How much of the world's xenon has been used in spaceflight altogether? Is it a lot? Did it cost a lot?
Mass ratio of solar-electric versus radioisotope thermo-electric power for propulsion; beyond how many AU do RTGs win?
Why was SERT-1 put in a suborbital trajectory (4000 km apogee) while SERT-2 (1970-009A) was put in a 1000 km circular polar orbit?
What is Australia's Bartolomeo platform? When does it arrive at the ISS; when and where will it be attached?
What's this small source of glowing blue plasma next to Psyche's Hall effect thruster for? What does it do and why does the plasma curve and connect?
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