-
#140
by
ppb
on 05 Dec, 2014 17:11
-
Seems like it's pretty common for multiple chutes to oscillate like that for awhile. The SRB chutes did the same thing until near splashdown.
Similar behaviour was common on Apollo CM splashdowns as well.
Thank you both for the feedback. I will have to look at some SRB and Apollo CM splashdown footage now!
I noticed that oscillation as well... in fact right near the point it went through the last cloud deck, one chute actually moved between the other two, which means the riser bundles below would have woven together one turn. I never saw this on Apollo (although I didn't see all existing footage). The riser length to canopy diameter ratio seems larger than what I remember on Apollo, which (**speculation**) may cause higher oscillation. Any parachute experts care to comment? Please direct me to other threads as appropriate.
-
#141
by
SWGlassPit
on 05 Dec, 2014 17:11
-
So, as ORION was falling back to earth, I was watching the altitude on the telemetry display, and it seemed to continuously fall at pretty close to one mile per second. That works out to 3600 mph. Why did it not increase in speed to closer to 5mps? Was I not watching correctly or perhaps looking at the wrong thing?
Orion wasn't falling straight down. That one mile per second is only the vertical component of Orion's velocity. It was coming in at a good 5.5 miles per second, but at an angle slightly below horizontal.
-
#142
by
SkipMorrow
on 05 Dec, 2014 17:18
-
Ah, that makes perfect sense!
-
#143
by
MarsInMyLifetime
on 05 Dec, 2014 18:33
-
Seems like it's pretty common for multiple chutes to oscillate like that for awhile. The SRB chutes did the same thing until near splashdown.
Similar behaviour was common on Apollo CM splashdowns as well.
Thank you both for the feedback. I will have to look at some SRB and Apollo CM splashdown footage now!
I noticed that oscillation as well... in fact right near the point it went through the last cloud deck, one chute actually moved between the other two, which means the riser bundles below would have woven together one turn. I never saw this on Apollo (although I didn't see all existing footage). The riser length to canopy diameter ratio seems larger than what I remember on Apollo, which (**speculation**) may cause higher oscillation. Any parachute experts care to comment? Please direct me to other threads as appropriate.
I went looking, PPB, and found a few useful reads about parachute stability. This is my rollup from several sources, the best being these:
https://www.wpi.edu/Pubs/ETD/Available/etd-0426102-134658/unrestricted/Desabrais.pdf (in particular, see 3.3: Canopy Dynamic Behavior)
http://www.nakka-rocketry.net/paracon.htmlImpounded air in a parachute system needs to go to a region of lower pressure. In the Soyuz descent videos where a single parachute is involved, you can easily see a breathing or pulsing type of oscillation as internal vortices build up and expand the parachute and then spill out causing some deflation, and the cycle repeats. Apex holes, annular rings, and permeable material are brought into the design in a trade-off between drag and instability, but you don't get one without the other.
When no spill management is involved in the design, the pressure escapes out of the higher side, which sets up a swinging or coning-type oscillation (to the vexation of early parachute jumpers). In the three-parachute system, all three parachutes are forced to be tilted, so their spill occurs continuously to the central high side. It is still a dynamic environment, and you can see breathing (the three chutes moving toward and away from that central point) and oscillation (some degree of swinging in and out by individual parachutes, and I'd include that crossover move as due to this mode). Long story short, both modes of oscillation are normal behavior for simple round chutes in single or ganged configurations. It can be abated by more specialized parachute designs that manage the spill by converting it into more of a Bernoulli effect--as in inflatable wing or asymmetric designs that may be less reliable for "must work now" space recovery (recalling the occasional resurgences of the Rogallo wing).
-
#144
by
Jim
on 05 Dec, 2014 18:36
-
NASA TV also mentioned a South Africa station - type???
Hartebeesthoek tracking site. Commercially procured tracking services.
-
#145
by
Jim
on 05 Dec, 2014 18:37
-
The Air Force Satellite Control Network is managed by the 50th Space Wing out of Schriever AFB, CA and has sites at Hawaii, Guam, Vandenberg AFB, and Diego Garcia.
Schriever AFB is in Colorado Springs, CO...
Oops, typo
-
#146
by
dks13827
on 05 Dec, 2014 19:02
-
If you'd like, you could say Orion is in it's (ridiculously elliptical and about to be really hot) post-deorbit-burn trajectory, but yeah ... no longer "in orbit".
Sure, but suppose they now circularize at apogee (I realize they have no intent to do this and no fuel to do it anyway, but supposing). So would you say that during this period they are *not* in orbit? That seems really weird, too.
Nope. I'd say they were in a transfer orbit, but that transfer orbit was "re-entrant".
Shuttle ascent trajectories were re-entrant until OMS-2. We weren't safely in orbit until then. 
This was also mention in the TV coverage: Executing the burn to absolute perfection, the DCSS-Orion stack entered a highly elliptical trajectory with a negative perigee – set up to allow Orion to re-enter the atmosphere at a precisely targeted location.
-
#147
by
Yeknom-Ecaps
on 05 Dec, 2014 19:39
-
In the Pacific for the recovery there was the USS Anchorage and the USNS Salvor ......
were there any other ships in the Pacific to support the recovery?
Were there any "abort" ships in the Atlantic by the launch site?
-
#148
by
thomson
on 05 Dec, 2014 19:52
-
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?
-
#149
by
Jim
on 05 Dec, 2014 20:06
-
Were there any "abort" ships in the Atlantic by the launch site?
There was no abort ships or any other ships
-
#150
by
Patchouli
on 05 Dec, 2014 20:07
-
In the Pacific for the recovery there was the USS Anchorage and the USNS Salvor ......
were there any other ships in the Pacific to support the recovery?
Were there any "abort" ships in the Atlantic by the launch site?
From what I read the abort system except for the separation motor was inert since it was an uncrewed test flight.
One thing I noticed is the reentry seemed rather steep as if it was designed to maximize the peak heating.
I wonder what sorta profile operational reentries will follow.
-
#151
by
Jim
on 05 Dec, 2014 20:08
-
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?
ULA is not under contract to NASA for this mission. You would have to see LM's contract to see what units it uses.
-
#152
by
MattMason
on 05 Dec, 2014 20:15
-
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.
However, as an American agency with a long history of how to make the complex understandable to the watching American viewers (who dominantly use Imperial units), the public affairs teams that comment throughout flights like EFT-1 use Imperial units or illustrate things as such.
You're speaking of the Mars Climate Orbiter. A link to the issue is in this Wikipedia page, which supports Jim's comment that designs and standards are a contractual thing.
https://en.wikipedia.org/wiki/Mars_Climate_OrbiterJim's comment, as he is in The Know, about contracts on this mission determine the proper answer if one can find that info from NASA's published sources online.
-
#153
by
Yeknom-Ecaps
on 05 Dec, 2014 20:18
-
Back in the Apollo/Skylab days the "Hurricane Hunter" HC-130s flew weather support for the launch and recovery areas - were there any such flights for EFT-1?
-
#154
by
tjchambers
on 05 Dec, 2014 20:28
-
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.
However, as an American agency with a long history of how to make the complex understandable to the watching American viewers (who dominantly use Imperial units), the public affairs teams that comment throughout flights like EFT-1 use Imperial units or illustrate things as such.
Jim's comment, as he is in The Know, about contracts on this mission determine the proper answer if one can find that info from NASA's published sources online.
I too found some cognitive dissonance on this. The simulated display of apogee and perigee was in NM while the PAO was describing things in statute miles. 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. I do know how to do the conversions for the Imperial vs. Metric and Nautical vs Statute, but if they want to appease the viewing audience they should IMHO pick something for a good reason and use it universally.
My two cents.
-
#155
by
ehb
on 05 Dec, 2014 20:28
-
I went looking, PPB, and found a few useful reads about parachute stability. This is my rollup from several sources, the best being these:
https://www.wpi.edu/Pubs/ETD/Available/etd-0426102-134658/unrestricted/Desabrais.pdf (in particular, see 3.3: Canopy Dynamic Behavior)
http://www.nakka-rocketry.net/paracon.html
...
Thanks for the feedback.
Looked through your references and some others & I watched multiple splashdown footage for SRB & Apollo (11 thru 17, Skylab 2,3 & ASTP). For those where the parachutes were visible and all 3 deployed (e.g. not Apollo 15), I did see some "oscillation", but nothing of the magnitude of what I saw today on ETF-1 and also apparent on Orion parachute test video footage.
I must assume this is expected and understood, but seeing the footage is still a bit disconcerting to me. I would certainly like to read any comments about the Orion parachute performance from the "Capsule Parachute Assembly System Government Furnished Equipment Project" (is Chris Johnson somewhere on this forum?)
-
#156
by
Jim
on 05 Dec, 2014 20:30
-
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.
-
#157
by
Jim
on 05 Dec, 2014 20:32
-
Back in the Apollo/Skylab days the "Hurricane Hunter" HC-130s flew weather support for the launch and recovery areas - were there any such flights for EFT-1?
No. EFT-1 did not use any assets that beyond those normally used for Delta IV launches. This wasn't a manned mission.
-
#158
by
tjchambers
on 05 Dec, 2014 20:39
-
I went looking, PPB, and found a few useful reads about parachute stability. This is my rollup from several sources, the best being these:
https://www.wpi.edu/Pubs/ETD/Available/etd-0426102-134658/unrestricted/Desabrais.pdf (in particular, see 3.3: Canopy Dynamic Behavior)
http://www.nakka-rocketry.net/paracon.html
...
Thanks for the feedback.
Looked through your references and some others & I watched multiple splashdown footage for SRB & Apollo (11 thru 17, Skylab 2,3 & ASTP). For those where the parachutes were visible and all 3 deployed (e.g. not Apollo 15), I did see some "oscillation", but nothing of the magnitude of what I saw today on ETF-1 and also apparent on Orion parachute test video footage.
I must assume this is expected and understood, but seeing the footage is still a bit disconcerting to me. I would certainly like to read any comments about the Orion parachute performance from the "Capsule Parachute Assembly System Government Furnished Equipment Project" (is Chris Johnson somewhere on this forum?)
I too had the concerned reaction when I saw 1 of the 3 parachutes "dance across" between the other 2.
My very limited experience suggested that should they wrap around in a braid of some sort, that the tension would naturally tend to recover and unwind as long as they were unfurled. I also infer that the way they are tethered to the craft itself could have an impact, whether that is a vertical loop with 3 connections (center being able to go back and forth), or a circular horizontal bar that allowed them some latitude to slide around a center point.
Interesting observations and probably cross wind influenced as well.
-
#159
by
tjchambers
on 05 Dec, 2014 20:43
-
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.
Thanks. It would therefore be easier for me to digest if the NASA PAO was speaking using statute miles while nautical miles were on screen. I will keep my calculator handy.
