Author Topic: An Alternative Lunar Architecture  (Read 597975 times)

Offline mkirk

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RE: An Alternative Lunar Architecture
« Reply #40 on: 02/16/2006 07:00 pm »
Quote
Jamie Young - 16/2/2006  1:33 PM

Could someone explain what Delta V is? Thanks.


Delta V stands for change in velocity.  More specifically it is a measure of a spacecraft's ability to change its velocity.  For U.S. spacecraft this is usually in feet per second.  The space shuttle has 1000 feet per second of delta v capability with the OMS (orbital maneuvering system) engines.  Also, for ballpark numbers a delta V of 1.78 feet per second equates to the shuttle's ability to change its orbital apogee by 1 nautical mile.

Mark
Mark Kirkman

Offline Jamie Young

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RE: An Alternative Lunar Architecture
« Reply #41 on: 02/16/2006 08:56 pm »
Thanks Mark. Got it :)

Offline Manel

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RE: An Alternative Lunar Architecture
« Reply #42 on: 02/16/2006 09:02 pm »
Concerning Delta V

Current in the ESAS planning, the LSAM brakes at perilune and injects into low lunar orbit, both itself and the CEV

I would like to comment

 Has it been studied the benefits of doing that maneuver on this another form?

The LSAM and CEV brakes at perilune injecting into a lunar orbit with a very high apolune  e.g. 10-15.000 mi

After that, on another revolution,  the LSAM separates and makes a normal lunar landing

At anytime of the surface stay, if necessary,  the lunar LSAM ascent stage returns to low orbit
Then the CEV, still in his excentric orbit, makes the appropiate plane change at apolune and the braking maneuver at perilune to rendezvous with the LSAM in low lunar orbit
 
Possible benefits
Lighter LSAM  (It not needs to fully brake the CEV into low lunar orbit)
The CEV needs less Delta V  to perform this anytime return maneuvers, as compared to ESAS plan   ( I hope so)

Your comments, please

Offline Jim

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RE: An Alternative Lunar Architecture
« Reply #43 on: 02/16/2006 10:32 pm »
LSAM would be performing LOI with H2 engines with high ISP.  I think you would lose with putting more of the delta V into the CEV.  Most studies are trying to shrink the CEV mass, for the ISS missions and other s

Offline Chris Bergin

RE: An Alternative Lunar Architecture
« Reply #44 on: 02/17/2006 11:57 am »
Found this of interest:

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Offline publiusr

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RE: An Alternative Lunar Architecture
« Reply #45 on: 02/17/2006 10:09 pm »
I really don't like this dock X times, then turn around and touch your nose nonsense. Earth Orbit dockings of two CaLVs, with both LOR and EOR would be my choice.

Get CaLV built, then Sea Dragon.

Offline chocolate

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RE: An Alternative Lunar Architecture
« Reply #46 on: 02/18/2006 07:18 pm »
Human Lunar Exploration Mission Architectures by John Connolly, circa March 2004.

Offline PlanetStorm

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RE: An Alternative Lunar Architecture
« Reply #47 on: 02/18/2006 08:15 pm »
Quote
vanilla - 9/2/2006  8:18 PM

While I can imagine that there will be some favorable cases, my read on this (and I'm a fairly good astrodynamicist) is that in general, the loitering time needed to reduce plane change penalties will outweigh the transit time penalties of the L2 architechure.  Same with DV--sometimes LOR will be better, but in general, due to the ESAS constraint of "global access, anytime return", I think it will be worse, and if we design to the worst-case DV scenario, then what does it really matter if sometimes it gets better?

Thoughts, comments?

Definitely an attractive idea, but in defense of ESAS, isn't it true that if we design for the worst case scenario, but usually don't require the loitering time, then we will usually have extra stay time on the surface?

Also, isn't L2 only "conditionally stable", and so any long-term stay there would need frequent RCS firings? (I must admit I haven't read the document so the answer might be in there)




Offline Manel

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RE: An Alternative Lunar Architecture
« Reply #48 on: 02/18/2006 09:29 pm »
Very interesting document

A pair of comments to PlanetStorm      Indeed,  L1 and L2 points are not stable. They require stationkeeping. But the fuel consumption is far below to which it requires a CEV in low lunar orbit  

The in orbit loitering time is needed because we don´t have the capability to abort anytime and we must wait the proper conditions to return home

Offline Mark Max Q

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RE: An Alternative Lunar Architecture
« Reply #49 on: 02/19/2006 06:17 am »
Quote
chocolate - 18/2/2006  2:18 PM

Human Lunar Exploration Mission Architectures by John Connolly, circa March 2004.

That's along the lines of the pre-ESAS documents on the extra features section. It's amazing to see how much the ESAS is a copy and re-vamp of a lot of older material.

Offline Jim

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RE: An Alternative Lunar Architecture
« Reply #50 on: 02/19/2006 01:28 pm »
ESAS was tooquick to really come up with something new.  Usually, there isn't very much that is new under the sun.. Studies are done and put on the shelf to be used at a latr date.

Offline Flightstar

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RE: An Alternative Lunar Architecture
« Reply #51 on: 02/24/2006 07:26 pm »
We might have to look at the alternatives as there seems to be major problems with the ESAS technicalities.

Offline kfsorensen

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RE: An Alternative Lunar Architecture
« Reply #52 on: 02/26/2006 05:32 am »
Another thing to consider in the L2 architecture...I was thinking about it and realized that most, if not all, of the major burns would take place in view of Earth.  So unlike most of the key burns of the LOR sequence, the ground support network would be able to monitor all the conditions and parameters of the spacecraft system before, during, and after the maneuvers.

Perhaps that might help a future Mrs. Borman to get a little more peace-of-mind.

Offline Manel

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RE: An Alternative Lunar Architecture
« Reply #53 on: 02/26/2006 02:49 pm »
Hi Vanilla
I am reading another time  "Enchanted Rendezvous"  and I think you should feel,  with your ideas about the L2 operative,  "somewhat as a voice in the wilderness"   and  as "John  (Houbolt)  that's no good.  We don't like at all  ( the LOR)”

But press on.   If we want that the next Lunar Program  has global acces and anytime return,  besides a future vision,  the road to go is through L2 point staging

Offline Carl G

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RE: An Alternative Lunar Architecture
« Reply #54 on: 02/26/2006 04:32 pm »
Still no mention of L2 and surely they would have looked at L2 in the ESAS. So why, if so, was it rejected?

Offline Manel

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RE: An Alternative Lunar Architecture
« Reply #55 on: 02/26/2006 08:13 pm »
ESAS  4th chapter,  15th page

      “LPR (libration point rendezvous) was eliminated early from the mission mode trade.
        Recent studies performed by NASA mission designers concluded que equivalent
        landing  site acces and “anytime abort” conditions could be meet by rendezvous
        missions in LLO with less propulsive delta-V and lower overall Initial Mass in
        Low Earth Orbit”
 
I think that they considered the L1 point only,  and apparently in direct missions from TLI  to L1.   These missions require more delta-V

There are other options.  The most interesting is using the  L2  point  and reaching it through a lunar swingy that allows you to save a lot of delta V and weight,  compared with the previous scenario to L1 point.   See you previous pages on this thread.  

Offline chocolate

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RE: An Alternative Lunar Architecture
« Reply #56 on: 03/02/2006 08:20 pm »
"Libration Point Rendezvous", T.N. Edelbaum, NASA CR-86337, February 1970.

—pg ii:
ABSTRACT
A study of the flight mechanics and mass requirements for one-shot lunar missions has been made utilizing rendezvous at the libration points in front of, and behind, the Moon. The flight mechanics studies were carried out using the restricted problem of three-bodies. It was found that the lowest delta-V requirement to reach either libration point was to go to the L2 point behind the Moon via a powered lunar swingby. It was also found that every point on the lunar surface is directly accessible from the L2 point, for transfer times greater than about 59 hours.

The mass calculations were carried out assuming advanced cryogenic propellants in all stages. For such propellants, the least mass in Earth orbit for rendezvous at the L2 point was determined. The mass requirement was found to be smaller than that for the standard lunar orbit rendezvous mode. Rendezvous at either the L2 point, or in a Halo Orbit about the L2 point, would also have operational advantages, including access to all points on the Moon and an infinite rendezvous launch window.

—pg 17:
CONCLUSIONS
1. Any point on the surface of the Moon can be reached by direct transfers to and from the L1 point, for flight times greater than about 51 hours. The same is true for the L2 point, or for the Halo Orbit, for flight times greater than about 59 hours.

2. The smallest mass requirements of any mission mode considered were for rendezvous at the L2 point.  Essentially the same performance could be obtained for rendezvous in a Halo Orbit around the L2 point and this latter mode would allow full-time communication with landing sites on either the near or the far side of the Moon.

3. Rendezvous at L2 also appears highly desirable for lunar shuttle missions, and should be investigated further for such missions.

Offline rsp1202

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RE: An Alternative Lunar Architecture
« Reply #57 on: 03/02/2006 08:30 pm »
My limited understanding of orbital mechanics leads me to ask this question: The L1, L2 and L3 points are considered to be unstable. In the context of this thread, this means that using L1 or L2 for lunar mission staging would still require X amount of fuel for station-keeping, but not as much as LOR or other techniques?


Offline kfsorensen

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RE: An Alternative Lunar Architecture
« Reply #58 on: 03/02/2006 08:37 pm »
Quote
rsp1202 - 2/3/2006  3:30 PM

My limited understanding of orbital mechanics leads me to ask this question: The L1, L2 and L3 points are considered to be unstable. In the context of this thread, this means that using L1 or L2 for lunar mission staging would still require X amount of fuel for station-keeping, but not as much as LOR or other techniques?
That's essentially correct.  Long-term maintenance of a low lunar orbit is further compounded by the lack of a global gravity map of the Moon, since gravitational variations (which are much stronger on the Moon due to strange internal mass distributions) lead to changes in the orbit which must be corrected to keep the vehicle from crashing in the lunar surface.

Offline rsp1202

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RE: An Alternative Lunar Architecture
« Reply #59 on: 03/02/2006 08:45 pm »
Will the new lunar orbiter mission or any others planned before The Return map out the mascons? I thought this had been done.

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