Space shuttle reentry problems

[MisterC]

Matte the S-turns are turns in shape of S, as Simfan says, Slalom Turns...

Juste because when you control your lift using banking angle, the shuttle deviates from the trajectory to target, i.e
Cape Canaveral or Edwards. So, when you flew a certain amount of time banked at 80° or so on the right, you must
do a "roll-reversal", to fly some time at 80° roll on the left, to correct your heading...

The slower you fly, the faster the heading deteriorates, and so you must change more often the bank side...

In the theory, i think you must bank on the right when vertical speed is about 100 m/s, to avoid bouncing on
atmosphere, then do a reversal at 50 km altitude, another at 35 kilometers altitude, again another around Mach 7, by
32 km of altitude (there's a phase where altitude must be maintened constant, otherwise speed is too great
regarding of air density), and after that, heading changes rapidly due to low speed, so you make all roll-reversals
necessaries to keep heading toward the target...

[SimFan]

Not possible to edit this morning!

Sorry, mistakes corrected :



"S-Turns"


= Slalom turns.

Alternatly use 1 and 3 keys

That seems as dirty piloting, but provides very efficient braking, as when skying.

A cleaner way is use of 4 and 6 keys.
The cleanest is use of 1/4 and 3/6 keys.
Both make the way longer, that reduces Hspeed in accordance to.

It's all explained here :

http://spaceflight.nasa.gov/shuttle/reference/shutref/events/entry/
http://www-pao.ksc.nasa.gov/kscpao/nasafact/pdf/landing.pdf


Btw, Matte, please be kind enough to reedit your first post in this thread and the title in lowercase letters (no
capitals, except
when beginning a sentence or a people's name)

Thks


SF



Post Edited ( 11-27-04 22:59 )

[Matte]

ok, i have reedited it!! i hope it's good!!
so, as i can understand, i have to burn at 18.500 km from landing site, obviously retrograde, till PED is 6370;
then, at 100/90 km height, press B and activate auto-pitch system.
then when V-speed is 100 m-sec, bank right, than at 50 km height left, then 35 km right again, and last one at 32 km:
then air density will avoid normal turns to reach base.

all right???

[Orbiter Fan]

The direction of the first roll depends on wheter your current trajectory will take you to the north or south over your
landing site. If your trajectory will take you too much north of your trajectory, you should roll to the right. If south then
roll to the left. This way you use your lift to correct any trajectory deviation. Hope this will help in making successfull
re-entries and landings!

[SimFan]

You may want to see an overhead approach there :

http://jeanpaj.free.fr/Videos_JP/Hac_Atl_Full_betaH1.wmv

Not to far from Italy whose you can see a little bit



And the landing as seen from ground :

http://jeanpaj.free.fr/Videos_JP/Atl_32_ldg1H.rm



And I don't remember if I sent Azimuth's tutorial link :

http://jeanpaj.free.fr/Duplis/Videos_AZ/ReentryTutorial.rmvb

A big file, 57 Mbytes!

[SimFan]

Btw, Matte, thks for reediting your first post

Netiquette is now respected

[C3PO]

Just to clarify this manouver a bit.

The reason for the S-turns is to control the vertical velocity. NASA calls them "roll reversals"

It's not so important when you switch roll direction, as long as you don't turn too far away from the direction to the
landing site.

When you bank the shuttle, you use the "lift" to change direction instead of bouncing out into space again. You can
use the vertical speed to judge how fast you are slowing down. Usually I keep the Vspeed between -50 and -100 m/s
during most of the reentry.

The first bank is very steep (I usually go to about 85 Deg) but this is going to decrease all the way down. I don't look
that much at  the bank angle because the most important things are the speed and Vspeed.

But the most important thing is practice, practice and more practice (untill someone makes a MFD for doing this by the
numbers)

Happy reentering

C3PO

[SimFan]

The reason for the S-turns is to control the vertical velocity. NASA calls them "roll reversals"

Roll reversals and S-turns are two different things :

Rolls occur when reaching upper layers of atmosphere. Their purpose is to avoid the shuttle bouncing on them, by
making the vertical component of airlift as low as required by rentry profile. So, the horizontal component is very strong, that requires reversals to aim the base.
 
S-turns occur when arrived around 1000 km from the base. Their purpose is to reduce airspeed to the right landing
value by making the path more or less long  using usual airdrag. This is like classical glider piloting. At this step,
aerobraking with split rudder is used too.

Manage your S-turns and aerobraking settings keeping in mind to arrive @ 200 m/s , 15000 m height when crossing
the runway axis @ 10 to 12 km from threshold for a beautiful overhead approach



Post Edited ( 11-23-04 09:49 )

[MisterC]

I agree with C3PO.

The direction of the first roll is not important. I deorbit is correct, the trajectory must drive you RIGHT on target, ther's
no initial deviation.

The bank purpose is ONLY to control drag by the mean of altitude and to avoid bouncing.

The deviation appears with the first bank, making roll reversals necessaries.

And SimFan is right about S turns...

[C3PO]

SimFan wrote:
Roll reversals and S-turns are two different things :

I know

I was just trying not to confuse things. I could have gone on about HAC's and PAPI/VASI's, but I believe the object of
this exercise was to arrive at the base at a sensible speed.

C3PO

[SimFan]

For the re-entry od the shuttle, take an angle of -5°

Ara, you're an heretic!

AOA must be +40° with strong banking

[Matte]

banking is controlled by buttons 1 & 3 on num-pad, in rotation mode, isn't is?
it's the left-right moving of the nose??
and how can i control what is it's value??

ty again

[SimFan]

banking is controlled by buttons 1 & 3 on num-pad, in rotation mode, isn't is?

Sorry, they're 4 and 6

it's the left-right moving of the nose??

They normally are 1 and 3

But banking also makes left-right moving of the nose, and I personally prefer to use banking with4 and 6 for turning. After I keep the vector speed in axis using 1 and 3

and how can i control what is it's value?  (left-right moving of the nose)

With HUD vector speed , circled +



Post Edited ( 11-23-04 16:44 )

[SimFan]

My personal procedure for reentry is the following :

This procedure tries to meet data found there :

www-pao.ksc.nasa.gov/kscpao/nasafact/pdf/landing.pdf


1. Begin undocking from ISS. Deorbit burn (retrograde) 19 000 km past base when on the orbit just before the one
passing overhead the base, until periapsis = 6432 km (60 000 m high). This will burn around 10% of a tank initially
15% filled (to be adjusted in scenario).

2. Before reaching 130 000 m high, turn prograde, keep wings level, pitchup + 40°, then set autopitchup when
around 90 000 m high and wait until algebraic value of Vspeed climbs up to -50 m/s (@ around 80 000 m high).

3. Begin first roll and adjust banking (80 to 90°) to keep Vspeed around - 50 m/s to -80 m/s.
Not easy at all... If you go down too fast, reduce autopitch setting and/or banking. Also take care that too high
autopitch with any banking values reduces too fast your airspeed.

Adjust yaw to keep speedvector in symetry plane of the vessel.

An autoalign yaw corrector would be welcome (many thks, Llyr, for giving a look !).

It easily happens that you fully lose control of the vessel and sadly transform it to a meteor (visual effect in next
Orbiter release?).

4. Reverse roll when required (watch at base indication on hud compass), next target will be "exit blackout" waypoint
@ 1000 km from base, 50 000 to 55 000 m high, 3500 to 4000 m/s airspeed. You'll have to reduce autopitch setting
and eventually disable it. Sometimes disabling/enabling/disabling/... will help.

True life for 3. and 4. is to get an AOA from +40° progressively reduced to +36°, then 16° for step 5

5. After this waypoint, you can fly wings level towards next one "TAEM entry" @ 100 km from base, 25 000 to 30 000
m high, 700 to 1000 m/s airspeed.

Check points will be :
750 km, 48000 m, 2800 m/s
500 km, 40000 m, 2000 m/s
250 km, 32000 m, 1300 m/s
100 km, 25000 m, 750 m/s

Enable "." key aerobraking.
Hang on to the stick and watch at Vspeed to keep it between -50 to -80 m/s. Always keep one eye on Vspeed
indicator, you could bounce several tens of km in a very short time.
Trim = 0.8 to 1 works well for vertical stability of flight.
You'll probably need S-turns. Take sea-sick pills. S-turns automatically hang together once started with "1" or "3"
keys. Try 15 to 20° max yaw.

6. Now, arrived @ 100 km from base, the trick is almost done. Its just a matter of training : Practice slight S-turns
(keys "1" and "3" provide very strong braking, prefer banking with "4" and "6" for turns to aim the base) if airspeed
above 800 m/s, aerobraking ("." and "," keys), 0.5 to 1 positive trim.

Checkpoint @ 50 km from base, 20 000 m high, 500 m/s

For overhead landing, fly 15000 m high above a point located 8 to 12 km outside from runway threshold on the side
of projected turn at airspeed 180 to 220 m/s, then begin turn for easy entry in HAC at the end of turn.

For U-landing, fly 15000 m high above a point located 5 to 8 km outside from runway and wait to be 15 to 18 km past
the base before turning.

In both cases before turning, adjust trim to +1, be sure to pitchdown -15° to -20° . If short in energy, for a tight turn,
bank strongly (i.e. 75° to almost 90°) and press "2" key almost continuously, watching speed vector which has not to
go down too low on the display, stay around 220 to 180 /m/s airspeed. If high in energy, delay a little the time of turn
and thks to the high trim value, make a beautiful large turn with only "moderate" banking (30 to 60°).

Avoid overshot at end of turn. S-turns in HAC are unpleasant!

When entered in HAC (12 km to 16 km from runway, 4000 to 6000 m high, reduce trim to 0.6 or 0.7, try to get PAPI
half red half white, align making slight banking corrections, use aerobraking in order to progressivly reduce airspeed
from 200 m/s down to 160 m/s @ 600m high, then proceed to flare, and disable aerobraking.

Dan's sound is very useful there.

Don't forget to gear down before 60 m high, 140 to 120 m/s airspeed, even if the Shuttle is tolerant about belly-
landing (would not be the case with Glider, try to see !).

Touchdown Hspeed has to be 90 to 100 m/s, Vspeed 0.25 m/s. This last is very difficult to check.
If several  ? m/s, you get crash sound. Ask to Dan the real value.

It seems that the quantity of tire smoke is related to Vspeed, because a soft touchdown makes very little smoke.



Good mission returns !

[SimFan]

More links about shuttle landing parameters are there, including sad Columbia mission :



http://www.caib.us/news/timeline/STS-107-GTrack-Rev15.pdf
http://www.caib.us/news/timeline/STS-107-Timeline-Rev15.xls

http://www.cbsnews.com/network/news/space/107_Entry_TimelineH.html

http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/stsref-toc.html
http://www.jsc.nasa.gov/history/mission_trans/mission_transcripts.htm


And a general link about all Shuttle missions and others :

http://groups.msn.com/SpaceCowboySaloon/abstract.msnw



Post Edited ( 11-30-04 09:18 )