Watched a NASA video of the Orion going around moon. During this time,
it appeared to do a burn to lower its altitude (I assume thrust aimed to
send it towards moon surface) to create a very very elliptical orbit. No
"live" coverage because that happened while moon was between Orion and
Earth.

So if you create an elliptical orbit where perigee is on far side of
moon and apogee is somewhere between Earth and Moon, and the goal is
flip this 180° so apogee is on far side of moon (to get the furthest a
manned vehicle has ever been from Earth) what sort of manoeuvers/burns
are needed?


Or did I totally misunderstand the burn that was done today?

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On 22/11/2022 10:12 am, JF Mezei wrote:

Watched a NASA video of the Orion going around moon. During this time,
it appeared to do a burn to lower its altitude (I assume thrust aimed to
send it towards moon surface) to create a very very elliptical orbit. No "live" coverage because that happened while moon was between Orion and
Earth.

So if you create an elliptical orbit where perigee is on far side of
moon and apogee is somewhere between Earth and Moon, and the goal is
flip this 180° so apogee is on far side of moon (to get the furthest a manned vehicle has ever been from Earth) what sort of manoeuvers/burns
are needed?

Or did I totally misunderstand the burn that was done today?

The general rule is that you do the burn at the opposite end of the
orbit from the bit you're trying to change. So if you want to change the
high part of the orbit, the apoapsis [*], then you do the burn at the
low point, the periapsis, and vice versa.

The initial burn behind the moon is done to get into orbit. Since that
is inevitably the initial periapsis, it determines how high the initial apoapsis is.

I don't know that there's an efficient way to swap the periapsis and
apoapsis in the short term. But wait two weeks, and it will happen
anyway, as the Moon orbits the Earth.

Sylvia

[*] Apogee and perigee relate specifically to orbits about the Earth.
For more info see https://en.wikipedia.org/wiki/Apsis
There's also https://www.thefreedictionary.com/pericynthion
and https://www.thefreedictionary.com/apocynthion

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Sylvia Else asserted that:

On 22/11/2022 10:12 am, JF Mezei wrote:

Watched a NASA video of the Orion going around moon. During this time,
it appeared to do a burn to lower its altitude (I assume thrust aimed to
send it towards moon surface) to create a very very elliptical orbit. No
"live" coverage because that happened while moon was between Orion and
Earth.

So if you create an elliptical orbit where perigee is on far side of
moon and apogee is somewhere between Earth and Moon, and the goal is
flip this 180° so apogee is on far side of moon (to get the furthest a
manned vehicle has ever been from Earth) what sort of manoeuvers/burns
are needed?


Or did I totally misunderstand the burn that was done today?

The general rule is that you do the burn at the opposite end of the orbit from the bit you're trying to change. So if you want to change the high part of the orbit, the apoapsis [*], then you do the burn at the low point, the periapsis, and vice versa.

The initial burn behind the moon is done to get into orbit. Since that is inevitably the initial periapsis, it determines how high the initial apoapsis is.

I don't know that there's an efficient way to swap the periapsis and apoapsis in the short term. But wait two weeks, and it will happen anyway, as the Moon orbits the Earth.

Sylvia

[*] Apogee and perigee relate specifically to orbits about the Earth. For more info see https://en.wikipedia.org/wiki/Apsis
There's also https://www.thefreedictionary.com/pericynthion
and https://www.thefreedictionary.com/apocynthion

The web site for one of the asteroid probes discussed various orbital
mechanics issues, with a rather serious plane change being done by
going very eccentric and doing the plane change at apoapsis. I think
this was Dawn during its encounter with Ceres in 2018; and I think I
found the animation from the "journal" (blog) the team posted at the
time, so you could look through the archives of sci.space.science to
find the usenet post pointing to the animation. Most likely to be a
post by "NASA via sci.space.science" and a topic beginning "Solar
System News".


Also see
<http://www.jamesoberg.com/eros.html>
for a discussion of orbital mechanics and the NEAR probe's path to
Eros.

And it looks like you do some practice with a PDF the FAA has: <URL:https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/cami/library/online_libraries/aerospace_medicine/tutorial/media/III.4.1.5_Maneuvering_in_Space.pdf>

And perhaps it's time for you to learn Kerbal Space, building your
rockets and trying out your own missions.

/dps "I need to get to bed"

--
Let's celebrate Macaronesia

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On 2022-11-22 04:48, Snidely wrote:

The web site for one of the asteroid probes discussed various orbital mechanics issues, with a rather serious plane change

But swapping high and low poits isn't a plane change is it (since the
satellite still travels in same plane).


If Orion has low point of 80 miles on far side of moon on day 1, and
high point of 30,000 miles above moon towards earth, will that not
remain the same arrangement as both orbit the earth over 28 days? or
would the satellite get its high point on far side of moon and low point
on earth facing side 14 days later ?

Coming in from the Earth during the burn done on far side of moon (thus
no live video) the computer animation showed the Orion facing down, and
thus its engine pushing Orion towards moon surface. And shortly after
burn, its altitude over moon dropped to 80 miles. In what way would
this be a lunar orbit injection? Wouldn't there need to be a drop in
horizontal velocity to prevent a slingshot that ends up escaping moon's
gravity and sending Orion to planet Vulcan or the Ferengi homeworld?

The pass behind moon (34 minutes) where the firing occured: https://youtu.be/BvWtNx3VOUA?t=7701

The burn link (40 secodns before OMS starts its burn) https://youtu.be/BvWtNx3VOUA?t=8741

Note orientation of vehicle in th "telemetry driven anumation).

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On 23/11/2022 4:14 am, JF Mezei wrote:

On 2022-11-22 04:48, Snidely wrote:

The web site for one of the asteroid probes discussed various orbital
mechanics issues, with a rather serious plane change

But swapping high and low poits isn't a plane change is it (since the satellite still travels in same plane).

If Orion has low point of 80 miles on far side of moon on day 1, and
high point of 30,000 miles above moon towards earth, will that not
remain the same arrangement as both orbit the earth over 28 days? or
would the satellite get its high point on far side of moon and low point
on earth facing side 14 days later ?

There may be some subtle orbital mechanic issue that I've overlook at
play here, but the Earth is a long way away compared with the size of
the orbit, and the fact that the Moon itself is turning shouldn't have
much effect. It's pulled out of a spherical shape by Earth's gravity and
its rotation speed rises and falls a bit, but I cannot see why they
combination of those should cause the space craft's orbit to rotate in
tandem. So it seems to me that the orbit should retain its orientation
relative to the "fixed" stars, and hence appear to rotate around the
moon as the moon orbits the Earth.

Sylvia

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