Contigency abort 2EO Green, Let's go to Bermuda

[Gingin]

Hello everybody,


I am still working on Abort Procedure, and I wanted to try a contigency one, the 2 EO Green abort to Bermdua
A link to Contigency abort workbook, very interesting reading. https://www.nasa.gov/centers/johnson/pdf/383441main_contingency_aborts_21007_31007.pdf

Contigency abort are the one dealing with multiple SSME failure.
It was created after Challenger disaster.
Before, if a 2 engine failure occured before 12000 ft/sec ( Single engine OPS 3) or a 3 engine before 18000 ft/sec ( Low energy TAL), both crew and shuttle would have certainly vanished.

Those aborts allow the shuttle to handle a tough re entry, in almost all phase of powered flight, even RTLS ( with still some black/lethel area). Aim is to stay below max structural limitations( EAS 470kt , G=4,2) and do a bailout once below 100 kfeet, or eventually proceed to BDA or ECAL landing site if in the right window.



Sum up of 2 EO color code

Between SRB separation and 12000ft/sec, we are in Green abort, we might try to reach Bermuda ( or ECAL for higher inclinaison)

Contigency procedure flight data files ( exept RTLS one)

Let's rock.
STS 3 scenario, 40° targeted inclinaison, we are good for a Bermuda Abort in case of dual failure late in the Green area.


Lift off, always eyes candy

Before SRB sep, we are in 2EO Blue

SRB Sep, we go to 2EO Green, a bit less dangerous in case of dual engine failure

I will put the double failure around 11400ft/sec.
Image below is STS 125 FDF for Powered bermuda Abort, it says than below 11400ft/sec, probabilies to finish in bailout are high, so let's give us a chance at least :lol:

Let's go, let's cut two engine :hello:

Just one engine is remaining. Vertical velocity is low.
Aim now is to pitch up around 90 ° to decrease the vertical deceleration.
In the mean time, we gonna yaw by 45° towards Bermuda ( Control Yaw Steering) and Roll To Heads Up if it's not down ( I did it just before the failure, very hard to roll with SERC)

We can notice also that Single Engine Roll Control is activated ( SERC On). It allows the RCS to wake up and help for attitude control.

Everything's gonna happen fast now.
We are quickly going down into atmosphere nightmare.
When KEAS increase above 4 kts, we have to start ET fast separation before we reach high density ( which would lead to....explosion of ET)

Normally, for a 2 EO Green, it's done by having a 3°/s pitch down and fast ET separation ( around 5 sec)

It's done, good.
Now we are diving at 2000ft/sec like a rocket into atmosphere.
Entry gonna be brutal and quick, we gonna have to handle carefully the shuttle to stay within max operationnal limits

First phase , Alpha recovery, we maintain a high angle of attack and a 20° bank roll towards Bermuda ( Delta azimuth is above 20°, quite offset)

2nd phase, Nz hold. We gonna have to hold a constant charge factor to stay within limitations.
We will have to calculate that manually, hopefully, NASA is here to help us.

At 1G, we take the vertical speed, we divide it by 1000 and add 0,65.
Gotcha, we will have to hold Nz=3,1G

Here we are, charge factor is increasing. At Nz=3,1G, I gently push on the stick and don't allow Nz to go to high ( I stayed below 3,5G) In the mean time, EAS doesn't have to excess 470 kts
Basically, if Nz increase, EAS decrease and vice versa. So it's a bit tricky, but doable ( well in real life, I wouldn't bet on manual flying those stuff )

 

[Gingin]

Burning like hell

We are now in a much more comfy zone. EAS didn't excess 400 kt and Nz stayed below 4G's.
Vertical velocity is increasing a lot now, we have to limit phugoid oscillation to not go high on path)

Third phase, Alpha transition
We will have to adjust angle of attack vs Mach, manage our drag with roll reversal and keep an eye on our lateral offset.
We are back to a " normal " late entry path (Normally Ops 603, almost the same visually)

Let's go for some roll reversal, we are becoming a bit high, time to catch higher density layer and increase our drag.

Bermuda, finally !!

HAC in sight

Almost there

In the HAC, looking good

Last turn, Cabien crew take your seat for landing :lol::lol:

Short final, preflare is coming next

Gear down and locked ( I hope)

Touch, wow it was tough

To allow approach/ground logic system to be in ground mode, a little trick to be sure to be in ground mode was to go in manual SEParation and press SRB SEParation after nose gear touchdown.
Weight on Wheels ( WOW) and Weight on nose wheels (WONG) were then manually selected to prevent a failure of the automatic discrete system.

When in ground mode logic, a G (ground) appears in the HUD next to the speed

Complete stop, let's go to beach

I love to test abort. And as usual, we can do some very good stuff, close to real with SSU ( even if there is no OPS 6 simulated)
Very nice and entertaining.

Next time, single engine TAL abort or single engine OPS 3 to test minimum droop altitude :lol:

 

[Donamy]

How are you going to get it back to the cape ?

 

[Gingin]

How are you going to get it back to the cape ?

Ahah :rofl:

:hmm: Maybe we can ask to Fedex or DHL for special delivery?

 

[Thorsten]

Heh - how many tries did you need before you made Bermuda? It's quite impressive to see you landing there!

Burning like hell

Okay, I don't get that one. You're not very fast during the Nz pullout, the thermal stress should be less than for an RTLS (the faster you go, the milder the pullout, and you have a fairly hard pullout) and the RTLS is the recommended abort mode if you fear issues with the TPS. You should not be seeing much heating.

Here we are, charge factor is increasing. At Nz=3,1G, I gently pull on the stick and don't allow Nz to go to high

Unless you mean 'push' here, the sentence makes no sense. The problem is that for given AoA Nz is going to sky-rocket as density increases, so to compensate for the density increase, you need to decrease AoA and hence push on the stick.

What's the plume seen here?

 

[Gingin]

Hey Thorsten, thank you for your comment

nless you mean 'push' here, the sentence makes no sense.

Yes, push I meant, typo mistake I m gonna correct that one :thumbup:


I made 4 or 5 tries, especially for Nz hold ( I wanted to do something quite realistic concerning G's and speed) I restarted 2 or 3 times when i exceeded 4,5 or 500 kts becauseI didn't push enough on the stick. ( handlng is really not comfy, even with a warthog aha )


For the burning, your sentence make a lot of sense yeah.
It's I think just the visual effect, even if temperature is less high in This abort.
But the angle of reentry is guite high for Contigency, I mean diving at mach 11 and more than 2000 ft/sec, it's gonna be high thermal stress for for a very short period compared to a TAL or normal entry.
I mean for this contigency abort, it was very quick the burn compared to RTLS or Normal. I am gonna check the minimum temperature to have some orange/red tiles.

I think the problem with TPS was to have a very long time exposed to thermal constraint ( like a TAL abort), for that a RTLS was prefered in case of problem with TPS maybe.


The plumes one the last one where just after engine failure, don't really know what is it ( it's not dump for sure)
Maybe some LOX which goes trough nozzle before main valve closes :shrug:

 

[Thorsten]

Maybe it's the angle of reentry, which is guite high for Contigency, I mean diving at mach 11 and more than 2000 ft/sec, it's gonna be high thermal stress for for a very short period compared to a TAL or normal entry.

Not sure how SSU computes entry temperatures.

The usual observation is that max. heat precedes max. force, because heating goes with the third power of the velocity and force with the second power and both go linear with the density.

Of course for the right density you can generate a lot of heat even at Mach 11, but at that density you should have plenty of aerodynamic lift already AND you'd get a terrific drag force - of course during an Nz you get quite a bit below equilibrium glide, but then again Mach 11 to the third is quite a bit less than Mach 24 to the third power...

Okay, that's hand-waving.

In my project, I have implemented a heating model based on the main physics scaling laws which I've tried to fit to actual data on temperatures from Columbia and the SR-71 (Mach 3 at 82.000 ft). I'm producing plasma in the altitude region where the documentation says communication is out. And I've never seen this go into the high temperature region where TPS glows a lot and the plasma tail is triggered during any RTLS or contingency entry I've ever flown (and since I have an AP that can do it, I've seen quite a few of these in outside view).

Doesn't mean it's right how I'm doing it, I was just wondering because I had flagged Nz mentally as a relatively 'cold' entry.

 

[Gingin]

Very interesting thought :thumbup:

I remember I read somewhere something very interesting about thermal constraint during different type of re entry, effect of length and angle of re entry etc with some very surprising results which blown my mind.
I have to find where :facepalm:

The thing is ( it's just some observations), for RTLS and Contigency I made, I observed that we are at the beggining ( before Nz hold) high above equilibrium glide and higher than max constraint line on OPS3 ( which is quite correct as we are certainly going to exceed 2,5G /330 KEAS normal Operations limit to recover the path)

During NZ hold, we dive fast to recover a normal path.
For me, it makes sense that during Nz hold, for like 20 30 seconds, the stress and heat is really high, as we are much closer to the base for the Mach/altitude data we are supposed to have on a normal profil.

I noticed that I am always going back on path on entry traj 4 ( end) by far above, quite like a vertical line ( at least much steeper than reference drag lines).

max. heat precedes max. force

Yeap, after max heat of Nz hold, Vertical speed was increasing like due to the lift force increasing a lot.

I had flagged Nz mentally as a relatively 'cold' entry

Me too
But I think it's " cold" on the total length, with a high short peak of constraint during 30 sec of Nz hold, and then back to normal during Alpha transition.

In my head, it's like if we don't let the time to the shuttle to loose calmy energy( speed) in lower density layer and we force her to go directly in high density layer with higher speed than normal ( very short timewise).

I mean I went from altitude 220kft to 120 kt in one minute, which would take several normally :lol:

Maybe a very short plasma was observed :shrug:

 

[GLS]

What's the plume seen here?

That's the SSMEs shutting down.

Not sure how SSU computes entry temperatures.

Hmmm... we don't.:lol: The plasma trail is "Orbiter supplied". The one thing we do is to decide when and how much to show the tile glow... can. of. worms.

 

[Thorsten]

I remember I read somewhere something very interesting about thermal constraint during different type of re entry, effect of length and angle of re entry etc with some very surprising results which blown my mind.

If you manage to find, please let me know. My main resource for entry heating dynamics has been a space engineering primer on the topic which introduces a couple of empirical models (albeit for ballistic entries) and my own attempts to fit data, and I'm not too happy with that.

Conceptually, a long entry is cooler than a short one - you always have the same amount of kinetic energy to dissipate - if you have a low heating rate and a long trajectory, you have more time to radiate off whatever reaches your spacecraft and isn't carried by the shockwave, if you have a fast entry the temperature needs to be higher to reach radiative equilibrium.

For me, it makes sense that during Nz hold, for like 20 30 seconds, the stress and heat is really high, as we are much closer to the base for the Mach/altitude data we are supposed to have on a normal profil.

Thing is, stress can be really high without heat being high. During launch, qbar peaks at 650 psf or so - that's twice as high than during peak entry stress and above what the actuators could control. But the TPS doesn't glow.

Anyway, I guess we can settle on we don't really know, and since nobody has tried a contingency green for real there's not much real data on it.

Before this gets lost in technicalities - please let me say again that I think manually flying a contingency abort is an extremely impressive feat, and adding a safe Bermuda landing just makes it a notch better. :thumbup:

That's the SSMEs shutting down.

Ah, interesting. I didn't know they do that - what is it we're seeing, just leftover LOX venting?

 

[Gingin]

If you manage to find, please let me know. My main resource for entry heating dynamics has been a space engineering primer on the topic which introduces a couple of empirical models (albeit for ballistic entries) and my own attempts to fit data, and I'm not too happy with that.

Conceptually, a long entry is cooler than a short one - you always have the same amount of kinetic energy to dissipate - if you have a low heating rate and a long trajectory, you have more time to radiate off whatever reaches your spacecraft and isn't carried by the shockwave, if you have a fast entry the temperature needs to be higher to reach radiative equilibrium.

Yes, sure I ll let u know.

It was saying also that for TPS problem before negative return, the RTLS was prefered for the reason you stated, it was apparently safer to have shorter entry (even with higher temp). Maybe even with less heat but longer heat exposure of TAL, it would have been more stressfull for Tiles and it would have eventually collapsed regarding time of exposure ( ??)

Thing is, stress can be really high without heat being high. During launch, qbar peaks at 650 psf or so - that's twice as high than during peak entry stress and above what the actuators could control. But the TPS doesn't glow

Make lot of sense

240 kft, Mach 12
120kft, Mach 9
Time between less than a minute
Maybe somewhere during this transition, Mach is really high for altitude density and Tiles glow shortly ( as you mentionned, higher temp to reach radiative equilibrium) :idk:

Anyway, I guess we can settle on we don't really know, and since nobody has tried a contingency green for real there's not much real data on it.

Before this gets lost in technicalities - please let me say again that I think manually flying a contingency abort is an extremely impressive feat, and adding a safe Bermuda landing just makes it a notch better

Let's call NASA and book a sim session to find out ahah Would be amazing
Thanks for the comment

 

[GLS]

Ah, interesting. I didn't know they do that - what is it we're seeing, just leftover LOX venting?

It's just the thrust tailoff, so that image was taken within 6s of the shutdown command.

 

[Wolf]

Gingin, how did you perform the emergency ET SEP? I tried the scenario and after MECO I selected the ET SEP switch to MAN, then depressed the ET SEP button (after uncaging it) but nothing happens, the ET stays mated with the SHuttle.
I noticed in the pic you posted that you depressed the SRB SEP button (?) and left the ET SEP switch to AUTO... is this a trick to get ET SEP immediately?

 

[GLS]

Gingin, how did you perform the emergency ET SEP? I tried the scenario and after MECO I selected the ET SEP switch to MAN, then depressed the ET SEP button (after uncaging it) but nothing happens, the ET stays mated with the SHuttle.
I noticed in the pic you posted that you depressed the SRB SEP button (?) and left the ET SEP switch to AUTO... is this a trick to get ET SEP immediately?

I don't remember the details but (currently) the ET SEP buttons only work to override an inhibited separation. I'm 99% sure I didn't implement the fast ET sep procedure yet.
The SRB SEP switches would also only override an inhibited separation, but that was "made impossible" in the 90s.
As for manually setting WOW and WONG on landing, I can't remember if it is implemented, but it shouldn't be needed.

 

[Wolf]

I don't remember the details but (currently) the ET SEP buttons only work to override an inhibited separation. I'm 99% sure I didn't implement the fast ET sep procedure yet.

So that means we have to wait a nominal ET SEP after MECO (8 seconds according to the books)?

 

[Thorsten]

Won't trouble you because the contingency procedure forsees a mated coast phase as well - you never blow the ET a second after MECO.

 

[Gingin]

I think i shuted down the third engine the initiate the et separation, which take like a normal one around 20 sec

 

[Wolf]

Ok. I took the challenge and after a few failed attempts I manged to land at BDA (with a g exceedance of 4.5 for a few seconds, so I probably in real life I would have f...ed the reentry).

Two things to report as I did further attempts:

1) at a certain point around Mach 5 and with all parameters within limits (g, KEAS, attitude, etc.) while I am banking for an S-Turn to the right the elevons go to full opposite deflection (to the left) despite my joystick inputs stays full right. I then loose control and the shuttle keeps rolling to the left (the full left deflections is also confirmed on the SPI display). This very unfortunate event caused me the loss of at least 3 Orbiters

2) In one case after at the beginning of the Nz Hold phase I was curious to see what the DAP would do and engaged AUTO P and R. Well I am sure it was pure luck but the autoflight system brought me all the way down to Bermuda in one piece (with the exception of a peak acceleration of 6g's) but man, that was something! Congrats to the SSU team :thumbup:

---------- Post added at 06:27 PM ---------- Previous post was at 06:15 PM ----------

Won't trouble you because the contingency procedure forsees a mated coast phase as well - you never blow the ET a second after MECO.

Well that is not what the manual says (Contingency Aborts 21007/31007) at page 25: for the 2EOUT C.A. case they talk about FAST ET sep which occurs 5 seconds after MECO is commanded (or 1 sec after SSME shutdown) so that means no mated coast at all.
Maybe FAST Sep was not always the procedure to follow and in some case they would perfom a manual SEP at a later stage..

 

[GLS]

So that means we have to wait a nominal ET SEP after MECO (8 seconds according to the books)?

I'd have to look at the code to be sure, but I think so.

 

[Gingin]

Nice Wolf dis u enjoy it ?

The entry autopilot is really well tuned but as U see for those kind of abort its better to do it in manual to avoid over g

For the loss of control it happened to me also