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Thread: Boosting to GEO

  1. #1
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    Boosting to GEO

    Yo folks!

    Many here will know that I write science fiction (poorly), and I often bring questions about science and technology here to the group.
    This is a simple one, but beyond my understanding.

    In my fictional universe, Earth's Spaceport is High Heaven, a gigantic ring-and-spindle city housing a populace of 1.6 million at GEO over North America.
    It has been a staple of my writing that it takes eighteen hours to get from Earth to High Heaven; while I've known it for some time, it never actually clicked that an actual spacecraft wouldn't need anything LIKE 18 hours to get to the Habitat.
    Apollo 11 did it in like three hours - once she burned into TLI she reached 36,000 Kms. in about 3 and a half hours - but Apollo wasn't aiming for GEO; she was zooming past it at Ludicrous Speed.

    My question is twofold:
    In my near-future world, spaceflight is common enough that personal and lite-ute transports (commonly called 'Flitters' though there is a wide range of light ship types for both commercial and personal use) regularly fly between Earth and High Heaven.
    Question 1: assuming a standard Hohmann transfer (if that applies in this case) how long would it take a spacecraft to travel from LEO to GEO?
    Question 2: Some of the more advanced Flitters (used by the government, medical transports and the military) are - to use Kylie's term - "Fast-burn fusion jobs" that can get to High Heaven MUCH faster than chemically-powered ships. While the power system of 'fast-burn Fusion models' are never described, we can assume it's nuclear in origin and has great advantages over chemical systems. Imagining a power source that can provide constant accelleration at - say - 0.5 G , how quickly could a "Fast burn Fusion" shuttle get to GEO?
    Thanks friends. Glad to be back with you and asking my oddball questions.
    "The difference between theory and practice is that in theory, there's no difference."

    "Aikido: the art of hitting people with planets."

  2. #2
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    I'm getting about seven-and-a-half hours for the Hohmann transfer, based on orbital periods of 24 hours (GEO) and 90 minutes (LEO), and the square-cube relationship between period and semimajor axis. I'd need to think about your 0.5g transfer for a while before answering. Probably someone else will pick it up.

    Grant Hutchison

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    DAVE! I've missed you. You vanished soon after the book you shared, which I rather liked, warts and all. Have you developed that novel any further?

    I can't answer the GEO question, though my gut tells me 18 hours is quite long for a routinized spaceflight culture for the trip.

    Good luck and I hope I get to read more of The Bulldog's adventures some day.

    CJSF
    P.S.
    Your Venus still scares the bejeebies out of me.
    "The sun is a quagmire
    It's not made of fire
    Forget what you've been told in the past
    Electrons are free
    (Plasma!) Fourth state of matter
    Not gas, not liquid, not solid"

    -They Might Be Giants, "Why Does The Sun Really Shine?"


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  4. #4
    I'm looking thru and old dynamics textbook.
    From the wilderness into the cosmos.
    You can not be afraid of the wind, Enterprise: Broken Bow.
    https://davidsuniverse.wordpress.com/

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    Spherical cows. LEO to GEO is about 35,000km, as the crow flies. At 0.5g with a stationary start and finish, in the absence of gravity, that takes about 90 minutes. Maximum velocity is about 13km/s, which is higher than Earth escape velocity, and also considerably higher than the necessary delta-v for LEO-GEO, which is around 4km/s, depending on the inclination of the LEO. So I'm thinking 90 minutes is on the low end of the right ballpark. But it would of course depend on where High Heaven was in its orbit relative to the departure point of your fast shuttle--if they have to drive a greater distance to make their rendezvous, that that will take up time.

    Grant Hutchison

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    Quote Originally Posted by grant hutchison View Post
    LEO to GEO is about 35,000km, as the crow flies.
    I really like this sentence. Those are some impressive crows.
    Conserve energy. Commute with the Hamiltonian.

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    Quote Originally Posted by Grey View Post
    I really like this sentence.
    Thank you. It made me smile when I typed it.

    Grant Hutchison

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    You folks are amazing - you really are. I ask the question, go to work and when I get back, look at what you've done. Awesome!
    I'm sure the math itself is pretty simple; I remember you guys trying to teach me Tsilokofsky's Rocket Equation - and me not getting it lol. It seems a fairly straightforward equation, I'm just dumb when it comes to math.
    A few quotes:
    Quote Originally Posted by grant hutchison View Post
    I'm getting about seven-and-a-half hours for the Hohmann transfer, based on orbital periods of 24 hours (GEO) and 90 minutes (LEO), and the square-cube relationship between period and semimajor axis.
    Awesome - that's perfect, and an ideal time I was hoping for. (I was privately thinking 9-ish would be about right. Long enough for things to happen, not too long that it slows down the story.)

    Quote Originally Posted by CJSF View Post
    DAVE! I've missed you. You vanished soon after the book you shared, which I rather liked, warts and all. Have you developed that novel any further?
    Hi, CJ! That book is on the back burner at the moment - I know what I need to do to fix it, but it's going to be a LOT of work. I started working on a different Kylie story - having a lot of fun with it too.
    I'll send you an excerpt via Dropbox - just a warning that it involves some pretty disturbing material. (Not quite as disturbing as a guy melting in his Powersuit lol)

    Quote Originally Posted by grant hutchison View Post
    Spherical cows. LEO to GEO is about 35,000km, as the crow flies. At 0.5g with a stationary start and finish, in the absence of gravity, that takes about 90 minutes. Maximum velocity is about 13km/s, which is higher than Earth escape velocity, and also considerably higher than the necessary delta-v for LEO-GEO, which is around 4km/s, depending on the inclination of the LEO. So I'm thinking 90 minutes is on the low end of the right ballpark. But it would of course depend on where High Heaven was in its orbit relative to the departure point of your fast shuttle--if they have to drive a greater distance to make their rendezvous, that that will take up time.

    Grant Hutchison
    Ye cats! I figured it would be fast, but THAT fast? That's fast.
    OK - given that since High Heaven is over North America, a ship taking off from (in this case) the Confederate States would need to reach LEO, then burn over the Indian Ocean, so that adds a good hour at least. 10-15 minutes to dock/undock from the Habitat so a full flight - let's say 2.5-3 hours as a round number. Thank you!

    Quote Originally Posted by Grey View Post
    I really like this sentence. Those are some impressive crows.
    I'm quite partial to the spherical cows myself.
    "The difference between theory and practice is that in theory, there's no difference."

    "Aikido: the art of hitting people with planets."

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    Quote Originally Posted by NorthernDevo View Post
    Ye cats! I figured it would be fast, but THAT fast? That's fast.
    OK - given that since High Heaven is over North America, a ship taking off from (in this case) the Confederate States would need to reach LEO, then burn over the Indian Ocean, so that adds a good hour at least. 10-15 minutes to dock/undock from the Habitat so a full flight - let's say 2.5-3 hours as a round number. Thank you!
    Maybe not quite so much time, since at constant acceleration the distance covered varies with the square of elapsed time. So double the time gives you four times the distance. And your trajectory is going to look hyperbolic in the middle, so you won't be starting your burn on the opposite side of the Earth from your destination.
    You've got wiggle room, though. For instance, would it actually be a good idea for your shuttle to exceed local escape velocity during its journey? An engine failure near turnover begins to have particularly serious consequences in that case. But if your story world has rescue vessels that can accelerate at 1g to recover shuttles lost in this way, it's maybe not such a big issue issue.

    Grant Hutchison

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    Quote Originally Posted by grant hutchison View Post
    Maybe not quite so much time, since at constant acceleration the distance covered varies with the square of elapsed time. So double the time gives you four times the distance. And your trajectory is going to look hyperbolic in the middle, so you won't be starting your burn on the opposite side of the Earth from your destination.
    You've got wiggle room, though. For instance, would it actually be a good idea for your shuttle to exceed local escape velocity during its journey? An engine failure near turnover begins to have particularly serious consequences in that case. But if your story world has rescue vessels that can accelerate at 1g to recover shuttles lost in this way, it's maybe not such a big issue issue.

    Grant Hutchison
    I was scratching my head for a moment at that - a Hohman transfer always starts opposite the planet from the target, correct? Then it clicked in: with constant acceleration it wouldn't be a Hohman so the burn for the destination would be closer to 90 degrees - so as a guess,more along the longitude of Fiji? It's something to keep in mind, and since you point out it has 'wiggle room' (and your example is bang on target, High Heaven does have a SAR detachment and Navy base; OSD has their own ships too) that helps the story immeasurably. Travel time can, basically, be whatever I need it to be.
    Now - obviously the fuel source is pure handwavium for both engine types and I wouldn't have a clue how a fusion engine works, but knowing how long the journey would be helps immeasurably - thank you!
    "The difference between theory and practice is that in theory, there's no difference."

    "Aikido: the art of hitting people with planets."

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    Yes, you can basically fire up over the Pacific somewhere, I'd guess. The trajectory of your shuttle peels up from LEO, increasingly approximates a straight line during transit, and then curves around to align with GEO, catching up with High Heaven as it does so. So a sort of long, tilted, reversed S shape as you look down on it from the north. With speeds much greater than local escape velocity in the middle of transit, you've probably got a wide choice of locations to start your burn, because you can readily change your heading as you climb towards GEO. Presumably there would be some sort of standard route, for traffic control purposes.

    Grant Hutchison

  12. #12
    Quote Originally Posted by The Backroad Astronomer View Post
    I'm looking thru and old dynamics textbook.
    Sorry, I found the equations but I don't like the calculator in windows, so now I am trying to figure out how to write a program to do it.
    From the wilderness into the cosmos.
    You can not be afraid of the wind, Enterprise: Broken Bow.
    https://davidsuniverse.wordpress.com/

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    Quote Originally Posted by CJSF View Post
    DAVE! I've missed you. You vanished soon after the book you shared, which I rather liked, warts and all. Have you developed that novel any further?

    I can't answer the GEO question, though my gut tells me 18 hours is quite long for a routinized spaceflight culture for the trip.

    Good luck and I hope I get to read more of The Bulldog's adventures some day.

    CJSF
    P.S.
    Your Venus still scares the bejeebies out of me.
    Here is an excerpt where Kylie begins an investigation in a much less terrifying place than Venus - but comes much closer to killing her.
    https://www.dropbox.com/s/9nt6scl8vl...Blues.pdf?dl=0
    "The difference between theory and practice is that in theory, there's no difference."

    "Aikido: the art of hitting people with planets."

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    In terms of his planet Venus...Talk about “atmosphere”
    Very nice.

    Speaking about about a boost to GEO, what would it take to move ISS there, over time?

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    Quote Originally Posted by publiusr View Post
    In terms of his planet Venus...Talk about “atmosphere”
    Very nice.

    Speaking about about a boost to GEO, what would it take to move ISS there, over time?
    About four kilometres per second, plus a fraction of a km/s for the plane change. Do it at very low acceleration to stop bits falling off. But why?

    Grant Hutchison

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    It is such a huge investment that dropping it into point Nemo would be a waste.
    If nothing else, at end of life, the truss segments can perhaps be a point where all dead geostationary comsats can be recycled as an Orbital Antenna Farm or SPSS prototype.

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    Quote Originally Posted by grant hutchison View Post
    About four kilometres per second, plus a fraction of a km/s for the plane change. Do it at very low acceleration to stop bits falling off. But why?

    Grant Hutchison
    ROAD TRIP!

    I believe that the thought is that ISS is currently in space. It is large, well-built and can comfortably house a crew of six for months. A single MPLM such as Leonardo can be loaded with a staggering amount of supplies - so since it's in orbit anyway could ISS be converted into an interplanetary explorer?
    I MUST stress that this is ONLY what I believe Publiusr was asking, and not in any way suggesting such a thing could be valuable.

    BUT:

    I have never made ANY attempt to pretend my knowledge of science is greater than it is. I am quite happy to be wrong, ask a silly question and have the concepts explained to me.

    THEREFORE:

    ISS is the biggest Human construction in space. She is self-sufficient in terms of power, she is reasonably tough, she has acres of storage space for a smaller crew and can be boosted by an external module, as far as I know. ISS could also be loaded to the eyeballs with food, water and necessary supplies. She could be reinforced against acceleration - I'm no Engineer but I know how to rig a guy-line - and the Delta-V needed to reach Venus is not that onerous. Dr. Grant has pointed out it would take 4000m/s and that's a LOT - but a careful, well-planned and prepared boost could do that, couldn't it?
    Of course, our mythical explorer would also need to burn into Venus's orbit, and THEN have the fuel to burn BACK to Earth...and THEN need the fuel to enter orbit AGAIN and....yeesh; I'm starting to get it. At this point I'm starting to answer my own question as I draw things out.
    MAN that would be a heck of a lot of fuel which would have to be CARRIED by the thing, adding mass.
    But using ISS as an explorer to Venus or Mars is at least theoretically possible...?
    Probably not, and in asking this question I've identified a few of the reasons why not. I'd just like to hear the word from someone who knows what he/she's talking about LOL.
    "The difference between theory and practice is that in theory, there's no difference."

    "Aikido: the art of hitting people with planets."

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    Quote Originally Posted by NorthernDevo View Post
    Here is an excerpt where Kylie begins an investigation in a much less terrifying place than Venus - but comes much closer to killing her.
    https://www.dropbox.com/s/9nt6scl8vl...Blues.pdf?dl=0
    Thanks for sharing that... it may not be your intent, but I like that this story comes off as a bit cheese-ball while keeping the flavor of The Burning Dark.

    CJSF
    "The sun is a quagmire
    It's not made of fire
    Forget what you've been told in the past
    Electrons are free
    (Plasma!) Fourth state of matter
    Not gas, not liquid, not solid"

    -They Might Be Giants, "Why Does The Sun Really Shine?"


    lonelybirder.org

  19. #19
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    Quote Originally Posted by CJSF View Post
    Thanks for sharing that... it may not be your intent, but I like that this story comes off as a bit cheese-ball while keeping the flavor of The Burning Dark.

    CJSF
    I'm glad that's how you saw it.
    The point is that this is a Kylie Wilson story, and the common theme is her - tough, smart and hugely entertaining (that's the goal anyway). In most cases, stories start with Kylie viewed in the 2nd. Person - from the viewpoint of another character encountering her. In this particular case, the story is intended for people who already know Kylie. They will know that Gwyneth is Kylie, doing a bad job at being undercover. Julian's immature fantasies and his resulting titanic mistake should have people either giggling or mentally shouting "NO! STOP NOW!!!"
    Boomship Blues is a classic box-mystery; similar to Burning Dark. Other than Kylie nearly being killed (a common theme - she nearly gets killed in EVERY mystery and may use her Enhancements ONCE to survive the attack...in this case, she doesn't) it's a much lighter, funnier (I hope) and fast-paced story as she solves the crime, deals with rich passengers, and makes poor Julian's life a living Hell for threatening to shoot her.
    "The difference between theory and practice is that in theory, there's no difference."

    "Aikido: the art of hitting people with planets."

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    Quote Originally Posted by NorthernDevo View Post
    ROAD TRIP!

    I believe that the thought is that ISS is currently in space. It is large, well-built
    I MUST stress that this is ONLY what I believe Publiusr was asking...ISS is the biggest Human construction in space. She is self-sufficient in terms of power, she is reasonably tough...Dr. Grant has pointed out it would take 4000m/s .
    Now you don’t ask too much right away mind you.

    First, say that “ISS needs to be boosted out of LEO to avoid debris”, adding even more solar panels as an SPSS prototype. Then, perhaps ask for large noble gas loads for other research.

    You are slowly turning ISS into a massive SEP spacecraft. Shhh!

    Once in GEO, it takes far less to thump it away from Earth than the very long time to spiral out to GEO.
    More hardy replacement modules to deal with higher rad-levels can be rocketed up.

    The key is to disguise each step as something else...

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