Image acquired by the VENµS satellite, 2018, over the Zin Valley, Negev Desert, Israel
VENµS technological mission is aimed at evaluating and qualifying the Israeli Hall Effect Thruster (IHET) performance in space and demonstrating its usefulness and capabilities in performing orbit control tasks such as transferring from Low Earth Orbit (LEO) to another LEO and autonomous orbit maintenance at low altitudes while enabling imaging in a high drag environment.
The Israeli Hall Effect Thruster (IHET)
Thrust is produced by accelerating mass to high exhaust velocity. Electrical Propulsion Systems (EPS) use solar energy (usually captured by solar panels) to accelerate propellant ions (Xenon). Chemical propulsion systems store all their energy in the consumable propellant (Hydrazine). Thus, the EPS is much more efficient in fuel consumption.
In technical terms, EPS has an Isp of 1300 sec, vs. 220 for Hydrazine. This means that for every kg of propellant onboard the satellite, EPS will produce a 1300-Newton-seconds impulse, while Hydrazine will produce only 220. EPS produces low level thrusts, typically in the range of 15-90 mili-Newton, while chemical systems produce high level thrusts (1 to 25 Newtons).
On low earth orbits such as VENuS (410 km altitude in the 3rd year), drag significantly decays the orbit over time. Required compensations in thrust are quite small but daily corrections are needed in order to accurately maintain the orbit.
The low but effective thrust of the electrical propulsion makes it perfectly fitted for low weight / long lasting operation. As a precursor, VENuS will demonstrate the feasibility of a new concept for low orbit satellites based on electrical propulsion.
I – First ~2 years – at this stage, the primary mission of VENuS is to provide imaging (the scientific mission). Nevertheless, during this time, as part of the technological mission, IHET will be operated and tested once a month. Each test will generate orbit and other telemetry data that will be processed by the TMC. After each test, the orbit will return to its nominal value (circular 720 km, sun-synchronous, 2 days earth repeating).
II – Following ~6 month – VENµS will change orbit to a lower LEO (circular, 410 km, sun-synchronous, 2 days earth repeating).
III – Last period, minimum 1 year – during this stage VENµS will continue acquiring images at 410 km, while maintaining the orbit. To keep the high drag orbit, IHET will be activated every fourth revolution to correct the orbit.
Scheme demonstrating the time-sharing between the scientific and the technical missions
