Turbomolecular air-scoop for satellite air-breathing electric propulsion
In one embodiment, an air-scoop includes an air inlet that air molecules enter the air-scoop through at an orbital speed when the air-scoop is moving through an atmosphere at the orbital speed. The air-scoop also includes a rotor that is rotated by a motor at a rotational speed, and the rotor includes multiple rotatable blade stages. A first one of the rotatable blade stages has a blade configuration that maximizes transparency of the first one of the rotatable blade stages to air molecules entering the air-scoop through the air inlet at the orbital speed when the rotor is rotating at the rotational speed. A last one of the rotatable blade stages has a blade configuration that maximizes opacity of the last one of the rotatable blade stages to air molecules in the air-scoop flowing directionally toward the air inlet when the rotor is rotating at the rotational speed.
1. An air-scoop comprising:
an air inlet that air molecules enter the air-scoop through at approximately an orbital speed when the air-scoop is moving through an atmosphere at approximately the orbital speed; and
a rotor configured to be rotated by a motor at approximately a rotational speed, wherein:
the rotor comprises a plurality of rotatable blade stages;
each of the rotatable blade stages comprises a blade configuration that comprises a blade aspect ratio and a blade attack angle, wherein the blade aspect ratio is a quotient of blade width and blade separation in the rotatable blade stage;
a first one of the rotatable blade stages is positioned closest among the rotatable blade stages to the air inlet, wherein the blade configuration of the first one of the rotatable blade stages substantially maximizes transparency of the first one of the rotatable blade stages to air molecules entering the air-scoop through the air inlet at approximately the orbital speed when the rotor is rotating at approximately the rotational speed; and
a last one of the rotatable blade stages is positioned farthest among the rotatable blade stages from the air inlet, wherein the blade configuration of the last one of the rotatable blade stages substantially maximizes opacity of the last one of the rotatable blade stages to air molecules in the air-scoop flowing directionally toward the air inlet when the rotor is rotating at approximately the rotational speed;
wherein the blade configuration of the first one of the rotatable blade stages is different from the blade configuration of the last one of the rotatable blade stages.
2. The air-scoop of claim 1 , wherein:
the transparency of the first one of the rotatable blade stages to air molecules entering the air-scoop through the air inlet is dependent on the blade attack angle of the first one of the rotatable blade stages; and
the blade attack angle of the first one of the rotatable blade stages is calculated based on a quotient of approximately the orbital speed and a linear-speed representation of approximately the rotational speed.
3. The air-scoop of claim 1 , wherein the rotor comprises one or more rotatable blade sections that each comprise one or more of the rotatable blade stages.
4. The air-scoop of claim 3 , wherein
the rotor comprises two or more rotatable blade sections that each comprise one or more of the rotatable blade stages; and
each of the rotatable blade sections is axially separated from each of one or more adjacent ones of the rotatable blade sections.
5. The air-scoop of claim 3 , wherein each of one or more of the rotatable blade sections comprises two or more rotatable blade stages and each of one or more of the blades of each of the rotatable blade stages in the rotatable blade section is contiguous with a corresponding one of the blades of each of one or more adjacent ones of the rotatable blade stages in the rotatable blade section.
6. The air-scoop of claim 3 , wherein, in each of one or more of the rotatable blade sections, the blade geometry varies substantially smoothly along an axial length of the rotatable blade section.
7. The air-scoop of claim 1 , wherein, in each of one or more of the rotatable blade stages, the blade aspect ratio and the blade attack angle vary along a radial length of rotatable blade stage.
8. The air-scoop of claim 7 , wherein the blade aspect ratio is wider and the blade attack angle is shallower farther out along the radial length of the rotatable blade stage.
9. The air-scoop of claim 1 , wherein a leading edge of the first one of the rotatable blade stages is substantially coincident with an inlet plane of the air inlet.
10. The air-scoop of claim 1 , wherein
one or more intermediate ones of the rotatable blade stages are positioned between the first one of the rotatable blade stages and the last one of the rotatable blade stages; and
each of the intermediate ones of the rotatable blade stages comprises a blade configuration that balances between transparency of the intermediate one of the rotatable blade stages to air molecules in the air-scoop flowing directionally away from the air inlet when the rotor is rotating at approximately the rotational speed with opacity of the intermediate one of the rotatable blade stages to air molecules in the air-scoop flowing directionally toward the air inlet when the rotor is rotating at approximately the rotational speed.
11. The air-scoop of claim 1 , wherein:
the blade attack angle of first one of the rotatable blade stages is between approximately 84° and approximately 79° and the blade aspect ratio of the first one of the rotatable blade stages is between approximately 1.0 and approximately 0.9;
the blade attack angle of the last one of the rotatable blade stages is between approximately 8° and approximately 3° and the aspect ratio of the last one of the rotatable blade stages is between approximately 0.9 and approximately 0.8.
12. The air-scoop of claim 1 , wherein the air-scoop further comprises stators between the rotatable blade stages.
13. The air-scoop of claim 1 , wherein the air-scoop further comprises counter-rotatable blade stages between the rotatable blade stages.
14. The air-scoop of claim 1 , wherein:
the air-scoop further comprises an air outlet that air molecules exit the air-scoop through when the air-scoop is moving through the atmosphere at approximately the orbital speed and the rotor is rotating at approximately the rotational speed; and
when the air molecules exit the air-scoop, the air molecules are substantially thermalized.
15. A spacecraft-propulsion system comprising:
a thruster operable to generate thrust; and
an air-scoop operable to supply air to the thruster as propellant, wherein the air-scoop comprises:
an air inlet that air molecules enter the air-scoop through at approximately an orbital speed when the air-scoop is moving through an atmosphere at approximately the orbital speed; and
a rotor configured to be rotated by a motor at approximately a rotational speed, wherein:
the rotor comprises a plurality of rotatable blade stages;
each of the rotatable blade stages comprises a blade configuration that comprises a blade aspect ratio and a blade attack angle, wherein the blade aspect ratio is a quotient of blade width and blade separation in the rotatable blade stage;
a first one of the rotatable blade stages is positioned closest among the rotatable blade stages to the air inlet, wherein the blade configuration of the first one of the rotatable blade stages substantially maximizes transparency of the first one of the rotatable blade stages to air molecules entering the air-scoop through the air inlet at approximately the orbital speed when the rotor is rotating at approximately the rotational speed; and
a last one of the rotatable blade stages is positioned farthest among the rotatable blade stages from the air inlet, wherein the blade configuration of the last one of the rotatable stages substantially maximizes opacity of the last one of the rotatable blade stages to air molecules in the air-scoop flowing directionally to ward the air inlet when the rotor is rotating at approximately the rotational speed
wherein the blade configuration of the first one of the rotatable blade stages is different from the blade configuration of the last one of the rotatable blade stages.
16. The spacecraft-propulsion system of claim 15 , wherein:
the air-scoop is a first one of two air-scoops; and
a second one of the two air-scoops comprises a rotor that is configured to rotate in an opposite direction from the rotor in the first air-scoop but is otherwise substantially identical to the first one of the two air-scoops.
17. The spacecraft-propulsion system of claim 15 , wherein the thruster is a Hall-effect thruster (HET) or a gridded ion thruster (GIT).
18. A spacecraft comprising:
a payload; and
a spacecraft bus comprising:
a thruster operable to generate thrust; and
an air-scoop operable to supply air to the thruster as propellant, wherein the air-scoop comprises:
an air inlet that air molecules enter the air-scoop through at approximately an orbital speed when the spacecraft is moving through an atmosphere at approximately the orbital speed; and
a rotor configured to be rotated by a motor at approximately a rotational speed, wherein:
the rotor comprises a plurality of rotatable blade stages;
each of the rotatable blade stages comprises a blade configuration that comprises a blade aspect ratio and a blade attack angle, wherein the blade aspect ratio is a quotient of blade width and blade separation in the rotatable blade stage;
a first one of the rotatable blade stages is positioned closest among the rotatable blade stages to the air inlet, wherein the blade configuration of the first one of the rotatable blade stages substantially maximizes transparency of the first one of the rotatable blade stages to air molecules entering the air-scoop through the air inlet at approximately the orbital speed when the rotor is rotating at approximately the rotational speed; and
a last one of the rotatable blade stages is positioned farthest among the rotatable blade stages from the air inlet, wherein the blade configuration of the last one of the rotatable stages substantially maximizes opacity of the last one of the rotatable blade stages to air molecules in the air-scoop flowing directionally toward the air inlet when the rotor is rotating at approximately the rotational speed
wherein the blade configuration of the first one of the rotatable blade stages is different from the blade configuration of the last one of the rotatable blade stages.
19. The spacecraft of claim 18 , wherein:
the air-scoop is a first one of two air-scoops; and
a second one of the two air-scoops comprises a rotor that is configured to rotate in an opposite direction from the rotor in the first air-scoop but is otherwise substantially identical to the first one of the two air-scoops.
20. The spacecraft of claim 18 , wherein:
the thruster is configured to generate a specific impulse I sp that is greater than
v
orb
C
D
2
g
η
s
;
v orb is approximately the orbital speed;
C D is approximately a drag coefficient of the spacecraft;
g is approximately a gravitational acceleration of Earth; and
η s is approximately a collection efficiency of the air-scoop.
21. The spacecraft of claim 18 , wherein the thruster is a Hall-effect thruster (HET) or a gridded ion thruster (GIT).
22. The spacecraft of claim 18 , wherein the spacecraft bus further comprises a propellant-storage tank and a propellant-flow-control system.
23. The spacecraft of claim 18 , wherein:
the spacecraft bus further comprises a solar array and a battery; and
the spacecraft is operable to supply electric power to the thruster from the solar array or the battery.