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#900
by
Complex39
on 24 Aug, 2007 20:55
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Apologies if this has already been asked but a search of the forum didn't reveal an answer to my question.
You hear and read a lot about launch windows and how the timing of a shuttle launch depends on things like the mission objectives (whether it be rendezvous with ISS or satellite launch/retrieval etc.), but I never see anything explaining landing opportunities and what factors determine when the shuttle can be brought back to Earth. A friend recently asked me why NASA sometimes land the shuttle at night....and I didn't know the answer! Could they not just wait untill a later orbit when daylight is available at the preferred landing site?
Thanks in advance.
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#901
by
Jim
on 24 Aug, 2007 21:00
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Complex39 - 24/8/2007 4:55 PM
A Could they not just wait untill a later orbit when daylight is available at the preferred landing site?
Thanks in advance.
There might not be daylight opportunities, depending on the orbit, inclination and launch time
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#902
by
Jim
on 24 Aug, 2007 21:04
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#903
by
ChrisGebhardt
on 24 Aug, 2007 21:26
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Complex39 - 24/8/2007 4:55 PM
Apologies if this has already been asked but a search of the forum didn't reveal an answer to my question.
You hear and read a lot about launch windows and how the timing of a shuttle launch depends on things like the mission objectives (whether it be rendezvous with ISS or satellite launch/retrieval etc.), but I never see anything explaining landing opportunities and what factors determine when the shuttle can be brought back to Earth. A friend recently asked me why NASA sometimes land the shuttle at night....and I didn't know the answer! Could they not just wait untill a later orbit when daylight is available at the preferred landing site?
Thanks in advance.
The Shuttle orbits the Earth roughly 14 times per day. Of those 14 orbits, there are only a certain number of orbits (about 8 per day) that allow the Space Shuttle to reach one of the 3 landing facilities in the U.S. If you look at a ground track of the Shuttle's orbit, you'll notice that the Shuttle doesn't always pass over, or near, the U.S. For that reason, those orbits are not available for landing opportunities. Therefore, sometimes the orbits available for landing mean the Shuttle lands at night. If you want more information, just PM me.
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#904
by
Complex39
on 24 Aug, 2007 21:31
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Jim - 24/8/2007 10:00 PM
There might not be daylight opportunities, depending on the orbit, inclination and launch time
Would you mind elaborating a little? I realise that in order for the orbiter to landing at a specific location (e.g. KSC) the de-orbit burn has to occur at a certain time and with the shuttle at a certain 'point' in orbit but I don't really understand how the 3 things you mentioned (orbit, inclination and launch time) are used to determine this.
Is there anywhere on the web that documents the de-orbit-burn/landing process and the theory behind it?
Thanks.
Edit: Many thanks Trekkie. I had already posted my repsonse to Jim before I read your post!
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#905
by
psloss
on 24 Aug, 2007 21:52
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Trekkie07 - 24/8/2007 5:26 PM
The Shuttle orbits the Earth roughly 14 times per day.
FWIW, the orbital period for the ISS (which orbiters are docked to a lot of the time they are in orbit nowadays) is ~90 minutes, which works out to ~16 orbits in a 24 hour period.
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#906
by
ChrisGebhardt
on 24 Aug, 2007 22:01
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Complex39 - 24/8/2007 5:31 PM
Jim - 24/8/2007 10:00 PM
There might not be daylight opportunities, depending on the orbit, inclination and launch time
Would you mind elaborating a little? I realise that in order for the orbiter to landing at a specific location (e.g. KSC) the de-orbit burn has to occur at a certain time and with the shuttle at a certain 'point' in orbit but I don't really understand how the 3 things you mentioned (orbit, inclination and launch time) are used to determine this.
Is there anywhere on the web that documents the de-orbit-burn/landing process and the theory behind it?
Thanks.
Edit: Many thanks Trekkie. I had already posted my repsonse to Jim before I read your post!
No prob. I'll take a crack at answering this one if I can. For my examples, I'll assume the Shuttle is landing at KSC. So, not only, does the Shuttle have to be at a specific point in its orbit, but it has to be on a certain orbit (i.e. Orbit 201, 202, 203 etc... [but understand that these are not the only orbit #s the shuttle has to be on]) to properly align with the desired runway's location. Orbital Inclination matters because this effects which orbit NASA targets for landing. For missions to the ISS, NASA usually targets "ascending trajectories" for landing opportunities. This means that the Shuttle is travelling in a Northeasterly direction as it passes over the Pacific Ocean and Central America before it makes its final series of turns to percisely align with the Shuttle Landing Facility (SLF). Finally, the time of day the Shuttle is launched at determines whether is lands in daylight or at night. For a 13day Shuttle mission to the ISS (which is what Endeavour just completed on STS-118), the first landing opportunity occurs roughly 12days and 18hours after launch. For Endeavour, that meant a landing at 12:32pm because is launched at 6:36pm. Atlantis' STS-115 flight back in September 2006 launched at 11:15am which in turn meant a landing around 6:30am... a nighttime landing. Hope this helps. Let me know if you want more information.
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#907
by
ChrisGebhardt
on 24 Aug, 2007 22:02
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psloss - 24/8/2007 5:52 PM
Trekkie07 - 24/8/2007 5:26 PM
The Shuttle orbits the Earth roughly 14 times per day.
FWIW, the orbital period for the ISS (which orbiters are docked to a lot of the time they are in orbit nowadays) is ~90 minutes, which works out to ~16 orbits in a 24 hour period.
Right you are. Sorry about that. Just bad math for a minute.
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#908
by
Thorny
on 24 Aug, 2007 22:02
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For a layman's explanation...
The space station is in an orbit inclined 51.6 degrees to the equator. That means the most northerly point of each orbit is 51.6 degrees north latitude and the most southerly is 51.6 degrees south latitude. The orbit is more or less fixed in space, relative to the background stars. The Earth rotates beneath the orbit... about 1,100 miles at the equator per orbit. (Earth is not a perfect sphere, so the orbit does 'precess' a little on each orbit, but that's a detail.) A point on the Earth's surface, say Cape Canaveral, will rotate beneath the Station's orbit twice per day, once on the "ascending node" (the Station is travelling on the northward leg of its orbit) and once on the descending node (southward.) That means a Shuttle coming home from the Space Station has two* opportunities to land at Cape Canaveral, think: about 12 hours apart. But one of those opportunities, the descending node, would bring the Shuttle in over the continental United States (coming down over Minnesota, Illinois, Tennessee, etc.) and since the Columbia accident, NASA prefers not to risk that approach anymore. That leave the ascending node, with a Shuttle coming in over Central America, the Caribbean, and Cuba.
That only happens once a day, and depending on the launch time, it might be at night.
*The Shuttle has enough cross-range capability, flying to the east or west of its orbit to reach Cape Canaveral, that it can make two attempts to land at Cape Canaveral, on succeeding orbits.
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#909
by
psloss
on 24 Aug, 2007 22:22
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Trekkie07 - 24/8/2007 6:02 PM
Right you are. Sorry about that. Just bad math for a minute.
No worries -- actually, you can see how many orbits per day in one of the fields in two line elements, which are updated frequently. The revs/day for the ISS and HST elements I got
here are highlighted:
ISS (ZARYA)
1 25544U 98067A 07236.22846339 .00011130 00000-0 73407-4 0 8467
2 25544 51.6358 112.6735 0008016 282.9306 175.5430 15.76194975501511
HST
1 20580U 90037B 07235.72978304 .00000290 00000-0 96584-5 0 9449
2 20580 28.4673 109.6773 0003754 99.1977 260.9037 15.00270904750110
(Fixed-width data formats don't display real well in proportional fonts like this...)
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#910
by
Complex39
on 24 Aug, 2007 22:23
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Thanks for taking the time to reply guys and for explaining it so clearly!
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#911
by
MKremer
on 25 Aug, 2007 01:14
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#912
by
DaveS
on 25 Aug, 2007 01:40
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#913
by
John2375
on 25 Aug, 2007 01:49
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Back when they did the Mir missions, it was basically the same thing, right?? Except I distinctly remember the early on in the program (STS-74, 76, 79,81, 84) the seemed to land about 4 hours AFTER launch time (STS-84 for example launched 4:07am and landed about 8:something am.
Does that mean they landed on the descending orbit?? I remember seeing a video about STS-74 and they definitely did, since they had spectacular footage coming in over the Canadian Rockies and down through the midwest and into Florida..
Doesn't that also have to do more w/the sleep cycles too?? When they're on the descending orbit, they're usually asleep??
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#914
by
ChrisGebhardt
on 25 Aug, 2007 01:58
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John2375 - 24/8/2007 9:49 PM
Doesn't that also have to do more w/the sleep cycles too??
It can. And on that mission it did. However, since RTF, all flights have (and it's my understanding that the remianing ones will) landed on ascending trajectories. My previous posts used an ISS mission scenario after RTF. But you are correct as well. I was trying to keep things as simple as possible and just explain why some missions landing at night.
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#915
by
ChrisGebhardt
on 25 Aug, 2007 02:06
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OK. Now it's time for me to ask a question. How long does it take to turn a High Bay around after a rollout to the start of SRB stacking for the next mission?
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#916
by
Jorge
on 25 Aug, 2007 02:12
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Thorny - 24/8/2007 5:02 PM
A point on the Earth's surface, say Cape Canaveral, will rotate beneath the Station's orbit twice per day, once on the "ascending node" (the Station is travelling on the northward leg of its orbit) and once on the descending node (southward.) That means a Shuttle coming home from the Space Station has two* opportunities to land at Cape Canaveral, think: about 12 hours apart.
Not quite right. It would be 12 hours if KSC was on the equator, but because it isn't, the descending opportunity is typically 4 orbits (6 hours) after the ascending opportunity.
But one of those opportunities, the descending node, would bring the Shuttle in over the continental United States (coming down over Minnesota, Illinois, Tennessee, etc.) and since the Columbia accident, NASA prefers not to risk that approach anymore. That leave the ascending node, with a Shuttle coming in over Central America, the Caribbean, and Cuba.
While true, that's not the main reason. NASA avoided the descending opportunities for ISS flights even before the Columbia accident because they typically required a lot of crew sleep-shifting, and because of concerns over noctilucent clouds during the summer months.
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#917
by
Thorny
on 25 Aug, 2007 02:23
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Here are launch / landing times and duration for Mir/ISS flights...
STS-63: 12:22am 6:50am (8 Days)
STS-71: 3:32pm 10:55am (10 Days)
STS-74: 7:30am 12:02pm (8 Days)
STS-76: 3:13am 8:29am (9 Days)
STS-79: 4:54am 8:13am (10 Days)
STS-81: 4:27am 9:23am (10 Days)
STS-84: 4:07am 9:27am (9 Days)
STS-86: 10:34pm 5:55pm (11 Days)
STS-89: 9:48am 5:36pm (11 Days)
STS-91: 6:06pm 2:00pm (10 Days)
STS-88: 3:35am 10:53pm (12 Days)
STS-96: 6:49pm 2:02am (10 Days)
STS-101: 6:11am 2:20am (10 Days)
STS-106: 8:45am 3:56am (12 Days)
STS-92: 7:17pm 1:50pm (13 Days)
STS-97: 10:06pm 6:04pm (11 Days)
STS-98: 6:13pm 3:33pm (13 Days)
STS-102: 6:42am 2:31am (13 Days)
STS-100: 2:40pm 3:10pm (11 Days)
STS-104: 5:04am 11:39pm (13 Days)
STS-105: 5:10pm 2:23pm (12 Days)
STS-108: 5:19pm 12:56pm (12 Days)
STS-110: 4:44pm 12:27pm (11 Days)
STS-111: 5:22pm 1:58pm (14 Days)
STS-112: 3:46pm 11:45am (11 Days)
STS-113: 7:50pm 2:37pm (14 Days)
STS-114: 10:39am 5:11am (14 Days)
STS-121: 2:38pm 9:15am (13 Days)
STS-115: 11:15am 6:21am (12 Days)
STS-116: 8:47pm 5:32pm (13 Days)
STS-117: 7:38pm 3:49pm (14 Days)
STS-118: 6:36pm 12:32pm (13 Days)
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#918
by
Jim
on 25 Aug, 2007 04:59
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Trekkie07 - 24/8/2007 10:06 PM
OK. Now it's time for me to ask a question. How long does it take to turn a High Bay around after a rollout to the start of SRB stacking for the next mission?
o minutes. Just like an OPF, there is nothing consumable that prevents another MLP form going ine
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#919
by
ChrisGebhardt
on 25 Aug, 2007 05:37
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Jim - 25/8/2007 12:59 AM
Trekkie07 - 24/8/2007 10:06 PM
OK. Now it's time for me to ask a question. How long does it take to turn a High Bay around after a rollout to the start of SRB stacking for the next mission?
o minutes. Just like an OPF, there is nothing consumable that prevents another MLP form going ine
Thanks. But how long would it take to reposition the work platforms from a rollout config to a SRB stacking config? Minutes... hours?
