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Deep Space Hardware (MARS)

Posted by: rpspeck - Tue Mar 22, 2005 4:57 am
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Deep Space Hardware (MARS) 
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Post Re: Deep Space Hardware (MARS)   Posted on: Sat Dec 12, 2009 7:57 pm
Congrats! Took them long enough to give you a project too... Good luck moving into phase II!

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Post Re: Deep Space Hardware (MARS)   Posted on: Thu Dec 31, 2009 11:55 pm
As the last hours of the 200x decade are draining away, a review of private “Deep Space” efforts is useful. It doesn't seem to me so long ago that all the Y2K fear was being played out, with none of the anticipated effects. At about that time I began seriously considering the possibility of private missions to our Moon and to Mars. I began public communication about these possibilities soon thereafter.

I must admit to being disappointed by the progress made in the past 10 years. However, the foundation has been laid – in many areas – and even the next few years could see real progress.

The most notable, real achievement has been Reid Stowe's “Mars Analog” sea voyage. Since I am a proponent of small, solo or two person initial missions to Mars, and have argued that today's computer communications would make the experience radically different from 1900 era expeditions, Reid's efforts prove my point nicely.

Sailing out of sight of land, nonstop for a longer time than a slow Mars mission, he has needed no added provisions and not gone mad! He has sailed nonstop for 976 days on his homebuilt 70 foot schooner “Anne”. Apparently he plans to return to his home port just over three years after he embarked. His communications have been severely reduced since his spare laptop computer failed earlier this month, but he still has a satellite phone and the electronic tracking system is working flawlessly. (see http://www.1000days.net)

On the space front, SpaceX is nearing launch of the Falcon 9, which I know to be sufficient to place an ultralight, manned Mars mission in LEO, ready for departure. I will review the systems status and other issues relative to such missions in the next few weeks. But the overriding question remains:

Who is preparing to go? Who is seriously raising the $100 Million such a flight will take?


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Post Re: Deep Space Hardware (MARS)   Posted on: Sat Jan 02, 2010 10:57 pm
And perhaps more importantly, who is willing (and able without going insane) to put up with Apollo-style toilet arrangements for years on end? David Blaine?

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Post Re: Deep Space Hardware (MARS)   Posted on: Mon Jan 04, 2010 3:53 pm
We have been pretty busy for the last two years doing SBIR proposals. They are interesting and at least address the needs of customers who want something for use in space and actually have the money to pay for it! If you try it, keep in mind that the customer usually has something specific in mind – which may not be all that obvious in the solicitation. Try to figure it out, since “Innovative” suggests a wider range of possibilities than most customers are ready to consider. Also keep in mind that these are small projects, from the funding standpoint, and won't carry a radically new idea very far toward a usable product. (Skip new SSTO launcher proposals!) In fact, these customers have a LOT of experience with “New Ideas” which went nowhere!

For years the SBIR customers (particularly in the DOD) have been trying to encourage companies who are organized to actually develop and produce products, and discourage “SBIR Mills” which produce only concept paperwork, which sits in a file, or a “prototype” with no potential for production.

A history of producing customized products for DOD, Researchers and Industry shows that focus and often gives you “Modules” you can reuse as you address the new need. A proposal has a lot better chance if it shows real insight and preliminary “Phase Zero” (self funded) effort to rough in some of the ideas. Although the process is slow, encouraging “debrief” notes can produce a “Win” the next year since the outlined need will often not be satisfactorily filled for several years.

We are doing preliminary work (unfunded until the contracts are signed) on our NASA “Lunar Navigator” with encouraging results. The wide field optical systems we have evaluated look pretty good, and will reduce the number of camera modules we need to monitor the entire sky with the required resolution. This effort has also led to the recognition of both enhanced operating modes and terrestrial applications for the same basic system in “GPS Compromised and GPS Denied” environments.

Another of our proposed technology efforts has received promising reviews from DARPA. This involves application of our operational, magnetic propulsion and sensing system for use to assemble and maintain formations of small satellites. In addition to our self funded efforts to upgrade our magnetic demonstration systems, we are now programming a microprocessor to do the signal analysis required for 6DOF magnetic position sensing and handle the orbital dynamics of planning, and generating, the forces needed to optimize the position of member satellites in the formation. It looks like these computing systems will mass only 2 to 5 grams – allowing their use in the smallest satellites.

We have plenty of operational hardware to implement representative sensing and propulsive fields, but a full demonstration will require operation in a tiny orbital satellite cluster. We have roughed in plans for conversion of our lab hardware to a demonstrator that could be run in a “Zero Gee” aircraft flight, but even those flights will require moderate funding.


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Post Re: Deep Space Hardware (MARS)   Posted on: Fri Jan 08, 2010 4:51 pm
The Way Forward

Those who are passionate about spaceflight and deep space exploration – including the possibility of personally participating – should keep in mind that nothing related to NASA is relevant to those interests. I once thought NASA's thinking, about how they would use their money, was really important: then I realized that NASA has no money! NASA only has orders from Congress with the promise that money will be sent as those orders are obeyed. (There can and has been some fudging involving not quite doing what they are being paid to do, but that is all in the accounting “noise” .) What we see is the “NASA-Congressional Complex” at work. Congress-critters are not interested in your passions – they are interested in theirs. This NASA+Complex has done some really neat stuff, and will continue to do so. Options are being hashed out – once again – which could change that picture modestly. But the “NASA Congressional Complex” is firmly committed to low risk activities which will create a lot of Jobs along with good publicity. Affordable exploration in space doesn't fit into that picture!

NASA's public domain information does, however, show us how to do what we want to do. Their “Paths not Taken”, including low cost space hardware options, also underscore and affirm the “Affordable Expedition” plans I continue to discuss. The fantasy of “What we could do...”, combining NASA+Complex money with our ideas and priorities, will forever remain a fantasy! We will get into space, but look more like “Linus Rawlings” (mountain man in “How the West Was Won”), or – eventually – a wagon train on the Oregon Trail, than any of the technology in “Avatar”!

Since you can't walk to the Moon, the result will look more like the early days of aviation than the Old West. Early aviation depended on Advertising/Publicity (associated with Air shows and Races), Communications (associated with the Air Mail contracts), Science/Technology (associated with aerial reconnaissance for both civil and military use) and Adventure (epitomized by Barnstormer Rides). There was a great deal of synergism between these components. Details change with time (particularly when a whole century goes by), but basics don't change much.

The picture for entrepreneurial spaceflight will closely resemble the one outlined for aviation history, and have the same four components. The “Adventure” component is the focus for “Virgin Galactic”, although (with typical synergism) the potential for these flights to increase productivity in space related Science/Technology is being recognized. Advertising/Publicity was the key in both of the Lunar Lander competitions. But Synergism will kick in big time when the fourth components starts feeding $$ Cash $$ into this community. And that will come with ComSat maintenance and repair!

More than $5 Billion is “sent into space” each year with high value Communications Satellites and similar equipment. Assets totaling some $100 Billion are working in space to serve humans on Earth. The ability to repair and maintain failed and dying satellites will, in some cases, bring immediate returns. But more important is the “virtuous spiral” which will result from the Possibility of repair! If things can be fixed, a risky new technology – which promises to quadruple ComSat capability – becomes a viable corporate option. Significantly better cost/performance ratios always open up new markets, and that boosts production rates to bring down costs further. Synergism again. If a compact Astronaut/Technician can reach an ailing ComSat, and fix it with only $16 Million costs (something marginally possible today), someone is going to make a hansom profit!

This is not a one shot proposition. Once demonstrated as a possibility, funding and capabilities will grow steadily. But it is far more economical to access GEO ComSats from the Moon than from Earth. So if the traveler can keep His/Her Wife/Husband happy at Moon Base One, that will support the existence of this outpost.

The existence of profitable “GEO On Site Service” will of course fuel vastly greater ambitions for space Adventure, Advertising/Publicity and Science/Technology, and hammer the costs for Deep Space activities down in every category.

It is not too early to begin assembling the equipment required to get a compact Astronaut/Technician from LEO (delivered by a Falcon 1) to GEO and back. Since this idea is no mystery, it may already be too late, for a startup with no preliminary experience, to capture this market!


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Post Re: Deep Space Hardware (MARS)   Posted on: Sat Jan 09, 2010 9:49 pm
This seems kind of like nitpicking, but is Falcon 1's vibration environment gentle enough for a human to actually survive launch without injury? The Malaysian satellite they launched was delayed for a while because of vibration concerns - and an unmanned satellite should be able to tolerate a lot more than a person. Or was the whole point of that delay that they permanently fixed the problem? As I recall they custom made a vibe dampener for the satellite but it was payload specific.

Other than that, I agree wholeheartedly! GEO satellite repair is an important and currently nonexistent market. It would allow operators to keep their fleet modern much easier, and greatly simplify bus design, freeing up mass for larger payloads and reflectors.

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Post Re: Deep Space Hardware (MARS)   Posted on: Mon Jan 11, 2010 1:25 pm
I don't know the whole answer. There are vibration frequencies which are dangerous to humans, but a lot of damping can be accomplished in the astronaut's seat. Humans regularly tolerate shock that instrument designers wouldn't like. Consider a high speed trip down a rough dirt road! And I am not thinking of OSHA standards, but something that could be approach what a football player experiences, if necessary, or a power boat racer. The pay won't be as good as a top football player's, but more than most of us in the real world can expect to pull down!


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Post Re: Deep Space Hardware (MARS)   Posted on: Mon Jan 11, 2010 1:27 pm
Satellite Formations

The potential performance of satellite formations is not widely discussed because practical methods for assembling and maintaining these clusters have never been demonstrated. But clusters of small satellites promise to exceed the performance of massive satellites at far lower costs!

For both Solar Power generation and RF Antenna performance, the area covered is the primary consideration. A 100 kg bundle of 1 kg satellites (totaling 1/10 the LEO payload of the Falcon 1), with simple foldout solar panels on each, could actually generate over 10,000 Watts of Solar power when dispersed in orbit. When cooperating as an Active Electronically Scanned Array (AESA), one form of Phased Array Antenna for Radio Frequency (RF) communication, this cluster could equal a 6 meter diameter antenna: One far too big to fly in the Space Shuttle!

With the cumulative power available, and the narrow focus of this power on Earth's surface (possibly a 30 meter diameter spot) awesome signal strength is possible! Practical applications would use the AESA system's ability to split the power, and send independent signals simultaneously focused on up to 100 customer's receivers. One Hundred Megabaud communication becomes possible for each subscriber, in even the most remote places on this planet, with modest ground equipment.

Other satellite formations will produce extreme resolution, overhead Synthetic Aperture Radar imagery, and even higher resolution interferometric data to locate objects on the surface. These estimates will not of course be reached in the first test versions, but they can be reached and exceeded. On top of this, individual satellites in the formation can be replaced, by maneuvering a failed unit out and an new one into its place. The entire formation can also be expanded by adding hundreds of new satellite members to support additional customers and enhance the overall performance.

I won't try to cram more about the vast possibilities into this message. But what is frustrating is that I have been trying to find funding (to show that our technology can make all this work) for over ten years without success. As noted, we at last have tentative (but far from firm) interest from DARPA.


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Post Re: Deep Space Hardware (MARS)   Posted on: Sat Jan 16, 2010 8:25 pm
The Way Forward - 2

Granting the real possibility of delivering a Solo, Deep Space Vehicle to LEO with a “Falcon-1” launch vehicle, the “Way Forward” is much simpler than might be assumed. The payload of the “Falcon-1e”, at 1000kg, is sufficient to carry a typical astronaut, with his/her life support equipment and a lightweight reentry system, not only to GEO altitude, but also around the Moon and back to Earth! The third stage propulsion can be produced using motors and propellant tanks Micro-Space already has in stock. Other entrepreneurs have also demonstrated adequate motors for “Trans Lunar Injection”, some using the storable fuels preferred. But the extra orbital angular momentum required to Rendezvous with a satellite in GEO makes getting there harder than a loop around the Moon. The return is also complicated, but Delta V for that leg can be reduced by passing around the Moon on the way back. Since, as with most everything in space, stage masses scale nearly linearly with Payload Mass, selecting a “compact astronaut” makes a GEO service mission feasible with the Falcon-1e.

Micro-Space and others have already demonstrated the lightweight life support equipment required. A number of adventurers have demonstrated comparable duration activities with similarly minimal “accommodations” and comparable risks, even without a multi million dollar $$$ bonus waiting at the end! The main technological barrier to launching tomorrow is the lack of a proven reentry system. Aerobraking into earth orbit, and rendezvous with a space station, is a possibility and can further reduce the vehicle mass flying above LEO, but that process has more risk and today would require coordination with space station owners who have shown no interest in cooperating!

Adequate reentry shield materials are easy to come by (the Chinese once used Oak wood successfully) but lab testing will be an unavoidable need. Entrepreneurs who have tried to use “National Labs” for tests have found that effort frustrating, very expensive and often unproductive. Entrepreneurial sources for appropriate testing are going to be necessary. Fortunately, such tests for reentry materials are not all that difficult to arrange – as I will detail next week – and could be offered by any entrepreneur who has produced a smooth running liquid fuel rocket motor of 200 to 500 pounds thrust, and has a good place to run static firing of that motor.


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Post Re: Deep Space Hardware (MARS)   Posted on: Thu Jan 28, 2010 11:27 pm
NASA Contract Real!

It is nice to see even a small dream realized! Our Funded NASA SBIR project: Automatic Solar and Celestial Navigation on the Moon and Mars‏ , is now covered by its official paperwork!

This effort taps decades of work we have done with high precision optical measurements and image analysis, and our work towards space applications of these technologies. Our professional products in this area use what we call an “Imaging Microphotometer” to emphasize the quality we obtain from each of the sensor Pixels. We have, however, managed to approximate this performance with more common, high resolution image sensors, including fraction of a gram mass sensor units.

The NASA work of course has direct application for both manned and unmanned exploration of the Moon, including our Google Lunar X PRIZE (GLXP) efforts. These sensors can verify the relocation required by the GLXP contest rules. Even more important, they will provide a very high resolution location for any and all interesting features found by one of our Lunar Rover/Prospector systems. (We have prototyped enhancements to the proposed NASA system which can push surface position accuracy to less than a meter!)

Some of our early comments noted that our “Stand Up” lander configuration can easily incorporate an automated core drilling system. Using just 3% of the landed mass as propellant, our unit can “Hop” and re-land with 500 meter displacement. (1% propellant allows 55 meter displacement.) Thus dozens of test holes can be analyzed in an interesting lunar field.

Related technology has already been evaluated for “Planetary/Star Cameras” to compute desired interplanetary and trans-lunar “mid course corrections” and guide Lunar and Planetary capture plus orbital insertion. A variant of that technology would be used for altitude determination before our prototyped LIDAR system began providing good Lunar Altitude information during descent.

We don't yet have a “Ticket to Orbit” (even for the 100 km mass in LEO we expect to use to win the Google Prize), but we have many of the pieces necessary to go the rest of the way!


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Post Re: Deep Space Hardware (MARS)   Posted on: Sat Feb 13, 2010 12:05 pm
Congratulations with the NASA Contract!

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Post Re: Deep Space Hardware (MARS)   Posted on: Sat Feb 13, 2010 5:19 pm
Lowest Mass Lunar Systems

It has been interesting to connect my closeup observation of “Jet Pack” fliers with my thoughts about Lunar Landings. (The “Rocket Man” was taking off just the other side of the fence from us at the “X PRIZE Cup event, 2006.) The roughly 22 seconds of flight available with a “Jet Pack” stretches to about 180 seconds on the Moon (at 1/6 G thrust, and assuming a 35% increase in ISP working into a vacuum.) What these skilled fliers do exceeded my expectations for what is humanly possible, in a difficult control environment! (Flying these is NOT EASY and involves a lot of cautious training!)

On the Moon, the control actions are effectively in slow motion, and much less demanding. The total energy and momentum involved do not, however, diminish and even greater caution is necessary. Good altitude and velocity measurements are highly desirable, since at the greater altitudes attainable, operation is less “instinctive”. Using ½ the fuel for lift off, vertical velocity can approach 150 meters per second, and reach 6,750 meters ( 22,000 feet) altitude or reach 13.5 km horizontal distance with optimally angled flight! (Both numbers are reduced by “gravity loss” with practical thrust values.) These calculations assume that ½ of the usable fuel is saved for landing (plus all of the normal 10% reserve for safety) since the 150 meter per second landing velocity represents a 1100 meter (3,300 foot) free fall on Earth, without the assistance of air drag!

But this is only the performance using the same “Jet Pack”! A practical limitation on Earth, is the mass of the unit strapped onto a flier's back. The standard system masses 50 to 60 pounds with full fuel. This reduces to 10 pounds weight on the Moon, added to the flier's 30 pound lunar weight. Keeping in mind that the flier's legs are not able to absorb much more momentum or energy on the Moon, with care, a user can handle much greater total backpack mass. A modest increase in fuel ISP can also be arranged, since 90% Hydrogen Peroxide monopropellant is far from the best obtainable storable propellant. Doubling the Delta V available quadruples the obtainable altitude and distance, giving 54 km distance for a single hop. The back pack could still “weigh” only 15 pounds (90 pounds mass). Gone are thoughts of Lunar Explorers slowly plodding over the surface to return from from an excursion!

I have just begun visualizing how this could change lunar operations, so I won't pursue those thoughts now. But consider that lightweight systems with a fueled mass equal to the suited astronaut's (about 100 kg (220 pounds) added to his suited 100 kg (220 pounds)), could allow him to achieve orbit, and rendezvous personally with a lunar orbit habitat. The weight on his legs, preparing to take off, would still be only 33 kg (73 pounds)!

Keeping in mind the astronaut's need to manage two and a half times his normal mass (and the greater resulting inertia with every motion), it is obvious that a he could also land with that mass on his back. Again, noting the “Rocket Man's” ability to conduct precision landings on Earth with three times that weight on his legs (landing just after takeoff, with nearly full fuel still in his backpack) – and without the “slow motion” - factor of 2.45 increase in time available for each flight adjustment at 1/6 G - it is obvious that this would be a very practical way to get astronauts down onto the Moon with their full orbital return equipment strapped on.


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Post Re: Deep Space Hardware (MARS)   Posted on: Wed Feb 17, 2010 6:47 pm
Rockets Gain Traction

(Of course, Rockets don't need “Physical Traction” and that allows them to work in Real Space. But they certainly need Financial Traction in “Cypher-Space”.
( = $Mx10^6 -- $Nx10^9)!)

The announcement that Tulsa, Oklahoma will conduct an Air Show April 24, 2010, highlighted with demonstration flights by the “Rocket Racing League” is very good news! It shows that rocket operations are finally gathering some of the attention they deserve! Those who have attended Northrup Grumman, Lunar Lander Competitions know that Rockets are fun to watch. Monstrous flames, accompanied by roaring noise, have always been fun to watch (from a safe distance!). These features of rocket flights have been augmented in recent Rocket Racing developments. Gone is the nearly transparent flame produced by alcohol fuels. Now long bright flames will be standard – reminiscent of the enormous flame behind a Saturn-V Moon Rocket on takeoff! Except that John Carmack, of Armadillo Aerospace – who makes the Racers new Propulsion System – has developed a way to “seed” the combustion and produce bright Red and Green rocket flames to distinguish specific race competitors.

Oklahoma has had a large aerospace industry for a very long time, and would like to increase it. This state has multiple advantages over California – many of them spelled $$$. Oklahoma has already spent quite a bit promoting entrepreneurial space and rocket efforts. These include turning the old “Burns Flat” military airfield into a Spaceport. It was originally a military airbase, then – with its 13,503 foot long runway – it was a primary base for SAC (Strategic Air Command). Now, it is a licensed Spaceport! I imagine that Oklahoma is negotiating to bring the Rocket Racing League headquarters to their state , and is willing to cut better deals than Las Cruces, NM, which insisted on being paid the promised rent.

In any case, these long awaited Rocker Racer flights will be showing up, at last!


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Post Re: Deep Space Hardware (MARS)   Posted on: Sat Feb 27, 2010 12:52 am
RE-ENTRY-1

I repeatedly discuss entrepreneurial Human Space Expeditions. Obviously, a proven Earth return and Re-entry system will be required for these efforts. I have made the point that entrepreneurial rocket motor developments are not far from what is needed for these flights (if expedition mass and cost are minimized as they are for extreme terrestrial adventures). Adequate control systems have been flown. Communications and navigation is no longer a difficult problem. Similarly we have demonstrated that SCUBA + Mountaineering hardware can be adapted and upgraded for human Life Support in space. A variety of problems NASA publicizes are simply not significant compared to the risks serious explorers are regularly facing. The regulatory, launch license issue, has also been addressed, and will not be a barrier. The return and re-entry systems remain the biggest obstacle, but are not out of reach if an appropriate approach is taken.

An “appropriate” approach provides what is necessary – reasonably available and affordable – and does not waste time dreaming about concepts which are not ready to use. Pioneers on the Oregon and California Trails did not wait for “Reusable” transportation. Neither wagons nor their animal propulsion systems returned to make regular, multiple trips! Leave dreams of reusable spacecraft to another generation and keep in mind the ENORMOUS cost of completing a railroad to the Pacific so that Reusable Transportation to those territories was available. Focus instead on an older idea: when transportation is expensive, pack light and go anyway!

I will continue to discuss the achievable costs and opportunities which will open “Entrepreneurial Spaceflight” using lightweight versions of conventional rocket propulsion. But for the moment I want to focus on “Conventional” re-entry. That involves, of course, the ablative heat shield used in the Mercury, Gemini and Apollo. This technology has virtually never failed. Of course it is possible for design or manufacturing of a future unit to be so poor that fatal failure results. And there lies a significant problem and entrepreneurial opportunity.

I will review details of re-entry design later, and provide insights to help others understand the available literature. But as an overview: Hypersonic re-entry with a traditional (blunt) heat shield brings the relative gas flow to a standstill at some central point, the “Stagnation Point”. This produces a “Detached Shock” some distance ahead of the heat shield as the supersonic gas flow is forced to accommodate the obstruction by slowing down or stopping. Such shock waves, and the accompanying deceleration of the relative gas flow, always increases the gas density, pressure and temperature in that region. Behind the Detached Shock, the hot, compressed gas follows the laws of classic, subsonic aerodynamics! This includes the formation of a boundary layer, separating the solid surface from the relatively uniform bulk gas in the flow field around the heat shield.

At some distance from the Stagnation Point, the gas flowing over the heat shield usually accelerates again to supersonic flow, with modestly decreased density, pressure and temperature. But experimental data proves that the greatest thermal load on the heat shield occurs at or near the Stagnation Point, so for our purposes this may be the only point we need to understand.

In these discussions, it makes no difference if the gas is rapidly moving past a fixed object, or if an object is moving rapidly through a gas initially at rest: the local physics is identical. In either case a large force is exerted on the solid object, and a correspondingly large amount of energy (that force times the flow velocity) is deposited in the gas flow behind as heat. The heated gas flows “gradually” inward when it is past the body, but a moderate taper can keep the after body separated from this hot gas.

A much smaller amount of heat is conducted through the boundary layer to the walls of the re-entry vehicle! (Often less than 1% of the total heat generated by re-entry.) Typically, the boundary layer will average half the flowfield velocity and temperature, and only the heat transferred out of that small portion of the gas flow will reach the heat shield. (In other words: the Boundary Layer itself is the most important Heat Shield!) The boundary Layer does not have a sharp boundary on the outside, nor a uniform velocity or temperature inside. Rather, it has a velocity gradient running from zero at the re-entry body wall to a speed approaching that of the adjacent gas flow at its outside. Its velocity profile tends to retain its shape as its thickness changes.

The aerodynamic boundary layer grows on the surface of a sharp edged plate, parallel to the gas flow for minimum drag, with the square root of the distance from its leading edge (where the gas flow first encounters the surface). This is required by the nature of classical viscosity and basic momentum equations. (The surface drag force acting on the body is balanced by the momentum loss of decelerated gas as the boundary layer grows into the slipstream.) The same equations require that the boundary layer Have Uniform Thickness over the spherical leading portion of a body obstructing the gas flow (and producing a stopped flow, Stagnation Point). (In this case, the flow stream lines are squeezed closer to the body as the gas flow accelerates away from the Stagnation Point. Some of these stream lines cross into the fixed thickness boundary layer and that gas slows down. This produces the momentum loss required to balance the surface drag, as in the flat plane case.)

Both flow situations are characterized by defining Reynold's Number (Re) = (Rho*V*L/Mu), where Mu is the standard viscosity, Rho is the gas density, V is the gas flow velocity and L is a characteristic dimension. Re is a dimensionless parameter when quantities in appropriated units are inserted in the calculation. The boundary layer has a typical thickness of L/Sqrt(Re), although a multiple of this is used to identify the distance at which the local flow practically equals its velocity outside the boundary layer. In many situations, including practical re-entry vehicles, Re = Reynold's Number runs from 10,000 to 1,000,000 or more, so the boundary layer often is < 1% of the scale parameter (L). (A similar situation exists inside pipes and rocket motors, where L is the inside diameter. The rocket nozzle is the smallest diameter section, and has an increased velocity and Reynold's Number, so the boundary layer is thinnest there. This layer also limits the heat transfer to the throat material, but its thinned dimension allows the greatest heat transfer in that throat region.)

Over a spherical “nose”, L is the radius of curvature of that spherical surface. Thus making that radius larger increases the boundary layer thickness and decreases the heat flow through that layer! The limit of “large radius” is flat, but that face is not stable in subsonic or hypersonic gas flow. The curved surface produces stable re-entry aerodynamics if the center of gravity of the capsule is more or less enclosed within that curved surface. Aerodynamic stability, like the boundary layer properties discussed, may be dominated by subsonic gas flow in the region behind the hypersonic shock and can be modeled by something as simple as a dropped Styrofoam bowel or plate.

Note that while the critical portion of re-entry involves a modest range of velocities (entry speed to about ½ that speed), a very large range of gas densities is involved. Thus Reynolds Number (Re) has a large range during the process. As the gas density increases, Re increases linearly (normal viscosity Mu does not change much with gas pressure and density, but DOES change with gas temperature.) As the density increases (deeper in the atmosphere) Re increases exponentially, and the boundary layer (proportional to L/Sqrt(Re)) becomes thinner, allowing greater heat transfer. Eventually, the large form drag of the blunt capsule reduces the velocity enough so that the reduced stagnation gas temperature drops the heat transfer below its peak value. Eventually, the reduced velocity also reduces Re, allowing the boundary layer to grow somewhat.

If the heat shield radius (L) is increased, Re increases proportionally, but L/Sqrt(Re) still increases producing a thicker boundary layer with less heat transfer.

Note that a low mass reentry vehicle of conventional (Mercury Capsule) size, will decelerate higher in the atmosphere, where the air density is lower. This will produce a Lower Reynolds number when the heat transfer is greatest, a thicker boundary layer and less heat transfer. However, the Heat Transfer is a Larger Portion of the total kinetic energy of reentry, so the heating problem is somewhat worse. If reentry mass is decreased by a factor of 6.25, the heat transferred is reduced to 40% of that for the heavier unit, but this still represents 2.5 times the relative proportion. So heat shield mass will become a modestly larger percentage of the reentry mass.

To Be Continued...


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Post Re: Deep Space Hardware (MARS)   Posted on: Fri May 28, 2010 6:04 pm
As described in the news item, posted yesterday in the NEWS thread of this forum, a group of tiny Micro-Space satellites are manifested for flight to orbit, nominally October 29, 2010. This was a surprising opportunity, but one we welcomed. It would have been impossible to do anything at all with this opportunity without a lot of preliminary work on small rocket systems capable of use in space. But having done that work on "Faith" - in the belief that we would would find a way to use the results although no possibility for a funded flight to orbit was even on the horizon - we where able to jump at this opportunity in spite of its short time window and severe technical constraints.

The satellites involved are “½ Scale CubeSats”, called “Pocket Qubes” by professor Robert Twiggs, who is handling launch integration for a larger group of these satellites, just 2 inches on a side and massing no more than 120 grams. Functional independent satellites this size would be a significant accomplishment if they just beeped (like Sputnik 1), but that is no longer allowable or interesting. Since we have long been flying instrumented payloads in rockets this size and smaller (including a telemetry package flown in a ½ inch diameter rocket), we already had a supply of relevant technology.

In addition, this is a good way to showcase both our innovative technology and our ability to work on a mass scale that makes spaceflight affordable: Including flight to the Moon and Planets! This won't end skepticism about our projections for “Ultralight Spaceflight”, but it will ratchet up credibility among those who aren't hopeless skeptics!

I will supply more information in this forum, but of course this effort (in addition to our funded NASA project) is keeping us busy! :D


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