Engine thrust/weight ratio

[sevenperforce]

This is more of a simple question than a topic, per se, but what's a ballpark T/W ratio for a monopropellant hydrazine thruster? How about for a monopropellant hydrogen peroxide thruster? I can see the T/W ratio for something like the Merlin 1D quoted online but comparable figures for monoprop thrusters aren't forthcoming.

[SomeGuy123]

Monoprop thrusters would be higher.

The reason is the exhaust is cooler (lower energy reaction) and so flat out you can dump more fuel into the engine faster.  More efficient engines have lower TWR.

Of course, you'd never want to do this, fuel mass isn't free, so nobody builds them this way.

[sevenperforce]

Huh. One of the hydrazine thrusters I saw for sale online (used in various spacecraft) weighed in at 650 grams but only had a peak thrust of 24.6 N.

[Streetwind]

13 hours ago, sevenperforce said:

Huh. One of the hydrazine thrusters I saw for sale online (used in various spacecraft) weighed in at 650 grams but only had a peak thrust of 24.6 N.

Reaction control thrusters aren't built for TWR. They're built for minimum ignition delays, maximum throttle range and speed, and infinite rapid restart capability. 25N is perfectly fine for reaction control on most robotic spacecraft.

[sevenperforce]

8 hours ago, Streetwind said:

Reaction control thrusters aren't built for TWR. They're built for minimum ignition delays, maximum throttle range and speed, and infinite rapid restart capability. 25N is perfectly fine for reaction control on most robotic spacecraft.

Wonder what the theoretical maximum TWR for monoprop thrusters is, then.