1992: SafetySat

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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.
Title text: 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.


CubeSat is a standard format for small satellites that can fit in a 10×10×10 cm format with a mass of less than 1.3 kg. They have been widely used by academics for research satellites, and by both small and large companies. CubeSats have been discussed both before and after this comic, in 1866: Russell's Teapot and 2148: Cubesat Launch.

CubeSats are often launched as an additional payload on commercial launches but also deployed from the International Space Station at the Kibo-Module or other airlocks. All these satellites are orbiting the Earth in a low orbit and since they have no propulsion system they also become a part of space debris when they are out of control; eventually they will reenter earth's atmosphere without any further hazard.

Only a few days before this comic was released the first interplanetary CubeSats called Mars Cube One was launched together with NASA's probe InSight (now offline) aiming to the planet Mars.

One of Randall's influences in creating this comic may have been controversy surrounding a commercial launch of a sub-CubeSat sized pico-satellite from a launch site in India, after the company had previously been denied launch permission within the US, due to safety concerns.

There are multiple safety rules to ensure that the CubeSat cannot damage the primary payload. However, the joke in this comic is that Randall's design seeks to break as many rules as possible.

Items clockwise from top left:

Rare-Earth Magnets
Violates CubeSat Design Specification Rev. 13 § 3.1.10.
Rare-earth magnets are very powerful magnets that have a high likelihood of messing up the functioning of nearby electronics, like other CubeSats. It might also cause the CubeSat to stick to other satellites, as the M-Cubed and Explorer-1 Prime CubeSats did.
BIC Mini-Lighter
Does not conform to AFSPCMAN 91-710, Volume 3 § 10.1.3, in turn violates CubeSat Design Specification Rev. 13 § 3.1.7
Fire source, resting on the can of crude oil. The pressurized butane could also make the lighter burst, but in space without oxygen the lighter never would ignite. And even if the inside of the CubeSat contains some oxygen in weightlessness a flame would go out very soon, of course if it set off the crude oil or the guncotton then it would not matter, as the CubeSat would be destroyed.
SDR/Software-Defined Radio (Code Editable via Public Wiki)
Violates Title 47 CFR Part 97 § 97.207(b), in turn violates CubeSat Design Specification Rev. 13 §
A radio which can be programmed to broadcast and receive in a range of frequencies, and formats. Software-Defined Radios are useful for development of new or modified wireless protocols, as well as for monitoring the raw waveform data of a transmission regardless of the protocols used. The radio in this comic is stated to run firmware which can be modified from a publicly editable Wikipedia-style webpage. Since anyone could change the radio's instructions, the radio could interfere with other satellites, or with the launch vehicle. This counts as a huge security risk, as anyone could edit it.
Laser Pointers (Fixed)
Does not conform to AFSPCMAN 91-710, Volume 3 § 8.2.2, in turn violates CubeSat Design Specification Rev. 13 § 3.1.7
These three laser points will effectively point in 3 different random directions, which is not safe for other objects around this Cubesat. It depends on the power of the laser pointers but, in general a laser over 5 mW can heat up and damage things given enough time.[actual citation needed] Of course, with the satellite being in orbit it could potentially mess up the optical sensors of other satellites, but it would be a matter of chance. This could also be a reference to the book What If?, specifically the chapter Laser Pointer.
Laser Pointer (Hubble-Seeking)
Does not conform to AFSPCMAN 91-710, Volume 3 § 8.2.2, in turn violates CubeSat Design Specification Rev. 13 § 3.1.7
Aiming a laser at a visible light telescope is potentially destructive to the telescope in question by damaging its optical sensors. This is because CCD & CMOS image sensors are designed to detect finite light sources, concentrated & focused by an optical lens. Lasers produce high light levels well beyond the (comparatively) very low intensity light which astronomical image sensors are designed to detect; The energy of these excess photons can heat up the circuits between rows of photosensitive cells to the point where they overheat and fuse. For much the same reason, originates the phrase "do not stare into laser with remaining eye". Unlike the fixed laser pointers above, this one would track and aim a laser at the Hubble, with potentially disastrous results.
CFCs/Ozone-depleting CFC Spritzer
Does not conform to AFSPCMAN 91-710, Volume 3 § 10.3, in turn violates CubeSat Design Specification Rev. 13 § 3.1.7
Chlorofluorocarbons (CFCs) are fully halogenated paraffin hydrocarbons that contain only carbon, chlorine, and fluorine, produced as volatile derivative of methane, ethane, and propane. Freon is a common example of a CFC, and the use of CFCs has been linked to a depletion of the Earth's ozone layer leading many countries to ban their use. Thus spritzing CFCs in an area relatively close to the Ozone layer may be a bad idea.
Celebratory Firework
Violates CubeSat Design Specification Rev. 13 § 3.1.3.
Does not conform to AFSPCMAN 91-710, Volume 3 § 13.2, in turn violates CubeSat Design Specification Rev. 13 § 3.1.7
Explosive fire source that could hit other satellites in the vicinity; Also potentially breaking the adjacent seal & igniting the crude oil behind it, turning it into crude oil that is also on fire. Could also set off the guncotton and result in an explosion that destroys the satellite. At the very least, the off-axis position of the firework within the CubeSat would most likely send the satellite into an uncontrolled spin, upon celebratory launch.
Crude Oil
Violates CubeSat Design Specification Rev. 13 § 3.1.6
Does not conform to AFSPCMAN 91-710, Volume 3 § 10.1.3, in turn violates CubeSat Design Specification Rev. 13 § 3.1.7
§ 3.1.6 permits 100 Wh of stored chemical energy, or about 9.8ml of crude oil. There appears to be more than that.
Volatile Epoxy Seal
Does not conform to AFSPCMAN 91-710, Volume 3 § 10.1.3, 12.1, in turn violates CubeSat Design Specification Rev. 13 § 3.1.7
Epoxy is a substance composed of long-chain molecules which exhibit very strong adhesive bonds. Many mixtures of epoxy are flammable & produce hazardous fumes when burned. If this particular epoxy seal fails, everything within splatter range gets coated in flammable crude oil.
Does not conform to AFSPCMAN 91-710, Volume 3 § 10.1.3, in turn violates CubeSat Design Specification Rev. 13 § 3.1.7
A form of nitrocellulose; an explosive. Could be set off by the firework, the crude oil, or the spark plug. Nitrocellulose does not work reliably in vacuum and possibly caused a failure of Philae space probe.
Americium corners
Does not conform to AFSPCMAN 91-710, Volume 3 § 9.1.1, in turn violates CubeSat Design Specification Rev. 13 § 3.1.7
Americium is a very dense and radioactive substance. Depending on the amount of americium involved, this alone could shoot the mass over the 1.3 kg mass limit. The isotope 241Am is used in smoke detectors but also proposed for use in radioisotope thermoelectric generators in spaceflight.
Spark Plug
Does not conform to AFSPCMAN 91-710, Volume 3 § 10.1.3, 10.1.4, in turn violates CubeSat Design Specification Rev. 13 § 3.1.7
Fire ignition source, if connected to electricity; excess mass if not. The electrodes on the spark plug are next to the guncotton which could ignite if the spark plug fires. Additionally, sparks cause electromagnetic interference and electrical shorts.
Solar Panel (Found)
The quality of the solar panel and the power it produces would have to be investigated thoroughly before being cleared for space flight. Also, it isn't clear on the design exactly what, if anything, it is supposed to power, or if it is just excess mass.
Batteries (eBay)
The quality of batteries bought on auction sites can vary widely, and certain batteries exposed to conditions outside their design specifications can explode or leak corrosive chemicals. These batteries might also be connected to the adjacent spark plug. Non-rechargable commercial batteries may leak or explode if a recharge is attempted, so if this is the intention of the Solar Panel, these would escalate into an even greater risk.
Wet Sand Dispenser
Violates CubeSat Design Specification Rev. 13 § 3.1.2, 3.4.3
Possible reference to the Kessler syndrome, which refers to a hypothetical situation wherein there are enough objects floating around in low earth orbit that collisions between objects might result in a "domino effect," each collision causing more collisions and breaking objects into smaller pieces of space debris, which increase the likelihood of further collisions. Wet sand exhibits a high grip:slip ratio, where the surface tension of the water tends to make particulates clingy. Sand (silica granules) can be very harmful to a wide variety of systems, due to its hardness & abrasive qualities. Depending upon the pattern of water sublimation in either shaded or sunlit zones, the exact behavior of various quantities of "wet sand" in low Earth-orbital space might be of interest to the designers of this and of other spacecraft.
Title text
Violates CubeSat Design Specification Rev. 13 § 3.4.4
Prongs that extend in the event of an unexpected sensor reading at launch could damage the rocket and/or nearby CubeSats/payloads. That the CubeSat reacts to an "unexpected" sensor reading - which could include any number of readings that aren't actually a problem - is also funny, as is the fact that this is described as "safely" securing the CubeSat and any surrounding CubeSats. Along with this, it is not unlikely that this CubeSat might be the source of any internal problem that might arise; in such a situation, having such a dangerous CubeSat further secure itself would be counterproductive, if spitefully entertaining.


[A prototype for a small cube-shaped "CubeSat" satellite, with labels on various components.]
[Labeled on top:]
Rare-Earth Magnets
Bic Mini Lighter
Software-Defined Radio (code editable via a public wiki)
[Labeled on right:]
Laser Pointers (fixed)
Laser Pointer (Hubble-seeking)
Ozone-Depleting CFC Spritzer
[Labeled on bottom:]
Celebratory Firework
Volatile Epoxy Seal
Filler (Guncotton)
[Labeled on left:]
Americium Corners
Spark Plug
Solar Panel (found)
Batteries (eBay)
Wet Sand Dispenser
[Labeled from within drawing in white text on top of a black rectangle:]
Crude Oil
[Caption below the panel:]
My CubeSat proposal was the first to be rejected for violating every design and safety requirement simultaneously.


  • The normal sized image was originally broken at xkcd and the BOT uploaded that image here. It was just a gigantic Γ shape at first (though with a rounded corner). The problem was fixed soon, but it happened later again at comic 1994: Repairs.

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I was excited that I might be the first to give an explanation (because the comic was so late in being posted), but when it finally arrived, I had no way to interpret it. It was just a gigantic Γ shape (though with a rounded corner). Now that the real comic[citation needed] has been posted, I find that I'm still not very qualified to explain it. (I can guess at some of the references, but not the important ones.) I guess my only constructive comment here is encouragement to have a section (trivia?) talking about the initial failed comic image. 19:38, 11 May 2018 (UTC)

There was a broken image a xkcd and uploaded by the BOT. It's now fixed at xkcd and here too. --Dgbrt (talk) 19:48, 11 May 2018 (UTC)

Someone should point out how much damage the "extends spikes in all directions" safety measure could do. And I note SpaceX scrubbed a satellite launch with 1 minute to go yesterday because of some anomaly. Maybe the impetus for this cartoon? Yngvadottir (talk) 20:23, 11 May 2018 (UTC)

I figured today's comic was in reference to this picosat launch from India, which was denied launch in the US for being below minimum size ("too hard to track if they go offline") & thus in violation of the requisite cubesat specs: https://spectrum.ieee.org/tech-talk/aerospace/satellites/fcc-accuses-stealthy-startup-of-launching-rogue-satellites Personally I'm in favor of these sub-cubesat launches; My concern is with liability, not safety, per-se. ProphetZarquon (talk) 20:47, 11 May 2018 (UTC)

I would be concerned with safety as well, if not for the radar reflector ... seriously, this looks more like FCC wanting to destroy the company for being innovative than trying to ensure the visibility. -- Hkmaly (talk) 23:01, 11 May 2018 (UTC)
Agreed, I feel like it's less about the satellites themselves & more about vilifying anyone who doesn't adhere to an industry specification that is being given the weight of law. ProphetZarquon (talk) 08:06, 14 May 2018 (UTC)

Considering that it says the solar panel was "found", I think that implies that perhaps it was stolen? Or just literally found on the side of the road. Either way, it seems kinda shady. Carrera (talk) 22:20, 11 May 2018 (UTC)

"shady"! I see what you did there... ProphetZarquon (talk) 08:05, 14 May 2018 (UTC)

Are there any rules regarding solar panels on spacecraft? Seeing that Randall "found" it, I'm wondering if this would be a violation of any rules. Herobrine (talk) 23:41, 11 May 2018 (UTC)

What would happen to wet sand if put in a cubesat and then released? Water released into space boils and then desublimates into a cloud of ice crystals. But what would the temperature and pressure be as the cubesat was launched? Starting from wet sand at one atmosphere and whatever ambient temperature, would it cool down fast enough for the water to freeze before it was dispensed? (Release a gritty snowball.) If the dispenser is not kept at atmospheric pressure, would the water boil as the satellite was ascending to orbit? I wish Randall was still doing what-if. 01:22, 12 May 2018 (UTC)

I have no idea, but would imagine that water in sand would freeze the sand together into small clumps that could penetrate other satellites, rather than just evaporate. We must try this soon... (Kessler...) ;) --Kynde (talk) 20:40, 13 May 2018 (UTC)
In our solar system the ice line is inside the asteroid belt beyond Mars. This means water in Earths orbit exposed to the vacuum and the sun will evaporate. And the heat from the Sun is even high enough to trigger this very fast. More far away - e.g. at Jupiter - that wet sand would freeze to a dirty snowball. --Dgbrt (talk) 21:32, 13 May 2018 (UTC)

> quality of the solar panel and the power it produces
Quality of the power ? Isn't all solar power clean and green quality ? Spongebob (talk) 04:28, 12 May 2018 (UTC)

Well a solar panel's efficiency depends on how well it's made, and what materials have been used to make it. Considering that it was just "found", it may not be efficient enough to actually run the satellite, or even work in a vacuum. Then again, it's not like the satellite does much other than point lasers and explode. Carrera (talk) 05:21, 12 May 2018 (UTC)

I am totally surprised that nobody either commented on or included a mention in the explanation of the obvious misnomer of the title of the comic! Doesn't anyone else think this cubesat is the opposite of a SafetySat in every way possible, which I think is the main joke of the comic? I would update the explanation accordingly, but I'm not sure where exactly this point should be made. Anyone else want to take a crack at it? Ianrbibtitlht (talk) 21:59, 13 May 2018 (UTC)

Well, it could be very useful in satellite design classes. "Here is how *NOT* to do it." Gene Wirchenko [email protected] 04:08, 14 May 2018 (UTC)

Shouldn't a link be made to comic http://www.explainxkcd.com/wiki/index.php/1337:_Hack, about hacking satellites? 11:38, 25 May 2018 (UTC)

At the comic page scroll to the bottom and you will find this: Category:Space probes. Shall we mention them all? --Dgbrt (talk) 18:03, 25 May 2018 (UTC)

Oh, again the good old americium. 08:30, 28 May 2018 (UTC)

This cubesat made its way to Space Exploration Stackexchange: https://space.stackexchange.com/questions/28345/cubesat-design-requirements-and-safety-restrictions I leave the link here just in case we could add something from it to the explanation.--Pere prlpz (talk) 19:36, 11 July 2018 (UTC)