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#1260 by mkirk on 13 Jul, 2010 18:11
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In a contingency situation, would one risk shutting down an APU? (Or for early failure, delaying startup of #2 and #3?) I assume that's the biggest heat load. IIRC, the flight surfaces still travel at full speed with two APUs.What is the contingency plan if the flash evaporator fails after reentry burn?
Timing of the failure is everything (how long after TIG), but generally you would rely on the “Cold Soak” of the radiators, which was conducted prior to payload bay door closure, and use of the ammonia boilers to provide enough cooling thru landing.
-Alex
No, the orbiter's Auxialiary Power Units (APUs) would be operated as normal. There should be sufficient cooling from the Radiator Cold Soak and (earlier) than normal operation of the Amonia Boiler [at entry interface as opposed to the nominal activation at ~120,000 feet].
APU/HYD cooling is really a separate animal entirely and not part of the ECLSS Freon Cooling Loops except for an interface thru the Hydraulic/Freon Heat Exchanger which is used to pick up heat [as opposed to rejecting it to the loop] from the loops to help keep the hydraulic fluid warm.
Mark Kirkman
(Space Shuttle Hugger)
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#1261 by 10W29 on 14 Jul, 2010 00:47
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When the APU's are up the hyd hx dumps heat (a lot actually) to the freon loops. It's the other way on orbit.
In a contingency situation, would one risk shutting down an APU? (Or for early failure, delaying startup of #2 and #3?) I assume that's the biggest heat load. IIRC, the flight surfaces still travel at full speed with two APUs.What is the contingency plan if the flash evaporator fails after reentry burn?
Timing of the failure is everything (how long after TIG), but generally you would rely on the “Cold Soak” of the radiators, which was conducted prior to payload bay door closure, and use of the ammonia boilers to provide enough cooling thru landing.
-Alex
No, the orbiter's Auxialiary Power Units (APUs) would be operated as normal. There should be sufficient cooling from the Radiator Cold Soak and (earlier) than normal operation of the Amonia Boiler [at entry interface as opposed to the nominal activation at ~120,000 feet].
APU/HYD cooling is really a separate animal entirely and not part of the ECLSS Freon Cooling Loops except for an interface thru the Hydraulic/Freon Heat Exchanger which is used to pick up heat [as opposed to rejecting it to the loop] from the loops to help keep the hydraulic fluid warm.
Mark Kirkman
(Space Shuttle Hugger)
Also the ammonia boilers are designed to be used below 100,000 ft, not sure if earlier activation would be effective.
And finally it would take multiple failures for a total loss of FES cooling. -
#1262 by mkirk on 14 Jul, 2010 01:52
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When the APU's are up the hyd hx dumps heat (a lot actually) to the freon loops. It's the other way on orbit.
In a contingency situation, would one risk shutting down an APU? (Or for early failure, delaying startup of #2 and #3?) I assume that's the biggest heat load. IIRC, the flight surfaces still travel at full speed with two APUs.What is the contingency plan if the flash evaporator fails after reentry burn?
Timing of the failure is everything (how long after TIG), but generally you would rely on the “Cold Soak” of the radiators, which was conducted prior to payload bay door closure, and use of the ammonia boilers to provide enough cooling thru landing.
-Alex
No, the orbiter's Auxialiary Power Units (APUs) would be operated as normal. There should be sufficient cooling from the Radiator Cold Soak and (earlier) than normal operation of the Amonia Boiler [at entry interface as opposed to the nominal activation at ~120,000 feet].
APU/HYD cooling is really a separate animal entirely and not part of the ECLSS Freon Cooling Loops except for an interface thru the Hydraulic/Freon Heat Exchanger which is used to pick up heat [as opposed to rejecting it to the loop] from the loops to help keep the hydraulic fluid warm.
Mark Kirkman
(Space Shuttle Hugger)
Also the ammonia boilers are designed to be used below 100,000 ft, not sure if earlier activation would be effective.
And finally it would take multiple failures for a total loss of FES cooling.
Thanks! I don’t want to be factually wrong but in my defense it has been almost 9 years since I have studied or practiced such scenarios.
Yes it does make more sense that the HYD fluid is dumping heat during ascent/entry…those lines get pretty hot when the HYD Pumps are running. Somehow I was always under the impression that the fluid bypassed the heat exchanger when the Freon Loops were at a specified temperature, but I really don’t know for sure. I have to plead system ignorance there and look it up in the books.
Yes this situation would be several failures deep but as for the original question however, procedurally the APUs are not a factor as I recall after the burn. The cold soak and the ammonia boilers are what you will rely on thru landing. On the other hand, failures that occur prior to the burn can be pretty diverse, and depending on the exact timing of the failure, can result in various power downs and/or use of the Contingency De-orbit procedures for “Loss of FES”.
As for the Ammonia Boilers; I was always taught that they could be used “off nominally” at Entry Interface (400,000 ft) if no “cold soak” was performed, or in the case we are discussing here, a total “Loss of FES”. Nominally the Ammonia Boiler Controller is commanded by the BFS below ~120,000 feet.
FYI: some of the details of this scenario should be in the Entry Pocket Checklist and the AESP (Ascent Entry Systems Procedures). I’m pretty sure those are available on the public NASA FDF page for those who are interested.
Mark Kirkman
(Space Shuttle Hugger)
P.S.
Here is that Public FDF NASA page;
http://www.nasa.gov/centers/johnson/news/flightdatafiles/index.html -
#1263 by sivodave on 19 Jul, 2010 22:51
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Hi all.
In this period I’m trying to understand the mechanics of the rendezvous maneuver with the ISS. Now I understand in which way the shuttle gets in proximity of the station, it’s a matter of orbital mechanics, neither more nor less. What I can’t understand is what happen during the manual phase of the maneuver.
For example see the first picture attached. The shuttle is after MC4, that’s to say the manual phase has taken over. We have to get from point 1 to point 7. how does the shuttle get there? It’s my understanding that RCS is fired in the direction of travel (+X axis) in order to increase the velocity of the shuttle, lifting therefore the altitude slowing down at the same time. This because the lower the altitude and the faster the orbital speed. Is that correct? Or is there anything else that happen? Or maybe the RCS is fired downward (+ Z axis) so that the Shuttle goes up? Does it work from an orbital mechanics’ point of view?
After the R bar pitch maneuver the Shuttle goes in front the station for a V bar approach. With reference to the second picture attached, is my understanding that through continuous firings of the RCS system the altitude of the shuttle respect to the station’s altitude is constantly changed in order to continually slow down till when the station “hit” the shuttle itself. I’ll explain this better. Always with reference to the second picture, at point 8 the shuttle fires the RCS upwards so that it goes in a slightly lower orbit than the station. In this way the shuttle goes a little bit fastener. Then a second faring (point 9) this time downward, taking the shuttle in a slightly higher orbit than the station has, decreasing this time the speed. And the story goes in this way till to docking. I’m trying to find another explanation but it seems to me the only one reasonable taken into account the principle of orbital mechanics.
Any help is very appreciated.
Thanks
Davide
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#1264 by Jorge on 20 Jul, 2010 01:33
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Hi all.
In this period I’m trying to understand the mechanics of the rendezvous maneuver with the ISS. Now I understand in which way the shuttle gets in proximity of the station, it’s a matter of orbital mechanics, neither more nor less. What I can’t understand is what happen during the manual phase of the maneuver.
For example see the first picture attached. The shuttle is after MC4, that’s to say the manual phase has taken over. We have to get from point 1 to point 7. how does the shuttle get there? It’s my understanding that RCS is fired in the direction of travel (+X axis) in order to increase the velocity of the shuttle, lifting therefore the altitude slowing down at the same time. This because the lower the altitude and the faster the orbital speed. Is that correct? Or is there anything else that happen? Or maybe the RCS is fired downward (+ Z axis) so that the Shuttle goes up?
Both, and more. MC4 is a Lambert-targeted maneuver from the MC4 point (900 ft behind, 0 ft out-of-plane, and 1800 ft below nominally, but dispersions generally take the trajectory away from the nominal MC4 point) to the Rbar at 600 ft (0 ft behind, 0 ft out-of-plane, and 600 ft below), with a transfer time of 13 minutes. The delta-V for MC4 is therefore whatever Lambert comes up with. It is nominally around 2 fps in the orbiter +X body direction, but considering dispersions there may be Y and Z components present.QuoteAfter the R bar pitch maneuver the Shuttle goes in front the station for a V bar approach. With reference to the second picture attached, is my understanding that through continuous firings of the RCS system the altitude of the shuttle respect to the station’s altitude is constantly changed in order to continually slow down till when the station “hit” the shuttle itself. I’ll explain this better. Always with reference to the second picture, at point 8 the shuttle fires the RCS upwards so that it goes in a slightly lower orbit than the station. In this way the shuttle goes a little bit fastener. Then a second faring (point 9) this time downward, taking the shuttle in a slightly higher orbit than the station has, decreasing this time the speed. And the story goes in this way till to docking. I’m trying to find another explanation but it seems to me the only one reasonable taken into account the principle of orbital mechanics.
Any help is very appreciated.
Thanks
Davide
At this point the control of the orbiter is automatic in rotation, but entirely manual in translation. The orbiter rotates to the Vbar attitude at 0.13 deg/sec. When the attitude maneuver is complete, the orbiter stops rotating but the upward momentum of the orbiter causes ISS to drop in the centerline camera. The CDR then performs -X RCS translation as necessary to null the motion of ISS in the centerline camera. Generally the CDR uses heuristic knowledge of orbital mechanics to "bend" the curve to make a smooth arrival at the Vbar, but it's entirely manual - this is not a targeted maneuver. -
#1265 by sivodave on 20 Jul, 2010 05:24
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Hi Jorge. Thanks for the explanation. I’d like however to ask you few other questions for clarifications.
1) when MC4 is fired, the trajectory followed by the shuttle for getting from point 1 to point 7 (always with reference to first picture of my first post) is basically dictated by orbital mechanics, there is no manual action taken by the CDR. Is that correct? The CDR takes over manually only during the Vbar approach, right? The MC4 is computed by Mission Control or by shuttle onboard computers?
2) During the Vbar approach, which is the physical phenomena thanks to which the shuttle can get till to the ISS? I mean, I understand that the CDR makes firings in order to stay centered with the ISS, but than why (from an orbital mechanical point of view) the shuttle slows down so that it can dock with the station? Or put it in another way, why does the shuttle goes toward the station rather then station keeping? If station keeping is required, how is performed and how you can resume the motion toward the station for docking?
3) Given a inertial reference system, let’s say a system centered on the Earth and fixed, is the shuttle that goes toward the ISS or is the ISS going toward the Shuttle?
4) For missions like STS-92 and STS-98 I suppose an Rbar approach has been used. In this case, was this Rbar approach the same of the Rbar approach used for the Shuttle-Mir missions?
Thanks
Davide
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#1266 by Jorge on 20 Jul, 2010 06:23
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Hi Jorge. Thanks for the explanation. I’d like however to ask you few other questions for clarifications.
1) when MC4 is fired, the trajectory followed by the shuttle for getting from point 1 to point 7 (always with reference to first picture of my first post) is basically dictated by orbital mechanics, there is no manual action taken by the CDR. Is that correct? The CDR takes over manually only during the Vbar approach, right?
No, the CDR takes over manually after the MC4 burn is completed, and flies the rest of the approach manually. Only translation is performed manually; rotation is performed by the digital autopilot (DAP), except for a period during the RPM when the DAP is in free drift and the orbiter is not under active control at all.
In theory, MC4 places the orbiter on a trajectory that will reach 600 ft on the Rbar with no manual action required, but due to limitations of the sensors (rendezvous radar), navigation Kalman filter, Lambert guidance, and burn trim accuracy, some manual action is always required. At the very least, the theoretical post-MC4 trajectory is too fast at 600 ft for the RPM (-0.8 fps vs the -0.2 to -0.3 fps required), so typically some manual braking is required.QuoteThe MC4 is computed by Mission Control or by shuttle onboard computers?
Onboard. On the standard shuttle day-of-rendezvous trajectory, only the NH and NC burns are nominally ground-targeted. NCC, Ti, and MC1-4 are all computed onboard.Quote2) During the Vbar approach, which is the physical phenomena thanks to which the shuttle can get till to the ISS? I mean, I understand that the CDR makes firings in order to stay centered with the ISS, but than why (from an orbital mechanical point of view) the shuttle slows down so that it can dock with the station? Or put it in another way, why does the shuttle goes toward the station rather then station keeping? If station keeping is required, how is performed and how you can resume the motion toward the station for docking?
Second question first. With the orbiter on the Vbar, the CG is near the orbital altitude of ISS. If the orbiter is traveling the same speed as ISS, it will remain at that altitude and naturally maintain a near-stable position. So to initiate stationkeeping, the CDR performs +Z (braking) until the rdot is zero. To resume the approach, the CDR performs -Z translations to establish the desired rdot.
Now, the first question. When the orbiter is approaching ISS on the Vbar (whether by the CDR performing -Z or by naturally "turning the corner" at Vbar arrival), the orbiter is traveling retrograde relative to ISS and is therefore flying too slow to remain at that orbital altitude, and will tend to drop. The CDR counters this tendency by performing +X translations, creating a series of small "hops" on the Vbar. The size of the hops is a matter of CDR preference. In theory it is possible to perform a Vbar approach using nothing but +X, and a few CDRs have approached that ideal, but total perfection is elusive, alas.
Typically at Vbar arrival, after "turning the corner", the orbiter is closing on ISS at around -0.2 fps. Nominal approach speed at docking is -0.1 fps. In theory that should require braking (+Z). But the orbiter +X RCS thrusters are canted to point through the CG, so +X translation also induces a bit of +Z. The CDR can take advantage of this by using the +X hops to "nibble away" at the approach speed and avoid braking.Quote3) Given a inertial reference system, let’s say a system centered on the Earth and fixed, is the shuttle that goes toward the ISS or is the ISS going toward the Shuttle?
I'm not sure there's a meaningful answer to that question. In an inertial reference system, both vehicles are moving in independent orbits at 25000 fps. Which is moving toward the other depends on which relative reference system one chooses, though since ISS never performs rendezvous maneuvers, it makes more sense to think of the shuttle approaching the ISS rather than the other way around.Quote4) For missions like STS-92 and STS-98 I suppose an Rbar approach has been used. In this case, was this Rbar approach the same of the Rbar approach used for the Shuttle-Mir missions?
STS-88, 96, 101, 106, and 92 performed -Rbar approaches, in which the orbiter flew 180 degrees around ISS and approached from above. This type of approach was not used during Shuttle-Mir.
STS-97 and 98 performed +Rbar approaches, with the orbiter approaching from below and yawing to a tail-forward orientation at 600 ft. This is essentially the same approach used for Shuttle-Mir missions STS-76, 79, 81, 84, and 86. -
#1267 by sivodave on 20 Jul, 2010 07:33
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ok it's getting clearer and clearer, but I still have few questions, if you don't mind.Quote
No, the CDR takes over manually after the MC4 burn is completed, and flies the rest of the approach manually. Only translation is performed manually; rotation is performed by the digital autopilot (DAP), except for a period during the RPM when the DAP is in free drift and the orbiter is not under active control at all.
The translation in performed along all the 3 axis or only along two axes? I mean translation along the Rbar shouldn't be controlled since the motion along this vector is due to the MC4 burn which, you've said, aims to take the shuttle to a position 600ft under the station.QuoteWhen the orbiter is approaching ISS on the Vbar (whether by the CDR performing -Z or by naturally "turning the corner" at Vbar arrival), the orbiter is traveling retrograde relative to ISS and is therefore flying too slow to remain at that orbital altitude, and will tend to drop. The CDR counters this tendency by performing +X translations, creating a series of small "hops" on the Vbar. The size of the hops is a matter of CDR preference. In theory it is possible to perform a Vbar approach using nothing but +X, and a few CDRs have approached that ideal, but total perfection is elusive, alas.
so the orbiter is travelling retrograde relative to ISS because after having turned the corner the GC is higher then the GC's station and therefore the shuttle goes slower, right? why do you say that the shuttle is flying to slow to and tends to drop? in the diagram I posted I see a firing aimed to lower shuttle altitudine so it doesn't seem it tends to drop. what am I missing?QuoteSTS-88, 96, 101, 106, and 92 performed -Rbar approaches, in which the orbiter flew 180 degrees around ISS and approached from above. This type of approach was not used during Shuttle-Mir.
I didn't know of this kind of approach. which is the reason behind this kind of approach? is there anything peculiar respect to a +Rbar approach, or is just a mirror copy of a +Rbar approach?
OT: just for curiosity, are you a flight controller? how do you know all this things? I've been founding documents explaining in detail the mechanics of flight of the shuttle during the rendezvous and proximity operation but till now I haven't found what I really want.
Thanks again
ps: probably I'll have some questions about the undocking and flyaround, but later. For today it's enough.
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#1268 by psloss on 20 Jul, 2010 21:55
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STS-88, 96, 101, 106, and 92 performed -Rbar approaches, in which the orbiter flew 180 degrees around ISS and approached from above. This type of approach was not used during Shuttle-Mir.
Could be bad memory, but it seemed like there were more -R bar approaches prior to Shuttle-Mir...or were those inertial approaches? One of the papers on rendezvous that I stumbled onto recently (on HST mission rendezvous, link) seems to suggest that the +R bar approaches started during Shuttle-Mir were then applied to at least some orbiter rendezvous approaches to other spacecraft, such as HST. It may just be that the memory of the LDEF rendezvous, with the orbiter flying out in front and then over the top, sticks out to me.
STS-97 and 98 performed +Rbar approaches, with the orbiter approaching from below and yawing to a tail-forward orientation at 600 ft. This is essentially the same approach used for Shuttle-Mir missions STS-76, 79, 81, 84, and 86.
FWIW, I threw in a screen capture of a figure from another reference, in NTRS:
http://hdl.handle.net/2060/20070018243
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#1269 by sivodave on 21 Jul, 2010 00:19
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Quote
Could be bad memory, but it seemed like there were more -R bar approaches prior to Shuttle-Mir...or were those inertial approaches? One of the papers on rendezvous that I stumbled onto recently (on HST mission rendezvous, link) seems to suggest that the +R bar approaches started during Shuttle-Mir were then applied to at least some orbiter rendezvous approaches to other spacecraft, such as HST. It may just be that the memory of the LDEF rendezvous, with the orbiter flying out in front and then over the top, sticks out to me.
FWIW, I threw in a screen capture of a figure from another reference, in NTRS:
http://hdl.handle.net/2060/20070018243
I read both links you posted...they are both very good. One thing that I can't understand is the difference between inertial and Rbar approach. -
#1270 by psloss on 21 Jul, 2010 00:58
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Jorge would definitely be a good person to take that...here's another interesting paper by John Goodman:QuoteCould be bad memory, but it seemed like there were more -R bar approaches prior to Shuttle-Mir...or were those inertial approaches? One of the papers on rendezvous that I stumbled onto recently (on HST mission rendezvous, link) seems to suggest that the +R bar approaches started during Shuttle-Mir were then applied to at least some orbiter rendezvous approaches to other spacecraft, such as HST. It may just be that the memory of the LDEF rendezvous, with the orbiter flying out in front and then over the top, sticks out to me.
FWIW, I threw in a screen capture of a figure from another reference, in NTRS:
http://hdl.handle.net/2060/20070018243
I read both links you posted...they are both very good. One thing that I can't understand is the difference between inertial and Rbar approach.
http://klabs.org/DEI/lessons_learned/shuttle/cr-2007-2136974.pdf
Based on more foggy memory, I was looking for whether or not a Ti Delay had ever needed to be used; the reference above notes one usage on STS-49, but has details on other historical events. (Some of those early missions with lots of flight testing would be fun to go back and revisit, like 41-B.)
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#1271 by TJL on 21 Jul, 2010 15:23
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Can someone explain why the launch and entry helmets, last used on STS 51L, are still used today for training?
Thanks.
http://spaceflight.nasa.gov/gallery/images/shuttle/sts-133/lores/jsc2010e075082.jpg -
#1272 by Jorge on 25 Jul, 2010 22:24
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Jorge would definitely be a good person to take that...here's another interesting paper by John Goodman:QuoteCould be bad memory, but it seemed like there were more -R bar approaches prior to Shuttle-Mir...or were those inertial approaches? One of the papers on rendezvous that I stumbled onto recently (on HST mission rendezvous, link) seems to suggest that the +R bar approaches started during Shuttle-Mir were then applied to at least some orbiter rendezvous approaches to other spacecraft, such as HST. It may just be that the memory of the LDEF rendezvous, with the orbiter flying out in front and then over the top, sticks out to me.
FWIW, I threw in a screen capture of a figure from another reference, in NTRS:
http://hdl.handle.net/2060/20070018243
I read both links you posted...they are both very good. One thing that I can't understand is the difference between inertial and Rbar approach.
http://klabs.org/DEI/lessons_learned/shuttle/cr-2007-2136974.pdf
Based on more foggy memory, I was looking for whether or not a Ti Delay had ever needed to be used; the reference above notes one usage on STS-49, but has details on other historical events. (Some of those early missions with lots of flight testing would be fun to go back and revisit, like 41-B.)
STS-49 was the only Ti delay to date. -
#1273 by Jorge on 25 Jul, 2010 22:26
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Quote
Could be bad memory, but it seemed like there were more -R bar approaches prior to Shuttle-Mir...or were those inertial approaches? One of the papers on rendezvous that I stumbled onto recently (on HST mission rendezvous, link) seems to suggest that the +R bar approaches started during Shuttle-Mir were then applied to at least some orbiter rendezvous approaches to other spacecraft, such as HST. It may just be that the memory of the LDEF rendezvous, with the orbiter flying out in front and then over the top, sticks out to me.
FWIW, I threw in a screen capture of a figure from another reference, in NTRS:
http://hdl.handle.net/2060/20070018243
I read both links you posted...they are both very good. One thing that I can't understand is the difference between inertial and Rbar approach.
The difference is how the orbiter attitude is maintained. In an inertial approach the orbiter attitude is held fixed in an inertial frame of reference, while in an Rbar (or Vbar) approach the attitude is held fixed in the rotating LVLH frame of reference. In both cases the CDR maintains a fixed line-of-sight to the target along the orbiter's -Z axis (straight above the payload bay). -
#1274 by Jorge on 25 Jul, 2010 22:36
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STS-88, 96, 101, 106, and 92 performed -Rbar approaches, in which the orbiter flew 180 degrees around ISS and approached from above. This type of approach was not used during Shuttle-Mir.
Could be bad memory, but it seemed like there were more -R bar approaches prior to Shuttle-Mir...or were those inertial approaches?
STS-97 and 98 performed +Rbar approaches, with the orbiter approaching from below and yawing to a tail-forward orientation at 600 ft. This is essentially the same approach used for Shuttle-Mir missions STS-76, 79, 81, 84, and 86.
I think STS-32 was the only -Rbar approach prior to STS-88. Would need to check, though.
There were several inertial approaches, including HST, EURECA, and some of the SPARTANs. These tended to be used for spacecraft that could not hold a grapple attitude in the LVLH frame of reference (which makes sense for astronomical spacecraft, since their intended targets are all inertial).QuoteOne of the papers on rendezvous that I stumbled onto recently (on HST mission rendezvous, link) seems to suggest that the +R bar approaches started during Shuttle-Mir were then applied to at least some orbiter rendezvous approaches to other spacecraft, such as HST.
That's true. But the +Rbar approach was first tested on STS-66, with CRISTA-SPAS, before being used on Mir.
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#1275 by Jorge on 25 Jul, 2010 22:48
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ok it's getting clearer and clearer, but I still have few questions, if you don't mind.
QuoteNo, the CDR takes over manually after the MC4 burn is completed, and flies the rest of the approach manually. Only translation is performed manually; rotation is performed by the digital autopilot (DAP), except for a period during the RPM when the DAP is in free drift and the orbiter is not under active control at all.
The translation in performed along all the 3 axis or only along two axes?
All three.QuoteI mean translation along the Rbar shouldn't be controlled since the motion along this vector is due to the MC4 burn which, you've said, aims to take the shuttle to a position 600ft under the station.
In theory, yes. In practice, *some* control in all three axes is always required.QuoteQuoteWhen the orbiter is approaching ISS on the Vbar (whether by the CDR performing -Z or by naturally "turning the corner" at Vbar arrival), the orbiter is traveling retrograde relative to ISS and is therefore flying too slow to remain at that orbital altitude, and will tend to drop. The CDR counters this tendency by performing +X translations, creating a series of small "hops" on the Vbar. The size of the hops is a matter of CDR preference. In theory it is possible to perform a Vbar approach using nothing but +X, and a few CDRs have approached that ideal, but total perfection is elusive, alas.
so the orbiter is travelling retrograde relative to ISS because after having turned the corner the GC is higher then the GC's station and therefore the shuttle goes slower, right?
No, it's based on relative velocity, not position. Retrograde means the relative velocity is directed toward the -Vbar. It's not strongly dependent on CG position.Quotewhy do you say that the shuttle is flying to slow to and tends to drop?
Because in order to remain in an orbit the same altitude as ISS, the orbiter needs to be traveling the same speed. That would imply zero relative velocity, so the orbiter would neither approach nor separate.Quotein the diagram I posted I see a firing aimed to lower shuttle altitudine so it doesn't seem it tends to drop. what am I missing?
You're missing the relative velocity part, which is not easy to depict directly on a plot of relative position but can be inferred from the direction of relative position over time. Prior to Vbar arrival, the orbiter is traveling mostly radially up and slightly retrograde. The firing you point out is intended not to lower the orbiter's altitude, but to null the radial up velocity so it doesn't shoot right through the Vbar.QuoteQuoteSTS-88, 96, 101, 106, and 92 performed -Rbar approaches, in which the orbiter flew 180 degrees around ISS and approached from above. This type of approach was not used during Shuttle-Mir.
I didn't know of this kind of approach. which is the reason behind this kind of approach?
To prevent the orbiter from blocking the line-of-sight between Russian ground stations and the antennas on ISS. Back in those days, before there was a crew aboard ISS, Russian commanding capability at docking was considered critical.Quoteis there anything peculiar respect to a +Rbar approach, or is just a mirror copy of a +Rbar approach?
I assume one of those was supposed to be a -Rbar. The difference is that the rendezvous is always from below and behind and ends on a trajectory intersecting the +Rbar. So a +Rbar approach can be performed directly after the rendezvous, while a -Rbar approach requires a 180 degree flyaround to place the orbiter above the target.QuoteOT: just for curiosity, are you a flight controller? how do you know all this things?
Did flight control up to 1995, have been an instructor since then. -
#1276 by psloss on 25 Jul, 2010 22:52
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Thanks for the answers, Jorge.
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#1277 by DaveS on 26 Jul, 2010 10:13
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Anyone know what the black upper wing chines on Columbia was? It doesn't look like to be HRSI tiles or black painted FRSI blankets.
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#1278 by Zpoxy on 26 Jul, 2010 22:32
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Anyone know what the black upper wing chines on Columbia was? It doesn't look like to be HRSI tiles or black painted FRSI blankets.
Your second guess was correct. It was a black thermal coating (paint) applied over the FRSI and white LRSI tiles with rollers. It was done prior to the OPF rollout for STS-1. Some of the thermal engineers thought it would help keep the hydraulic lines on the floor of the payload bay at a more constant temperature. -
#1279 by SiameseCat on 02 Aug, 2010 04:06
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Another question about the HUD: during the HDG phase, the HUD guidance diamond shows pitch and roll errors. During the PREFINAL and FLARE phases, when the fixed flight director symbol is replaced by the velocity vector symbol, does the guidance diamond show the target velocity vector, or does it still show pitch/roll errors?
