PRISMS Secondary School Student Builds a Sun Sensor

The Princeton International School of Mathematics and Science is a private secondary school in Princeton New Jersey.

http://www.prismsus.org

One of their students, Savva Morozov, undertook a project to build a miniature 2-axis sun sensor for a CubeSat. Here is his blog post!

My name is Savva, I’m a senior at Princeton Int’l School of Math & Science. This summer I designed, built and tested a 2-axis solar tracking sensor for Princeton Satellite Systems.

The sensor can determine the relative position of the sun using a set of photodiodes. Bearing in mind that the solar sensor would be used in vacuum environment, I decided to make the sensor out of printed circuit boards (PCBs) and solder them to each other. Originally, I wanted to 3D print the sensor, but shifted to the PCB solution to eliminate the risk of outgassing.

Picture 1: solar tracking sensor, 2nd prototype.

My solar sensor design resembles the shape of a square-based pyramid that is approximately the size of a quarter. It consists of 5 PCBs: 4 sides and a base to which the sides are attached. Each side contains a photodiode, and by measuring the voltage outputs from at least 2 of the diodes, the device can determine the sunlight’s direction.

One of the initial problems I encountered was the handling and attachment of the photocells to the side PCBs. Each cell came with an anode and cathode wires already soldered to its front and back. I desoldered the cathode wire from every cell and affixed them to the PCB using a space grade silver conductive epoxy. This way I attached the cell to the device and grounded its cathode at the same time. I thought I killed two birds with one stone, but instead I killed two photodiodes: they were damaged in the soldering process. I resolved the issue in the second prototype: I threaded the cathode wire into a hole in a side PCB and then glued the diode to that same board. This way I didn’t have to use soldering iron at all, preventing possible risks. I then connected the cathode of every photodiode to a common ground and outputted the voltage readings from each cell in a single data bus.

Picture 2: Solar sensor, 2nd prototype, quarter for scale.

The diode, being attached to the outer side of the satellite, might be exposed to light that is reflected off the Earth or satellite surfaces. To partially prevent this, I soldered a shield to the edge of the sensor. Each surface of the shield would be covered with non-reflective material to further decrease the amount of ambient light.

To protect the diodes from the impacts of micrometeoroids and other space debris, I plan to cover the diodes with a thin shield of hard glass crystalline window (tempered glass or sapphire).

Testing the first prototype indicated a number of drawbacks that were solved in the second. Such problems are attaching the shield and the cells to the device, decreasing sensor’s size while increasing its aperture, and making the assembly process simpler.

I also calibrated photocell’s voltage outputs and their exact positions to account for manufacturing imperfections and for those created during the manual assembly of the device. I wrote a program to calculate the vector of sunlight direction and using Processing IDE created a visual representation of my sensor as well as its output result:

Picture 3: Visual illustration of a working solar sensor.

In order for my sensor to survive the vacuum environment, I attempted to use only space qualified materials in the device’s assembly: PCBs, solder, epoxy, and sheets of copper. I have finished working on the development stage of designing the solar sensor. Testing procedures on my last prototype showed that such device would be ready for further usage and launch.

AIAA Space Forum paper on Pluto mission is live

Sadly, the AIAA Space Forum in Orlando, FL was canceled due to hurricane Irma. So, we didn’t get to present our paper on our DFD mission to Pluto. AIAA has, however, published all the forum papers and is providing free access for a few months in lieu of the actual conference. This means anyone can download it!

Fusion-Enabled Pluto Orbiter and Lander paper:
https://arc.aiaa.org/doi/abs/10.2514/6.2017-5276

Open access to the AIAA Space Forum technical program:
https://arc.aiaa.org/doi/book/10.2514/MSPACE17

Enjoy!

Sun Sensor Design Project

Hello!

My name is Anna Cruz and I am Mechanical Engineering major and rising sophomore at The College of New Jersey (TCNJ). This summer I was given the opportunity to work at Princeton Satellite Systems (PSS) as their engineering intern. The most recent project I have been working on is the mechanical design and 3D model of the sun sensor that will be made using a 3D printer. All the models I have created were done using SolidWorks. I have been working alongside my coworker Gary, and manager of the project Mike that have done a wonderful job in giving me helpful tips when I needed it the most.

Figure 1.1

This sun sensor will fly on a CubeSat or small spacecraft in low earth orbit. The main body of the sensor has a pyramid shape with a solar cell on each side. I had already been given a drawing and STEP file of the circuit board that will be attached to the sun sensor so the dimensions for the sensor I am making were based on that single part. To start, I did some research on different sun sensor models to get a sense of how they work. I first needed to figure out how these parts would be assembled. To make it simple, I decided to use 4 screws on each corner to attach the sensor to the circuit board. The base is rectangular with dimensions a bit larger than the circuit board to allow space for the screw clearance holes and room for the screw head as shown in figure 1.1.

Then it was time to design the pyramid itself. I created a pyramid with a flat top and placed it at the center leaving space from each edge of the pyramid to the edge of the rectangular base adjusting the dimensions as needed. The pyramid holds one solar cell on each side. To make sure that the cells fit nice and snug, I added a placeholder feature deep enough to hold the chip. However, after discovering that the solar cell did not have a flat surface and that there was a wire attached to the back and front of the chip, my original design had to change completely! After a few days of trying out new designs and working with Gary to find the best solution, we liked the idea of creating a trench like feature in the middle of the placeholder extruding a bit further into the pyramid. This will accommodate the wire from the back of the solar cell as well as increase the tolerance regarding the location of the wire for each chip. As for the wire coming out the front of the chip, I added a rectangular slot feature next to the placeholder which channels all the way down the pyramid shown in figure 1.2. This will help gather and guide both wires all the way down one channel to the circuit board. There is one channel on each side of the pyramid, a total of 4. Aside from these hollow channels, the entire pyramid is a solid piece.

Figure 1.2

The placeholder for the solar cell is deep enough so that nothing sticks out of the pyramidal faces. This will aid in the application of the glass window on top of each solar cell using a space qualified adhesive. The same adhesive will be used to attach the solar cells to their placeholders.

Because the sun sensor is attached to a spacecraft, there is a high change of reflective light bouncing off the spacecraft and onto the sensors. To prevent this, a lip feature around the pyramid needed to be added. I went along and added an extruded frame like feature surrounding the pyramid leaving a gap between the end of the frame and the end of the pyramid. The outside edge of this feature is perpendicular to the base surface. The inside edge is at about a 50 degree angle from the base surface as shown in the section view in figure 1.3.

Figure 1.3

Since this sun sensor will be used in space, the plan is to do a vacuum test of this part. As of right now, I am currently waiting on the entire part to be printed so that it could be tested. I am very excited to see the final product!

WHYY Radio Story Featuring DFD

WHYY reporter Alan Yu has done a radio show featuring our work for The Pulse, which presents stories of health, science, and innovation. You can read the article and listen to a podcast of the show segment, which features Stephanie, Mike, Sam, and members of the NASA NIAC program including director Jason Derleth, external council member Ariel Waldman, and NIAC fellow Phil Lubin.

http://www.newsworks.org/index.php/thepulse/item/105669-inside-the-nasa-program-that-makes-science-fiction-technology-real-

The headline for the show is, aptly, “Inside the NASA program that makes science fiction technology real.” Reporter Alan Yu visited the lab to see the PFRC in action during development of the show. The show played on the radio today, July 21, at 9 am and will repeat on Sunday at noon. Enjoy!

The 2017 Edition of Princeton Satellite Systems’ MATLAB Toolboxes is Now Available!

Version 2017.1 of Princeton Satellite Systems MATLAB toolbox suite is now available! Over 60 new functions were added and updates to dozens of existing functions were made to improve their performance and expand their applications.

In the Aircraft Control Toolbox we added an inlet loss function to compute losses due to shockwaves. Our Unscented Kalman Filter algorithm was updated.

We expanded our support for heliocentric missions. This includes functions to compute solar eclipses in heliocentric orbits, heliocentric sphere of influence, heliocentric trajectory plotting and thermal models for heliocentric spacecraft.

Several new component models were added for use with the CAD modeling functions. These included a liquid apogee Engine, curved tubes and triangular trusses.

We have added all new star identification functions. These are based on a pyramid star identification algorithm using four stars for a definitive match during lost-in-sky conditions. The algorithm provides reliable star identification with almost any star catalog and in any orientation. We have updated image processing algorithms for star centroid determination.

New attitude determination demos and algorithms were added for mixtures of different sensors, such as sun measurements, earth chords and magnetic field measurements. You can compare the performance of extended and Unscented Kalman Filters. A new second order guidance law was added for planetary and lunar landing that provides a simple and effective algorithm for landers.

Contact Princeton Satellite Systems or your distributor for more information!

Asteroid Day

June 30 is Asteroid Day. Asteroid Day is a reminder that we need to protect the Earth from asteroids. We need both an early warning system and a means for deflecting asteroids. The B612 Foundation is working on an early warning system. Direct Fusion Drive, a nuclear fusion rocket engine technology under development jointly by Princeton Satellite Systems and the Princeton Plasma Physics Laboratory could provide the means to deflect asteroids that are on a course to collide with the earth. We published a paper in October 2013 on how this might be done

Direct Fusion Drive Rocket for Asteroid Deflection [PDF], J. Mueller, Y. Razin, S. Cohen, A. Glasser, et al, 33rd International Electric Propulsion Conference.

Samuel Cohen, inventor of the Princeton Field Reversed Configuration reactor that is the core of our engine, co-authored a paper on comet deflection.

We are currently supported by a DOE grant, two NASA STTRs and a NASA Phase II NIAC grant! For more information go to our nuclear fusion page.

Foundations of Interstellar Studies Workshop

Dr. Sam Cohen and I had a good time at the Foundations of Interstellar Studies Workshop this week in NY! While we were only able to stay for the first day on “Energetic Reaction Engines”, there were many thoughtful discussions on applying fusion technology to interstellar travel. Here I am in the group photo from the welcome event Monday night, held at the Harvard Club with an interesting and wide-ranging display of interstellar art! (I’m in the first row on the far right).

Group photo

Group photo from Foundations of Interstellar Studies workshop

The workshop was almost a mini-NIAC reunion, as NIAC fellows Phil Lubin and Ray Sedwick were there, and Heidi Fern was due to present her Mach Effect thruster on Thursday. Also NIAC External Council member Lou Friedman of the Planetary Society was in attendance (very back of the photo).

Our presentation for this conference focused on how the PFRC addresses the key parameters needed for a “net positive” fusion reactor: energy confinement, current drive, plasma heating, and plasma stability. We are often asked “why fusion will work this time”, and this paper does a good job of explaining why the PFRC is different enough from other approaches to work! The workshop is going to submit all of the papers to the Journal of the British Interplanetary Society, which is the oldest astronautical journal in the world (1934).

We also discussed the parameters the propulsion system will need to achieve to reach Alpha Centauri in various time scales, as well as a more near-term mission deliver a gravitational lens telescope to 550 AU. Reaching Alpha Centauri in anything close to a human lifetime remains a significant challenge, but PFRC could be part of an architecture to reach the star in 300 to 500 years, and slow down enough to go into orbit around the potentially Earth-like planets there! The 550 AU telescope mission, however, could be achieved in as little as 12 years with just one small PFRC and is an exciting new mission possibility.

Our next interstellar appearance will be at the Tennessee Valley Interstellar Workshop in October in Huntsville, AL!

DFD paper accepted for Workshop of Interstellar Flight

Our paper “Direct Fusion Drive for Interstellar Exploration” has been accepted for the Workshop of Interstellar Flight that will be held at CUNY City Tech, 13-15 June 2017! The workshop is organized by the Institute for Interstellar Studies and City Tech’s Physics Department and Center for Theoretical Physics.

We will present the latest results from our NASA NIAC work on DFD design as well as applications to interstellar missions, including:

  • A mission to 550 AU to perform gravitational lensing imaging of exoplanets;
  • Flyby missions to the nearest star;
  • A mission to go into orbit about a planet orbiting either Alpha-Centauri A or Alpha-Centauri B.