. The RAMA PROJECT: Converting an Asteroid Into Spacecraft - CONCEPT STUDY*

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 THE PROJECT RAMA FUNCTIONAL BLOCK 

The mechanical spacecraft's mission objectives require a simple Guidance Navigational & Control (GNC) system, provided by the flywheel. To keep the RAMA spacecraft in orbit, the flywheel gyros feeds momentum data into the analog computer. It also commands the propulsion system to propel asteroid materials and makes course corrections. 

The heart of the RAMA spacecraft is a 3D-printed analog computer operating on a series of single gears. This computer is powered by a store of potential energy found in the 3D-printed springs and flywheels.

Note that, the flywheel can easily be printed. 

THE ARCHITECTURE OF THE SEED CRAFT

The Seed Craft has a modular solar electric propulsion system attached to a common bus. Placed in the front, are the many modules needed to perform specific tasks in the asteroid.

A common robotic traverse is used by modules to transport materials between the operations. And, when required, robotic manipulators also perform some maintenance.

Because the interior of the spacecraft remains un-pressurized, manufacturing operations are free of atmospheric contamination.

CAN WE TRANSFORM AN ASTEROID INTO A SPACECRAFT?

The micro-gravity and partial artificial gravity in Cislunar space will be used to control precisely the manufacturing of products made from exotic materials. Thus, this place will become useful to produce physical goods, create future jobs, and expand our global economy.

To feed the Cislunar space with exotic materials, Made In Space proposes the RAMA architecture, which turns asteroids into self-sufficient spacecrafts capable returning to this location. The architecture can transport asteroids from 10 m-long to 100 . Thus, RAMA will solve the problem of transporting large supplies of resources from their natural orbits to orbits of greater use.

THE RAMA ARCHITECTURE CONCEPT OF THE ASTEROID SPACECRAFT

This report describes the results of the Phase I study funded by the NASA Innovative Advanced Concepts (NIAC) program for Made In Space. The goal is to establish the concept of feasibility of using space manufacturing process to convert asteroids into autonomous, mechanical spacecrafts. Project RAMA, for Reconstituting Asteroids into Mechanical Automata, is designed to improve the future advances of Additive Manufacturing (AM), In-Situ Resource Utilization (ISRU) and In-Situ Manufacturing (ISM) to achieve greater efficiency in repeated asteroid redirect missions.

The Seed Craft

The concept is based on a “Seed Craft” using a high performance ion engine. Designed around a single bus, it includes the minimum features required for every mission, such as the propulsion, the power distribution and regulation, as well as the communication and the Attitude Determination and Control System .

To produce the components of the RAMA spacecraft from the asteroid feedstocks, the Seed Craft will use advanced ISRU, Additive Manufacturing and robotic capabilities. The extent of these manufacturing capacities depends on the type of asteroid targeted.

So, if the size and the composition of the asteroid are known, the Seed Craft can be fitted with the required manufacturing modules and the right power system before it leaves the Cislunar orbit.

For the remainder of this concept study, only the four most massive systems of the RAMA craft must be built from the asteroid materials. These systems are the propulsion, the structures, the power storage and the attitude control. 

In general, an asteroid has a similar composition to the Earth but without the gravity and the geologic processing that have concentrated and dispersed materials throughout its interior. This means that, asteroid contains abundant supplies of iron/nickel, present in the Earth’s core, silicates and oxides, present in the Earth’s mantle, and water-ice and other volatiles, present on the Earth’s surface. Thus, these asteroid resources can be combined to produce almost anything required by a space civilization.

The Asteroid-Target

Adapted from J.L Lewis “Mining the Sky”, Figure IX2.

The figure on the left shows the range of finished products and required processes available on a S-type asteroid.

The S-type asteroid presents a middle way between the C and M types, permitting the use of metals and stones as manufacturing materials. With the S-type, the use of excess stone as projectiles in a high strength steel sling is an option for the propulsion.

That said, the problem with the S-type is the availability of materials that can be used to make propellant. By comparison, the C-type contains volatiles that can be useful as propellant because they can be converted to Liquid Oxygen-Liquid Hydrogen (LOX-LH2), or thermal water rockets. 

Also, the S-type asteroid contains almost no water or organism and the chemical compounds that make up the bulk of its mass appear in the form of inert oxides and rocks. But, the asteroid has a higher proportion of iron/nickel, which is useful for local manufacturing and for reinforcing its structure. In addition, it represents a higher fraction of Near-Earth Asteroids (NEAs), and so, is generally easier to reach and return from.

Thus, turning an S-type asteroid into a self-propelled spacecraft requires separating the valuable metals, and employing the less valuable silicate rocks as propellant. Due to the chemically inert nature of silicates, the most direct option available would be some form of mechanical propulsion, such as a sling.

TARGET: ASTEROID 2009 UY19

The S-type Asteroid 2009 UY19 has been targeted for the report at an estimated diameter of 50-150 m with an Albedo of 0.26. For its mission to the Earth-Moon L5, the Seed Craft will need nearly a decade of In-Situ conversion.

Mission Scenario

In 2038, the Seed Craft will start its maiden voyage using its electric propulsion and gravity assists to fly towards and intercept the 36-163 m-wide Near Earth Asteroid (NEA) 2009 UY19. Scheduled to be within 15 Lunar Distance (LD) of the Earth in 2039, the asteroid will be at the same orbit approximately every 33 years thereafter.

Mission Timeline

So, the Seed Craft is boosted away from its Cislunar space base on a trajectory to intercept the asteroid. It ignites its 60-kW solar electric propulsion system 4 months later for the rendezvous. Once it is close, the Seed Craft passes 2-4 days orbiting the asteroid and mapping details of its mass distribution and gravity. After, it docks on it along its spin axis, and anchors itself to the surface. The Seed Craft is now part of the asteroid.

Because of its prevalence of organism and volatiles, the C-type asteroid leads to the exclusion of meta-based manufacturing methods. It will use polymer structures and chemical propulsion systems.

The C-type asteroid has the materials to produce high performance rocket propellant, which can be used to propel the RAMA spacecraft to new locations.

The polymers give the possibility to manufacture composite structures with crushed rock and regolith. The products obtained have excellent tensile and compressive strengths.

Manufacturing techniques on the M-type asteroid would employ methods such as the carbonyl-based Mond process and the powder sintering method to produce strong metallic structures.

Propulsion options are much more limited, but one possibility would be using surplus metal to produce an electromagnetic cannon powered by locally manufactured photovoltaics.

During the process of reconfiguration of its operations, the Seed Craft deploys a group of independent robots for assistance. These robots secure it, remove obstructions and do any precision work.

To be able to convert the asteroid into a RAMA spacecraft, the Seed Craft deploys its four 27 x 34 m solar arrays, which give the 4 MW of solar power required.

With its assumed composition and size, gravity at the asteroid’s surface is only .00002 g’s, making mechanical excavation very difficult. To overcome this obstacle, the optical mining system will be used.

Optical mining methods have been previously studied as ways of overcoming both difficulties in mining C-type asteroid by Sercel et al. With a 10kW Optical Mining system operating at a temperature of 1000K, an excavation rate of ~5 mm3/min of material per W of power was observed.

Then, to provide the full power necessary to operate the optical mining system, the Seed Craft directs the power of its solar array on it.  That will be enough to work at the higher temperature required to decompose the stone and the metal. It is expected that, the excavation rate will be around 200 cm3/second.

With the physical dimensions of the asteroid confirmed, it is possible to estimate the materials available at the asteroid to build the RAMA spacecraft components. Under the standard composition model assumed by Rock Finder, the composition breakdown for UY19 is:

Rock, Olivine (Mg,Fe)2SiO4 / Mass Fraction 42% / Volume Fraction 33.75% /Rock, Orthopyroxene (Mg,Fe)2Si2O6 / MF 36% / VF 30.54%/ Iron / MF 15%/ VF 5.14%/ Nickel / MF 7% / VF 2.21%

When presented with an S-type asteroid like UY19, RAMA is forced to make use of mechanical methods of propulsion.

Seed Craft Architecture

With no known sources of volatiles at UY19, the Seed Craft is customized for metal working and stone mining. No chemical processing equipment is included.

Instead, the spacecraft is loaded with 4 modules containing the following equipment:

. An Optical mining rig, containing a bank of one hundred 10 kW lasers and a collection of inlets capable of spalling and collecting asteroid material at a rate of  about 0.5 kg/s,

. 5 kW of furnace for smelting and electromagnetically separate iron/nickel from rock,

. 5000 kg of alloying elements and equipment for producing high strength steel;

. A Die Extruder for extruding high strength steel into a circular beam 16 cm in diameter, and

. A 750 kg electromagnetic bearing assembly for permanent installation on the asteroid.

In the beginning, debris from the mining site are lost in space. But, once the Seed Craft has bored a hole deep enough to insert the mining module, a closed cavity is formed to prevent any more debris outside the asteroid. The material is then directed to an inlet adjacent to the optimal mining rig, where it is collected and conveyed away from the mining site. There, the material will be purified and smelted.

The melted rock cools in measured “shots” of 18 cm in diameter in the presence of an electromagnetic field. It is the remnant of this magnetic field that makes the shots stick together. These shots are then pilled up at the bottom of the ever-growing interior of the asteroid and used as propellant for the mechanical propulsion system.

The process of optically hollowing out the interior of the UY19 takes 8 years, and produces a new shot every 17 seconds.

For the first decade of this process, a small fraction of the iron and nickel extracted from the material is not returned inside the asteroid or embedded in the shots. In fact, this fraction is separated and combined with the carbon and other alloying elements from the Seed Craft to produce high strength steel. This steel is extruded from a die through radial bore holes in the asteroid until the rod is 40 m-long. These holes are excavated by robots.

The RAMA Architecture for the S-type asteroid 2009 UY19.

These long steel rods or “slings” are used as the main component of the RAMA’s propulsion system. The base of each sling is strongly anchored inside the asteroid. During this process, a series of 16 slings will be extruded at equal distance around the asteroid. 

While the quantity of material used in the slings' production is large, (300 mT of materials to produce 80 mT of metal) it is small compared to the quantity required to produce the shots. 

To have all the slings needed for the propulsion, it is necessary to extrude 29 kg of metal per day for beams 220 mm-long . At this rate, the production is completed in less than a year.

Once done, the metal becomes available to reinforce the interior of the asteroid or provide scaffolding for the robots. It can also be reduced into a powder by the Laser Engineered Net Shaping technology (LENS), for future uses.

The Laser Engineered Net Shaping (LENS).

The LENS: The Powder is conveyed through a nozzle using a carrier gas and blown onto a built surface. A laser is then used to melt the powder or the layers.

The Die Extrusion.

The Die Extrusion: The materials (usually fibers) are driven (pushed or pulled) through a resin bath, cured and extruded from a die to form a structure. 

-> The Extrusion Based Additive Manufacturing: The material is extruded in a molten state from a heated nozzle, then placed in consecutive layers using 3-axis control methods. The part is built up gradually layer-by-layer.

The Optical Mining™/Manufacturing

The Optical Mining™/Manufacturing comes from previous NIAC work by Joel Sercel. This material processing technique may be used for manufacturing process when deployed with the RAMA architecture project. This method uses a concentrated solar light to process the asteroid materials into useful constituents.

After 8 years when the asteroid is ~50% hollowed, the 750 kg electromagnetic bearing assembly is detached from the Seed Craft and transported inside by robots to the opposite wall. The base is then welded to this wall, with its drive axis parallel to the spin axis of the asteroid. As construction continues, surplus iron and nickel from the smelter are combined with the remaining alloying elements from the Seed Craft to produce Inconel powder.

Under robotic control using the LENS technology, the powder is again sintered radially outward from the electromagnetic bearing system. So, the remaining metal composition becomes a single mass, mounted on the electromagnetic bearing. That will be enough to create a crude mechanical spin stabilization and energy storage system for the RAMA craft.

Schema of the complete RAMA spacecraft en route to Cislunar space.

During the manufacturing process, the Seed Craft has gradually used its own propulsion system to stabilize and point the asteroid’s spin axis in the right direction. The system must now wait 13 years for the Earth return window to open. The Seed Craft stows its solar panels to protect them from debris and then powers down its manufacturing systems. During this time, it periodically reawakens to perform status checks and remote sensing operations on any targets the asteroid may pass close to.

One month before the window opens, the Seed Craft restarts, and redeploys its power systems. For 25 days, it will transfer to the flywheels' motors its 4 MW photovoltaics power. At the end of this sequence, the 2 flywheels will be spinning at their approximate material limit of ~4000 rpm, which equals a storage of ~1 GJ of energy. This is the energy required to return the asteroid to Earth. 

Slightly charging one flywheel over the other imparts a greater rotation to the reinforced asteroid shell. That produces significant artificial gravity at the surface, further adhering the shots up against the interior and the electro-mechanical exit ports bored by the robots.

In the Voyage, the Seed Craft uses its own propulsion system to provide a series of forward “kicks” to the asteroid. These kicks impart no significant ΔV, but are properly timed to match the fundamental frequency of the 16 extended slings protruding from the asteroid. The Seed Craft, its decade-long task completed, disengages from the asteroid and departs to its next target.

The fluctuations of the sling arms back and forth would make the movement of the RAMA spacecraft look similar to a jellyfish swimming through the ocean currents.

The slings begin to oscillate back and forth, and after 3 days of continuous kicks, they rock with enough amplitude to bent all the way back to the asteroid’s surface. Their slenderness ratio is large enough to remain fully elastic when bent this far, allowing the slings to continue to oscillate like a pendulum with only thermal losses.

The motion of the slings starts at a velocity of 2.1 seconds and, at the peak, the tips are swinging at 312 m/sec, which is the theoretical maximum velocity of the material. 

This low impulse maneuver persists for 27 days. Each shot carries away a small fraction (0.55%) of the sling’s energy with it. Over time, this loss will cause the slings to oscillate through a smaller arc and the asteroid to spin at a slower rate. To compensate for this loss of energy, the flywheels spinning since they were charged by the Seed Craft, are slowed each time the slings reload, imparting a slight transfer of angular momentum to the asteroid itself, and thus to the swing arms.

The abundance of shield material can make an asteroid spacecraft 100% radiation-free and completely shielded from micrometeorite debris. This is why, RAMA spacecrafts are ideal for long-term missions of 5-50 years.

CREDIT & SOURCE: MADE IN SPACE, NIAC PHASE I FINAL REPORT, PROJECT RAMA: RECONSTITUTING ASTEROIDS INTO MECHANICAL AUTOMATA, 2017.

Credit: Fox News Published on Jun 8, 2016 SUBSCRIBE 727K Four4Four Science: NASA is funding a concept that will turn asteroids into spaceships so that we can mine them. Will it work?

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THE ANTIKYTHERA MECHANISM

The complex gear structure of the Antikythera Machine. © Markos Skoulatos, Eternal Gadgetry

In 1901, the Antikythera Mechanism was found at the bottom of the sea. Its fabrication dates back to the 2nd century BC. Because of its complex inner structure, it took more than 100 years to reveal its secrets. Using techniques such as the epicyclic theory (developed by Appollonius and Hipparchus), scientists have been able to rotate gears within gears through elliptic routes. In all, they found 40 gears on 20 axles in it. Then, doing additions and subtractions, scientists can calculate the positions of the Moon, the Sun and other planetary bodies with great accuracy.