All satellites are vulnerable to a wide variety of EMC and environmental effects, from launch to deployment. Of particular concern is the effects of Coronal Mass Ejection (CME) events. These are caused by sun activities that result in waves of cosmic rays and particles and electromagnetic energy.
Significant CME events occur in sync with the “11 Year Sunspot Cycle” which, for reasons known to nature, pulse with this particular rhythm, caused by magnetic flux pushing up from the interior to the surface of Old Sol (source).
Sunspots are indicative of surface-sun activity and occur at periodic maxima. These cycles have been “numbered” since 1755, but have obviously been occurring in the 4.8B years or so of the solar system’s existence.
The approximate cycle of 11 years is fairly easy to predict with the current cycle (as of June 2024) is numbered as 24, beginning in 2008.
The sunspots (or, rather, the phenomena that causes them) create so-called “Space Weather,” so the Space Weather Prediction Center prepares a daily report on sunspot activities with a “Solar Region Summary Report.”
It may be said, or interpreted, that sunspot activity is a result of some internal resonance of the Sun’s complex “magnetic heartbeat.” “A new solar cycle is considered to have begun when sunspot groups emerge at the higher latitudes with the magnetic polarities opposite to that of the previous cycle” (source).
Space weather has tremendous impacts on satellite and terrestrial systems. The protective blanket provided by Earth’s magnetic field, provides a shield for systems and life itself.
Arguably, life on this planet would be impossible if not for the magnetic field of old Gaia. This protection is provided at lower/below the ionosphere, but for GPS and other satellites operating in upper orbits, such protection doesn’t exist.
Thus, for those systems, satellite systems must be designed with this threat in-mind. See ‘Space Weather – Predicting EMC Effects of Solar Storms’ for more on that.
For CubeSats, the main issues occur when getting the devices through launch and on to deployment. This article discusses the main design issues with these devices, which take on many functions, but must follow a common form-factor and other operational/design considerations.
So, what is a CubeSat?
By definition, these micro-satellites are 10X10X10 cm form-factor, hence the “cube” denomination. A CubeSat has an international standard ISO 17770:2019, which defines the requirements for physical, mechanical, electrical and operational requirements, including interface requirements between the CubeSat and the launch vehicle.
According to Nanoavionics.com, CubeSats are typically developed for the following uses:
- Scientific Research, including water and other resource monitoring
- Earth monitoring and Relay
- Communications
- Technology Trials, feasibility assessments
- National Security and Defense
Typical costs of CubeSat projects range from $50-100k for educational/research applications and $500K-$MM for commercial and science missions. This is compared with the hundreds of millions for development and deployment of a traditional satellited.
The low cost benefit has an upside: many satellites can be deployed and the failure of a single unit may not compromise the entire mission. The downside is that the functions and applications may be limited by the small
size and ability to incorporate many functions.
ORBITAL DEFINITIONS
At CubeSat orbital altitudes, so-called Low Earth Orbit (LEO), “Space Weather” is less concern because of the lower levels of ionizing radiation is relatively low.
This is important because the use of Common Off-The-Shelf (COTS) equipment keeps the price of the CubeSat device low. Use of COTS components also allows for mass production of the CubeSats.
Many of the constellations that have been deployed or are planned rely on hundreds, if not thousands of these devices.
There are several orbital altitudes that are used in the vernacular of satellite deployment.
Notionally, and there are no strict boundaries, the orbital levels are described thus:
- Low Earth Orbit: <800 km above sea level (ASL)
- Medium Earth Orbit: 800-2000 km ASL
- High Earth Orbit: Less than GEO
- GEO: 35,786 km ASL
- Graveyard Orbit: Above operational orbits
- Disposal Orbit: Way out there…
Sputnik flew between 212 and 950 km ASL as the first human-made object to orbit the Earth. The highly elliptical orbit was maintained for three months before the satellite burned up in the Earth’s atmosphere on January
5, 1958.
CubeSats, because of their sheer number and occupancy of LEO orbits, are required to de-orbit (disposed of in the atmosphere) after their operational lifetime.
This is normally accomplished by a de-orbit burn, scuttling the craft into the upper atmosphere until the aether sets its drag on the device, slowing and eventually causing the satellite to burn up.
The risk of debris reaching the Earth’s surface is low, because of the small mass of the CubeSat; for the most part it is assumed that the CubeSat will be completely consumed before reaching the Earth’s surface.
One aspect of CubeSat’s orbital behavior is the relatively fast orbital period (i.e., transit around the globe) and hence, they are inherently non-Geo-Stationary.
Geo-Synchronous Positioning Systems (GPS) are set in geo-synchronous or near-geo-stationary (or semi-synchronous), passing over the same point on Earth twice-daily.
GPS systems (including GNSS and GLONASS) are subject to the whims of the Solar Wind; at GEO orbits, the electronics must be hardened and the materials carefully selected to withstand the bombardment of Solar emanations— typically not an issue with CubeSats (exceptions noted).
CubeSat design, as stated earlier, must survive partus and the post-partum of the launch. Notably critical the vibration and mechanical stresses of ascent and deployment.
The vibration “profile” simulates the intense forces of launch deployment, the profile most often depends on the launch vehicle being used for the mission.
The vigorous (and LOUD) vibration profile only lasts a few minutes until flight is achieved, with the shaking settling down for the rest of the orbital insertion. More on that later in this article.
CUBESAT LIFETIMES
A feature/drawback of CubeSat operation, compared to traditional satellites, that may be on-orbit for many years, is the relatively short orbital lifetimes, which may be, by design, a few months to a few years.
Yet, during that time, the majority of the “things in orbit” (a technical term) are so-called “Space Debris.” According to Sciencedirect.com, “It is estimated that more than 22,000 human made objects are in-orbit above the
Earth.”
What is remarkable is that approximately 90% of the devices may be considered space junk, that is they are no longer operational (or controllable!).
A concern with the CubeSat concept is the additional future ‘debris’ posed by launching these new technologies is the sheer number of constellations, to wit:
- Flock > 100 devices
- Amazon > 3000
- Starlink > 4000
- Boeing > 1000
Not to mention the constellations in-orbit or planned by foreign governments. Not all actors will ascribe to the notion to de-orbit their systems after their operational lives are over (just a guess…).
NASA has released NASA-STD-8719.14 “Process for Limiting Orbital Debris” which (probably) only applies to NASA-launched devices.
Private launch vehicle providers may or may not have their own requirements for “fly” on their vehicles, but permission from the government may dictate compliance to this critical aspect of flying above the planet.
MISSION SUCCESS FOR CUBESAT
NASA GSFC-HDBK-8007: “Mission Success for CubeSat Missions” which was released 16 December 2019 is now up for validation in December 2024.
Under Appendix A of this document is a list of recommendations derived from the legacy General Environmental Verification Standard (GEVS) that has been part of the verification requirements evolved during the Space Shuttle program.
A tailoring of the requirements is appropriate as a “full GEVS-defined approach would be overkill for CubeSats.” GEVS is written to assume a very low tolerance for on-orbit risk (emphasis added).
This posture is appropriate because of the high-risk assumed with the large cost of the Shuttle and the not-so-small fact that human space flight is involved.
A summary of Appendix A includes: Section 2.3 Electrical Function Test Requirements, including electrical interface, compliance performance, limited performance, operating time, structural and mechanical performance, structural loads and other modal necessities (anything else), EMC (based on MIL-STD-461—which has subsumed into the GEVS, anyway).
EMC ISSUES FOR CUBESAT
Regarding Electromagnetic Compatibility (EMC) issues, because CubeSats operate singularly, i.e., not connected to other systems, typically) and are only connected with the launch vehicle during pre-launch checkout and
ascent.
For most cases the CubeSats are, ostensibly, dormant or only nominally functional until placed in orbit (as always, exceptions noted).
Card-level tests (to vendors) are called-out, notably CE101 for low frequency emissions, CS (conducted susceptibility) and Radiated Emission (RE101) for low frequency emissions (tailored).
The ultimate EMC test occurs at the integrated level, that is, the thing has to be self-compatible (and that’s ‘motherhood’ or the obvious).
CubeSat integrated tests reference MIL-STD-464, which is used to assess platform-level EMC. The level of testing is to a function of mission. It is suggested (and this is an editorial comment).
EARTH-TO-ON-ORBIT INTERFERENCE
Once into orbit, CubeSats (and all satellites) are subject to on-orbit RF (human-made) threats, notably ground-based radars and other RF sources. A profile of the RF threats may be available (either publicly available or via
classified sources, as appropriate).
Knowledge of the frequency and expected field levels is critically important if the CubeSat is performing Earth observatory functions, such as sensing, radiometry or employing other passive techniques as might be used for ground imaging and quantification.
The ground-based systems are typically fixed (radars, etc.), but not all may be known. For critical missions, notably for defense and national security missions, the threats may be fed into the operational commands of the
satellite and, as the satellite passes over the threat, the systems may be temporarily “blanked” until the threat is over-flown.
Fortunately, system planners realize that the passage of the satellite over ground is relatively fast. Often, the interference may be ignored.
However, because of the very wide bandwidths inherent in radiometric and sensing functions, understanding the RF profile on-orbit is critical.
Other specification and performance targets include RF link margin analysis, which includes various factors such as propagation losses, fading, atmospheric absorption, coding and error-correction, antenna beam-angle, output powers and receiver sensitivity.
Typically, a link margin analysis includes some overhead to compensate for the uncertainties in the data and physical performance of the RF link.
The CubeSat integrated platform tests reference MIL-STD-464, which has long been used to asses platform-level EMC. The level of testing is to be a function of mission and operational requirements.
It is highly suggested that specifications and applicability of the testing be carefully tailored to the mission requirements.
Program planners must not accept carte-blanche the general requirements less an overly-exuberant end-user hold the system’s feet to the fire in case there are non-compliances that are really not critical to mission success.
We have seen this in the lab numerous times and, test targets need to have the option to waive a certain level of non-compliances that may exist once the device is on the bench.
This not only applies to CubeSats, but can be generally applied to nearly every program of this kind.
Finally, the Mechanical Section of 2.6.1 summarizes the most critical aspects of design and development, notably the following test protocols:
- Bake-out (outgassing)
- Balance (thermal balance across the devices volume)
- Temperature and humidity
- Thermal cycling and stresses (temperature shock, for example)
- Thermo-vacuum assessment
- Contamination
- Coatings
- Planetary protection (in case the CubeSat is leaving Earth Orbit*)
- End-to-end testing
*This, notably, applies to any device that may be making its way to the moon (very rare, but potentially feasible, although the energy required to escape Earth’s gravity grip is significant).
The most common sets of test that we run at Washington Labs is NASA GEVS, both qualification at 10.0G and proto-flight 14.1G tests.
Space-X has their own for the Falcon 9 Heavy, and others have a “soft-stow” profile (wherein the test units gets ratchet-strapped to the table while wrapped in foam – an unusual configuration).
METEOR/DEBRIS THREATS
A final note on our exploration of CubeSat discussion is the threat of natural objects (meteors) and man-made (space junk) on mission operation.
Although most meteors are small in size, the large velocities impart significant kinetic energies. The smallest object, whether it be mineral/rock from outer space or a missing bolt or launch ascent debris can rip through any satellite with ease.
Mission planning typically includes a loss of some percentage of the constellation due to any number of factors (electronics failure, mechanical or collisions) and the networks have, to a degree a self-healing nature.
CONCLUSION
CubeSats are here to stay, that is a given. The design and deployment of these devices requires careful planning and consideration for the environment from launch to deployment and on-orbit functionality. Resources exist and considerations for the EM/ENV environment must be assessed at an early stage to improve (maybe not assure) mission success.
