degree down you will end up close to 30km and at 0.5 km a sec.
+If you made it down safely to where you are now flying like an airplane. WELL DONE and CONGRATULATIONS!  You just completed your first safe operational reentry!!  Go and get a drink and celebrate!!!
-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_flight|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 [[acceleration|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 [[acceleration|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 [[artificial horizon|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===
 [[Image:caution.png|right]]
-* 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 fight the [[lift]] being placed on your vessel with pitch or thrusters you will risk over-stressing the air frame and losing bits from it, and causing injury or death.  However if you need to help slow your descent rate, thrust downwards (F9) 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.
+* If you are going to overshoot, no problem.  Stop maneuvering 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.