Orbital mechanics question DSCOVER L1 orbit

I'd imagine that one has to be travelling pretty slow to get captured in
fact. Its not like a little well one can fall into, its more like a shallow
saucer of gravity.
In relation to posting here, I think most other groups are moderated and
hence the immediacy of it is not there.
There does really need to be another group of unmoderated general space
stuff.
Brian

--
From the Sofa of Brian Gaff Reply address is active
"Snidely" wrote in message
news:mn.60b07df2448f18a8.127094@snitoo...
Just this Wednesday, JF Mezei explained that ...
SpaceX is about to launch a NOAA satellite to L1 between earth and sun.

Appears the launch window is very small (no 5 minute leaways on eaither
end of prefered launch time), and that today is last possible launch
date since the moon would prevent launch later on.


How does such a launch work ? Obviously, they launch at Cape's orbital
inclination. Do they correct it to equatorial 0° inclination prior to
MECO ? Or do they correct to an inclination that would be between tro]ic
of capricorn and equator to be directrly below sun ? (and in such a
case, can they launch south east or are they restricted to north-east
like shuttle ?

Does the vehicle first enter earth orbit conventionally and then uses
second/thirst stages to raise orbit progressively until it is at the
million mile distance at which point the L2 forces kick in and grab the
vehicle into a stationary position relative to axis between earth and sun
?

Or does the vehicle shoot straight up (more or less) to reach that L1
point where it no longer has to worry about orbital speed because
gravity on both sides keep the vehicle stationary relative to earth/sun ?

(seems odd to post this in dot-station, since it isn't going to the
station and there is launch discussion in dot-policy)

I don't have the full answer, but note this from the AP report:

"DSCOVR will spend nearly four months traveling 1 million miles, four
times farther than the moon, to the so-called Lagrange point, a
gravity-neutral position in direct line with the sun. "

URL:
http://seattletimes.com/html/businesstechnology/2025669167_apxscideepspaceobservatory.html

The 2 main ways of going deep a

1) Apollo-style, where a big "top stage" provides a lot of boost
short-term, and that boost is applied from LEO. (The last Russian Mars
mission ended at this point, apparently due to booster issues.) Expect a
transfer orbit; something like a Hohmann orbit would be the low-cost (and
slow) way to get there.

2) Ion-engine, SMART-1 style: low-thrust over a long period of time. The
orbit will be very different for this; I haven't seen too many diagrams.
SMART-1 did a "spiral" lasting about a month, if memory and a quick scan
of the wikicle serve.
URL:http://en.wikipedia.org/wiki/SMART-1
Going 4 times farther in 3 times the travel time seems reasonable.

The NOAA press kit doesn't say anything about an ion engine, so they may
be using the restartable Falcon upper stage the way Apollo used the SIV-B.

URL:http://www.nesdis.noaa.gov/DSCOVR/press.html


Ah, looks like I'm right:

quote
At T+30 minutes and 9 seconds, the MVac engine re-ignited for a burn of 58
seconds to boost the stack into an L1 Transfer Orbit. DSCOVR was targeting
an insertion orbit of 187 by 1,241,000 Kilometers inclined 37 degrees
which will be modified through propulsive maneuvers by the spacecraft to
reach the L1 point 1.5 Million Kilometers from Earth for orbital
insertion. The achieved insertion orbit was 187 by 1,371,145 Kilometers at
an inclination of 37.09° marking a very precise insertion with a minute
overperformance of just a handful m/s.
/quote
URL:http://www.spaceflight101.com/dscovr-mission-updates.html
[scroll down more than 1/3 page past the picture of the 2nd stage engine
aglow]

HTH.

/dps "still some fu for my goo"

--
Ieri, oggi, domani

Lo, on the 2/13/2015, Brian Gaff did proclaim ...
I'd imagine that one has to be travelling pretty slow to get captured in
fact. Its not like a little well one can fall into, its more like a shallow
saucer of gravity.
In relation to posting here, I think most other groups are moderated and
hence the immediacy of it is not there.
There does really need to be another group of unmoderated general space
stuff.

sci.space.policy is not moderated, and often has timely discussion of
launches, including DSCOVR.

/dps


"Snidely" wrote in message
news:mn.60b07df2448f18a8.127094@snitoo...
Just this Wednesday, JF Mezei explained that ...
SpaceX is about to launch a NOAA satellite to L1 between earth and sun.

Appears the launch window is very small (no 5 minute leaways on eaither
end of prefered launch time), and that today is last possible launch
date since the moon would prevent launch later on.


How does such a launch work ? Obviously, they launch at Cape's orbital
inclination. Do they correct it to equatorial 0° inclination prior to
MECO ? Or do they correct to an inclination that would be between tro]ic
of capricorn and equator to be directrly below sun ? (and in such a
case, can they launch south east or are they restricted to north-east
like shuttle ?

Does the vehicle first enter earth orbit conventionally and then uses
second/thirst stages to raise orbit progressively until it is at the
million mile distance at which point the L2 forces kick in and grab the
vehicle into a stationary position relative to axis between earth and sun
?

Or does the vehicle shoot straight up (more or less) to reach that L1
point where it no longer has to worry about orbital speed because
gravity on both sides keep the vehicle stationary relative to earth/sun ?

(seems odd to post this in dot-station, since it isn't going to the station
and there is launch discussion in dot-policy)

I don't have the full answer, but note this from the AP report:

"DSCOVR will spend nearly four months traveling 1 million miles, four times
farther than the moon, to the so-called Lagrange point, a gravity-neutral
position in direct line with the sun. "

URL:
http://seattletimes.com/html/businesstechnology/2025669167_apxscideepspaceobservatory.html

The 2 main ways of going deep a

1) Apollo-style, where a big "top stage" provides a lot of boost
short-term, and that boost is applied from LEO. (The last Russian Mars
mission ended at this point, apparently due to booster issues.) Expect a
transfer orbit; something like a Hohmann orbit would be the low-cost (and
slow) way to get there.

2) Ion-engine, SMART-1 style: low-thrust over a long period of time. The
orbit will be very different for this; I haven't seen too many diagrams.
SMART-1 did a "spiral" lasting about a month, if memory and a quick scan of
the wikicle serve.
URL:http://en.wikipedia.org/wiki/SMART-1
Going 4 times farther in 3 times the travel time seems reasonable.

The NOAA press kit doesn't say anything about an ion engine, so they may be
using the restartable Falcon upper stage the way Apollo used the SIV-B.

URL:http://www.nesdis.noaa.gov/DSCOVR/press.html


Ah, looks like I'm right:

quote
At T+30 minutes and 9 seconds, the MVac engine re-ignited for a burn of 58
seconds to boost the stack into an L1 Transfer Orbit. DSCOVR was targeting
an insertion orbit of 187 by 1,241,000 Kilometers inclined 37 degrees which
will be modified through propulsive maneuvers by the spacecraft to reach
the L1 point 1.5 Million Kilometers from Earth for orbital insertion. The
achieved insertion orbit was 187 by 1,371,145 Kilometers at an inclination
of 37.09° marking a very precise insertion with a minute overperformance of
just a handful m/s.
/quote
URL:http://www.spaceflight101.com/dscovr-mission-updates.html
[scroll down more than 1/3 page past the picture of the 2nd stage engine
aglow]

HTH.

/dps "still some fu for my goo"

-- Ieri, oggi, domani

--
Trust, but verify.

The last time I was there there seemed to be a bit of a war on about what
was on and off topic. The word policy, seems a little odd if its used for a
general discussion group.
Brian

--
From the Sofa of Brian Gaff Reply address is active
"Snidely" wrote in message
news:mn.70407df20a43c788.127094@snitoo...
Lo, on the 2/13/2015, Brian Gaff did proclaim ...
I'd imagine that one has to be travelling pretty slow to get captured in
fact. Its not like a little well one can fall into, its more like a
shallow saucer of gravity.
In relation to posting here, I think most other groups are moderated
and hence the immediacy of it is not there.
There does really need to be another group of unmoderated general space
stuff.

sci.space.policy is not moderated, and often has timely discussion of
launches, including DSCOVR.

/dps


"Snidely" wrote in message
news:mn.60b07df2448f18a8.127094@snitoo...
Just this Wednesday, JF Mezei explained that ...
SpaceX is about to launch a NOAA satellite to L1 between earth and sun.

Appears the launch window is very small (no 5 minute leaways on eaither
end of prefered launch time), and that today is last possible launch
date since the moon would prevent launch later on.


How does such a launch work ? Obviously, they launch at Cape's orbital
inclination. Do they correct it to equatorial 0° inclination prior to
MECO ? Or do they correct to an inclination that would be between
tro]ic
of capricorn and equator to be directrly below sun ? (and in such a
case, can they launch south east or are they restricted to north-east
like shuttle ?

Does the vehicle first enter earth orbit conventionally and then uses
second/thirst stages to raise orbit progressively until it is at the
million mile distance at which point the L2 forces kick in and grab the
vehicle into a stationary position relative to axis between earth and
sun ?

Or does the vehicle shoot straight up (more or less) to reach that L1
point where it no longer has to worry about orbital speed because
gravity on both sides keep the vehicle stationary relative to earth/sun
?

(seems odd to post this in dot-station, since it isn't going to the
station and there is launch discussion in dot-policy)

I don't have the full answer, but note this from the AP report:

"DSCOVR will spend nearly four months traveling 1 million miles, four
times farther than the moon, to the so-called Lagrange point, a
gravity-neutral position in direct line with the sun. "

URL:
http://seattletimes.com/html/businesstechnology/2025669167_apxscideepspaceobservatory.html

The 2 main ways of going deep a

1) Apollo-style, where a big "top stage" provides a lot of boost
short-term, and that boost is applied from LEO. (The last Russian Mars
mission ended at this point, apparently due to booster issues.) Expect
a transfer orbit; something like a Hohmann orbit would be the low-cost
(and slow) way to get there.

2) Ion-engine, SMART-1 style: low-thrust over a long period of time.
The orbit will be very different for this; I haven't seen too many
diagrams. SMART-1 did a "spiral" lasting about a month, if memory and a
quick scan of the wikicle serve.
URL:http://en.wikipedia.org/wiki/SMART-1
Going 4 times farther in 3 times the travel time seems reasonable.

The NOAA press kit doesn't say anything about an ion engine, so they may
be using the restartable Falcon upper stage the way Apollo used the
SIV-B.

URL:http://www.nesdis.noaa.gov/DSCOVR/press.html


Ah, looks like I'm right:

quote
At T+30 minutes and 9 seconds, the MVac engine re-ignited for a burn of
58 seconds to boost the stack into an L1 Transfer Orbit. DSCOVR was
targeting an insertion orbit of 187 by 1,241,000 Kilometers inclined 37
degrees which will be modified through propulsive maneuvers by the
spacecraft to reach the L1 point 1.5 Million Kilometers from Earth for
orbital insertion. The achieved insertion orbit was 187 by 1,371,145
Kilometers at an inclination of 37.09° marking a very precise insertion
with a minute overperformance of just a handful m/s.
/quote
URL:http://www.spaceflight101.com/dscovr-mission-updates.html
[scroll down more than 1/3 page past the picture of the 2nd stage engine
aglow]

HTH.

/dps "still some fu for my goo"

-- Ieri, oggi, domani

--
Trust, but verify.

"Brian Gaff" wrote in message ...

The last time I was there there seemed to be a bit of a war on about what
was on and off topic. The word policy, seems a little odd if its used for a
general discussion group.
Brian


Per the charter though, it is supposed to be the catch-all for anything
that's not covered by the other groups.

I do wish there was perhaps a sci.space.general or sci.space.talk, but given
we can't get more than 5-6 regular sane posters to the existing groups,
there's no way a new group would make more sense.



--
Greg D. Moore http://greenmountainsoftware.wordpress.com/
CEO QuiCR: Quick, Crowdsourced Responses. http://www.quicr.net

In article om,
says...

On 15-02-14 04:04, someone wrote:

URL:
http://seattletimes.com/html/businesstechnology/2025669167_apxscideepspaceobservatory.html

Based on that article, stage 2 left DSCOVR in a elliptical orbit around
earth, with 37° inclination and 1,2 milion km * 187km orbit.

Would it be correct to state that L1 is an orbit around the sun, but at
a speed that matches Earth's orbit around the sun despite being at a
lower orbit than the Earth, which is made possible by Earth's gravity
compensating. ?

It looks like an orbit around the sun, but it's not. It's correct to
state that L1 is the location in space where the gravitational forces on
a satellite from the sun and the earth cancel out.

So, how does a vehicle go from elliptical orbit around earth to
an orbit around the sun ?

Roughly the same way one goes from a geosynchronous transfer orbit to
geosynchronous orbit. The satellite uses its propulsion system to
perform one or more orbital maneuvers.

Does the vehicle get into such an eccentric orbit that it hopes to be
nabbed by the sun's gravity on apogee and not fall back to Earth, a bit
like a trampoline jumper going high enough to grab some hooks on ceiling
and not fall back down ?

If you want to see what it looks like, I'm sure there is a graphic which
shows DSCOVR's path to sun-earth L1.

I an also curious about orbital inclination which is now roughly 37°.

On the day it is grabbed by the sun and no longer falls back to earth,
do they have to plan orbit such that apogee happens at a momemt where
its orbit places the vehicle directly between sun and earth ? (for
instance, tropic of cancer if the grabbing is to happen on June 21).

At what point does DSCOVER lose synch with earth's inclination ? Between
march 21 and june 21t, the inclination changes by roughly 23° (as sun
"moves" from being over equator to being over the tropic of cancer).
Normal satellites follow this, but this one will eventually no longer
follow this change of earth realative to sun.

When it settles into L1, orbital inclination with respect to earth kind
of becomes meaningless since it's not in earth orbit anymore.

Jeff
--
"the perennial claim that hypersonic airbreathing propulsion would
magically make space launch cheaper is nonsense -- LOX is much cheaper
than advanced airbreathing engines, and so are the tanks to put it in
and the extra thrust to carry it." - Henry Spencer

In article ,
says...

"Brian Gaff" wrote in message ...

The last time I was there there seemed to be a bit of a war on about what
was on and off topic. The word policy, seems a little odd if its used for a
general discussion group.
Brian


Per the charter though, it is supposed to be the catch-all for anything
that's not covered by the other groups.

I do wish there was perhaps a sci.space.general or sci.space.talk, but given
we can't get more than 5-6 regular sane posters to the existing groups,
there's no way a new group would make more sense.

Considering Usenet News, in general, is pretty much dead, I'd say you're
correct. Everything these days is web blogs and web based discussion
forums. I'm mostly here for nostalgia and spend very little of my space
reading/discussion time here.

Jeff
--
"the perennial claim that hypersonic airbreathing propulsion would
magically make space launch cheaper is nonsense -- LOX is much cheaper
than advanced airbreathing engines, and so are the tanks to put it in
and the extra thrust to carry it." - Henry Spencer

On 15-02-15 17:15 , Jeff Findley wrote:
In article om,
says...

On 15-02-14 04:04, someone wrote:

URL:
http://seattletimes.com/html/businesstechnology/2025669167_apxscideepspaceobservatory.html

Based on that article, stage 2 left DSCOVR in a elliptical orbit around
earth, with 37° inclination and 1,2 milion km * 187km orbit.

Would it be correct to state that L1 is an orbit around the sun, but at
a speed that matches Earth's orbit around the sun despite being at a
lower orbit than the Earth, which is made possible by Earth's gravity
compensating. ?

It looks like an orbit around the sun, but it's not.

It is, in the geometrical sense: the L1 locus follows an (approximately)
closed, nearly circular path with the Sun close to its centre. Orbital
period = 1 Earth year.

It's correct to
state that L1 is the location in space where the gravitational forces on
a satellite from the sun and the earth cancel out.

No, if the forces cancelled, then an object placed in L1 would move in a
straight-line path. Instead, it follows an orbit around the Sun, which
means that there is a net gravitational acceleration towards the Sun.

As JF Mezei said, at L1 the gravitational attraction between the Earth
and the satellite counteracts not all, but just enough of the
gravitational attraction between the Sun and the satellite to increase
the orbital period of the satellite from its sans-Earth value (less than
one year) to one year, thus making it keep pace with the Earth.

--
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
. @ .

On 15-02-15 21:40 , JF Mezei wrote:
On 15-02-15 10:15, Jeff Findley wrote:

It looks like an orbit around the sun, but it's not. It's correct to
state that L1 is the location in space where the gravitational forces on
a satellite from the sun and the earth cancel out.


Is it correct to state that the satellite no longer goes around the earth ?

Geometrically, with respect to the "fixed stars", the vector from the
Earth to a satellite at L1 rotates around the Earth with a period of one
year. So does the vector from the Earth to the Sun, which means that in
the geometric sense, from our viewpoint on the Earth, the satellite and
the Sun go around the Earth, once per year.

However, for a satellite at L1 the gravitational force between the
satellite and the Sun is larger than that between the satellite and the
Earth, so from the physical, forces and motions point of view it is more
correct to say that the satellite goes around the Sun.

It is correct to state that the satellite goes around the sun at an
orbital frenency that matches Earth's ? 365.25 days per rotation ?

Yes.

I understand that once at L1, inclination is no longer an issue. But it
is an issue to go from an eartn orbit with an inclination to reaching
the exact spot where it is grabbed by L1 and stays there.

Satellites "at L1" are not really exactly at L1, because that would be
unstable, and also the Sun would be direcly behind the satellite, as
seen from Earth, which would make communication difficult because of
noise from the Sun. Instead, the satellites "at L1" are put in so-called
"halo orbits" or "Lissajou orbits" around L1. For example, the SOHO
satellite
(http://en.wikipedia.org/wiki/Solar_a...ic_Observatory) is in
an elliptical halo orbit around L1 with a period of 6 months and a
distance to L1 varying between about 120 000 km and 670 000 km.

--
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
. @ .

In article ,
lid says...

On 15-02-15 17:15 , Jeff Findley wrote:
In article om,
says...

On 15-02-14 04:04, someone wrote:

URL:
http://seattletimes.com/html/businesstechnology/2025669167_apxscideepspaceobservatory.html

Based on that article, stage 2 left DSCOVR in a elliptical orbit around
earth, with 37° inclination and 1,2 milion km * 187km orbit.

Would it be correct to state that L1 is an orbit around the sun, but at
a speed that matches Earth's orbit around the sun despite being at a
lower orbit than the Earth, which is made possible by Earth's gravity
compensating. ?

It looks like an orbit around the sun, but it's not.

It is, in the geometrical sense: the L1 locus follows an (approximately)
closed, nearly circular path with the Sun close to its centre. Orbital
period = 1 Earth year.

But, the velocity is *wrong* for an orbit at that distance from the sun
(in the sun frame of reference). The velocity is also *wrong* for an
orbit at that distance from the earth (from the earth frame of
reference). It's not truly in an orbit around either body.

It's correct to
state that L1 is the location in space where the gravitational forces on
a satellite from the sun and the earth cancel out.

No, if the forces cancelled, then an object placed in L1 would move in a
straight-line path. Instead, it follows an orbit around the Sun, which
means that there is a net gravitational acceleration towards the Sun.

As JF Mezei said, at L1 the gravitational attraction between the Earth
and the satellite counteracts not all, but just enough of the
gravitational attraction between the Sun and the satellite to increase
the orbital period of the satellite from its sans-Earth value (less than
one year) to one year, thus making it keep pace with the Earth.

True, but one could say it *exactly* the same thing, but replacing the
earth with the sun and vice-versa. In other words, in the earth frame
of reference, it also goes around the earth once a year.

This is a three body problem. The terminology reserved for the two body
problem does not exactly apply because the two body equations don't work
for this three body problem.

Jeff
--
"the perennial claim that hypersonic airbreathing propulsion would
magically make space launch cheaper is nonsense -- LOX is much cheaper
than advanced airbreathing engines, and so are the tanks to put it in
and the extra thrust to carry it." - Henry Spencer

On 15-02-16 06:49 , Jeff Findley wrote:
In article ,
lid says...

As JF Mezei said, at L1 the gravitational attraction between the Earth
and the satellite counteracts not all, but just enough of the
gravitational attraction between the Sun and the satellite to increase
the orbital period of the satellite from its sans-Earth value (less than
one year) to one year, thus making it keep pace with the Earth.

True, but one could say it *exactly* the same thing, but replacing the
earth with the sun and vice-versa. In other words, in the earth frame
of reference, it also goes around the earth once a year.

Sure.

This is a three body problem. The terminology reserved for the two body
problem does not exactly apply because the two body equations don't work
for this three body problem.

Correct in principle. But with the three bodies being the Sun, the
Earth, and the satellite, their relative masses show which of them is
the dog, which is the wagging tail, and which is the flea.

--
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
. @ .