# CubeSat Design Requirements and Safety Restrictions?

I was reading XKCD, and came across this beautifully designed CubeSat:

It is dubbed SafetySat: "During launch, in the event of an unexpected sensor reading, SafetySat will extend prongs in all directions to secure itself and any other cubesats safely in the launch vehicle until the source of the problem can be determined."

Jokes aside, obviously NASA isn't sending potential IEDs into space, so what exactly are the specifications and restrictions for sending your own CubeSat into space? Is there a concrete list of things you should and should never do?

Seems like something that could be a case-by-case proposal with approval and rejection.

EDIT(s): Page 24 here has some good information.

Bonus points if someone can explain/speculate the broken rules with the following:

• Rare-earth Magnets
• Wet Sand Dispenser
• Spark Plug
• Americium
• Software-Defined Radio (SANS public wiki editability).

All other elements are fairly straightforward in stupidity.

• One thing not to do would be to put crude oil on it. – GdD Jul 11 '18 at 15:21
• @GgD especially not putting crude oil next to a firework, separated by flammable/volatile epoxy, next to a spark plug and under a BIC lighter. – Magic Octopus Urn Jul 11 '18 at 17:55
• Permanent magnets (probably rare-earth as it's the cheapest per unit-mass/volume) are commonly used on CubeSats for passive attitude control and were likely involved in the conjoining of M-Cubed and Explorer 1 Prime. – Nick T Jul 12 '18 at 0:06
• @NickT I feel that your comment warrants a fully qualified answer, if you feel up to it, I would love to understand altitude control based on magnets, provided it was sourced. If you provide one it's an emphatic +1 from me. – Magic Octopus Urn Jul 12 '18 at 0:07
• Not much to say about it, Earth has a magnetic field [citation needed] and magnets align [citation needed] :P – Nick T Jul 12 '18 at 0:08

## 3 Answers

Is there a concrete list of things you should and should never do?

As it happens, there is!

NASA's CubeSat Launch Initiative requires that designs adhere to the requirements listed in CubeSat Specification section of the 'CubeSat design specification' document embedded in the hyper link above. The restrictions are too numerous to detail here, but I will list one that caught my eye:

3.1.3 No pyrotechnics shall be permitted

• Coolio! That's the type of reference I was looking for, I could only find the link I mentioned in my question, which was basically the CubeSat 200 page handbook. I also have to wonder how many people tried before they added 3.1.3 No pyrotechnics shall be permitted, or if it was just day one, "Some moron is gonna try this..." Given a bottle-rocket CubeSat would be interesting for all of 4 seconds. – Magic Octopus Urn Jul 11 '18 at 14:24
• I came across that book too; it's slightly bizarre that it has the feeling of an elementary school pamphlet with the content and dryness of a technical document. Glad I was able to help! – A McKelvy Jul 11 '18 at 14:26
• Pretty much every classic chemical rocket engine (save for cold gas thrusters) is 'pyrotechnic' in nature. The means of propulsion accessible to cubesats are actually very limited compared to what is used in space. – SF. Jul 11 '18 at 14:40
• @SF I read in the other book (the one I linked) that propulsion actually isn't restricted as much as you think in the design specifications. HOWEVER, getting a company to actually eat the risk of launching a cubesat with propellant in it is harder than getting it approved. Basically like having an untested IED onboard. – Magic Octopus Urn Jul 11 '18 at 14:46
• @MagicOctopusUrn: Oh, the specs changed since the last time I checked. In particular a lot of restrictions were removed. I remember restriction on pressure vessels (some puny pressure allowed, something like 2 bar, totally excessive durability margin), also no liquids of any kind. With no pyrotechnics, which SRB qualify as, that meant no chemical propulsion, except for possibly some puny cold gas thrusters. There was some hope for electric solid propellant (which would give the cubesat some 40cm/s of delta-V) and of course the expensive ion engines from Busek. Now it looks much better. – SF. Jul 11 '18 at 15:09

These answers entirely address the main question of the topic but do not cover the sub questions which I can attempt to do.

https://space.stackexchange.com/a/28346

https://space.stackexchange.com/a/28347

I do not know the exact reasoning behind each of the sub points however I have a pretty good guess:

Wet Sand Dispenser

In a zero G environment, dust particulates can be (depending on location) problematic as they can jam up moving parts or cause shorts in electrical circuits. Adding water increases the potential for shorts. Also due to the temperature fluctuations in space, the presence of water can increase structural degradation. There's also the potential for them to become micrometeorites but no one really focuses on that aspect.

Rare-earth Magnets

This one's a bit of a stretch because magnets are used in a plethora of electronics, especially scientific equipment that you would expect in space. My guess here is it has to do with the size and location of the magnets on the diagram. Obviously, having super strong permanent magnets located near the hull of the spacecraft invites all kinds of headaches from possible interference of sensors to needless build up of magnetic materials. Most importantly though, I would expect it to hinder the serviceability of the craft. Imagine a drone, astronaut, or arm getting caught in the magnetic field and being unable to break away.

Spark Plug

A golden rule in space: Fire + Zero G + Oxygen rich environment = A very bad day

Americium

Is a soft/malleable radioactive element. Obviously, there is very little value in putting a radioactive substance on the outermost exterior of a device that could be handled by humans. Then put it on the corners, which generally suffer the most impact forces and you end up with a high risk of it breaking off and contaminating everything in the production pipeline.

Software-Defined Radio (SANS public wiki editability).

This one's my favorite. The radio is the critical life line of a satellite responsible for transmitting information and receiving instruction. Making this mutable(editable) invites all kinds of vulnerabilities. Even worse, making it accessible/programmable by the wild west of the internet just invites comical levels of malicious intentions.

It would be like opening your windows laptop, turning off your firewall, uninstalling antivirus, and downloading whatever arbitrary and random application you found online. Only worse, because your satellite is in space, no one has immediate physical access to it so no one can even attempt to fix it.

• I added the sub-questions when the original question was answered, because I cared more about the cube-sat safety requirements, but +1 for attempting to answer the "fun" part :). I suppose I assumed the spark-plug wasn't connected to anything, was thinking a "dormant" spark plug wouldn't be too harmful. – Magic Octopus Urn Jul 11 '18 at 20:17

NASA has provided a somewhat-intimidating overview of the whole process of proposing, building, certifying and flying CubeSats under their CubeSat Launch Initiative.

There are performance specs for both the CubeSats and their dispenser interfaces on the NASA Resources page. But they don't contain a lot of "don't do this" standards, instead using language like "CubeSats shall comply with NASA guidelines for hazardous materials."

The most fundamental safety standard in this area, the one that i.e. the CubeSat dispenser docs refer to, is called "RANGE SAFETY USER REQUIREMENTS MANUAL VOLUME 3 LAUNCH VEHICLES, PAYLOADS, AND GROUND SUPPORT SYSTEMS REQUIREMENTS" a.k.a "AFSPCMAN 91-710, Volume 3" by the Air Force Space Command. It's a big document, but the relevant parts are probably Chapter 12 "Flight Hardware Pressure Systems and Pressurized Structures", Chapter 13 "Ordnance Systems" and Chapter 18 on rocket motors. They generally don't set specific standards on performance. Rather, they specify that analysis has to be done to ensure that the designed performance is met. For example, Chapter 12 has language like:

12.1.2.1. Airborne hazardous pressure systems shall be designed to be single fault tolerant against inadvertent actuations that could result in a critical hazard during prelaunch operations. Structural failure of tubing, piping, and vessels shall not be considered single failures provided they meet the requirements of this volume.

12.1.2.2. A pressure system shall be dual fault tolerant if the failure of two components could result in a catastrophic hazard.

That approach extends to operations (it's not safe if you don't ensure it's operated safely):

12.1.4. Flight Hardware Pressure System Operations. The requirements for operating hazardous pressure systems found in Volume 6 of this publication shall be taken into consideration in the design and testing of these systems in addition to the general requirements identified in 12.5 of this chapter.

The detailed analysis standards are, well, detailed:

12.1.5.3.1. General Requirements:

12.1.5.3.1.1. A detailed and comprehensive stress analysis of each pressure vessel and pressurized structure shall be conducted under the assumption of no crack-like flaws in the structure

12.1.5.3.1.2. The analysis shall determine stresses resulting from the combined effects of internal pressure, ground or flight loads, and thermal gradients.

12.1.5.3.1.3. Both membrane stresses and bending stresses resulting from internal pressure and external loads shall be calculated to account for the effects of geometrical discontinuities, design configuration, and structural support attachments.

12.1.5.3.1.4. Loads shall be combined by using the appropriate design limit or ultimate safety factors on the individual loads and comparing the results to material allowables.

12.1.5.3.1.5. Safety factors shall be as determined in 12.2.

12.1.5.3.1.6. Safety factors on external (support) loads shall be as assigned to the primary structure supporting the pressurized system.

The basic requirement that these analyses be done and documented is perhaps easiest met by not having pressurized systems, ordnance, and rocket motors on board. The second easiest approach is to use pre-approved units in standard configurations. Trying to roll your own is likely to be very, very hard. Getting XKCD's Safety Sat approved would be an interesting training exercise...

• I feel like writing up a detailed analysis of the "fault points" of the SafetySat would basically be like trying to write a paper justifying a flat-earth mathematically. But also, thank you for the multitude of sources, I will begin to look at them when I have time after work :). – Magic Octopus Urn Jul 11 '18 at 17:49