Background Information
- Space exploration would be much easier if spacecraft could pinpoint their location
- This can be done similarly to GPS systems on earth
- Instead of GPS satellites, pulsar stars are used
- The X-rays emitted by these pulsars must be detected
- The detection of X-rays is therefore an important technology to improve
- In addition, the transmission of data via X-rays is important to allow spacecraft-to-spacecraft communications, for further aid in space navigation
- Long-distance, light-speed, digital communication is made possible on earth via fiber optic cables; in space, it is made possible by X-ray or laser transmission
- We are helping design a digital X-ray transmission system with bitrates of up to 100 Mb/s (that’s probably faster than your Internet connection, but slower than your USB cable)
Our mentor, Dr. Keith Gendreau, has developed a Modulated X-ray Source (MXS) that allows him to modulate, transmit, and detect X-rays. X-ray communication is the "outer-space equivalent" of fiber optic cables on earth, making long-distance, high-speed digital communication possible. Technological advancements in x-ray communication could lead to interstellar X-ray navigation, communications with spacecraft reentering the atmosphere during the "blackout" period, and secure interplanetary communication.
Dr. Gendreau has successfully used the MXS to transmit audio through analog X-ray communication. In the current setup, he connects an MP3 player to the MXS, which transmits a signal via X-ray to a speaker on the receiver end. When he plays a song on the MP3 player, the music plays through the speaker after it was transmitted by the MXS. Originally, he suggested that our team attempt to transmit digital video over the MXS using a USB webcam, but we concluded that it would be too much of a challenge for a summer project. Therefore, our current task is to improve that demo by transmitting data digitally in the hopes of future work improving this demonstration to transmit video.
The Modulated X-ray Source (MXS)
This diagram to the right depicts a high-level overview of how the MXS works. The ultraviolet LED shines onto a photocathode, which emits electrons due to the photoelectric effect. The electrons then travel through the electron multiplier, which increases the number of electrons by several orders of magnitude. The electron target produces X-rays when the electrons hit it.
We modulate the LED to modulate the electrons and thus the X-rays. The output of the X-ray detector shows voltage jumps that correspond to the "on" times for the LED.
Displayed below is a picture of the physical MXS device that we have been using to test our system. Our team has been using a high voltage power supply to power the electron target and electron multiplier and a signal generator to drive the LED. We have been viewing the output signal of the detector on an oscilloscope.
