Main Structure of the Solar Thruster Sailor solar sail spacecraft

The design showīn on Fig. 1 underneath is the basic design of a highly steerable spacecraft through the combination of solar sail propulsion and thrusters. This design has evolved further through Using roller reefing for fuelless steering, station keeping and attitude control, - additional mobile dockingable thruster units for STS-spacecrafts.
Fig.13 - Fig.14-15 - Fig.16 Mobile Thruster Unit - Fig.17 - Fig.18 Fuelless Steering -

As an alternative to the STS which has to get constructed in space, take a look onto Fig.19-21d - The Solar Sail Launch System, which uses also roller reefing for fuelless steering, station keeping and attitude control, carries a docking and payload station, ample solar cell arrays and additional thruster units.

1. to serve as a carrier for fleets of saucer shaped Thruster Ring Space crafts and satellites as daughter units.
2. to serve as a Container Carrier Ship ( freighter ) for fleets of flying containers as daughter units.
3. to serve as a Carrier ship for asteroid landers and docking able equipment units.
4. to serve as a Carrier ship for mobile space processing and manufacturing utilities and equipment.
5. to serve as a Mobile Solar Power Station ( MOPS ).
6. to serve as a Space Tug.
7. to serve as a mobile carrier unit for space based telescopes, radar / broadcast stations, mirrors, lenses.

This enables for secure handling of the center payload through low thrust electric thrusters which are strong enough to turn the sail through the large lever which their location on the Outer Ring provides. Moreover the pairwise placement of thrusters on the Outer Ring enables acceleration and deceleration of a Thruster Ring Spacecraft without moving parts and without having to turn the craft for deceleration. That gives the STS an unprecedented high level of smooth steerage which no other solar sail design provides. This high level of steer ability is only possible through low thrust steerage propulsion devices.

The Solar Thruster Sailor as a mother carrier ship provides cheap transportation through the possibility to hold a huge free photonic thrust producing sail (and therefor saving fuel mass and costs) with the ability to carry a lot of payload combined with the secure docking ability for also highly steerable Thruster-Ring daughter units.

This is done mainly through combining Low Tech KISS (keep it simple stupid) lightweight and few parts spacecraft design with High Tech materials and High Tech but proven electric thruster technology.

In conjunction with authomatic - remote controlled docking actions for similar shaped daughter units and with authomatic remote controlled payload handling the carrier-/daughter-units design allows to serve all space based transportation needs in the inner Solar system - from Sun to Mars and short beyond Mars without involving humans in space. This is a huge cost and security advantage for transportation, processing and manufacturing in space - not having to take care for humans and their life support and yet getting things done like asteroid mining for instance.

That does not mean, the author prefers not to send humans into space. I would like to get things done for less, getting infrastructure into space first and sending out humans later when we have already the ability to transport and process space materials cheaply and to produce and spread energy were needed.

Since light pressure is a very weak force it is essential to get extremely large solar sails and yet light construction for appropriate photonic propulsion.

This is possible through the Ring Segment System ( RSS ) which enables simple and fast mounting of very large structures using a lot of ring segments from carbon fibre reinforced light weight plastic pipes. The pipes are just sticked together in space.

The Outer Ring

Think about it, with an outer ring holding several thrusters each sitting on a large lever, because they are located on the structures edge, youīll get optimal steerage. The ring does provide also lots of room for payload with a net of belts or stringing inside.

In contrast if you have a huge solar sail with a boom. How large could the boom get with all the load dragging at the structures center? You will have a stress point on the masts foot. So the solution would be a short mast, but that means weak steerage for such a big sail. The boom sail may be of use for smaller crafts but what if it getīs bigger?

The STS sail through itīs outer ring will have at least two thrusters working together on opposite sides of the ring to turn the craft - each pushing on a large lever, the levers getting bigger with the sails size. So it is possible to use the weak but fuel effective ion thrusters for steerage even for gigantic structures. Result - no stress point, no self employing needed and optimum control.

Comparison

Can we compare the 4 square-km structure above with a Thruster Ring Spacecraft of the same sail area?

Mass

How did I get those numbers?

The pipe Rings:

Compressed Volume of a pipe ring is d1 x pi x wall thickness x length of the wall which is d2 x pi were d1 is tube diameter (8 cm) and d2 is ring diameter (2260 m) for the Outer Ring.

The compressed mass volume of the Outer Ring is about 0.08 m x 3.14 x 2260 m x 3.14 x 0.001 m = 1.783 mģ.
Those 1.783 mģ for the Outer Ring have a weight of about 3566 kg when using 2 g/cmģ for CNT reinforced plastics.

The compressed mass volume of the Inner Ring plus four 30-m support pipes as a magazine docking station is
(0.08 m x 3.14 x 30 m x 3.14 x 0.001 m) + (0.08 m x 3.14 x 30 m x 4 x 0.001 m) = about 0.054 mģ.
The Inner Ring plus support pipes would just account for a mass of 108 kg.

Stringing Net

The net supports the sail cloth keeping it pretty flat and therefore avoiding the application of tension forces to the edges of the sail and can carry also payload like solar cells which are placed around the Inner Ring. The stringing got square fields of 50 cm size what amounts to about 10 Mio. meters of fiber threads with a thickness area of 0.5 mmē. Because of the immense strength of the fibers the net can take on a lot of load. It would have a weight of about 4850 kg. Enough for mission designers to look for some more weight to save here.

Than we have to add the sail itself.
Through the net the sail cloth can get a lot thinner than those used for self deploying sails. The most mass adding component is the substrate which getīs a coating with a suitable metallic reflector. Since the plastic substrate is only used in favor to support a pure much thinner ( mostly aluminium ) coating, it could even be possible to skip the substrate or let it vaporise when the sail is already set. But in this example I choosed a substrate of KaptonĐ film which can get etched down as thin to provide a area density of 1 g/mē (Mc. Innes, Solar Sailing, page 62) along with an aluminium coating of about 0.27 g/mē and a much thinner coating on the backside a high-emissity chromium coating for thermal control through re-radiation.
When assuming 1.3 g/mē the whole sail cloth of the solar sail would have a mass of about 5200 kg.

Those 4850 kg invested into the supporting net help to use a much thinner sail of 5200 kg instead of 26000 kg when using conservative 7/g per mē sail cloth. They also help to avoid other structural components like masts, booms and struts. And they help to hold a docking station in the sails center which enables properties like docking and payload handling - just what is needed for the main purpose of a huge solar sail - to serve as a carrier- or mother ship.

For the Thruster steering unit I choosed 24 double thruster units, each carrying 2 Russian SPT-60 electric thrusters which have a weight of about 1.3 kg each, 1200 g of fuel for each double unit and 200 g structural materials. So we get (1.400 kg x 24) + (1.3 kg x 48) = 96 kg for the thruster propulsion.

• A solar sail needs to be very large to provide sufficient thrust. The Solar Thruster Sailor (STS) provides just that - the possibility to assemble huge solar sails in space.
• The Solar Thruster Sailor (STS) provides a docking station for daughter units, the Inner Ring.
• The docking station serves at the same time as a payload handling station, able to hold and handle large objects which makes it possible to use the STS as a space tug.
• Unlike spin stabilized solar sails or sails with moving blades (like Cosmos 1), the STS solar sail can place payload onto itīs whole disk area (while placing it in the Inner Ring is preferred). Therefore it is the ideal platform for space transportation due to itīs net of belts or stringing making it possible to unlash the main benefit of all solar sails - free fuel from the sun for cheap space transportation.
• Hybrid combination of photonic and thruster propulsion - will get out the best of both propulsion systems.
• For a solar sail very good steering and handling due to the crafts thruster part.
• Reaching very high speeds is possible (much faster than ion propulsion).
• High versatility, converting and retooling of a space craft is simple.
• Changing direction is possible without large fuel consumption for instance forward and backward direction.
• Acceleration and deceleration through the electric thrusters without having to turn the craft is possible.
• Rotating is possible and enables artificial gravitation for manned space travel.
• Almost no size limitation for payload.
• Light weight structure, using less fuel for ion thrusters.
• The ring-structure is reuse able, update able and repair able -
  the STS is not a throw away article, it is a long time investment and can be used for numerous missions!
• Landing and starting on and of asteroids or moons without atmosphere and with low gravitation should be possible.

Main elements of fig 1 are thruster-ring "1.", solar sail and solar cells with carbon belts stretched within "2", carrying a (carbon) payload-platform in the middle "3". Thruster units 1.5 are for moving sideway or for right - left- rotation around the pole. Thruster units 1.6 are for up - downwards propulsion or for rotation around the diameter.

Instead of the payload platform 3 an Inner Ring as a docking and payload handling station can be used, to carry swarms of spacecrafts and satellites and to handle payload and even big objects using winch devices, so that the solar sail becomes a huge space tug.

Fig. 2.a and Fig. 2.b - Thruster Units up - down and right - left

Thruster units, parts 1.9 are at the same time brackets and tank units for xenon-gas. Parts 1.10 are jet tubes consisting of two thrusters with outlet to opposed directions.

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Fig. 2.c - Thruster Unit - Installation

The two splints of the bracket 1.9 run completely through the segment-pipes and are bolted onto them with counter nuts. The splints are also conductors for the electric power yielded from the solar-cells near the thruster-unit. Half-pipes (could be from metal) 1.9.2 enfold the segment pipes to give this joints some more strength since they have to resist heavy rotational forces.

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Fig. 2.d - Double Thruster Unit with two typical ion thrusters.

The bracket for the unit is at the same time tank for xenon gas

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Fig. 3.a - 3.b - (carbon) belts bolted to the pipe segments

As simple as it can get. If you have one plate with inbuilt screws and the other plate with holes there is not much work to do to mount the belt.

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The Magazine Docking station - held in the center of the craft enabling docking and payload handling.

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Fig. 4.a, Fig. 4.b, Fig. 4.c - Launcher Transport Head (LTH) Getting the pipe segments into space

Fig. 4.c Launcher Transport Head (LTH) pipes transported outside of the launcher	Fig. 4.a one layer LTH from above	Fig. 4.b multiple layer LTH from above
	If the upper stage of the launcher has a diameter of 4 m and the pipe segments a diameter of about 6 cm, it is possible to transport up to 200 pipes. Given a length of about 15 m per segment youīll get a perimeter of 3000 m from one layer. The compressed mass volume of this layer is about 0,6 cubic meter of lightweight material. Not a weight to worry about for a big solar sailor-structure.	A multilayer LTH could transport pipes for very large ring structures.

to the next Fig.5 -

Mini STS

The Mini STS is a little solar sail based on the Solar Thruster Sailor (STS) design steered with the help of ion thrusters. It getīs transported to itīs near sun orbit using a mothership or with the Rotational Slingshot Catapult (RSC). This craft could even land on asteroids with low gravitation using the ion thrusters in this case as main propulsion and the thruster brackets as landing feet.

How could a small solar sail work at all carrying relative heavy ion thrusters too? Shouldnīt it have a pretty big sail area because of the low force of the light pressure?
This is correct - in principle, but as you get nearer to the sun as stronger getīs the photonic force also. At 0,25 AU this force should be 16 fold stronger than at near earth position!

A solar sail of about 10 m diameter (about 78,5 square metre area) could gain the force of a 1256 square metre solar sail on near earth position. This would be considerable more than the area (and the force available) of the 30 m diameter Cosmos 1 solar sail of the Planetary Society, hopefully to be launched soon (written on Dec. 2002). Building and launching such a lightweight STS to LEO would be a special offer compared with the costs (if possible at all) of missions to and around the sun with other propulsion technics. Planning and installing the Slingshot Catapult at LEO would be more demanding but this could be a one time investment for a multitude of cheap missions enabling a cluster installation of near sun satellites, with many fly by observations of venus and mercury.

In contrast to conventional satellites this Mini STS would be able to fully navigate for a long time, spiraling towards the sun through positive declination and changing direction spiraling away from the sun through negative declination. The ion thrusters would have to do just this one turn to steer the craft when changing direction hence staying functional for a long time of operation since they need only sparse fuel.

Mission Proposal for a Mini STS- Asteroid Sample Return

using Mini-STS Solar Thruster Sailors (solar sails which are compounding solar sail with ion thruster propulsion) to retrieve samples of asteroid regolith to land on one or several asteroids, drill asteroidal sample cores and bringing them back to earth or to the ISS for analysation. One craft would do all this tasks, no other equipment would be needed.

The Mini-STS ion thrusters will enable the craft to navigate like a lander. Better yet itīs special structure (and the micro gravity environment on asteroids) allows to hover for finding sampling places or to pitch up and down without turning the craft. While even a very heavy Prospector equipment would get in trouble not to throw itself off the asteroid when pressing to remove samples off the ground, the Mini-STS can do that without problems. That is because itīs thrusters can press the craft down while drilling or removing samples. If you take a look on Fig. 2.a youīll see why the craft can change movement into the opposite direction or press itself down to the ground. Each thruster is located in a jet tube together with a twin thruster firing into the opposite direction when needed. Each thruster pair has an identical twin pair on the other side of the thruster ring for symmetric reasons. In fig 1 the up- down-pressing thruster pair is designated with the part number 1.6.

The favoured asteroids would be located very close up to 0,25 AU to the sun, since solar flux for photonic propulsion and solar electric energy is about 16 times as strong there as near earth. So the Mini-STS sample prospectors could be made pretty small. To get the same propulsion force as a 30 m near earth sail the prospectors would only need 7.5 m diameter (or about 44 square metres sail area) even so they could be faster than the 30 m sail at earth level because they would be smaller and lighter having the same force available.

On fig.5 you see a mothership with 6 smaller sails thought for sample prospecting. The mother ship is for space usage only, it has to transport the prospector sails to asteroids letting all of them or only one ore two off at the first place of action. Letting a smaller sail off would happen through tourning the mother sails backside (were the payload would be located) to sun. The sun pressure would push the sails away. Since the mother sail with itīs lower specific weight and bigger sail area would accelerate faster than the smaller prospectors it could be possible to separate without using the thrusters. The mothershipīs size is 135 m diameter, - about 14320 square metres sail area. The four smallest of the daughter sails in the example would be 30 m (100 ft) diameter - about 707 square metres sail area. I did chose this size because it is about the same as the size of Cosmos 1 the first solar sail hopefully getting into space and showing that solar sailing is feasible.

If Cosmos 1 would be able to prove the feasibility of solar sailing, perhaps even sailing out of earthīs gravity well, than my prospector crafts which feature also ion thrusters besides sail propulsion would be able to navigate near earth as well, even with some more payload when getting back from their asteroid missions. When the prospectors have drilled their samples they could get off the asteroid with the help of their ion thrusters and accelerate with suns light pressure pushing the sail with high force. So they would not need to accelerate that long because at the end of the journey a longer deceleration phase is needed because of the weaker sailing force near earth. But perhaps some gravity assists from moon or earth could help with the deceleration task also.

Near earth the prospectors could deliver their samples to the ISS or some other sort of space station or landing on earth using the sail as a parachute. How could the rather "flimsy" sail serve as a parachute? Since those prospectors would need only to return of a location with very high light pressure it would be possible to use strong enough sail cloth for parachuting. The added weight should be no problem in this case.

So, is this a feasible task? What would YOU think.
I do appreciate any commentaries on this subject. Thank you. Frank And here are some links for robotic sample returns from the moon which has be done the first time in 1970.

Taking samples, the first step to space mining operations

"The drill was deployed and penetrated to a depth of 35 cm before encountering hard rock or large fragments of rock. The column of regolith in the drill tube was then transferred to the soil sample container. After 26 hours and 25 minutes on the lunar surface, the ascent stage, with the hermetically sealed soil sample container, lifted off from the Moon carrying 101 grams of collected material...".