Author Topic: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion Thread 1  (Read 592913 times)

Offline jpo234

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #220 on: 12/03/2017 08:26 AM »
Not just a Roadster post, information about the orbit:

http://www.syfy.com/syfywire/elon-musk-on-the-roadster-to-mars

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No, itís not going to Mars. Itís going near Mars. He said itíll be placed in ďa precessing Earth-Mars elliptical orbit around the sun.Ē What he means by this is whatís sometimes called a Hohmann transfer orbit, an orbit around the Sun that takes it as close to the Sun as Earth and as far out as Mars. This is a low-energy orbit; that is, it takes the least amount of energy to put something in this orbit from Earth. That makes sense for a first flight.
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Offline SmallKing

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #221 on: 12/03/2017 10:34 AM »
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Offline MarekCyzio

Does anyone have an idea on what the inclination will be near launch for a Mars trip? Will that impact what viewing location would be better? Will Playalinda and/or the causeway be open for the FH launch?

Expect Playalinda to be closed.

Online Michael Baylor

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #223 on: 12/03/2017 04:31 PM »
Does anyone have an idea on what the inclination will be near launch for a Mars trip? Will that impact what viewing location would be better? Will Playalinda and/or the causeway be open for the FH launch?

Expect Playalinda to be closed.
Why? I thought it was approved to be open for all launches.

Online tleski

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #224 on: 12/03/2017 04:47 PM »
Does anyone have an idea on what the inclination will be near launch for a Mars trip? Will that impact what viewing location would be better? Will Playalinda and/or the causeway be open for the FH launch?

Expect Playalinda to be closed.
Why? I thought it was approved to be open for all launches.
My recommendation is to call the park headquarters before the launch to confirm if the beach is open. This is what I did when visiting the area last summer.
See the website below:
https://www.nps.gov/cana/planyourvisit/hours.htm

Offline dodo

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #225 on: 12/03/2017 06:11 PM »
Layman question: in such a Hohmann transfer orbit (and when not terminated by Mars orbit insertion), is there a risk of the trajectory intersecting Earth at some point in the future? (Presumably not right on the first orbit, since Earth is no longer there, but at some common multiple of the Earth's and payload's orbital period, I imagine.)

Edit: s/Hoffman/Hohmann/
« Last Edit: 12/03/2017 06:12 PM by dodo »

Offline Kaputnik

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #226 on: 12/03/2017 06:29 PM »
Layman question: in such a Hohmann transfer orbit (and when not terminated by Mars orbit insertion), is there a risk of the trajectory intersecting Earth at some point in the future? (Presumably not right on the first orbit, since Earth is no longer there, but at some common multiple of the Earth's and payload's orbital period, I imagine.)

Edit: s/Hoffman/Hohmann/

Yes, but it's also possible to be in an orbit that has an exact resonance with Earth and will not intersect Earth's position.
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Offline dodo

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #227 on: 12/03/2017 06:34 PM »
Layman question: in such a Hohmann transfer orbit (and when not terminated by Mars orbit insertion), is there a risk of the trajectory intersecting Earth at some point in the future? (Presumably not right on the first orbit, since Earth is no longer there, but at some common multiple of the Earth's and payload's orbital period, I imagine.)

Edit: s/Hoffman/Hohmann/

Yes, but it's also possible to be in an orbit that has an exact resonance with Earth and will not intersect Earth's position.

Follow up: are Mars and Earth in resonant orbits, like Jupiter's inner moons? (I don't think so.) If not, I reckon it may not be possible to compute an orbit that avoids BOTH Earth and Mars.

Online kevin-rf

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #228 on: 12/03/2017 06:54 PM »

Follow up: are Mars and Earth in resonant orbits, like Jupiter's inner moons? (I don't think so.) If not, I reckon it may not be possible to compute an orbit that avoids BOTH Earth and Mars.

Think 3d, if you change the inclination slightly, it is possible to always have an apogee that is above, or below Mar's orbital plane, forever missing. Though I do think the perigee will always intersection with Earth's plane.
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Offline shooter6947

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #229 on: 12/03/2017 07:01 PM »

Follow up: are Mars and Earth in resonant orbits, like Jupiter's inner moons? (I don't think so.) If not, I reckon it may not be possible to compute an orbit that avoids BOTH Earth and Mars.

No; none of the planets in the Solar System are resonant, though we've found resonant exoplanets.  Pluto is 3:2 resonant with Neptune, but, you know, not really a planet. 

Offline Ictogan

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #230 on: 12/03/2017 08:42 PM »
Layman question: in such a Hohmann transfer orbit (and when not terminated by Mars orbit insertion), is there a risk of the trajectory intersecting Earth at some point in the future? (Presumably not right on the first orbit, since Earth is no longer there, but at some common multiple of the Earth's and payload's orbital period, I imagine.)

Edit: s/Hoffman/Hohmann/

Yes, but it's also possible to be in an orbit that has an exact resonance with Earth and will not intersect Earth's position.
Under the assumption that there will be no system that is able to do any burns after the roadster has left earth's vincinity, wouldn't it be impossible for it to enter such a resonant non-earth-intersecting orbit?

Offline dodo

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #231 on: 12/03/2017 08:55 PM »
Under the assumption that there will be no system that is able to do any burns after the roadster has left earth's vincinity, wouldn't it be impossible for it to enter such a resonant non-earth-intersecting orbit?

Why? The final orbit is determined by the delta-V at Earth's departure, plus whatever change results from the close shave to Mars. (I imagine the shave won't be that close, if they have no way of fine-tuning the approach.)

Offline Ictogan

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #232 on: 12/03/2017 08:58 PM »
Under the assumption that there will be no system that is able to do any burns after the roadster has left earth's vincinity, wouldn't it be impossible for it to enter such a resonant non-earth-intersecting orbit?

Why? The final orbit is determined by the delta-V at Earth's departure, plus whatever change results from the close shave to Mars. (I imagine the shave won't be that close, if they have no way of fine-tuning the approach.)
A resonant orbit would mean that it has the same position relative to earth every x years. If it starts at earth and goes into an orbit that has a resonance with earth, it should return to earth after x years.

Offline Space Ghost 1962

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #233 on: 12/03/2017 09:19 PM »
Any C3 escape launch will have its orbit intersect with Earth's orbit, because the US+payload are now in a new orbit that only differs by the net effective delta-v vector of the launch itself. (The exceptions to this would be in exceeding heliocentric escape velocity (never returns) or cancels enough of Earths orbital velocity to never intersect the orbit.)

Lets say you're not in the two above cases - what means could you use to avoid such intersection? Another propulsive maneuver out of the gravitational influence of the Earth (in significance) could change a parameter to never fall into the influence/intersection, or a gravitational interaction with a third body for like effect. One could also inject in/through/near a gravitational equipotential and cause a chaotic orbit that would never have a stable interaction with the Earth/Moon system that would coincide with an orbital intersection. You could never prove a solution that would ever cause it to return.


Online rsdavis9

venus and earth are in a 3:2 resonance?

EDIT: a resonance of its rotation with the earths orbit.

https://en.wikipedia.org/wiki/Tidal_locking

Quote
Venus's 583.92-day interval between successive close approaches to Earth is equal to 5.001444 Venusian solar days, making approximately the same face visible from Earth at each close approach. Whether this relationship arose by chance or is the result of some kind of tidal locking with Earth is unknown.[14]
« Last Edit: 12/04/2017 02:14 PM by rsdavis9 »
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Offline IanThePineapple

venus and earth are in a 3:2 resonance?

I looked it up and couldn't find anything on it.

EDIT: They're in a near 8:13 resonance according to Wikipedia.
« Last Edit: 12/04/2017 02:17 PM by IanThePineapple »

Offline llanitedave

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #236 on: 12/05/2017 05:12 AM »

Follow up: are Mars and Earth in resonant orbits, like Jupiter's inner moons? (I don't think so.) If not, I reckon it may not be possible to compute an orbit that avoids BOTH Earth and Mars.

Think 3d, if you change the inclination slightly, it is possible to always have an apogee that is above, or below Mar's orbital plane, forever missing. Though I do think the perigee will always intersection with Earth's plane.

Only in the absence of future perturbations.  But its orbit will be subject to at least semi-close encounters with Earth and Mars, and with small but frequent perturbations by Jupiter.  I suspect that over the ages, both perigee and apogee will change.  Maybe drastically.
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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #237 on: 12/05/2017 06:03 AM »
The typical dynamical lifetime of near Earth asteroids is on the order of a few 10 million years. Within that typical time frame, they either collide with the sun, a planet, or might even be ejected from the inner solar system. This of course applies for the roadster too. There is no orbit where it would be fully protected from destabilization, although some orbits are more stable than others. But since the roadster's orbit will always pass close to the Earth, its biggest risk for orbit destabilization will always be an Earth encounter.
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Offline Pete

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #238 on: 12/05/2017 06:33 AM »
The typical dynamical lifetime of near Earth asteroids is on the order of a few 10 million years. Within that typical time frame, they either collide with the sun, a planet, or might even be ejected from the inner solar system.
Collide with the sun? From a earth-mars orbit?
Where would the object get the needed 20-25km/s of speed change?
.
Also for ejecting from the inner solar system, you would need to find some 10km/s++ from somewhere. That is possible with a series of gravity slings, but *ludicrously* unlikely.
Lifting the apoapse out of the inner solar system is a lot easier, and even that will take multiple fortuitous gravity encounters, most likely with earth.

Offline dodo

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #239 on: 12/05/2017 06:08 PM »
Lifting the apoapse out of the inner solar system is a lot easier, and even that will take multiple fortuitous gravity encounters, most likely with earth.

I am trying to imagine, without much success, where periapsis and apoapsis would be, if (I believe) the Earth-Mars trip is only a short arc of a much longer heliocentric orbit.

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