One can often spot that liquid apogee engines are 440 N and attitude control systems are 22 N.
Is there a reason why the thrusts are proportional? If the engines are scaled for reducing development cost and time, are there any engineering advantages to have them proportional? Or more specifically, why is a 22N and 440N engine quite common?
- In the opening abstract of High Temperature Thruster Technology for Spacecraft Propulsion
Stationkeeping class 22 N engines fabricated from iridium-coated rhenium have demonstrated steady state specific impulses 20 to 25 seconds higher than niobium chambers. Ir-Re apogee class 440 N engines are expected to deliver an additional 10 to 15 seconds
- Again in the opening abstract of Low-Thrust Liquid Engines of ISRO
The 440N thrust bi-propellant Liquid Apogee Motor(LAM) is used in INSAT-2 series of spacecraft for orbit raising and the 22N thrust bi-propellant engines are used for attitude control and station keeping.
- Though Rocketdyne list so many engines of various thrust range, one cannot miss the 22N and 440N engine among the Monopropellant and Bipropellant engines
- The GOES handbook on Propulsion subsystem mentions a similar 490N apogee thruster(which is close to 440N) and 22N attitude and orbit control thrusters.
The subsystem consists of one 490-N (110-lb) apogee thruster and twelve 22-N (5-lb) attitude and orbit control thrusters, using liquid bipropellants
- There is an ESA requirement document precisely requesting a 22N engine.