Microgravity in low earth orbit with continuous electric propulsion
Systems and methods for achieving pristine microgravity in low earth orbit (LEO) using electric propulsion. Long-duration, low thrust, electric thrusters provide a constant thrust force for a pristine microgravity environment within a given volume of a space vehicle experiencing drag forces in LEO. Large space vehicles in LEO configured to be pressurized for human habitation, for instance having a mass of at least 40,000 kg and an internal volume of at least 400 m 3 , can use the electric propulsion systems and methods to achieve a quasi-steady acceleration less than or equal to 1.0 μg for durations of 180 consecutive days or longer.
1. A system for maintaining a micro-gravity environment in low earth orbit (LEO), the system comprising:
a space vehicle having an internal volume of at least 400 m 3 configured to be pressurized for human habitation, a mass of at least 40,000 kg, and configured to travel in LEO along an orbit in a forward direction, wherein a drag force acts on the space vehicle in an aft direction opposite the forward direction when the space vehicle travels in LEO; and
a solar electric propulsion system comprising:
a propellant storage tank configured to hold at least 300 kg of Xenon; and
a plurality of electric propulsion thrusters configured to collectively generate a thrust force in the forward direction continuously for a time period of at least 180 days and with a magnitude substantially equal to the drag force such that the internal volume within the space vehicle maintains over the time period a quasi-steady acceleration less than or equal to 1.0 μg.
2. The system of claim 1 , wherein the plurality of electric propulsion thrusters are configured to collectively generate the thrust force such that at least 160 m 3 of the internal volume maintains over the time period a quasi-steady acceleration less than or equal to 0.5 μg.
3. The system of claim 1 , wherein the plurality of electric propulsion thrusters are configured to collectively generate the thrust force such that at least 8 m 3 of the internal volume maintains over the time period a quasi-steady acceleration less than or equal to 0.1 μg.
4. The system of claim 1 , further comprising a drop tower space within the space vehicle, wherein the plurality of electric propulsion thrusters are configured to collectively generate the thrust force such that a payload released within the drop tower space experiences pristine microgravity continuously for at least 15 minutes.
5. The system of claim 1 , wherein the drag force is greater than or equal to 0.050 Newtons.
6. The system of claim 1 , wherein the plurality of electric propulsion thrusters comprises a plurality of Hall effect thrusters each having at least 1 kW power output.
7. The system of claim 1 , wherein the plurality of electric propulsion thrusters are gimballed.
8. The system of claim 1 , wherein the plurality of electric propulsion thrusters each have a specific impulse of 2,600 s.
9. The system of claim 1 , wherein the propellant storage tank is configured to hold at least 500 kg of Xenon.
10. The system of claim 1 , where the space vehicle further comprises a solar array configured to generate electrical energy for use by the solar electric propulsion system.
11. The system of claim 1 , wherein the time period is at least 1800 days in the absence of external forces other than drag.
12. The system of claim 1 , wherein the time period is at least ten years.
13. The system of claim 1 , wherein the plurality of electric propulsion thrusters draw 1 kW while in operation.
14. The system of claim 1 , wherein the plurality of electric propulsion thrusters comprises five or more electric propulsion thrusters.
15. The system of claim 1 , wherein one or more of the plurality of electric propulsion thrusters is redundant.
16. The system of claim 1 , wherein the plurality of electric propulsion thrusters are configured to generate the thrust force continuously such that a first derivative of the orbital altitude with respect to time exists over the entire time period.
17. The system of claim 1 , wherein the plurality of electric propulsion thrusters are configured to generate the thrust force continuously such that a plot of orbital altitude versus time contains no points over the entire time period.
18. The system of claim 1 , wherein the plurality of electric propulsion thrusters are configured to generate the thrust force continuously such that a plot of orbital altitude versus time is substantially planar over the entire time period.
19. The system of claim 1 , wherein the plurality of electric propulsion thrusters are configured to collectively generate the thrust force such that the orbit is maintained between +/−10 km of a desired orbital altitude during the time period.
20. The system of claim 19 , wherein the desired orbital altitude is between about 350 km and about 450 km.
21. The system of claim 1 , wherein the space vehicle comprises a first habitat portion and a second habitat portion.
22. The system of claim 21 , wherein the first habitat portion has a volume of at least 400 m 3 , and the second habitat portion has a volume of at least 550 m 3 .
23. The system of claim 21 , wherein the first habitat portion and the second habitat portion each have a length of at least 14 meters and an outer diameter of at least 6 meters.
24. The system of claim 21 , further comprising a service module containing the solar electric propulsion system, wherein the service module is configured to couple with the first habitat portion.
25. The system of claim 21 , further comprising a docking node configured to couple the second habitat with the first habitat.
26. The system of claim 25 , wherein the docking node is an integral part of the first or the second habitat.
27. The system of claim 25 , wherein the docking node has a volume of at least 250 m 3 .