Author Topic: Promise to reliable and economic space access: candidates of future propulsion tech  (Read 30823 times)

Offline IsaacKuo

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An orbital ring is just a string of satellites in LEO so it is easier in almost every respect to construct than say a space elevator.

My favorite concept starts off a little like this, except:

1) The satellites are single use.  Each satellite is a small ~1 gram solar sail about 30cm x 30cm.  They transfer momentum to the spacecraft almost by direct impact.  (Rather than directly hitting the spacecraft, they are vaporized by collision with the exhaust of a small cold gas thruster.  This converts the sail itself into a puff of gas, which can then be diverted by a bowl shaped pusher plate rather than causing an impact crater.)

2) The satellites are in solar orbit rather than Earth orbit.  They fly in a retrograde solar orbit, resulting in an impact velocity of 50+km/s.  The way the pusher plate works, this translates to a specific impulse of 100+km/s.

3) The satellites are solar sails, so they take a few years to spiral in/out from the sun and crank orbit inclination.  See, for example, Solar Sail Trajectory Optimization for Intercepting,
Impacting, and Deflecting Near-Earth Asteroids
for an explanation of how a solar sail would fly itself into a solar retrograde orbit.

The nice thing about this technology, which I call "solarkinetic pulse propulsion", is that the mass investment of the propellant is an order of magnitude less than the payload.  In order to boost a 10 ton suborbital spacecraft to Earth escape velocity, you only need 1 ton of sailbots.

This is why you don't need the sailbots to be reusable.  You get a lot of bang for your buck just from a single use!  For every ten missions, you can devote one or two to launching more batches of sailbots.

In contrast, space elevators and orbital rings and tethers require large infrastructure mass compared to the payload mass.  In order to be worth doing, they need to be heavily reusable and/or built using matter from somewhere other than Earth.  Neither of these will offer economic space access in the near future!  Either way, we're talking about a huge infrastructure investment.  You don't get cheap access to space if you need to spend oodles of gigabucks to start it up!

Solarkinetic pulse propulsion only requires an infrastructure investment of a tenth of the payload mass.  A one ton demonstrator mission would require only a hundred kilograms of sailbots (at 1 gram each, that's still an impressive batch of 100,000 sailbots).  A ten ton mission would require only 1 ton of sailbots.

(About the name--"solarkinetic pulse propulsion" is based on "nuclear pulse propulsion".  Nuclear pulse propulsion involves using high velocity pulses of plasma from nuclear bombs to push a pusher plate.  Solarkinetic pulse propulsion is much the same, except the pulses of plasma come from sailbots.  The individual pulses are puny compared to nuclear bombs, though, so it doesn't need extreme shock absorbers.)

Offline mlorrey

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Space elevators have to have their centers of gravity at GEO, and stretching far enough to reach earth means an insanely large amount of mass to put in orbit, which makes it impossible for at least the next century.


not really. A single space shuttle can launch a space elevator to its orbit.

well, not the entirety of it. Just a single strand. The proposal is to build the space elevator just like cable bridges are built. One strand, and then you use a machine that goes up and down that cable and with each pass, it adds other strand and the cable gets thicker and thicker.

This implies that a single strand can handle a load twice its own mass. Firstly, the single strand method wont cut it, because the tensile load at GEO is going to be MASSIVE. The cable has to be rather thick at GEO and taper as it goes out in either direction.
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Online RobLynn

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I still think the best solution is the rotating tether (bolo) launch method where a fast jet or rocket plane docks with a rotating tether in LEO.

The tether and  a large mass (asteroid ) can be made to keep up to speed by solar electro- magnetic means. 

The space craft releases at the top of  rotating tethers cycle and then can head off at twice orbital velocity.

I think this would make a great X-Prize

Entrants fly a trajectory that rendezvous with a non-existant simulated rotovator.  Prize based on minimum approach distance at precise time achieved on two consecutive launches by same launcher to eliminate flukes.  Measure using a suitable gps/inertial guidance system (or perhaps use earth based radar).

This is largely a control and thrust modulation problem, but set the delta V to a relevant 3-5km/s level to make it more challenging - and give some delta V growth from past and current prizes.
The glass is neither half full nor half empty, it's just twice as big as it needs to be.

Offline MikeAtkinson

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If the NOFBX fuel is as good as is claimed, then it would make 1st stages much simpler and cheaper. A stage would need only a single tank, no helium pressurant, simplified plumbing, no insulation and a simple engine (a reduction in parts count by a factor of 2 or more). A single, safe, non-toxic, non-cryogenic propellant would make pad operations easier.

My guess is that it would allow a reasonable SSTO (but making a cheap reusable SSTO would still be a big challenge) payload.

The most cost effective would probably be a TSTO with flyback 1st stage.

As a propellant it probably needs a few years yet of experience before it is ready for main propulsion applications.

thread:
http://forum.nasaspaceflight.com/index.php?topic=24352.0

AIAA presentation:
http://www.aiaa.org/pdf/industry/presentations/Greg_Mungas.pdf

Offline aceshigh

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Space elevators have to have their centers of gravity at GEO, and stretching far enough to reach earth means an insanely large amount of mass to put in orbit, which makes it impossible for at least the next century.


not really. A single space shuttle can launch a space elevator to its orbit.

well, not the entirety of it. Just a single strand. The proposal is to build the space elevator just like cable bridges are built. One strand, and then you use a machine that goes up and down that cable and with each pass, it adds other strand and the cable gets thicker and thicker.

This implies that a single strand can handle a load twice its own mass. Firstly, the single strand method wont cut it, because the tensile load at GEO is going to be MASSIVE. The cable has to be rather thick at GEO and taper as it goes out in either direction.

can a single strand of steel cable handle a load twice its own mass, when you build a cable bridge by the same method??

http://www.spaceward.org/elevator-feasibility

Offline mlorrey

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Space elevators have to have their centers of gravity at GEO, and stretching far enough to reach earth means an insanely large amount of mass to put in orbit, which makes it impossible for at least the next century.


not really. A single space shuttle can launch a space elevator to its orbit.

well, not the entirety of it. Just a single strand. The proposal is to build the space elevator just like cable bridges are built. One strand, and then you use a machine that goes up and down that cable and with each pass, it adds other strand and the cable gets thicker and thicker.

This implies that a single strand can handle a load twice its own mass. Firstly, the single strand method wont cut it, because the tensile load at GEO is going to be MASSIVE. The cable has to be rather thick at GEO and taper as it goes out in either direction.

can a single strand of steel cable handle a load twice its own mass, when you build a cable bridge by the same method??

http://www.spaceward.org/elevator-feasibility

We are talking a thread 46,000 miles long vs bridge cables that are a few miles long at most. The tensile strength of CNT's may be high, but not high enough for that sort of load. All Space elevator estimates of any seriousness to date have expected the cable to be tapered in thickness.

Another problem with elevator feasibility is that climber cars will travel so slowly that a single trip to GEO will take a couple weeks, so the space elevator will have the same lift capacity as a normal chemical rocket. You can't get enough power from solar panels to make a climber car go more than a few dozen miles per hour.
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Offline ANTIcarrot

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Another problem with elevator feasibility is that climber cars will travel so slowly that a single trip to GEO will take a couple weeks, so the space elevator will have the same lift capacity as a normal chemical rocket. You can't get enough power from solar panels to make a climber car go more than a few dozen miles per hour.

Then give it a reactor. If polywell works (if) then a small unshielded 'power car' could push/pull the cargo up and down. All you'd then need is a 'shunting engine' to get the polywell up to a few hundred meters high so it can turn on safely - and that can be done in any number of conventional ways.

Offline mlorrey

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Another problem with elevator feasibility is that climber cars will travel so slowly that a single trip to GEO will take a couple weeks, so the space elevator will have the same lift capacity as a normal chemical rocket. You can't get enough power from solar panels to make a climber car go more than a few dozen miles per hour.

Then give it a reactor. If polywell works (if) then a small unshielded 'power car' could push/pull the cargo up and down. All you'd then need is a 'shunting engine' to get the polywell up to a few hundred meters high so it can turn on safely - and that can be done in any number of conventional ways.

Doesn't matter. If you get beyond 100-200 mph, your climber gripper is going to be heating the carbon nanotube so much that it will cause the CNT to dissociate (in vacuum thats at about 2200F, in atmosphere thats only 750F). And imagine the snarl you will get when a bearing blows out...

Minimum trip time to GEO on an elevator is going to be 4 or more days, one way, unless you can figure out a way for the cable to carry a TON of electric current for the car to climb inductively with no physical contact.
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Founder, Lorrey Aerospace, B&T Holdings, ACE Exchange, and Hypersonic Systems. Currently I am a venture recruiter for Family Office Venture Capital.

Offline jiffylube84

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My canidate would be a blast from the past, Orion or Prometheus. To my knowledge nuclear explosions are the most powerful things man has created and we know a lot about how to build them. The biggest problem is fear, I have a big problem with people that would hamstring humanity because of the fear that we will blow ourselves up. Nuclear explosions have a place, just could we all stop building them to kill one another and maybe use them for some good like exploring our solar system. From this point on many new discoveries and powersources could be used to create very powerful weapons so should we not develope those power sources?

Offline pummuf

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First of all, whatever the solution it will require massive reductions in infrastructure, maintenance, servicing and personnel. You can't have economic space flight that relies on standing armies of thousands to run just the launch side of it. That will have to be one of the things this new propulsion technology gives.

Next, I think 'economic' can also be reliable. Some space agencies spend huge premiums for small gains in performance ... so go the other way with slightly lower performance when there is a large economic benefit. Shoot for reliability through simplicity when possible. Sacrifice a few points of performance when needed.

Reusable designs ... This is doable, just hasn't been done in a way that saves money and labor, yet.

An obvious first idea is flyback boosters. Look at glide back, power back, power ahead, and so on ... Can simple ramjets be incorporated into the wings for powered return, and to add some boost during favorable parts of the ascent? Can the flyback booster have a common core with latter stages of the launch system?  Sea recovery probably wouldn't save any money.

Idea two. The X-33 was to demonstrate concepts for SSTO, and the design got close but at massive expense. Can it be simplified and cost reduced, accepting a performance hit? And then can it be paired, belly to belly w/crossfeed, to make a TSTO - fully reusable? The two stages would be identical. On launch, the booster would have some extra fuel tanks and the final stage would carry the payload.

Idea three. Similar to the Pegasus system but with an autonomous, purpose built first stage. The carrier would go faster and higher, and it might attract additional funding as a test bed for airbreathing/hypersonic research. The mothercraft would be designed for minimal servicing between launches, as well as being autonomous. This fits nicely with solid stages that require minimal attention.

The space industry could take better advantage of new technology that's becoming commonplace and less costly - autonomous flight has been mentioned above, another is robotic manufacturing;

Robotic manufacturing used to be really expensive, and it's used for the filament winding of some solid boosters. But the price has come way down - many people build cnc equipment in their garages as a hobby, using discarded printers. I think there is an opportunity for a new space company to make solid stages less expensively than the current big US manufacturers. Some additional ideas; thermoplastic binders instead of thermosets (pvc has equitable performance to HTPB). This allows less manufacturing infrastructure because you can manufacture the propellant as ingots, a little at a time. Less capitol equipment needed. The ingots are easier to store and move. Then the grain can be injection molded as needed from those ingots. There's an opportunity here for smaller companies with less overhead using lower cost equipment. 

To improve space launch economics, the expensive things have to become much simpler, while cheap things should be relied on more; infrastructure, manpower, launch complexity and expensive designs for small performance gains have to be re-thought. Conversely, electronics, automated flight and automated manufacturing is becoming less expensive and should be used more. These can be mutually reinforcing.
« Last Edit: 04/12/2011 06:00 PM by pummuf »

Offline DLR

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I think that on the long run, if there's a desire to industrialize space (perhaps through the construction of space solar power satellites), very large, expendable, sea-launched boosters (Sea Dragon) would provide reasonable prices for the launch of large masses, if the launch rate is sufficiently high. I could see them working together with smaller reusable boosters (K1, Skylon, etc. ...) for high-value cargo and people.

Now this requires solving the chicken and egg problem of cheap access to space. Without payloads you're not going to get large expendable rockets mass produced and without cheap, mass-produced expendable rockets you won't get payloads. Also the cost of payloads has to come down. No wonder a launch is expensive when you're launching a unique multi-million or multi-billion dollar satellite or space probe. In that case, a launch failure is not an option. If you launch a constellation of identical satellites which are produced on some form of assembly line, a certain risk of launch failure may be tolerable.

Reducing the cost of space access is not an engineering issue, but a political and economic question.
« Last Edit: 04/14/2011 12:13 PM by DLR »

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