Acronyms and Definitions
NH:SDC – New Horizons: Student Dust Counter
The Student Dust Counter is an instrument attached to the New Horizons spacecraft, built by students at the University of Colorado and designed to detect miniscule particles of dust in space.
AU – Astronomical Unit
The distance from the Sun to the Earth — the value that is most often used is 149,598,000 km.
For more precise calculations, you may use 149,597,870.691±0.030 km.
Hit
A ‘hit’ is defined as being a particle of dust detected by one of the 14 detector channels on the SDC.
Important!:
The sizes of the images of the planets and the sun are not exactly to scale.
SDC Diagram –> Click on a number to skip to its section of this help document.
1. Data display window.
The main feature of the interface is the two large data display windows. The type of data shown is specified by clicking one of the “view buttons”(9).
2. Y-axis zoom buttons.
The y-axis zoom buttons allow you to zoom in and out on the data currently loaded into the display windows, stretching the y-axis only. There is a limit to how far in or out the data can be zoomed.
3. Scroll arrows.
These arrows allow you to scroll the data in the display windows by a small amount if you click on the single arrow, or by a large amount if you click the double arrow.
4. X-axis zoom buttons.
The x-axis zoom buttons allow you to zoom in and out on the data currently loaded into the display windows, stretching the x-axis only. Like the y-axis zoom, there is a limit to how far in or out the data can be zoomed.
5. Help button.
The help button brings up this help document.
6. Calculate button.
After you enter 2 AU values in the “Low AU” and “High AU” fields, you can push the ‘calculate’ button to get 3 results:
The number of detected particle hits between the 2 given AU values,
the average mass in kilograms per particle between the 2 AU values,
and the average mass density in kilograms per meter cubed for the given span of distance.
When determining the amount of distance between the two specified AU values, the ‘calculate’ button only takes into account the distances over which the SDC was turned on.
7. On/Off indicator line.
This red line indicates the intervals (corresponding with the AU scale (11)) during which the SDC was turned off. If the red line is visible, this indicates that data was not being collected during that time, and vice versa.
8. Y-axis Scale.
The scale along the y-axis displays different units for each data type viewed:
Geography: Mass of dust particles, in kilograms, on a logarithmic scale.
# of Hits: Number of detected hits on a linear scale.
Hit Mass: Average mass of dust hits, in kilograms, on a logarithmic scale.
Density: Average mass density, in kilograms per meter cubed, on a logarithmic scale.
9. View buttons.
The 2 sets of view buttons correspond to the 2 windows. Clicking on any of these will display that data in the button’s respective window. You cannot have one kind of data appearing in both windows at once. The 4 different kinds of data are as follows:
Geography: The ‘geography’ view shows the physical location of each individual dust hit (marked by a single vertical line), as well as the location of the planets and the New Horizons spacecraft. This view makes it look like New Horizons is travelling in a straight line away from the Sun, but in reality it ventures along more of a spiral-shaped route.
The color of each hit corresponds to a different dust detector channel on the SDC (as shown below), and the length of the line corresponds to the hit’s mass in kilograms. When multiple hits are detected at once, several lines will be drawn on top of each other, making it appear that one line has several different colors (as in the rightmost line in the diagram below). The properties of each hit in these cases can be found by placing the mouse cursor over the different segments of the line. Many hits detected at once will also result in brigher lines. To create a look of symmetry, each hit is mirrored vertically along the botom of the y-axis scale, marked by a thin grey line going straight though the middle of the window.
# of Hits: This view displays the number of hits detected over given distance intervals.
Hit Mass: The ‘hit mass’ view shows the average mass (the total summed mass in kilograms of each hit divided by the number of hits) over given distance intervals.
Density: This option will show the mass density, in kilogams per meter cubed, over given distance intervals. This is calculated by dividing the summed mass by the surface area of the SDC, and dividing that result by the distance over which the hits were detected.
10. Crosshairs feedback.
These two lines of text display the x-axis and y-axis values of the current position of the crosshairs. The value of the x-axis is always distance from the sun (AUs), and the value of the y-axis differs by data type:
Geography: Individual hit mass in kilograms.
# of Hits: Number of dust hits per span of distance.
Hit Mass: Average mass, in kilograms per hit, of particles detected over a span of distance.
Density: Average hit density per span of distance, in kilograms per meter cubed.
11. AU scale.
The AU scale runs along the x-axis, displaying the distance from the sun in astronomical units.
12. Crosshairs.
When the cursor is placed over either of the display windows, it changes to the crosshairs. The crosshairs let you quickly compare data to the scales on the ‘x’ and ‘y’ axes though feedback given by the Crosshairs Feedback (10). Placing the crosshairs over data will pop up the Info Window (14), displaying information about the specific hit or averaged data the crosshairs are focused on.
13. ‘End of data’ line.
Information from the SDC gets sent back to Earth in periodic intervals to be decoded and processed into useful data. This dotted red line indicates the last point of data that has been sent back by the SDC.
14. Info Window.
When the crosshairs are placed over any data, the specific numbers are shown in this popup window. The units are as follows:
Mass: kilograms
Density: kilograms per meter cubed
15. The New Horizons spacecraft.
This image shows the current location in space of the New Horizons spacecraft.
