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#120 by Patchouli on 15 Nov, 2011 21:58
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As with so many others here, I find this very disheartening - but sadly unsurprising. It seems clear the Russians tried to do too much with too few resources. There were so many failure modes over the long mission to begin with; unfortunately, they may have been thrown off the horse right out of the chute.
Short of their restoring communications and control, AND being somehow able to successfully launch for Mars, the ideal scenario would be building F-G #2 for the next window, doing more testing, and taking to heart lessons learned.
That seems too logical to be possible in real life, doesn't it...?
Well they did attempt a Mars moon sample return mission on a budget that was less then the cost of a Discovery class mission.
I'm sure they skimped on the testing in ways NASA and the ESA would not even dream about.
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#121 by Michael J on 15 Nov, 2011 21:59
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Shooting it down may put ISS at risk as some of the debris may end up in a higher orbit.
My guess is that any intercept attempt would not be done until it reaches a low enough orbit where the remnants would reenter quickly, such as the USA-193 intercept. -
#122 by JimO on 15 Nov, 2011 22:03
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I wonder if shooting it down may put ISS at risk as some of the debris could possibly end up in a higher orbit.
Excellent point -- which also applies to an accidental explosion, a fate that has befallen a large number of derelict Russian booster stages in the past. But fortunately, only after a long time of orbital cruising, as I recall.
Some of the debris fragments might have sufficient forward energy to reach high enough to endanger the ISS. But not for long, because of their low perigee.
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#123 by Blackstar on 15 Nov, 2011 22:44
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Shooting it down (regardless of who does it) will be a PR nightmare.
It's more than that--IT WOULD BE BAD.
Look, do we really want a world where more and more countries are developing ASATs? That's happening now, but do we want to encourage it?
No.
Remember which country has the most to lose if other countries develop ASATs. -
#124 by iamlucky13 on 15 Nov, 2011 22:44
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The orbital plane precesses about 6 degrees per day in geocentric reference because of Earth's equatorial oblateness. So the geocentric plane of the departure asymptote is sweeping across the celestial sphere at some combination of this rate, earth's axial tilt, and Earth's movement around the sun.
I'm afraid I'm not following. Do you know of any resources that explain this better? I tried sketching out some rough diagrams, but I don't really see what drives this precession, in particular how oblateness is relevant. -
#125 by HIPAR on 15 Nov, 2011 23:14
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I've given up any hope the mission will be saved. There's been zero credible reports of progress. I doubt anyone will shoot it so this thing's coming down.
My understanding is there's hypergolic fuel aboard so I'm envisioning the tanks rupturing from reentry forces causing the binary components to ignite and explode.
If that doesn't happen, will the fuel be dispersed as an aerosol and subsequently be carried off by upper level winds?
Or, will tanks filled with fuel reach the ground?
Then there are those who believe the fuel will freeze but that must not represent the thoughts of Russians who still cling to hope. You cannot operate an engine with frozen fuel.
--- CHAS -
#126 by Lee Jay on 15 Nov, 2011 23:26
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The orbital plane precesses about 6 degrees per day in geocentric reference because of Earth's equatorial oblateness. So the geocentric plane of the departure asymptote is sweeping across the celestial sphere at some combination of this rate, earth's axial tilt, and Earth's movement around the sun.
I'm afraid I'm not following. Do you know of any resources that explain this better? I tried sketching out some rough diagrams, but I don't really see what drives this precession, in particular how oblateness is relevant.
The oblateness is relevant because it means the gravitational field isn't a perfect point source or that of a perfectly symmetrical sphere. -
#127 by HIPAR on 15 Nov, 2011 23:36
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The orbital plane precesses about 6 degrees per day in geocentric reference because of Earth's equatorial oblateness. So the geocentric plane of the departure asymptote is sweeping across the celestial sphere at some combination of this rate, earth's axial tilt, and Earth's movement around the sun.
I'm afraid I'm not following. Do you know of any resources that explain this better? I tried sketching out some rough diagrams, but I don't really see what drives this precession, in particular how oblateness is relevant.
The oblateness is relevant because it means the gravitational field isn't a perfect point source or that of a perfectly symmetrical sphere.
That is so but is it a 1st order effect on the orbit? GPS satellites go around that same ellipsoid and get corrected for nth order effects only once per year.
--- CHAS -
#128 by jcm on 15 Nov, 2011 23:52
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I've been trying to assemble a better understanding of the mass breakdown of FG (Anatoly Zak had a good first go at http://www.russianspaceweb.com/phobos_grunt_design.html)
All the various authoritative sources give only a subset of the needed info, and contradict each other (of course, and as usual :-))
Here is my guess... I throw it out in an attempt to provoke corrections.
'Propellant' is meant to include other consumables (usually a minor contribution)
SA (Descent module) 7 kg
VA (Return module) dry 139 kg
VA propellant 135 kg
PM (Flight module) dry 730 kg (including 180 kg propulsion system)
PM propellant 1050 kg (but another source suggests 529 kg)
Truss 172 kg
YH-1 satellite 115 kg
MDU (Prop'n module) dry 735 kg
MDU propellant 7015 kg
SBB (drop tank) dry 335 kg
SBB propellant 3001 kg
Total at launch 13434 kg
A few of these are pulled out of my.... well, somewhere.
Anyone want to have a better go?
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#129 by ddunham on 16 Nov, 2011 00:14
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That is so but is it a 1st order effect on the orbit? GPS satellites go around that same ellipsoid and get corrected for nth order effects only once per year.
GPS satellites are significantly farther away. At their distance, the effects from the oblateness are much smaller. -
#130 by simonbp on 16 Nov, 2011 00:22
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That is so but is it a 1st order effect on the orbit? GPS satellites go around that same ellipsoid and get corrected for nth order effects only once per year.
Strictly speaking, it's the axisymmetric spherical harmonic component of the second-order gravity field (aka J2), first-order order being the fully symmetric monopole field.
And yes, J2 is quite strong at a few hundred km above the Earth's surface. It drops off quite fast, though (1/r^4, as opposed to monopole's 1/r^2), so it is much weaker at the altitudes GPS sats fly (~20,000 km, or 10,000 times weaker). -
#131 by Comga on 16 Nov, 2011 00:25
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The orbital plane precesses about 6 degrees per day in geocentric reference because of Earth's equatorial oblateness. So the geocentric plane of the departure asymptote is sweeping across the celestial sphere at some combination of this rate, earth's axial tilt, and Earth's movement around the sun.
I'm afraid I'm not following. Do you know of any resources that explain this better? I tried sketching out some rough diagrams, but I don't really see what drives this precession, in particular how oblateness is relevant.
Try Bate, Mueller, & White Fundamentals of Astrodynamics P156 (of my old book) Chapter 3.1.3 Perturbation of Low Altitude Orbits due to the Earth's Oblatness.
Or any other basic astrodynamics or orbital mechanics book. -
#132 by ChileVerde on 16 Nov, 2011 00:29
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The orbital plane precesses about 6 degrees per day in geocentric reference because of Earth's equatorial oblateness. So the geocentric plane of the departure asymptote is sweeping across the celestial sphere at some combination of this rate, earth's axial tilt, and Earth's movement around the sun.
I'm afraid I'm not following. Do you know of any resources that explain this better? I tried sketching out some rough diagrams, but I don't really see what drives this precession, in particular how oblateness is relevant.
It's like gyroscopic precession. Think of it as the Earth as being a sphere (effectively a point mass) with a massive torus around the equator and the orbit as being the gyroscope. The torus tugs the gyroscope, changing the direction of its angular momentum vector, and it precesses.
https://en.wikipedia.org/wiki/Precession
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#133 by Chris Bergin on 16 Nov, 2011 00:45
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Firstly, a big welcome to the site's forum to Michael!
Secondly, sure, it's not looking good - but from an overly optimistic standpoint, this isn't over until they say it's over. There will be some very clever people thinking on alternative options and you never know if one of them turns out to be successful.
There's a lot of "giving up" on here lately, with the "shoot down" talk. -
#134 by robertross on 16 Nov, 2011 00:50
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There's a lot of "giving up" on here lately
Well I would be one or those, on account of all the heavy technical jargon being thrown around lately. Yikes!
Orbital mechanics and me will never be friends
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#135 by iamlucky13 on 16 Nov, 2011 01:12
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The orbital plane precesses about 6 degrees per day in geocentric reference because of Earth's equatorial oblateness. So the geocentric plane of the departure asymptote is sweeping across the celestial sphere at some combination of this rate, earth's axial tilt, and Earth's movement around the sun.
I'm afraid I'm not following. Do you know of any resources that explain this better? I tried sketching out some rough diagrams, but I don't really see what drives this precession, in particular how oblateness is relevant.
Try Bate, Mueller, & White Fundamentals of Astrodynamics P156 (of my old book) Chapter 3.1.3 Perturbation of Low Altitude Orbits due to the Earth's Oblatness.
Or any other basic astrodynamics or orbital mechanics book.
Well what do you know!
http://books.google.com/books?id=UtJK8cetqGkC&lpg=PP1&dq=fundamentals%20of%20astrodynamics&pg=PA156#v=onepage&q&f=false
Between the diagram on p156 pointing out the torque and ChileVerde's mention of gyroscopes, I've got my head half wrapped around it now.
(Side note: Price on the back cover is $15.95 - it's a pity college textbooks aren't that cheap anymore...correcting for the CPI for 1971, they're twice as much!) -
#136 by Michael J on 16 Nov, 2011 01:13
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Firstly, a big welcome to the site's forum to Michael!
Secondly, sure, it's not looking good - but from an overly optimistic standpoint, this isn't over until they say it's over. There will be some very clever people thinking on alternative options and you never know if one of them turns out to be successful.
There's a lot of "giving up" on here lately, with the "shoot down" talk.
Thanks for the welcome. Like I noted before, this has been my primary source for updates on PB, and I've been tweeting the URLs for both threads to my followers. Keep up the great work! -
#137 by ChileVerde on 16 Nov, 2011 01:19
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Try Bate, Mueller, & White Fundamentals of Astrodynamics P156 (of my old book)
Lots of people deprecate BMW, but I still like it a lot, at least as an introduction to the subject. The units they use are funky, but converting them back into real SI isn't that hard. And the book costs less than $10 at Amazon. -
#138 by Jim on 16 Nov, 2011 01:32
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China can do it, problem solved…
The vehicle is not made for on orbit repair.
Pretty much all you could do from a Shenzhou is try and see if some switch had not been tripped as in SYNCOM IV-3 during STS-51-D.
If it's a more serious problem it cannot return the probe the only vehicles that could do that was the Shuttle or Buran and even then you'd need some sorta jig to place it into.
I think he was talking about China intercepting PG with it direct-ascent ASAT capability.
think it might be better to bring Phobos Grunt down from above. Just use the Progress on it "trash run" return from the ISS to earth. Turn it around and use the Kurz radar to lock on then......bring them both down in a safe area.
Not feasible, not the same orbit and Kurs is not a radar -
#139 by JimO on 16 Nov, 2011 02:01
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The orbital plane precesses about 6 degrees per day in geocentric reference because of Earth's equatorial oblateness. So the geocentric plane of the departure asymptote is sweeping across the celestial sphere at some combination of this rate, earth's axial tilt, and Earth's movement around the sun.
I'm afraid I'm not following. Do you know of any resources that explain this better? I tried sketching out some rough diagrams, but I don't really see what drives this precession, in particular how oblateness is relevant.
It's like gyroscopic precession. Think of it as the Earth as being a sphere (effectively a point mass) with a massive torus around the equator and the orbit as being the gyroscope. The torus tugs the gyroscope, changing the direction of its angular momentum vector, and it precesses.
https://en.wikipedia.org/wiki/Precession
Actually, I really don't like the gyroscope analogy because the physical effects are different, and they do not produce the same detailed motion -- it just LOOKS sort of the same.
I wrote a chapter on orbitology for my US Space command sponsored book on 'space power theory' [no, NOT the electrical kind]. Let me get a link.
Here's the specific passage where I explain the effect to pilots:
In practice, there are some other significant influences on the orbit
of a satellite. One of those is the influence of the equatorial
gravitational “bulge.” Since the Earth rotates, it flattens slightly at the
poles and bulges outward at the Equator. Probably the most
significant and mysterious impact of the equatorial bulge is how it
causes the path of an orbit to “twist” in space. Twist isn’t really the
right word; it’s more like a long, gentle “S” turn. However, “twist” is
the term used by most space operators. It’s as hard to understand and
as complicated as the not-right terminology indicates. But, orbital
twist is important enough to be explained. For better and more
detailed explanations, there are several good textbooks on orbital
mechanics.
Various analogies have been suggested in orbital mechanics
textbooks, having to do with right-angle forces on spinning wheels,
and other strained parallels with earthside experience. But the most
useful way to grasp the concept is to keep visualizing your space
vehicle moving under the influence of gravity and its own forward
speed—with extra localized gravitational pull as your satellite crosses
the equator. Think of Earth’s equatorial bulge as a ring around the
planet’s waist. It has its own mass, and will pull anything nearby
towards it.
Now imagine your satellite approaching Earth’s equator, say, from
the southwest, at an angle (remember that angle with which it crosses
the Equator is called the orbital inclination) greater than a few degrees.
It’s just been over a point well away and south of the Equator. It’s
aimed straight ahead for a spot above the Equator.
As it approaches the Equator, the nearest portion of the “bulge” is
also pulling on it, directly toward the Equator. Its path will veer
slightly toward the bulge, to the left. It will reach the Equator at a point
somewhat to the left of where it had originally been headed.
North of the Equator the process is symmetrical but in the opposite
direction. Now the nearest parts of this extra equatorial bulge are on
the right, and it is in this direction that the satellite veers. As it finally
distances itself from the Equator, the two effects—the veer to the left
(south of the Equator) and the veer to the right (north of the
Equator)—have balanced out to return the satellite to its original
direction.
However, the original swerve to the left (westwards) is NOT
counterbalanced, so the satellite’s orbital plane has been effectively
shifted a small amount. For a typical space shuttle flight from Florida,
this shift per Equator crossing amounts to about 20 to 25 km. That’s
not much on an orbit that is 40,000 km long per revolution, but it can
add up. For space shuttle flights, it can amount to a westwards plane
shift of about five to seven degrees per day.
Now, if we apply the principles of gravitation to this effect, we can
see how it works for different altitudes and inclinations. Since it is
caused by the extra gravity from the equatorial bulge, the closer you
are and the longer you stay close to this bulge, the bigger you should
expect the effect to be.
This is exactly the case. The lower the inclination of an orbit, the
longer it skirts “near” the Equator and the more it is twisted. The
higher the orbital altitude, altitude, the more distant its approach to the extra
mass, and so the less its orbital plane is twisted.
An interesting and very useful application of this orbital twisting
is connected with those orbits that are nearly perfectly north-south
(near-polar) orbits that are slightly “retrograde”—that is, they
approach the Equator from slightly east of south when northbound.
The twisting still occurs, but this time (think of where the extra mass
is closest), it is first to the right, towards the east and then to the left.
Sketch this out to convince yourself.
As Earth circles the Sun once per year, it moves in its orbit and the
Sun appears to move through the constellations. The rate is a little less
than one degree per day, which works out to be 360 degrees in 365
days plus some hours.
If a satellite is placed in a slightly retrograde near-polar orbit, the
equatorial bulge will twist the plane eastwards. The ideal situation is
that the orbital plane shifts (“twists”) eastward at the same rate as the
Sun appears to move against the background stars, and as a result, the
relationship of the orbital plane and the Earth-Sun line remains the
same. This means that as the satellite passes over ground locations, the
angle of sunlight—and the resulting shadows—remain fairly uniform,
no matter how much time, or how many orbits, have gone by.
This is called a “sun-synchronous” orbit. It has many obvious
applications to different types of observation platforms. The
applications are so obvious that any object in such an orbit is
presumed to be in some sort of Earth surface observation. There are a
few other satellites in the same type of orbit to remain in continuous
sunlight for reasons such as power, astronomical work, etc.
Recall that because the degree of orbital twisting depends on the
satellite’s altitude above the Earth, achieving the same amount of
orbital twisting (the technical term is “precession”) requires the
selection of different inclinations for different operational altitudes.
As the orbit gets higher (and farther from the Equatorial bulge), it
must have a lower inclination so as to spend a proportionately longer
time “close” to the bulge to accumulate the same amount of twisting.
As a result, it will pass over a lessened north to south range of the
Earth’s surface; therefore, sun synchronous orbits can’t be very high.
