Do the tanks HAVE to be full on launch?
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"
Posting from Part 4:Quote from: elmarko on 06/11/2009 08:23 pmWhile "boundary" is self explanatory as an abort boundary, can anyone tell me what the crew mean when they mention "window"
While "boundary" is self explanatory as an abort boundary, can anyone tell me what the crew mean when they mention "window"
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?
Could be because that gain would be smaller than increased gravity losses of a heavier orbiter earlier in the ascent.
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-
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?
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.
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
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.
Quote from: elmarko on 06/15/2009 03:48 pmI 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?