# Cubesats in lunar orbit and beyond - how does communication work?

Somewhere I read that there are serious plans to send a cubesat into lunar orbit. A few years ago, the ISS was also offering a launch opportunity for such a mission. I guess that it was actually booked.

How is the communication supposed to work with a cubesat over such long distances? Has it been researched or proposed for 1U cubesats? Are there any special requirements on frequencies, antennas, power consumption ... ? What needs to be taken care of if you want to use your hobby ground station for something like this, if it is already working for cubesats in LEO?

EDIT A few interesting links ...

• Could you link a source for lunar cubesats? Consider that cubesats usually piggyback on other launches and have no propulsion of their own, I'm quite surprised. – gerrit Jul 22 '13 at 11:34
• @gerrit: Then I need to dig deep into my old emails. ISIS provides contacts for piggibacks on a comercial basis but conceals the details unless you book the launch or at least sign an NDA. – s-m-e Jul 22 '13 at 11:42
• @gerrit: Found. Announced in 2011 for a launch in Q1/2014 towards Low Lunar Orbit. Launcher kept secret, I even asked at that time. – s-m-e Jul 22 '13 at 11:44
• This question and its answers have relevant discussions. See also the BoomStarter lunar cubesat project website and YouTube video. – uhoh Aug 22 '16 at 3:04

So, let's first compare the distances. Your average LEO satellite is placed in orbit maybe 600 km. The distance to the moon is 384000 km. That is 640 times further. Using $r^2$ losses, and converting to decibels, that is an additional 56 dB loss. Of course, a groundstation needs to be able to communicate in LEO beyond directly overhead, so let's just assume it's at the horizon at that distance. I'm going to estimate that horizon distance at about 3000 km. That reduces the difference in power requirements to just 42 dB difference. So, is that achievable for an amateur station?

Most cubesats are build by students or other hobbyists, and use the Amateur Radio frequencies to communicate. There is actually a pretty common feat to test out an amateur radio station that involves pointing an antenna at the moon, and trying to communicate with other people. For the most part, the data rates are quite low, but a large station can actually talk using morse code, which can be fairly fast. This is actually quite a bit harder than talking to a satellite orbiting the moon, for a couple of reasons. First of all, the moon don't reflect all of the energy back to earth, and then you have to consider the two way path loss in signals. So, it can in theory be done, so, how do you do it?

First of all, you will need to use a lower data rate than the LEO satellite. If you cut the rate down by 16, that's about a 12 dB gain. If you use a preamplifier/amplifier, you can get another 20 dB or so. And then using higher gain antennas will get you the rest of the way, all the way to the required 42 dB extra gain. The lower data rates could be compensated by the fact that you have near constant communication for 12 hours each day. Alternatively, you could use a higher frequency, and a dish antenna, which will allow you to get much higher gain, and a similar feat could be ensured.

Bottom line is, this is a doable problem, although it would be a bit tricky to manage. It should be tested first by bouncing a signal off of the moon and verifying you hear the echo. This should be done using the same modulation you plan on listening with. If you pull this off, you should be good to go.

• Informative answer, but most of it could hold for any satellite. Cubesats have several unique challenges: power, size, etc. What design considerations need to be made for them? For instance, you mention a dish antenna, but how does that fit in a cubesat form factor? Do components like this exist for cubesats? – user29 Aug 18 '13 at 21:02
• The dish is on earth. Otherwise, the cubesat is the same. – PearsonArtPhoto Aug 18 '13 at 21:17
• The free space path loss depends on the distance $d$, but also on the communication wavelength $\lambda$ (that is, frequency, because $c = f\lambda$), as per $$FSPL = 20 \log_{10} \frac{4 \pi d}{\lambda}$$ May I ask which frequency did you assume to obtain the value of 56 dB? – Alessandro Cuttin Apr 18 '16 at 17:59
• @AlessandroCuttin I don't see the words "free space path" in front of the word "loss". "56dB loss" is just another way to say "(384000/600)^2 times weaker". It's a nice way to work the problem from "grounded" points of reference. – uhoh Apr 20 '16 at 18:23
• @uhoh yes, that's correct. Using the same frequency, there's an additional loss of 56 dB. It's the "additional" that I was missing. – Alessandro Cuttin Apr 21 '16 at 9:12

Yes, it's being researched. For instance, this JPL paper describes a design for a parabolic antenna with a diameter of 50 cm that can be folded and stowed in 1.5 U, and provides a gain of 42 dB.

Another approach is the reflectarray, an antenna that uses a flat panel instead of a dish, with structures on the panel that look like a Fresnel lens to focus the radio waves.

JPL is looking into this as well.
MMA Design is working on a reflectarray of 1 m diameter, packs into 1U, also gain in the region of 40 dB. This design combines the antenna with the solar panel:

I think that Earth - Moon communications with a CubeSat in lunar orbit are feasible, even though it would require a lot of effort.

Closing the link is a trade off between operational frequency, the available power on the satellite, and the volume on the satellite available for the antenna (the higher the frequency, the higher the path losses, the smaller the antenna).

How is the communication supposed to work with a cubesat over such long distances?

Mostly in the same way, except for the very long path, which means very high losses. The spacecraft tracking would be less demanding in terms of speed, but more demanding in terms of pointing accuracy.

Has it been researched or proposed for 1U cubesats?

I don't think so, only 3U or (preferably) 6U cubesats have been considered so far for beyond-LEO missions.

Are there any special requirements on frequencies, antennas, power consumption ... ?

Basically, you would require a very good pointing mechanism, a very directive and high gain antenna, and a very good low noise amplifier. Which is something uncommon for the usual backyard ground station.

What needs to be taken care of if you want to use your hobby ground station for something like this, if it is already working for cubesats in LEO?

Answers to the previous questions are all points that require some effort.