LB002 Observing the Cosmic Dawn with the LWA Bowman, J. (AsU), judd.bowman@asu.edu The formation of the first stars, galaxies, and black holes during Cosmic Dawn is the next frontier in observational cosmology. During this epoch, the intergalactic medium (IGM) is dominated by neutral hydrogen gas, accessible to observations through its redshifted 21 cm line. The thermal and ionization history of the early IGM is highly anticipated to encode unique information about the properties of the first luminous objects. Once the first stars form at z ≈ 30, they produce a background of Lyman-α photons that couples the neutral hydrogen spin temperature to the physical gas temperature in the IGM. This causes the 21 cm line to become visible in absorption against the warmer cosmic microwave background (CMB). Later, after the early stars die, many will leave behind black holes that generate X-rays through accretion. The X-rays travel long distances, depositing their energy as heat and raising the IGM temperature. This heating will drive the average 21 cm signal to switch into emission above the CMB, until the neutral gas is eventually ionized during the epoch of reionization, leaving no detectable signal. The evolution of these absorption and emission features in the early IGM will be imprinted in the all-sky radio spectrum since redshift maps to frequency for the 21 cm line. But significant observa- tional challenges must be addressed to separate the ∼ 100 mK signal from the dominant Galactic foreground emission. Existing efforts to measure this signal have just recently demonstrated the first successful results, but only for later times during the epoch of reionization at z < 13. We propose a focused, two-year program utilizing a novel observing strategy that has the potential to extend the probe of the IGM to much earlier times of 15 < z < 50. We will use the existing first Long Wavelength Array station (LWA1) in New Mexico, consisting of 256 dual-polarization dipole antennas, operating between 10 and 88 MHz, that are digitally combined to form multiple beams on the sky. We will exploit the unique beamforming capability to remove calibration uncertainties that plague other instruments by simultaneously targeting both science and calibrator fields. We plan to manipulate the weighting coefficients of the individual antennas to carefully control the frequency- dependent sidelobes of the beams, drastically reducing the primary mechanism responsible for coupling angular sky structure into deep radio spectra. Neither of these techniques are possible with traditional radio telescopes. We expect their application to lead to the first detection of the 21 cm absorption signal at z ≈ 25, opening a new window on early star formation and the IGM.