# X-Band range and data

In summary I am working on a network consisting of 8 cubesat 1U that will be at an orbit altitude of 850Km. The question is that I am working on communications, the idea is that this network of cubesats transmit and receive to earth with UHF band, but that they also have a receiver and transmitter for X-Band to be able to receive and transmit to deep space.

Sorry for the basic image is that I wanted to explain myself better.

My question is, what power does the antenna have to have in order to reach Titan? Would you need a straight or dish antenna? I rely on the Cubesat MarCO, but I don't think it's the same antenna to reach Mars as it is to reach Saturn.

• To make an estimate of a communication range we need: 1) distance in wavelengths, 2) the size of the antennas at each ends in wavelengths, and 3) the effective temperature of the receiver's front end amplifier. We can use 20 C for the temperature and we know how far it is on average from Earth to Titan, so it's down to the sizes of two antennas divided by the typical X-band wavelength. Will the transmit and receive antennas be the same size?
– uhoh
Commented Mar 12, 2020 at 1:10

You want to use a X-band communication link from a cubesat in Earth orbit to another cubesat in orbit around Titan?

I don't think it is possible, at least at an acceptable data rate.

Lets compare this link to a deep space probe down to the DSN antennas in Goldstone, near Madrid and Canberra.

• Deep space probes use a transmitter with about 10 to 20 W power, a cubesat may use about 1 W or only 100 mW.
• The antenna dish of deep space probes is about 3 m diameter, a cubesat may use less than about 1 m.
• The DSN uses fairly large antennas on Earth, 34 and 70 m diameter.
• The DSN has very powerful transmitters, up to 20 kW and even 400 kW.
• The preamplifiers of the DSN antennas are low noise cooled with liquid helium.

If we compare a 1 m antenna dish to a large one with 34 m, we get -30 dB and -37 dB for the 70 m dish.

Comparing 20 kW to only 0.1 W is -53 dB, 400 kW to 0.1 W is -66 dB.

But when you want to receive very weak signals of about -100 to -120 dBm, you can't afford loses of -30 dB.

The distance from Earth to Saturn is about 8 to 11 AU (astronomical units) or about 1.2E9 to 1.6E9 km. If we assume for comparison a 1200 km distance of a cubesat to ground station on Earth, that is a free space loss of -120 dB.

• Great answer! If you can find an instance when DSN has ever actually used anything like 400 kW, please write an answer to Has DSS-43 ever been used in high power mode (>>20 kW) for an emergency situation?
– uhoh
Commented Mar 12, 2020 at 15:50
• Energy is not a factor, suppose I solve this. Communication from cubesat (orbiting Earth) to Earth's surface is via UHF, so with an SDR and a well-targeted omni-directional antenna you would have almost full-time communication. The cubesat's orbit height is 850 km on earth. Can the antenna be foldable? like MarCO's but in another way, like an umbrella or something like that. (I get the energy from these solar arrays: cubesatshop.com/product/solar-panels) Commented Mar 12, 2020 at 17:08
• and use a version of this antenna: jpl.nasa.gov/spaceimages/details.php?id=PIA22457 Commented Mar 12, 2020 at 18:39
• If you have developed a cubesat-sized nuclear reactor and are holding out on us, every user on this site will be rather cross. Commented Mar 13, 2020 at 4:57
• Good answer - FWIW there is a large constellation of cubesats in operation with 6 W x-band transmitters feeding ~15 dBi helical antennas. It works great for data downlink to ~5 m earth stations, but it wouldn't cut the mustard for talking to Titan. Commented Mar 13, 2020 at 7:25

Assume you can still get all the power you want, you'll be limited by the volume of your 1U cubesat. You'll be hard pressed to find reaction wheels, a computer, star trackers (or other sensors) and a radio that will all fit within the volume of your 1U; any radio that enables you to close your link budget with whatever power is going to be much bigger than a 1U.

I don't think all is lost though with a 1U setup. You could launch several 1Us staggered by some time on the order of days or weeks to create a daisy-chain type network that could relay a signal from your Titan cubesat to intermediate cubesats. These would boost the signal to the next one in the line and so-on back to Earth. Your mission would effectively be over only once your last cubesat is out of range of Earth.

• The daisy chain relay network of cubesats would not work, you need far too many of them. If you need several hundreds or even thousands of them, the probability of a single failure breaking the chain is much too high.
– Uwe
Commented Mar 12, 2020 at 21:04
• I'm not surprised that it wouldn't work from a sniff test. I suppose you could build in some margin so that one or two failures is okay, but you'll probably need a near-continuous line of cubesats all the way to Titan! Commented Mar 12, 2020 at 21:07
• @Uwe ok, one problem at a time, first the issue of solar panels, let's start designing the network that will be in Earth's orbit. And for the second, what size would I need? a 2U? I need to know the diameter of the antenna to calculate how much it would measure vertically folded and add the electronics and base frame. I still have 465w, remember Commented Mar 12, 2020 at 21:13
• If the daisy chain still works with several distant failures, it will fail when there are two or three failures in direct neighbourhood.
– Uwe
Commented Mar 12, 2020 at 21:23
• The question doesn't specify the nature of the data stream. With batteries power can be stored over a long period and then used for transmission during short intervals. The cubesat at Titan may not need to livestream over FB, it might send much more compact data sets spectroscopy from the atmosphere, radio recordings, electromagnetic maps, charged particle spectra, etc. and then once in a while an image.
– uhoh
Commented Mar 13, 2020 at 3:29