If I'm understanding you correctly, you're saying additional deceleration is possible using the additional xenon generated by the reactor. My immediate reaction is that you're overestimating the amount generated. I think you need to quantify the xenon produced by the reactor versus the xenon consumed by the additional acceleration.
This also assumes the Hermes has the power to sustain the additional ion thruster use. That needs to be justified. if your reactor has too much power, then that's weight that can be designed out to give a cheaper mission.
And the one that sneaks up on you over the longer term: What does slowing down do to the long term mission. Do they catch the MAV, but miss Earth....
Let's see. The Hermes weighs 110 tonnes and the article suggests it might have a 17MW power plant and 30 X3 thrusters.
From the linked paper, it does not seem unreasonable to suggest we might get an Isp of 4000s and hence an exhaust velocity of 40km/s or so. For the Hermes to accelerate at 2 mm/s/s the thrusters must exert a force of 220N. Hence we consume .55 grams of xenon per second, wanting about 6 tonnes of xenon for the maneuver. (Do I get about the same answer from conservation of momentum? Yes, I do. Hooray!)
And... no, you're right. The xenon production of the reactor is miniscule compared to that. Good catch.
I think they're OK in terms of the long-term mission since I had them decelerating into orbit; they can then accelerate again (using the xenon they, sigh, have not got) into something like the Earth-catching trajectory in the book.
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(no subject)
If I'm understanding you correctly, you're saying additional deceleration is possible using the additional xenon generated by the reactor. My immediate reaction is that you're overestimating the amount generated. I think you need to quantify the xenon produced by the reactor versus the xenon consumed by the additional acceleration.
This also assumes the Hermes has the power to sustain the additional ion thruster use. That needs to be justified. if your reactor has too much power, then that's weight that can be designed out to give a cheaper mission.
And the one that sneaks up on you over the longer term:
What does slowing down do to the long term mission. Do they catch the MAV, but miss Earth....
(no subject)
From the linked paper, it does not seem unreasonable to suggest we might get an Isp of 4000s and hence an exhaust velocity of 40km/s or so. For the Hermes to accelerate at 2 mm/s/s the thrusters must exert a force of 220N. Hence we consume .55 grams of xenon per second, wanting about 6 tonnes of xenon for the maneuver. (Do I get about the same answer from conservation of momentum? Yes, I do. Hooray!)
And... no, you're right. The xenon production of the reactor is miniscule compared to that. Good catch.
I think they're OK in terms of the long-term mission since I had them decelerating into orbit; they can then accelerate again (using the xenon they, sigh, have not got) into something like the Earth-catching trajectory in the book.