Back to the Moon

John · Senior Member

Back to the Moon

GoogleNaut · Guru

Approximately where is the propellant depot located? (orbital height above Earth.)

John · Senior Member

Good question. I think it would have to be in a fairly low Earth orbit. The parking orbit for the Apollo missions was too low to be permanent installation. There was a very experienced NASA FDO on the Space Show a few weeks ago that discussed this. How about a 200 mile orbit? It will require a little more delta v to get to into translunar trajectory from there but I would think it would be that much.

NUKE ROCKY44 · Senior Member

Parking Orbital Fuel Depots (OFD) ...an enquiry,

Don't claim to be an expert in astrodynamics. But a central tenant on the subject is all natural satellites have elliptical type orbits. To forcibly make a satellite hug to an orbit close to it's center of gravity of the second body requires lots more energy than a natural elliptical one. Another is escape speed though the gravitiational field of the Sun or a planet theoretically extends to infinity, its strength decreases so rapidly with distance that only a finite amt. of kinetic energy is needed to overcome the effects of gravity and allow an object to coast to an infinite distance without the 'fall back' effect. The speed which is just sufficient to do this is called escape speed. A spacecraft which is given escape speed in any direction will travel on a parabolic escape trajectory. (2 body orbital mechanics, Astrodynamics-BMW)

An of course you want to park an OFD where it's easily accessible without excessive fuel consumption to get there or depart from.

John · Senior Member

Bruce, I'm a little unclear about the question or perhaps objection. The OFD would would be in a LEO selected to optimize between the propellant launches from the Cape and parking orbit for Earth/Moon transist. It would of course be elliptical probably somewhat like the ISS but I not sure what the best inclination would be. I'd think an average of about 200 mile above Earth would be about correct.

The really Apollo parking orbits were lower but the limited time of about 2.5 orbits didn't result in much air drag. You want it high enough that station orbit maintenance isn't major. Otherwise, you want it lower in order to make supply from Earth efficient.

The once prepared for the mission the rocket will be launched into a standard "free return trajectory" like used on Apollo missions. The velocity is slightly below theorectical Earth escape velocity. The "payload" spacecraft separates and uses its own propulsion to enter Lunar orbit. The rocket stage is still on the free return trajectory and whips around the Moon heading back to Earth. It would have to have some facility to make course corrections (tweaks) to carry out the aerocapture maneuver with the inflatable heat shield. Then it will need a bit more significant thrust to make the orbit changes to rendezvous with the OFD.

I hope that I didn't give the impression that the OFD is orbiting around both Earth and the Moon. As Lunar operations would expand it might be good to put a second OFD in orbit around the Moon to resupply Lunar landers. But that is a separate issue. What I'm amazed by is the effectiveness of using a refueled "second-stage" of my mini-shuttle booster to be a super EDS.

NUKE ROCKY44 · Senior Member

I was just floating an observation.

You are correct a selected optimized OFD parking orbit is best.

I think I heard from a FIDO the best parking zone is around 5 degrees (orbit of the Moon is inclined by about 5° on the ecliptic) from the earth's ecliptic plane at 150-200 miles altitude of perigee escape trajectory.

Anyway... your mini-Shuttle, utility medium HLV, and an Earth-to-Moon transportation system all in one development program.

Do you have a Power Point/PDF/Word on this ???

John · Senior Member

No. I haven't written this up save for what I posted. I'm still tweaking it but this looks promising.

To give you an idea of the basis of my approach, I have made a spreadsheet model. I had been looking for a way to do these calculations knowing that there are a lot of things invovled. I came up with a very top-level approach. I make an analogy with an existing rocket (in this case the Saturn IB), take the parameters from www.astronautix.com and enter them in my spreadsheet, i.e., specific impulse, empty weights for each stage, propellant weight for each stage, and payload. The model uses the rocket equations to the free space delta v of each stage. Then I compare the free space delta v to what is really achieved given air drag, gravity, etc. The difference gives the impact of these effects. Then I scale to the designed payload.

GoogleNaut · Guru

Just to toss some ideas around. The architecture that I am currently envisioning technically calls for two depots: one, a relatively low earth orbit at roughly 250 nmi (300 statute miles) above the Earth. This is high enough for atmospheric drag to be fairly negliable, and still low enough to be beneath the lower Van Allen radiation belts. This installation would ultimately include a rotating hab ring and support numerous space indrustrial, research, tourist (space hotel) support, and of course a supply/equipment/wet and dry raw material/propellant depot. It would grow into these functions, and would be a primary trans-shipment point for equipment, supplies, and people. Most volatiles (propellants too) and raw materials would be shipped from the outer station, probably located at EML-4 or EML-5 halo orbits.

The second and larger depot at EML-4 (or 5) would be typically a large, modular station with continuous growth capacity: it would serve as a hub for inbound and outbound traffic; it would include processing facilities to flash refine comet water to remove ammonia, carbon monoxide, salts, etc; it would have the capability to electrolyze some of that water to make liquid hydrogen and liquid oxygen. It would be capable of fully seperating asteroid derived materials such as PGMs (platinum group metals.) And it would have pretty extensive fabrication and manufacturing capability. It would also be a service and support center for deeps space ship refits. And it would need to have an orbital "Hot Cell" to service the nuclear components of nuclear powered space craft. In short, the HEO station is like a giant Swiss Army Knife: it does whatever needs to be done, with whatever materials are on hand.

What is critical is the idea of modularity; on standardizing the primary industrial utilities: power, data, cooling, consumable gasses, pressurized access. Supplying all of these from an expandible, modular platform is critical to starting small, and growing large. Only then can asteroid and comet resources be efficiently exploited.

-- Edited by GoogleNaut on Monday 29th of March 2010 06:00:36 AM

-- Edited by GoogleNaut on Monday 29th of March 2010 06:02:09 AM

NUKE ROCKY44 · Senior Member

Other OFD concepts:

EELV concept with offical Augustine commission blessing and cooling lamp shade structure. And the comment:

"...the orbital refuel is a a BAD idea and a way to gain lots of funds for nothing." as explained in this site http://www.ghostnasa.com/posts/045suggestions09.html

"United Launch Alliance (ULA) is proposing on-orbit propellant depots to increase the capability of NASAs Constellation exploration architecture. The plan to use depots derived from an advanced upper stage for the Atlas V and Delta IV evolved expandable launch vehicles (EELV) has caught the attention of the Augustine panel, which has included in-space refueling in four of seven options identified."

link here

Investigating Novel Approaches to Spaceflight
With $7.8 billion over the next five years, the agency will investigate novel approaches to spaceflight, such as in-orbit fuel depots and rendezvous and docking.

link here

...And the electromagnetic launcher that fires heat-shielded fuel tanks into high Earth orbit. Claims for less than 10 bucks per kilo. That's cheaper than some cuts of meat at the grocery store.

link here

But it's obvious what the space agencies don't realise is John and Googlenaut have designs on better OFD systems. wink

John · Senior Member

I try. biggrin

VASIMR was one of my ideas from back in the 1990s. I was quite pleased when I found out that Dr. Chaing-Diaz was working on it. I was looking at something that might be a "bridge" between current tech and my He-3/D fusion concepts. That was when I came up with the idea of varying the propellant flow to get more of less thrust as needed. (I may not be the first but I was independent but of course the basic plasma rocket concept goes way back before that.)

I'm not proposing this as a let's end Constellation and do this. But, it might be the way to go if the administration gets its way if could be the way to go on the come back. It really started as study of if Shuttle was such a big mistake what should we have done.

On the fuel depot it is notable that a lot of early studies were based on the NERVA program and how to apply it to various projects.

NUKE ROCKY44 · Senior Member

"On the fuel depot it is notable that a lot of early studies were based on the NERVA program and how to apply it to various projects."

You just hit the nail on the head this is exactly the strategy of OFD's even as far back as NERVA/ROVER in fact this separated the military from the explorer space advocates types. OFD was strictly a method/strategy to build infrastructure in space this is why people advocating nuclear space are always far beyond the limited space program advocates. Military types advocate LEO earth based ops nothing more maybe power for laser STAR WARS stuff but in reality they could care less about beyond LEO. They think space ops beyond LEO is stupid and wasteful.

LEO advocates have been the rule in space for years.

-- Edited by NUKE ROCKY44 on Tuesday 30th of March 2010 07:47:25 PM

John · Senior Member

The next step is the Moon "package". I've been focused for a while on the topic of what propellant for this. My current thought is CH4/LOX. At around 355 sec vacuum it has enough specific impulse to support a one-stage lunar transfer vehicle that will go from lunar orbit to land and then back to lunar orbit. This would allow a reusable vehicle that would support multiple transfers.

At some point a smaller lunar orbiting fuel depot makes sense. Then we can have a shuttle vehicle that would be launched by the booster stage discussed before. It would also be powered by CH4/LOX which could decelerate into lunar orbit and then orbit the Moon and rendezvous with the fuel depot/service station what would fuel and checkout the landers. I would assume that they would aerobrake and rendezvous with the Earth depot on return.

With this we have an outline of a Lunar transportation architecture. None of this really requires a technology leap.

-- Edited by John on Saturday 3rd of April 2010 11:12:59 PM

NUKE ROCKY44 · Senior Member

Do you have any info on how CH4, propane keeps in space?

The obvious extra expense to launch heavy gases is one disadvantage wondering if a special OFD could accommodate these gases and if propane/methane could also take advantages of a solar ray blind to keep from boiling off from sun?

John · Senior Member

This is the real issue. Methane is easier to maintain than LOX and it is a lot less of problem then LH2. It burns cleaner than RP-1. The alternative would be hypergolics but I'm worried about refueling operations in space. Unless totally automated how do you handle the case of an astronaut gets srayed with hydrazine on his space suit? If he comes back into the station that seem like a real problem. Methane/LOX give a higher specific impulse too! This is what I was thinking for what its worth.