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Archive for the ‘General’ Category

Going to Small Sat

Tomorrow begins the Small Sat conference in Logan Utah. It is 6 days immersed in space science, technology, policy, and inspiration. The format looks to be a new presentation every 15 minutes! Of special interest is a presentation about in-orbit thrust measurements on the CanX-2 satellite. It will be interesting to see how their technique compares to the FRETS1 spin technique. There are also several presentations on high voltage for pulsed plasma thrusters. Since FRETS1 uses elements of a pulsed plasma thruster to make its plasma, these should be very useful sessions. Watch for tweets (@iondragonfly) during the conference.

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The engine used by the FRETS1 satellite is patent pending and has been 3D printed! The patent is pending in the US and was filed under the older first-to-invent rules. Because it is not yet an international patent, images and descriptions will be limited to those that don’t reveal enough information to reproduce the engine. Perhaps a future post will expound on how the US ITAR law prevents me from disclosing this information anyway.

Onto something more fun: 3D printing. The engine is pretty small and requires some interesting interior detail for experimentation. Things like embedded wires, high voltage guards, mounting holes, and sockets for sensors are all required. And it all has to be made from a good strong dielectric that can withstand the electric field stress required for the engine to be useful. Acrylic is my choice as it is plenty strong and still clear enough to see what is occurring within the chamber. The first plans were to laser cut pieces and use plastic cement to weld them together.

Then I found that TechShop offers 3D printing in acrylic and wax. In this process, voids are filled with wax, avoiding the use of supporting struts that would have to be cut away. Instead, the part is placed in hot oil and the wax drains away. Some of our wire slots are 0.5 mm diameter and the wax didn’t fully drain. To get the wire into these slots, we heated a test wire and worked it in until the wax melted and pulled out.

Draft 1 of the engine is show below, near a US quarter coin for size comparison. There are plenty of mounting holes, wire slots, and holes for sensors. OpenSCAD was used to create the model. I must say it was quite nice to script an engine design.

3D printed acrylic

FRETS1’s ion engine – 3D printed acrylic

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Launch provider news

Our launch provider, Interorbital Systems, recently appeared on The Space Show. The podcast is here. (Rules say we can’t really transcribe it, so you’ll have to listen.)

Key news includes a change to the launch location, another upcoming engine test, options to do suborbital testing (including the prized ability to leave the launch rocket), modular rocket motors, rocket motor tradeoffs, and insider information about the politics of rocket building. A trivia question: How much does a launch license cost?

I am particularly intrigued by the idea of using a suborbital rocket to test the ion engine. A suborbital flight provides 10-15 minutes of microgravity in outer space, which should be plenty to do testing without the hassle of power conservation needed for longer, solar-powered missions. All other providers I’ve seen will not eject payload, meaning we couldn’t test the effectiveness of an engine. Sure, we won’t get the engine back, but maybe we could turn that into a feature, learning limits for the longer orbital mission by running the engine destructively.

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Our presentation with mission details is now on SlideShare at:

http://www.slideshare.net/wes_faler/frets1-satellite

Interorbital, our launch provider, is hard at work on their launch vehicle.  They had a very successful test of their new rocket motor and posted a video on YouTube:

http://www.youtube.com/watch?v=It-Q-lhDlbg&feature=youtu.be

and a nice high-res photo of the burn:

http://www.interorbital.com/Main%20Engine%20Test%20Photo%20Large_1.htm

We’re preparing for the upcoming Tampa Mini-Maker Faire in March, 2013.  I’m quite anxious to meet my new maker neighbors!

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Elevator Pitch

Imagine you find yourself in an elevator with someone you know has the money and time to help start your new business.  You’ve only seconds to make your pitch, hoping to pique their interest enough to get a real presentation opportunity.  This is the “elevator pitch” concept.  People spend months refining their speeches and there are even high value competitions for these short bits of business-poetry.  What follows isn’t really poetry or even short, but was meant to start that journey.  Hopefully it will help explain our project.

Short Description
We’re build and flying a TubeSat-style satellite to test new effects on ion engine performance and power requirements.

Introduction
Ion engines are fantastically fuel efficient but their thrust is too low for general use.  By finding ways to increase thrust and lower power consumption, ion engines can be used for more mission profiles.  This is especially important when fueling a craft from expensive local resources such as on a lunar base.

Three new effects on ion engine performance will be tested by FRETS1 – my TubeSat-style satellite flying in early 2012.

The experiment tests three techniques:  one to increase thrust density beyond the traditional Child-Langmuir limit, another to reduce plasma formation power requirements, and one to reduce exhaust neutralization power requirements.

Supporting the experiment is an adaptive machine learning algorithm that maximizes the impact of the effects and adjusts alignment of internal parts to compensate for thermal effects and unwanted internal ablation.

A few details
Extracting charge from a plasma is governed by space-charge limits. In a low density plasma, the limit is described by the Child-Langmuir law:

where:

  • j is the current density (A/m^2)
  • e0 is the permittivity of free space (F/m)
  • e is the charge of a single electron or singly charged ion (C)
  • M is the mass of a single charge carrying electron or ion (kg)
  • V is the voltage drop across the extraction region (Volts)
  • d is the distance across the extraction region (m)

An ion engine’s Isp is also set by its voltage:

where:

  • Isp is the specific impulse (seconds)
  • v is the exhaust velocity (m/s)
  • g is earth gravitational acceleration (9.81 m/s/s)
  • e is the charge of a single electron or singly charged ion (C)
  • M is the mass of a single charge carrying electron or ion (kg)
  • V is the voltage drop across the extraction region (Volts)

Work by others on laser/plasma fusion has shed light on how to decouple these, raising the current density, and therefore the thrust density, without altering Isp.  Researchers have shown 1,000x the Child-Langmuir flow rates in lab conditions.

Adapting this work to ion propulsion and scaling it to realistic power requirements is a goal of this project.

Project Steps
The major steps needed, some of which are already well underway, are:

  • Initial concepts
  • Project feasibility
  • Market feasibility
  • R&D of Effects and Systems
  • 2 near-space balloon launches to test equipment
  • Flight and Ground operations

Challenges Ahead
Power and mass.  Both are extremely limited on the TubeSat platform.  Mission obstacles stem from these two:

  • High power is needed to affect the engine’s plasma.  TubeSats have extremely little power available.  Possible solution: rapid discharge capacitors to produce pulses.
  • Holding mechanical alignment over temperature extremes and launch vibration could require massive supports.  Possible solution: piezo-electric positioning tied to the core learning algorithm.
  • Fuel consists of compressed gas.  Managing the flow of the expanding gas requires massive parts.  Lowering the gas pressure makes the issue easier but reduces the amount of fuel available.  Further research is needed, likely by continuing work with the model engineering community, especially those building working miniature steam engines.

More Help Needed
Advice and information is needed in at least these areas:

  • Market information on forecasted use of low thrust engines.
  • Thrust stand design.
  • Financial sources for a second, larger version.
  • Vibration dampening and testing.
  • Resources for micro-machining of gas flow channels.
  • Data on response of various sensors in the LEO environment.

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Hello world!

What is it?
FRETS1 is a TubeSat-style picosatellite provided by and launched by Interorbital Systems. It will orbit the Earth at 310 kilometers in a sun-synchronous polar orbit. Its primary mission is to test a new kind of ion engine.

Who’s doing this project?
FRETS1 is being funded by Fluid & Reason, LLC. Thus the name: Fluid & Reason Engine Test Satellite 1.
Working on the project are Wes Faler, Don Smith, Ed Campbell, and anyone else with something to contribute.
Special thanks go to the Part Time Scientists GLXP team for their to-be-announced contributions and to Alex “Sandy” Antunes at Project Calliope for paving the way.

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