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#160
by
LouScheffer
on 05 Dec, 2014 20:56
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Being from these United States I tend to be more familiar with the Statute Mile, and since Nautical Miles are based on degrees of latitude, it seems unusual to quote them in terms of vertical distance away from Earth surface.
NASA has always used nautical miles for orbital altitude.
Agree that they are customary for NASA. I remember Walter Cronkite explaining what they were back in the Mercury days.
However, I'm not sure this a good tradition. You could make an argument for statute miles, which at least are familiar to all Americans, and NASA is an American agency. But if you are not using statute miles, you should use kilometers. As a space fan, I watched Hayabusa launch on Tuesday. They use km. I will watch Ariane launch tomorrow - they use km. So if you are going to make Americans use a (to them) unfamiliar unit, at least make it one they can use in watching all other space programs. Furthermore, the international watchers will be pleased, and NASA can help fulfill its STEM education mandate.
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#161
by
mr. mark
on 05 Dec, 2014 21:01
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Nice launch picture. So proud of NASA and ULA!
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#162
by
Malderi
on 05 Dec, 2014 21:07
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A question about NASA and the units used. During EFT-1 live cover, three units were used to describe distance: nautical miles, statute miles and feet. I thought that NASA moved to mertic system after one of the probes failure was traced back to units confusion.
At first, I thought that maybe that data is converted to miles for general US audience, but that doesn't seem to be the case.
So, which units are used in NASA, LM and ULA: metric or imperial?
Others who actually work in the field can confirm this, but an internet search notes that NASA generally sticks to the metric system since 2007 for many functions and designs.
Heh, if only. I don't know what Orion uses today, but Shuttle was Imperial and Constellation started in Imperial. Back in the 08-09 timeframe a big effort was spent to convert Constellation (Orion included) to metric, which eventually failed and was rolled back. It's possible that it was done successfully later; I don't know.
The difficulty I've always heard is with manufacturing. So many large, expensive, (possibly custom) factory floor hardware is programmed in Imperial. So you've got to do the conversion at that end, or retool everything. I'm just a software guy so don't know how true that is.
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#163
by
Targeteer
on 05 Dec, 2014 21:54
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Was anyone else waiting/getting nervous for the mains to open as Rob Navias ticked off altitude? It seems the Soyuz gets on its main chute much higher up. I don't a feel for when Apollo got on it's mains because I've never seen film of how high up the chutes opened.
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#164
by
Targeteer
on 05 Dec, 2014 21:59
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What are mechanics of how a burn that raised apogee dropped the perigee at the same time? Was the centroid of the elliptical orbit somehow shifted?
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#165
by
Pheogh
on 05 Dec, 2014 22:01
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Are there any updates on how recovery is proceeding?
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#166
by
pippin
on 05 Dec, 2014 22:35
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During reentry they reported that Orion was pulling 8g. Is that what it would be designed to do with astronauts, too, when returning for deep space or was this to create more extreme conditions to test the heat shield and manned returns would use a skip-reentry?
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#167
by
enkarha
on 05 Dec, 2014 23:45
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During reentry they reported that Orion was pulling 8g. Is that what it would be designed to do with astronauts, too, when returning for deep space or was this to create more extreme conditions to test the heat shield and manned returns would use a skip-reentry?
Apollo would take something like 6.5-7.2 g's on reentry, so I would think this is not that abnormal.
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#168
by
IslandPlaya
on 06 Dec, 2014 00:34
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Did anyone notice how the UAV seemed to lose track of the landed Orion?
We saw still frames from the helo, but I was getting worried for a while as the flotation spheres seemed to deflate one by one...
At one point I thought it may have sunk...
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#169
by
treddie
on 06 Dec, 2014 01:12
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Hello.
I have a question that maybe someone in guidance systems can respond to. Being knowledgeable about guidance systems and Astrodynamics in general, I know that a perfect solution is never possible when the equations are solved. They are for the most part a numerical solution suffering to one degree or another between truncation and round-off errors. Add to that, the inherent sensitivity errors indicative of any gyro or accelerometer, and burn errors of the engines or thrusters themselves. Thus, the most often need for a midcourse correction (planned and unplanned) at one or more points in an orbit.
It was reported by Mission Control during EFT-1 that the guidance system performed so well (better than expectations) that the orbit was calculated such that no midcourse was required and re-entry ended in a "spot-on" landing in the Pacific Ocean. It was stated (in so many words) that this was unusual for such a long flight path.
My big question is, were the algorithms and techniques used truly capable of such precision, considering all of the numerous sources of error, OR, was it simply a matter of all of those sources of error canceling each other out in one of those rare "sweet moments" when all was said and done?
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#170
by
Ronpur50
on 06 Dec, 2014 02:18
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It took me about 3 or 4 views of the videos, but I noticed each parachute had it's own distinct pattern of stripes. I assume this was used to track the deployment and movement of each during descent.
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#171
by
treddie
on 06 Dec, 2014 02:49
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What are mechanics of how a burn that raised apogee dropped the perigee at the same time? Was the centroid of the elliptical orbit somehow shifted?
Targeteer, You can never shift the centroid of a conic orbit such as an ellipse...A conic orbit is always centered on one of the foci. The only way to keep perigee constant is if the burn occurs exactly at perigee and the flight path angle is exactly tangent to the orbit at the moment of the burn (Local Horizontal). But it is impossible to do a perfect impulse burn (a thrust period only lasting for an instantaneous moment) so even if the above rules are followed, any burn occurs over a time span, so realistically, perigee would always change to one extent or another.
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#172
by
Targeteer
on 06 Dec, 2014 02:59
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What are mechanics of how a burn that raised apogee dropped the perigee at the same time? Was the centroid of the elliptical orbit somehow shifted?
Targeteer, You can never shift the centroid of a conic orbit such as an ellipse...A conic orbit is always centered on one of the foci. The only way to keep perigee constant is if the burn occurs exactly at perigee and the flight path angle is exactly tangent to the orbit at the moment of the burn (Local Horizontal). But it is impossible to do a perfect impulse burn (a thrust period only lasting for an instantaneous moment) so even if the above rules are followed, any burn occurs over a time span, so realistically, perigee would always change to one extent or another.
How does a 4.5 minute posigrade burn raise one part of an orbit while dropping another part of the orbit? You lower an orbit by decreasing velocity so how is velocity decreased in such a short burn for another part of the orbit?
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#173
by
sdsds
on 06 Dec, 2014 04:31
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How does a 4.5 minute posigrade burn raise one part of an orbit while dropping another part of the orbit?
I think it is sufficient to consider the case of an impulsive burn at perigee.
The burn could not have been purely posigrade, as you suggest. There must have been a component of the burn orthogonal to the direction of motion, radially outward from the Earth. Now run time backwards
and see that the new trajectory intersects the atmosphere. Of course with time moving forward it will do so again just short of one revolution around the Earth.
PS: I think this video shows it well, just at the 1 minute mark.
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#174
by
mr. mark
on 06 Dec, 2014 04:48
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This launch brought back a LOT of memories for me. I remember as a kid watching the Apollo 4 launch which also tested out the command module as well.
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#175
by
treddie
on 06 Dec, 2014 07:26
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How does a 4.5 minute posigrade burn raise one part of an orbit while dropping another part of the orbit? You lower an orbit by decreasing velocity so how is velocity decreased in such a short burn for another part of the orbit?
A 4.5 min burn at say a circular orbit of 280 miles altitude above the Earth will be completed in about 1282.6 miles of travel, or about 17.3 degrees of arc. That's a lot.
If the posigrade burn is at perigee, and you assume a perfect instantaneous impulse, you get an increase in apogee with no change in perigee. On the other hand, if the posigrade burn is at apogee, there is an increase in perigee with no change in apogee. So what happens if the LH-burn is somewhere between apogee and perigee? Both perigee and apogee change.
During EFT-1, as we watched the orbit climb out to 3600 miles altitude, you could clearly see perigee change as well. So I can only assume the burn was intentionally started early or late relative to perigee. Add about 17.3 degrees of travel over the burn and you get what you get, which is what they needed to shape the flight path so that reentry was what they needed it to be.
It's been awhile but I think that also, if you burn early or late relative to the peripoint or the apopoint, you also steer the resulting orbit so that the major axis has rotated in the plane of the orbit (argument of the peripoint).
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#176
by
mheney
on 06 Dec, 2014 16:08
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You can also affect both perigee and apogee by thrusting "off-vector" - i.e, not along the velocity vector. If you pitch up 90 degrees (engine nozzle pointing down toward the ground) and thrust, you'll change the shape of your orbit. It's not as efficient as a well-timed along-vector impulse (it's a vector sum, so you get cosine losses... ) but it's an option.
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#177
by
Rocket Science
on 06 Dec, 2014 16:27
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Gerst mentioned in the post splashdown presser that he is going to appear at hearing in a week’s time. In all the afterglow of EFT-1 I hope the congressmen don’t start mentioning the movie “Interstellar” like they did after “Gravity” came out because I’m really going to puke this time...
“Money talks”...you know the rest...
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#178
by
Avron
on 06 Dec, 2014 18:04
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This launch brought back a LOT of memories for me. I remember as a kid watching the Apollo 4 launch which also tested out the command module as well.
Now that the propaganda machine has run out of steam, time to reflect, compare and face reality.
http://www.americaspace.com/?p=72662
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#179
by
Jason1701
on 06 Dec, 2014 18:25
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Sorry if this has already been answered, but in the video of the launch taken from the service gantry it looked like a few wires remained attached to the rocket until it had risen a couple hundred feet. Does anyone know what those do and why they stay attached so long?
and see that the new trajectory intersects the atmosphere. Of course with time moving forward it will do so again just short of one revolution around the Earth.
“Money talks”...you know the rest...