The International Space Station (ISS) is about to place a call. But not just any old ISS call. It’s going to be via X-rays: the first test of NASA’s newly developed X-ray communication system, called XCOM.
XCOM could revolutionise communications between Earth and far-flung spacecraft, being able to transfer gigabits per second. Think of how much data spacecraft like New Horizons or Juno could send! Or how much better it will be for astronauts on Mars to phone home! Or even enabling new kinds of communication outside the Solar System!
“We’ve waited a long time to demonstrate this capability,” said NASA Goddard engineer Jason Mitchell. “For some missions, XCOM may be an enabling technology due to the extreme distances where they must operate.”
Currently, Earth-space communications rely on radio waves. Both X-rays and radio waves are forms of electromagnetic radiation that travel at light-speed, but radio waves are easier to generate, and easier to modulate – that is, to encode signals on the waveform.
We probably don’t want to use them for Earth-based communications, since X-rays can’t be transmitted using wires, and high-energy radiation like X-rays flying around can be hazardous, but for space, it could be incredibly beneficial for a number of reasons.
X-rays have a much shorter wavelength than radio waves or infrared waves. This means that they should be able to transmit more data – a lot more data – than radio waves using the same amount of power, and to do so in a tightly focused beam.
They also aren’t subject to some of the limitations of radio waves. Space capsules returning to Earth, for instance, experience what is known as a re-entry blackout, when the heat of re-entry creates an envelope of plasma around the spacecraft, through which radio waves can’t penetrate.
This can last for several minutes, which as you can probably imagine is pretty tense for something as dicey as literally falling out of space. But X-rays can cut through this plasma sheath, allowing ground control to communicate with astronauts returning to Earth.
And, because it’s a new technology that has never been tried before, NASA’s engineers believe it could even have future applications no one has thought of yet.
NASA is going to test it by using several pieces of equipment. The NavCube GPS receiver was installed on the ISS last year. The Modulated X-ray Source (MXS), due to be sent up at the end of April, according to IEEE Spectrum, will be mounted on the outside of the space station and controlled by the NavCube.
It will generate rapid-fire X-ray pulses, switched on and off multiple times per second by the NavCube, to encode GPS-like signals on the waveforms. These will be sent to the modulated X-ray detectors on the Neutron-star Interior Composition Explorer (NICER) mounted 50 metres (165 feet) away.
If all goes well, future tests will be more ambitious, but for the first attempt, “[it’s] important that we transmit a known code we can identify to make sure NICER receives the signal precisely the way we sent it,” Mitchell said.
It will probably need a smidge more development from that point until it’s ready for use, but there’s no point developing it further until it’s been proven.
But then? Bring on interstellar communications!