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Atlas V payload capability to TMI?
by
spacetraveler
on 07 Apr, 2011 03:19
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I'm starting this thread because there was a discussion around this going on in another thread but it was not on topic, and also because I'm curious to hear what others have to say.
The question I have is, what is the most payload mass a currently available Atlas V vehicle (any variant) can push to TMI?
There was a claim made in the other thread that Atlas V 552 with a STAR-48 kick-stage can put 13.6mt (30klbs) on a TMI trajectory.
Personally I feel that this is completely unsubstantiated and not supported by any of the ULA literature or basic facts, since they list even the GTO performance as less than this.
But it was stated that in certain cases TMI could be done for less engine delta-v budget than GTO. Can anyone provide a more detailed explanation on exactly what the TMI capability of Atlas is?
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#1
by
Downix
on 07 Apr, 2011 03:28
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Also be sure to compare Low Energy Transfers vs Hoffmann Transfers as well.
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#2
by
spacetraveler
on 07 Apr, 2011 03:38
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Downix, to reply to your statement in the other thread.
It would also help to note that EML1 is not that much further away than GTO's apogee either. 61k km over 37k km. Add to it the lower perigee and minimal planar changes, yes, you need less energy to hit EML1 than GTO.
EML1 is ~61k km from
the moon, not from earth.
EML1 is over 300k km from earth, you know where we would be launching from.
It's almost a TLI burn.
To say that you need less energy to get to EML1 than GTO apogee is just nonsensical.
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#3
by
Downix
on 07 Apr, 2011 04:09
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How about this. Let us do the total LEO first:
To a basic 185km orbit at 26 degree inclination, the Atlas 552 can bring 20,050 kg. Which means, at 13,600 kg payload, plus STAR-48's weight of 2134 kg, so a total of 15634 kg in total. Which means that your Centaur can retain 4416 kg of fuel. Now, doing a 20 second burn at every Perigee would expand the orbit, adding approximately 176 m/s DeltaV (154 m/s actual impulse, 22 m/s gravity assist). By limiting your burns to just this narrow window, you get full effect of the earths gravity to help you. This would also use 229.4 kg of fuel. The Centaur could as a result add a total of 3388 m/s Delta V from this once it's fuel is used up. EML1 is 3768 m/s, to remind you. Now you ignite the STAR-48, which with the gravity asist slingshotting through EML1, around the moon then earth adds another 984 m/s delta v, giving you a total of 4372 m/s Delta V. The total needed for TMI, mind you, is 4298 m/s. So there you are, 13,600 kg on TMI, and it only took a *lot* of burns, 19 of them in fact.
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#4
by
Downix
on 07 Apr, 2011 04:25
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Downix, to reply to your statement in the other thread.
It would also help to note that EML1 is not that much further away than GTO's apogee either. 61k km over 37k km. Add to it the lower perigee and minimal planar changes, yes, you need less energy to hit EML1 than GTO.
EML1 is ~61k km from the moon, not from earth.
EML1 is over 300k km from earth, you know where we would be launching from. It's almost a TLI burn.
To say that you need less energy to get to EML1 than GTO apogee is just nonsensical.
I went and looked this all up. It is 2831 m/s Delta-V to GTO. It is 3768 m/s to EML1. Less than a km/s difference. You do need more energy, but not necessarily from the upper stage itself. Low Energy Transfer maneuvers can enable you to push that up, if you are willing to live with longer in-orbit operational times. Some LET's take months, if not years, to line up properly.
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#5
by
spacetraveler
on 07 Apr, 2011 04:26
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EML1 is 3768 m/s
Now we're getting somewhere.
This, as far as I can tell, is correct.
EML1 from LEO takes around 3.8km/sec additional delta-v.
But GTO only takes around 2.5km/sec additional delta-v.
What this means again, is my original point and the opposite of what you just said. The energy needed to get to EML1 is MORE than GTO, not less.
So even if I were to assume that your above analysis is correct, I would also then have to assume that the payload available to GTO is far more than ULA claims. So unless ULA has been seriously understating the performance of their launch vehicles, you must have an error in that analysis.
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#6
by
Downix
on 07 Apr, 2011 04:33
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EML1 is 3768 m/s
Now we're getting somewhere.
This, as far as I can tell, is correct.
EML1 from LEO takes around 3.8km/sec additional delta-v.
But GTO only takes around 2.5km/sec additional delta-v.
What this means again, is my original point and the opposite of what you just said. The energy needed to get to EML1 is MORE than GTO, not less.
So even if I were to assume that your above analysis is correct, I would also then have to assume that the payload available to GTO is far more than ULA claims. So unless ULA has been seriously understating the performance of their launch vehicles, you must have an error in that analysis.
You can do more to GTO, if you are willing to sacrifice time. Remember, I'm doing 19 separate burns, of which you can do one every two or three weeks. How many companies would want to spend that much time setting that up?
ULA is promoting the direct insertion, or two burn payloads. The opportunity for larger payloads through such maneuvers are limited, and time consuming. Truth in advertising is that ULA needs to publish direct payloads, as these kinds of maneuvers are not something for the regular mission, and cannot be guaranteed from day to day launching.
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#7
by
spacetraveler
on 07 Apr, 2011 04:47
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You can do more to GTO, if you are willing to sacrifice time. Remember, I'm doing 19 separate burns, of which you can do one every two or three weeks. How many companies would want to spend that much time setting that up?
One every two or three weeks?
The period of a GTO orbit is roughly 10 hours, hence the period of any intermediary ascent orbits would be less than that. So if your maneuver did what you claim, you would only have to wait less than 10 hours until the next perigee burn, not 3 weeks.
You are making less and less sense.
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#8
by
Downix
on 07 Apr, 2011 05:01
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You can do more to GTO, if you are willing to sacrifice time. Remember, I'm doing 19 separate burns, of which you can do one every two or three weeks. How many companies would want to spend that much time setting that up?
One every two or three weeks?
The period of a GTO orbit is roughly 10 hours, hence the period of any intermediary ascent orbits would be less than that. So if your maneuver did what you claim, you would only have to wait less than 10 hours until the next perigee burn, not 3 weeks.
You are making less and less sense.
In that 10 hours you'd no longer be in alignment to get the gravity boost to point you in the right direction.
Here's a good book to explain how a portion of this works:
http://press.princeton.edu/titles/7687.htmlPortions of this idea have been used in the past, including the Hiten lunar probe. The model I used was to adapt the Apollo Applications approach using an early version of this technique, which I then applied what we've learned every since.
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#9
by
alexw
on 07 Apr, 2011 05:05
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You can do more to GTO, if you are willing to sacrifice time. Remember, I'm doing 19 separate burns, of which you can do one every two or three weeks. How many companies would want to spend that much time setting that up?
ULA is promoting the direct insertion, or two burn payloads. The opportunity for larger payloads through such maneuvers are limited, and time consuming. Truth in advertising is that ULA needs to publish direct payloads, as these kinds of maneuvers are not something for the regular mission, and cannot be guaranteed from day to day launching.
They cannot be achieved at all, much less guaranteed by ULA.
Centaur's life is a few hours on batteries. You could conceivably build a hyper-mission kit of batteries, but hydrolox boiloff is not so long, either. (One of the FISO reports may have had some estimates on stock Centaur and DCSS.) Meanwhile, depending on the thermal paths, the hypergols may freeze. Finally, Centaur isn't (IIRC) controllable from the ground, and those repeated tiny burns will surely require precisely updated state vectors, no?
-Alex
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#10
by
spacetraveler
on 07 Apr, 2011 05:06
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In that 10 hours you'd no longer be in alignment to get the gravity boost to point you in the right direction.
According to your previous statement, yes you would.
doing a 20 second burn at every Perigee
This is at least the second time you have completely contradicted your own argument.
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#11
by
Downix
on 07 Apr, 2011 05:12
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You can do more to GTO, if you are willing to sacrifice time. Remember, I'm doing 19 separate burns, of which you can do one every two or three weeks. How many companies would want to spend that much time setting that up?
ULA is promoting the direct insertion, or two burn payloads. The opportunity for larger payloads through such maneuvers are limited, and time consuming. Truth in advertising is that ULA needs to publish direct payloads, as these kinds of maneuvers are not something for the regular mission, and cannot be guaranteed from day to day launching.
They cannot be achieved at all, much less guaranteed by ULA.
Centaur's life is a few hours on batteries. You could conceivably build a hyper-mission kit of batteries, but hydrolox boiloff is not so long, either. (One of the FISO reports may have had some estimates on stock Centaur and DCSS.) Meanwhile, depending on the thermal paths, the hypergols may freeze. Finally, Centaur isn't (IIRC) controllable from the ground, and those repeated tiny burns will surely require precisely updated state vectors, no?
-Alex
ULA does offer a long duration upgrade to the Centaur, which does address the issues at hand.
Now, this is not an ideal method, as stated before, but it does work if you're willing to put the effort in to doing it.
I do find it funny how people love to nit-pick right after they insist it is impossible rather than discuss the mechanics of it.
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#12
by
Downix
on 07 Apr, 2011 05:12
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In that 10 hours you'd no longer be in alignment to get the gravity boost to point you in the right direction.
According to your previous statement, yes you would.
doing a 20 second burn at every Perigee
This is at least the second time you have completely contradicted your own argument.
Good catch. It should have been "20 second burn at every aligned Perigee". My error.
You need it going in the right direction, yes?
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#13
by
spacetraveler
on 07 Apr, 2011 05:20
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Good catch. It should have been "20 second burn at every aligned Perigee". My error.
You need it going in the right direction, yes?
I'm unclear what you mean by alignment. What orbital parameter is varying over a period of 2-3 weeks?
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#14
by
Downix
on 07 Apr, 2011 05:28
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Good catch. It should have been "20 second burn at every aligned Perigee". My error.
You need it going in the right direction, yes?
I'm unclear what you mean by alignment. What orbital parameter is varying over a period of 2-3 weeks?
The moon. There are gravity bonuses, slight ones, if you fire off depending on lunar alignment. You get two opportunities per lunar orbit. When dealing with low energy, you grab every percentage point you can for that extra delta v.
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#15
by
spacetraveler
on 07 Apr, 2011 05:47
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The moon. There are gravity bonuses, slight ones, if you fire off depending on lunar alignment.
Let me get this straight.
You are claiming that the payload capacity of a rocket to TMI is going to dramatically increase depending on the orientation of the moon's gravitational attraction during an engine firing, near the earth.
That is what you are saying?
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#16
by
alexw
on 07 Apr, 2011 05:49
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You can do more to GTO, if you are willing to sacrifice time. Remember, I'm doing 19 separate burns, of which you can do one every two or three weeks. How many companies would want to spend that much time setting that up?
ULA is promoting the direct insertion, or two burn payloads. The opportunity for larger payloads through such maneuvers are limited, and time consuming. Truth in advertising is that ULA needs to publish direct payloads, as these kinds of maneuvers are not something for the regular mission, and cannot be guaranteed from day to day launching.
They cannot be achieved at all, much less guaranteed by ULA.
Centaur's life is a few hours on batteries. You could conceivably build a hyper-mission kit of batteries, but hydrolox boiloff is not so long, either. (One of the FISO reports may have had some estimates on stock Centaur and DCSS.) Meanwhile, depending on the thermal paths, the hypergols may freeze. Finally, Centaur isn't (IIRC) controllable from the ground, and those repeated tiny burns will surely require precisely updated state vectors, no?
ULA does offer a long duration upgrade to the Centaur, which does address the issues at hand.
Now, this is not an ideal method, as stated before, but it does work if you're willing to put the effort in to doing it.
I do find it funny how people love to nit-pick right after they insist it is impossible rather than discuss the mechanics of it.
"The standard Centaur incorporates park orbit coasts as short as 8 minutes and as long as 2 hours. [...] Longer coast times can also be accommodated although hardware changes are required. A Centaur GSO Kit is required to support Centaur long-coast durations. For the Atlas V 400 series this includes the addition of two 150 amp-hour main vehicle batteries. For some long- coast missions that also incorporate long first Centaur burns, white paint may be required for the Centaur tank sidewalls. [...]
For the Atlas V 500 series vehicles, the GSO Kit consists of the same additional battery power and Centaur LH2 tank sidewall radiation shield. Coasts of up to 6 hours in duration and/or Centaur three-burn missions are achievable with these GSO Kit items." --- AV User's Guide, rev.11
You're also probably aware of the work they did for LCROSS, IIRC certifying the thrusters for a few extra hours.
Can you point to where ULA offers this supposed month-long extended mission kit? How does it keep the hydrogen and LOX from boiling away, and the hypergols from freezing? Does it add solar panels, fuel cells, or radioisotope heaters and colossal batteries?
I'm not disputing the orbital mechanics, I'm saying that it sounds impossible for *Centaur* to achieve such a mission. ULA could surely build an upper stage capable such durations (probes do it all the time, ACES aims to, and we both agree that would be a great idea), but that's not what you're claiming.
-Alex
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#17
by
Downix
on 07 Apr, 2011 06:04
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You can do more to GTO, if you are willing to sacrifice time. Remember, I'm doing 19 separate burns, of which you can do one every two or three weeks. How many companies would want to spend that much time setting that up?
ULA is promoting the direct insertion, or two burn payloads. The opportunity for larger payloads through such maneuvers are limited, and time consuming. Truth in advertising is that ULA needs to publish direct payloads, as these kinds of maneuvers are not something for the regular mission, and cannot be guaranteed from day to day launching.
They cannot be achieved at all, much less guaranteed by ULA.
Centaur's life is a few hours on batteries. You could conceivably build a hyper-mission kit of batteries, but hydrolox boiloff is not so long, either. (One of the FISO reports may have had some estimates on stock Centaur and DCSS.) Meanwhile, depending on the thermal paths, the hypergols may freeze. Finally, Centaur isn't (IIRC) controllable from the ground, and those repeated tiny burns will surely require precisely updated state vectors, no?
ULA does offer a long duration upgrade to the Centaur, which does address the issues at hand.
Now, this is not an ideal method, as stated before, but it does work if you're willing to put the effort in to doing it.
I do find it funny how people love to nit-pick right after they insist it is impossible rather than discuss the mechanics of it.
"The standard Centaur incorporates park orbit coasts as short as 8 minutes and as long as 2 hours. [...] Longer coast times can also be accommodated although hardware changes are required. A Centaur GSO Kit is required to support Centaur long-coast durations. For the Atlas V 400 series this includes the addition of two 150 amp-hour main vehicle batteries. For some long- coast missions that also incorporate long first Centaur burns, white paint may be required for the Centaur tank sidewalls. [...]
For the Atlas V 500 series vehicles, the GSO Kit consists of the same additional battery power and Centaur LH2 tank sidewall radiation shield. Coasts of up to 6 hours in duration and/or Centaur three-burn missions are achievable with these GSO Kit items." --- AV User's Guide, rev.11
You're also probably aware of the work they did for LCROSS, IIRC certifying the thrusters for a few extra hours.
Can you point to where ULA offers this supposed month-long extended mission kit? How does it keep the hydrogen and LOX from boiling away, and the hypergols from freezing? Does it add solar panels, fuel cells, or radioisotope heaters and colossal batteries?
I'm not disputing the orbital mechanics, I'm saying that it sounds impossible for *Centaur* to achieve such a mission. ULA could surely build an upper stage capable such durations (probes do it all the time, ACES aims to, and we both agree that would be a great idea), but that's not what you're claiming.
-Alex
You realize it's gone long past the initial comment, that under the right conditions an Atlas V can deliver a similar payload with the Falcon 9 Heavy due to it's use of a higher energy / restartable upper stage capacity in the same time frame, that is, by 2013. The argument was that the orbital mechanics would not allow for it, which is where this thread comes from.
I'd already agreed that the stock centaur is not up to this job, but that ULA does list a long duration capacity in their order capacity, which has been utilized for LCROSS as far as I know for the only time. More work, such as CRYOTE, would be necessary for an actual production unit to arrive, but all discussions on that list that it would be ready within 18-20 months of order, so it would meet the time requirements for this particular mental exercise.
I find exploring mental exercises like this stimulating, but do get fustrated when people come along and dismiss an idea for the simple fact that they don't know how it works, nor do they honestly care to know.
If I were to seriously discuss this as a long term mission goal, I wouldn't use a Centaur nor a Falcon 9 upper stage, I'd be looking more at modifying the Delta-II's upper stage, possibly a cluster of them, due to the long term storage of propellant. While as an intellectual exercise, it is nice, for pragmatist me, I would want to do this with the least amount of potential failure points as possible. And that means Hypergolics.
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#18
by
Downix
on 07 Apr, 2011 06:06
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The moon. There are gravity bonuses, slight ones, if you fire off depending on lunar alignment.
Let me get this straight.
You are claiming that the payload capacity of a rocket to TMI is going to dramatically increase depending on the orientation of the moon's gravitational attraction during an engine firing, near the earth.
That is what you are saying?
No, and if that is what you are reading into it I don't think you understand the system of low energy transfers. If we're going to have a genuine discussion on this, we need a basic level of understanding of how these work, or else everything I can tell you will look like so much gobledy-gook.
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#19
by
MikeAtkinson
on 07 Apr, 2011 06:33
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How about this. Let us do the total LEO first:
To a basic 185km orbit at 26 degree inclination, the Atlas 552 can bring 20,050 kg. Which means, at 13,600 kg payload, plus STAR-48's weight of 2134 kg, so a total of 15634 kg in total. Which means that your Centaur can retain 4416 kg of fuel. Now, doing a 20 second burn at every Perigee would expand the orbit, adding approximately 176 m/s DeltaV (154 m/s actual impulse, 22 m/s gravity assist). By limiting your burns to just this narrow window, you get full effect of the earths gravity to help you. This would also use 229.4 kg of fuel. The Centaur could as a result add a total of 3388 m/s Delta V from this once it's fuel is used up. EML1 is 3768 m/s, to remind you. Now you ignite the STAR-48, which with the gravity asist slingshotting through EML1, around the moon then earth adds another 984 m/s delta v, giving you a total of 4372 m/s Delta V. The total needed for TMI, mind you, is 4298 m/s. So there you are, 13,600 kg on TMI, and it only took a *lot* of burns, 19 of them in fact.
Ahh, I thought you might have been describing resonance effects with the moon.
"(154 m/s actual impulse, 22 m/s gravity assist)" this is just for the last burn which moves the orbit towards a apogee where lunar influence starts to dominate isn't it? Previous burns would give a smaller gravity assist I think, and a circular LEO would not be able to get any assist.
The stage starts at 185km orbit at 26 [28?] degree inclination, could you give a table of the burns and their assists?
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#20
by
spacetraveler
on 07 Apr, 2011 06:41
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No, and if that is what you are reading into it I don't think you understand the system of low energy transfers.
I understand it enough to know that what I've read on it doesn't sound anything like what you have been saying.
The idea with a low energy transfer is that you get to an initial position and velocity that places you inside a stable manifold tube of your combined system, such that the combined gravitational effects of the Earth-Moon-Sun or Earth-Moon-Sun-Mars system eventually take you within the target destination's influence at which point you expend a small amount of delta-v and attain ballistic capture.
In getting to the desired initial point and initial velocity, there is no scenario I can think of where you would have to wait in a parking orbit for 3 weeks, do another small burn, then wait another 3 weeks. You can either, calculate the motion of the planetary bodies and time the launch date so that only a main initial burn places you on the proper trajectory, or if what you are saying really works where you can attain some kind of gravity assist by doing multiple small burns, then couldn't you time the launch so that you are where you want to be after the final burn in a sequence of consecutive ones?
IMO, that whole scenario you have described gets you a negligible benefit at best, certainly nothing on the order of magnitude you have claimed. The LET does let you do a transfer with less fuel, but I don't understand how it relates to everything that you just stated as far as the process.
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#21
by
Downix
on 07 Apr, 2011 07:01
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How about this. Let us do the total LEO first:
To a basic 185km orbit at 26 degree inclination, the Atlas 552 can bring 20,050 kg. Which means, at 13,600 kg payload, plus STAR-48's weight of 2134 kg, so a total of 15634 kg in total. Which means that your Centaur can retain 4416 kg of fuel. Now, doing a 20 second burn at every Perigee would expand the orbit, adding approximately 176 m/s DeltaV (154 m/s actual impulse, 22 m/s gravity assist). By limiting your burns to just this narrow window, you get full effect of the earths gravity to help you. This would also use 229.4 kg of fuel. The Centaur could as a result add a total of 3388 m/s Delta V from this once it's fuel is used up. EML1 is 3768 m/s, to remind you. Now you ignite the STAR-48, which with the gravity asist slingshotting through EML1, around the moon then earth adds another 984 m/s delta v, giving you a total of 4372 m/s Delta V. The total needed for TMI, mind you, is 4298 m/s. So there you are, 13,600 kg on TMI, and it only took a *lot* of burns, 19 of them in fact.
Ahh, I thought you might have been describing resonance effects with the moon.
"(154 m/s actual impulse, 22 m/s gravity assist)" this is just for the last burn which moves the orbit towards a apogee where lunar influence starts to dominate isn't it? Previous burns would give a smaller gravity assist I think, and a circular LEO would not be able to get any assist.
The stage starts at 185km orbit at 26 [28?] degree inclination, could you give a table of the burns and their assists?
Right. There is some assist on the ellipticals, the longer the elliptical, the better the boost. So, your initial burn has no assist, but as it goes on, you get slightly more, and more. The burns are done to maximize what little assistance you can get, which is why the exact timing of the burn is not always on the same orbit, which is why I say 2-3 weeks. You're using gravities effects, from the earth, moon, sun and several lagrange points to gently push your weight into alignment necessary for the STAR-48 to then do the kick burn.
I can turn the raw numbers into a table if you'd like.
I came up with the scenario about a month ago to teach myself about low energy transfers, before attempting to make such scenarios for AJAX test runs. It was thanks to studying them that I identified a mechanism to push an Orion + Bigelow Genesis module with a fully loaded DCSS onto a Venus flyby mission with free return trip, which did not require any newer technologies than to be able to loiter the DCSS for 24 hours. Very tricky alignment, however, as it only lines up right once every 8 years. (earth- moon- SEL2- earth- Venus- moon- earth)
I've grown to love the challenge of low energy transfer systems.
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#22
by
Downix
on 07 Apr, 2011 07:07
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No, and if that is what you are reading into it I don't think you understand the system of low energy transfers.
I understand it enough to know that what I've read on it doesn't sound anything like what you have been saying.
The idea with a low energy transfer is that you get to an initial position and velocity that places you inside a stable manifold tube of your combined system, such that the combined gravitational effects of the Earth-Moon-Sun or Earth-Moon-Sun-Mars system eventually take you within the target destination's influence at which point you expend a small amount of delta-v and attain ballistic capture.
In getting to the desired initial point and initial velocity, there is no scenario I can think of where you would have to wait in a parking orbit for 3 weeks, do another small burn, then wait another 3 weeks. You can either, calculate the motion of the planetary bodies and time the launch date so that only a main initial burn places you on the proper trajectory, or if what you are saying really works where you can attain some kind of gravity assist by doing multiple small burns, then couldn't you time the launch so that you are where you want to be after the final burn in a sequence of consecutive ones?
IMO, that whole scenario you have described gets you a negligible benefit at best, certainly nothing on the order of magnitude you have claimed. The LET does let you do a transfer with less fuel, but I don't understand how it relates to everything that you just stated as far as the process.
It's negligible to start, correct, but it slowly adds up. While you start off with less than 0.4% benefit, the next pass gives you 0.6%, then 1.1%, and so on. Each one accumulates over time. At no time did I claim it was a magnitude shift, if you check the Delta-V involved we're at less than 900 m/s difference between what Atlas V 552 w/ STAR-48 can normally place 13500kg to this. So, it's how to gain that extra 900 m/s in delta-v, that is the focus. While, yes, we're going it by a few meters/second here and there, it adds up. That is precisely why it takes so blasted long.
Something to point out, the GTO performance of Atlas V is it without the Star-48. The Star-48 adds an extra 575682 kgf-sec of impulse at the end. On a 13,500 kg load, that's a good kick in the pants, yes?
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#23
by
spacetraveler
on 07 Apr, 2011 07:08
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As an example, this was a mission that used a LET to the moon.
http://www.lpi.usra.edu/meetings/lpsc2007/pdf/1915.pdfIt took roughly one year and 2 months to do the transfer, and resulted in 288 thruster firings or around 1 every 1.5 days.
So clearly the moon's alignment over a 2-3 week period had nothing to do with it. The alignment mattered for timing the launch and capture.
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#24
by
Downix
on 07 Apr, 2011 07:09
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As an example, this was a mission that used a LET to the moon.
http://www.lpi.usra.edu/meetings/lpsc2007/pdf/1915.pdf
It took roughly one year and 2 months to do the transfer, and resulted in 288 thruster firings or around 1 every 1.5 days.
So clearly the moon's alignment over a 2-3 week period had nothing to do with it (other than timing the position for the launch and capture).
Right, but that was going to the moon. This is to Mars. Needs a different set of parameters.
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#25
by
spacetraveler
on 07 Apr, 2011 07:14
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As an example, this was a mission that used a LET to the moon.
http://www.lpi.usra.edu/meetings/lpsc2007/pdf/1915.pdf
It took roughly one year and 2 months to do the transfer, and resulted in 288 thruster firings or around 1 every 1.5 days.
So clearly the moon's alignment over a 2-3 week period had nothing to do with it (other than timing the position for the launch and capture).
Right, but that was going to the moon. This is to Mars. Needs a different set of parameters.
There's still nothing that would require you to wait 3 weeks between burns if all you are after at first is raising the orbit.
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#26
by
Downix
on 07 Apr, 2011 07:31
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As an example, this was a mission that used a LET to the moon.
http://www.lpi.usra.edu/meetings/lpsc2007/pdf/1915.pdf
It took roughly one year and 2 months to do the transfer, and resulted in 288 thruster firings or around 1 every 1.5 days.
So clearly the moon's alignment over a 2-3 week period had nothing to do with it (other than timing the position for the launch and capture).
Right, but that was going to the moon. This is to Mars. Needs a different set of parameters.
There's still nothing that would require you to wait 3 weeks between burns if all you are after at first is raising the orbit.
But that's just it, I'm not just raising the orbit. I'm also changing the plane and angel of the ellipse of orbit without using fuel, to get it into alignment for final TMI burn. Slight gravity tugs over weeks can do that.
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#27
by
spacetraveler
on 07 Apr, 2011 07:52
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But that's just it, I'm not just raising the orbit. I'm also changing the plane and angel of the ellipse of orbit without using fuel, to get it into alignment for final TMI burn. Slight gravity tugs over weeks can do that.
The moon's gravity over 3 weeks is not going to change your orbital plane.
Also, this is an example LET to mars proof of concept that I found, and from what I can tell it basically just does an initial burn to escape from a circular LEO.
http://www.technion.ac.il/~dssl/papers/49810_proof2.pdf
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#28
by
Downix
on 07 Apr, 2011 08:00
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But that's just it, I'm not just raising the orbit. I'm also changing the plane and angel of the ellipse of orbit without using fuel, to get it into alignment for final TMI burn. Slight gravity tugs over weeks can do that.
The moon's gravity over 3 weeks is not going to change your orbital plane.
Also, this is an example LET to mars proof of concept that I found, and from what I can tell it basically just does an initial burn to escape from a circular LEO.
http://www.technion.ac.il/~dssl/papers/49810_proof2.pdf
'I studied that one awhile back. And you're right, over 3 weeks, the change would be slight. But as with thrust, over time, it accumulates. Remember, we're talking 18 burns, over almost 40 weeks. In 40 weeks you'll have changed your plane by 3 degrees. Without using any fuel. That alignment if paired with a precise final burn will save you almost 70 m/s of Delta V. Normally, nobody would care, but this is not a normal scenario.
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#29
by
Downix
on 07 Apr, 2011 08:04
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You know, this should show me not to get too smart for my own good. Just because something *can* be done does not make it something that *should* be done. Would do a lot better job if we just launched an empty Atlas 401 to use it's half-full Centaur as a second booster.
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#30
by
MikeAtkinson
on 07 Apr, 2011 08:08
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How about this. Let us do the total LEO first:
To a basic 185km orbit at 26 degree inclination, the Atlas 552 can bring 20,050 kg. Which means, at 13,600 kg payload, plus STAR-48's weight of 2134 kg, so a total of 15634 kg in total. Which means that your Centaur can retain 4416 kg of fuel. Now, doing a 20 second burn at every Perigee would expand the orbit, adding approximately 176 m/s DeltaV (154 m/s actual impulse, 22 m/s gravity assist). By limiting your burns to just this narrow window, you get full effect of the earths gravity to help you. This would also use 229.4 kg of fuel. The Centaur could as a result add a total of 3388 m/s Delta V from this once it's fuel is used up. EML1 is 3768 m/s, to remind you. Now you ignite the STAR-48, which with the gravity asist slingshotting through EML1, around the moon then earth adds another 984 m/s delta v, giving you a total of 4372 m/s Delta V. The total needed for TMI, mind you, is 4298 m/s. So there you are, 13,600 kg on TMI, and it only took a *lot* of burns, 19 of them in fact.
Ahh, I thought you might have been describing resonance effects with the moon.
"(154 m/s actual impulse, 22 m/s gravity assist)" this is just for the last burn which moves the orbit towards a apogee where lunar influence starts to dominate isn't it? Previous burns would give a smaller gravity assist I think, and a circular LEO would not be able to get any assist.
The stage starts at 185km orbit at 26 [28?] degree inclination, could you give a table of the burns and their assists?
Right. There is some assist on the ellipticals, the longer the elliptical, the better the boost. So, your initial burn has no assist, but as it goes on, you get slightly more, and more. The burns are done to maximize what little assistance you can get, which is why the exact timing of the burn is not always on the same orbit, which is why I say 2-3 weeks. You're using gravities effects, from the earth, moon, sun and several lagrange points to gently push your weight into alignment necessary for the STAR-48 to then do the kick burn.
I can turn the raw numbers into a table if you'd like.
I came up with the scenario about a month ago to teach myself about low energy transfers, before attempting to make such scenarios for AJAX test runs. It was thanks to studying them that I identified a mechanism to push an Orion + Bigelow Genesis module with a fully loaded DCSS onto a Venus flyby mission with free return trip, which did not require any newer technologies than to be able to loiter the DCSS for 24 hours. Very tricky alignment, however, as it only lines up right once every 8 years. (earth- moon- SEL2- earth- Venus- moon- earth)
I've grown to love the challenge of low energy transfer systems.
I'm also interested in how you are doing the math.
Its a 3 body problem (actually 4 as there is the Sun involved as well), so there are no exact solutions. I would have thought you would need to optimise each burn duration by tracking the entire trajectory until the next burn and hill climbing. But that would only optimise individual burns, I would have thought there were overall better sequences of burns where each burn need not give the maximum delta-v boost.
I am sceptical about whether it will actually lead to higher TMI payloads in practice, clearly it would require a completely new stage, perhaps ACES would be capable of it. Even with zero boil off, things like engine losses due to start/stop transients and residual drag at perigee could reduce the advantage to zero.
On optimising single launch performance it is probably best not to start in a circular orbit, but that depends on many factors.
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#31
by
Joris
on 07 Apr, 2011 08:09
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How about this. Let us do the total LEO first:
To a basic 185km orbit at 26 degree inclination, the Atlas 552 can bring 20,050 kg. Which means, at 13,600 kg payload, plus STAR-48's weight of 2134 kg, so a total of 15634 kg in total. Which means that your Centaur can retain 4416 kg of fuel. Now, doing a 20 second burn at every Perigee would expand the orbit, adding approximately 176 m/s DeltaV (154 m/s actual impulse, 22 m/s gravity assist). By limiting your burns to just this narrow window, you get full effect of the earths gravity to help you. This would also use 229.4 kg of fuel. The Centaur could as a result add a total of 3388 m/s Delta V from this once it's fuel is used up. EML1 is 3768 m/s, to remind you. Now you ignite the STAR-48, which with the gravity asist slingshotting through EML1, around the moon then earth adds another 984 m/s delta v, giving you a total of 4372 m/s Delta V. The total needed for TMI, mind you, is 4298 m/s. So there you are, 13,600 kg on TMI, and it only took a *lot* of burns, 19 of them in fact.
Filling in an the rocket equation:
DV=9.81*451*ln(20050/15634)
DV=1100 m/s
This is nowhere near the 3388 m/s you stated.
DV=9.81*451*ln(20050/19820.6)
DV=50.9
This is nowhere near the 176 m/s you stated.
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#32
by
Downix
on 07 Apr, 2011 15:49
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How about this. Let us do the total LEO first:
To a basic 185km orbit at 26 degree inclination, the Atlas 552 can bring 20,050 kg. Which means, at 13,600 kg payload, plus STAR-48's weight of 2134 kg, so a total of 15634 kg in total. Which means that your Centaur can retain 4416 kg of fuel. Now, doing a 20 second burn at every Perigee would expand the orbit, adding approximately 176 m/s DeltaV (154 m/s actual impulse, 22 m/s gravity assist). By limiting your burns to just this narrow window, you get full effect of the earths gravity to help you. This would also use 229.4 kg of fuel. The Centaur could as a result add a total of 3388 m/s Delta V from this once it's fuel is used up. EML1 is 3768 m/s, to remind you. Now you ignite the STAR-48, which with the gravity asist slingshotting through EML1, around the moon then earth adds another 984 m/s delta v, giving you a total of 4372 m/s Delta V. The total needed for TMI, mind you, is 4298 m/s. So there you are, 13,600 kg on TMI, and it only took a *lot* of burns, 19 of them in fact.
Filling in an the rocket equation:
DV=9.81*451*ln(20050/15634)
DV=1100 m/s
This is nowhere near the 3388 m/s you stated.
DV=9.81*451*ln(20050/19820.6)
DV=50.9
This is nowhere near the 176 m/s you stated.
Let us compare to the Falcon 9 Heavy. It looks to use half of it's upper stage propellant in getting to LEO, so let us work from that:
DV = 9.81*342*ln(25000/13500)
DV = 2067
Nowhere near TMI
So, there is something amiss in the calculation, or both of us (myself and SpaceX) are wrong.
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#33
by
Joris
on 07 Apr, 2011 15:52
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Let us compare to the Falcon 9 Heavy. It looks to use half of it's upper stage propellant in getting to LEO, so let us work from that:
That is not known, they haven't said anything about the upper stage.
We don't even know its mass, wet or dry...
DV = 9.81*342*ln(25000/13500)
DV = 2067
Nowhere near TMI
So, there is something amiss in the calculation, or both of us (myself and SpaceX) are wrong.
Rocket equation is correct, so you must be wrong.
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#34
by
Downix
on 07 Apr, 2011 16:11
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Let us compare to the Falcon 9 Heavy. It looks to use half of it's upper stage propellant in getting to LEO, so let us work from that:
That is not known, they haven't said anything about the upper stage.
We don't even know its mass, wet or dry...
DV = 9.81*342*ln(25000/13500)
DV = 2067
Nowhere near TMI
So, there is something amiss in the calculation, or both of us (myself and SpaceX) are wrong.
Rocket equation is correct, so you must be wrong.
If the equation is correct, then how did we get Hiten to the moon from it's original 3192 delta-v:
DV = 9.81 * 248 * ln(197/174)
DV = 302 m/s
if the equation is correct, Hiten never made it to the moon. But it did.
As for upper stage, the F9H appears to use the same US as the F9, if you check the rocket's new height according to the SpaceX website. No stretching of the US, and the US is the same diameter. The F9's upper stage is a known quantity, with 43mT of fuel and an unloaded mass of 4.1 mT.
So, now the question is, how much Delta-V is the F-9H imparting to the upper stage? That is the unknown here I would think, yes?
Not arguing, I am genuinely curious.
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#35
by
Downix
on 07 Apr, 2011 16:16
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I'm going to make a bit of a leap here. Slight redirection of topic:
What methods could be used to push more mass to TMI from an Atlas, would you say? I've been thinking on it some, if we needed to get 10mT to mars, and had a single Altas 552 launch, it means we could get 20mT into LEO. What could we do to give enough throw to push something in the direction of Mars, hmm?
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#36
by
Joris
on 07 Apr, 2011 16:23
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If the equation is correct, then how did we get Hiten to the moon from it's original 3192 delta-v:
DV = 9.81 * 248 * ln(197/174)
DV = 302 m/s
if the equation is correct, Hiten never made it to the moon. But it did.
http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1990-007AHiten was launched into highly elliptical Earth orbit on a Mu-3SII-5 rocket from Kagoshima Space Center in Japan at 11:46:00 UT (20:46:00 JST) on 24 January 1990. Injection velocity was 50 m/s less than the nominal value, resulting in an apogee of only 290,000 km compared to the expected 476,000 km
Seems like only a small push is need to send it to TLI from an orbit with a apogee of. 290.000km. And not 3192m/s
The MU-3SII can launch 800kg to LEO, and HITEN weighed 200kg.
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#37
by
Downix
on 07 Apr, 2011 16:25
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If the equation is correct, then how did we get Hiten to the moon from it's original 3192 delta-v:
DV = 9.81 * 248 * ln(197/174)
DV = 302 m/s
if the equation is correct, Hiten never made it to the moon. But it did.
http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1990-007A
Hiten was launched into highly elliptical Earth orbit on a Mu-3SII-5 rocket from Kagoshima Space Center in Japan at 11:46:00 UT (20:46:00 JST) on 24 January 1990. Injection velocity was 50 m/s less than the nominal value, resulting in an apogee of only 290,000 km compared to the expected 476,000 km
Seems like only a small push is need to send it to TLI from an orbit with a apogee of. 290.000km. And not 3192m/s
The MU-3SII can launch 800kg to LEO, and HITEN weighed 200kg.
Then, what orbit should Atlas be putting it's payload in, hmm?
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#38
by
Joris
on 07 Apr, 2011 20:59
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If the equation is correct, then how did we get Hiten to the moon from it's original 3192 delta-v:
DV = 9.81 * 248 * ln(197/174)
DV = 302 m/s
if the equation is correct, Hiten never made it to the moon. But it did.
http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1990-007A
Hiten was launched into highly elliptical Earth orbit on a Mu-3SII-5 rocket from Kagoshima Space Center in Japan at 11:46:00 UT (20:46:00 JST) on 24 January 1990. Injection velocity was 50 m/s less than the nominal value, resulting in an apogee of only 290,000 km compared to the expected 476,000 km
Seems like only a small push is need to send it to TLI from an orbit with a apogee of. 290.000km. And not 3192m/s
The MU-3SII can launch 800kg to LEO, and HITEN weighed 200kg.
Then, what orbit should Atlas be putting it's payload in, hmm?
Hiten was first launched to HEO, and than HITEN performed a very small TLI. Which was probably about be 300m/s.
And I don't know what orbit Atlas should launch into, but that is not the point.
The point is that your calculations were not correct and you still have no evidence for your statement about Atlas payload.
How about this. Let us do the total LEO first:
To a basic 185km orbit at 26 degree inclination, the Atlas 552 can bring 20,050 kg. Which means, at 13,600 kg payload, plus STAR-48's weight of 2134 kg, so a total of 15634 kg in total. Which means that your Centaur can retain 4416 kg of fuel. Now, doing a 20 second burn at every Perigee would expand the orbit, adding approximately 176 m/s DeltaV (154 m/s actual impulse, 22 m/s gravity assist). By limiting your burns to just this narrow window, you get full effect of the earths gravity to help you. This would also use 229.4 kg of fuel. The Centaur could as a result add a total of 3388 m/s Delta V from this once it's fuel is used up. EML1 is 3768 m/s, to remind you. Now you ignite the STAR-48, which with the gravity asist slingshotting through EML1, around the moon then earth adds another 984 m/s delta v, giving you a total of 4372 m/s Delta V. The total needed for TMI, mind you, is 4298 m/s. So there you are, 13,600 kg on TMI, and it only took a *lot* of burns, 19 of them in fact.
Filling in an the rocket equation:
DV=9.81*451*ln(20050/15634)
DV=1100 m/s
This is nowhere near the 3388 m/s you stated.
DV=9.81*451*ln(20050/19820.6)
DV=50.9
This is nowhere near the 176 m/s you stated.
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#39
by
Downix
on 07 Apr, 2011 21:15
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If the equation is correct, then how did we get Hiten to the moon from it's original 3192 delta-v:
DV = 9.81 * 248 * ln(197/174)
DV = 302 m/s
if the equation is correct, Hiten never made it to the moon. But it did.
http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1990-007A
Hiten was launched into highly elliptical Earth orbit on a Mu-3SII-5 rocket from Kagoshima Space Center in Japan at 11:46:00 UT (20:46:00 JST) on 24 January 1990. Injection velocity was 50 m/s less than the nominal value, resulting in an apogee of only 290,000 km compared to the expected 476,000 km
Seems like only a small push is need to send it to TLI from an orbit with a apogee of. 290.000km. And not 3192m/s
The MU-3SII can launch 800kg to LEO, and HITEN weighed 200kg.
Then, what orbit should Atlas be putting it's payload in, hmm?
Hiten was first launched to HEO, and than HITEN performed a very small TLI. Which was probably about be 300m/s.
And I don't know what orbit Atlas should launch into, but that is not the point.
The point is that your calculations were not correct and you still have no evidence for your statement about Atlas payload.
I don't see that. I've been crunching my numbers some more, so I am not against discussion, but here I see only "you're wrong" without anything else.
So, I ask again, what orbit should Atlas launch into? If you don't have an answer, you've brought what you had to the table and should leave it at that and let us move the discussion onward shall we?
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#40
by
Joris
on 07 Apr, 2011 21:29
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I don't see that. I've been crunching my numbers some more, so I am not against discussion, but here I see only "you're wrong" without anything else.
Your calculations were wrong.
I said they were not, and showed why.
Than you rejected that, by saying that HITEN did it.
Which is not the case.
I again state this fault in your calculations:
How about this. Let us do the total LEO first:
To a basic 185km orbit at 26 degree inclination, the Atlas 552 can bring 20,050 kg. Which means, at 13,600 kg payload, plus STAR-48's weight of 2134 kg, so a total of 15634 kg in total. Which means that your Centaur can retain 4416 kg of fuel. Now, doing a 20 second burn at every Perigee would expand the orbit, adding approximately 176 m/s DeltaV (154 m/s actual impulse, 22 m/s gravity assist). By limiting your burns to just this narrow window, you get full effect of the earths gravity to help you. This would also use 229.4 kg of fuel. The Centaur could as a result add a total of 3388 m/s Delta V from this once it's fuel is used up. EML1 is 3768 m/s, to remind you. Now you ignite the STAR-48, which with the gravity asist slingshotting through EML1, around the moon then earth adds another 984 m/s delta v, giving you a total of 4372 m/s Delta V. The total needed for TMI, mind you, is 4298 m/s. So there you are, 13,600 kg on TMI, and it only took a *lot* of burns, 19 of them in fact.
Filling in an the rocket equation:
DV=9.81*451*ln(20050/15634)
DV=1100 m/s
This is nowhere near the 3388 m/s you stated.
DV=9.81*451*ln(20050/19820.6)
DV=50.9
This is nowhere near the 176 m/s you stated.
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#41
by
MikeAtkinson
on 07 Apr, 2011 22:49
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I don't see that. I've been crunching my numbers some more, so I am not against discussion, but here I see only "you're wrong" without anything else.
Your calculations were wrong.
I said they were not, and showed why.
Than you rejected that, by saying that HITEN did it.
Which is not the case.
I again state this fault in your calculations:
How about this. Let us do the total LEO first:
To a basic 185km orbit at 26 degree inclination, the Atlas 552 can bring 20,050 kg. Which means, at 13,600 kg payload, plus STAR-48's weight of 2134 kg, so a total of 15634 kg in total. Which means that your Centaur can retain 4416 kg of fuel. Now, doing a 20 second burn at every Perigee would expand the orbit, adding approximately 176 m/s DeltaV (154 m/s actual impulse, 22 m/s gravity assist). By limiting your burns to just this narrow window, you get full effect of the earths gravity to help you. This would also use 229.4 kg of fuel. The Centaur could as a result add a total of 3388 m/s Delta V from this once it's fuel is used up. EML1 is 3768 m/s, to remind you. Now you ignite the STAR-48, which with the gravity asist slingshotting through EML1, around the moon then earth adds another 984 m/s delta v, giving you a total of 4372 m/s Delta V. The total needed for TMI, mind you, is 4298 m/s. So there you are, 13,600 kg on TMI, and it only took a *lot* of burns, 19 of them in fact.
Filling in an the rocket equation:
DV=9.81*451*ln(20050/15634)
DV=1100 m/s
This is nowhere near the 3388 m/s you stated.
DV=9.81*451*ln(20050/19820.6)
DV=50.9
This is nowhere near the 176 m/s you stated.
I think the 176 m/s was supposed to come from the last burn, not the first. So we have:
DV=9.81*451*ln((15634+229.4)/15634)
DV=64.5
which is still far short of 176 m/s.
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#42
by
Downix
on 07 Apr, 2011 23:15
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I don't see that. I've been crunching my numbers some more, so I am not against discussion, but here I see only "you're wrong" without anything else.
Your calculations were wrong.
I said they were not, and showed why.
Than you rejected that, by saying that HITEN did it.
Which is not the case.
I again state this fault in your calculations:
How about this. Let us do the total LEO first:
To a basic 185km orbit at 26 degree inclination, the Atlas 552 can bring 20,050 kg. Which means, at 13,600 kg payload, plus STAR-48's weight of 2134 kg, so a total of 15634 kg in total. Which means that your Centaur can retain 4416 kg of fuel. Now, doing a 20 second burn at every Perigee would expand the orbit, adding approximately 176 m/s DeltaV (154 m/s actual impulse, 22 m/s gravity assist). By limiting your burns to just this narrow window, you get full effect of the earths gravity to help you. This would also use 229.4 kg of fuel. The Centaur could as a result add a total of 3388 m/s Delta V from this once it's fuel is used up. EML1 is 3768 m/s, to remind you. Now you ignite the STAR-48, which with the gravity asist slingshotting through EML1, around the moon then earth adds another 984 m/s delta v, giving you a total of 4372 m/s Delta V. The total needed for TMI, mind you, is 4298 m/s. So there you are, 13,600 kg on TMI, and it only took a *lot* of burns, 19 of them in fact.
Filling in an the rocket equation:
DV=9.81*451*ln(20050/15634)
DV=1100 m/s
This is nowhere near the 3388 m/s you stated.
DV=9.81*451*ln(20050/19820.6)
DV=50.9
This is nowhere near the 176 m/s you stated.
I think the 176 m/s was supposed to come from the last burn, not the first. So we have:
DV=9.81*451*ln((15634+229.4)/15634)
DV=64.5
which is still far short of 176 m/s.
Last burn is of the STAR-48:
DV=9.81*262*ln(15634/14600) (incl the dry weight of kick motor)
DV= 176 m/s
It's almost a TLI burn.