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Next Generation Ion-Atomic Clock for Earth Orbit and Deep Space

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Jet Propulsion Laboratory California Institute of Technology Next Generation Space Atomic Clock Space Communications and Navigation (SCaN) Technology Deep Space Atomic Clock John D. Prestage- 1 Next Generation Space Atomic Clock Jet Propulsion Laboratory California Institute of Technology !! Hg Ion Clock Technology was selected as NASA OCT TDM !! Outline - Motivation for clocks in space, NASA deep space navigation - Key features and inherent strengths - DSAC Technology Demonstration Mission Overview - GPS infusion path - Ion Atomic Clock Hardware - Miniaturization via DARPA IMPACT Deep Space Atomic Clock Stanford 2011 PNT Challenges and Opportunities, Nov 18th John D. Prestage- 2 Next Generation Space Atomic Clock Jet Propulsion Laboratory DSAC Compared to Other Space Based Clocks California Institute of Technology Planetary orbit eclipse period Deep Space Atomic Clock Stanford 2011 PNT Challenges and Opportunities, Nov 18th John D. Prestage- 3 Next Generation Space Atomic Clock Jet Propulsion Laboratory Simple Design/ Inherently Insensitive California Institute of Technology • No Lasers • No Cryogenics • No Microwave cavities • No Light Shift (as in Rb cell clocks) • No Consumables (as in H-maser, Cs beam clocks) A comparison of microwave space atomic clock technologies and the Hg Ion Clock. H-Maser Cesium Clock Rubidium Clock Hg Ion Clock No Consumables; H dissociation, flow 2 Hg vapor sealed in vacuum through. Cesium oven, Cs beam. Glass cell with Rb vapor; Lifetime limits tube. Life limited by H supply. Life limited by Cs supply Rb not consumed 2 Ions held by rf/dc force fields. Life limited by pump life. No wall collisions. Microwave cavity 9.2 GHz; No microwave cavities, Microwave; Microwave cavity 6.8 GHz; Microwave cavity 1.4 GHz. laser or magnetic deflection RF excited Hg lamp. RF excited Rb lamp state-selection state selection No lasers. Rad-tolerant with magnetic Rad-tolerant; Rad-tolerant; Radiation tolerant Radiation state selectors; Used in GPS; Used in GALILEO. (Similar to GPS Rb) less tolerant with laser. ~100 krad/yr for >10 yrs Several shield layers; Magnetic Reference field ~ 1 mG. 3 layer shields; Several shield layers Several shield layers Sensitivity Highest inherent Lowest magnetic sensitivity sensitivity. ~ 10-13/C Temperature Cavity stabilized to Laser cooled clocks ~ 10-15/C ~ 10-13/C Sensitivity ~ 0.001 C require 0.002 C Lowest temp sensitivity stabilization Deep Space Atomic Clock Stanford 2011 PNT Challenges and Opportunities, Nov 18th John D. Prestage- 4 Next Generation Space Atomic Clock Jet Propulsion Laboratory Mission Architecture California Institute of Technology Experiment • Data collection for a year on orbit – Collect line-of-site GPS pseudo- range/carrier phase data on Iridium NEXT Hosted Payload with GPS receiver/atomic clock – On selected GPS satellite, collect GPS pseudo-range/phase at JPL and other IGS ground stations GPS receiver/atomic clock (needed to solve for time scale) • Processing – Monitor atomic clock stability to verify 1.e-13 @ 60 sec and 1.15e-15 @ 10 days – Perform precision orbit determination to verify < 20 cm Deep Space Atomic Clock Stanford 2011 PNT Challenges and Opportunities, Nov 18th John D. Prestage- 5 Next Generation Space Atomic Clock Jet Propulsion Laboratory California Institute of Technology KEY FEATURES: • Based on other space vacuum tubes (TWTA) - 5,000-fold improvement in vacuum - 10-fold reliability improvement • 106-107 199Hg+ trapped ions • Clock Transition: 40,507,347,996.8 Hz • No wall collisions, high Q microwave line • State selection via optical pumping from 202Hg+; • 1-2 UV photons per second scattered • Ions are buffer-gas (Ne) cooled to ~300K • Ion Shuttling from Quadrupole to Multipole trap where best isolation from disturbances is achieved • Frequency de-tunings and drift of USO are detected via UV light scattering from trapped ions UV Light Collected UV Frequency de-tuning (in Hz) at 40.507 GHz Deep Space Atomic Clock Stanford 2011 PNT Challenges and Opportunities, Nov 18th John D. Prestage- 6 Next Generation Space Atomic Clock Jet Propulsion Laboratory Trap design minimizes relativistic Time Dilation clock shift California Institute of Technology Advantages of moving ions between 2 traps • Easily executed with charged ions – lossless, reversible atomic ‘beam’ • Removes light shift • Better magnetic shielding • Reduce Space charge, ion number shift, N/L: (k-1) reduction of micro-motionTime Dilation Deep Space Atomic Clock Stanford 2011 PNT Challenges and Opportunities, Nov 18th John D. Prestage- 7 Next Generation Space Atomic Clock Jet Propulsion Laboratory Sealed Tube Life Test California Institute of Technology ~3.5 years 5/4/2005 11/1/2005 3/9/2006 10/14/2008 4/27/2009 Tube Seal-Off Tube Seal-off Trap Time ∼ 1000 hours Trap Time ∼ 3000 hours Trap Time ∼ 5000 hours Monitor Rabi clock signal size vs time: Loss rate slow: 1000’s of hours Breadboard Clock Unit No Charge conversion for 1000’s hr Thermo-Vac baseplate UV Light Collected UV Frequency de-tuning (in Hz) at 40.507 GHz Getter Sealed Tube Method has demonstrated adequately long life Right Angle UHV Valve -- Eliminates moving parts (Closed to seal system) -- Converts technology to No Consumables (No gas-flow) -- Hg Oven not turned on for years -- Reduce Hg within tube by >> 1000-fold Comparison: Original ground clocks with mechanical pumps have ~ 1 hr hold time Deep Space Atomic Clock Stanford 2011 PNT Challenges and Opportunities, Nov 18th John D. Prestage- 8 Next Generation Space Atomic Clock Jet Propulsion Laboratory California Institute of Technology Vacuum Tube is loaded with Hg vapor after de-gas, ……then sealed off for long term operation under passive getter pump vacuum. Confining Field Switched Off Electron gun switched off Electron gun switched on To generate ions inside trap Deep Space Atomic Clock Stanford 2011 PNT Challenges and Opportunities, Nov 18th John D. Prestage- 9 Next Generation Space Atomic Clock Jet Propulsion Laboratory California Institute of Technology • Plasma UV Light source is radiation tolerant. • 2 Isotopes of Hg are used: - Isotopic Pumping, 202/199Hg+ (as in 87/85Rb, and 106/113Cd+) • Ionizing source is used inside vacuum tube, to create Hg+ Deep Space Atomic Clock Stanford 2011 PNT Challenges and Opportunities, Nov 18th John D. Prestage- 10 Next Generation Space Atomic Clock 202 Jet Propulsion Laboratory UV Light Source – Hg Lamp California Institute of Technology GPS Clock Technologies/ideas are incorporated into Physics package • Long term degradation of UV (194 nm) is due to Hg-fused silica chemistry. • Life extended by lowering power in discharge by ~3x • Sapphire bulb material is more resistant to Hg chemistry and should enable >10-year bulb lifetime. Deep Space Atomic Clock Stanford 2011 PNT Challenges and Opportunities, Nov 18th John D. Prestage- 11 Next Generation Space Atomic Clock Jet Propulsion Laboratory California Institute of Technology Instrument includes embedded processor, digital signal acquisition, analog dc/rf,… ION CLOCK Assembly ION CLOCK Power A1. Power Supply Cond. Interface A14. C- Field A3. Controller Coils A4. C-field Drv A5. Res. Trap (RT) Drv A6. Load Trap (LT) Drv A15. Physic Package DACS A7. Trap DC • Algorithms: A8. Electron Emitter 1. Setup/optimization Drv ION CLOCK 2. Clock Acquisition, Emitter Cmd/Ctl Tracking, Recovery Assy 3. Diagnostics A9. Lamp A10. A11. Input Interface Lamp & Optics 4. Health and Status Driver & housing Assy LT Pulse Thermal Control Assy Counter Tunable- A12. PMT A13. USO Dig. Ctl & Output housing Optics Assy Ctl (in air) Assy Interface RT Assy 10MHz input A16. Multiplier/ Getter from USO Synthesizer A2. Chassis Assembly & Signal Cables Deep Space Atomic Clock Stanford 2011 PNT Challenges and Opportunities, Nov 18th John D. Prestage- 12 Next Generation Space Atomic Clock Jet Propulsion Laboratory California Institute of Technology Miniaturization of large, high performance space clock is well along… Deep Space Atomic Clock Stanford 2011 PNT Challenges and Opportunities, Nov 18th John D. Prestage- 13 Next Generation Space Atomic Clock Jet Propulsion Laboratory 3 Performance of the 10 cm Vacuum Package California Institute of Technology JPL Titanium Vacuum Package Fluorescence Collection Laser Port Port Trap 19 mm Electrodes Deep Space Atomic Clock Stanford 2011 PNT Challenges and Opportunities, Nov 18th John D. Prestage- 14 Next Generation Space Atomic Clock Jet Propulsion Laboratory California Institute of Technology • Requires no consumables (as H-maser or Cesium beam); • Modern vacuum tube fabrication enables long lived operations; • Frequency insensitive to temperature variations; better than 10-15 per C • Radiation tolerant; • Miniaturized with no severe loss of performance; • Unmatched ultra-high stability in a small, lightweight package Ion Trapping Electrodes 40 GHz waveguide window Titanium vacuum tube Hermetic Electrical Feedthroughs Deep Space Atomic Clock Stanford 2011 PNT Challenges and Opportunities, Nov 18th John D. Prestage- 15 .
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