SunStation in Operation!

SunStation is in operation! The system produces a peak of 7.8 kW solar power. It has 14 kWh of lithium batteries. The SunStation electronics are shown below. The inverter is on the left. The batteries are in the cabinet on the right.

SunStation

The SunStation has a web interface. You can see that when this screen shot was made the SunStation was selling 5.1 kW back to the power company! The batteries are fully charged. Usage was very small. The house has a whole house ventilator that is drawing most of the power. The homeowners also own a Nissan Leaf and a Toyota Prius Plugin. The solar array is enough to fully recharge those cars and run the house electrical devices when the air conditioning is not on.

SunStationWebInterface

Unlike gasoline, diesel or natural gas systems SunStation provides power year round! There is no noise and no toxic emissions. SunStation has no moving parts and is zero maintenance. Solar power systems are eligible for Solar Renewable Energy Credits which are cash payments for having an operating solar power system. It is estimated that this system will bring in $3700/year revenue between selling power and SRECs.

SunStation Installed!

The first SunStation installation is done! This system includes 14 kWh of Valence lithium batteries and an Outback inverter. Unlike most other solar power systems, the solar panels will deliver power to the house with or without the grid active.

SunStationInstalled

An existing 3.8 kW array was augmented with the new Panasonic solar panels on the right. They are about the same size as the older Sharp panels but much more efficient. In the bottom picture you can see the Outback inverter. The cabinet on the lower right houses the Valence batteries. The system will power the entire house in an outage with the exception of the central air conditioning system.

Unlike gasoline, diesel or natural gas systems this system provides power year round! There is no noise and no toxic emissions. SunStation has no moving parts and is zero maintenance. Solar power systems are eligible for Solar Renewable Energy Credits too which are cash payments for having an operating solar power system so you save money two ways.

Check out our SunStation page for more information!

DFD for Europa Exploration

Europa-luna

The Galileo moons of the Jovian system are of great interest for future space exploration due to the belief that three of the four of the largest moons (Europa, Ganymede, and Callisto) contain water (in liquid and/or ice form). So far the eight spacecraft that have visited the vicinity of Jupiter are Pioneer 10 and 11, Voyager 1 and 2, Ulysses, Galileo, Cassini, and most recently New Horizons. NASA has ambitions to send another probe to further study Europa.

At Princeton Satellite Systems, in collaboration with Dr. Samuel Cohen at the Princeton Plasma Physics Laboratory, we’ve been working on the Direct Fusion Drive (DFD) engine, an advanced technology for space propulsion and power generation. Using the DFD, we have simulated two potential missions to Europa, an orbiter mission and a lander mission. The simulations were completed in MATLAB using functions contained within our Spacecraft Control Toolbox.

Continue reading

Adaptive Cruise Control

The automotive industry continues to incorporate advanced technology and control systems design into new vehicles. Features such as adaptive cruise control, lane keep assist, autonomous park assist, and adaptive lights are becoming more common in the automotive market. These exciting technologies greatly increase vehicle safety!

Adaptive cruise controls measure the distance and speed of nearby vehicles and adjust the speed of the vehicle with the cruise control to maintain safe following distances. Typically a system will use a radar that measures range, range rate and azimuth to vehicles in its field of view.

A typical situation is shown below. The car with adaptive cruise control is traveling near three additional vehicles. Two cars have been tracked for awhile but a third is passing and plans to insert itself into the space between the tracking car and one of the tracked cars. How does the cruise control keep the three cars straight?

MHTAuto

Every measurement has uncertainty. The following drawing shows the uncertainty ellipsoids for the three vehicles. As you can see they overlap so a measurement could be associated with more than one car.

UncertaintyEllipsoids

The Princeton Satellite Systems Target Tracking Module for MATLAB implements track oriented Multiple Hypothesis Testing (MHT). MHT is a Bayesian method for reliably associating measurements with tracks. The system is shown below:

MHTSystemSimplified

The system includes a powerful track pruning algorithm that eliminates the need for ad-hoc track pruning. Without track pruning the number of tracks maintained would grow exponentially. The system generates hypotheses that are collections of tracks that are consistent, that is the tracks do not share any measurements. Measurements are incorporated into tracks and tracks are propagated using Kalman Filters. The MHT system also can handle multiple sensors for automobiles with cameras and radar.

Check out what all our MATLAB toolboxes have to offer!
Core Control Toolbox
Aircraft Control Toolbox
CubeSat Toolbox
Spacecraft Control Toolbox

6U CubeSat to Mars

We’ve been working on Asteroid Prospector, a 6U CubeSat to explore Near Earth Objects, for the past two years. It is quite a challenge to pack all the hardware into a 6U frame. Here is our latest design:

APExploded

CAD

The nadir face has both an Optical Navigation System camera and a JPL designed robot arm. The arm is used to grapple the asteroid and get samples. The camera is used both for interplanetary navigation and close maneuvering near the asteroid.

Our fuel load only allows for one way missions but could be increased for sample return missions by adding another xenon tank, making it more of a 12U CubeSat. With that in mind, we wondered if we could do a Mars orbital mission with our 6U. It turns out it is possible! We would start in a GPS orbit, carried there by one of the many GPS launches. The spacecraft would spiral out of Earth orbit and perform a Hohmann transfer to Mars. Even though we are using a low-thrust ion engine, the burn duration is a small fraction of the Hohmann ellipse time making a Hohmann transfer a good approximation. We then spiral into Mars orbit for the science mission as seen in a VisualCommander simulation.

SimSummary

The low cost of the 6U mission makes it possible to send several spacecraft to Mars, each with its own instrument. This has the added benefit of reducing program risk as the loss of one spacecraft would not end the mission. Many challenges remain, including making the electronics sufficiently radiation hard for the interplanetary and Mars orbit environments. The lifetime of the mechanical components, such as reaction wheels, must also be long enough to last for the duration of the mission.

We’ll keep you posted in future blogs on our progress! Stay tuned!

Space Rapid Transit – Landing Gear Design

Hello everyone, I am an MIT extern here at Princeton Satellite http://dailyhealthymale.com Systems through MIT’s Externship Program. Over the past three weeks, I have been able to play a part in and help out with a number of assignments. The most recent assignment is what I will be detailing in this post.

One of the projects PSS is working on is Space Rapid Transit, a two-stage-to-orbit launch vehicle with horizontal takeoff (think space vehicle that can “launch” like an airplane).  I was given the task of designing the nose landing gear, and in particular figuring out what type of linear electric actuator should be used to handle the load of retracting the landing gear.  Here is a preliminary design drawing I sketched to conceptualize the task.

prelimdesign

In order to find a solution, I first needed to make a few design assumptions.  The first assumption was that the landing gear would retract toward the nose (which is a reasonable assumption because it allows more space behind the landing gear).  Next, I chose to model the retraction under the assumption that the vehicle is undergoing a 2-g turn.  I then selected the strut and tire sizes and found the maximum speed and altitude at which operation of the landing gear is allowed, using the specifications of the Airbus A320 because of its similar takeoff mass.  I now had enough information to approximate the force on the linear actuator.  For this I made a simplified sketch, drawing the side and top view of the landing gear as it undergoes retraction.

LandingGear

Using the side view in the diagram above, I simplified the landing gear retraction into a torque balance problem, where all torques were evaluated about the fixed pivot.  I found the time it takes to retract the landing gear to be around 10 seconds and estimated a full sweep angle of the landing gear (from fully extended to fully retracted) to be 90 degrees.  Assuming constant angular acceleration, I was able to calculate this angular acceleration using the time and angle noted above.  I then calculated the distance of the center of mass of the wheel and strut configuration from the pivot as well as the moment of inertia.  After this I computed the drag force and gravitational force (from the 2-g turn) on the strut and wheels and computed how much torque each force would apply about the pivot.  Since the angular acceleration was so small that the resultant torque was negligible, the problem became a balance of the torque applied by the actuator with the torques resulting from air flow and the 2-g turn.

With this new found torque required from the actuator, I searched for linear electric actuators that could supply the force and stroke length.  The stroke length was approximated as the distance of the applied actuator force from the pivot.  As a result, I selected a Size 5 Moog Standard Linear Electric Actuator because it fit the design requirements.

 

Europa Report

Europa Report is a movie about a human mission to Europa, a moon of Jupiter, to explore the moon for signs of life. Europa has an oxygen atmosphere and a surface composed of water ice that has led to the hypothesis that there is an ocean under the ice.

Europa Report does a great job of being scientifically accurate. The spacecraft shown in the movie addresses the major issues that travelers would experience on a voyage to Jupiter. The crew section of the spacecraft is spun for artificial gravity and accommodations are made to deal with the high radiation environment around Jupiter.

Our Spacecraft Control Toolbox can be used to design the spacecraft and simulate every phase from Earth Orbit to Europa landing. We have a script for a powered Europa landing. Here are the results!

EuropaLanding

For more information about how you can design your space missions visit our Spacecraft Control Toolbox page!

Princeton Satellite Systems at the Princeton University Inventors Receptions

Gary Pajer and Mike Paluszek attended the

Princeton University Inventors Showcase:

We were invited because of our joint patent applications with Dr. Samuel Cohen of Princeton University, “METHOD TO PRODUCE HIGH SPECIFIC IMPULSE AND MODERATE THRUST FROM A FUSION-POWERED ROCKET ENGINE,” and “METHOD TO REDUCE NEUTRON PRODUCTION IN SMALL CLEAN FUSION REACTORS”.

The event, held Thursday, Nov. 21, at Chancellor Green Rotunda on the Princeton University campus, offered opportunities for University inventors to present their discoveries and meet leaders from industry and the venture capital community.

IR Imaging with the Spacecraft Control Toolbox

Many spacecraft are incorporating cameras, both visible and IR, to image other nearby objects. These may be other satellites or space debris. This blog entry shows how you can simulate imaging with the Spacecraft Control Toolbox.

In this simulation a target 1U CubeSat is illuminated by several sources of radiant flux and imaged by a camera located on a chase vehicle. The CubeSat panels have different optical and thermal properties. An exploded view is shown below. The surface properties are for radiators (black), solar panels (blue) and gold foil (yellow).

SatelliteBlog

The target is located in a circular orbit and the chase vehicle is in a similar but slightly eccentric orbit. A camera is mounted on the chase vehicle. The chase vehicle keeps its camera pointed at the target. Solar radiation, earth radiation, and earth albedo illuminate the target. The motion of the two vehicles is simulated for one revolution. The target spacecraft remains between approximately 75 m and 150 m from the chase vehicle.

RelativePos

As the target and chase vehicle move in their respective orbits, the change in temperature of the target CubeSat is simulated. Each of the 6 panels are composed of two triangles. The temperatures of the panels vary based on the thermal properties of each face and the orientation of the spacecraft. The orientation affects the incoming flux for each particular face.

Temp

Solar radiation is the dominant source over the course of the simulation but earth radiation and earth albedo also effect the total flux. The solar radiation, plotted in dark blue, clearly shows the times when the earth is blocking the line of sight from the spacecraft to the sun.

Flux

A photon detector model is assumed for the IR imaging device. The following flow chart describes the imager model.

FlowCharts

The initial output observed by the imager is shown below. It should be noted that for the particular orbit and orientation initial conditions specified, the z component of the relative position is always equal to zero. This means that only the x and y panels of the cube will be visible throughout the simulation. It is possible to specify different initial conditions that would result in a z relative position, and in this case, up to three faces of the cube can be detected.

DetectIm1

We have created a video that displays the imager results as a sequence.

IRImaging