Shuttle Q&A Part 5

[mkirk]

Mark: thanks for the answer. It was something that had been on my mind on and off again for a few years. In my mind up until now was that the "north" that the MCC PAO stated was in relation to the orbiter coordinate system where "north" was +X.

Another DPS question: Did MM104 OMS-1 MNVR EXEC take in account the additional dV of the MPS propellant dump when calculating the dV targets?

Yes, but not directly in the OMS 1 Targets, but in how the orbiter achieved the desired Targets.

The OMS 1 Burn was conducted using a “closed loop” guidance scheme known as PEG 4 (powered explicit guidance).  PEG 4 was trying to achieve specific vertical and horizontal velocity changes (Delta V) over a certain point above the earth.  Closed loop guidance meant the orbiter knew where it was at the start of the burn (state vector at the time of ignition) and where it wanted to be (state vector at the end of the burn).  During the burn, sensed accelerations (i.e. IMU data) were used to update the current state vector - this was then compared to the desired OMS cutoff conditions.

On a “Standard Insertion”  mission like STS-1, the “Automatic” MPS Dump started at OMS 1 Ignition.  If I recall correctly, the Dump contributed about 10 to 11 feet per second of Delta V. 
Btw, the rule of thumb was that 2 fps of Delta V contributed 1 nautical mile to the Perigee Altitude (Hp).

So, if the Dump occurred as planned during the OMS 1 Burn, the continuously updated OMS cutoff conditions needed to achieve the desired target conditions, would occur slightly earlier than if the Dump was not taking place.



(Someone like Jorge - if he still lurks within these threads - would probably be able to give you a much better explanation.)


Mark Kirkman
“NASA Space Shuttle Hugger”

[John2375]

Thanks, Mark -  I understand what you’re saying and it especially makes sense when determining runway 17 vs 23, for example. And I know sometimes at KSC they’d accept  a little tailwind component so the sun angle wasn’t a factor.
I was just curious about my example of STS-36: runway 23 vs 22- the winds component would be similar, sun angle as well, and the previous flight STS-32 used 22.

Also- STS-37 had some issues with the upper level winds not being as forecast on the HAC. Eileen  Collins writes in her book that STS-63 had stronger winds on the HAC than they excepted.. we’re there any other flights you know of that had to do some good piloting to get the orbiter to the runway?!

[John2375]

https://www.americaspace.com/2021/01/03/stopping-the-shuttle-remembering-the-drag-chute-30-years-on/

First paragraph.. references a landing that “almost bounced…” ? Any idea which flight that refers to?

[penguin44]

Either the final landing test of Enterprise or sts-3 perhaps

[John2375]

most likely- and certainly STS-51D for the seized brakes/blown tire (why didn’t the orbiter have nose wheel steering from the get-go?

STS-91 kind of bounced, not hard but there are 2 distinct main gear  touchdowns ..

[Nicolas PILLET]

I've seen this replica in storage in Steven F. Udvar-Hazy Center two months ago. Someone knows from which display model it comes ?

[AS_501]

I'm curious about one aspect of the radiators inside the payload bay doors.  When the orbiter was flying on its own (i.e. not docked to Mir or ISS), was the payload bay oriented away from the Sun as often as possible to minimize Solar heating of the radiators?  When the bay was facing the Sun, did the radiators lose some of their cooling efficiency?  I'm not well versed in the underlying physics of the radiators.
Thx

[Jorge]

I'm curious about one aspect of the radiators inside the payload bay doors.  When the orbiter was flying on its own (i.e. not docked to Mir or ISS), was the payload bay oriented away from the Sun as often as possible to minimize Solar heating of the radiators?  When the bay was facing the Sun, did the radiators lose some of their cooling efficiency?  I'm not well versed in the underlying physics of the radiators.
Thx

The TL; DR answer is that soon after the start of the program the "free-flight" attitude standardized on payload bay toward Earth with one wing pointed at the velocity vector. Later in the program the standard was payload bay to Earth, tail to velocity vector.

Long answer: It was a balance between thermal, comm, and orbital debris concerns. On early flights it was learned that pointing one axis of the Orbiter at the sun for too long caused too much of a thermal imbalance between the sunlit and shaded sides, resulting in difficulty closing the payload bay doors before deorbit. Payload bay to Earth maintained thermal balance for closing the doors while still providing adequate heat rejection through the radiators. Once TDRSS was available, wing to velocity vector (therefore nose out of plane) ensured that at least one S-band antenna (arranged around the nose) was pointed at a TDRS satellite for near-continuous comm. Later, when orbital debris became more of a concern, tail to velocity vector was chosen to shield the cabin from MMOD. By this time TDRS-Z was available to mitigate the comm loss due to S-band blockage "off the tail".

[John2375]

I’ve tried searching but to no avail;  I recall somewhere on here, there was a dramatic photo of the forward fire team “caught” outside their bunker during launch.. I think the story was that a hold was called for T-31 so they went outside.. then the hold was cancelled and they didn’t have time to get back inside..  there was talk on here of which launch it was but idk if it was ever determined ?

[Thorny]

I’ve tried searching but to no avail;  I recall somewhere on here, there was a dramatic photo of the forward fire team “caught” outside their bunker during launch.. I think the story was that a hold was called for T-31 so they went outside.. then the hold was cancelled and they didn’t have time to get back inside..  there was talk on here of which launch it was but idk if it was ever determined ?

I'm not sure if it was ever identified as to which mission it was, but here is the photo...

https://www.thedrive.com/content-b/message-editor%2F1642726676274-lzajden.jpeg?auto=webp&optimize=high&quality=70&width=1440

[joncz]

I'm not sure if it was ever identified as to which mission it was, but here is the photo...

https://www.thedrive.com/content-b/message-editor%2F1642726676274-lzajden.jpeg?auto=webp&optimize=high&quality=70&width=1440

Yes, the carrier vehicle is outside the pad's perimeter fence. This was M-113/Hard Top One's astronaut rescue vehicle and team (I think Unit #HE-704-080) on station at A/B 4, just under a mile from the shuttle on Pad B, during the launch of STS-26/Discovery in Sept. 1988. I think the photo seen is one that had been autographed by one of the 12-member astronaut pad rescue teams that Bob had gotten from me long ago.

From http://www.collectspace.com/ubb/Forum29/HTML/001965.html

[DaveS]

Can someone with a bit more knowledge than me, explain how the PLBD NO-GO diagram is supposed to be read in terms of the position assessment outlined in the STS-1 Post Insertion checklist? Crippen reported that it was "Position 1A" that was determined during the PLBD latch and cycle tests.

[catdlr]

Hi All.

Quick one: I know that Endeavour was the first Orbiter to have the GPS system on board. Had also all the other Orbiters (Columbia included) received the GPS systems?

Thanks very much

Davide

Davide, that's a more difficult question than you might think.

The way the GPS (MAGR) was put onboard was that the orbiters first had a GPS unit put in a locker and a PGSC recorded the data from the GPS for post-flight analysis.  This started with just on-orbit and proceeded to ascent/entry data collection (which meant we had to park the PGSC's spinning hard drive and use a solid state drive long before those became popular).  This level of testing was done in the mid-1990s.

The next step was to allow the BFS to see the GPS data and then have that shipped to the ground as part of the BFS telemetry.  This was followed by incorporating the GPS data into PASS on-orbit only.  It was then we hit our first real issue in 1998.  That showed the various software (PASS and GPS) needed some work and so it was a few years before the MAGR-3S was ready to be used in PASS again.

The original intent was that all three (really at that time, four) vehicles would get three-string GPS and the TACANs would be removed.  However, PASS and BFS software allowed for no GPS, 1 GPS/3 TACANs and 3 GPS/no TACAN configurations (the configuration had to be programmed into that flight's software).  So, once the MAGR-3S was being used the initial vehicles received one GPS and OV-105 during her final KSC OMDP received MEDS and a 3 string GPS configuration.  Had long OMDPs been available for the other vehicles, they would have also received a 3-string GPS configuration.

So to say that OV-105 was the first to get GPS is incorrect.  It is correct, however, to say that OV-105 was the first to get three string GPS and the first to fly entry using GPS  units instead of TACANs.

Besides my memory, I'll list this as a reference in case you need more details:
http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=4570031&url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F4557992%2F4569960%2F04570031.pdf%3Farnumber%3D4570031

Andy

[penguin44]

This has been bugging me all day. I know I've read posts on it, blog and a video but for the life of me I can't remember. It was about a shuttle, post landing having an over heat issue and mcc wasn't listening because they were basically signed off early. Its not sts 9. Maybe Wayne hale talked about it? Please help my feeble mind

[DaveS]

This has been bugging me all day. I know I've read posts on it, blog and a video but for the life of me I can't remember. It was about a shuttle, post landing having an over heat issue and mcc wasn't listening because they were basically signed off early. Its not sts 9. Maybe Wayne hale talked about it? Please help my feeble mind

It was STS-27:

[eric z]

 Thanks DaveS, and Penquin44 too, for this fascinating video. That's why I love NSF so much - you can learn something every day! I hope as time goes by the lessons learned by NASA the hard way are not lost in the shuffle by future generations.

[penguin44]

Holy cow. That's the one thank you! It was driving me crazy. I knew to just ask here.

[John2375]

It seems that early on, the nose-gear slapped down pretty hard, but later flights it was pretty smooth.
Was this because of pilot feedback that improved technique by the pilots?? Or was a software change made that helped make it gentler??

[mkirk]

It seems that early on, the nose-gear slapped down pretty hard, but later flights it was pretty smooth.
Was this because of pilot feedback that improved technique by the pilots?? Or was a software change made that helped make it gentler??

The short answer is yes. 
Over time the techniques and cues for derotation changed.  Beginning with STS-1, the standard procedure was to push the RHC (rotational hand controller, i.e. the stick) forward - as the orbiter slowed below 165 knots - to establish and hold a derotation rate of about 2 degrees per second.  Maintaining that precise rate using the RHC as the orbiter’s nose lowered, and the angle of attack changed from a positive to a negative value, was pretty challenging. 
Among many other factors, that is why it appears like the nose gear “slaps” down near the end of that process in the videos of many early landings.

However, by the end of the space shuttle program, the standard technique was to push and hold the “beep trim” switch (located on top of the RHC) forward with your thumb beginning at 185 knots.  The orbiter was a fly-by-wire rate command system.  Using the “beep trim” switch in this manner allowed the crew to command a “constant” pitch rate of 1.5 degrees per second.  The flight control system was able to maintain that rate more efficiently/precisely via the trim input than by a manual deflection of the RHC control stick.

I am massively over simplifying the explanation.  This small portion of a shuttle flight actually involves some very complex interactions between the orbiter’s aerodynamics, ground effect, flight control system, landing gear (and related loading), and vehicle stability.

For the true nerds in the group, I am including a couple of images (attached below) from one of our training workbooks that explains some of these variables.


Mark Kirkman
“Space Shuttle Hugger”

[John2375]

What was the Hottest shuttle launch?? Obviously STS-51L was the coldest.. STS-51C I believe was the second coldest..
Was there a launch recorded during those hot Florida summers that was the hottest??