Space station future?

OK, it seems to me that with the current situation we will have a position
where the station is just at the end of life as the new vehicles come into
operation. I'd think maybe we need a station for storing stuff etc, and as a
way station, or is the idea still to perhaps go to the moon with a base?
Brian

--
Brian Gaff -
Note:- In order to reduce spam, any email without 'Brian Gaff'
in the display name may be lost.
Blind user, so no pictures please!

On 11/10/2011 4:25 AM, Brian Gaff wrote:
OK, it seems to me that with the current situation we will have a position
where the station is just at the end of life as the new vehicles come into
operation. I'd think maybe we need a station for storing stuff etc, and as a
way station, or is the idea still to perhaps go to the moon with a base?
Brian


My preference is the Moon. No need to store anything in LEO, not even
propellant - too expensive.

JF Mezei wrote:
If the Russians are to participate in this and want to use Baikonour
instead of Korou, then 51.6° might be required too. IF so, then using
the ISS as a base from which to assemble the expedition ship makes sense.

[etc. rationale for building a Mars vehicle using ISS as a construction base]

Well that makes some good sense to me, however, at that high an inclination,
it seems problematical for a Mars vehicle to depart for Mars w/o some fancy
LEO maneuvers first to get it back into a trajectory that would intersect
Mars. I suppose you could launch on some type of parabolic trajectory that
would intersect the ecliptic at the right time that Mars shows up, but that
doesn't look a whole lot like the low energy Hohmann transfer orbits I've read
about.

?

Dave

In sci.space.station message tNCdnV_0RfPKjgjTnZ2dnUVZ_vKdnZ2d@giganews.
com, Wed, 12 Oct 2011 00:11:02, David Spain posted:

JF Mezei wrote:
If the Russians are to participate in this and want to use Baikonour
instead of Korou, then 51.6° might be required too. IF so, then using
the ISS as a base from which to assemble the expedition ship makes sense.

[etc. rationale for building a Mars vehicle using ISS as a construction
base]

Well that makes some good sense to me, however, at that high an
inclination, it seems problematical for a Mars vehicle to depart for
Mars w/o some fancy LEO maneuvers first to get it back into a
trajectory that would intersect Mars. I suppose you could launch on
some type of parabolic trajectory that would intersect the ecliptic at
the right time that Mars shows up, but that doesn't look a whole lot
like the low energy Hohmann transfer orbits I've read about.


The inclination and precession of the orbit of ISS mean that, about once
a month, it will be heading in the direction that Earth is; and that is
approximately what is wanted. One of those per synodic period will be
near enough the right time for a near-enough Hohmamm orbit to Mars.

--
(c) John Stockton, nr London, UK. Turnpike v6.05 MIME.
Web http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms and links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

Dr J R Stockton wrote:
The inclination and precession of the orbit of ISS mean that, about once
a month, it will be heading in the direction that Earth is; and that is
approximately what is wanted. One of those per synodic period will be
near enough the right time for a near-enough Hohmamm orbit to Mars.

OK I'll bite.

Orbital mechanics is not my specialty. If you don't have the time to explain,
I'll settle for a reference link. But here is what I don't understand from
your posting:

I thought precession was a ground-based phenom. because the Earth is rotating
underneath the ISS. But that type of precession has nothing to do with its
orbital inclination which is fixed. 51.6 degrees relative to the Equator, 75
degrees to the Sun vector*. Is there another form of precession I'm missing?
I mean the precession of the Earth's axis is like 50,000 years so I'm sure
we're not talking about that.

For an ideal Hohmann orbit wouldn't you want the Sun vector to be nearly zero
or let's say opposite the 23.4 degree tilt of the Earth's axis? Or better yet,
for a Mars mission, the Sun vector being as close a match to the difference in
solar orbital angles between Earth and Mars?

Who can set me straight?

Thanks,
Dave

* http://suzymchale.com/ruspace/issorbit.html

In sci.space.station message 1dWdnbI0SYcj5gXTnZ2dnUVZ_uidnZ2d@giganews.
com, Fri, 14 Oct 2011 14:13:17, David Spain posted:

Dr J R Stockton wrote:
The inclination and precession of the orbit of ISS mean that, about once
a month, it will be heading in the direction that Earth is; and that is
approximately what is wanted. One of those per synodic period will be
near enough the right time for a near-enough Hohmamm orbit to Mars.

OK I'll bite.

Orbital mechanics is not my specialty. If you don't have the time to
explain, I'll settle for a reference link. But here is what I don't
understand from your posting:

I thought precession was a ground-based phenom. because the Earth is
rotating underneath the ISS. But that type of precession has nothing to
do with its orbital inclination which is fixed. 51.6 degrees relative
to the Equator, 75 degrees to the Sun vector*. Is there another form of
precession I'm missing?
I mean the precession of the Earth's axis is like 50,000 years so I'm
sure we're not talking about that.


It may be difficult; it seems that you are not an ISS watcher.

Go to
http://www.heavens-above.com/PassSum...&lat=0&lng=0&l
oc=Home&alt=0&tz=UCT
which is set for location 0 N 0 E & UTC. Select "All".

Look at the times of the highest pass before Noon each day : I see, for
October 15-24
04:15 04:52 03:54 02:56 03:33 02:35 03:13 02:14 01:16 01:53
That's a shift of something like three hours in nine days.

But the interval is 9/360 of a year, and the effect on the time of the
sun's apparent motion around the Earth will be 24 * 9/360 hours = 0.6
hours.

The difference shows that dominant effect is that the plane of the orbit
of ISS must be shifting by something like three hours-worth in nine
days, or once round in 72 days, which is about what I said.

Alternatively, set location to London UK, use "Visible Only", and note
that a period of evening visibility begins on Oct 17. Step to the next
such period, starts on Dec 17. Then 13 Feb, 9 Apr, 3 Jun, 4 Aug, 7 Oct,
9 Dec ... - average, 6 cycles per year.



See also http://en.wikipedia.org/wiki/Nodal_precession, which has an
equation. For a rough estimate, set e = 0, r = a, cos i = 0.5, and the
ratio of precessional to orbital frequencies is then -0.75 * J2; and J2
is given as 1.08e-3. The ratio is therefore roughly 1 to 1300; and, as
ISS does 16.5 orbits per day or 100 in 6 days, the precessional period
must be about 6*13 = 65 days - very satisfactory agreement.



For an ideal Hohmann orbit wouldn't you want the Sun vector to be
nearly zero or let's say opposite the 23.4 degree tilt of the Earth's
axis? Or better yet, for a Mars mission, the Sun vector being as close
a match to the difference in solar orbital angles between Earth and
Mars?


The important thing, since the orbits of Earth and Mars are nearly
coplanar, is that the orbital velocity of ISS should reinforce the
Earth's orbital velocity. They must therefore be in essentially the
same direction, which is the direction you want for starting your
Hohmann transfer. That must happen on average once per month,
alternately for the north part of ISS's orbit and the South part.


See also http://en.wikipedia.org/wiki/Sun-synchronous_orbit, where
cos i is much smaller and precession is annual.

http://en.wikipedia.org/wiki/Orbital...s_%28spacecraf
t%29#Perturbation_of_the_orbital_plane_2.

--
(c) John Stockton, near London.
Web http://www.merlyn.demon.co.uk/ - FAQish topics, acronyms, and links.
Correct = 4-line sig. separator as above, a line precisely "-- " (RFC5536/7)
Do not Mail News to me. Before a reply, quote with "" or " " (RFC5536/7)

Dr J R Stockton wrote:
See also http://en.wikipedia.org/wiki/Nodal_precession, which has an
equation. For a rough estimate, set e = 0, r = a, cos i = 0.5, and the
ratio of precessional to orbital frequencies is then -0.75 * J2; and J2
is given as 1.08e-3. The ratio is therefore roughly 1 to 1300; and, as
ISS does 16.5 orbits per day or 100 in 6 days, the precessional period
must be about 6*13 = 65 days - very satisfactory agreement.

OK, got it. The key here is that the Earth is not a perfect sphere but a
spheroid with equatorial bulge which causes the nodal precession.

The day job is consuming my time heavily next week, but when I get some time
back I'll run some numbers.

Thanks John.

Dave

David Spain wrote:
OK, got it. The key here is that the Earth is not a perfect sphere but a
spheroid with equatorial bulge which causes the nodal precession.


Or to put it a little more accurately, the ISS is orbiting within the
gravitational field of a rotating oblate spheroid.

Dave

Originally Posted by David Spain

David Spain wrote:
OK, got it. The key here is that the Earth is not a perfect sphere but a
spheroid with equatorial bulge which causes the nodal precession.


Or to put it a little more accurately, the ISS is orbiting within the
gravitational field of a rotating oblate spheroid.

Dave

website: http://www.discount-caps.com


Our company can supply more than 50 brands and over 1500 styles of hats/caps. All are with good price and top quality. As we have been doing international business for over 5 years, we have lots of clients spread all over the world, most of which are from USA, Canada, UK, France, Australia etc.
Monster energy hats, rockstar energy hats and new era dc hats are now hot sell hats in the world, if you are interest, you can go to www.discount-caps.com to take a look, too.

Our price for hats/caps relates with the quantity you want, if your quantity is large, we will give you big discount, and with free shipping.

kevinposada wrote:
David Spain;1180224 Wrote:
Or to put it a little more accurately, the ISS is orbiting within the
gravitational field of a rotating oblate spheroid.

Dave

website: http://www.discount-caps.com


Our company can supply more than 50 brands and over 1500 styles of
hats/caps. All are with good price and top quality. As we have been
doing international business for over 5 years, we have lots of clients
spread all over the world, most of which are from USA, Canada, UK,
France, Australia etc.
Monster energy hats, rockstar energy hats and new era dc hats are now

....

Yes! Yes!

In fact I've noticed the propensity for those wearing NASCAR hats to be a
simulacrum of the oblate spheriod.

;-D

Dave