STS 1:"A remarkable flying machine" My first full mission

[Thorsten]

From memory, the SPEC 50 doesn't show the graphics in OPS 1 and above 200Kft in OPS 3,

Thanks - if you find the reference, please let me know, I've been wondering about this a while ago.

TACAN, what is that?!

A thing you'll find completely useless if you have a GPS aboard...

Wow It's hard
I a managed with 3 engines, but need practice with two engines.

Yes - writing an AP capable of flying RTLS was the hardest challenge in automatic flight I've had to deal with so far.

RTLS is difficult in many ways:

- targeting of the MECO condition needs to be much more exact than for a TAL if you want to be able to land (or a contingency abort where you don't really target anyway)
- there's a huge dispersal of initial conditions ranging from lots of fuel, two good engines to less fuel, three good engines for a late abort, no payload to heavy payload,...
- there's the restriction from droop altitude and ET heating constraints
- in the late phase, the atmosphere actually already influences flight dynamics
- the target qbar at MECO is again a fairly narrow window
- the safe window during Nz holding is again pretty narrow, and you can easily get into an actuator jam condition (well, that's more of a manual restriction, for the AP it's quite doable - for a contingency entry you basically can't do it by hand any more)
- while the end-point of the Nz pullout is intuitively clear to a human pilot, formulating the set of conditions for the AP is also not so trivial

From personal experience, having the OPS 601 display helps a lot in staying in the safe corridor during powered RTLS, And GRTLS tends to be a rough affair with hard S-turns.

So if you made it without guidance display, that's quite an achievement. :thumbup:

 

[PhantomCruiser]

TACtical Air Navigation. It and ADF still have their uses I know more about both than I care to admit though.

 

[GLS]

I know what TACAN is , I was just saying SSU doesn't have that.

 

[Gingin]

So if you made it without guidance display, that's quite an achievement.

I didn't manage yet with 2 engines only.

Well,I am following some written data card, and trying to follow some guidance.
It's really tough as you said with all the different parameters, but I am addicted

With two engine, the main problem I have is not enough distance when I have to do the PPA. Propellant around 51 % ( like in unconverged data table) but too close in range.
So after all manoeuver and PPD, I end up really high over KSC ( Like 90000kft in the HAC, twice higher).

I am gonna try harder S turn maybe during GRTLS, trying to stay below 4G's It's really addicting.

By any chance, do you have some chart/graph very detailled about RTLS (or CSS RTLS), like some altitude vs range vs pitch angle. I looked in SCOM, ascent FDF, and Abort workbook, but there is nothing very exhaustive.

 

[Urwumpe]

No need to stay below 4G ... AFAIR anything up to 5.5g is considered acceptable during the alpha recovery.

 

[Thorsten]

Contingency abort workbook speculates that the Shuttle is likely to break at 4.2 g (aka, this is beyond certification already and nobody has ever tried) and contingency abort software is written to always keep you below 3.9 g and rather risk high qbar.

I don't think the Shuttle takes Nz of 5.5 g, I've never seen this number anywhere.

By any chance, do you have some chart/graph very detailled about RTLS (or CSS RTLS), like some altitude vs range vs pitch angle. I looked in SCOM, ascent FDF, and Abort workbook, but there is nothing very exhaustive.

There really isn't - it depends on too many factors - when you lost the engine, what your payload is, when you initiated RTLS,... it's not a simple targeting problem, it's a closed loop guidance problem.

Your best chance is to start with the flyout pitch from the card. Unfortunately the fly-back fuel fraction depends on your payload (the published chart seems to be for a heavy Shuttle), if you are light, even with two engines you pitch around too early with the card.

During flyback, I'd try to aim for a combination of vertical speed and altitude - allow some initial sink, aim for ~270.000 ft altitude and manage pitch to get there smoothly. Once you are at altitude, manage pitch to stay there.

MECO is a tricky combination of distance to site, qbar and altitude you have. If you are at 270.000 ft, qbar between 1 and 2 should work., It also depends on whether you do the proper ET-sep procedure or not, that costs you some extra seconds in coast and some altitude loss.

 

[Gingin]

Your best chance is to start with the flyout pitch from the card. Unfortunately the fly-back fuel fraction depends on your payload (the published chart seems to be for a heavy Shuttle), if you are light, even with two engines you pitch around too early with the card.

During flyback, I'd try to aim for a combination of vertical speed and altitude - allow some initial sink, aim for ~270.000 ft altitude and manage pitch to get there smoothly. Once you are at altitude, manage pitch to stay there.

Gonna try that, maybe gonna PPA later with a low weight Shuttle. I read max speed before PPA is around mach 7.2 and at MECO around mach 5.4.

I am gonna stay at 104% Pc even after PPA ( Cue card says Pc 100% after PPA), and modulate as you said the inbound Theta to not descend below minimum Droop Altitude and aim for 220 kft at MECO.

Then the alpha recovery, 4G max and pray

 

[Urwumpe]

I don't think the Shuttle takes Nz of 5.5 g, I've never seen this number anywhere.

I had it mixed up - it was 55 ft/s² or about 2.2 g for the alpha recovery and Nz Hold.

Design limit of the orbiter is 2.5g.

As the orbiter falls further into the atmosphere, the increasing dynamic pressure will cause more and more lift to be generated by the wings of the shuttle. This lift produces an acceleration along the Z-axis called the Nz acceleration (normal to the Z-axis). The 50° alpha is held until the Nz acceleration reaches about 1.8g (~53 ft/s2). During this period of increasing dynamic pressure, several other events are taking place. The aerosurfaces are becoming increasingly effective, so fewer RCS jet firings are required. For roll maneuvers, the RCS jets are no longer used after a q of 10 psf, while the pitch jets are turned off after 40 psf.

Because of the reduced effectiveness of the rudder at high angles of attack, RCS firings for yaw control are required down to Mach 1. After about 1.8g, the DAP begins to reduce the angle of attack to hold the target Nz. The target Nz that is calculated is usually about 2.2g.

It is shown on PASS VERT SIT 1 and 2 next to TGT Nz. The 2.2g is comfortably below the design limit of 2.5g and provides adequate normal force for the pullout maneuver. This change in angle of attack marks the transition to the Nz hold phase.

https://www.nasa.gov/centers/johnson/pdf/383447main_intact_ascent_aborts_workbook_21002.pdf

Still, considering the limitations of the module right now, less than 5.5g still qualifies as "survived the wrath of the developers".

 

[Thorsten]

So after all manoeuver and PPD, I end up really high over KSC ( Like 90000kft in the HAC, twice higher).

I don't know how much you've tried already, but...

... changing the runway direction and TAEM pattern can give you an extra 30 miles if the geometry works out if you come with too much energy - worth trying

... if you come with way too much energy, you can try a fish-hook pattern. Aim some 20 miles laterally away from the landing site, fly past the site in a shallow turn, steadily increase turn angle till you're again pointed at the site - if done well, you can enter a normal TAEM pattern, just from the nearly opposite direction and you don't log nearly has hard g-load as you'd need when trying S-turns.

This doesn't seem to be an official procedure, but I found it very useful for the Bermuda abort landing after a GREEN contingency scenario where you have a really hard time with the range.

 

[Wolf]

Gingin, it looks like you are one of the very few who are actually using SSU, or at least the only one posting something about running a full mission. Would it be possible to release a tutorial where you explain how you flew your STS mission (and if that is not asking too much also how do you simulate an RTLS). A very simple checklist covering step by step procedures for OPS-1, 2 and 3 could do the job. That would be very kind of you :thumbup:
Thanks

 

[Gingin]

Thanks for the advice Thorsten, I am almost there. I managed to land safely back couple of times without exceeding 5G during Alpha recovery. I should use my warthog stick instead of Keyboard, hard to do a constant Nz phase

I am aiming to really not to go over 4 G, and to be back on path on Entry traj 5 around 150kft.

Wolf: For the RTLS sure, I will do a separate post with Pictures and some explanations in the evening or tomorrow, when I will be happy enough with my performance.

For the Checklist why not I am gonna think to it and see how I can do something not too long.

---------- Post added at 04:42 PM ---------- Previous post was at 04:12 PM ----------

Do you know if there is a MFD like the map MFD but with Nm instead of Km?

 

[Thorsten]

I am aiming to really not to go over 4 G, and to be back on path on Entry traj 5 around 150kft.

I'm actually not sure that's what you should be aiming at - GRTLS never goes into the late entry phase procedurally, and in reality the flight software is different. The alpha hold phase (if you have a pronounced one during RTLS) is not really similar to the late entry - you get sizeable phugoid oscillations for instance.

And yeah, keyboard sucks for pulling a constant Nz...

Do you know if there is a MFD like the map MFD but with Nm instead of Km?

The PFD should show distance to landing site (both in MM 602 and MM 304/305) in NM if that's what you need.

@Wolf:

A very simple checklist covering step by step procedures for OPS-1, 2 and 3 could do the job.

Manual RTLS (especially without guidance!) is pure piloting. You can outline the rough steps of what you need to do, but you can't really learn it step by step, you need to do it. The vehicle characteristics changes dramatically - initially you hardly have any excess thrust, towards the end even two good engines can deliver you nearly 3 g, and how agressively you need to steer very much depends on where and when you are. You need to develop a feel for your ride.

You can't learn that kind of thing by watching a video or reading a tutorial.

You'll get it wrong the first dozen times but eventually you'll learn.

 

[Gingin]

You'll get it wrong the first dozen times but eventually you'll learn.

I can't disagree :lol:

Yep for the distance in MM304/05, problem is I don't switch to OPS 3 until MECO, until then I would like to have distance in Nm from KSC.
I converted the distance in km, so it's pretty much ok with map MFD.

 

[Wolf]

Thanks for the advice Thorsten, I am almost there. I managed to land safely back couple of times without exceeding 5G during Alpha recovery. I should use my warthog stick instead of Keyboard, hard to do a constant Nz phase

I am aiming to really not to go over 4 G, and to be back on path on Entry traj 5 around 150kft.

Wolf: For the RTLS sure, I will do a separate post with Pictures and some explanations in the evening or tomorrow, when I will be happy enough with my performance.

For the Checklist why not I am gonna think to it and see how I can do something not too long.

---------- Post added at 04:42 PM ---------- Previous post was at 04:12 PM ----------

Do you know if there is a MFD like the map MFD but with Nm instead of Km?

Thanks a lot, some kind of tutorial would be very helpful: rerally looking forward to it.
About your question GPCMFD shows your range in NM but it is a Shuttle Fleet "custom made" MFD though OPS3 and OPS4 will work with any Orbiter ship (including SSU I believe)

 

[Gingin]

Ok, thanks

One very good thing to read to start understand GPC and OPS mechanic is this one:


https://www.nasa.gov/centers/johnson/pdf/383444main_crew_software_interface_21002.pdf

And you can complete with the full dictionnary, and you look on OPS 1, 2 or 3 for the meaning of each screen

https://www.nasa.gov/centers/johnson/pdf/359895main_DPS_G_K_7.pdf

 

[Thorsten]

Yep for the distance in MM304/05, problem is I don't switch to OPS 3 until MECO, until then I would like to have distance in Nm from KSC.

That... um... makes totally sense. Seems I was confused - you primarily need the distance during powered flight of course.

I'm so used to having OPS 6 software and displays available around for flying aborts that I have a hard time picturing how it would work otherwise, sorry.

I hope you'll find my comments helpful anyway - I much appreciate your spirit of taking the piloting challenge and just try. I must have done a dozen RTLS aborts under CSS to understand the basic mechanics of it (crashing the majority of them), then half a dozen to record trajectory data and then two dozen more fine-tuning the AP to get somewhere useful, and I remember the feeling of taking the challenge and just trying to fly it by the seat of your pants.

If you ever get the urge to try the procedure as outlined in the aborts workbooks (OPS 601 displays and flight software, interconnected fuel dumps, automatic MPS propellant dump after RTLS MECO, 601 guidance symbology and 'fly-to' needles on the PFD, contingency abort region determination for engine loss during RTLS, tight limit checks on qbar and Nz...) you're cordially invited to take a look over here - alas, I can't offer you anything more helpful for SSU (or Orbiter) than tips from my flight experiences.

But you seem to be doing fine :thumbup:

 

[Gingin]

I hope you'll find my comments helpful anyway

Of course
It helped a lot, I was confusing a bit with after MECO phase, your comments were helpfull.

I much appreciate your spirit of taking the piloting challenge and just try

I am like a armchair test pilot :lol:
I like that kind of challenge. Like you I made dozen to begin to be comfortable, and I have dozen and dozen to do again ahah

Thanks for the link, I am gonna give it a very serious look

 

[ItaLiaNKiinG]

This is not a tutorial, a tutorial will have every step in it.. this only has starting steps

 

[garyw]

Where in this thread does it say that this is a tutorial?

 

[Gingin]

This is not a tutorial, a tutorial will have every step in it.. this only has starting steps

Indeed, it's not a tutorial.
But its show that we can do some really nice stuff,very realistic with SSU.
And I just covered 10% of full capability ( RMS, Rendez vous etc)
I am working on a tutorial, but it takes time, hard to sum up the essential parts of hundreds/thousands of pages