Spatial scanning PNT
The present invention provides a global, cislunar, interplanetary, local navigation system that can provide position, navigation, and/or time (PNT) to users. Embodiments may use scanning active electronically steerable antennas (AESA) on multiple satellite (or other) sources that scan their beams over a volume of interest. This enables the use of high-gain antenna beams while at the same time spanning an operating volume with multiple users. Users and satellite sources can establish bilateral links and perform two-way time transfer (TWTT) to provide users with range and time correction. Bilateral links can provide authentication, registration of users, user-specific security keying, a means for allowance and/or denial of access, and enables a paid service. The scanning beam approach means each user can get a ranging/time update for only a fraction of the time.
1 . A position, navigation, and/or time (PNT) system comprising:
at least one satellite configured to transmit PNT signal transmissions at a fixed interval;
at least one receiver unit bidirectionally linked to the at least one satellite via a bidirectional link;
a satellite active electronically steerable antenna (AESA) coupled to each satellite of the at least one satellite and a receiver AESA coupled to each receiver unit of the at least one receiver unit, wherein the satellite AESA is configured to scan a beam over a volume of interest and the receiver AESA is configured to scan to acquire the beam;
wherein the bidirectional link is configured to use two-way time transfer to acquire time and range updates, and wherein the at least one receiver unit is configured to receive and transmit for the two-way time transfer during a dwell time of the scanned beam that is less than the fixed interval; and
an inertial navigation system coupled to the at least one receiver unit configured to provide PNT between successive time and range updates by using an extended Kalman filter to fuse inertial navigation system data with the time and range updates.
2 . The PNT system of claim 1 , wherein the satellite AESA is configured to scan a narrow beam over the volume of interest.
3 . The PNT system of claim 1 , wherein each receiver unit is bidirectionally linked to each satellite using two-way time transfer.
4 . The PNT system of claim 3 , wherein each satellite is further configured to transmit pseudo-noise (PN) codes with correlations for pseudo-range calculations.
5 . The PNT system of claim 1 , wherein the at least one satellite includes a unidirectional link to the at least one receiver unit, wherein said unidirectional link is configured to use pseudo-noise (PN} codes with correlations for pseudo-range calculations at the at least one receiver unit.
6 . The PNT system of claim 1 , further comprising a control station including a master reference clock.
7 . The PNT system of claim 6 , wherein each satellite performs periodic time updates by utilizing two-way time transfer with said master reference clock.
8 . The PNT system of claim 1 , wherein each satellite further includes an oscillator calibrated by a master reference clock using two-way time transfer.
9 . The PNT system of claim 1 , wherein the satellite AESA and the receiver AESA utilize a time division multiplexing scheme when scanning.
10 . The PNT system of claim 1 , wherein the at least one satellite comprises a plurality of satellites that are in communication with each other by an optical inter-satellite link.
11 . A position, navigation, and/or time (PNT} system comprising:
a plurality of satellites;
a plurality of receiver units;
a bidirectional link between each receiver unit of the plurality of receiver units and at least one satellite of the plurality of satellites, wherein each bidirectional link is configured to use two-way time transfer,
a satellite active electronically steerable antenna (AESA) coupled to each satellite of the plurality of satellites and a receiver AESA coupled to each receiver unit of the plurality of receiver units, wherein each satellite AESA is configured to scan a beam over a volume of interest during an update period, wherein each update period occurs after a fixed interval of time, and wherein each receiver unit is configured to receive and transmit for the two-way time transfer during a dwell time of the scanned beam that is less than the fixed interval; and
an inertial navigation system coupled to each receiver unit of the plurality of receiver units,
wherein at each update period, a receiver unit of the plurality of receiver units is configured to establish the bidirectional link to at least one satellite of the plurality of satellites to determine PNT; and
wherein the inertial navigation system is configured to provide PNT between successive update periods by utilizing an extended Kalman filter to fuse inertial navigation system data with time and range updates obtained via the two-way time transfer.
12 . The PNT system of claim 11 , wherein each bidirectional link is configured to use pseudo-noise (PN) codes with correlations for pseudo-range calculations.
13 . The PNT system of claim 11 , further including a unidirectional link between at least one satellite of the plurality of satellites and at least one receiver unit of the plurality of receiver units.
14 . The PNT system of claim 13 , wherein each unidirectional link is configured to use pseudo-noise (PN) codes with correlations for pseudo-range calculations at the at least one receiver unit.
15 . The PNT system of claim 11 , further comprising a control station including a master reference clock.
16 . The PNT system of claim 11 , wherein an intersection of the scanned beams from three satellites of the plurality of satellites creates an operational volume.
17 . The PNT system of claim 16 , wherein the operational volume is configured such that a user in the operational volume is visible to at least three satellites.
18 . A method for determining position, navigation, and/or time (PNT) using a receiving unit, the method comprising the steps of:
performing a first update by bidirectionally linking the receiving unit to a first satellite using two-way time transfer between the receiving unit and the first satellite to acquire a time and range update at a first location of the receiving unit;
performing a second update, a fixed amount of time after the first update, by bidirectionally linking the receiving unit to a second satellite using the two-way time transfer between the receiving unit and the second satellite to acquire a time and range update at a second location of the receiving unit;
performing a third update, the fixed amount of time after the second update, by bidirectionally linking the receiving unit to a third satellite using the two-way time transfer between the receiving unit and the third satellite to acquire a time and range update at a third location of the receiving unit;
determining inertial navigation system (INS) data, using an inertial navigation system, the INS data including the relative motion of the receiving unit between the first, second, and third time and range updates; and
determining the PNT of the receiving unit utilizing an extended Kalman filter, the INS data, and the first, second, and third time and range updates,
wherein the first, second, and third updates are discrete and sequential, not simultaneous, and the receiving unit receives and transmits for the two-way time transfer only during respective dwell times of beams scanned over a volume of interest by active electronically steerable antennas (AESAs) of the receiving unit and the respective satellites, wherein the respective dwell times are less than the fixed amount of time.
19 . The method according to claim 18 , wherein each respective satellite includes a satellite AESA configured to scan a narrow beam over the volume of interest at each respective update.
20 . The method according to claim 18 , further including the step of using pseudo-noise (PN) codes with correlations to make pseudo-range calculations.