Technical notes

Articles

Worked engineering notes that go one level deeper than the encyclopedia. Each one states its assumptions, computes its tables in the page and ends with references you can check.

DOC // NL-001(SQ-TN-2026-008)VECTOR -ZREV 0.1

G/T from first principles: what makes a good amateur ground station

For a weak downlink such as that of a PocketQube, the ground station contributes a single number to the link budget: its figure of merit G/T. We build the system noise temperature of five amateur receive chains with the Friis cascade. A 13 dBi crossed Yagi with a low-noise amplifier at the mast reaches about 200 K and −10.0 dB/K; moving the same amplifier indoors behind 1.8 dB of cable raises the noise to 366 K, and leaving it out to about 1600 K. Applied to Grizu-263A’s 20 dBm, 4800 Bd downlink, the three chains decode above 5°, 13° and 42° elevation, which at 41.45° N means about 32, 16 and 2 minutes of usable contact a day. Omnidirectional antennas never close at 4800 Bd. We end with a checklist for building and measuring a station.

  • Ground station
  • Noise
  • G/T
  • LNA
  • UHF
  • Grizu-263A
Engineering7 min read
DOC // NL-002(SQ-TN-2026-016)VECTOR -ZREV 0.1

Tracking a 5 cm satellite

A bare 50 mm cube sits deep in the Rayleigh scattering regime for UHF space-surveillance radars, yielding a radar cross-section near −43 dBsm. Once its 437 MHz tape-spring monopole or dipole deploys, resonant wire scattering boosts RCS by 25–30 dB. We examine radar cross-section across UHF, S-band and X-band and explain how Differential Doppler resolves rideshare TLE lotteries.

  • Radar cross-section
  • TLE
  • Space surveillance
  • Rideshare
  • UHF antenna
  • PocketQube
Basic2 min read
DOC // NL-003(SQ-TN-2026-014)VECTOR -ZREV 0.1

Atomic oxygen and polymers in low Earth orbit

Polymers on the exterior of a PocketQube—solar-panel substrates, Kapton insulation, PEEK spools, UHMWPE burn lines and exposed FR-4 edges—face both high-vacuum volatile condensation and 4.5 eV ram atomic oxygen (AO). We review ECSS-Q-ST-70-02C / ASTM E595 screening limits and compute annual AO fluence and recession depth from 350 to 600 km.

  • Atomic oxygen
  • Outgassing
  • Polymers
  • Kapton
  • Materials
  • PocketQube
Academic2 min read
DOC // NL-004(SQ-TN-2026-015)VECTOR -ZREV 0.1

First natural frequency of the backplate and launch loads

Unlike a CubeSat held along four corner rails, a PocketQube is cantilevered in its deployer by a single 1.6 mm thick sliding backplate. We derive the plate's flexural rigidity and fundamental modal frequency across Al 6061-T6, Al 7075-T73, Ti-6Al-4V and FR-4, and evaluate 3σ dynamic deflection under GSFC-STD-7000B (GEVS) random vibration.

  • Backplate
  • Structural dynamics
  • Natural frequency
  • Random vibration
  • GEVS
  • PocketQube
Engineering3 min read
DOC // NL-005(SQ-TN-2026-012)VECTOR -ZREV 0.1

The 1P battery: capacity, depth of discharge and cycle life

A low Earth orbit satellite experiences roughly 5500 eclipse charge–discharge cycles per year. We model cycle life to 80% state of health against depth of discharge (DoD), charge cutoff voltage and temperature, and explain why 1P PocketQubes run at 5–15% eclipse DoD with a 4.10 V ceiling.

  • Battery
  • EPS
  • Depth of discharge
  • Lithium-ion
  • PocketQube
Engineering2 min read
DOC // NL-006(SQ-TN-2026-013)VECTOR -ZREV 0.1

LoRa from low Earth orbit

LoRa chirp spread spectrum (CSS) demodulates signals 7.5 to 20 dB below the thermal noise floor, enabling PocketQube reception on simple omnidirectional ground antennas. However, high spreading factors (SF11–SF12) at narrow bandwidths suffer symbol-bin drift when the orbital Doppler rate peaks near zenith. We derive the sensitivity, link margin and maximum tolerable Doppler rate across SF7–SF12.

  • LoRa
  • Chirp spread spectrum
  • Doppler rate
  • UHF
  • Link budget
  • PocketQube
Engineering2 min read
DOC // NL-007(SQ-TN-2026-020)VECTOR -ZREV 0.1

CubeSat corner rail tribology, PC/104 stack mechanics and PQ9/CS14 backplanes

We examine the mechanical and electrical backbone of a CubeSat: the four 8.5 mm corner rails that interface with the deployer, the tribology of MIL-A-8625 Type III hard anodizing against vacuum cold welding, and the dynamic stiffness of a four-rod M3 PC/104 PCB stack compared against PocketQube 42×42 mm M2 stacks and the PQ9/CS14 backplane standard.

  • CubeSat
  • PC/104
  • Structures
  • Rails
  • Anodizing
Engineering2 min read
DOC // NL-008(SQ-TN-2026-011)VECTOR -ZREV 0.1

Disturbance torques at PocketQube scale

We evaluate the four environmental disturbance torques—gravity gradient, aerodynamic drag, solar radiation pressure and residual magnetic dipole—for a 50 mm 1P PocketQube across 350 to 700 km altitude and show why residual current loops and battery ferromagnetic cases dominate picosatellite attitude dynamics.

  • Disturbance torques
  • Scaling laws
  • ADCS
  • Magnetic cleanliness
  • PocketQube
Engineering1 min read
DOC // NL-009(SQ-TN-2026-010)VECTOR -ZREV 0.1

Passive magnetic attitude control for a 1P: sizing the magnet and damper rods

We formulate the coupled magnetostatic design rules for passive magnetic attitude control (PMAC) inside a 50 mm PocketQube: sizing the permanent dipole against aerodynamic torque, keeping the magnet's stray field below the apparent saturation field of the hysteresis dampers, selecting rod aspect ratio to overcome shape demagnetization, and bounding the final dead-band angle.

  • PMAC
  • Attitude control
  • Hysteresis rod
  • Demagnetization
  • PocketQube
Academic5 min read
DOC // NL-010(SQ-TN-2026-019)VECTOR -ZREV 0.1

Scaling from 437 MHz UHF to S-band and X-band high-rate CubeSat downlinks

A 9.6 kbps UHF downlink transfers at most ~3–4 MB per day—sufficient for housekeeping telemetry on a 1P PocketQube or 1U CubeSat, but four orders of magnitude below the output of a multispectral imager. We compare link budgets across 437 MHz UHF, 2.2 GHz S-band (2 Mbps), and 8.2 GHz X-band (100 Mbps DVB-S2) into a 2.4–3.7 m parabolic dish.

  • CubeSat
  • S-band
  • X-band
  • Link budget
  • Downlink
Engineering2 min read
DOC // NL-011(SQ-TN-2026-009)VECTOR -ZREV 0.1

How much data can a PocketQube download per day?

We compute the daily contact time of a single ground station for a 525 km Sun-synchronous orbit across station latitudes and elevation masks, apply framing efficiency for AX.25 and CSP, and tabulate the net payload volume delivered per day at 1200 to 9600 bit/s.

  • Data budget
  • Contact time
  • UHF
  • AX.25
  • CSP
  • PocketQube
Basic3 min read
DOC // NL-012(SQ-TN-2026-018)VECTOR -ZREV 0.1

3-axis reaction wheels, star trackers and momentum dumping in CubeSat ADCS

While 1P PocketQubes and 1U educational CubeSats rely on passive magnetic stabilization or B-dot detumbling, imaging and optical-downlink CubeSats require 3-axis reaction wheels paired with miniature CMOS star trackers. We formulate the Euler rigid-body wheel exchange equations, size wheel momentum capacity against secular disturbance torques, and derive continuous magnetorquer momentum desaturation.

  • CubeSat
  • ADCS
  • Reaction wheels
  • Star tracker
  • Pointing
Engineering2 min read
DOC // NL-013(SQ-TN-2026-007)VECTOR -ZREV 0.1

Pass geometry and Doppler for small-satellite ground stations

Everything a ground station does with a low Earth orbit satellite is set by a few lines of geometry. For a 525 km Sun-synchronous orbit, a pass lasts at most 11.9 minutes above the horizon and 7.7 minutes above 10°, and the range shrinks from 2641 to 525 km, a 14 dB swing in path loss. At 437.19 MHz the Doppler shift sweeps from +10.2 to −10.2 kHz, fastest at closest approach, where it changes by up to 148 Hz per second. A station at 41.45° N sees 3.3 passes a day above 10°, about 20 minutes in total, with gaps of up to 13 hours; one at Svalbard sees 11. We derive these numbers, show how a Doppler curve measures the orbit, and close with rules for tracking PocketQubes and CubeSats.

  • Orbital mechanics
  • Doppler
  • Ground station
  • SatNOGS
  • UHF
  • Grizu-263A
Basic10 min read
DOC // NL-014(SQ-TN-2026-017)VECTOR -ZREV 0.1

3U and 6U CubeSat power budgets: body-mounted vs. deployable solar arrays

We derive the sunlit and orbit-average electrical power generated by 1U, 3U, and 6U CubeSats in a 525 km Sun-synchronous orbit across tumbling body-mounted configurations and Sun-pointed deployable solar wings. While a tumbling 1U CubeSat averages ~1.5–2.4 W, a 3U with dual deployable wings reaches 18–24 W and a 6U with four deployed panels exceeds 40–55 W, unlocking high-duty-cycle X-band downlinks, reaction wheel slews, and radar/optical payloads.

  • CubeSat
  • EPS
  • Solar arrays
  • Power budget
  • 3U
  • 6U
Engineering3 min read
DOC // NL-015(SQ-TN-2026-006)VECTOR -ZREV 0.1

Meeting the five-year rule without propulsion

Satellites launched after 29 September 2024 under FCC authorization must re-enter within five years of the end of their mission. For a spacecraft without propulsion the rule becomes an altitude ceiling that depends on its ballistic parameter and on the Sun. With the lifetime model of the PocketQube review, a fully loaded 1P stays within five years below 559 km at moderate activity, between 493 and 627 km from low to high activity, while 1U, 3U and 12U CubeSats are limited to 525, 513 and 494 km. Above the ceiling, a tumbling drag sail of 80 cm² brings a 1P down from 600 km at moderate activity, but about eight times more at low activity, and a perigee-lowering burn costs 70–150 m/s, a seventh of a 1P’s mass in cold gas at 600 km. For PocketQubes the release orbit is the compliance strategy.

  • Space debris
  • Regulation
  • Lifetime
  • Drag sail
  • Propulsion
  • PocketQube
  • CubeSat
Engineering9 min read
DOC // NL-016(SQ-TN-2026-005)VECTOR -ZREV 0.1

Thermal response of a PocketQube: why a lighter spacecraft cycles harder

We quantify, with two lumped models of increasing fidelity, why PocketQubes follow the orbital forcing more closely than CubeSats. Linearized radiation gives a thermal time constant of 56 minutes for a fully loaded 1P against 104 minutes for a 2 kg 1U. Integrating a single-node energy balance at 550 km gives bulk swings of 30 K for a 250 g 1P and 37 K at 200 g, against 23 K and 16 K for 1U CubeSats of 1.33 and 2.00 kg. The surface finish moves the mean temperature by tens of kelvin, while the cells that cover most faces leave little freedom. An Engelmaier screening turns the swings into median lives of about one year for germanium-based cells soldered rigidly to FR-4. We close with design rules for the bulk node, the battery and the joints.

  • Thermal
  • Simulation
  • Solder fatigue
  • Battery
  • PocketQube
  • CubeSat
Academic11 min read
DOC // NL-017(SQ-TN-2026-004)VECTOR -ZREV 0.1

The power budget of a 1P PocketQube

We build the energy balance of a freely tumbling 1P PocketQube with body-mounted triple-junction cells in a 525 km Sun-synchronous orbit. The tumbling-body model of the PocketQube review gives about 0.86 W in sunlight and 0.55 W on orbit average. With a reference load list the mean consumption is 134 mW, the energy margin per orbit is large and the depth of discharge of a 1.85 Wh battery stays near 4%. We then show why the margin is fragile: the transmitter duty cycle, cold charging, end-of-life degradation and power peaks, and why pointing one face at the Sun gives less power than tumbling.

  • PocketQube
  • EPS
  • Power budget
  • Battery
  • Eclipse
Engineering8 min read
DOC // NL-018(SQ-TN-2026-003)VECTOR -ZREV 0.1

Magnetic detumbling with B-dot: a 1U and a 1P compared

The first job of a small satellite after separation is to remove the angular rate the deployer gave it. We derive the B-dot law, which needs only a magnetometer and magnetorquers, show why it can never increase rotational energy, and simulate rigid-body detumbling in a 500 km Sun-synchronous orbit with a tilted-dipole field. From about 9.6°/s, a 1U with 0.05 A·m² coils falls below 1°/s within minutes, while a 1P with 0.005 A·m² board coils takes about one orbit; both converge to a residual rate of the order of twice the orbital rate. We close with a flight-code sketch and design rules for PocketQubes.

  • ADCS
  • B-dot
  • Simulation
  • Magnetorquer
  • PocketQube
  • CubeSat
Academic8 min read
DOC // NL-019(SQ-TN-2026-002)VECTOR -ZREV 0.1

A UHF downlink budget for a 1P PocketQube

We compute, line by line, the downlink budget of a 1P PocketQube transmitting telemetry at 437.2 MHz from a 500 km Sun-synchronous orbit with 0.5 W of RF. At 10° elevation, 9.6 kbit/s non-coherent FSK closes with only +0.1 dB of margin, while 1.2 kbit/s keeps more than 5 dB even at the horizon. Integrating over passes shows that low passes deliver almost nothing at 9.6 kbit/s. We then recompute the budget of Grizu-263A, whose 20 dBm EIRP and dual 4800/2400 Bd modes reproduce the margins reported in the PocketQube review, and argue for adaptive data rates and forward error correction.

  • PocketQube
  • RF
  • Link budget
  • UHF
  • AX.25
  • Grizu-263A
Engineering10 min read
DOC // NL-020(SQ-TN-2026-001)VECTOR -ZREV 0.1

Orbital decay and lifetime of PocketQubes and CubeSats

We derive the drag-driven decay of a circular low Earth orbit from the energy equation, evaluate it with the single-scale-height density model of Kennewell driven by F10.7 and Ap, and produce lifetime tables for PocketQube and CubeSat form factors from 300 to 650 km. From 500 km at moderate activity a fully loaded 1P lives 1.7 years and a 1U 3.1 years; solar activity alone moves the 1P between 0.7 and 5.8 years. Checked against the re-entries of Grizu-263A and Delfi-PQ, both released from Transporter-3, the model overestimates lifetime at constant flux, as expected from a single scale height and the fast rise of Solar Cycle 25. We close with how lifetimes should be reported.

  • Orbital mechanics
  • Atmospheric drag
  • Lifetime
  • Solar activity
  • PocketQube
  • CubeSat
Academic10 min read