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#1860
by
ChrisGebhardt
on 18 Apr, 2011 15:20
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Next, realize that the ascending and descending nodes are around 12 hours apart. So, in one case you might have to sleep-shift a bit forward (earlier) during the mission to meet that timeline, in the other case you might have to sleep-shift later (by a total of up to a maximum of 12 hours), thus "earning" some extra time in the mission because you are living 25 hour days or so during the mission.
The principle is correct, but ascending and descending nodes are ~6 hours apart.
Okay, I've thought about this all day, and I don't understand why these are 6 hours apart and not 12. Can someone help me please?
They would be 12 hours apart if the landing site was on the equator.
Let me try to paraphrase to see if I've got this. The ascending node is going to move largely from South-West to North-East while the descending node is going to move largely from West to East. This means the descending node is going to travel a lot farther East from initiation than the ascending node is, and this is because of the latitude of the landing site and because of the inclination of the orbit. So, to extremely simplify, the ascending node is going from the bottom of the sine wave to the top (looking on a flat map instead of a globe), while the descending node is going from a little left of the top peak of the sine wave to a little right of the top peak.
Basically, yes -- though the exact locations on the since curves are a little off.
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#1861
by
JayP
on 18 Apr, 2011 15:22
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As I watch LC39B coming down in pieces, I am wondering about the initial construction of the two FSS towers.
I have read the FSS were the tops of two of the three towers from the MLP's in the Saturn era. What I am wondering about is the process they used to get them off the MLP and onto the ground.
I doesn't seem likely they could have lifted the whole thing off the MLP in one chunk. How many sections did they have to cut it into? Comparable to the sections they are lobbing off the top of 39B right now?
If anyone has any historical links to the Shuttle pad transition from Saturn to Shuttle, I would appreciate it. Thanks.
This is the best historical information, but the text is in French. The photos give you a good idea what was done.
http://www.capcomespace.net/dossiers/espace_US/shuttle/index.htmOn the left pane, scroll down to the 1976 section and click on the "le Pad 39" link. Scrool to the bottom of the page and click on the "Launch Complex 39 Historie" link.
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#1862
by
Lee Jay
on 18 Apr, 2011 16:04
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Basically, yes -- though the exact locations on the since curves are a little off.
Just to closeout my own question, here are the long-range entry ground tracks for STS-131 (descending node) and STS-132 (ascending node):
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#1863
by
psloss
on 18 Apr, 2011 16:21
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This is the quickest plot I could find of most/all the daily orbits for a high inclination orbit, not ISS, but close enough to that inclination to illustrate...taken from this paper:
http://space.au.af.mil/documents/orbital_dynamics.pdfMaybe it helps, maybe not...but it does show the ascending (like orbits 1 and 2, for example) and descending nodes (orbits 6 and 7, for example) together.
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#1864
by
kaphonius
on 19 Apr, 2011 02:51
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I've searched online and have found many dead ends and conjecture to this question. I hope this is the right place to ask. What is the Space Shuttle return cargo payload mass?
I ask because I don't see any replacement capability since Bush's 'I see a picture in the stars' aka Constellation debacle. What happens if an ISS module gets damaged and needs repair beyond a spacewalk? Anyone else see an issue here?
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#1865
by
Jorge
on 19 Apr, 2011 02:55
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I've searched online and have found many dead ends and conjecture to this question. I hope this is the right place to ask. What is the Space Shuttle return cargo payload mass?
No simple answer, since the landing weight limits are a function of both weight and CG location.
What happens if an ISS module gets damaged and needs repair beyond a spacewalk?
Same thing that happened with Spektr on Mir.
Anyone else see an issue here?
Yes, many people have, and have been saying so for years. Nevertheless, the capability will not be retained, because it is deemed too expensive.
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#1866
by
Lee Jay
on 19 Apr, 2011 02:59
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Welcome to the NSF forum.
In the future, you can use the Q&A section and put questions into the appropriate thread in that forum.
The downmass (and volume) capabilities of the planned replacement vehicle don't allow the return of an ISS module. However, I'm not all that sure that Shuttle would have been particularly suited to that either, not because it couldn't do it, but because ISS is now very interconnected and it would be quite difficult to separate a module and prep it for return.
The bigger downmass issue is that there are parts on ISS that can be returned practically on Shuttle that can't be practically returned on other vehicles. These are much smaller than a whole module but still too large for Dragon, Orion/MPCV or Soyuz. They're cramming all they can into the last few flights but I'm sure this will eventually cause issues.
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#1867
by
Jim
on 19 Apr, 2011 11:29
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What happens if an ISS module gets damaged and needs repair beyond a spacewalk? Anyone else see an issue here?
Not really an issue. Even if the shuttle was available, most of the modules can't be removed from the ISS. Node 1 &2 and the Lab are permanent fixtures as well as most of the truss. There is no way to remove these without disrupting the whole ISS.
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#1868
by
Jim
on 19 Apr, 2011 11:31
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The design max return mass was 32Klbs. Abort return masses were higher, but then again, they were aborts.
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#1869
by
jsmjr
on 20 Apr, 2011 23:12
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Found this which pretty much answers it.... http://www.savethelut.org/MLDocs/ML_History.html
As I watch LC39B coming down in pieces, I am wondering about the initial construction of the two FSS towers.
I have read the FSS were the tops of two of the three towers from the MLP's in the Saturn era. What I am wondering about is the process they used to get them off the MLP and onto the ground.
I doesn't seem likely they could have lifted the whole thing off the MLP in one chunk. How many sections did they have to cut it into? Comparable to the sections they are lobbing off the top of 39B right now?
If anyone has any historical links to the Shuttle pad transition from Saturn to Shuttle, I would appreciate it. Thanks.
Any chance the LC 39 Observation Gantry is also a remnant of the Apollo LUTs? As far as I can tell it serves no current purpose other than a viewing site for tour groups (
http://www.kennedyspacecenter.com/lc-39-observation-gantry.aspx) but I've wondered if it ever did something more meaningful.
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#1870
by
DaveS
on 20 Apr, 2011 23:30
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Found this which pretty much answers it.... http://www.savethelut.org/MLDocs/ML_History.html
As I watch LC39B coming down in pieces, I am wondering about the initial construction of the two FSS towers.
I have read the FSS were the tops of two of the three towers from the MLP's in the Saturn era. What I am wondering about is the process they used to get them off the MLP and onto the ground.
I doesn't seem likely they could have lifted the whole thing off the MLP in one chunk. How many sections did they have to cut it into? Comparable to the sections they are lobbing off the top of 39B right now?
If anyone has any historical links to the Shuttle pad transition from Saturn to Shuttle, I would appreciate it. Thanks.
Any chance the LC 39 Observation Gantry is also a remnant of the Apollo LUTs? As far as I can tell it serves no current purpose other than a viewing site for tour groups (http://www.kennedyspacecenter.com/lc-39-observation-gantry.aspx) but I've wondered if it ever did something more meaningful.
Nope. Not a LUT remnant. The design is very different to the LUTs. The LUT levels were made up of upside down "V" struts and the LC 39 Observation Gantry doesn't have them.
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#1871
by
jsmjr
on 21 Apr, 2011 20:02
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Found this which pretty much answers it.... http://www.savethelut.org/MLDocs/ML_History.html
As I watch LC39B coming down in pieces, I am wondering about the initial construction of the two FSS towers.
I have read the FSS were the tops of two of the three towers from the MLP's in the Saturn era. What I am wondering about is the process they used to get them off the MLP and onto the ground.
I doesn't seem likely they could have lifted the whole thing off the MLP in one chunk. How many sections did they have to cut it into? Comparable to the sections they are lobbing off the top of 39B right now?
If anyone has any historical links to the Shuttle pad transition from Saturn to Shuttle, I would appreciate it. Thanks.
Any chance the LC 39 Observation Gantry is also a remnant of the Apollo LUTs? As far as I can tell it serves no current purpose other than a viewing site for tour groups (http://www.kennedyspacecenter.com/lc-39-observation-gantry.aspx) but I've wondered if it ever did something more meaningful.
Nope. Not a LUT remnant. The design is very different to the LUTs. The LUT levels were made up of upside down "V" struts and the LC 39 Observation Gantry doesn't have them.
Yep, looks like LC 39 was built in 1997, wholly as a visitor amenity, by Delaware North Park Services (operator of the KSC VC) following the completion of their excellent Apollo-Saturn V center. See
http://www-pao.ksc.nasa.gov/kscpao/release/1997/64-97.htm and attached Spaceport News for April 25, 1997 (which also describes the arrival of the ET at the visitors center (apparently the one now on display with attached SRBs).
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#1872
by
Mvossman
on 25 Apr, 2011 03:55
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First post!
1) When viewing the reentry videos, cabin view, the orange occasionally, about every 2 or 3 seconds, flickers brightly. Why is that? Random turbulence causing momentary increase in plasma density?
2) I read someplace that STS-1 was the one flight where the SRBs were lit after T-0. True? If so, what is the reason, to allow a little more time for SSME problems to appear on the pad rather than after launch commit? Cannot find anything online here or elsewhere. The STS-1 video does indeed give a sense that the engines ran longer before SRB ignition.
Mitch
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#1873
by
AS-503
on 25 Apr, 2011 04:08
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With regard to SRB ignition.
The off center thrust of the SSME forces the entire shuttle stack to "twang".
When the stack flexes back to it's original vertical position the SRB's are ignited.
I do not think there is much leeway on SRB ignition relative to the "Twang".
This twang does not entirely settle down. The vehicle has a slight lateral resonance of about 5hz IIRC.
This specific frequency was also noted on the Challenger accident because the SRB leak at the moment of ignition (and for a few seconds after lift off) had puffs of smoke coming from the SRB joint at the same frequency.
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#1874
by
Jim
on 25 Apr, 2011 11:44
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2) I read someplace that STS-1 was the one flight where the SRBs were lit after T-0. True? If so, what is the reason, to allow a little more time for SSME problems to appear on the pad rather than after launch commit? Cannot find anything online here or elsewhere. The STS-1 video does indeed give a sense that the engines ran longer before SRB ignition.
Mitch
2. For STS-1, main engine start was at T-3 and SRB ignition was at T+3. The extra 3 seconds was for the SRB twang to dampen out. Countdown was adjusted to account for this on STS-2.
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#1875
by
Mvossman
on 25 Apr, 2011 17:15
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2) I read someplace that STS-1 was the one flight where the SRBs were lit after T-0. True? If so, what is the reason, to allow a little more time for SSME problems to appear on the pad rather than after launch commit? Cannot find anything online here or elsewhere. The STS-1 video does indeed give a sense that the engines ran longer before SRB ignition.
Mitch
2. For STS-1, main engine start was at T-3 and SRB ignition was at T+3. The extra 3 seconds was for the SRB twang to dampen out. Countdown was adjusted to account for this on STS-2.
So does this mean: the STS-1 SSMEs started sequentially around T-3, that they would have been ready for liftoff at T-0 except for wating for the twang to dampen? And the reason for liftoff not being defined as T-0.00 is that the exact time required for twang to dampen was not known with encough certainty to have a specific SRB ignition time but rather the twang was empirically observed until it was dampened enough for SRB ignition and that period turned out to be an extra 3 seconds? No doubt the twang had some terrific predictions, mechanically, but perhaps just enough uncertainty in the period of oscillation and severity existed to merit waiting a variable period? Sort of a "mini-hold"?
And after that, this observed requirement for approx. 6 seconds from first SSME to SRB igntion was embraced from STS-2 forward, with the entire countdown slid backward those empirically derived approx. 6 seconds so liftoff is defined as T-0.00?
If this is all incorrect, and in fact the STS-1 countdown was defined and configured for a planned T+3 liftoff, I fail to understand why that is important - 6 seconds from T-6 to T-0 vs. T-3 to T+3 is six seconds either way.
Which raises two interesting questions. 1) If my interpretation is correct, was the twang watched on STS-1 by a human with his finger poised over a button or was there an automatic observation, perhaps accelerometer at the top of the ET, that triggered the continued countdown? 2) Currently, is SRB ignition and liftoff subject to any kind of extra delay for anything, such as excessive twang or other factors (aside from a cutoff obviously)?
Anyway, the reason I am so interested in this is I dropped everything this week, I am fulfilling a lifelong goal of seeing a launch on Friday (we all hope)- flying there myself to Titusville. Been a space buff from Apollo to STS-1 and to here. My heart rate may have been greater than Crippen and Young that morning and love it to this day. I think it may be a mistake to abandon reuseable, glideable spacecraft entirely.
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#1876
by
Jim
on 25 Apr, 2011 17:25
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1. So does this mean: the STS-1 SSMEs started sequentially around T-3, that they would have been ready for liftoff at T-0 except for wating for the twang to dampen?
2. And the reason for liftoff not being defined as T-0.00 is that the exact time required for twang to dampen was not known with encough certainty to have a specific SRB ignition time but rather the twang was empirically observed until it was dampened enough for SRB ignition and that period turned out to be an extra 3 seconds? No doubt the twang had some terrific predictions, mechanically, but perhaps just enough uncertainty in the period of oscillation and severity existed to merit waiting a variable period? Sort of a "mini-hold"?
3. And after that, this observed requirement for approx. 6 seconds from first SSME to SRB igntion was embraced from STS-2 forward, with the entire countdown slid backward those empirically derived approx. 6 seconds so liftoff is defined as T-0.00?
4. If this is all incorrect, and in fact the STS-1 countdown was defined and configured for a planned T+3 liftoff, I fail to understand why that is important - 6 seconds from T-6 to T-0 vs. T-3 to T+3 is six seconds either way.
5. Which raises two interesting questions. 1) If my interpretation is correct, was the twang watched on STS-1 by a human with his finger poised over a button or was there an automatic observation, perhaps accelerometer at the top of the ET, that triggered the continued countdown?
6) Currently, is SRB ignition and liftoff subject to any kind of extra delay for anything, such as excessive twang or other factors (aside from a cutoff obviously)?
1. Not just for STS-1 but for all missions
2. No, the countdown hadn't accounted for it at the time and they didn't want to change things for STS-1.
3. No, it was slid back only 3 seconds, since SSME start was around T-3 seconds.
4. So that liftoff occurs at T-0/T+0. It is easier for event planning to key off of liftoff.
5. Neither, it was a fixed interval in the countdown
6. no, it is fixed.
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#1877
by
Mvossman
on 25 Apr, 2011 17:39
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1. So does this mean: the STS-1 SSMEs started sequentially around T-3, that they would have been ready for liftoff at T-0 except for wating for the twang to dampen?
2. And the reason for liftoff not being defined as T-0.00 is that the exact time required for twang to dampen was not known with encough certainty to have a specific SRB ignition time but rather the twang was empirically observed until it was dampened enough for SRB ignition and that period turned out to be an extra 3 seconds? No doubt the twang had some terrific predictions, mechanically, but perhaps just enough uncertainty in the period of oscillation and severity existed to merit waiting a variable period? Sort of a "mini-hold"?
3. And after that, this observed requirement for approx. 6 seconds from first SSME to SRB igntion was embraced from STS-2 forward, with the entire countdown slid backward those empirically derived approx. 6 seconds so liftoff is defined as T-0.00?
4. If this is all incorrect, and in fact the STS-1 countdown was defined and configured for a planned T+3 liftoff, I fail to understand why that is important - 6 seconds from T-6 to T-0 vs. T-3 to T+3 is six seconds either way.
5. Which raises two interesting questions. 1) If my interpretation is correct, was the twang watched on STS-1 by a human with his finger poised over a button or was there an automatic observation, perhaps accelerometer at the top of the ET, that triggered the continued countdown?
6) Currently, is SRB ignition and liftoff subject to any kind of extra delay for anything, such as excessive twang or other factors (aside from a cutoff obviously)?
1. Not just for STS-1 but for all missions
2. No, the countdown hadn't accounted for it at the time and they didn't want to change things for STS-1.
3. No, it was slid back only 3 seconds, since SSME start was around T-3 seconds.
4. So that liftoff occurs at T-0/T+0. It is easier for event planning to key off of liftoff.
5. Neither, it was a fixed interval in the countdown
6. no, it is fixed.
1. Got it.
2. See below.
3. Roger that.
4. Of course it is better to T-0 as liftoff as a very important event... but see below.
5. Roger.
6. Roger.
Regarding answer #2 - I get it now, tell me if this is it. The countdown was designed for STS-1 to have SRB ignition at T-0, based upon time required for SSMEs to be ready (and perhaps other factors?). However, at some late date close enough to the earliest possible launch date that it would be inconvenient to renumber the countdown, someone realized it was necessary to wait for an extra 3 seconds twang to dampen so rather than an inconvenient re-write of the entire countdown backsliding it 3 seconds, an extra 3 seconds was tacked on and SRB ingition/liftoff took place at T+3.
Fascinating, I picture a desk surrounded with folks when someone raises his hand and says "hey, we forgot to allow enough time for twang to dampen. Our simulations show approx. 6 seconds are needed even though the SSMEs require only 3 to be ready!" And people drop their pencils.
Which raises an interesting couple points. 1) 3 more seconds of propellant are "wasted", did that make a meaningful impact on useful payload capacity? 2) Why is it necessary for twang to subside? I would think (hazardous activity to think intuitively of course) that it would result in more lateral translation in a favorable direction, toward the ET, as all launches do anyway.
Mitch
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#1878
by
AS-503
on 25 Apr, 2011 18:09
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If SRB ignition was made before the stack returned to vertical you would have too much lateral drift (among other things).
Minimizing lift-off drift is a good idea (even for wear and tear on the MLP).
The 3 seconds of "wasted" propellant could be factored into the perfomance margin.
Does anyone have the link to mkirk's explanation of the performance margin? It was in one of these Shuttle Q&A forums.
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#1879
by
Jim
on 25 Apr, 2011 18:33
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The countdown people and the dynamicists are completely different groups. The countdown people were probably aware of it and see the following. The shuttle stack (Enterprise, inert SRB's and an ET) were subject to a MGVT (mated ground vibration test) at Marshall. This is how the vibe modes were determined/verified. Also, Columbia performed an FRF early in the year before its first flight and this would have provided an actual period of oscillation. I believe that this why the countdown was developed the way it was. The countdown could be developed independent of the actual delay, since everything is ready at T-0 and the length of the delay could just be tacked on.
Yes, the extra three seconds does "waste" propellant and did have an impact on payload to orbit. They did look at eliminating it, see below. The reason for waiting for the twang to "subside" is the amount of energy that is "stored" in the structure when it is bent over (not lateral drift). Look at any cantilevered load and what would happen if the base were released. The moment at the base of the SRB's never goes back to zero since the SSME's are burning but it is at a minimum when the bolts are fired.
When they tried to eliminate the delay, they looked at the moment as it built up from SSME's start up. The time in the SSME start sequence where the moment was equivalent to the moment after delay was too early in the start sequence to verify that the SSME's were ok.
