Mission to bring back Moon samples

[Enthalpy]

Hello, stone collectors and everyone!

Moon rocks help understand our world, but all we have are meteoroids and 382kg of samples quickly collected from 6 small sites by the Apollo missions
http://en.wikipedia.org/wiki/Moon_rock
so a mission to bring back Moon samples from new sites would be exciting.

I propose here a script to prospect many sites - including at Moon's far side :good: - taking the time needed to explore larger areas and pick the best samples.

We don't need six Saturn-V for that goal because robots exist now and my sunheat rocket engine changes the game
http://www.scienceforums.net/topic/76627-solar-thermal-rocket/
so one middleweight launch suffices.

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The mission comprises

• Several prospector robots that start from Lunar orbit, land, choose and collect samples over a long ground path, take-off to bring the samples to the Lunar orbit;
• And a ferry that transfers them from low-Earth orbit to Lunar orbit, and brings the samples from there to Earth.

In addition, the ferry can have remote-sensing capabilities, like a sunlight-pumped laser and a hydrogen gun (if aiming properly).

----- Transmissions -----

I imagine robots that move autonomously to human-designated targets within an observed landscape, carry out simple sampling and analyses alone, but get help at sample choice and obstacles. The ferry relays the transmissions between Earth and Moon's far side - and its near side for pictures, limited video and heavy data at least.

 

The ferry's 1000km high orbit overflies points 50° beyond our horizon while visible from Earth. The antipodal one-fourth of the far side is accessible to stored data transmission and often to real-time. While landing a prospector at nadir there, humans can't intervene - but the ferry's transmissions reach 37° farther than its nadir with 15° elevation, so real-time transmission with a landed prospector is often possible.

Prospectors see the ferry with >15° elevation for >26 passes of >31min spaced by 3.6h spread over 4 days in daylight every 27 days.

The ferry's orbital plane is essentialy fixed. I imagine it polar and, at the beginning, about aligned with Sun's direction. As the Moon rotates in 27 days around itself and Earth, prospectors of varied landing sites get active in sunlight, work and communicate. As Earth rotates around the Sun, the ferry's orbital plane changes from favourable noon-midnight to 6h-18h then improves again.

Marc Schaefer, aka Enthalpy

[Enthalpy]

----- Earth to Moon -----

 

The ferry carries the prospectors to the Lunar orbit from a 400km low-Earth orbit, where one Atlas V 551, H-IIB or Ariane 5 has put the 18.8t.

 

 

The ferry first (1) raises the apogee to the Moon's 384Mm. Fifteen 4.572m sunheat engines totalling 39N achieve the 3084m/s in approximately nine months, with pushes that must extend much around the perigee, hence exploit only 90% of the isp=1267s. This leaves 14268kg there.

I've forgotten the eclipses. A polar Earth orbit improves that - or raise the perigee.

Then (2) the ferry adds 532m/s to the apogee in about two pushes to be 300m/s slower than the Moon. It's at the North or South of the Moon.

The ferry brakes 380m/s before periapsis and 11m/s after during the capture by the Moon, to reach a polar orbit with 2737km periapsis and 20260km apoapsis, according to the spreadsheet
[MoonWeakBrake.xls in this folder]

This leaves 13238kg.

The ferry (3) brakes by 455m/s to circularize the orbit. Few months demand 90% efficient long pushes, leaving 12710kg on Lunar orbit, 1000km over the Moon's 1737km radius. We can begin to tinker seriously.

This script can send other payloads to the Moon, for instance preset a lunar module in orbit for a manned mission, or a habitat on the Moon, or equipment that builds the habitat - pretty much everything that can wait. An Ariane V Me, a Heavy Falcon or Atlas, maybe an Atlas V 552, have more capacity.

Marc Schaefer, aka Enthalpy

[Enthalpy]

----- Samples boxes -----

Many boxes shall separate the samples and keep them clean - in vacuum like on the Moon. Though, the mass of the boxes competes with the samples, or alternately, the box mass fraction determines the mission launch mass.

Milled aluminium, with thin walls and stiffeners, would make boxes 3 times as heavy as the samples, so here's a lighter design.



The walls and cap are electrodeposited of Ni or Ni-Co. For a D=80mm box, 100µm let the bottom resist >3bar, the walls as well if corrugated by 3mm peak-to-peak (if I didn't botch it), and the cap is slightly thicker. A box 200mm long weighs 80g, two 60mm pebbles in it 560g.

A Ni sandwich is possible, especially with balsa wood plus syntactic foam, but bare Ni eases cleaning and sterilization.

Solder shall seal each filled box, for instance fluxless Sn-Pb-Ag. The mating faces are covered with readily wettable Sn, surrounded by rings of non-wettable material (like anodized Cr) to contain the solder, which is pre-applied on both parts.

The prospector can use a funnel to pour or drop the samples more cleanly, it has varied brushes anyway, and may remove some dust-protection layer or part. Then it applies the cap on the box and remelts the solder by induction with a ring coil half-surrounded by laminations.

A different process tightens food tin cans: possible source of inspiration.

The prospectors have boxes of several sizes to optimize the volume and mass.

Samples that resist crushing can travel in a simpler bag made of two swollen sheets of Ni welded or brazed at three sides; after filling, the prospector folds strongly the fourth side and solders its tip. Such bags are even lighter, like 15g for 300g samples; I'd let them travel as bulk. Bags and boxes have non-removeable identifications - readable in 50 years please, hence with the naked eye.

The boxes and bags need a high emissivity: maybe an anodized coating of Cr. I like bare Ni as the inner face, but some boxes or bags can have Cr, Au, Ta, ceramic... coating for contamination double-check.

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Boxes hold permanently at 45° by polymer or metal straps at a central truss, building a magazine, with the bags dumped at the truss' middle. Arbitrary 60kg samples per prospector would occupy about D=0.8m H=1.0m. A D=0.6m 6-node truss that breaks at 50kN (50g during atmospheric re-entry) can consist of 340mm*17mm*0.5mm welded AA7020 tubes and weigh 3.5kg.

An mobile impact protection is necessary at Moon landing, lift-off, and rendez-vous with the ferry. Thin aramide sandwich weighs 3kg.

Arbitrary 60kg samples per prospector then need 9kg bags, boxes and straps, 4kg mobile truss, 3kg protection, or 300g per kg of samples - without the prospector's tools.

A second vacuum barrier protects the samples. This one shall wait on Lunar orbit, and be the atmospheric reentry capsule.

Marc Schaefer, aka Enthalpy

[Enthalpy]

-------- Descent and ascent --------

Each prospector leaves the ferry at 1000km altitude, descends to its location on the Moon, collects samples, and joins the ferry at 1000km with its samples.



With 6m/s² acceleration, 2° orbit correction (one window every third month) and 50m/s navigation, the ascent costs 2215m/s.

3 landing trials take 2 hops to 200m distance and three hover periods of 20s, or 160m/s together: the descent costs 2375m/s.

The ferry won't see the prospectors as they land. On the Moon's near side, the Deep Space Network antennas can receive some bad video for human decision. At the far side, the ferry at 100km altitude would have seen the landing prospectors but not the Earth. So: automatic landing and take-off, after training on the near side.

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This landing script needs simple behaviour and sensors yet brings resilience:

• The prospector extends its legs (A1) and fires its engine (A2) to join a landing site.
• Descending at moderate pace at the landing site, it touches with a first foot (B1) which optionally climbs during the brake (B2) to zero speed.
• Each other foot descends until it touches the ground (B3), in which case the engine stops.
• If the ground is too far below a foot, the prospector hops ( C) to 200m distance and resumes landing (D).

This leg movement shall happen within 20s hover. 6kWe are available at that time. Tiny hydraulic dampers could save a hard landing at 2.5m/s.

I imagine prospectors walking on 6 landing legs, though wheels are possible. Vertically rotating hips and knees extend the legs easily, make a smooth walk together with the feet's vertical moves, and fit well a truss body.

This is not limited to our Moon.

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The 3.3kN engine burns diethyl-trimethyl-dipropylene-triamine (mp -100°C hopefully)
http://www.chemicalforums.com/index.php?topic=56069.msg272080#msg272080
or commercial pentamethyl-dipropylene-triamine (mp-78°C), with liquid oxygen cooled actively
http://saposjoint.net/Forum/viewtopic.php?f=66&t=2051
stored in a superinsulated balloon tank hold by polymer straps
http://www.scienceforums.net/topic/60359-extruded-rocket-structure/page-2#entry761740

It has 11kWe electric screw pumps for 100bar in the chamber
http://www.scienceforums.net/topic/73571-rocket-engine-with-electric-pumps/#entry734835 (and nearby messages)
Expansion in D=0.8m to 135Pa brings Isp=3989m/s=407s.

The 12.4kg Li-poly battery is recharged before the ascent and outperforms any pressure-fed solution. It's very useful for the prospector's operation and nighttime hibernation.

Pumped Mon-33 would bring 1/3 less samples than oxygen and is toxic. Strained fuels like spiropentane would add only 5% samples, methane less. Hydrogen would have brought 1/2 samples more; a fuel cell wouldn't improve over batteries, except for nighttime if the water is electrolyzed during daytime, hum.

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Starting from orbit at arbitrary 1000kg for later scaling, each prospector lands with 551kg. More details should come.

Marc Schaefer, aka Enthalpy

 

[Enthalpy]

Each prospector shall observe and sample many sites spanning a good distance, which takes months. Though, night lasts for 2 weeks on our Moon. The craft gets no heat, no photovoltaic electricity, and the ground cools down from 380K (Equator) or 220K (70°N) to 90K:
http://diviner.ucla.edu/
but there is no blizzard, good news.

The following figures on a prospector example explain how to spend the night without radioactive heaters.

-------- Hibernation --------

The parts of the prospector fall in categories of thermal protection at varied locations.

• The temperature of these parts swings freely but a skirt protects them at night:
  - The uncooled niobium nozzle extension and the lower legs must live with sunlight, ground heat, flames and flying pebbles.
  - A metal sheet protects the cooled part of the engine and the attitude thrusters against flying pebbles, and the upper legs and the fuel tank against flames too. It insulates somewhat against ground heat.
• The oxygen tank is superinsulated and actively cooled.
• The arms and tools, eyes, Lunar samples are exposed to daylight but enclosed in pockets during the night.
• The battery and the electronics get a regulated temperature.

The pockets also keep the arms, tools, samples boxes clean during the propulsion phases. The prospector walks away from the landing site, but the legs are still contaminated, and the propellants may leak a bit. If sampling the ground before the body passes isn't clean enough, then a different design must separate the walker from the flyer. To avoid nitrogen at the propellant, replace CCN( C)CCCN( C)CCN( C)CC with farnesane or phytane.

In the evening, the prospector finds a smooth terrain, groups its legs, and lowers its skirt of multilayer insulation when the ground is comfortable. Many small masses press to the ground the skirt's last 0.5m, and optionally the arms put regolith there. 17m² of 25 plies at 270K lose 2W, while 90kg ascent fuel store 150kJ/K and the ground helps, so this group cools by 15K.

3m² of 25 plies multilayer insulation leak 0.6W in the oxygen tank, polymer belts 0.1W, pipes must insulate (polymer?), so the cryocooler consumes 5W at least and is shut off at night. 200kg ascent oxygen store 340kJ/K and warm by 3K overnight. The Osr cold sink is decoupled mechanically at night, it faces the sky and brings e=0.9 a=0.1 (one tool is a brush), so 4dm² achieve 2*5W at 265K for the cryocooler.

The 13kg Li-poly battery common with the engine provides 5W over a night, so every activity ceases but for a few sensors like seismometers. The prospector folds its arms and eyes in its pockets and closes them. The multilayered insulation is tapered at the joints. 23m² of 25 plies around the batteries, equipment and pockets at 278K lose 3W, while twenty L=0.2m D=30mm tubes holding this part leak 0.8W as they consist of 2mm balsa and 2*300g/m² fiberglass composite. The battery can increase easily if needed, the multiplayer insulation too, and alone the thermal inertia would suffice. The 0.5m² equipment's Osr heat sink achieves 300K, regulation is by mechanical decoupling. Solar cells on several 0.6m2 faces provide 200W electricity and, if any needed, a warm source, otherwise they're insulated.

If electric motors can't work in the legs, they can reside at the hips and operate all joints over tendons or shafts and gears. For instance, W=10mm e=50µm steel breaks at 1kN and 200K over 200mm leak only 43mW; titanium improves and composites more. The skirt eases many parts but isn't mandatory neither, if the fuel tank is with the equipment and the legs or hips of sandwich tubes.

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Robotics is a challenge at the prospectors, which aren't in permanent contact at the Moon's far side. Beyond walking semi-autonomously, they should gather a list of small unbroken samples alone and pack the man-chosen ones, change the tools at their arms and clean the solar panels, cold sinks, samples containers, clean away or sample the regolith, conduct a list of laser chemical analyses... I've taken 1000kg starting from orbit as a basis for scaling, but the unfolded prospectors would be 2.5m huge then, so over a dozen smaller prospectors are possible and desired to sample more sites, and they should move quickly to explore varied terrains. Prospectors autonomy is a key to relieve the operations team.

Marc Schaefer, aka Enthalpy

[Enthalpy]

-------- Ascent --------

Each prospector goes once to the Moon' surface and back. Refuelling at the ferry, or even at a later ferry, would have multiplied the landing sites but reduced the samples mass and the reliability.

Still for provisional 1000kg leaving the ferry, hence 551kg landed on the Moon, here are rough masses ascending from the surface to the ferry.

Before a prospector takes off, it abandons its working and analysis tools on the ground (-20kg). Just after take-off, it separates its legs (-80kg). It keeps the arms and an eye (15kg) to dock at the ferry and transfer the samples. The engine and attitude thrusters (40kg), battery (14kg), tanks (8kg) served for the descent, as well as the bus (60kg), equipment (20kg), undetailed items (20kg).

2215m/s ascent need a mass ratio of 1.75, which permits +119kg samples in 30kg boxes plus rack and 245kg propellants. The craft weighs 571kg without tools nor legs but with samples and propellants and 326kg when docking.

Ask geologists: twice as many explored regions and prospectors bringing each one-third the samples mass, or 40kg, should make better science. Each prospector would then weigh 500kg when leaving the ferry.

Marc Schaefer, aka Enthalpy

[Enthalpy]

-------- Moon to Earth --------

All prospectors bring their samples in hermetic boxes and racks to the ferry. A capsule hosts the racks and is sealed. The prospectors are abandoned and the ferry brings the capsule towards Earth. They separate before reentry, where the ferry burns and the capsule aerobrakes unpiloted, then opens parachutes and lands in a quiet area: Antarctica, central Australia...

Little extra hydrogen would leave the ferry in transfer orbit or even in Leo, ready for refuelling.

With its Isp=1267s sunheat engine, the ferry accelerates by 455m/s to raise the apoapsis to 20260km. This is 90% efficient because the pushes are long so the operation takes goes in a few months.

11m/s before and 380m/s after periapsis let the ferry leave the Moon on a nearly circular Earth orbit, 300m/s slower than the Moon at apogee.

In very few apogee pushes, the ferry brakes by ~550m/s to plunge to Earth. The timing adjusts the landing zone and date for good weather, and 100m/s during the last leg fine-tune the landing point.

This sums to equivalent 1547m/s which need a mass ratio of 1.13 thanks to the game changer.

 

The reentry capsule comprises:

• A structure that resists the aerobraking, the landing and keeps the air out: 29% of the reentry mass.
• It may have legs that absorb the landing shock.
• A heat shield: 16%.
• A parachute: 13%.
• A battery and electronics that opens the parachute, optionally separates the heat shield and deploys the legs, detaches the parachute after landing, transmits a radio signal: lightweight.

This leaves 42% of the reentry mass for the samples in their boxes and racks. The volume of the boxes and racks determines the capsule's size, not the mass nor the heat shield, so it must be optimized.



The masses permit 18 half-ton prospectors . Arriving at Lunar orbit:

0.45t 15 sunheat engines
0.32t Tank with foam, Mli, glassfiber truss
0.36t Return leg propellant
0.2t Command and control, robotics
0.05t Capsule adapter
1.3t Empty capsule
1.0t Bus and prospectors adapter
9.0t 18 prospectors
------
12.7t Fits the 18.8t launch and transfer

Standard payload fairings date back to the chemical propulsion era and can't host this full mission, but the Atlas V User's Guide claims :
"Longer and wider payload fairings can be developed. Up to D=7.2m and L=32.3m have been considered."
Fine, this mission needs just 1/3 more volume. Hey Ariane, Atlas has the same fairing manufacturer as you!

These are the masses leaving Lunar orbit:

0.09t 3 sunheat engines, others dropped
0.32t Tank with foam, Mli, glassfiber truss
0.36t Return leg propellant
0.2t Command and control, robotics
0.05t Capsule adapter
2.2t Full capsule
------
3.2t Fits the return leg mass ratio

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Thanks to the sunheat engine, this single mission can bring back 720kg lunar samples from 18 regions . That's twice the mass and three times more sites than we have from Apollo. Better, the prospector robots have months and years to choose the samples over wide and more varied areas, including at the far side.

Marc Schaefer, aka Enthalpy

[Enthalpy]

The ferry can see the prospectors as they land. I was pessimistic on September 14, 2014.

Instead of making the full de-orbiting kick at once, a prospector can brake a bit, wait until it has drifted from the ferry by the right amount, the complete the de-orbitation.

[Raider5678]

So. How's funding going to be accomplished?