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#3680
by
Gingin
on 18 Aug, 2020 10:05
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#3681
by
Albert Lapatin
on 18 Aug, 2020 17:53
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can someone explain to me what it is PREBANK
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#3682
by
Gingin
on 20 Aug, 2020 17:12
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can someone explain to me what it is PREBANK
It is usually used for underburn during deorbit or during Abort Once Around .
It is associated in general with propellant failure, or limited DeltaV for those burns.
By Banking the Orbiter before the Entry Interface , vertical component of the lift vector will be decreased slighlty.
It will then cause a steeper entry trajectory early on.
Steeper entry angle = increased drag = Delta V dissipated faster, helping to recover from a shallow entry angle.
Prebank value will depend by how far is the current perigee after deorbit burn compared to the forecasted one.
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#3683
by
Albert Lapatin
on 25 Aug, 2020 10:15
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can someone explain to me what it is PREBANK
It is usually used for underburn during deorbit or during Abort Once Around .
It is associated in general with propellant failure, or limited DeltaV for those burns.
By Banking the Orbiter before the Entry Interface , vertical component of the lift vector will be decreased slighlty.
It will then cause a steeper entry trajectory early on.
Steeper entry angle = increased drag = Delta V dissipated faster, helping to recover from a shallow entry angle.
Prebank value will depend by how far is the current perigee after deorbit burn compared to the forecasted one.
thanks for the good answer
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#3684
by
Albert Lapatin
on 25 Aug, 2020 11:20
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for Mark Kirkman
very impressive video
what does H-double dot mean?
how astronauts use H-double dot when performing manual control?
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#3685
by
DaveS
on 25 Aug, 2020 11:36
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for Mark Kirkman
very impressive video
what does H-double dot mean?
how astronauts use H-double dot when performing manual control?
It's just HDOT or Height Delta Over Time, AKA vertical velocity. In normal aviation terms it would climb rate/sink rate.
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#3686
by
Proponent
on 25 Aug, 2020 12:47
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for Mark Kirkman
very impressive video
what does H-double dot mean?
how astronauts use H-double dot when performing manual control?
It's just HDOT or Height Delta Over Time, AKA vertical velocity. In normal aviation terms it would climb rate/sink rate.
Surely H-
double-dot is the rate of change of vertical velocity, i.e., the vertical acceleration?
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#3687
by
Albert Lapatin
on 25 Aug, 2020 16:26
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It's just HDOT or Height Delta Over Time, AKA vertical velocity. In normal aviation terms it would climb rate/sink rate.
I wanted to know about H-double-dot
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#3688
by
Fequalsma
on 25 Aug, 2020 18:09
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While "DOT" makes a nice backronym, it is simply engineering shorthand notation for the time derivative of a quantity, d(...)/dt. So Hdot = dH/dt, and H-double-dot = d(dH/dt)/dt.
F = mdv/dt = md(dx/dt)/dt
Source: my engineering degree(s)
It's just HDOT or Height Delta Over Time, AKA vertical velocity. In normal aviation terms it would climb rate/sink rate.
I wanted to know about H-double-dot
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#3689
by
mkirk
on 25 Aug, 2020 19:41
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for Mark Kirkman
very impressive video
what does H-double dot mean?
how astronauts use H-double dot when performing manual control?
H double dot is altitude acceleration
H dot is altitude rate (analogous to rate of climb or descent in an airplane)
H double dot is a very valuable tool for flying a manual entry.
Background:
For a Space Shuttle entry, range to the landing site is controlled by managing drag. You manage drag by controlling altitude. You control altitude by adjusting roll.
For example; if you are high energy and need to slow down so you don’t go zipping by the runway at the landing site; you obviously want to increase your current drag in order to reduce your high total energy condition.
Where can you find more drag?
Well, right below you in the thicker part of the atmosphere.
If you roll the orbiter, the vertical component of lift is reduced and the orbiter begins to descend (fall) faster into the thicker part of the atmosphere.
This is somewhat counter intuitive from a piloting point of view because in a traditional airplane you manage altitude by pitching up or down. Unfortunately, the shuttle had a very small alpha (angle of attack) envelope during entry of only +/- 3 degrees. If you exceeded that alpha it would result in loss of control and you’d “burn the wings off”.
The amount of roll needed to achieve the desire descent rate (H dot) to get you to the desire drag - was provided by the GPC (general purpose computer) displays. If that wasn’t available or couldn’t be trusted, the astronauts could do a little math in public and use the formula Hdot Desired = Hdot + 20 * (Drag current - Drag desired)......sounds like a great job for the Flight Engineer (MS2).
H double dot provided a means for the pilot to evaluate the amount of roll being used. An H double dot of close to zero meant you had a stable H dot.
All of the above is an overly simplistic explanation, but it hopefully gives you a little insight.
Mark Kirkman
“NASA Space Shuttle Hugger”
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#3690
by
Gingin
on 25 Aug, 2020 20:12
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for Mark Kirkman
very impressive video
what does H-double dot mean?
how astronauts use H-double dot when performing manual control?
If you have a L 2 subscription, you can have a look to the Entry TAEM, Approach Landing Guidance Workbook to have even more informations.
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#3691
by
wolfpack
on 26 Aug, 2020 00:32
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So if you are controlling H dot with roll angle, are you applying counter yaw to keep the ground track "straight" or are you allowing the Orbiter to turn and then counter-rolling later to get back on track?
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#3692
by
mkirk
on 26 Aug, 2020 06:25
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So if you are controlling H dot with roll angle, are you applying counter yaw to keep the ground track "straight" or are you allowing the Orbiter to turn and then counter-rolling later to get back on track?
When you use bank angle to control descent rate, the nose of the orbiter starts to track away from the intended landing site. We let this “DELAZ” (delta azimuth) - defined as the angle between the landing site and the direction of the orbiter’s nose - build up to between 10.5 degrees and 17.5 degrees.
After the DELAZ gets to those values, you then reverse the orbiter’s bank angle (i.e. a roll reversal) to the opposite direction. Doing this allows the orbiter’s nose to track back in the opposite direction until it again gets to 10.5 to 17.5 degrees of DELAZ. Although you don’t point the orbiter directly at the landing site (DELAZ of zero), you keep it within a manageable tolerance of 17.5 degrees for most of the entry.
This entire process of roll reversals is referred to as cross range control.
Mark Kirkman
“NASA Space Shuttle Hugger”
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#3693
by
Albert Lapatin
on 26 Aug, 2020 06:43
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for Mark Kirkman
very impressive video
what does H-double dot mean?
how astronauts use H-double dot when performing manual control?
If you have a L 2 subscription, you can have a look to the Entry TAEM, Approach Landing Guidance Workbook to have even more informations.
Yes, I have Entry TAEM, Approach Landing Guidance Workbook, but I do not understand many points because I have to translate into my own language.
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#3694
by
Albert Lapatin
on 26 Aug, 2020 08:11
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for Mark Kirkman
H double dot is altitude acceleration
H dot is altitude rate (analogous to rate of climb or descent in an airplane)
H double dot is a very valuable tool for flying a manual entry.
Background:
For a Space Shuttle entry, range to the landing site is controlled by managing drag. You manage drag by controlling altitude. You control altitude by adjusting roll.
For example; if you are high energy and need to slow down so you don’t go zipping by the runway at the landing site; you obviously want to increase your current drag in order to reduce your high total energy condition.
Where can you find more drag?
Well, right below you in the thicker part of the atmosphere.
If you roll the orbiter, the vertical component of lift is reduced and the orbiter begins to descend (fall) faster into the thicker part of the atmosphere.
This is somewhat counter intuitive from a piloting point of view because in a traditional airplane you manage altitude by pitching up or down. Unfortunately, the shuttle had a very small alpha (angle of attack) envelope during entry of only +/- 3 degrees. If you exceeded that alpha it would result in loss of control and you’d “burn the wings off”.
The amount of roll needed to achieve the desire descent rate (H dot) to get you to the desire drag - was provided by the GPC (general purpose computer) displays. If that wasn’t available or couldn’t be trusted, the astronauts could do a little math in public and use the formula Hdot Desired = Hdot + 20 * (Drag current - Drag desired)......sounds like a great job for the Flight Engineer (MS2).
H double dot provided a means for the pilot to evaluate the amount of roll being used. An H double dot of close to zero meant you had a stable H dot.
All of the above is an overly simplistic explanation, but it hopefully gives you a little insight.
Mark Kirkman
“NASA Space Shuttle Hugger”
Mark thanks for your answer.
The ENTRY TRAJ has a Phugoid scale.
Is this scale used for manual control?
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#3695
by
mkirk
on 29 Aug, 2020 01:07
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Mark thanks for your answer.
The ENTRY TRAJ has a Phugoid scale.
Is this scale used for manual control?
It helped provide situational awareness on how auto guidance was doing, but it also could be used as a “fly to” indicator during manual control of the orbiter during entry. It would start flashing, and the needle would deflect, to signal to the crew when a roll reversal was needed.
Mark Kirkman
“NASA Space Shuttle Hugger”
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#3696
by
Albert Lapatin
on 31 Aug, 2020 14:08
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After the DELAZ gets to those values, you then reverse the orbiter’s bank angle (i.e. a roll reversal) to the opposite direction. Doing this allows the orbiter’s nose to track back in the opposite direction until it again gets to 10.5 to 17.5 degrees of DELAZ. Although you don’t point the orbiter directly at the landing site (DELAZ of zero), you keep it within a manageable tolerance of 17.5 degrees for most of the entry.
This entire process of roll reversals is referred to as cross range control.
Mark Kirkman
“NASA Space Shuttle
Hugger”
I've heard two versions of what roll reversals look like.
1.This is a roll around the X axis
2. This is yaw turn around the velocity vector.
3. What does it look like in reality?
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#3697
by
mkirk
on 31 Aug, 2020 17:12
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After the DELAZ gets to those values, you then reverse the orbiter’s bank angle (i.e. a roll reversal) to the opposite direction. Doing this allows the orbiter’s nose to track back in the opposite direction until it again gets to 10.5 to 17.5 degrees of DELAZ. Although you don’t point the orbiter directly at the landing site (DELAZ of zero), you keep it within a manageable tolerance of 17.5 degrees for most of the entry.
This entire process of roll reversals is referred to as cross range control.
Mark Kirkman
“NASA Space Shuttle
Hugger”
I've heard two versions of what roll reversals look like.
1.This is a roll around the X axis
2. This is yaw turn around the velocity vector.
3. What does it look like in reality?
The roll reversals are rolls around the velocity vector. Because of the orbiter’s very high angle of attack (40 degrees for most of the entry until below Mach 10), this roll maneuver is actually a body axis yaw.
If viewed externally, it would look like the orbiter is yawing from side to side.
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#3698
by
Albert Lapatin
on 31 Aug, 2020 20:02
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After the DELAZ gets to those values, you then reverse the orbiter’s bank angle (i.e. a roll reversal) to the opposite direction. Doing this allows the orbiter’s nose to track back in the opposite direction until it again gets to 10.5 to 17.5 degrees of DELAZ. Although you don’t point the orbiter directly at the landing site (DELAZ of zero), you keep it within a manageable tolerance of 17.5 degrees for most of the entry.
This entire process of roll reversals is referred to as cross range control.
Mark Kirkman
“NASA Space Shuttle
Hugger”
The roll reversals are rolls around the velocity vector. Because of the orbiter’s very high angle of attack (40 degrees for most of the entry until below Mach 10), this roll maneuver is actually a body axis yaw.
If viewed externally, it would look like the orbiter is yawing from side to side.
Thanks Mark.
The "Shuttle Crew Operations Manual" mentions additional displays called "Bearing Displays - SPEC 54".
Нave they been used on at least one Shuttle flight?
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#3699
by
Proponent
on 01 Sep, 2020 14:15
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Dumb question: what prevented the Shuttle's SRB's from filling with water and sinking after ocean impact? Were balloons used?
