Low Frequency Cosmology & Astrophysics

•Use the H I emission/absorption signatures against the CMB as cosmological & astrophysical probe

Significant science return — Direct probe of this cosmic epoch

•NASA’s Exploration infrastructure opens avenue for science exploitation of lunar farside

•LUNAR Consortium engaged in crucial technology development

Builds on conclusions of concept studies funded by Astrophysics Mission Concept Studies program

Year 1 Work Plan• Theoretical Tools

– Analytical tools and simulations being developed (Mesinger, Cen, Furlanetto, Hallman, Burns)

– Papers submitted or in preparation (Carilli, Loeb, Lazio, Darling, Furlanetto)

• Array Concept & Algorithm Development

• Technology Development (Science Antenna)– Thermal-vac chamber constructed and in test (Burns, Hallman)

– Helical antenna simulations underway; model antenna constructed (Bradley, Hewitt)

– Polyimide-film antenna simulations underway; joint antenna+transmission line simulations being discussed (Stewart, Lazio, MacDowall)

ROLSS Antenna Gain

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

0 1 2 3 4 5 6 7 8 9 10

Frequency (MHz)

Ga

in (

dB

i) CST, IEEE Gain

IE3D, Realized Gain

IE3D, IEEE Gain

ADS, IEEE Gain

Year 1 Work PlanTheoretical Tools I

Burns, Hallman, & Furlanetto will assess semi-analytical models of 21-cm signals, particularly with regard to global signals expected for a dipole experiment in lunar orbit.

Burns, Hallman, Furlanetto, & Norman will design a new large-scale cosmological N-body + gas hydrodynamics numerical simulation of the Dark Ages and/or EoR based upon evaluation of semi-analytical models.

• Darling & Stocke will explore molecular and atomic line processes from both nearby galaxies and those at cosmological distances that would arise at low radio frequencies.

Burns & Hallman will conduct evaluation, modeling, and potential observations of very steep spectrum radio sources in galaxy clusters both nearby and cosmologically distant.

Year 1 Work PlanTheoretical Tools II

Furlanetto & Mesinger will modify analytic and semi-numeric methods currently tuned for use during the EoR to the high redshifts of interest to the LRA.

• Loeb will develop a computer code that calculates the 21-cm power spectrum efficiently and at high precision for a set of input parameters; develop a Fisher-matrix code that provides constraints on cosmological parameters for a particular implementation of a low-frequency observatory; and combine the above codes to a master code that will be able to determine the cosmological constraints achievable by a future lunar radio array.

• Taylor will develop some of the Secondary Astrophysics goals and explore how these will benefit from a lunar platform.

Lazio will develop some of the Secondary Astrophysics goals, specifically transients and extrasolar planets.

From S. Furlanetto

The three panels show the 21 cm signal for three different prescriptions for the X-ray heating by black holes during the early stages of reionization (81% neutral). Note how different the signals are—ranging from lots of weak absorption (left) to lots of strong emission (right). So far as I know, this is the first "map" including this effect—everything else has made the simple assumption of the right panel. (Mesinger, Cen, & Furlanetto, in prep.)

1 Gpc

Secondary Astrophysics

• “A Blind Search for Magnetospheric Emissions from Planetary Companions to Nearby Stars” (Lazio et al., AJ, submitted)

Stacking analysis using the VLSS of “adolescent” nearby stars

• “Surveying the Dynamic Radio Sky with the Long Wavelength Demonstrator Array” (Clarke et al.)

• “Radio Recombination Lines at Decametric Wavelengths: Prospects for the Future” (Lane Peters et al.)

Year 1 Work PlanArray Concept & Algorithm

Development

• Taylor will consider the technical parameters needed to achieve the scientific aims of the project.

• Lazio and potentially a postdoctoral fellow will assess what existing data might be suitable for testing algorithms or processing approaches for LRA data.– 2 applicants to NRC post-doc program– NLSI in NASA post-doc program?

Year 1 Work PlanTechnology Development

(Science Antenna)

Burns & Hallman and undergraduate students will conduct environmental tests of polyimide film strips with deposited metallic antenna material.

Bradley, Villasenor, Williams, & Hewitt will initiate the first year of a two-year effort of refining and optimizing the electromagnetic performance of helical antennas.

Lazio, Stewart, Hicks, Weiler, & Jones, in consultation with MacDowall & Kasper (Radio Heliophysics), will model the performance of polyimide-film based antennas on the lunar surface.

Year 1 Work PlanTheoretical Tools

– Analytical tools and simulations being developed (Mesinger, Cen, Furlanetto, Hallman, Burns)

– Papers submitted or in preparation (Carilli, Loeb, Lazio, Darling, Furlanetto)

• Array Concept & Algorithm Development

Technology Development (Science Antenna)– Thermal-vac chamber constructed and in test (Burns, Hallman)

– Helical antenna simulations underway; model antenna constructed (Bradley, Hewitt)

– Polyimide-film antenna simulations underway; joint antenna+transmission line simulations being discussed (Stewart, Lazio, MacDowall)

ROLSS Antenna Gain

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

0 1 2 3 4 5 6 7 8 9 10

Frequency (MHz)

Ga

in (

dB

i) CST, IEEE Gain

IE3D, Realized Gain

IE3D, IEEE Gain

ADS, IEEE Gain

From R. Bradley• Current LUNAR activities:

1. I have been modeling a 137 MHz version of the tapered helical antenna using the CST Microwave Studio software. The 0.775-m diameter helix has 10 turns of #24 gauge wire for a height of 5.175 meters. The taper is about 13% of the diameter over this height.

2. I'm also exploring the possibility of using a planar ground screen rather then the fold-out flaps for the cavity. The flaps are a bit cumbersome to deploy. Early results from CST simulations of the planar fan-fold version indicate quite good performance.

3. I've designed and built a dual-polarization dipole reference antenna for 137 MHz. The antenna is very rugged and completely encapsulated in PVC tubing. A low noise amplifier (PAPER type) is also integrated into the design. CST was used to carefully model this antenna.

4. The in-situ antenna power pattern measurement system is being upgraded. It incorporates an Orbcomm "Subscriber Communicator" to extract satellite information (ID & transmit channel). An improved receiver was also constructed and housed in an EMC enclosure. We are currently taking data from the reference antenna with this new system.

• Planned activities over the next six months: 1. Construct a second reference antenna and take differential measurements for calibration purposes.

2. Develop a proof-of-concept tapered helical antenna (based on the modeling). This construction will use a fixed PVC tubing tower. The goal is to evaluate the basic helical design and the associated ground structure. Initially it will be deployed as a replacement for one of the reference antennas in the power pattern measurement system. The helical will then be deployed in Green Bank for drift scan measurements (Galactic plane).

3. Develop the three-antenna triad using the PVC tower configuration. This will include amplifiers, receivers, and power combiners. This will be used to verify proper operation of the three-antenna array. Simulations and field measurements are planned.

4. Further the development of the deployable version once the basic helical design has been verified.

ROLSS AntennaCalculated Gain

Frequency (MHz)

IEEE Gain

1 -15.47

2 -7.992

3 -5.167

4 -3.957

5 -3.352

6 -2.961

7 -2.701

8 -2.452

9 -2.206

10 -1.946

11 -1.667

12 -1.365

13 -1.043

14 -0.711

15 -0.397

16 -0.162

17 -0.116

18 -0.41

19 -1.403

20 -3.056

Regolithε = 3, tan δ = 0.01

7 m

Kapton

Regolithε = 3, tan δ = 0.01

7 m

Cu

Kapton

ROLSS Antenna Gain

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

0 1 2 3 4 5 6 7 8 9 10

Frequency (MHz)

Ga

in (

dB

i) CST, IEEE Gain

IE3D, Realized Gain

IE3D, IEEE Gain

ADS, IEEE Gain

Including impedance mismatch(50 Ω feedline)

Results from3 differentsimulationprograms