Langmuir probe

Abstract

A method of determining payload potential may include the steps of receiving data on a first bias voltage and a resulting first collected current of a first needle of a multi-needle Langmuir probe, receiving data on a second bias voltage and a resulting second collected current of a second needle of the multi-needle Langmuir probe, assigning a value for the electron temperature in which the multi-needle Langmuir probe was operating, and using the current and voltage data, the assigned electron temperature value and Langmuir probe theory to calculate the platform potential of the multi-needle Langmuir probe.

Claims

1. A method of determining a platform potential, the method comprising: receiving data on a first bias voltage and a resulting first collected current of a first needle of a multi-needle Langmuir probe; receiving data on a second bias voltage and a resulting second collected current of a second needle of the multi-needle Langmuir probe; assigning a value for an electron temperature in which the multi-needle Langmuir probe was operating; and using the resulting first collected current data, the resulting second collected current data, the first bias voltage data, the second bias voltage data, and the value for the electron temperature to calculate the platform potential of the multi-needle Langmuir probe.

2. A method as claimed in claim 1, wherein the step of using the data to calculate the platform potential is performed in-orbit.

3. A method as claimed in claim 1, wherein the step of using the data to calculate the platform potential is performed in real-time.

4. A method as claimed in claim 2, comprising controlling the platform potential based on the calculated platform potential.

5. A method as claimed in claim 1, wherein the data is received from the multi-needle Langmuir probe with cylindrical probes and the platform potential is calculated using the following equation ${\left(\frac{I_2}{I_1}\right)}^2=\frac{V_e+V_{b2}-V_f}{V_e+V_{b1}-V_f}$ wherein I.sub.2 is the second collected current, I.sub.1 is the first collected current, V.sub.b2 is the second bias voltage, V.sub.b1 is the first bias voltage, V.sub.e is Boltzmann's constant times the electron temperature divided by the charge of an electron, and V.sub.f is the platform potential.

6. A non-transitory computer readable medium carrying computer-executable instructions which when executed by a processor cause the processor to be arranged to carry out the method of claim 1.

7. A device for determining a platform potential, the device comprising: a multi-needle Langmuir Probe; and a processor, wherein the processor is arranged to receive data on a first bias voltage and a resulting first collected current of a first needle of the multi-needle Langmuir probe; receive data on a second bias voltage and a resulting second collected current of a second needle of the multi-needle Langmuir probe; assign a value for an electron temperature in which the multi-needle Langmuir probe is operating; and use the resulting first collected current data, the resulting second collected current data, the first bias voltage data, the second bias voltage data, and the value for the electron temperature to calculate the platform potential of the multi-needle Langmuir probe.

8. A device as claimed in claim 7, wherein the processor is arranged to be able to calculate the platform potential when in orbit.

9. A device as claimed in claim 7, wherein the processor is arranged to calculate the platform potential when in real-time.

10. A device as claimed in claim 8, wherein the device comprises a controller that is arranged to control the platform potential based on the in orbit and/or real-time calculations.

11. A device as claimed in claim 10, wherein the device comprises an electron emitter which is arranged to be able to control the platform potential on the basis of the calculated platform potential.

12. A device as claimed in claim 7, wherein the multi-needle Langmuir probe has cylindrical probes.

13. A device as claimed in claim 12, wherein the processor is arranged to calculate the platform potential using the following equation ${\left(\frac{I_2}{I_1}\right)}^2=\frac{V_e+V_{b2}-V_f}{V_e+V_{b1}-V_f}$ wherein I.sub.2 is the second collected current, I.sub.1 is the first collected current, V.sub.b2 is the second bias voltage, V.sub.b1 is the first bias voltage, V.sub.e is Boltzmann's constant times the electron temperature divided by the charge of an electron, and V.sub.f is the platform potential.

14. A device as claimed in claim 7, wherein the multi-needle Langmuir probe has more than two probes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Certain preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

(2) FIG. 1 shows a representative response of a Langmuir probe;

(3) FIG. 2 shows an exemplary payload configuration with a m-NLP; and

(4) FIG. 3 shows an exemplary probe.

DETAILED DESCRIPTION

(5) Typical sounding rockets have a two-stage motor configuration consisting of a first stage motor, and a second stage motor. A payload after motor separation is shown in FIG. 2.

(6) The exemplary payload 10 comprises a number of devices 12, measuring i.e. plasma parameters. The payload also comprises a multi-Needle Langmuir Probe (m-NLP) 14 towards the aft of the payload 10. The m-NLP instrument 14 consists of four miniaturized cylindrical Langmuir probes 16. Each probe has the configuration shown in FIG. 3.

(7) The probes comprise a centre conductor 18, a dielectric insulator 20 and an outer braid 22. The dimensions mentioned below refer to a specific probe developed for use in the near Earth ionosphere. The exposed part of the centre conductor 18 has a length of 25 mm. Covering the unexposed part of the centre conductor is a dielectric insulator 20 which has an exposed length of about 1 mm. The unexposed part of the dielectric insulator 20 is surrounded by a braid 22 which has an exposed length of 15 mm. This is held within an insulation portion 24. The short insulation area 20 between the braid 22 and the centre conductor 18 is provided to avoid a short-circuit between the braid 22 and the centre conductor 18.

(8) The central conductor 18 has a diameter of 0.51 mm. A probe diameter of 0.51 mm gives a probe with a radius which is significantly smaller than the typically experienced Debye length. This means that sheath effects around the probe can be ignored in most circumstances.

(9) The dimensions may be scaled, for example, depending on the size of the spacecraft. For example, in a CubeSat the centre conductor 18 may have a diameter of 0.29 mm.

(10) In operation the probes 16 are each biased at different voltages ranging between typically +2.5 V and +10 V. Two probes 16 are mounted on one boom 26 on the aft deck of the payload. The other two probes 16 are mounted on another boom 28, mounted 180 degrees from the boom 26 with the other probes. The probes can be used simultaneously to measure the absolute electron density and the platform potential.

(11) When the m-NLP is in a plasma and the voltages are applied to each probe, the collected current of each probe is measured.

(12) A value for electron temperature in which the measurements are taken is estimated using a model. This value may be assigned before the measurements are taken.

(13) Using the bias of one of the probes (V.sub.b1) and the measured collected current of that probe (I.sub.1), the bias of another of the probes (V.sub.b2) and the measured collected current of that probe (I.sub.2) and the estimated value for electron temperature, the platform potential is calculated using the following equation:

(14) $R={\left(\frac{I_2}{I_1}\right)}^2=\frac{V_e+V_{b2}-V_f}{V_e+V_{b1}-V_f}$

(15) where V.sub.e is Boltzmann's constant times the electron temperature divided by the charge of an electron, V.sub.f is the platform potential and which when it is rearranged gives:

(16) $V_f=\frac{\left({\mathrm{RV}}_{b1}\right)-V_{b2}}{R-1}+V_e$

(17) The calculated value of platform potential is determined in orbit and in real time by a processor on board the payload 10. This calculated value of the platform potential is used to control an electron emitter (not shown) which controls the platform potential on the basis of the calculated platform potential.

(18) It should be apparent that the foregoing relates only to the preferred embodiments of the present application and the resultant patent. Numerous changes and modification may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.