Radiofrequency method and system for determining, by pairs of spacecraft, the relative angular position between a plurality of remote spacecraft

Patent metadata

Field	Value
Publication number	US-10126405-B2
Application number	US-201514610827-A
Country	US
Kind code	B2
Filing date	Jan 30, 2015
Priority date	Jan 31, 2014
Publication date	Nov 13, 2018
Grant date	Nov 13, 2018

Abstract

A system comprises: onboard a first craft, called host craft, a triplet of antennas comprising a transmitting and receiving antenna and two transmitting antennas, a transmission chain that can be successively coupled to each antenna of the triplet of antennas by a radiofrequency switch, a reception chain that can be coupled to the transmitting and receiving antenna, and a processing device intended to determine a relative angular position between, on the one hand, the host craft and, on the other hand, a plurality of spacecraft, called companion craft, from measurements of path differences performed and transmitted by the companion craft; onboard the companion craft, a transmitting and receiving antenna, a transmission chain and a reception chain coupled to the transmitting and receiving antenna and a measurement device intended to measure path differences between three signals originating from the three antennas of the triplet of antennas of the host craft.

First claim

The invention claimed is:

1. A method for determining, by pairs of spacecrafts, a relative angular position of a plurality of companion spacecrafts with respect to a host spacecraft, the method comprising:
sequentially transmitting radiofrequency signal from a triplet of host antennas mounted on a first face of the host spacecraft, the triplet of host antennas comprising a main transmitting and receiving antenna and two secondary transmitting antennas, the triplet of host antennas forming two antenna baselines of a known length and orientation in a reference frame attached to the host spacecraft, the sequential transmission including connecting an electronic source of the radiofrequency signal successively to each of the triplet of host antennas during an allocated time slot of a TDMA sequence containing at least 3+N time slots, N being a number of the companion spacecrafts, the radiofrequency signal comprising at least one radiofrequency carrier modulated by signaling data necessary for TDMA synchronization, both carrier and signaling data of the radiofrequency signal being synchronized to a host clock of the host spacecraft;
receiving the radiofrequency signal on a transmitting and receiving companion antenna of at least one of the companion spacecrafts;
measuring from the radiofrequency signal, onboard the at least one of the companion spacecrafts, three ranging measurements, each ranging measurement resulting from the receiving of the radiofrequency signal during a TDMA time slot associated with one of the host antennas and representing the length of a path between the one of the host antennas and the companion antenna, the three ranging measurements being equally biased by an imperfect synchronization between the host clock and a companion clock;
computing, onboard the at least one of the companion spacecrafts, an unbiased measurement of a path difference with respect to a first antenna baseline of the host spacecraft and an unbiased measurement of path difference with respect to a second antenna baseline of the host spacecraft;
transmitting, by the at least one of the companion spacecrafts from the transmitting and receiving companion antenna to the host spacecraft, in the TDMA time slot allocated to the at least one of the companion spacecraft, a radiofrequency signal transporting the unbiased measurements of path difference with respect to the antenna baselines of the host spacecraft;
receiving, onboard the host spacecraft on the main transmitting and receiving antenna, the radiofrequency signal; and
deducing, from the measurements of the radiofrequency signals and the known length and orientation of the two antenna baselines in the reference frame, an azimuth angle and an elevation angle of the companion antenna of the at least one of the companion spacecrafts with respect to a reference frame attached to the host spacecraft.

2. The method of claim 1 , wherein all the radiofrequency signals transmitted or received are modulated by an identical frequency carrier F 1 .

3. The method of claim 2 , further comprising: performing a first rotation of the host spacecraft about an axis Z parallel to a pointing axis of the triplet host antennas, the first rotation being performed in a first direction and having a rotation angle of a predetermined value;
acquiring measurements of path differences, at successive measurement instants during the first rotation;
computing path difference variations between the successive measurement instants;
measuring variations of inertial attitude of the host spacecraft at each successive measurement instant to determine the relative angular position between the host spacecraft and each companion spacecraft;
performing a second rotation of the host spacecraft about the axis Z to align the host spacecraft and each companion spacecraft, the second rotation being performed in a second direction opposite the first direction and having a rotation angle of a value substantially identical to the first rotation; and
performing a new measurement of the relative angular position between the host spacecraft and each companion spacecraft.

4. A system for determining, by pairs of spacecraft, a relative angular position of a plurality of companion spacecraft with respect to a host spacecraft configured to implement the method according to claim 1 , the system comprising a host spacecraft and a companion spacecraft, wherein:
the host spacecraft comprises:
at least one triplet of host antennas mounted on a first face, the triplet of host antennas comprising a main transmitting and receiving antenna and two secondary transmitting antennas, the triplet of host antennas forming two antenna baselines of known length and known orientation in a reference frame attached to the main craft,
a transmission chain configured to be successively coupled, in transmission, to each host antenna of the triplet of host antennas,
a reception chain configured to be coupled, in reception, to the main antenna,
a radiofrequency switch configured to sequentially select different host antennas of the triplet of host antennas, and
a processing device configured to determine azimuth and elevation angles of companion antenna of the companion spacecraft with respect to the reference frame linked to the host spacecraft from measurements of path differences transmitted by the companion spacecraft, and

the companion spacecraft comprises:
at least one transmitting and receiving antenna placed on a first face,
a transmission chain and a reception chain respectively coupled to the transmitting and receiving antenna, and
a measurement device configured to measure path difference with respect to the first antenna baseline of the host spacecraft and path difference with respect to the second antenna baseline of the host spacecraft.

5. The system according to claim 4 , wherein each of the host and companion spacecrafts further comprises a second transmitting and receiving antenna placed on a second face opposite the first face of the host and companions spacecrafts.

6. The system according to claim 5 , wherein each host and companion spacecraft comprises a triplet of antennas, a processing device and a device for measuring path differences.

7. The system according to claim 5 , further comprising, onboard each host and companion spacecraft, means for measuring the power level of the radiofrequency signal received by each transmitting and receiving antenna and means for selecting the transmitting and receiving antenna that has the greatest power level.

8. The system according to claim 4 , wherein the host spacecraft further comprises a device for measuring attitude variations of the host spacecraft.

Assignees

• Thales Sa

Inventors

• Thevenet Jean-Baptiste
• Mehlen Christian

Classifications

• B64G1/36

  using sensors, e.g. sun-sensors, horizon sensors · CPC title

• B64G1/1085

  Swarms and constellations · CPC title

• B64G1/24

  Guiding or controlling apparatus, e.g. for attitude control · CPC title

• G01S5/0247

  Determining attitude · CPC title

• G01S5/0284 Primary

  Relative positioning · CPC title