Microsatellite platforms (50–150 kg)
The 50–150 kg class is where national programmes get their first operationally useful imagery: metre-class optical, small synthetic aperture radar, real propulsion and genuine redundancy, at a price a single sovereign contract can absorb.
Why this mass class became the workhorse
Below 50 kg, payload volume and power budgets force compromises that matter operationally: apertures shrink, radar transmitters lose duty cycle, attitude control becomes coarser. Above 150 kg, unit costs climb steeply and launch options narrow. The 50–150 kg band sits at the point where a satellite can carry a telescope with a 20–40 cm aperture, a synthetic aperture radar antenna of useful size, or a signals-intelligence payload with a real dish, while still fitting as a rideshare secondary or a dedicated small-launcher primary.
Several commercially operated constellations have validated this in public. Planet's SkySat series, at roughly 110 kg, demonstrated sub-metre optical collection from a mass class that launches on a Falcon 9 rideshare. ICEYE's SAR microsatellites, in the same bracket, achieve sub-metre range resolution in spotlight mode. NanoAvionics and several European primes offer bus platforms in this range with heritage on orbit. The class is no longer experimental; it is the standard entry point for a nation building its first sovereign imaging asset.
What the bus actually provides
A microsatellite bus in this class typically delivers 100–300 W of average payload power (peak bursts higher with battery support), three-axis stabilisation to better than 0.05° pointing accuracy on mature platforms, and a propulsion system, usually green monopropellant or cold-gas, capable of 50–150 m/s delta-v. That delta-v budget is enough to raise or lower orbit by tens of kilometres, perform collision avoidance, and extend mission life by compensating for atmospheric drag at 450–550 km altitude.
Onboard storage has grown significantly. Current platforms routinely carry 256 GB to 1 TB of solid-state memory, which matters when a SAR or optical sensor generates several gigabits per pass. Downlink is typically X-band at 150–300 Mbps, though some platforms add optical inter-satellite or ground links. The structural envelope, usually aluminium or CFRP panels with a central tube, is designed around standard launch interfaces: ESPA Grande, NSSL, or a dedicated dispenser for rideshare.
Redundancy architecture is where this class separates itself from cubesats. Dual-string power management, redundant reaction wheels, and a watchdog-capable flight computer are standard on any platform sold for a national programme. Single-string cubesat designs accept higher risk in exchange for lower cost; this class does not have to.
Payload pairings and what they demand from the bus
Metre-class optical imagers at this mass typically use a TDI push-broom sensor behind a 20–35 cm aperture. Ground sampling distance at 500 km altitude runs 1.0–2.5 m in panchromatic, 2–5 m in multispectral. Achieving that requires pointing stability below 0.01° during imaging, which in turn demands reaction wheels with low jitter and, on demanding designs, a vibration isolation mount between bus and payload.
Small SAR payloads in the 15–30 kg range, such as those flown by ICEYE, require peak RF power of 1–3 kW for millisecond pulses, which the bus must supply from battery storage without disrupting the attitude control system. The thermal load from the transmitter is a genuine design driver: heat pipes or deployable radiators are often necessary.
AIS, ADS-B and GNSS-RO payloads are far less demanding and can share the bus with a primary imager as a secondary payload, adding maritime or aviation monitoring capability for modest mass and power increments. This stacking is one of the practical advantages of the class: a single satellite can serve two operational users.
The honest limits of the class
A single microsatellite has a revisit time measured in days, not hours. At 500 km in a sun-synchronous orbit, a 50–150 kg satellite passes over any given point roughly once every two to three days at mid-latitudes, less frequently near the equator. For time-critical monitoring, one satellite is not a solution; it is a proof of concept. A minimum operationally useful constellation is three to five satellites for daily revisit, and that multiplies both cost and programme complexity.
Cloud cover is an absolute limit for optical payloads. Tropical nations planning optical Earth observation must account for the fact that cloud obscures imagery on 60–80% of passes in wet seasons. SAR penetrates cloud but introduces its own interpretability challenges: speckle, layover in hilly terrain, and the need for analysts trained in radar phenomenology.
At 50–150 kg, on-orbit reprogrammability is real but bounded. Software-defined radios can be updated; optics cannot. If the mission requirement changes substantially after launch, the payload is fixed. This argues for spending more time on requirements definition before integration than most programmes budget for.
Lead times are also a constraint that surprises buyers. A custom bus with a custom payload integrated and tested to flight standard typically takes 24–36 months from contract to launch readiness. Off-the-shelf bus platforms with standard interfaces can compress this to 18 months in favourable conditions, but procurement, export licensing and launch scheduling add time that no manufacturer controls.
Designing for sovereignty from the start
A microsatellite bought as a black box delivers imagery; a microsatellite delivered with source access, hardware audit rights and trained national operators delivers a capability. The distinction matters when the supplier's geopolitical situation changes, when the satellite needs an anomaly response at 2 a.m. local time, or when the nation wants to build a second satellite without starting from zero.
Staged handover is practical at this mass class in a way it is not for large GEO platforms, where complexity makes national operation genuinely difficult. A 100 kg satellite with a well-documented bus, a trained ground team and access to the flight software repository is an asset a government can operate and extend. Satellize structures contracts around exactly this: source-access terms agreed before signature, hardware audit rights, and handover to national teams as a defined deliverable rather than an afterthought. The Tonga sovereign-communications restoration after the 2022 undersea cable break illustrated why that architecture matters when external dependencies fail.
Engineering parameters
| Mass class | 50–150 kg (dry, fully integrated with payload) |
| Average payload power | 100–300 W continuous; 500–1,500 W peak (battery-buffered) |
| Pointing accuracy (3-axis stabilised) | 0.01–0.1° depending on platform maturity and payload demand |
| Propulsion delta-v | 50–150 m/s (green monopropellant or cold-gas; electric options emerging) |
| Onboard storage | 256 GB–1 TB solid-state |
| Downlink rate (X-band typical) | 150–300 Mbps; optical inter-satellite links available on some platforms |
| Design lifetime | 3–7 years (orbit-dependent; LEO below 550 km benefits from natural deorbit) |
| Optical GSD at 500 km (20–35 cm aperture) | 1.0–2.5 m panchromatic; 2–5 m multispectral |
| Typical build-to-launch lead time | 18–36 months depending on customisation, export licensing and launch slot |
| Launch compatibility | ESPA Grande, dedicated small launchers (Vega-C, Electron, SSLV and equivalents) |
One contract, one accountable engineer
Commissioned as one programme, not a stack of contracts: spacecraft, launch, ground segment, mission control, training and handover are priced together. Source-access terms and audit rights are agreed in writing before signature. Review your payload requirements with our engineers.