DSAC Technology Demonstration Mission Results and Future

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DSAC Technology Demonstration Mission Results and FutureTodd Ely (PI/PM)John Prestage (co-I), Robert Tjoelker (co-I), Eric Burt, Angela Dorsey, Daphna Enzer, Da Kuang, Dave Murphy, David Robison, Jill Seubert, and Rabi Wang

October 28, 2021

j p l . n a s a . g o vOctober 2021

The DSAC Mission

sftp

GA MOC/SOCColorado

ViaSat GS(Atlanta)

CMD & TLM

GPS Sat 1

GPS Sat 2

GPS Sat n

GA Orbital Test Bed (OTB)• 720 km altitude• 24° inclination

DSAC teamJPL

Launch June 25, 2019USAF STP-2(SpaceX Falcon Heavy)

• Collect GPS phase & range data• Collect DSAC telemetry• Validate clock instability < 2 ns @ one-day

• achieved < 0.3 ns @ one-day and more• Validate as a navigation instrument

• sufficient accuracy for onboard radio nav• Operate for at least one year

• Actually over two – mission completed September 18, 2021


To have a space demo mission you need a launch …

USAF STP-2SpaceX Falcon Heavy

OTB one of 26 spacecraft

Launch June 25, 2019


DSAC Payload on the Orbital Test Bed Spacecraft

GPS Receiver

Ultra-Stable Oscillator (USO)

General Atomics Electromagnetic SystemsGroup (GA-EMS)Orbital Test Bed (OTB)

DSAC Physics Unit


DSAC has proven to be very reliable and robust

DSAC 2020-2021 Operations Overview

• Mission operations from 8/20/2019 to 9/18/2021 for a duration of 760.2

• Operations periods include:• USO on: 84.6%• Clock on: 78.2%• GPS data: 74.9%

• 10 long runs (67 days longest)• All run terminations due to S/C

safe modes• 2 known radiation-induced clock

faults – recovered• No known clock hardware faults


DSAC Technology: How it Works

Key Reliability Features: - practical• No lasers • No cryogenics • No microwave cavity• Low light shift (QP), no light shift (MP)• Low consumables

Microwave Input

Input light system

Detection light system

Local Oscillator

Controller

Key Performance Features:106-107 199Hg+ trapped ions• No wall collisions, high Q microwave line• Buffer gas cooled to ~300K • Two trap system• Quadrupole (QP) trap – low Doppler sensitivity• Multi-pole (MP) trap – lower Doppler sensitivity

(Flight demo operated with only the QP trap)

State selection• Optical Pumping from 202Hg+ lamp• 1-2 UV photons per second scattered

High Clock Transition• 40,507,347,996.8 Hz – low magnetic sensitivity

Adapts to variety of Local Oscillators - flexible


Nature Journal Publication of DSAC Results

Stability at one-day of 3e-15➡ significantly better than required 2e-14

Drift of 3.0e-16/day➡ establishes space clock record

Two subsequent long runs had similar long term stability

10-15

2

3

45678

10-14

2

3

45678

10-13

2

3

4

Alla

n D

evia

tion

100 101 102 103 104 105 106

Time (s)

NO DRIFT REMOVAL

Measurement system + DSAC

DSACOptimized DSAC

DSAC measured on the ground (MP mode)

DSAC requirement


DSAC Flight Experience Overview: What we have learned to date• Improved temperature predictions vs. beta angle • USO performance in space nominal• Lamp function in space – better than on ground!• Degree of interaction with the SAA – USO and Clock (9)• Relativity corrections require J2 effects (10)

• Measure fundamental clock sensitivities in space:Ø Background pressure: Limits on gas evolution (11)Ø Magnetic: Characterization of external magnetic field variations (12)Ø Doppler Effects: Ion number sensitivity and method to reduce (13)Ø Overall temperature: measured sensitivity with caveats (14)


-2.0 x10-3

-1.5

-1.0

-0.5

0.0

0.5

Clo

ck F

requ

ency

Erro

r

600005000040000time (s)

55 x103

50

45

40

35

30

PMT counts191002a Daily

average clock_frequency_errorcompared to dim_count(CFE consists of data from10/2, 10/3, 10/4, 10/6, and 10/9)

Clock control loop efficiently filters out SAA-induced PMT variations

South Atlantic Anomaly (SAA) Impact on Operations

PMT variations due to SAA passage

Clock control loop response to orbital environmental variations – USO responding to temperature changes

Clock control loop response to SAA transits – radiation is causing the USO to ‘pull’ in frequency and the clock is responding to control it out

Clock Control Loop:

PMT counts:


GPS phase dynamically corrected for gravitational effects (red shift)

Characterizing Gravitational Effects

Must include higher order terms (J2) in the gravitational potential

10-15

10-14

10-13

10-12

Alla

n De

viatio

n

102 103 104 105 106

Averaging Time (s)

NO DRIFT REMOVAL

No corrections

Relativity corrections, but no GPSR temperature corrections

Measurement floor after relativity and GPSR temp correction

Estimated clock noise


Limit on 𝝙f/f due to background gas evolution at < 4e-16/day

Characterizing Background Gas Evolution Effects

Residual frequency offsets when ion number stable and known temperature effect removed

-1.5 x10-13

-1.0

-0.5

0.0

0.5

1.0

1.5Fr

eque

ncy

Offs

et

800 x1036004002000Time (s)


Strength of this technology - no magnetic perturbations observed

Characterizing External Magnetic Field Effects

Peak effect below clock sensitivity

15

10

5

0

-5

-10M

agne

tic F

ield

(uT)

2.0 x1061.51.00.50.0Time (s)

200110a MagnetometerMagnetic field as measuredby magnetometerC (weak clockdirection) where sensitivity is7e-14/G. Data from 12/15/19 to1/10/20.

250 mGpp (100x lab!!)

AD of external magnetic field-induced frequency variations

20 days

Optimal clock noise level

Clock + Measurement noise during

52-day run


Ion number stability 𝝙f/f ~ 1e-15/day achieved after 1 day of warmup

Characterizing Doppler Effects

4 x10-13

3

2

1

0

Frac

tiona

l Fre

quen

cy

6005004003002001000Signal Size Measurement Number

200110 yt_ss_qptempcomparison: real freq (red)to frequency derived from-5.9e-17*D_ss - 7e-16*D_qpt

y(t) actual yf_ss_qpt

• Red: Measured y(t)• Blue: Predicted y(t) using only ion number variations (2nd-order Doppler effect)• Excellent agreement Ion number variations dominant effect• Temperature effect relatively small

Actual freq offsets (re

d trace)

Modeled freq response

using ONLY second order

Doppler shift (blue tra

ce)

j p l . n a s a . g o vOctober 2021DSAC-2 will remove stray magnetic effects to achieve typical 2e-15/C

Characterizing Temperature Effects• Measured sensitivity @ +/- 1e-14/C – varying slowly with time • Should be closer to 2e-15/C and not time dependent• Doesn’t limit performance, but higher than expected• Time variability indicated by a stray magnetic effect & may be reduced by smaller ion cloud• Long-term AD may improve with smaller cloud – one test below

• Small cloud yields signal with ~5400 counts vs ~20K for larger cloud (52 day result published in Nature)

• Final long run with small cloud still being analyzed• Temperature sensitivity time variability correlated with beta angle - beta angle causes thermal

gradients - can aggravate stray magnetic fields

Large signal run

Small signal run


DSAC Performance Summary

• Demonstrated operational robustness and met 1-day stability requirementü 3e-15 (2e-14 required)

• Set stability records for space clocksü 3e-16/day drift

• Refined understanding of temperature sensitivityü < 1e-14/ºC and able to achieve 2e-15/ºC

• Improved life time estimates due to Hg, Neon, and background gasesü > 7 years

• DSAC lamp life: ü > 4 years (expected 3-5 years), no degradation in space

15


What is Possible with a Deep Space Atomic Clock?

Lunar Gateway

Enhanced Autonomous Navigation

DSN Extension

Radio Science & Fundamental Physics

Lunar/MartianPositioning System


Autonomous Nav Example – Mars Approach & Entry

• Onboard one-way uplink radiometric data using DSAC combined with optical improves on optical-only navigation by an order of magnitude

• Radio tracking reduced by 90% relative to traditional two-way, ground based tracking• Atmosphere entry knowledge ~ 150 m (order of magnitude improvement compared to

ground-based navigation)

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Elapsed Time (hrs) Elapsed Time (hrs)

Onboard Gimbaled Optical Only Onboard CPF-Phase from 2 hr/day DSN & Onboard Gimbaled Optical


DSAC-2 significantly reduces SWaP, increases operational life, and improves stability for improved navigation and radio science

DSAC-2 TDO Hosted on VERITAS

Free running USO

DSAC-1 in spaceDSAC-2 expected

10-16

10-15

10-14

10-13

10-12

10-11

Alla

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evia

tion

100 101 102 103 104 105Time (s)

courtesy D. Enzer (JPL 335E)

DSAC-2 DSAC-1Required CBE Actuals

Stability2E-13 at 1-s2E-14 at 1000 s3E-15 at 1-d

1e-13 at 1-s 1e-14 at 1000 s 1e-15 at 1-d

1.5E-13 at 1-s< 3E-14 at 1000 s~ 3E-15 at 1-d

Power 42 W 33 W 56 WMass 13 kg 10 kg 19 kgVolume 13 L 10 L 19 LLifetime 2 yr >5 yr 2–3 yrs

DSAC-1USO

PIU

+ +

DSAC-2 concept• includes USO & clock control• fits inside a GPS footprint and/or

commercial rack mount• the TDO will raise TRL to 9

jpl.nasa.gov

DSAC Technology Demonstration Mission Results and Future

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