Author Topic: Reusable earth departure stages  (Read 18799 times)

Offline Hop_David

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Re: Reusable earth departure stages
« Reply #40 on: 06/01/2014 08:15 pm »
Reposting Farquhar's Route, this time as attached rather than embedded image.

A few important numbers: 72 hours from EML2 to perilune and then 140 hours from perilune to perigee.

A small EML2 burn and a small perilune burn suffice to send the EDS and payload towards a deep perigee. These two burns total about .4 km/s.

At perigee the whole shebang's moving about 10.8 km/s. Since 11.4 km/s is enough for TMI, a mere .6 km/s burn suffices for Trans Mars Insertion.

Offline Hop_David

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Re: Reusable earth departure stages
« Reply #41 on: 06/01/2014 09:01 pm »
Am reposting the ~50 day route back to the moon but as attached image.

During 140 hours the moon advances 76 degrees and the EDS and payload advance 180º. So I start the sim with the perigee 104 degrees ahead of the moon. I found a 10.85 km/s perigee speed will give the EDS an orbit with a 396,000 km apogee and an orbit whose period is about 2/5 of the moon's period.

From perilune at the beginning to the perilne at the end is about 54 days. Add in two 3 day trips between perilune and EML2 and the total trip takes 60 days.

Reading earlier comments I was coming to the conclusion that 60 day round trip was a show stopper. Hydrogen boil off seemed to be too high over two months.

I liked A. M. Swallow's notion of using methane and thus the EDS have propellent and parts in common with the lander. That would simplify a number of things. However my notion rests on propellent sources either from an carbonaceous asteroid parked in lunar orbit or volatiles from the lunar cold traps. LCROSS gave evidence of some carbon compounds, so maybe methane is a possibility.

Then I read Jon Goff's comments that boil of could be mitigated -- he seemed to be talking about the same techniques that Goff, Zegler,  Kutter and Bar have written about in their propellent depot papers.

I Had been thinking of modeling my EDS after a Centaur stage with 99.2 K newton thrust, 20,830 kg fuel and oxidizer mass and 2,247 dry mass. Maybe I should up the dry mass to accommodate some extra MLI and apparatus for exploiting boil off.
« Last Edit: 06/01/2014 09:02 pm by Hop_David »

Offline sdsds

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Re: Reusable earth departure stages
« Reply #42 on: 06/01/2014 09:44 pm »
Am reposting the ~50 day route back to the moon but as attached image.

I love images like these; thanks for reposting them!

Does your software have the ability to show the pellet trajectories in a rotating frame of reference where both the Earth and Moon appear fixed? I understand a rotating frame is strange, and I won't try here to justify its use, but note it is used in e.g. the Farquhar route shown in your previous post....
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Offline Hop_David

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Re: Reusable earth departure stages
« Reply #43 on: 06/02/2014 02:51 pm »
Am reposting the ~50 day route back to the moon but as attached image.

I love images like these; thanks for reposting them!

Does your software have the ability to show the pellet trajectories in a rotating frame of reference where both the Earth and Moon appear fixed? I understand a rotating frame is strange, and I won't try here to justify its use, but note it is used in e.g. the Farquhar route shown in your previous post....

Not my software, I use Bob Jenkins' Java orbital sim. I wish I could get it to hold motionless the central and orbital body as well as the line between them. But I don't know how.

Offline muomega0

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Re: Reusable earth departure stages
« Reply #44 on: 06/02/2014 03:33 pm »
The ULA depot adds a conical sunshield to the transfer stage, which brings these rates down an order of magnitude, perhaps 0.1%/day for LH2 away from LEO....
Its not just about boil off, long duration loiter for Centaur involves multiple other adjustments that need to be made, including things like batteries.

That's part of what the whole Integrated Vehicle Fluids project is about. It replaces the batteries, the hydrazine thrusters (used for settling and ACS), and the helium pressurization (for repressurizing the tanks prior to a burn) with their IVF system. It taps boiled-off GOX/GH2 from the tanks to run a small internal combustion engine, which recharges the batteries, and runs a compressor for boosting the pressure of the GOX/GH2 prior to warming it for autogenous pressurization. With IVF you can run the stage as long as there is LOX and LH2 left in the tank. They had a lot of the prototype hardware for it at the Space Symposium. It's looking like they were going to fly part of it in 2015, and the rest of it in I think 2016. Once it's there, the duration of Centaur goes way up, the dry weight goes down quite a bit, and refuelability becomes easier since you're just dealing with two fluids.

Combine that with the improved insulation (MLI or a sun-shield), and using the rotational settling, and there's no reason you couldn't handle months-long missions.
~Jon
Its in the sun once out of LEO...use solar arrays.
Adding two more technologies to the above (advanced batteries and coolers) reduces the LH2 boiloff to zero and adds additional contingency operational modes including settling.  Using propellant for power is quite expensive and allows more efficient (longer) trajectories.

Offline john smith 19

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Re: Reusable earth departure stages
« Reply #45 on: 06/04/2014 03:23 pm »

Then I read Jon Goff's comments that boil of could be mitigated -- he seemed to be talking about the same techniques that Goff, Zegler,  Kutter and Bar have written about in their propellent depot papers.
Depots and IVF share many of the same techniques and approaches. Current Centaur stages have a life measured in hours due to consumables depletion and propellant boil off. Boil off reduction is a critical technology to increase mission duration. I'd say 1st generation upgrades are good to a week or two. 60 days will probably need to go to the full sun shield and active cryo cooler upgrades.
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