Yesterday, I introduced the idea of deploying a neutral flagged facility at one or both of the key lunar LaGrange points (EML-1 and/or EML-2):
American Exceptionalism and Lunar Exploration proposes a shared use EML depot equipped with reuseable lunar landers (RLLs) to be owned and operated by an entity not under the jurisdiction of any current spacefaring nation, such as Singapore, Dubai, Isle of Man, Gibraltar or perhaps even Switzerland (unless the Swiss are part of ESA).
Yesterday, I proposed three categories of benefits:
(a) Support robust lunar exploration;
(b) Support global geo-political stability; and
(c) Support United States geo-political interests.
and today I shall amplify and extend my thoughts on the first category.
A brief digression . . .
First I wish to thank Vladislaw as I again dip my ladle into his Photobucket and I encourage everyone to read his April 12th diary and all of his previous and upcoming diaries:
Another question, Vlad. How can I place text next to the above image?
Babylon 5, an imperfect analogy . . .
Babylon 5 is an imperfect analogy to my proposed neutral flagged EML depot however it is a suggestive one. According to the Babylon 5 canon, and Wikipedia:
Described as a "window on the future" by series production designer John Iacovelli, the story is set in the 23rd century on a large space station named "Babylon 5"—a five-mile-long, 2.5 million-ton rotating colony designed as a gathering place for the sentient species of the galaxy, in order to foster peace through diplomacy, trade, and cooperation.
* * *
The Babylon 5 space station is a modified version of an O'Neill Cylinder, rotating to provide artificial gravity.
* * *
The station is situated in the Epsilon Eridani binary star system, located at the fifth Lagrangian point between the fictional planet Epsilon III and its moon.
The fifth La Grange point? As in L5? That is obvious homage to the L5 Society:
The L5 Society was founded in 1975 by Carolyn and Keith Henson to promote the space colony ideas of Dr. Gerard K. O'Neill.
The name comes from the L4 and L5 Lagrangian points in the Earth-Moon system proposed as locations for the huge rotating space habitats that Dr. O'Neill envisioned. L4 and L5 are points of stable gravitational equilibrium located along the path of the moon's orbit, 60 degrees ahead or behind it.
An object placed in orbit around L5 (or L4) will remain there indefinitely without having to expend fuel to keep its position, whereas an object placed at L1, L2 or L3 (all points of unstable equilibrium) may have to expend fuel if it drifts off the point.
As shall be explained below, EML-1 and EML-2 are FAR more useful locations for accessing the lunar surface than the other 3 LaGrange points -- and -- while O'Neill cylinders are WAY COOL they are likely beyond humanity's current capabilities.
Where the "L" is EML-1 . . .
As background and introductory illustration, here is a 17 second You Tube depicting the SOHO telescope located at SEL-1 (the Sun - Earth LaGange point 1)
SEL-1 = Sun-Earth-Lagrange 1
If we were to replace the Sun with the Earth and the Earth with the Moon, a facility located at the 1st Lagrange point would be at EML-1.
EML-1 = Earth-Moon-Lagrange 1
This link explains the Earth-Moon Lagrange points and has a nice diagram showing the 5 EML points. Key quotes:
An object at L4 or L5 is truly stable, like a ball in a bowl: when gently pushed away, it orbits the Lagrange point without drifting farther and farther, and without the need of frequent rocket firings. The Sun's pull makes any object in the Earth-Moon L4 and L5 locations "orbit" the Lagrange point in an 89-day cycle. These regions could be ideal for the Space habitats devised by Gerard K. O'Neill in 1969.
An object at L1, L2, or L3 is meta-stable, like a ball sitting on top of a hill. A little push or bump and it starts moving away. A spacecraft at one of these points has to use frequent, small rocket firings or other means to remain in the area. Orbits around these points are called 'halo orbits'. The Solar and Heliospheric Observatory (SOHO) is in a halo orbit around the Sun-Earth L1 position, about a million miles Sunward from Earth, and the Microwave Anisotropy Probe (MAP), is in a halo orbit around the Sun-Earth L2 Position, about a million miles in the opposite direction. These are the first spacecraft to be positioned in Lagrange orbits.
Well, yes and no. The math is correct -- objects are EML4 and/or EML 5 are stable however "meta-stable" is better for transportation nodes as they offer greater dynamic opportunity.
Again, with the Wikipedia and a cis-lunar delta v budget table:
Delta v is a critical term to know:
Delta-v budget (or velocity change budget) is a term used in astrodynamics and aerospace industry for velocity change (or delta-v) requirements for the various propulsive tasks and orbital maneuvers over phases of the space mission.
When the distance between two points is expressed in "delta v" we are basically talking about how much fuel (or $$$) is needed to travel between those points. Delta v tables also shape the "geography" of space travel.
Here are the relevant numbers.
Starting in LEO (at 28 degrees inclination) the delta v needed to travel to various points:
EML-1: 3.77
EML-2: 3.43
EML-4/5: 3.97
Well okay, but now what does it take to land on the Moon, from those locations, in other words to end up in low lunar orbit, starting at the following:
EML-1: 0.64
EML-2: 0.64
EML-4/5: 0.98
EML-3 is omitted because it is on the other side of the Earth from the Moon.
Why not low lunar orbit stations?
The Moon has abnormal concentrations of mass, creating "lumpy gravity" and screwball orbits -- the following quotes are from a NASA page titled Bizarre Lunar Orbits:
"If the Moon were a uniform sphere, you could have an orbit that was perfect ellipse or circle," [Alex S.] Konopliv explained. "The Moon has no atmosphere to cause drag or heating on a spacecraft, so you can go really low: Lunar Prospector spent six months orbiting only 20 miles (30 km) above the surface."
* * *
"The Moon is extraordinarily lumpy, gravitationally speaking," Konopliv continues. "I don't mean mountains or physical topography. I mean in mass. What appear to be flat seas of lunar lava have huge positive gravitational anomalies—that is, their mass and thus their gravitational fields are significantly stronger than the rest of the lunar crust." Known as mass concentrations or "mascons," there are five big ones on the front side of the Moon facing Earth, all in lunar maria (Latin for "seas") and visible in binoculars from Earth.
In other words, underneath the surface of the Moon are several concentrations of material that are more dense (more massive) than the surrounding materials and this alters the normal elegance of orbital mathematics.
"Lunar mascons make most low lunar orbits unstable," says Konopliv. As a satellite passes 50 or 60 miles overhead, the mascons pull it forward, back, left, right, or down, the exact direction and magnitude of the tugging depends on the satellite's trajectory. Absent any periodic boosts from onboard rockets to correct the orbit, most satellites released into low lunar orbits (under about 60 miles or 100 km) will eventually crash into the Moon. PFS-2 released by Apollo 16 was simply a dramatic worst-case example. But even its longer-lived predecessor PFS-1 (released by Apollo 15) literally bit the dust in January 1973 after less than a year and a half.
So what does this mean for eventual lunar exploration?
Be careful of the orbit chosen for a low-orbiting lunar satellite. "What counts is an orbit's inclination," that is, the tilt of its plane to the Moon's equatorial plane. "There are actually a number of 'frozen orbits' where a spacecraft can stay in a low lunar orbit indefinitely. They occur at four inclinations: 27º, 50º, 76º, and 86º"—the last one being nearly over the lunar poles. The orbit of the relatively long-lived Apollo 15 subsatellite PFS-1 had an inclination of 28º, which turned out to be close to the inclination of one of the frozen orbits—but poor PFS-2 was cursed with an inclination of only 11º.
EML-1 and EML-2 are unaffected (for all practical purposes) by these mascons.
24/7 global access
Orbital inclination constrains access to and from the surface of any body. The International Space Station is at 51 degrees of orbital inclination (its orbit is tilted 51 degrees from the equator) while an equatorial orbit would trace the equator at zero degrees of inclination.
A satellite at 90 degrees of orbital inclination would pass over the North Pole and South Pole on each pass.
The orbital inclination of an orbiting station constrains when and where launches can occur to that station. For example, there are limited "launch windows" to the International Space Station from the Kennedy Space Center in Florida and if there were to be a 30 minute delay (for example) and the launch window missed, the launch needs to be scrubbed until the next window opens.
Lunar launches from the surface to orbiting stations (or the Apollo LEM to the Apollo Command module) require precise timing to achieve rendezvous as orbital plane changes are very expensive in terms of delta v. For example, to alter a 28 degree terrestrial orbit to an equatorial terrestrial orbit requires MORE delta v (4.24) than it does to travel from that 28 degree orbit to EML-1.
Also, with respect to lunar exploration and development, any lunar version of ISS would face an erratic and rapidly decaying orbit unless in one of those four "frozen" orbits and as of today we simply do not know whether the most interesting places on the Moon are best served by those orbits.
Of RLVS and RLLS . . .
RLVs ("Reusable launch vehicles") capable of repeated flights from the Earth's surface to low Earth orbit are the "Holy Grail" for space advocates. Without question, the development of genuine low cost RLV technology would revolutionize human access to space.
But, how do we get there? And, are there intermediate steps that might grow demand for RLV technology and help test and prove the technologies needed for RLV deployment?
RLLS ("Reusable lunar landers") are a far easier technology project given the 1/6th gravity on the Moon and the lack of an atmosphere. After all thermal protection for a re-entering RLV is one of more difficult aspects of RLV deployment AND the delta v to travel from the Earth's surface to LEO is over 5 times that needed to lift off the surface of the Moon.
1.87 for Moon to low lunar orbit
9.3 to 10 for Earth to low Earth orbit
It has been said that using disposable rockets to reach low Earth orbit is foolish but to the extent this is true, it is double or triple foolish to use disposable lunar landers. If genuine RLLs were deployed to EML-1 or EML-2 then the total net cost of regular travel to the lunar surface would be greatly reduced, especially once lunar produced oxygen becomes available.
As an aside, lunar ISRU LOX is a huge topic all by itself. At this point, I will make one observation -- the target fixated RLV advocates appear to dismiss or downplay luanr ISRU LOX apparently believing that their NewSpace RLV space planes will reduce the cost of launch by such huge margins that it will be cheaper to ship LOX from Earth than extract LOX from the Moon.
Perhaps, but perhaps not and perhaps lunar ISRU LOX combined with reusable lunar landers and EML depots will create the demand for launches needed to justify RLV development in the first place.
Planting flags . . .
Almost forty years ago, the Apollo astronauts planted American flags on the Moon. I assert there is little point in going back to the Moon merely to plant more American flags.
That said, there are plenty of nations around the world who might desire to see one of their astronauts plant one of their flags on the Moon and perhaps by helping those nations satisfy their objectives we can develop and deploy the infrastructure that will reduce the costs of lunar access, making it easier to do useful things other than merely planting flags.
For a future diary? Further explanation of the benefits of EML depots and a debate between hydrogen, kerosene and hypergolics . . .