Instrument & Data Mgmt. System ● Items to be controlled: – Receiver subsystems (mixer bias, LO, synthesizer, etc...). (RS232 and I 2 C/SPI interfaces) – IF processor (USB interface) – Spectrometer and Data system (ethernet) ● Interplay of these items with “gondola systems” – data system needs TCS header (timestamp, RA/DEC, etc.) – need synchronization with telescope for OTF – data system may need to amend observing sequence... or ask for attention! Craig Kulesa & Chris Martin

Control Hardware ● Embedded systems are robust and simple solutions. 1 watt, 200 MHz ARM board: CF and USB storage, ethernet, serial, ADC, digital I/O, PC/104 bus (Linux and *BSD) 5 watt, 500 MHz AMD board: CF, USB, IDE storage, ethernet, serial, audio, VGA, digital IO, PCI bus (Linux and *BSD)

Control Software ● Each hardware component has a separate TCP/IP socket server associated with it. The server listens on that socket's port for ASCII text commands to perform. ● Watchdog timers allow software and hardware to be automatically reset should they become unresponsive. ● Low-level server code is written in C; client code for observing programs is written in object-based higher level languages; e.g. perl or python. ● Instrument and control interfaces will be performed through a standalone GUI or a web browser. ● We (C. Kulesa and C. Martin) have downloaded the SBI control code from Pietro and Harry, and are learning how the STO instrument code will dovetail into the existing SBI system. ● The OTF mapping scheme is the principal addition.

On-The-Fly Mapping Strategy ● ~30 second OTF scans as per Allan variance measurements ● Normally, we would position the secondary or the telescope off-source for a reference scan. For STO, this may not be practical. Instead, we will use internal cold load(s) for immediate reference. ● Off-source reference scans and cals to be performed at regular intervals.

Sensitivity: How deep do we need to go? ● Detecting diffuse clouds in the process of becoming GMCs represent the most challenging observations that we will propose. ● How bright will the lines be in the Galaxy? – Model Galactic clouds in [C II] using escape probability code; level populations computed assuming collisions with e -, H and H 2 – Ambient ISM pressure using scaling relation from Wolfire et al and assuming P thermal = 0.1 P total P/k ~ 1.4x10 5 exp(-R/5.5 kpc) K cm -3 – Typical line strengths: ● 3 K km s -1 per cm -2 hydrogen column at R=3 kpc ● 0.5 K km s -1 per cm -2 hydrogen column at R=8.5 kpc ● 0.1 K km s -1 per cm -2 hydrogen column at R=11 kpc

Let's distribute COBE Galactic Plane [CII] flux into several ISM components and observe with ~50 seconds per independent 1.5' beam. This requires ~4 passes at 10”/sec scan rate, and results in a ~2 deg 2 /day mapping rate. This yields 28 deg 2 for the baseline STO mission. WI M diffuse CNM clouds A v = PDRs

Effect of Spectral Resolution Native resolution: 2048 channels, 0.16 km/s each Smoothed: 512 channels, 0.64 km/s each

Test Flight Coverage ● Ideal case: 2 backend spectrometers, one HEB mixer each at [C II] and [N II]. – 10”/s scan rate yields T RMS =0.76K for one pass. Nominal coverage is 6 o /hr. – Repeat 5x: get T RMS =0.34K, about the GPS sensitivity. Nominal coverage is 1.2 o /hr. – Single test pointings to achieve Deep Survey sensitivity. ● A suitable science plan is being developed.

Visibilities: Orion is only well-placed in the morning...

By mid-day, the Galactic Plane has set. Suggest the Polaris Flare as a suitable target.

The 1 st Galactic quadrant becomes visible in the evening.