What are the internal factors that limit Shuttle visit times at ISS? Yes, I know there are constraints due to visiting vehicles not docking with ISS while Shuttle is attached, but I am trying to figure out why otherwise the Shuttle could not stay attached for 30 days, now that ISS can provide power and other consumables to Shuttle.
The fuel cell H2 boils off (the boiloff is still used to produce electrical power). The shuttle needs the fuel cells to provide power post undocking, no H2, no electricity.
It's my understanding, also, that it's possible to turn down the fuel cells only so far before they start choking on their own exhaust, so to speak -- there have been a couple of recent shuttle missions where there was a concern that it would be necessary to throttle the fuel cells up to keep them operational, which would have required cutting the mission short. I have no idea if the fuel cells can be shut down and restarted on orbit -- I know Apollo's couldn't, it required Ground Support Equipment. Or, perhaps NASA just isn't interested in experimenting with the Shuttle these days.
Fuel cells were not my system, but I understand the "essential" dc busses can be used to start a cell on orbit. I just heard this as cross talk while I was teaching astronauts how to fly the darn thing.
Danny Deger
What are the internal factors that limit Shuttle visit times at ISS? Yes, I know there are constraints due to visiting vehicles not docking with ISS while Shuttle is attached, but I am trying to figure out why otherwise the Shuttle could not stay attached for 30 days, now that ISS can provide power and other consumables to Shuttle.
The fuel cell H2 boils off (the boiloff is still used to produce electrical power). The shuttle needs the fuel cells to provide power post undocking, no H2, no electricity.
It's my understanding, also, that it's possible to turn down the fuel cells only so far before they start choking on their own exhaust, so to speak -- there have been a couple of recent shuttle missions where there was a concern that it would be necessary to throttle the fuel cells up to keep them operational, which would have required cutting the mission short. I have no idea if the fuel cells can be shut down and restarted on orbit -- I know Apollo's couldn't, it required Ground Support Equipment. Or, perhaps NASA just isn't interested in experimenting with the Shuttle these days.
Fuel cells were not my system, but I understand the "essential" dc busses can be used to start a cell on orbit. I just heard this as cross talk while I was teaching astronauts how to fly the darn thing.
Danny Deger
The essential buses are themselves powered by the fuel cells, so you have to have at least one fuel cell already running for this to work.
The X-Plane manual states that the re-entry has been flown manually, which frankly, I find hard to believe.
In reality, the autopilot flies the entire 30-minute re-entry, and the astronauts do not take over the controls of the shuttle until the final 2 minutes of the glide. The astronauts COULD fly the entire re-entry by hand, but it is officially discouraged by NASA. The reason is obvious. These speeds and altitudes are way outside of normal human conception, so our ability to "hand-fly" these approaches is next to nil.
In the history of Shuttle missions (the 100th mission has just come to a close as I write this), the real space shuttle has been hand-flown for the entire re-entry only ONCE, by an ex-marine pilot, as I understand it, who was ready for the ultimate risk and challenge.
Has anybody got more information on this?
I know that there were problems with oscillations in sideslip after the first roll reversal maneuver in STS-1, so in subsequent flights that first bank maneuver was flown by hand until they fixed the software (
From Runway to Orbit p.221ff), but besides that, to my knowledge, the commander does not take control until the shuttle goes sub-sonic.
I also doubt that
"COULD fly the entire re-entry by hand" part. This is a fly-by-wire system, and as far as I know the vehicles response varies dramatically with Mach numbers (especially in the hypersonic regime), so the computer always "translates" the control input and, depending on Mach number, determines which surfaces to move and which RCS jets to fire (M.I.T. open courseware 16.885J / ESD.35J Aircraft Systems Engineering)
Would still be interesting to know where that information comes from and if it's true.
Thanks!
The X-Plane manual states that the re-entry has been flown manually, which frankly, I find hard to believe.
Has anybody got more information on this?
This may be related
http://forum.nasaspaceflight.com/index.php?topic=17623.msg427231#msg427231 (you'll have to read through some noise and back and forth to get the whole picture)
Note that flying "manually" in any case wouldn't mean flying without computer aid. No computer, no control.
edit:
typo
The fuel cell H2 boils off (the boiloff is still used to produce electrical power). The shuttle needs the fuel cells to provide power post undocking, no H2, no electricity.
It's too late for that now, but had such a requirement been in place earlier in the program, could the Shuttle have been relatively easily designed/modified to support this? Say by using active cooling with power supplied by the ISS or by using differently designed APUs for electrical power as well as hydraulics during deorbit and descent?
Edit: or using noncryogenic fuel cells...
The simplest solution was just to carry more cryo, and it was indeed designed in early. The EDO pallet first flew in the early 90's, taking up some mass and space in the payload bay, and Endeavour and Columbia were plumbed to accommodate it. IIRC, Columbia even flew a 17 day mission. She had it on -107, which is why later analysis showed the crew could have lasted about a month in orbit at minimum power consumption, long enough, perhaps, to rush Atlantis to the pad.
The electric APU was a separate proposed mod. Not sure where the energy would have come from. More cryo fuel cells, charging batteries to deliver big currents to the hydraulic pumps during entry?
-Alex
-Alex
The simplest solution was just to carry more cryo, and it was indeed designed in early. The EDO pallet first flew in the early 90's, taking up some mass and space in the payload bay, and Endeavour and Columbia were plumbed to accommodate it. IIRC, Columbia even flew a 17 day mission. She had it on -107, which is why later analysis showed the crew could have lasted about a month in orbit at minimum power consumption, long enough, perhaps, to rush Atlantis to the pad.
Interesting, thanks!
The electric APU was a separate proposed mod. Not sure where the energy would have come from. More cryo fuel cells, charging batteries to deliver big currents to the hydraulic pumps during entry?
I was thinking of an APU driving an electric generator as well as a hydraulic pump, not a source of electrical power driving a hydraulic pump. As an aside, weren't there also plans for electromechanical actuators to avoid the need for hydraulics?
The simplest solution was just to carry more cryo, and it was indeed designed in early. The EDO pallet first flew in the early 90's, taking up some mass and space in the payload bay, and Endeavour and Columbia were plumbed to accommodate it. IIRC, Columbia even flew a 17 day mission.
Sort of -- IIRC, there were multiple 16-day EDO missions that used one or two weather extension days. STS-80 used two and flew for almost 18 days. Most of the EDO mods were removed from Endeavour during the OMDP period that brought in the set of changes to fly to ISS.
1. The simplest solution was just to carry more cryo, and it was indeed designed in early.
2. The electric APU was a separate proposed mod. Not sure where the energy would have come from. More cryo fuel cells, charging batteries to deliver big currents to the hydraulic pumps during entry?
1. Not viable, it would have reduced payload weight and volume to the ISS.
2. Dedicated batteries.
The simplest solution was just to carry more cryo, and it was indeed designed in early. The EDO pallet first flew in the early 90's, taking up some mass and space in the payload bay, and Endeavour and Columbia were plumbed to accommodate it. IIRC, Columbia even flew a 17 day mission. She had it on -107, which is why later analysis showed the crew could have lasted about a month in orbit at minimum power consumption, long enough, perhaps, to rush Atlantis to the pad.
On the outline for early space station Freedom utilization, there was planned for an orbiter to use both an EDO pallet and what is now known as SSPTS for one to two month docked times. At that phase the station would not have had a permanent crew as there was not a CRV.
Hi all.
I have been looking at defintions to what "nadir" means (the point below the observer that is directly opposite the zenith on the imaginary sphere against which celestial bodies appear to be projected) and "still can't wrap my head around it".
Can anyone simplify it for me.
Thanks
Oxford750
Hi all.
I have been looking at defintions to what "nadir" means (the point below the observer that is directly opposite the zenith on the imaginary sphere against which celestial bodies appear to be projected) and "still can't wrap my head around it".
Can anyone simplify it for me.
Thanks
Oxford750
Nadir is the direction that points toward the Earth's center of mass.
The X-Plane manual states that the re-entry has been flown manually, which frankly, I find hard to believe.
I have read several times (I can't cite a source at the moment) that it was Joe Engle on STS-2 who manually flew the re-entry from Mach 24 to landing as part of the OFT program. He did it because it was one of his flight test objectives to prove that it
could be done if it ever had to be done. I'm pretty sure he would have also been able to turn over control to the computer very quickly if he determined that he wasn't within his margins but I'm not sure what that would have meant for the Shuttle program.
Story confirmed here:
http://www.jsc.nasa.gov/history/oral_histories/EngleJH/EngleJH_6-3-04.pdf
That's a fun one -- read his recounting of the 51-I launch.
(One of the tests during the early flights was an autoland test, and there was a short period after the orbiter was on final prior to flare and touchdown where the autoland system was in control. IIRC, they did that for STS-2 through STS-5.)
Anyone aware of plans for a new edition of the Jenkins STS book after the program ends? I'd love to pick up a copy of the 3rd edition (2001), but as it's 9 years and 30+ missions out of date I'd prefer to wait on an update if one is forthcoming.
You should still get the older editions. Looking through all three editions that I have, there are slight differences from one to another. Anyway, how could you possibly stand to wait!
You should still get the older editions. Looking through all three editions that I have, there are slight differences from one to another. Anyway, how could you possibly stand to wait!
If practical, the fourth edition will restore materials that had to be deleted from the previous editions for space reasons.
