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Lunar Tourism

Posted by: campbelp2002 - Fri Feb 11, 2005 9:36 pm
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Post    Posted on: Wed Feb 23, 2005 2:16 pm
Takes more energy to get there. You end up needing something like a saturnV class vehicle or using a lot of smaller launches to assemble your craft. In LEO you can assemble useful size components to make your CEV. Also lets not make the task to difficult, the commercial world will struggle to get to LEO with a manned vehicle getting higher might be a step to far.

Also I dont think there are to many designs for manned High Earth Orbital craft and I was trying to think about craft that had been previously developed and discarded that might have a use in a possible lunar tourism/exploration vehicle. Because the X-33 has a VTOVL capability it is a possible craft to use as a basis for a lunar lander vehicle (IMO).

Anything that can be used now to speed up the development process would be useful. :)

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Post    Posted on: Wed Feb 23, 2005 2:29 pm
spacecowboy wrote:
why LEO? Why not higher

I am trying to find the right place; the break even point; the place that is equally hard, or equally easy, to get to from the surface of either the Moon or Earth. That way the “load” is equally distributed to both sides of the two part transportation system. LEO may place an undue burden on the lunar vehicle, but a free return trajectory around the Moon would put the burden too much on the Earth based vehicle. If the lunar shuttle can be designed to aerobrake using a ballute or traditional heat shield without adding too much weight, it may shift the balance more to LEO. If not, some higher Earth orbit may be in order. GTO may be a better choice, but I would prefer not to pass through the Van Allen belts more often than necessary.

spacecowboy wrote:
do the same thing that Apollo 8 and all the NASA vehicles have always done, and just sling yourself around the back side of the Earth without dropping into orbit.

Apollo 8 did drop into lunar orbit.
http://nssdc.gsfc.nasa.gov/database/Mas ... =1968-118A
says, “Orbit insertion took place on 24 December at 09:59:20 UT into an elliptical 310.6 km by 111.2 km lunar orbit. Two orbits later a second burn placed Apollo 8 into a near-circular 110.4 by 112.3 km orbit for eight orbits. The transearth injection burn took place on 25 December at 06:10:16 UT after a total of 10 lunar orbits.”
And of course the Apollo 10,11,12,14,15,16 and 17 CM stayed in lunar orbit while the LM did it’s mission.


Last edited by campbelp2002 on Wed Feb 23, 2005 2:37 pm, edited 1 time in total.



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Post    Posted on: Wed Feb 23, 2005 2:34 pm
Andy Hill wrote:
I was trying to think about craft that had been previously developed and discarded that might have a use in a possible lunar tourism/exploration vehicle. Because the X-33 has a VTOVL capability it is a possible craft to use as a basis for a lunar lander vehicle (IMO).

What about the DC-X? That is a very “Armadillo like" vehicle, only more “professional” and expensive. And unlike the X-33, it actually flew.


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Post    Posted on: Wed Feb 23, 2005 4:08 pm
My mistake I was actually talking about the DC-X and not the X-33 :oops:

please excuse my confusion I'm obviously going prematurely senile. The figures I quoted in my earlier posts are for the DC-X and not the X-33 which was considerably larger.

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Post    Posted on: Wed Feb 23, 2005 7:55 pm
Andy Hill wrote:
I was actually talking about the DC-X

Much better. An X-33 derived vehicle takes off from Earth and rendezvous with a DC-X derived vehicle that takes off from the Moon. Rendezvous takes place somewhere in Earth orbit. High Earth orbit if the X-33 technology is more advanced and low Earth orbit if the LUNOX fuleld DC-X technology is more advanced.
http://www.abo.fi/~mlindroo/Station/Slides/sld051p.htm

By the way, one reason the X-33 was cancelled was the failure of it's carbon fiber LH2 tank. The SSTO follow on version of the DC-X would have relied on a similar tank. And since the problem was with the epoxy and not with the carbon fibers themselves, I don’t think carbon nanotubes would have worked any better.
http://www.hq.nasa.gov/office/pao/History/x-33/2000.htm


Last edited by campbelp2002 on Wed Feb 23, 2005 10:06 pm, edited 1 time in total.



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Post    Posted on: Wed Feb 23, 2005 8:34 pm
Urgh. <slap> I feel stupid now. 8 went into orbit. The only one that used a "slingshot" or free-return trajectory was 13:

NSSDC Master Catalog: Apollo 13 (NSSDC ID:1970-029A) wrote:
At 08:43 UT a mid-course maneuver (11.6 m/s delta V) was performed using the lunar module descent propulsion system (LMDPS) to place the spacecraft on a free-return trajectory which would take it around the Moon and return to Earth, targeted at the Indian Ocean at 03:13 UT 18 April.


The question is if the reverse could be done without undue use of fuel, using the Earth as the focus of the ellipse, with the Moon as the landing point.

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Post    Posted on: Wed Feb 23, 2005 9:22 pm
spacecowboy wrote:
Urgh. <slap> I feel stupid now.

You better get used to that feeling. You will encounter it many more times before you reach my age! I speak from experience.

I don’t really understand why you don’t want to enter orbit for rendezvous. In order for both vehicles to rendezvous, they must have the same trajectory, or the same speed and direction. It doesn’t really matter where the rendezvous takes place, but both vehicles must match velocities.

For example, the Earth shuttle leaves Earth on a free return trajectory to the Moon. The lunar shuttle takes off and rendezvous with it at it’s closest approach to the Moon. At this point, both vehicles are on a free return trajectory to Earth. The Lunar shuttle would not have to expend any propellant to continue all the way to Earth. In fact, it has to expend propellant to avoid going to Earth.
Consider the other option. A lunar shuttle takes off from the Moon on a free return trajectory around the Earth (is that even possible? Assume it is.) The Earth shuttle takes off and rendezvous with it at it’s closest approach to Earth. To do so, the Earth shuttle has to be in a translunar trajectory. It would not need to expend any propellant to continue all the way to the Moon. In fact, it has to expend propellant to avoid going to the Moon.

So your proposal would in effect say that we should expend enough propellant to send two vehicles around both the Earth and Moon, but then expend extra propellant to keep one of them from going all the way. That does not sound very efficient, does it?

If LEO is too far from the Moon, we could use a more elliptical Earth orbit. GTO never gets anywhere near the Moon in distance, but from an energy standpoint, it is about 90% of the way to the Moon. The lunar shuttle would require very little propellant to enter GTO. It may even aerobrake into GTO if the structure (heat shield or ballute) needed weighs less than the extra propellant for the same DeltaV. After rendezvous, the Earth shuttle would need only a very small deltaV to lower it’s perigee into the atmosphere for landing and the lunar shuttle would need only a small deltaV to get back on a translunar trajectory. Depending on the comparative capabilities of the two vehicles, various elliptical Earth orbits lower than GTO but higher than LEO could be chosen.


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Post    Posted on: Thu Feb 24, 2005 8:27 am
campbelp2002 wrote:
By the way, one reason the X-33 was cancelled was the failure of it's carbon fiber LH2 tank. The SSTO follow on version of the DC-X would have relied on a similar tank. And since the problem was with the epoxy and not with the carbon fibers themselves, I don’t think carbon nanotubes would have worked any better.


Didn't they come up with a replacement aluminium fuel tank that didn't suffer from the same cracking problem at low temperatures that was actually less weight than the original?

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Post    Posted on: Thu Feb 24, 2005 1:47 pm
Yeah. That explains why. For whatever reason, I never thought of it from the energy standpoint (my excuse being that I haven't really learned orbits yet, although I still should've seen that).

I do really like elliptical orbits and (especially) aerobraking, though. The aerobraking should save quite a lot of propellant on the part of the lunar vehicle, although then it would have to carry a whole aerobraking/heat shielding system..... Would the propellant savings be greater than the extra mass cost? Keep in mind that it will still have to have a rocket-braking system in order to drop into Lunar orbit. Blech, it looks like retrorockets are still cheaper and certainly easier. LEO is probably the easiest, as well, being the energy "halfway point" between the Earth and the Moon -- or so close as to call it.

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Post    Posted on: Thu Feb 24, 2005 2:00 pm
Andy Hill wrote:
Didn't they come up with a replacement aluminium fuel tank that didn't suffer from the same cracking problem at low temperatures that was actually less weight than the original?

No, the aluminum tank was heavier. SSTO was marginal anyway and the added weight of the aluminum tank eroded the payload even more.
It seems to me that the added weight of wings can only be justified if the engines are air breathing. Then the weight of the wings is more than offset by not having to carry all that LOX. That is what makes the SKYLON so attractive. It would get to orbit with a mass ratio of less than 6 to 1.
And I was reading about the DC-X accident. It had nothing to do with the tank, it was a simple landing gear failure. That is not to say that the carbon fiber tank would have worked better than on the X-33, but the thing had flown! And they cancelled it anyway. What a waste.


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Post    Posted on: Thu Feb 24, 2005 2:04 pm
spacecowboy wrote:
LEO is probably the easiest, as well, being the energy "halfway point" between the Earth and the Moon

It also has the advantage of not passing repeatedly through the Van Allen belts.


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Post    Posted on: Thu Feb 24, 2005 2:19 pm
campbelp2002 wrote:
It also has the advantage of not passing repeatedly through the Van Allen belts.


Ooh, good point.

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Post    Posted on: Thu Feb 24, 2005 6:07 pm
I wonder if NASA consigns all its past designs to history as technical deadends or does it review them in light of advances in technology and meterials?

Afterall some of the projects were probably cancelled because they relied on breakthroughs that didn't happen. Possibly some of these breakthroughs have happened since that would mean the project was now viable.

Why does it ask people like T-Space to define a means of getting to the moon when it could do it theirself using equipment already designed or partially designed.

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Post    Posted on: Thu Feb 24, 2005 6:59 pm
Look at the panoramic picture of the south pole station:
http://astro.uchicago.edu/cara/vtour/pole/
and imagine that C-130 is a space craft. Could be a Moon base, no?
You too can go there:
http://www.adventure-network.com/subsub ... id=1&id=42
I really think this is a good analog for lunar tourism.


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Post    Posted on: Fri Feb 25, 2005 4:09 pm
Here is a great link showing the deltaVs required to go to Mars or the Moon.
http://www.pma.caltech.edu/~chirata/deltav.html
To get to LEO from Earth requires 9.7km/s, plus a small amount more to initiate reentry. To go from the lunar surface to LEO and back to the lunar surface again adds up to 11 km/s. Modern LH2/LOX engines have an exhaust velocity of 4.5km/s. A lunar shuttle with such an engine would need to start from the Moon with at least 1-1/e^(11/4.5) = 91.3% of it’s mass as propellant. Say 92% for a small reserve. This mass fraction would probably be tough to launch from the surface of the Earth, but the lunar vehicle will encounter no atmospheric loads, only has to support it’s own weight on the ground at 1/6 G and probably will not accelerate at more than 1G under full power. So the structure can be very light weight. Naturally all the major structural components will be made with carbon nanotube composites! The Apollo LM, which had a mass fraction of about 71%, enjoyed some of these advantages, but it had to endure the rough ride to orbit abroad the Saturn rocket, used lower performance engines and was made of aluminum. My hypothetical vehicle would have an empty mass of 10,000kg, no payload, and 115,000 kg of propellant. But 19,167kg of that propellant is LH2. Assuming no LH2 is available on the Moon, the shuttle leaves with 95,833 kg LOX and half a load of LH2 (left over from its previous trip to LEO). Payload takes the place of the missing 9,583 kg of LH2. The shuttle takes off from the Moon and enters LEO with no LH2 left and half a load of LOX. It obtains a full tank of LH2 from the Earth shuttle and departs LEO. To simplify LH2 transfer, it uses a detachable tank. It drops off the empty LH2 tank and docks with the full tank. It arrives on the Moon with a half load of LH2 and no LOX left. The earth shuttle has to place 28,750kg into LEO, 19,167 kg of LH2 plus 9,583 kg of payload. A number of existing launch vehicles are capable of doing that.
So, after low cost access to LEO, the main thing we need for affordable travel to the Moon is lunar LOX (LUNOX). Is anybody working on that?

(EDIT) If the lunar vehicle can aerobrake into LEO, that saves 3.2km/s deltaV. The mass fraction could go down to 82.3%. Say 83% for a small reserve. That would allow the empty mass to go above 20,000kg, I can imagine that a ballute or heat shield, plus extra insulation to keep the LOX from boiling off too much, could be less than 10,000kg. But I am just guessing about that.

(ANOTHER EDIT) Decelerating at 1G for only 5 1/2 minutes reduces the speed by 3.2km/s. That doesn't sound too hard, does it?

(YET ANOTHER EDIT) OK, I did a more complete calculation, including a big change. The real LM had a total deltaV of 4.6km/s, well above the 3.2 I had used before.1.6 is lunar escape velocity, but that is too simple. First, there are losses fighting gravity at slower speeds. This could be minimized with a higher acceleration. Second, the real LM had reserve propellant, they did not depend on using it all, like I am doing with the cislunar parts of this calculation.
So the new vehicle looks like this. Empty mass is 9,500 kg. The engine burns LOX / LH2 in a 6 / 1 ratio, isp = 459 seconds, exhaust velocity = 4.5 km/s.

At lunar departure we have:
Full tank of LOX = 90,000 kg.
Partial tank of LH2 = 7473 kg.
535 kg payload. (5 people).
Lunar takeoff mass 107,508 kg, mass ratio 10.71.
After arobraking into LEO all the LH2 is gone and 54,162 kg of LOX remains.

In LEO the LH2 tank is filled with 15,000 kg of LH2. 790 kg of passengers and cargo are loaded, 5 people plus 255 kg of supplies for the Moon base.
LEO departure mass 70,452 kg, mass ratio 6.85.
Arrive on the Moon with no LOX and 7,473 kg of LH2 remaining.

Note that I have no reserve propellant at all, beyond what the LM had. Also, the 9,500 kg empty mass would include all other vehicle consumables, such as RCS propellant. I'll assume consumables for the passengers is included in the payload.

So, it is not so easy after all. The biggest surprise to me was the high penalty for bringing all the LH2 rom Earth. It would really help a lot if it could be gotten on the Moon.


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