Electrical/chemical thruster using the same monopropellant and method

Patent metadata

Field	Value
Publication number	US-2017191471-A1
Application number	US-201615391430-A
Country	US
Kind code	A1
Filing date	Dec 27, 2016
Priority date	Dec 31, 2015
Publication date	Jul 6, 2017
Grant date	—

Abstract

A thruster operable in a chemical mode or in an electrospray mode using the same liquid monopropellant for operation in both modes is described having a multiplicity of a microthrusters made of a catalytic material having a bore therethrough, where, when operated in the chemical mode, the microthrusters are heated to decompose the monopropellant the monopropellant flows therethrough to generate relatively high thrust. An extractor is positioned downstream of the outlet ends of the microthrusters, such that when the system is operated in its electrospray mode the flowrate of the monopropellant through the microthrusters is substantially lower than in the chemical mode and the extractor is energized with an electric field so that ions and droplets are discharged from the microthrusters and accelerated so as to yield a relatively high specific impulse.

First claim

What is claimed is:

1 . An electrical/chemical thruster for a spacecraft operable in a chemical mode and in an electrospray mode that utilizes a liquid monopropellant for operation in both of said modes, said thruster having a plurality of microthrusters, each said microthruster comprising a microtube having a bore therethrough and having an inlet end and an outlet end with said inlet ends of said microtubes being in communication with a supply of said monopropellant, each said microtube being of a catalytic material capable of being heated to a preheat temperature sufficient to substantially decompose said monopropellant as said monopropellant flows therethrough at a first flowrate so as to generate relatively high thrust when operated in said chemical mode as compared to when operated in said electrospray mode, and wherein said thruster further includes a extractor proximate the outlet ends of said microtubes, whereby when said thruster is operated in its electrospray mode with said extractor being energized with an electric field so that as said monopropellant flows through said microtubes at a second flowrate substantially less than said first flowrate ions and charged droplets discharged from said microtubes are accelerated so as to yield a relatively high specific impulse as compared to operation of said microtube when operated in its chemical mode.

2 . A thruster as set forth in claim 1 wherein said monopropellant comprises a mixture of one or more nonvolatile fuels and an oxidizer, at least one of which is an ionic liquid.

3 . A thruster as set forth in claim 2 wherein said monopropellant has a fuel/oxidizer mixture ratio such that solid carbon forms are substantially not present in the exhaust after chemical decomposition.

4 . A thruster as set forth in claim 2 wherein said monopropellant comprises [Bmim][NO 3 ] and hydroxyl ammonium nitrate (HAN).

5 . A thruster as set forth in claim 2 wherein said monopropellant comprises [Emim][EtSO 4 ] and hydroxyl ammonium nitrate (HAN).

6 . A thruster as set forth in claim 3 wherein said microtube is a capillary emitter having an inner diameter of about 100 μm, plus or minus about 50%, and having a length of about 30 mm., plus or minus about 50%.

7 . A thruster as set forth in claim 6 wherein said capillary emitter is made substantially from a catalytic metal, such as platinum, rhenium, rhodium, or iridium.

8 . A thruster as set forth in claim 7 wherein said microtube, when operated in its chemical mode, is heated to the said preheat temperature by an electric current.

9 . A thruster as set forth in claim 8 wherein said preheat temperature is about 300° C., plus or minus about 50° C.

10 . A thruster as set forth in claim 8 , wherein said first flowrate when said microtube is operated in its chemical mode is about 20 μL/second/microtube, plus or minus about 10 μL/sec/microtube such that each microtube will generate a thrust of about 50 μN, plus or minus about 50%.

11 . A thruster as set forth in claim 8 , wherein said second flowrate when said microtube is operated in its electrospray mode is about 3 pL/second/microtube, plus or minus about 1 pL/second/microtube, and wherein when so operated in its electrospray mode each said microtube generates a specific impulse of about 800 seconds, plus or minus about 90%.

12 . A thruster as set forth in claim 7 where thrust may be scaled up by a thruster having a plurality of said microthrusters.

13 . A thruster as set forth in claim 1 wherein said thruster is supplied with said monopropellant from a monopropellant tank, and wherein said thruster has a propellant manifold in communication with said tank, said manifold containing a supply of said liquid monopropellant so that when said thruster is actuated said monopropellant is supplied to the inlet ends of said microthrusters such that monopropellant flows through substantially all of said microthrusters at said first flowrate when operated in said chemical mode.

14 . A thruster as set forth in claim 1 wherein said first flowrate is sufficiently low to initiate decomposition of the monopropellant prior to exiting the end of the emitter, and wherein said first flow rate is sufficiently high to prevent the reaction front from propagating back into said supply of monopropellant

15 . A thruster as set forth in claim 1 wherein said monopropellant flows through substantially all of said microthrusters at said second flowrate when operated in said electrospray mode.

16 . A thruster for use in a spacecraft propulsion system that is operable in a chemical mode and in an electrospray mode and that utilizes a liquid monopropellant for operation in both of said modes, said thruster having a plurality of microthrusters, each said microthruster comprising a microtube having a bore therethrough and having an inlet end and an outlet end with said inlet end being in communication with a supply of said monopropellant, said microtubes being of a catalytic metal that is capable of being heated to a preheat temperature sufficient to substantially decompose said monopropellant in said microtube as said monopropellant flows therethrough at a first flowrate so as to generate relatively high thrust when operated in its chemical mode as compared to when operated in its electrospray mode, and wherein said thruster further includes a extractor downstream of the outlet end of said microtubes, which, when said thruster is operated in its electrospray mode, is energized with an electric field such as said monopropellant flows through said microtubes at a second flowrate substantially less than said first flowrate ions and droplets discharged from said microtubes are accelerated so as to yield a relatively high specific impulse as compared to operation of said microtube when operated in its chemical mode.

17 . A thruster as set forth in claim 16 wherein said monopropellant comprises a mixture of one or more nonvolatile fuels and an oxidizer, at least one of which is an ionic liquid.

18 . A thruster as set forth in claim 17 wherein said monopropellant comprises [Bmim][NO 3 ] and hydroxyl ammonium nitrate (HAN).

19 . A thruster as set forth in claim 17 wherein said monopropellant comprises [Emim][EtSO 4 ] and hydroxyl ammonium nitrate (HAN).

20 . A multimode propulsion system for a spacecraft that may be operated in a chemical mode and in an electrospray mode using the same monopropellant, said propulsion system having at least one thruster having a plurality of microthrusters, each microthruster comprising a microtube of a suitable catalytic metal and having an inlet end and outlet end with a bore therethrough, with the bore having an internal diameter of about 100 μm, plus or minus 50%, said microtube having a length of about 30 mm., plus or minus 50%, a monopropellant system for supplying said monopropellant to the inlet ends of said microtubes at a first flowrate for operation of said microthrusters in either their said chemical mode or at a second flowrate for operation of said microthrusters in their said electrospray mode, said first flowrate being substantially greater than said second flowrate, means for heating said microtubes when said thruster is operated in said chemical mode to a temperature sufficient to initiate chemical decomposition of said monopropellant and where said first flowrate of said monopropellant through said microtubes is sufficient to allow ignition of said monopropellant in said microtubes but prevents the propagation of chemical decomposition of said monop

Assignees

• Univ Missouri

Inventors

• Berg Steven P
• Rovey Joshua L

Classifications

• F02K9/52

  Injectors · CPC title

• F02K9/425 Primary

  Propellants · CPC title

• F03H1/0012

  Means for supplying the propellant · CPC title

• F02K9/94

  Re-ignitable or restartable rocket- engine plants; Intermittently operated rocket-engine plants · CPC title

• F03H1/0037 Primary

  Electrostatic ion thrusters · CPC title