Author Topic: Shuttle Q&A Part 5  (Read 863315 times)

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 31279
  • Cape Canaveral Spaceport
  • Liked: 9563
  • Likes Given: 299
Re: Shuttle Q&A Part 5
« Reply #20 on: 06/15/2009 11:41 AM »
Do the tanks HAVE to be full on launch?

It makes ground ops and flight ops planning easier.

Offline Analyst

  • Senior Member
  • *****
  • Posts: 3337
  • Liked: 1
  • Likes Given: 1
Re: Shuttle Q&A Part 5
« Reply #21 on: 06/15/2009 12:38 PM »
I don't understand why they don't do the OMS burn after ET sep, e.g. after staging, call it OMS-0. Would be more efficient without the ET mass.

Analyst

Online ugordan

  • Senior Member
  • *****
  • Posts: 7366
    • My mainly Cassini image gallery
  • Liked: 1519
  • Likes Given: 331
Re: Shuttle Q&A Part 5
« Reply #22 on: 06/15/2009 12:57 PM »
Could be because that gain would be smaller than increased gravity losses of a heavier orbiter earlier in the ascent.

Offline elmarko

  • I am very curious about THIS little conundrum
  • Full Member
  • ****
  • Posts: 1295
  • Preston, UK
    • ElMarko.org
  • Liked: 2
  • Likes Given: 0
Re: Shuttle Q&A Part 5
« Reply #23 on: 06/15/2009 01:37 PM »
Posting from Part 4:

Secondly, watch this video, if you would be so kind :)



While "boundary" is self explanatory as an abort boundary, can anyone tell me what the crew mean when they mention "window"

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 31279
  • Cape Canaveral Spaceport
  • Liked: 9563
  • Likes Given: 299
Re: Shuttle Q&A Part 5
« Reply #24 on: 06/15/2009 01:38 PM »
Posting from Part 4:



While "boundary" is self explanatory as an abort boundary, can anyone tell me what the crew mean when they mention "window"

At what time is "window" said?

Offline elmarko

  • I am very curious about THIS little conundrum
  • Full Member
  • ****
  • Posts: 1295
  • Preston, UK
    • ElMarko.org
  • Liked: 2
  • Likes Given: 0
Re: Shuttle Q&A Part 5
« Reply #25 on: 06/15/2009 01:47 PM »
Apologies Jim, I'll go through it now. Should have thought about doing that.

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 31279
  • Cape Canaveral Spaceport
  • Liked: 9563
  • Likes Given: 299
Re: Shuttle Q&A Part 5
« Reply #26 on: 06/15/2009 01:51 PM »
ok i dont understand. by "range" im assuming NASA means the entire sky right? maybe a certain radius of it anyway? since the sky is all open and just "there" I dont get what this conflict is about? so what if numerous ships have a launch schedule close together, launch one, say at 10am, then launch another at 1030am---so what?  why does the range only allow a certain vessel at a time to only launch at a certain period? the sky is the sky. Once something launches and clears, why cant another go right after it? even a day later, why is it still closed off?

"Range" is the Eastern Range formerly the Eastern Test Range which is managed by the 45th Space Wing.   The "Range" include comm, telemetry, tracking, photo/video, range safety systems, weather forecasting systems, and security assets located on KSC, CCAFS, JDMTA, Antigua, and Ascension Island.  The configuration of these assets is different for each launch vehicle type.   For example,  the launch trajectory information to allow for telemetry and tracking antenna pointing has to be distributed, loaded  and verified.   Same goes for the abort limits for range safety computers and displays.  Comm channels have to be reconfigured, tracking camera moved and aligned.  Road blocks moved and established. There is a finite amount of time required to do this work from one launch to another.

« Last Edit: 06/15/2009 01:53 PM by Jim »

Offline elmarko

  • I am very curious about THIS little conundrum
  • Full Member
  • ****
  • Posts: 1295
  • Preston, UK
    • ElMarko.org
  • Liked: 2
  • Likes Given: 0
Re: Shuttle Q&A Part 5
« Reply #27 on: 06/15/2009 01:59 PM »
Window is mentioned at 3m58 seconds at the first instance, and then periodically during the ascent.

Edit: 5m15 too
« Last Edit: 06/15/2009 02:06 PM by elmarko »

Offline Analyst

  • Senior Member
  • *****
  • Posts: 3337
  • Liked: 1
  • Likes Given: 1
Re: Shuttle Q&A Part 5
« Reply #28 on: 06/15/2009 02:20 PM »
Could be because that gain would be smaller than increased gravity losses of a heavier orbiter earlier in the ascent.

Could be. But I doubt it. Do ~60kN (OMSs) out of ~6,000kN (SSMEs) really make such a difference with respect to gravity losses? I still think having to push a 30mt ET or not would be the bigger difference.

Analyst

Online ugordan

  • Senior Member
  • *****
  • Posts: 7366
    • My mainly Cassini image gallery
  • Liked: 1519
  • Likes Given: 331
Re: Shuttle Q&A Part 5
« Reply #29 on: 06/15/2009 02:24 PM »
Note I said *heavier* orbiter. I didn't mean the OMS engines provided extra oomph as much as consumed extra weight early on, thus giving SSMEs less mass to push.

edit: wow, mixing weight and mass... a physicist could have me shot  :D
« Last Edit: 06/15/2009 02:28 PM by ugordan »

Offline Jorge

  • Senior Member
  • *****
  • Posts: 6177
  • Liked: 21
  • Likes Given: 0
Re: Shuttle Q&A Part 5
« Reply #30 on: 06/15/2009 02:56 PM »
Hi folks:

I am using a Quote from Jorge near the bottom of page one.

"OMS assist is performed if 1) the OMS prop required for the mission itself does not require full tanks and 2) the mission could benefit from the additional payload capacity gained by filling the OMS tanks full and burning the difference as OMS assist (IIRC it's roughly 200 lb payload for 4000 lb OMS prop). CG location is a secondary consideration on the amount"

I thought OMS assist was used if payload was -TOO heavy-


Same thing, read 2) more carefully.
JRF

Offline Jorge

  • Senior Member
  • *****
  • Posts: 6177
  • Liked: 21
  • Likes Given: 0
Re: Shuttle Q&A Part 5
« Reply #31 on: 06/15/2009 02:58 PM »
I still don't really understand why they don't just not fill the amount of OMS that they'd burn off on the ascent anyway.

Am I missing something?

You're missing the part where I said that burning it off during ascent allows additional payload.
JRF

Offline elmarko

  • I am very curious about THIS little conundrum
  • Full Member
  • ****
  • Posts: 1295
  • Preston, UK
    • ElMarko.org
  • Liked: 2
  • Likes Given: 0
Re: Shuttle Q&A Part 5
« Reply #32 on: 06/15/2009 03:48 PM »
I guess what I'm wondering is what gives the greater benefit, loading those OMS tanks with fuel and then burning them, or not filling the amount that would be burned.

I assume from your answer that it's the former.

Offline Jorge

  • Senior Member
  • *****
  • Posts: 6177
  • Liked: 21
  • Likes Given: 0
Re: Shuttle Q&A Part 5
« Reply #33 on: 06/15/2009 04:29 PM »
I guess what I'm wondering is what gives the greater benefit, loading those OMS tanks with fuel and then burning them, or not filling the amount that would be burned.

I assume from your answer that it's the former.

That is correct, and that is why OMS assist is done.
JRF

Offline Jorge

  • Senior Member
  • *****
  • Posts: 6177
  • Liked: 21
  • Likes Given: 0
Re: Shuttle Q&A Part 5
« Reply #34 on: 06/15/2009 05:02 PM »
Sorry if I steped on Jorge's answers earlier but they weren't visible when I typed mine.

As for RTHU, after STS-87 I think ALL flights performed the roll because it was implemented based on the performance enhancement certifications. Flight Procedures Handbook states it is REQUIRED for low inclination flights for that reason alone.  FPH also states that roll costs about 35 lbs in performance.

I have the STS-97 checklist Jorge referred to in my files so I can look that up to confirm.

Mark Kirkman

This is what the STS-97 FLT cycle FOP minutes had to say about it:

Quote
The Program Office has recently approved a change in design to remove the Roll-to-Heads-Up from the ascent profile as a performance enhancement of ~50 to 100 lbs. The Flight Design community deems this change as undesirable to STS-97 because it requires a change to ascent design procedures and internal software verification tools before implementation. The time required to incorporate these changes may not be adequate to ensure all procedures and off-line software tools are implemented properly. However, ADFD management felt that the risk to implement the No RTHU on this flight was acceptable when weighted against the very low APM and future APM threats. The ADFD flight team will work to mitigate any risks due to this change by aggressively communicating details through the design community and carefully implementing any changes associated with a No RTHU maneuver. As a result, the SSP directed Flight Design not to perform the Roll-To-Heads-Up maneuver for STS-97 Flight Cycle in order to realize the APM gain. The STS-97 CDR asked if the Engineering Cycle load could be updated to include this change in training. This is being investigated and will be updated is possible.

So at one point no-RTHU was the baseline for STS-97. If STS-97 did fly RTHU, it must have been restored after the FLT cycle.
JRF

Offline psloss

  • Veteran armchair spectator
  • Senior Member
  • *****
  • Posts: 16914
  • Liked: 997
  • Likes Given: 444
Re: Shuttle Q&A Part 5
« Reply #35 on: 06/15/2009 05:21 PM »
So at one point no-RTHU was the baseline for STS-97. If STS-97 did fly RTHU, it must have been restored after the FLT cycle.
FWIW, it's hardly definitive, but I don't hear any mention of a roll to heads up in the public broadcast of STS-97.  On STS-98, Ken Cockrell added "and we're rollin'" when acknowledging the 'Press to MECO' call...

Offline oxford750

  • Member
  • Posts: 82
  • Liked: 0
  • Likes Given: 0
Re: Shuttle Q&A Part 5
« Reply #36 on: 06/15/2009 08:39 PM »
Thanks Jorge.

Oxford750

Offline ChrisGebhardt

  • Assistant Managing Editor
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 5441
  • ad astra scientia
  • ~1 AU
  • Liked: 2053
  • Likes Given: 336
Re: Shuttle Q&A Part 5
« Reply #37 on: 06/15/2009 09:59 PM »
I guess what I'm wondering is what gives the greater benefit, loading those OMS tanks with fuel and then burning them, or not filling the amount that would be burned.

I assume from your answer that it's the former.

That is correct, and that is why OMS assist is done.

IIRC, the OMS tanks have to be filled completely (or as close to full as possible) because there is no sensor gage to tell you how much prop is in them.  They have to fill OMS tanks completely to know with a high degree of certainty how much prop is in them at launch.  Then, you burn what you don't need for the miss during ascent -- OMS assists -- and use calculations once on orbit to approximate how much OMS prop is left in the tanks after each firing of the OMS engines.

Am I remember incorrectly?

Offline psloss

  • Veteran armchair spectator
  • Senior Member
  • *****
  • Posts: 16914
  • Liked: 997
  • Likes Given: 444
Re: Shuttle Q&A Part 5
« Reply #38 on: 06/15/2009 10:27 PM »
IIRC, the OMS tanks have to be filled completely (or as close to full as possible) because there is no sensor gage to tell you how much prop is in them.  They have to fill OMS tanks completely to know with a high degree of certainty how much prop is in them at launch.  Then, you burn what you don't need for the miss during ascent -- OMS assists -- and use calculations once on orbit to approximate how much OMS prop is left in the tanks after each firing of the OMS engines.

Am I remember incorrectly?
The OMS/RCS load may work this way, too, but you may be thinking of Steve Payne answering a question during a recent countdown briefing about PRSD offload and why it takes an extra shift or half-shift to do that.  (His answer sounds similar to what you're describing.)

Offline DansSLK

  • Member
  • Posts: 77
  • Liked: 0
  • Likes Given: 0
Re: Shuttle Q&A Part 5
« Reply #39 on: 06/15/2009 10:58 PM »

IIRC, the OMS tanks have to be filled completely (or as close to full as possible) because there is no sensor gage to tell you how much prop is in them.  They have to fill OMS tanks completely to know with a high degree of certainty how much prop is in them at launch.  Then, you burn what you don't need for the miss during ascent -- OMS assists -- and use calculations once on orbit to approximate how much OMS prop is left in the tanks after each firing of the OMS engines.

Am I remember incorrectly?

They do have level sensors in them but if they are used during fill i don't know.

Tags: